CN109428544B

CN109428544B - Switching method for realizing access or removal of photovoltaic module in battery string group

Info

Publication number: CN109428544B
Application number: CN201710786790.4A
Authority: CN
Inventors: 张永
Original assignee: Fonrich Shanghai New Energy Technology Co ltd
Current assignee: Fonrich Shanghai New Energy Technology Co ltd
Priority date: 2017-09-04
Filing date: 2017-09-04
Publication date: 2020-11-20
Anticipated expiration: 2037-09-04
Also published as: CN109428544A

Abstract

The invention relates to a switching method for switching in or removing a photovoltaic module in a battery string group, wherein the battery string group comprises a plurality of photovoltaic modules connected in series, and each photovoltaic module is provided with an access switch for coupling the photovoltaic module into the battery string group and a removal switch for shielding the photovoltaic module from the battery string group. The method comprises the steps that a cascade voltage provided by a battery string group to which a photovoltaic component to be switched belongs is subjected to transient short-circuit for one time or multiple times, a processor configured by the photovoltaic component to be switched detects whether a transient short-circuit event occurs in the battery string group, and the detected transient short-circuit event is used as a basis for judging whether the photovoltaic component is switched in or removed from the battery string group, so that the component can be controlled to be switched between a normal switching working mode or a shielding removal mode.

Description

Switching method for realizing access or removal of photovoltaic module in battery string group

Technical Field

The invention mainly relates to the field of photovoltaic power generation, in particular to a switching module which can control a photovoltaic module to be switched on or off and is adopted in an application occasion containing a photovoltaic cell, and the switching module can be determined to be switched between a normal access working mode of a switched-on component or a removal mode of a shielded photovoltaic component and the like according to actual conditions.

Background

The individual photovoltaic module outputs are often insufficient to provide the actual power requirements, and therefore arrays of photovoltaic modules must be constructed in series and parallel to meet the design requirements. When a photovoltaic module is selected to form an array, the condition that the output power after series-parallel connection is smaller than the sum of the output power of a single module due to the fact that the electrical parameters of the modules in series-parallel connection are inconsistent or the series group is partially or intermittently shielded or aged and the like is usually encountered, the mismatching loss is called by the professional term, and the actual power generation of the whole power station is influenced to different degrees along with the increase of the operation life of the photovoltaic power station. The traditional centralized photovoltaic power generation system is subjected to unpredictable factors such as surrounding buildings, cloud positions, sizes of adjacent obstacles and the like, so that power of the photovoltaic module array is lost which is difficult to estimate. Therefore, in recent years, researchers at home and abroad research and search various global maximum power points for the problem of multiple peaks of the power of the photovoltaic array generated by the local shadow to obtain some remarkable results, but all photovoltaic modules cannot work at the respective maximum power points, and the loss of the overall power of the string group caused by the problem of shielding of the local shadow is not completely solved. For a concentrated photovoltaic power generation system, only one energy conversion link is used for voltage conversion from direct current to direct current, the maximum power point of a tracking battery panel is considered during control, the amplitude phase and the sine degree of the output voltage of a power grid are ensured, the inverter is controlled to use the same MPPT by multiple inputs, the difference of photovoltaic modules with serial and parallel branches cannot be identified, the power generation efficiency can be greatly reduced, and therefore, the energy loss caused by the discreteness of parameters of the photovoltaic modules or the difference of solar radiation conditions is useless. Meanwhile, if currents are not matched during series connection, when the array works in a certain state, a certain photovoltaic module in the array is in a reverse bias state to form a hot spot, if voltages are not matched during parallel connection, when the module array works in a certain state, a circulating hot spot and a circulating current formed in the array can enable the certain module in series-parallel connection to be in a power consumption state, the service life of the module can be damaged, particularly, when the photovoltaic module array cannot work under uniform illumination, mismatch loss is larger, the module can bypass a battery string with abnormal work through connection of bypass diodes in a junction box, power loss caused by current mismatching between batteries or modules is partially reduced, and the problem of current matching caused by any battery module with low current in the battery string group cannot be solved.

The power generation lifting of the power optimizer is greatly related to the actual conditions of the power stations, for example, the lifting proportion of a large power station and a distributed photovoltaic power station which are not shielded by obstacles on a flat ground is different, and the lifting proportion of a power optimizer installed in the photovoltaic power station which is just put into operation and the power station which runs in a grid-connected mode for a certain number of years is also different, so that experiments need to be carried out through actual scenes, data are accumulated for series analysis, and beneficial references can be provided for the optimized operation of the power stations. The annual photovoltaic output gain after the optimizer is increased is different in the promotion proportion under different irradiations. Due to the fact that the photovoltaic modules in the array are inconsistent in characteristics, the current mismatch problem is easily caused, and the overall power generation efficiency of the system is greatly reduced. The array architecture of the distributed photovoltaic power optimizer is provided for solving the problem in the industry, and a new way is provided for solving the current mismatch problem of the photovoltaic array series component. The power optimizer can be directly integrated with the battery assembly into a matched set of power equipment when the battery assembly leaves a factory, and the power optimizer can be separately and additionally installed on the battery assembly. For the industry, the newly built photovoltaic power station is more cost-effective by adopting a scheme of integrating a power optimizer and a battery assembly, and the upgrading and modification of the existing old photovoltaic power station needs to additionally install an additional power optimizer on the original assembly. The safety working mode or the maximum power point tracking mode or the sleep mode is a problem to be considered, and no matter in conditions of maintenance, initial power-on or installation and the like, the safety working mode or the maximum power point tracking mode or the sleep mode needs to be switched between the normal working mode and the safety mode to ensure the safety of workers or owners.

Disclosure of Invention

In an optional non-limiting embodiment, the present application discloses a method for switching between different operation modes of a power optimizer for photovoltaic modules, wherein any one of cell string sets includes a plurality of photovoltaic modules connected in series, each photovoltaic module is configured with a power optimizer for performing maximum power point tracking, and the power optimizers corresponding to the respective photovoltaic modules in each cell string set are connected in series to form a link so as to provide a string level voltage;

the method comprises the following steps: transiently short-circuiting cascade voltage provided by a link to which the power optimizer of any one to-be-switched working mode belongs; and detecting whether a transient short-circuit event occurs in a link, wherein the power optimizer of the working mode to be switched switches from one working mode to another working mode when detecting the transient short-circuit event.

The above method is characterized in that: transiently short-circuiting cascade voltage provided by a link to which the power optimizer of any one to-be-switched working mode belongs; detecting the variation of a preset index induced by the short circuit of the cascade voltage in the transient short-circuited link; and when the variable quantity meets a preset variable condition, switching the power optimizer of the working mode to be switched from one working mode to another working mode.

The above method is characterized in that: the predetermined indicator includes at least a transient short-circuit current flowing through the transient short-circuited link and/or a transient rate of change of a cascade voltage including the transient short-circuited link.

The above method is characterized in that: the operating modes of the power optimizer include at least: a safe mode in which the output voltage of the power optimizer is continuously lower than the input voltage; the power optimizer operates the photovoltaic module with which it is paired in a power tracking mode at the maximum power point.

The above method is characterized in that: the safe mode of the power optimizer includes at least: the ratio of the output voltage to the input voltage of the power optimizer is clamped below a predetermined proportional relationship.

The above method is characterized in that: the power optimizer used as the switch mode power supply outputs an output voltage after the photovoltaic module matched with the power optimizer performs direct current voltage conversion; the way that the power optimizer of the operation mode to be switched from one operation mode to another operation mode comprises the following steps: and changing the switching operation frequency or duty ratio of the pulse width modulation signal for driving the power optimizer, wherein the switching operation frequency or duty ratio of the pulse width modulation signal in two different working modes is different.

The above method is characterized in that: the predetermined indicator of the induced short-circuiting of the cascade voltage in the link further comprises: the counted number of times of short circuit of the cascade voltage in the preset time period accords with the expected number of times.

The above method is characterized in that: each power optimizer comprises a first input end and a second input end which are coupled to the positive electrode and the negative electrode of one photovoltaic module, a first output end and a second output end which provide output voltage, and an output capacitor of each power optimizer is connected between the first output end and the second output end; in a chain circuit formed by serially connecting a plurality of stages of power optimizers, the second output end of the previous stage of power optimizer is coupled to the first output end of the adjacent next stage of voltage conversion circuit; the respective output capacitors of the multi-stage power optimizers are connected in series with each other, and the chain provides a cascade voltage equal to the sum of the voltages on the respective output capacitors of the multi-stage power optimizers.

The above method is characterized in that: a control switch is coupled between a first output end of a first-stage power optimizer and a second output end of a last-stage power optimizer in the multi-stage power optimizers connected in series in the link; the mode of the cascade voltage provided by the transient short-circuit link is as follows: the control switch is turned off or turned off rapidly after being turned on, and continuous turning on is not allowed.

The above method is characterized in that: the control switch is switched on for an indication time in transient short-circuit of the link and then is rapidly switched off; when the detected variation of the preset index meets the preset variation condition and the duration time meeting the preset variation condition is the same as the indication time, the power optimizer of the working mode to be switched executes the switching of the working mode.

In an alternative non-limiting embodiment, the present application discloses a method for a power optimizer of a photovoltaic module to switch between different operating modes, wherein a string of cells includes a plurality of photovoltaic modules connected in series; each photovoltaic module is provided with a power optimizer for executing maximum power point tracking; the power optimizers corresponding to the photovoltaic modules in each battery string group are connected in series to form a link so as to provide a cascade voltage;

the method comprises the following steps: transient short-circuiting cascade voltage provided by a link to which the power optimizer of the working mode to be switched belongs for one or more times; and detecting whether a transient short-circuit event occurs in the link by the power optimizer of the working mode to be switched, and taking the detected transient short-circuit event as a basis for switching from one working mode to another working mode.

The above method is characterized in that: the method for detecting the transient short-circuit event comprises the steps of detecting the variation of a preset index induced by short-circuit of the cascade voltage; and when the variable quantity meets a preset variable condition, the power optimizer of the working mode to be switched switches from one working mode to another working mode.

The above method is characterized in that: the predetermined indicator includes at least a transient short-circuit current flowing through the transient short-circuited link and/or a transient change rate of a cascade voltage of the transient short-circuited link.

The above method is characterized in that: the operating modes of the power optimizer include at least: a safe mode in which the output voltage of the power optimizer is continuously lower than the input voltage; and a power tracking mode in which the power optimizer operates the photovoltaic module with which it is paired at a maximum power point.

The above method is characterized in that: the safe mode of the power optimizer includes: the ratio of the output voltage to the input voltage of the power optimizer is clamped below a predetermined proportional relationship.

The above method is characterized in that: outputting an output voltage subjected to direct-current voltage conversion by a photovoltaic module matched with a power optimizer used as a switch mode power supply; the mode for implementing the switching of different working modes by the power optimizer of the working mode to be switched comprises the following steps: and changing the switching operation frequency or the duty ratio of the pulse width modulation signal for driving the power optimizer to ensure that the switching operation frequency or the duty ratio of the pulse width modulation signal under two different working modes is different.

The above method is characterized in that: detecting the transient shorting event further comprises defining: the counted number of times of short circuit of the cascade voltage in the preset time period accords with the expected number of times.

The above method is characterized in that: each power optimizer comprises a first input end and a second input end which are coupled to the positive electrode and the negative electrode of one photovoltaic module, a first output end and a second output end which provide output voltage, and an output capacitor of each power optimizer is connected between the first output end and the second output end; in a chain circuit formed by serially connecting a plurality of stages of power optimizers, the second output end of the previous stage of power optimizer is coupled to the first output end of the adjacent next stage of voltage conversion circuit; the respective output capacitors of the multi-stage power optimizers are connected in series with each other, and the link provides a total string voltage equal to the sum of the voltages on the respective output capacitors of the multi-stage power optimizers in the link.

The above method is characterized in that: a control switch is coupled between a first output end of a first-stage power optimizer and a second output end of a last-stage power optimizer in the multi-stage power optimizers connected in series in the link; the mode for implementing transient short circuit on the cascade voltage provided by the link is as follows: the control switch is turned on and then turned off rapidly.

The above method is characterized in that: the method for detecting the transient short-circuit event comprises the steps of detecting the variation of a preset index induced by short-circuit of the cascade voltage; and switching on the control switch for an indication time and then rapidly switching off the control switch; therefore, when the fact that the variable quantity of the preset index meets the preset change condition and the duration time of the transient short-circuit event is the same as the indication time is detected, the power optimizer of the working mode to be switched executes the switching of the working mode.

In an optional non-limiting embodiment, the present application discloses a switching method for implementing the access or removal of a photovoltaic module in a battery string, wherein: the battery string group comprises a plurality of photovoltaic modules which are connected in series; each photovoltaic module is configured with an access switch for coupling the photovoltaic module into the battery string and a removal switch for shielding the photovoltaic module from the battery string;

the method comprises the following steps: transient short-circuit is carried out on the cascade voltage provided by the battery string group to which the photovoltaic module to be switched belongs for one or more times; and a processor configured with the photovoltaic module to be switched detects whether the battery string group has a transient short-circuit event, and the detected transient short-circuit event is used as a basis for judging the access or removal of the photovoltaic module from the battery string group.

The above method is characterized in that: the method for detecting the transient short-circuit event comprises the steps of detecting the variation of a preset index induced by short-circuit of the cascade voltage; and when the variable quantity meets a preset variable condition, the photovoltaic module to be switched is switched from one mode of access or removal to the other mode.

The above method is characterized in that: the predetermined indicator includes at least transient short current induced by transient short and/or transient change rate of cascade voltage caused by transient short.

The above method is characterized in that: the switching module for realizing the access or removal of each photovoltaic module from the battery string group comprises: first and second input terminals and first and second output terminals; the first input end and the second input end are correspondingly and respectively coupled to the anode and the cathode of the corresponding photovoltaic module; the access switch is coupled between the first input end and the first output end or between the second input end and the second output end; a removal switch is coupled between the first output terminal and the second output terminal; when the multi-stage switching modules are connected in series, the second output end of any previous stage switching module is coupled to the first output end of the adjacent next stage switching module; so that the total string voltage provided by the multi-stage switching modules is equal to the sum of the voltages between the first output terminal of the first stage switching module and the second output terminal of the last stage switching module.

The above method is characterized in that: when all the photovoltaic modules in the battery string group are in bypass short circuit by the respective removal switches, or when at least one part of the photovoltaic modules are in bypass short circuit by the respective removal switches, the mode of switching the photovoltaic modules from the removal mode to the access mode is as follows: and generating a potential difference on the battery string group to inject current into the battery string group, and restoring the connection mode when a processor of the photovoltaic module configuration senses the injected current.

The above method is characterized in that: any one switching module is coupled with a current divider for sensing the injection current between the first output end of the switching module and the second output end of the switching module in the previous stage; or any one of the switching modules is coupled with a current divider for sensing the injection current between the second output end of the switching module and the first output end of the switching module of the next stage.

The above method is characterized in that: any one photovoltaic module is provided with an energy storage capacitor for supplying power to a processor configured with the photovoltaic module, and the energy storage capacitor is charged from the anode of the photovoltaic module through a diode in one-way transmission.

The above method is characterized in that: a control switch is coupled between the first output end of the first stage switching module and the second output end of the last stage switching module in the series-connected multi-stage switching modules; the mode of implementing transient short circuit to the cascade voltage that the battery string group provided does: the control switch is turned on and then turned off rapidly.

The above method is characterized in that: the method for detecting the transient short-circuit event comprises the steps of detecting the variation of a preset index induced by short-circuit of the cascade voltage; and switching on the control switch for an indication time and then rapidly switching off the control switch; therefore, when the variable quantity of the preset index is detected to meet the preset change condition and the duration time of the transient short-circuit event is the same as the indication time, the photovoltaic module to be switched executes the mode switching.

Drawings

To make the above objects, features and advantages more comprehensible, embodiments accompanied with figures are described in detail below, and features and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the following figures.

Fig. 1 is a schematic diagram of photovoltaic modules connected in series to form a battery string and then connected in parallel by the battery string to power an inverter.

Fig. 2 is a schematic diagram of an example of a plurality of photovoltaic modules connected in series with each other in the same cell string.

Fig. 3 is an exemplary diagram of a photovoltaic module corresponding to power optimization by a voltage conversion circuit.

Fig. 4 is a schematic diagram of a link with a multi-stage voltage conversion circuit being short-circuited one or more times.

Fig. 5 is a schematic diagram of a link with a multi-stage power optimizer being shorted to produce a short circuit current in the loop.

FIG. 6 is a logic diagram of a power optimizer switching between different modes of operation for a mode of operation to be switched.

Fig. 7 is a schematic diagram of a photovoltaic module connected in series using switching modules that enable access to or removal of the photovoltaic module.

Fig. 8 is an exemplary illustration of a photovoltaic module being accessed or removed by a switching module.

Fig. 9 is a schematic diagram of a link with multiple stages of switching modules being shorted to generate a short circuit current in the loop.

Detailed Description

The present invention will be described more fully hereinafter with reference to the accompanying examples, which are intended to illustrate and not to limit the invention, but to cover all those embodiments, which may be learned by those skilled in the art without undue experimentation.

In a switching power supply system, a power supply generally employs a power semiconductor device as a switching element, and a duty ratio of the switching element is controlled to adjust an output voltage by periodically turning on and off the switch. The switch power supply mainly comprises an input circuit, a conversion circuit, an output circuit, a control unit and the like. The power conversion is a core part and mainly comprises a switching circuit, and a transformer is applied to some occasions. In order to meet the requirement of high power density, the converter needs to work in a high-frequency state, the switching transistor needs to adopt a crystal arm with high switching speed and short on and off time, and a typical power switch comprises a power thyristor, a power field effect transistor, an insulated bipolar transistor and the like. The control mode is divided into various modes such as pulse width modulation, mixed modulation of pulse width modulation and frequency modulation, pulse frequency modulation and the like, and the pulse width modulation mode is commonly used. The switching mode power supply SMPS is classified into an alternating current to alternating current (AC/AC) converter such as a frequency converter, a transformer, according to the form of input and output voltages; also classified as alternating current to direct current (AC/DC) converters such as rectifiers; and into direct current to alternating current (DC/AC) converters such as inverters and the like; and into direct current to direct current (DC/DC) converters such as voltage converters, current converters. The switched mode power supply applied in this application is primarily a dc to dc voltage converter. Switching noise generated by switching operations when operating a switched mode power supply may cause electromagnetic interference to be generated in an electronic device including the switched mode power supply. Switching noise represents noise components occurring due to the switching operating frequency of the power switches configuring the switched mode power supply, as well as certain harmonic components. When electromagnetic interference occurs, the operation of peripheral electronic devices of the power device including the switch mode power supply is disturbed. A conventional method for suppressing the occurrence of electromagnetic interference is a method of changing the operating frequency of a modulation switch. The frequency modulation method generates an output voltage ripple modulated according to the switching operation frequency, which is superimposed on an output voltage ripple component caused by the ripple of the input voltage, thereby generating a larger output voltage ripple.

In a switching power supply system, the characteristic of a switching power supply is fully utilized, namely a direct current-to-direct current voltage converter which is regarded as a power optimizer, and an inductance/capacitance element is added into a voltage conversion circuit, so that the voltage output by the switching operation generated by the voltage conversion circuit is coupled to the input end or the output end of the circuit and is further transmitted to a common direct current transmission line for providing the total cascade voltage.

The power optimizer is a voltage converter of a voltage reduction and boost type from direct current to direct current, and is also a single-component-level battery maximum power tracking power device. And after the single component is subjected to maximum power optimization by the power optimizer, the single component is transmitted to a terminal inverter to be subjected to direct current-to-alternating current processing, and then the single component is supplied for local use or power generation internet surfing. The terminal inverter can be generally a pure inverter device without maximum power tracking or an inverter device equipped with two-stage maximum power tracking. The mainstream power optimizers are mainly classified into series connection type and parallel connection type, and the topologies are slightly different, such as BUCK or BOOST or BUCK-BOOST circuits.

The design concept of fixed voltage is adopted by the series type power optimizer. In brief, the inverter control board determines a stable voltage of a direct current bus according to the alternating-current voltage, summarizes the maximum power collected by each serially-connected optimizer, and further calculates the bus current and transmits the bus current to the optimizer through wireless or power carrier. The voltage at the output of each optimizer is then equal to the power of the maximum power of the collected component divided by the bus current. When the assembly is blocked, the optimizer can re-determine the maximum output power value according to the volt-ampere curve and transmit the maximum output power value to the inverter control panel through wireless or power carrier waves. On the premise of maintaining the voltage of the direct current bus unchanged, the control board recalculates the bus current (becomes smaller) and feeds the bus current back to each optimizer. At this point, the power of the shielded components is reduced, and the optimizer also steps down to confirm that the output current is up to standard. The optimizers for other non-occluded components are boosted to meet the output current. If a component is too heavily shaded, the power optimizer bypasses the heavily shaded component until it returns to a workable state, and this regulation is essentially a voltage-balancing process, thereby providing the most stable and optimized dc-side bus voltage to the inverter.

The parallel type power optimizer also uses a fixed voltage mode. The inverter determines the bus voltage according to the closed loop of the direct current and the alternating current, each optimizer boosts the voltage of the respective output end to a designated value, and the current input into the inverter is equal to the sum of the maximum power collected by each optimizer and the current obtained by dividing the maximum power by the rated voltage. Because the shielding of the thick cloud layer has little influence on the voltage of the component and mainly influences the output current, the parallel optimizer generally does not have frequent voltage mismatching regulation, and because of the parallel relationship, the output currents do not influence each other, so that the parallel optimizer can be regarded as the advantage of the parallel optimizer compared with the serial optimizer. Meanwhile, if the individual components are seriously shielded and cannot start the boosting equipment, the optimizer automatically disconnects and sends a fault reporting signal, and restarts until the shielding problem is removed. However, compared with the series topology, the parallel topology also has the same defects as the micro-inverter, and the boost span is larger. At present, the open-circuit voltage of the popular components is about 38V, the working voltage is about 30V, the voltage boosting and reducing range of the series topology is controlled between 10% and 30% under the normal condition, and the variation range is increased to between 10% and 90% under the condition of insufficient voltage. However, both the parallel topology and the micro-inverter require boosting the component input voltage to a fairly high value, around 400V, which is obviously equivalent to more than 10 times the boost amplitude. This is a challenging duty cycle for boost devices that do not use a transformer, but are only switch controlled.

One of the biggest topological features of the power optimizer is to separate the components and the inverter functionality, which is different from the traditional photovoltaic system. It appears that the components are connected to the inverter through the optimizer, and in fact the components are only used to start the optimizer, and the optimizer collects the maximum power of the components and then cooperates with each other to give the inverter function. Due to the technology of fixing the voltage, the problem of partial shielding of the photovoltaic power generation system is solved, the number of the components in each group of strings does not need to be equal for a system with a plurality of groups of strings, and even the orientation of the components in the same group of strings does not need to be the same. For the series type optimizer, the open-circuit voltage after the circuit breaking is only a tiny voltage such as 1V, and for the parallel type optimizer, the open-circuit voltage after the circuit breaking is at most the open-circuit voltage of the component, so the safety performance and the reliability of the power generation system are also a leap-type improvement.

Besides the advantages of the circuit topology on the structure, the power optimizer has inherent advantages on the maximum power point tracking algorithm. The traditional tracking algorithm of the maximum power point is basically based on two types: hill climbing method and logic measurement algorithm. Methods for tracking points of advance these also use a combination of: for example, a hill climbing method is combined with a constant range method, and a full scanning method with a fixed time interval is matched to find a maximum power point; the maximum power point is also found by combining a slope polarity method and a conductance increment method and matching with a detection step control method. Under ideal test conditions, the accuracy of the algorithms can reach over 99 percent, and actually, the biggest current challenge is the situation of multiple peaks and steep illumination increase. By multi-peaked is meant that multiple power peaks appear in the power-current or power-voltage graph of an array. The formation reasons of the array are various, one of the reasons is that a bypass diode is deflected in the forward direction due to shielding of part of assemblies, one third of batteries are bypassed, the working voltage of the string is reduced, and further, voltage mismatching of the array occurs, and a multi-wave peak condition occurs. Or a multi-peak condition caused by current mismatch in the same string due to blocking and the bypass diode is still in a reverse deflected inactive state. Multiple peaks and steep increases in illumination have a huge impact on many maximum power point algorithms, which can confuse the tracker's decision on the direction of detection and on which peak is the maximum power point due to its uncontrollable and variable nature. In fact, the root cause of the problem is that too many components are accessed. It is tried to connect only one component to each optimizer, each component has only two to three bypass diodes, and the components do not influence each other, which greatly reduces the difficulty of analyzing and tracking the maximum power point, and is also very concise and accurate for logic editing of the controller. Because only one IV plot of 38 volts and 8.9 amps is used, the maximum power point tracking of the optimizer does not require the use of conventional algorithms to track the maximum power point, and two methods are currently used, namely, a tangent point tracking method, and a combination of a resistance control method and a voltage control method with two-stage tracking. Based on the advantages, the capacity of the optimizer can be improved by about 30% compared with the traditional inverter. In addition, unlike the limited ac power of the micro-inverter, the power optimizer may fully transfer the collected power to the inverter.

The power optimizer is compatible with all silicon cells and can be matched with part of thin film battery systems, and efforts are being made to make the optimizer have a wider compatibility range. However, most micro-inverters are incompatible or self-functionally grounded, which makes them incompatible with some mainstream components currently on the market. At the same time, the input voltage range of the power optimizer is between about 5 volts and 50 volts, which ensures that the optimization circuit can still be started and continue to operate even if the components are severely covered. The power optimizer can be matched with a third-party inverter, and communication with the third-party inverter and regulation and control of a system are carried out through an additional control box. The power optimizer or voltage conversion circuit is essentially a dc-to-dc converter such as BUCK, BOOST and BUCK-BOOST circuits. It should be emphasized that any scheme for tracking the maximum power of the photovoltaic cell in the prior art is also applicable to the voltage conversion circuit of the present application, and the common maximum power tracking methods include a constant voltage method, a conductance increment method, a disturbance observation method, and the like, and the present application does not describe any scheme how the voltage conversion circuit performs maximum power tracking MPPT.

In the field of photovoltaic power generation, a photovoltaic module or a photovoltaic cell PV is one of the core components of power generation, and a solar cell panel is divided into a monocrystalline silicon solar cell, a polycrystalline silicon solar cell, an amorphous silicon solar cell and the like in the direction of mainstream technology, so that the number of the battery modules adopted by a large-scale centralized photovoltaic power station is large, and the number of the battery modules adopted by a small-scale distributed household small-scale power station is relatively small. Long-term and durable monitoring of the panels is essential since silicon cells typically require a service life in the field of up to twenty or more years. Many internal and external factors cause the reduction of the power generation efficiency of the photovoltaic module, and factors such as manufacturing difference or installation difference between the photovoltaic modules themselves or shading or maximum power tracking adaptation cause low efficiency. Taking a typical shadow shielding as an example, if a part of photovoltaic modules is shielded by clouds, buildings, tree shadows, dirt and the like, the part of the photovoltaic modules can be changed into a load by a power supply and does not generate electric energy any more, the local temperature of the photovoltaic modules in places with serious hot spot effect may be higher, and some of the photovoltaic modules even exceed 150 ℃, so that the local area of the photovoltaic modules is burnt or forms a dark spot, welding spots are melted, packaging materials are aged, glass is cracked, corrosion and other permanent damages are caused, and the long-term safety and reliability of the photovoltaic modules are caused to be extremely hidden. The problems to be solved by photovoltaic power stations/systems are as follows: the working state of each installed photovoltaic cell panel can be observed in real time, the early warning can be carried out on abnormal conditions such as over-temperature, over-voltage, over-current and output end short circuit of the battery, and the emergency warning device is very meaningful for taking active safety shutdown or other emergency measures for the abnormal battery. Whether centralized photovoltaic power plants or distributed small power plants, it is essential to judge and identify those components that have potential problems based on the operating parameter data collected for the photovoltaic components.

In the field of photovoltaic power generation, photovoltaic modules or photovoltaic cells need to be connected in series to form a cell string, and then the cell string is connected in parallel to supply power to power equipment such as a combiner box or an inverter, so that the installation of the modules or the cells is required to be absolutely safe. If the photovoltaic modules have abnormal conditions such as over-temperature, over-voltage or over-current, the abnormal photovoltaic modules are required to be actively triggered to be turned off, and when the abnormal photovoltaic modules exit from the abnormal state and return to the normal state, the abnormal photovoltaic modules are required to be connected again, so that absolute safety is also required. In addition, in some occasions, the generated energy of the component needs to be detected or the output power condition needs to be monitored, which is the basis for judging the quality of the component, for example, if the generated energy of the component is obviously reduced, an abnormal event of power generation is likely to occur and is shielded by bird droppings, dust, buildings, tree shadows, clouds and the like, and measures such as cleaning batteries or changing the installation direction are needed. As known to those skilled in the art, a monocrystalline silicon solar cell, a polycrystalline silicon solar cell, an amorphous silicon solar cell, and the like are materials whose characteristics are easily degraded, and it is essential to monitor the degradation degree of a module, which is very important for determining the quality of a battery. The problems are that: we do not know how to discriminate in a large array of components those components are anomalous and those components are normal, and the following will address this problem. Many times, the battery or the component with poor quality needs to be directly judged in the installation stage, the battery with the quality defect is never allowed to be assembled/installed in the photovoltaic battery array, otherwise, the battery with the quality problem enters the photovoltaic battery array to cause low power generation efficiency of the whole array, and worse, the abnormal voltage value or current value of one or more problem batteries can cause damage to the whole battery string group, so that great loss is caused.

Referring to fig. 1, the difference from the conventional photovoltaic module in direct series is that: firstly, any photovoltaic module is provided with a power optimizer, the power optimizer completes voltage matching and electrical isolation between a battery and an inverter, and then the inverter completes inversion conversion from direct current to alternating current and supplies power to a terminal load. Similar to the conventional solution, the photovoltaic power generation system has a plurality of photovoltaic modules PV1, PV2 … … PVN connected in series, which are connected in series to form a battery string, and the battery string is formed by connecting N-stage series-connected photovoltaic modules PV1 to PVN in series. The photovoltaic modules or photovoltaic cells PV are each provided with a power optimization circuit PO that performs maximum power tracking MPPT: for example, the photovoltaic voltage generated by the first PV module PV1 in the cell string is converted from dc to dc by the first power optimization circuit PO1 to perform power optimization, the photovoltaic voltage generated by the second PV module PV2 is converted from dc by the second power optimization circuit PO2, and the photovoltaic voltage generated by the PV module PVN to the nth stage is converted from dc by the nth stage power optimization circuit PON to perform power optimization. In essence, the voltage output by the power optimization circuit PO corresponding to each photovoltaic cell PV can be indicative of the actual voltage that the photovoltaic cell PV provides across the string of photovoltaic cells. Setting an arbitrary string of lightsThe photovoltaic cell string is connected with a first-stage photovoltaic module PV1, a second-stage photovoltaic module PV2 … to an Nth-stage photovoltaic module PVN in series: the first stage power optimization circuit PO1 performs maximum power tracking on the photovoltaic voltage source of the first stage photovoltaic cell PV1 to perform voltage conversion and output V₁The second stage power optimization circuit PO2 outputs V₂The power optimization circuit PON of the Nth level performs maximum power tracking on the voltage of the photovoltaic cell PVN of the Nth level to perform direct-current voltage conversion and output V_N。

Referring to fig. 1, it can be calculated that the total string level voltage on any string of pv cell strings is roughly equal to: voltage V output by first stage power optimization circuit PO1₁Plus the voltage V output by the PO2 of the second stage power optimization circuit₂And the voltage V output by the third stage power optimization circuit PO3₃… … to the Nth stage of the power optimization circuit PON_NThe operation result of the cascade voltage is equal to V₁+ V₂+……V_N. The topology of the power optimization circuit/optimizer or the voltage conversion circuit PO in this context is essentially a DC/DC converter from DC to DC, typical BUCK converters BUCK, BOOST converters BUCK, BUCK-BOOST converters BUCK-BOOST, etc. are all suitable for the power optimization circuit. It should be emphasized that any scheme for tracking the maximum power of the photovoltaic cell disclosed in the prior art is also applicable to the voltage conversion circuit of the present application, and the common maximum power tracking methods include a constant voltage method, a conductance increment method, a disturbance observation method, and the like, and the detailed description of the scheme for performing maximum power tracking on the voltage conversion circuit is not repeated herein. The voltage output by the power optimization circuit corresponding to each photovoltaic cell is explained before to characterize the actual voltage that the photovoltaic cell provides across the string of photovoltaic cells: the first-stage power optimization circuit PO1, the second-stage power optimization circuit PO2 to the Nth-stage power optimization circuit PON and the like are connected in series through a serial connection transmission line LAN, N is a natural number, and serial voltage superposed by the optimizer on the transmission line is transmitted to power equipment INVT such as a combiner box/an inverter through a direct current bus for combination/inversion. A bus capacitor CD for stabilizing voltage is also connected in series between the positive and negative poles of the transmission line LAN as a dc bus.

Referring to fig. 2, in an alternative embodiment: the first input end of the first stage voltage conversion circuit PO1 is connected to the positive electrode of the paired photovoltaic cell PV1 and the second input end of the first stage voltage conversion circuit PO1 is connected to the negative electrode of the photovoltaic cell PV1, and the voltage conversion circuit PO1 outputs a stable voltage between its first output end or first node N1 and second output end or second node N2, i.e. the first stage voltage conversion circuit PO1 extracts a voltage source generated by the photovoltaic cell PV1 through the photovoltaic effect between the first input end and the second input end to perform power optimization to provide an output voltage.

Referring to fig. 2, in an alternative embodiment: the first input end of the nth stage voltage conversion circuit PON is connected to the positive electrode of the paired photovoltaic cell PVN and the second input end of the nth stage voltage conversion circuit PON is connected to the negative electrode of the photovoltaic cell PVN, the nth stage voltage conversion circuit PON outputs a stable voltage between its first output end or first node N1 and second output end or second node N2, and the nth stage voltage conversion circuit PON extracts a voltage source generated by the photovoltaic cell PVN through the photovoltaic effect between the first input end and the second input end to perform power optimization to provide an output voltage.

Referring to fig. 2, in practical applications, a large number of photovoltaic cells or photovoltaic modules are connected in series to form a desired battery string, assuming that a total of N levels of photovoltaic cells PV1, PV2 … … PVN are connected in series, where N is usually a natural number greater than 1, and the string voltage of the battery string is roughly equal to: voltage V output by first stage photovoltaic cell PV1₁Plus the voltage V output by the second stage PV2₂Adding the voltage … output by the third stage PV3 to the voltage V output by the Nth stage PV PVN_NIs equal to V₁+ V₂+……V_N. The string-level voltage of the battery string is sent to the power equipment INVT such as a combiner box or an inverter. A total of N levels of PV1, PV2 … … PVN are connected in series, wherein the series connection of the PV cells results in a total voltage supplied that is high and dangerous for the service or installation personnel, or the actual measured voltage of the individual components is low, but high in series, etc.

Referring to fig. 2, each photovoltaic module or photovoltaic cell is configured with a voltage conversion circuit that performs voltage boosting or voltage dropping or voltage boosting and voltage dropping: for example, the photovoltaic voltage generated by the first PV module PV1 in a cell string is DC/DC voltage converted by the first voltage conversion circuit PO1 to perform voltage step-up and step-down, the photovoltaic voltage generated by the second PV module PV2 is voltage converted by the second voltage conversion circuit PO2, and the photovoltaic voltages generated by the photovoltaic modules PON from … … to the nth stage are voltage converted by the nth stage voltage conversion circuit PON to perform voltage step-up and step-down functions. It is only the voltage output by the voltage conversion circuit PO corresponding to each photovoltaic cell PV that can represent the actual voltage that the photovoltaic cell PV provides on the photovoltaic cell string. The voltage conversion circuit PO or voltage converter is essentially a dc-to-dc voltage converter topology. In addition to collecting data for the photovoltaic module, the processor 200 described herein also outputs a switch control signal for driving the voltage converter: the on or off state of the power switches in the voltage converter is substantially controlled by a switch control signal or modulation signal output by the microprocessor 200, such as a logic device, a plurality of processors, a control device, a state machine or controller or chip, a software driven control, a gate array, and/or other equivalent controller, with a pulse width modulation signal being particularly typical as the switch control signal. The switching control signal output by the processor drives a power switch in a switching power supply system to perform operations between on and off, and the switching power supply system generally adopts a power semiconductor device as a switching element, and controls the duty ratio of the switching element to adjust the output voltage by periodically switching on and off the switch.

Referring to fig. 2, the first-stage voltage conversion circuit PO1, the second-stage voltage conversion circuit PO2, up to the so-called N-th-stage voltage conversion circuit PON, and the like shown in the figure are connected in series by a series line LAN, and in a link in which a multistage voltage conversion circuit or a power optimizer PO1-PON are connected in series, the connection relationship is: the second output terminal of any previous stage power optimizer is coupled to the first output terminal of an adjacent subsequent stage voltage conversion circuit, so that the respective output capacitors of the multi-stage power optimizers PO1-PON are connected in series with each other, and the link provides a total cascade voltage equal to the sum of the voltages on the respective output capacitors of the multi-stage power optimizers in the chain. The second output terminal N2 of the first stage voltage converting circuit PO1 is coupled to the first output terminal N1 of the adjacent succeeding stage voltage converting circuit PO2, the second output terminal N2 of the second stage voltage converting circuit PO2 is coupled to the first output terminal N1 of the adjacent succeeding stage voltage converting circuit PO3, and so on, the second output terminal N2 of the N-1 th stage voltage converting circuit is coupled to the first output terminal N1 of the adjacent succeeding stage voltage converting circuit PON. The output capacitor CO of each power optimizer is connected between its first and second output terminals N1-N2, and the total cascade voltage provided by the link is equal to the superimposed value of the voltage of CO on the output capacitor of each of the multi-stage power optimizers PO1-PON, so that the cascade voltage superimposed by the voltages output by the voltage conversion circuits PO1-PON on the transmission line is transmitted to the electric power equipment INVT similar to a combiner box or an inverter for combination and re-inversion, etc.

Referring to fig. 3, the basic principle of implementing the maximum power point tracking algorithm is explained by taking an optional two photovoltaic modules PV _ M and PV _ N as an example: the adjacent or non-adjacent photovoltaic modules PV _ M and PV _ N supply power to a voltage conversion circuit or voltage converters PO _ M and PO _ N, respectively, which performs maximum power tracking on the photovoltaic cells. The conversion efficiency of a photovoltaic module or cell is mainly affected by two aspects: the first is the internal cell characteristics of the photovoltaic cell; the second is the surrounding use environment of the battery, such as the solar radiation intensity, load condition, temperature condition, and the like. Under different external conditions, the photovoltaic cell can operate at different and unique maximum power points, and the real-time optimal working state of the photovoltaic cell under any illumination condition should be searched to convert the light energy into electric energy to the maximum extent.

Referring to fig. 3, the photovoltaic module PV _ M generates a desired output voltage using the voltage conversion circuit PO _ M while performing maximum power point tracking. The first input NI1 of the voltage conversion circuit PO _ M is connected to the positive pole of the photovoltaic module PV _ M and the second input NI2 of the voltage conversion circuit PO _ M is connected to the negative pole of the photovoltaic module PV _ M. It is noted that the first output terminal NO1 of the voltage converting circuit PO _ M is coupled to the only first node N1 of the voltage converting circuit PO _ M, the second output terminal NO2 of the voltage converting circuit PO _ M is coupled to the second node N2 of the voltage converting circuit PO _ M, and further an output capacitor CO is connected between the first node N1 and the second node N2. The voltage conversion circuit performs DC/DC voltage conversion on the voltage provided by the photovoltaic module and performs maximum power tracking calculation synchronously, and the DC output voltage output by the voltage conversion circuit is generated between the first output terminal and the second output terminal of the voltage conversion circuit PO _ M, and the output voltage is loaded on the output capacitor CO between the first node N1 and the second node N2. That is, the output capacitor is connected between the first node N1 and the second node N2 of the voltage converting circuit itself in the figure. The power switch S1 and the power switch S2 of the BUCK conversion circuit BUCK module in the voltage conversion circuit PO _ M are connected in series between the first input NI1 and the second input NI2, and the power switch S3 and the power switch S4 of the BOOST conversion circuit BOOST in the voltage conversion circuit PO _ M are connected in series between the first output NO1 and the second output NO 2. Wherein both the power switch S1 and the power switch S2 in the Buck converter circuit module are connected to the first interconnection node NX1, and both the power switch S3 and the power switch S4 in the Boost converter circuit module are connected to the second interconnection node NX2, then a main inductive element L is disposed between the first interconnection node NX1 to which both the front-side power switches S1-S2 are connected and the second interconnection node NX2 to which both the rear-side power switches S3-S4 are connected in the Buck-Boost circuit topology, and the second output terminal NO2 and the second input terminal NI2 can be directly coupled together and set their potentials to a reference potential REF 1. Corresponding to the output capacitance CO provided between the first and second output terminals is the input capacitance CIN provided between the first and second input terminals NI1, NI2 of the converter. The direct driving capability of the processor configured in the voltage conversion circuit PO _ M is weak, and sometimes it is impossible to directly drive the switches such as the power MOSFET or the IGBT, and the driver/buffer with stronger driving capability can be used to enhance the strength of the switch control signal to drive the power switches S1-S4.

Referring to fig. 3, the photovoltaic module PV _ N generates a desired output voltage while performing maximum power point tracking using the voltage conversion circuit PO _ N, the first input terminal NI1 of the voltage conversion circuit PO _ N being connected to the positive electrode of the photovoltaic module PV _ N and the second input terminal NI2 of the voltage conversion circuit PO _ N being connected to the negative electrode of the photovoltaic module PV _ N. Note that the first output terminal NO1 of the voltage conversion circuit PO _ N is coupled to a first node N1 corresponding exclusively to the voltage conversion circuit PO _ N itself, and the second output terminal NO2 of the voltage conversion circuit PO _ N is coupled to a second node N2 corresponding exclusively to the voltage conversion circuit PO _ N itself, and an output capacitor CO is connected between the first node N1 and the second node N2. The voltage conversion circuit PO _ N performs DC/DC voltage conversion on the voltage of the photovoltaic module PV _ N and performs maximum power tracking calculation synchronously, so that the DC output voltage output by the voltage conversion circuit PO _ N is generated between the first output terminal NO1 and the second output terminal NO2 of the voltage conversion circuit PO _ N, that is, the output voltage is applied to the output capacitor CO of the voltage conversion circuit PO _ N. The output capacitor CO is connected between the first node N1 and the second node N2 of the voltage conversion circuit itself in the figure. The power switch S1 and the power switch S2 of the BUCK conversion circuit block BUCK in the voltage conversion circuit PO _ N are connected in series between the first input NI1 and the second input NI2, and the power switch S3 and the power switch S4 of the BOOST circuit BOOST in the voltage conversion circuit PO _ N are connected in series between the first output NO1 and the second output NO 2. Both the power switch S1 and the power switch S2 of the Buck are connected to a first interconnection node NX1, both the power switch S3 and the power switch S4 in the Boost module are connected to a second interconnection node NX2, a main inductance element L is arranged between the first interconnection node NX1 to which both the front side power switches S1-S2 are connected and the second interconnection node NX2 to which both the rear side power switches S3-S4 are connected in the Buck-Boost, and the second output NO2 and the second input NI2 in the voltage conversion circuit PO _ N may be directly coupled together and set their potentials to a reference potential REF 2. Also in the voltage conversion circuit PO _ N, corresponding to the output capacitance CO normally provided between the first output terminal NO1 and the second output terminal NO2, is an input capacitance CIN provided between the first input terminal NI1 and the second input terminal NI2 in the voltage conversion circuit PO _ N. The direct driving capability of the processor configured in the voltage conversion circuit PO _ N is weak, sometimes the switch such as the power MOSFET or the IGBT cannot be directly driven, and the driver/buffer with stronger driving capability can be used to enhance the strength of the switch control signal to drive the power switch.

Referring to fig. 3, the voltage converting circuit PO _ M and the voltage converting circuit PO _ N are adjacent and connected in series, and in the series relation of the voltage converting circuits, for example: the second node N2 of the previous stage voltage conversion circuit PO _ M is connected to the first node N1 of the next stage voltage conversion circuit PO _ N. The plural voltage conversion circuits PO1, PO2, … PON are connected in series in this manner, and the second node N2 of any preceding-stage voltage conversion circuit PO _ M is coupled to the first node N1 of the adjacent succeeding-stage voltage conversion circuit PO _ N through the transmission line LAN, or the output capacitance CO of any preceding-stage voltage conversion circuit PO _ M is connected in series by the transmission line LAN and the output capacitance CO of the adjacent succeeding-stage voltage conversion circuit PO _ N. In the same way, when the multi-stage voltage conversion circuit PO1-PON is connected in series, the output capacitors C of the multi-stage voltage conversion circuit PO1-PON are connected in series_OSeries connection: i.e. the output capacitance CO of the voltage conversion circuit PO1 and the output capacitance CO of PO2 and the output capacitance CO … of PO3 and the output capacitance CO of the PON, etc. are connected in series by the transmission line LAN, the series of conversion circuits etc. in series provide a total cascade voltage equal to the sum of the voltages over their respective output capacitances CO of the voltage conversion circuits PO 1-PON.

Referring to fig. 2, the total cascade voltage of the multi-stage optimizer is provided between the first node N1 of the first stage voltage conversion circuit PO1 and the second node N2 of the last stage voltage conversion circuit PON, the first node N1 of the first stage voltage conversion circuit PO1 is equivalent to being the equivalent positive pole of the link PO1-PON, and the second node N2 of the last stage voltage conversion circuit PON is equivalent to being the equivalent negative pole of the link PO 1-PON.

Referring to fig. 3, to explain the inventive spirit of the scheme for implementing mode switching, taking the illustrated voltage converter for implementing power conversion as an example, the voltage converter, if it is a BUCK circuit, i.e., the switch S1 and the switch S2 constitute a BUCK single arm. In the BUCK circuit, the illustrated switches S3-S4 can be directly eliminated from the circuit topology, and the main inductive element L of the BUCK circuit can be directly connected between the interconnection node NX1 and the first output NO 1. Or if the voltage converter is operated in the BUCK state, the switch S4 can be continuously turned on and the switch S3 can be continuously turned off, only the front side power switch S1 and the front side power switch S2 are driven to switch at high frequency, and the power conversion BUCK circuit can operate independently.

Referring to fig. 3, to explain the inventive spirit of the scheme for implementing mode switching, the voltage converter for implementing power conversion is illustrated as an example, and the voltage converter is a BOOST circuit, i.e., the switch S3 and the switch S4 constitute a BOOST single arm. In a BOOST circuit, the switches S1-S2 may be directly eliminated from the circuit topology, and the main inductive element L in the BOOST circuit may be directly connected between the interconnection node NX2 and the first input NI 1. Or if the voltage converter is operated in the BOOST state, the switch S1 can be continuously turned on and the switch S2 can be continuously turned off, only the rear power switch S3 and the rear power switch S4 are driven to switch at high frequency, and the BOOST circuit of the power converter can operate independently.

Referring to fig. 3, another alternative voltage converter for implementing power conversion is taken as an example: the power switches S1 and S2 are connected in series between the first input NI1 and the second input NI2, the switches S3 and S4 using power transistors are connected in series between the first output NO1 and the second output NO2, note that both the power switch S1 and the switch S2 are connected to the interconnection node NX1 and both the power switch S3 and the switch S4 are connected to the interconnection node NX2, and additionally a main inductive element L is connected between the first interconnection node NX1 and the second interconnection node NX 2. Therefore, the single arm S1-S2 used as the BUCK of the previous stage and the single arm S3-S4 used as the BOOST of the later stage form a BUCK-BOOST circuit, and the BUCK-BOOST circuit has power conversion capability of BUCK and BOOST, and is in an H bridge type.

Referring to fig. 4, in the method for controlling the power optimizer to switch between different working modes, the transient short circuit is performed on the cascade voltage provided by the link to which the power optimizer of the working mode to be switched belongs for one or more times; and detecting whether a transient short-circuit event occurs in the link by a power optimizer of the working mode to be switched, wherein the detected transient short-circuit event is used as a basis for switching from one working mode to another working mode. In one embodiment: the first node N1 of the first stage of the voltage conversion circuit PO1 is equivalent to the equivalent anode EA of the link PO1-PON, and the Nth stage of the power supplyThe second node N2 of the voltage conversion circuit PON is equivalent to the equivalent negative EC of the link PO 1-PON. Transient-short (transient-short) any link to which the power optimizer of the to-be-switched operating mode belongs, for example, the link voltage converting circuit PON in fig. 4 to be shorted belongs to the power optimizer of the to-be-switched operating mode, and the voltage converting circuit PO1 also belongs to the power optimizer of the to-be-switched operating mode, and assuming that the link needs to be forced into a safe sleep or safe mode from a dangerous operating state of a high voltage, the voltage converting circuit of the to-be-switched operating mode is switched from an original first operating state to a second operating state. Cascade voltage V of link to which power optimizer of transient short-circuit to-be-switched operating mode belongs₁+V₂…+V_NThe following characteristics exist: the first node N1 of the first-stage voltage conversion circuit PO1, that is, the equivalent positive electrode EA, and the second node N2 of the last-stage voltage conversion circuit PON, that is, the equivalent negative electrode are short-circuited according to the illustration in the figure, for example, the first short-circuit ST1, the second short-circuit ST2, and the third short-circuit ST3 are performed until a short-circuit operation is performed more times, and the link in series with the multi-stage dc voltage converter is still a voltage source/stable battery essentially, and short-circuiting between the equivalent positive electrode EA-EC thereof will produce several different effects, which are used as an instruction in the present application. The issuance of the command is artificial, that is, it is necessary to actively short the EA-EC, and the reception of the command is the processor 200, and the processor 200 is originally used to drive the power switch of the voltage conversion circuit to turn on or off at a high speed, so as to control the duty ratio of the switching element to adjust the output voltage, but here, the processor 200 also needs to assist in capturing the command from the link through its own or an additional detection module capable of monitoring the change of the current/voltage/power, etc.

Referring to fig. 4, transient short-circuiting one or more times a cascade voltage V provided by a link to which the power optimizer of the operating mode to be switched belongs₁+V₂…+V_NThe method has various ways, and the conductors such as metal sheets or metal strips or wires can be used for directly trying connection/coupling between the equivalent positive electrode EA-EC and the equivalent negative electrode EA-EC of the equivalent battery of the link, and the like, and the attention must be paid toThe transient short circuit means that the short circuit is not allowed to be continuously connected, and generally, the short circuit must be disconnected immediately after each short circuit is connected, for example, the equivalent positive electrode and the equivalent negative electrode are disconnected immediately after being connected for 1 to 3 seconds, or the equivalent positive electrode and the equivalent negative electrode are disconnected after being connected for 6 seconds.

Referring to fig. 5, in addition to the transient short circuit realized by directly trying connection or coupling between the equivalent positive and negative electrodes EA-EC of the link through the external conductor, a connection power switch Q may be disposed between the equivalent positive and negative electrodes EA-EC of the link. Note that as an alternative, a diode D for unidirectional conduction is connected between the equivalent anode EA of the link and the positive receiving end of the energy collecting device, for example, the equivalent anode EA of the link is connected to the anode of the diode D, and the cathode of the diode D is connected to the positive receiving end of the energy collecting device. Or the anode of a not shown diode is connected to the negative receiving terminal of the energy scavenging means and the cathode of this not shown diode is connected to the equivalent negative pole EC of the link. The energy collecting device may be an energy storage device with an energy storage battery or the like, in addition to the aforementioned inverter or the junction box or the like. The power switch Q between the equivalent positive and negative electrodes of the link may be driven by a control signal with a high level or a low level generated by a control unit like a processor, or may be turned on/off directly by pressing or touching the power switch Q manually, where the manually controlled switch typically includes a button switch, a touch switch, a remote control switch, or the like. Each photovoltaic module PV is provided with a power optimizer PO for executing maximum power point tracking, the cascade voltage provided by a link to which the power optimizer of the working mode to be switched belongs is subjected to transient short-circuit for one or more times, whether a transient short-circuit event occurs to the link is detected by the power optimizer PO of the working mode to be switched, and the detected transient short-circuit event is used as a basis for switching from the previous working mode to the other latter working mode. It should be appreciated that: the true transient short event allows a short to be considered valid, while various non-true transient short events need to be masked out and considered invalid shorts. Various types of unexpected noise present in the circuit may cause the presence of non-realistic transient short events to be detected, for example, an arc or various similar surges cause the appearance of the circuit in the link to be similar to that caused by transient shorts that short the equivalent anode and cathode EA-EC.

Referring to fig. 5, the power switch Q is turned on transiently one or more times, the turn-on time: resulting in a closed loop formed by the link between the first node N1 of the voltage conversion circuit PO1 of the first stage and the second node N2 of the voltage conversion circuit PON of the nth stage, including the multistage voltage conversion circuit PO1-PON, with the switch Q switched on. The method for detecting the transient short-circuit event comprises the steps of detecting the variable quantity of a preset index induced by the short-circuit of the cascade voltage, and when the variable quantity meets a preset change condition, the transient short-circuit event is regarded as a real transient short-circuit event, and at the moment, the power optimizer of the working mode to be switched switches from one working mode to another working mode. The closed loop LOP goes from the first node of the voltage converting circuit of the previous stage to the second node of the voltage converting circuit of the previous stage and then to the first node of the voltage converting circuit of the next stage and to the second node of the voltage converting circuit of the next stage, and so on, with the result that: from the first node N1 of the voltage conversion circuit PO1 of the first stage, then to the second node N2 of the voltage conversion circuit PON of the nth stage, and back to the first node N1 of the voltage conversion circuit PO1 of the first stage through the switch Q. The predetermined index is, for example, one of the discrimination criteria that the transient change rate of the cascade voltage of the link during transient short circuit is measured by measuring the transient voltage change rate of the closed loop, and the transient short circuit event is considered to be real and effective only if the variation of the transient change rate of the cascade voltage is not lower than the preset transient voltage change rate (i.e., meets the change condition). Transient change of voltage, transient for short, transient reaction generated when external interference signals such as change of cascade voltage are generated mainly comprises three characteristics: ultrahigh pressure, instantaneous state and high frequency. It can be classified into the following three types according to its performance: firstly, the transient voltage wave is an impact transient and is propagated along a line or a circuit, and the characteristic is that the voltage slowly falls after rapidly rising. The second is an oscillating transient, a sudden change in signal voltage or current at steady state, which oscillates at the system natural frequency and which causes the power signal to alternately amplify and attenuate at a very fast rate, usually decaying to zero in one cycle. And moreover, the voltage waveform is notched, continuous voltage oscillation transient phenomenon occurs, and the power voltage waveform distortion is caused by short-term interphase short circuit in the rapid switching-on and switching-off processes of the control switch. For example, the predetermined indicator is, for example, a transient short-circuit current (transient current) flowing through the transient short-circuited link, and the detecting of the transient short-circuit event includes detecting a variation of the transient short-circuit current in a closed loop induced by the short-circuited cascade voltage, and when the variation of the transient short-circuit current is not lower than a predetermined transient current value (i.e. meets a variation condition), the transient short-circuit event is regarded as a real transient short-circuit event rather than an accidental event. The transient short-circuit current and the transient voltage change rate in the closed loop are mainly dominated by a series of output capacitors CO respectively connected in series with a series of voltage conversion circuits PO1-PON, so that the accuracy can be increased by synchronously detecting the transient short-circuit current and the transient voltage change rate by a power optimizer or a conversion circuit of a working mode to be switched, and a real transient short-circuit event is only generated when the variation of the transient voltage change rate is not lower than the preset transient voltage change rate and the variation of the transient short-circuit current is not lower than the preset transient current value. The change amount of the predetermined index is generally and significantly reflected in that the short-circuit current increases once per short-circuit and the cascade voltage decreases once per short-circuit, which is the most direct reflection of the transient short-circuit event, the processor 200 monitors that the short-circuit current increases/the cascade voltage decreases transiently, the change condition of the current or the voltage actually meets the preset change condition (increase or decrease), the processor can consider that the transient short-circuit event occurs, and the measurement of the change rate of the transient short-circuit current/the transient voltage is only for increasing the measurement accuracy.

Referring to fig. 6, the power optimizer or converter circuit to be switched in operation mode is allowed to switch in different operation modes, which basically should include a safety mode and a normal operation mode according to the desired output rated voltage in the battery application of the photovoltaic power station. The so-called safe mode naturally requires that the voltage output by the voltage conversion circuit, such as a PON, is so low that the cascade voltage provided by the whole link is also so low that when the voltage output by any one power optimizer in the whole link is so low, it does not pose a potential personal threat. Such as: the power optimizer is in a safe mode in which the output voltage of the power optimizer is continuously lower than the input voltage, and it is mentioned that the power optimizer may be a BUCK-BOOST topology, so that the safe mode may cause the topology to operate in a BUCK mode to have its output voltage lower than the received voltage supplied by the components, and in the simplest manner, the output voltage of each stage of the power optimizer is made to be zero and safest. However, each stage of power optimizer output voltage is completely zero or close to zero, which also has the disadvantage that the dc bus LAN has no voltage or a voltage close to zero, and the reception of external commands by the processor 200 sometimes needs to be carried out by a carrier signal loaded or injected on the bus, which is a negative effect that if the dc bus drops to a potential close to zero, the carrier cannot be propagated with high quality. Therefore, another measure is to clamp the ratio of the output voltage and the input voltage of the power optimizer to be lower than a predetermined proportional relationship, for example, the output voltage VIN of a certain stage of the voltage conversion circuit PON comes from the component PVN, and its output voltage VN is used to be superimposed on the foregoing dc bus, so as to limit VN/VIN to be lower than the predetermined proportional relationship RAT, for example, lower than 1/5 or 1/20. It must be recognized that the only transitory action of a power optimizer operating in a safe mode is that the primary purpose of the power optimizer is to modulate its output voltage and output current such that the paired photovoltaic module operates at the maximum power point. The operation mode of the optimizer also includes a power tracking MPPT mode in which the power optimizer PO operates the photovoltaic module PV with which it is paired at the maximum power point.

Referring to fig. 6, the power optimizer or switching circuit to switch the operating mode is allowed to switch in different multiple operating modes: the first MOD1, the second MOD2, and the third MOD3 are assumed to be several common operation modes, such as MPPT tracking mode of maximum power point, safety mode, and standby sleep mode, which generally means the optimizer is not in standby. The aforementioned processor 200 outputs a switching control signal for driving the voltage converter, i.e. the voltage conversion circuit PO, wherein a pulse width modulation signal is particularly typical as the switching control signal, and the switching control signal outputted by the processor drives a power switch (e.g. S1-S4) in the switching power supply system SMPS to operate at a high frequency between on and off, and the switching power supply system usually employs a power semiconductor device as a switching element, and the duty cycle of the switching element is controlled by periodically switching on and off the switch to adjust the output voltage. The control modes of the switch control signal are divided into pulse width modulation, mixed modulation of pulse width modulation and frequency modulation, pulse frequency modulation and the like. In a switching power supply system, the voltage output by the switching operation generated by the voltage conversion circuit is coupled to the input or output of the circuit itself and further transferred to a common dc transmission line for providing the total cascade voltage. How to switch the voltage converter, i.e. the power optimizer, between the first mode MOD1 and the second mode MOD2 and the third mode MOD3 by using the switch control signal is a problem to be considered: it is one of the approaches to change the switching frequency or duty ratio of the switching control signal so that the switching frequency or duty ratio of the pwm signal in two different operating modes is different. For example, the switching frequency or duty ratio of the switching control signal driving the power optimizer is decreased, so that the switching mode can be switched from the tracking mode of the maximum power point, such as the first mode MOD1, to the second mode MOD2, such as the safety mode, and then the switching frequency or duty ratio of the switching control signal driving the power optimizer is decreased, so that the switching mode can be directly switched from the second mode MOD2, such as the safety mode, to the standby mode, such as the third mode MOD 3. For example, if the switching operation frequency or duty ratio of the switching control signal for driving the power optimizer is rapidly increased, the switching operation mode can be switched from the standby sleep mode, such as the third mode MOD3, to the mode for performing the maximum power point tracking, such as the first mode MOD1, thereby realizing the switching between the different modes.

Referring to fig. 5, the foregoing illustrates: the true transient short event allows a short to be considered valid, while various non-true transient short events need to be masked out and considered invalid shorts. In another embodiment, detecting the transient shorting event further comprises defining: the counted number of times of short circuit of the cascade voltage in the preset time period accords with the expected number of times. This also means that the processor on the power optimizer side must be allowed to perform a mode switch if the number of short events actually occurring matches the expected number even if a short event is detected, otherwise no switch is made. For illustration and not limitation, fig. 5 is a specific embodiment, the number of times the switch Q is short-circuited in the transient state is about 3, the power optimizer detects the variation of the predetermined index induced by the short-circuiting of the string voltage, and the total number of times the variation satisfies the predetermined variation condition is 3, which means that the number of short-circuiting events actually occurring completely meets the expected number of times 3, so as to allow the mode switching to be performed, and conversely, if the power optimizer detects the variation of the predetermined index induced by the short-circuiting of the string voltage and the total number of times the variation satisfies the predetermined variation condition is 1 or 4, the short-circuiting event is considered as an invalid short-circuiting event and should be ignored. In order to be able to monitor and capture and record voltage/current transient variations, current power quality measuring instruments are implemented, whose equivalent measuring instruments generally have the following properties: high sampling rate, more than 10kHz steady state level and more than transient MHz level. And has a high dynamic range: the input signal changes more than 20 times from dozens of volts to 8kV instantaneously. Some specifications/consensus, like IEC61000-4-30, to refer to defines the measurement of transient voltages: for example, the envelope method sets a waveform envelope range on the basis of a sine wave, and can be used for monitoring transients such as surge and waveform notch as a transient recording starting condition. The method comprises the following steps: very fast sampling and calculation at intervals much less than one fundamental period, the root-mean-square value is compared to a set threshold. For example, peak detection method: and setting a fixed absolute threshold, wherein the transient voltage value is transient when the transient voltage value exceeds the fixed absolute threshold, and the transient voltage value is used for measurement under models such as surge monitoring. For example, the rolling window method: the instantaneous value is compared with the corresponding value in the previous period, and the method can be used for monitoring the low-frequency transient phenomenon of the switching of the power factor correction capacitor. Taking the transient short-circuit current measured by the rogowski coil current transformer SR in fig. 5 as an example, a bus or a transmission line LAN passes through a sensor, the transformer SR can measure a fast-changing harmonic current in time and accurately, the amplitude ranges from a few amperes to thousands of amperes, and the frequency ranges from 0.1 hz to a few mhz, and the transient voltage measuring instrument is mainly characterized in that no direct electrical connection exists between the transformer and a measured link, a measuring signal of the transformer SR such as the transient short-circuit current can be directly transmitted to the processor 200 to inform whether a short-circuit event occurs in the processor, and the transient voltage measuring instrument can also transmit the transient voltage change rate thereof as a measuring signal to the processor 200 to inform whether a short-circuit event occurs in the processor. In addition, as an option, the processor 200 may measure the link voltage change before and after the short circuit by cooperating with the voltage sensor, and the processor may calculate the voltage change rate according to the voltage value before the short circuit and the voltage value after the short circuit measured by the voltage sensor, and the voltage sensor is also electrically isolated and needs to detect the voltage change of the transmission line LAN or the bus. In other words, based on the various options offered by the current technology, both current sensors capable of measuring short circuit currents and voltage sensors capable of measuring transient voltages are suitable for use in the present application.

Referring to fig. 5, the foregoing illustrates that various non-real transient shorting events need to be masked out and treated as invalid shorting events. In another embodiment, to enhance the identification accuracy, the detecting the transient short-circuit event includes detecting a variation of a predetermined index induced by the short-circuit of the string level voltage; and switching on the control switch for an indication time and then rapidly switching off the control switch; therefore, when the fact that the variable quantity of the preset index meets the preset change condition and the duration time of the transient short-circuit event is the same as the indication time is detected, the power optimizer of the to-be-switched working mode identifies the real short-circuit event. Let us assume that the artificially controlled control switch Q is turned on for an indicated time of 5 seconds, the variation of the actually measured transient voltage change rate is not lower than the preset transient voltage change rate VTRAN, and/or the variation of the actually measured transient short-circuit current is not lower than the preset transient current value ITRAN, i.e. the detected variation of the predetermined index induced by the short-circuiting of the cascade voltage must first satisfy the previously preset variation condition. On the premise of meeting the preset change condition, when detecting that the change amount of the preset index meets the preset change condition (for example, the transient voltage change rate is not lower than the VTRAN and/or the transient short-circuit current is not lower than the ITRAN) and the duration of the transient short-circuit event is the same as the indication time of 5 seconds, that is, the duration of the transient voltage change rate is not lower than the VTRAN is approximately 5 seconds and/or the duration of the transient short-circuit current is not lower than the ITRAN is approximately 5 seconds, the power optimizer of the to-be-switched operating mode performs the switching of the operating mode. In an alternative, but not necessary, embodiment, it is assumed that: when the power optimizer of the to-be-switched operating mode, that is, the voltage conversion circuit PON of the to-be-switched operating mode, detects a transient short-circuit event of a link, in addition to that it is required to detect that a variation (for example, a transient voltage variation rate and/or a transient short-circuit current) of a predetermined index induced by a short-circuit of a string voltage satisfies a preset variation condition, it is necessary to measure an instantaneous output power of a photovoltaic module PVN associated with the voltage conversion circuit PON of the to-be-switched operating mode, and only if it is simultaneously satisfied that the instantaneous output power of the photovoltaic module PVN associated with the voltage conversion circuit PON is approximately equal to zero and the variation of the predetermined index induced by the short-circuit of the string voltage satisfies the preset variation condition, it is a true valid short-circuit event, and the power optimizer PVN of the to-be-switched operating. In an alternative, but not necessary, embodiment, it is assumed that: the controlled control switch Q is turned on forcibly for an indicated time of 4 seconds, the variation of the transient voltage variation rate of the measurement loop in 4 seconds of Q-on is not lower than a preset transient voltage variation rate VTRAN, and/or the variation of the transient short-circuit current of the measurement loop in 4 seconds of Q-on is not lower than a preset transient current value ITRAN, taking a voltage conversion circuit PO1 of a certain to-be-switched operating mode as an example, on the premise that the variation of the predetermined index induced by sensing the short-circuit of the string-level voltage must satisfy the previously preset variation condition first (for example, the transient voltage variation rate is not lower than VTRAN and/or the transient short-circuit current is not lower than ITRAN), and the time of the transient short-circuit event is the same as the indicated time of 4 seconds, that is the duration of the transient voltage variation rate is not lower than VTRAN is about 4 seconds and/or the duration of the transient short-circuit, during the period, the output power of the photovoltaic module PV1, i.e. the product of the output current and the output voltage thereof, must be measured within 4 seconds of Q being turned on, and if the output power of the photovoltaic module PV1 is nearly zero during the period and cannot provide the output power to the outside, the voltage conversion circuit PO1 performs the switching of the operation mode. The output current and the output voltage of the photovoltaic module can be detected by a current detector (e.g., a shunt) and a voltage detector (e.g., a voltage divider), respectively.

Referring to fig. 7, the difference with the photovoltaic module in indirect series connection through the optimizer is that: any photovoltaic module is equipped with a switching module SH that determines whether its corresponding module PV supplies power to the string: the component may provide power to the string if the switching module is on and not allow power to the string if the switching module is off. Similar to the conventional solution, the photovoltaic power generation system has a plurality of photovoltaic modules PV1, PV2 … … PVN connected in series, which are connected in series to form a battery string, and the battery string is formed by connecting N-stage series-connected photovoltaic modules PV1 to PVN in series. The photovoltaic modules are each provided with a switching module that performs access or shielding: for example, the photovoltaic voltage generated by the first photovoltaic module PV1 in the cell string is determined by the first switching module SH1 to be connected into the cell string, the photovoltaic voltage generated by the second photovoltaic module PV2 is determined by the second switching module SH2 to be connected into the cell string, and the photovoltaic voltage generated by the photovoltaic module PVN of the nth stage is determined by the switching module SHN of the nth stage to be connected into the cell string. In essence, the voltage output by the switching module SH corresponding to each photovoltaic cell can be representative of the actual voltage that the photovoltaic cell provides on the string of photovoltaic cells: if the switching module shields the paired components, the output voltage of the paired components is zero, and if the switching module is connected to the paired components, the output voltage of the paired components is the actual battery voltage.

Referring to fig. 7, it is assumed that the first stage PV1, the second stage PV2 …, and the nth stage PV modules PVN are connected in series in any string of PV cell string, and in some embodiments: the first-stage switching module SH1 outputs V when switching on the photovoltaic voltage source of the first-stage photovoltaic cell PV1₁₁Or 0 is output when shielding is carried out, and the second-stage switching module SH2 outputs V when the photovoltaic voltage source of the second-stage photovoltaic cell PV2 is switched on₂₁Or 0 is output when shielding is carried out, and the switching module SHN of the Nth stage outputs V when the voltage of the photovoltaic cell PVN of the Nth stage is switched in_N1Or 0 when masked. It can be calculated that the total string voltage when all the components of any string of photovoltaic cell strings are connected is roughly equal to: first stage switching module SH1 output voltage V₁₁Plus the output voltage V of the second stage switching module SH2₂₁Then, the output voltage V of the third-stage switching module SH3 is added₂₃… added to the DC voltage V output by the switching module SHN of the Nth stage_N1The operation result of the cascade voltage is equal to V₁₁+ V₂₁+……V_N1. The output voltage V of a photovoltaic module PVK if a certain module PVK is shielded by its switching module SH K_K1It should be subtracted from the total string voltage, K being a natural number, which in the most extreme case is that all components on the battery string are shielded by the respective switching module, resulting in the string voltage being nearly equal to zero.

Referring to fig. 8, the photovoltaic module PV _ M performs switching into or out of the cell string using the switching module SH _ M. The first input NI1 of the switching module SH _ M is connected to the positive pole of the photovoltaic module PV _ M and the second input NI2 of the switching module SH _ M is connected to the negative pole of the photovoltaic module PV _ M. In an alternative but non-limiting embodiment, the first output NO1 of the switching module SH _ M may be coupled to the only first node N1 of the switching module SH _ M by means of a current divider not shown in the figure, and the second output NO2 of the switching module SH _ M may be coupled to the only second node N2 of the switching module SH _ M by means of a current divider RS in the figure. The output capacitor CO may be selectively connected between the first node N1 and the second node N2 or the capacitor CO may be selectively removed. The embodiment of fig. 8 replaces the power optimizer in fig. 3 with a switching module. The topology of the photovoltaic module PV _ M is as follows: the access switch SQ1 is coupled between the first input NI1 and the first output NO1, or the access switch SQ1 is coupled between the second input NI2 and the second output NO 2. The topology removal switch SQ2 is coupled between the first output NO1 and the second output NO 2. If the processor 200 of the switching module SH _ M configuration drives the access switch SQ1 on, the photovoltaic module PV _ M is accessed into the battery string and contributes its voltage component to the string voltage, at which point the processor 200 also drives the removal switch SQ2 off. Conversely, if the processor 200 of the switching module SH _ M configuration drives the removal switch SQ2 on, the photovoltaic module PV _ M is shielded/bypassed from the string of batteries and cannot contribute its voltage component to the string voltage of the string of batteries, at which point the processor 200 also drives the access switch SQ1 off. Note that in this embodiment the second output NO2 and the second input NI2 set their potentials to the reference potential REF 1. Comparing the present embodiment with the embodiment of fig. 3, if the fourth switch S4 in the buck-boost circuit PO _ M is continuously turned on and the second switch S2 is continuously turned off, the first switch S1 may be equivalent to an on switch and the third switch S3 may be equivalent to a off switch. Equivalent to the previous step-up and step-down circuit in fig. 3 not operating in the step-up and step-down voltage conversion mode, but being used in the switching mode to switch in or remove the photovoltaic module, the topology of fig. 3 is utilized in one embodiment instead of the switching module of fig. 8.

Referring to fig. 8, the photovoltaic module PV _ N performs switching into or out of the cell string using the switching module SH _ N. The first input NI1 of the switching module SH _ N is connected to the positive pole of the photovoltaic module PV _ N and the second input NI2 of the switching module SH _ N is connected to the negative pole of the photovoltaic module PV _ N. In an alternative but non-limiting embodiment, the first output NO1 of the switching module SH _ N may be coupled to the only first node N1 of the switching module SH _ N via a current divider RS in the figure, and the second output NO2 of the switching module SH _ N may be coupled to the only second node N2 of the switching module SH _ N via a current divider not shown in the figure. The output capacitor CO may be selectively connected between the first node N1 and the second node N2 or the capacitor CO may be selectively removed. The embodiment of fig. 8 replaces the power optimizer in fig. 3 with a switching module. In the topology of the switching module SH _ N: the access switch SQ1 is coupled between the first input NI1 and the first output NO1, or the access switch SQ1 is coupled between the second input NI2 and the second output NO 2. The opposite removal switch SQ2 in the topology is coupled between the first output NO1 and the second output NO 2. If the processor 200 of the switching module SH _ N configuration drives the access switch SQ1 on and the photovoltaic module PV _ N is accessed to the battery string and contributes its voltage component to the string voltage, the processor 200 also drives the removal switch SQ2 off at this time. Conversely, if the removal switch SQ2 is driven to turn on by the processor 200 of the switching module SH _ N configuration, the PV module PV _ N is shielded/bypassed from the string of cells and cannot contribute its voltage component to the string voltage of the string of cells, at which point the processor 200 also drives the access switch SQ1 to turn off. Note that in this embodiment the second output NO2 and the second input NI2 are set to their potentials at the reference potential REF 2. Comparing the present embodiment with the embodiment of fig. 3, if the fourth switch S4 in the buck-boost circuit PO _ N is continuously turned on and the second switch S2 is continuously turned off, the first switch S1 may be equivalent to an on switch and the third switch S3 may be equivalent to a off switch. Equivalent to the previously disclosed voltage step-up and step-down circuit of fig. 3 not operating in a step-up and step-down voltage conversion mode, but being used in a switching mode to switch in or remove photovoltaic modules, the topology of fig. 3 is utilized in one embodiment instead of the switching module of fig. 8.

Referring to fig. 8, taking the photovoltaic module PV _ M and the switching module SH _ M as an example, the power supply of the photovoltaic module PV _ M can directly supply power to the processor 200 at the stage of being connected to the battery string, and if the switching module SH _ M is switched from the on mode to the off mode, that is, the access switch SQ1 of the switching module SH _ M is turned off and the removal switch SQ2 is turned on, the power supply of the photovoltaic module PV _ M may not continuously supply power to the processor 200. The solution is as follows: the PV module PV _ M is provided with an energy storage capacitor CS for supplying power to the processor 200 configured to the PV module PV _ M, and even in a stage where the PV module PV _ M is bypassed by the on removal switch, the switching module SH _ M can still supply power to the processor as a redundant backup power source because the energy storage capacitor CS is charged. The energy storage capacitor CS is connected between the positive pole of the photovoltaic module PV _ M and the reference potential REF1 of the photovoltaic module PV _ M in the topology: the anode of the diode DS is connected to the anode of the photovoltaic module PV _ M and the storage capacitor CS is connected between the cathode of the diode DS and the reference potential REF 1. The end of the storage capacitor CS connected to the cathode of the diode DS provides power to the processor 200. The optional shunt RS may detect whether current flows in or out from the output NO1 or NO2 of the PV module PV _ M, and generally supplies the current detection result of the shunt RS to the processor 200, as will be described further below. Alternatively, the voltage drop across the shunt can be detected by the output value of an operational amplifier coupled to the positive and negative ports of the shunt, and the voltage drop across the shunt can be used to substantially characterize the detection of the current flowing through the shunt.

Referring to fig. 8, the energy storage capacitor CS is charged from the anode of the photovoltaic module PV _ M through the diode DS for unidirectional transmission and can be regarded as a redundant battery. If the photovoltaic module PV _ N is also equipped with an energy storage capacitor, it should be noted that the energy storage capacitor of the photovoltaic module PV _ N should be connected between the positive pole of the photovoltaic module PV _ N and the reference potential REF2 of the photovoltaic module PV _ N, specifically: the anode of a certain diode is connected to the anode of the photovoltaic module PV _ N, and the energy storage capacitor matched with the photovoltaic module PV _ N is connected between the cathode of the diode and the reference potential REF 2. This is similar to the storage capacitor CS of the photovoltaic module PV _ M in fig. 8, but it is noted that the two differ with respect to the reference potential. In addition, the current divider RS referred to in fig. 8 can also be applied to the buck-boost topology of fig. 3.

Referring to fig. 8, assuming that the switching module SH _ M and the switching module SH _ N are adjacent and connected in series, in the series connection relationship of the multi-stage switching modules: the second node N2 of the previous stage switching module SH _ M is coupled to the first node N1 of the next stage switching module SH _ N. The multi-stage switching modules SH1, SH2, … SHN are connected in series in this manner, and the second node N2 of any preceding stage switching module SH _ M is coupled to the first node N1 of the adjacent succeeding stage switching module SH _ N through the transmission line LAN. Or the output capacitor CO of any previous stage switching module SH _ M is connected in series with the output capacitor CO of the adjacent next stage switching module SH _ N by the transmission line LAN. By analogy, when the multi-stage switching modules SH1-SHN are connected in series, if they employ output capacitors CO, these capacitors are connected in series: i.e. the output capacitance CO of the switching module SH1 and the output capacitance CO of the switching module SH2 and the output capacitance CO … of the switching module SH3 and the output capacitance CO of the switching module SHN, etc., are connected in series by the transmission line LAN, the total cascade voltage provided by a series of switching modules in series is equal to the sum of the voltages over their respective output capacitances CO of the switching modules SH 1-SHN. However, the output capacitances are not necessarily used, and they can also be omitted from the topology of the individual switching modules.

Referring to fig. 9, the cascade voltage of the multi-stage switching module is provided between the first node N1 of the switching module SH1 of the first stage and the second node N2 of the switching module SHN of the last stage in the multi-stage switching module, the first node N1 of the switching module SH1 of the first stage is equivalent to an equivalent positive pole of the link SH1-SHN, and the second node N2 of the switching module SHN of the last stage is equivalent to an equivalent negative pole of the link SH 1-SHN.

Referring to fig. 9, a method for controlling a switching module to switch between different working modes includes transiently shorting a cascade voltage provided by a link to which a photovoltaic module of one or more working modes to be switched belongs, detecting whether a transient short event occurs on the link by a processor configured with the photovoltaic module of the working mode to be switched and the switching module thereof, and using the detected transient short event as a basis for switching the photovoltaic module from one working mode (for example, access) to another working mode (for example, removal). In alternative but not required embodiments: the first node N1 of the switching module SH1 of the first stage is equivalent to the equivalent positive EA of the link SH1-SHN, and the second node N2 of the switching module SHN of the nth stage at the end is equivalent to the equivalent negative EC of the link SH 1-SHN. Similarly, a link to which any one of the photovoltaic modules to be switched in the operating mode belongs in the transient-short (transient-short), for example, a photovoltaic module PVN in the battery string group in fig. 9 to be shorted belongs to a certain photovoltaic module to be switched in the operating mode, and whether the certain photovoltaic module is connected to the battery string group or removed from the battery string group, is implemented by controlling the on or off of the switching module SHN paired with the certain photovoltaic module SHN. The photovoltaic module PVN belongs to a working mode to be switched, and is switched from access to removal or vice versa. Assuming that the pv module PVN needs to be forced to enter the safe sleep or safe mode of the removal phase from the over-temperature abnormal operating state generated in the access phase, the pv module PVN to be switched to the operating mode is switched from the initial first operating state to the second operating state. Cascade voltage V of link to which photovoltaic module PVN of transient short circuit to-be-switched working mode belongs₁₁+V₂₁…+V_N1The following characteristics exist: the first node of the first-stage switching module SH1 is alsoThat is, the second node of the equivalent positive electrode EA and the last switching module SHN at the end, that is, the equivalent negative electrode, is short-circuited according to the illustration in the figure, for example, the first short-circuit ST1, the second short-circuit ST2, and the third short-circuit ST3 are performed up to more times of short-circuit actions, and the link in series with the multi-stage photovoltaic module or the switching module SH is still a voltage source/stable battery in nature, and short-circuit between the equivalent positive electrode EA-EC thereof will generate several different effects, which are used as an instruction in the present application. The issuing of the instruction is artificial, that is, the short circuit EA-EC needs to be actively removed, and the receiving of the instruction is the processor 200 matched with the switching module SH. The processor 200 is originally mentioned as being used to drive the switch modules to turn on or off the removal switch and the access switch, but here the processor 200 also needs to assist in capturing such instructions from the link by its own or additional detection modules that can monitor changes in current/voltage/power, etc.

Referring to fig. 9, transient short-circuiting one or more times a cascade voltage V provided by a link to which a pv module PVN of the to-be-switched operating mode belongs₁₁+V₂₁…+V_N1The method has various ways, conductors such as metal sheets or metal strips or wires can be used for directly trying connection/coupling between the equivalent positive electrode EA-EC and the equivalent negative electrode EA-EC of the equivalent battery of the link, attention must be paid to transient short circuit which means that the short circuit is not allowed to be continuously connected, generally, the short circuit is connected each time and then immediately disconnected, for example, the equivalent positive electrode and the equivalent negative electrode are immediately disconnected after being connected for 1 to 3 seconds, or the equivalent positive electrode and the equivalent negative electrode are disconnected after being connected for 4 to 6 seconds, or the time is less than 10 seconds, and the specific time is only taken as an example. The transient short circuit is realized by directly trying connection or coupling between the equivalent positive and negative electrodes EA-EC of the link through the external conductor, and in addition, a connection power switch Q can be arranged between the equivalent positive and negative electrodes EA-EC of the link. Note that as an alternative, a diode D for unidirectional conduction is connected between the equivalent anode EA of the link and the positive receiving end of the energy collecting device, the equivalent anode EA of the link is connected to the anode of the diode D, and the cathode of the diode D is connected to the positive receiving end of the energy collecting device. Or an anode of a diode not shown is connected to the negative receiving terminal of the energy collecting means, andthe cathode of this not shown diode is then connected to the equivalent negative pole EC of the link. The energy collecting device may be an energy storage device with an energy storage battery or the like, in addition to the aforementioned inverter or the junction box or the like. The power switch Q between the equivalent positive and negative electrodes of the link may be driven by a control signal with a high level or a low level generated by a control unit like a processor, or may be turned on/off directly by pressing or touching the power switch Q manually, where the manually controlled switch typically includes a button switch, a touch switch, a remote control switch, or the like. In an alternative embodiment, in consideration of the fact that a short-circuit current caused by a short circuit is large and the transient voltage change rate is also large, a snubber circuit 300 connected in series with the power switch Q is further arranged between the equivalent positive electrode and the negative electrode EA-EC, and may include a capacitor or a resistor, an RC snubber circuit of a resistor and capacitor series connection type, and the like, or may be another type of snubber circuit, and the snubber circuit 300 is not necessary but may be omitted. The photovoltaic modules PV are all provided with switching modules SH used for executing access or removal, cascade voltage provided by a link to which the switching modules SH matched with the photovoltaic modules PV with the working modes to be switched belong is subjected to transient short circuit for one time or multiple times, a processor of the photovoltaic modules PV with the working modes to be switched detects whether transient short circuit events occur on the link, and the detected transient short circuit events serve as the basis for switching from the previous working mode to the other latter working mode. We should recognize that: the true transient short event allows a short to be considered valid, while various non-true transient short events need to be masked out and considered invalid shorts.

Referring to fig. 9, the power switch Q is turned on transiently one or more times, at which time: resulting in a closed loop consisting of the link between the first node N1 of the switching module SH1 of the first stage and the second node N2 of the switching module SHN of the nth stage, which contains the multi-stage switching modules SH1-SHN, and the switched-on switch Q. The method for detecting the transient short-circuit event comprises the steps of detecting the variable quantity of a preset index induced by the short circuit of the cascade voltage, and when the variable quantity meets a preset variable condition, the transient short-circuit event is regarded as a real transient short-circuit event, and at the moment, the photovoltaic module to be switched into the working mode is switched from one working mode to another working mode. The closed loop is mainly from the first node of the switching module of the previous stage to the second node of the switching module of the previous stage, then to the first node of the switching module of the next stage and to the second node of the switching module of the next stage, and as a result: from the first node N1 of the switching module SH1 of the first stage, to the second node N2 of the switching module SHN of the nth stage, and back to the first node N1 of the switching module SH1 of the first stage through the switch Q. The loop from the first node of the switching module to the second node of the switching module at any stage has two options: the first is that the first node is directly connected to its second node through the removal switch SQ2 when the removal switch SQ2 is turned on but the access switch SQ1 is turned off; the second is that when the removal switch SQ2 is off but the access switch SQ1 is on, the path through the access switch SQ1 and the photovoltaic module causes the first node of the switching module to be coupled to its second node through the module. For example, when the cascade voltage is provided by the multi-stage switching module link with the component in the transient short circuit, the transient voltage change rate of the cascade voltage can be regarded as one of the predetermined indexes, and the change amount of the transient voltage change rate of the cascade voltage should meet the condition that the transient voltage change rate is not lower than the preset transient voltage change rate (meets the change condition) and is regarded as a true and effective transient short circuit event. For example, the predetermined indicator is a transient short-circuit current flowing through the transmission line LAN of the transient short-circuited link, and the detecting of the transient short-circuit event includes detecting a variation of the transient short-circuit current in a closed loop induced by the short-circuit of the cascade voltage, and when the variation of the transient short-circuit current is not lower than a predetermined transient current value (meets a variation condition), the transient short-circuit event is regarded as a real transient short-circuit event rather than an accidental event. The transient short-circuit current and the transient voltage change rate in the closed loop are mainly dominated by a series of photovoltaic modules PV1-PVN corresponding to a series of switching modules SH1-SHN respectively, so that the accuracy can be improved when the photovoltaic modules or the switching modules of the working modes to be switched synchronously detect the transient short-circuit current and the transient voltage change rate, and a real transient short-circuit event is only generated when the variation of the transient voltage change rate is not lower than the preset transient voltage change rate and the variation of the transient short-circuit current is not lower than the preset transient current value. Taking the current transformer SR of fig. 5 as an example for measuring the transient short-circuit current, the bus or the transmission line LAN passes through the transformer, the transformer SR can measure the transient current value which changes rapidly and accurately in time, and the measured signal, such as the transient short-circuit current, can be directly transmitted to the processor 200 to inform the processor whether a short-circuit event occurs. The processor 200 can measure the change of the cascade voltage before and after the short circuit by matching with the voltage sensor, and the processor can calculate the voltage change rate according to the voltage value before the short circuit and the voltage value after the short circuit measured by the voltage sensor. Sensors for transient voltage measurement are known in the art. In other words, both a current sensor capable of measuring a short-circuit current and a voltage sensor capable of measuring a transient voltage are suitable for the present application.

Referring to fig. 9, in order to enhance the identification accuracy, in an alternative embodiment, the detecting of the transient short-circuit event includes detecting a variation of a predetermined index induced by the short-circuit of the cascade voltage; and switching on the control switch for an indication time and then rapidly switching off the control switch; therefore, when the variable quantity of the preset index is detected to meet the preset change condition and the duration time of the transient short-circuit event is the same as the indication time, the processor configured for the photovoltaic module with the working mode to be switched identifies the photovoltaic module with the working mode to be switched as a real short-circuit event. Let us assume that the artificially controlled control switch Q is turned on for an indicated time of 2 seconds, the variation of the actually measured transient voltage change rate is not lower than the preset transient voltage change rate VTRAN, and/or the variation of the actually measured transient short-circuit current is not lower than the preset transient current value ITRAN, i.e. the detected variation of the predetermined index induced by the short-circuiting of the cascade voltage must first satisfy the previously preset variation condition. On the premise of meeting the previously preset change condition, when it is detected that the change amount of the predetermined index meets the preset change condition (for example, the transient voltage change rate is not lower than the VTRAN and/or the transient short-circuit current is not lower than the ITRAN) and the duration of the transient short-circuit event is the same as the indication time of 2 seconds, that is, the duration of the transient voltage change rate is not lower than the VTRAN is approximately 2 seconds and/or the duration of the transient short-circuit current is not lower than the ITRAN is approximately 2 seconds, the photovoltaic module PV in the working mode to be switched performs the switching of the working mode: i.e. its mating switching module SH switches it to the removed state or the access state. In an alternative, but not necessary, embodiment, it is assumed that: when detecting a transient short-circuit event of a link, the processor 200 configured in the PV device PVN to be switched to the operating mode additionally measures the instantaneous output power of the PV device PVN to be switched to the operating mode, except that the detected change amount (such as the transient voltage change rate and/or the transient short-circuit current) of the predetermined index induced by the short-circuit of the string voltage satisfies the preset change condition, and only if the instantaneous output power of the PV device PVN is almost equal to zero and the change amount of the predetermined index induced by the short-circuit of the string voltage satisfies the preset change condition, the actual effective short-circuit event is a true effective short-circuit event, the PV device to be switched to the operating mode is switched from the access mode to the removal mode or vice versa, otherwise, the actual short-circuit event is regarded as an invalid instruction and is not switched. In an alternative embodiment: controlling the switch Q to be switched on for an indicated time of 1.2 seconds, wherein the variation of the transient voltage variation rate within 1.2 seconds of the Q switching on is not lower than a preset transient voltage variation rate VTRAN, and/or the variation of the transient short-circuit current within 1.2 seconds of the Q switching on is not lower than a preset transient current value ITRAN, taking a photovoltaic module PV1 of a certain to-be-switched operating mode as an example, under the premise that the variation of a preset index induced by sensing the short-circuiting of the cascade voltage is required to meet a preset variation condition (for example, the transient voltage variation rate is not lower than VTRAN and/or the transient short-circuit current is not lower than ITRAN), and the time of the transient short-circuit event is the same as the indicated time of 1.2 seconds, namely the duration of the transient voltage variation rate is not lower than the VTRAN is about 1.2 seconds and/or the duration of the transient short-circuit current is not lower than the ITRAN is about 1.2 seconds, and measuring the output power of the photovoltaic module PV1 and the output voltage, the switching module SH1 performs a mode switching from access to removal or removal to access if the output power of the mating photovoltaic module PV1 is nearly zero during this period and cannot be provided to the outside.

Referring to fig. 9, as long as some of the PV modules PV1-PVN in the cell string are not bypassed by the switching module associated therewith, a voltage exists between the equivalent positive electrode and the equivalent negative electrode EA-EC, so that the voltage is transiently shorted for one or more times, and then the processor 200 detects a change in a predetermined indicator, that is, an increase in the shorting current and/or a transient decrease in the voltage, so that the processor 200 executes a corresponding operation according to the change in the predetermined indicator as an instruction: turn on SQ1 and turn off SQ2 upon detection of a transient shorting event and switch the photovoltaic device into the string, or turn off SQ1 and turn on SQ2 upon detection of a transient shorting event and remove the photovoltaic device from the string. Consider another real problem: the number of photovoltaic modules connected to the string of cells among the individual photovoltaic modules PV1-PVN is very small, even if all the photovoltaic modules PV1-PVN are bypassed, and the voltage cascade between the equivalent positive and the equivalent negative poles EA-EC is very small or even zero, resulting in an increase in the short-circuit current and/or an insignificant transient decrease of the voltage cascade, even without any change in the predetermined criterion, and switching becomes difficult. For example, if the photovoltaic module was previously switched on state-SQ 1 on/SQ 2 off, and then switched by the command issued by the transient short event to make the photovoltaic module enter the sleep/standby state-SQ 1 off/SQ 2 on, the cascade voltage between the equivalent positive and equivalent negative electrodes EA-EC is very small or even zero, at which point the command issued by the transient short event is not functional, since it was mentioned before that the shunt RS can be set in the switching module SH topology, one solution at this time is: a potential difference is generated across the battery string, for example, between the equivalent positive and the equivalent negative poles EA-EC, and since the removal switches of the switching modules in the removed state of each stage are all turned on, an injection current is generated across the transmission line LAN and each shunt RS, and if the processor 200 senses the injection current, the access switch SQ1 is turned back on. There are two cases here: the switching modules SH1-SHN all turn on the removal switch SQ2 and turn off the access switch SQ 1; or in another case: the removal switch SQ2 of a partial switching module is turned on and the access switch SQ1 is turned off, and the removal switch SQ2 of the remaining partial switching module is turned off and the access switch SQ1 is turned on, at which time the removal switch SQ2 of the switching module with the access switch SQ1 in the access state is turned off but the access switch SQ1 thereof is turned on, so that the first node and the second node are still on, so that the injection current can still be effectively detected by the shunt RS. The potential difference is easy to generate between the equivalent anode and the equivalent cathode EA-EC, other power sources can be directly utilized to generate the potential difference, and the simpler scheme is that the inverter INVT and the like in the figure 1 are used on the basis of the application occasion of the photovoltaic module, so that the inverter INVT generates the potential difference between the equivalent anode and the equivalent cathode EA-EC reversely.

Referring to fig. 3, if the fourth switch S4 of the voltage conversion circuit PO _ M is continuously turned on and the second switch S2 is continuously turned off, as explained in the foregoing: the first switch S1 may be equivalent to an on switch and the third switch S3 may be equivalent to an off switch, then the original buck-boost circuit function of the voltage conversion circuit PO _ M is eliminated, as an alternative function it may be considered as a switching module to switch in or off the photovoltaic module PV _ M, similar to the switching module SH _ M of fig. 8. In essence, whether the voltage conversion circuit is used as the original buck-boost circuit or as the switching module, it is possible to make the cascade voltage very weak or even zero, for example, the original buck-boost circuit/power optimizer is controlled by the processor to be in a standby/sleep state, the output voltage of the voltage conversion circuit is very small or even zero, and the total cascade voltage is also very small. For example, when the voltage conversion circuit is used as a switching module, the number of the photovoltaic modules connected to the cell string by the voltage conversion circuit used as a switching module among the photovoltaic modules PV1-PVN is very small, and even if all the photovoltaic modules PV1-PVN are bypassed, the voltage in the string between the equivalent positive pole and the equivalent negative pole EA-EC is very small or even zero. If the voltage conversion circuit is switched to the dormant/standby state by an instruction given by the transient short-circuit event after the mode of maximum power tracking, the cascade voltage between the equivalent anode and the equivalent cathode EA-EC is very small or even zero, and at the moment, the instruction given by the transient short-circuit event requires the voltage conversion circuit to recover to the power tracking or safety mode, so that the voltage conversion circuit does not work. Since it was mentioned before that the shunt RS can be provided in the voltage conversion circuit topology, the voltage conversion circuit serving as the switching module can be restored from the standby/sleep mode to the power tracking operation mode by detecting the current of the shunt RS as above. Another solution for recovering the power tracking mode of the voltage conversion circuit is: the voltage difference is generated on the battery string, the voltage difference is generated between the equivalent positive electrode and the equivalent negative electrode EA-EC, the output voltage of the standby voltage conversion circuit is close to zero, transient pulses are generated on each output capacitor CO due to the applied voltage difference at the moment of generating the voltage difference, the processor 200 drives the voltage conversion circuit again to perform maximum power tracking if the generated pulses are sensed, and the sensing of the spike pulse belongs to a mature technology in the detection means in the prior art. Based on the condition that the cascade voltage is very small or even zero, when the voltage conversion circuit corresponding to each of at least one part of the photovoltaic modules in the battery string group is in the sleep/standby state, the mode of switching the photovoltaic modules from the sleep/standby mode to the maximum power tracking mode is as follows: a potential difference is generated between the first output terminal of the first stage voltage converting circuit PO1 and the second output terminal of the last stage voltage converting circuit PON, and the potential difference can be generated in reverse by the inverter, and when the processor of the photovoltaic module arrangement senses a spike on the output capacitor CO due to the application of a momentary potential difference, the power tracking mode is resumed from sleep/standby.

While the present invention has been described with reference to the preferred embodiments and illustrative embodiments, it is to be understood that the invention as described is not limited to the disclosed embodiments. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above description. Therefore, the appended claims should be construed to cover all such variations and modifications as fall within the true spirit and scope of the invention. Any and all equivalent ranges and contents within the scope of the claims should be considered to be within the intent and scope of the present invention.

Claims

1. A switching method for realizing the access or removal of a photovoltaic module in a battery string group is characterized in that:

the battery string group comprises a plurality of photovoltaic modules which are connected in series;

each photovoltaic module is configured with an access switch that couples the photovoltaic module into the battery string and a removal switch that shields the photovoltaic module from the battery string;

the method comprises the following steps:

transient short-circuit is carried out on the cascade voltage provided by the battery string group to which the photovoltaic module to be switched belongs for one or more times;

a processor configured by the photovoltaic module to be switched detects whether a transient short-circuit event occurs in the battery string group, and the detected transient short-circuit event is used as a basis for judging the access or removal of the photovoltaic module from the battery string group;

the method for detecting the transient short-circuit event comprises the steps of detecting the variation of a preset index induced by short-circuit of the cascade voltage; and

measuring the instantaneous output power of the photovoltaic module to be switched to the working mode;

only if the instantaneous output power of the photovoltaic module is equal to zero and the variation of a preset index caused by short circuit of the cascade voltage meets a preset variation condition, the actual effective transient short-circuit event is the real effective transient short-circuit event, and the photovoltaic module to be switched into the working mode is switched from one mode of connection or removal to the other mode;

the switching module for realizing the access or removal of each photovoltaic module from the battery string group comprises:

the first input end and the second input end are correspondingly and respectively coupled to the anode and the cathode of the corresponding photovoltaic module;

the access switch is coupled between the first input end and the first output end or between the second input end and the second output end;

a removal switch is coupled between the first output terminal and the second output terminal;

when the multi-stage switching modules are connected in series, the second output end of any previous stage switching module is coupled to the first output end of the adjacent next stage switching module; thereby to obtain

The total cascade voltage provided by the multistage switching modules is equal to the superposition value of the voltages between the first output end of the first stage switching module and the second output end of the last stage switching module;

when at least one part of the photovoltaic modules in the battery string group are in bypass short circuit by the respective removal switches, the mode of switching the photovoltaic modules from the removal mode to the access mode is as follows:

and generating a potential difference between the first output end of the first stage switching module and the second output end of the last stage switching module, and restoring the photovoltaic module to the access mode when a processor configured with the photovoltaic module senses the injected current generated by the potential difference.

2. The method of claim 1, wherein:

the predetermined index at least comprises transient short-circuit current generated by transient short-circuit and/or transient change rate of cascade voltage caused by transient short-circuit.

3. The method of claim 1, wherein:

detecting the transient shorting event further comprises defining:

the counted number of times of short circuit of the cascade voltage in the preset time period accords with the expected number of times.

4. The method of claim 1, wherein:

any one switching module is coupled with a current divider for sensing the injection current between the first output end of the switching module and the second output end of the switching module in the previous stage; or

Any one of the switching modules is coupled with a current divider for sensing the injection current between the second output terminal of the switching module and the first output terminal of the switching module of the next stage.

5. The method of claim 1, wherein:

each photovoltaic module is provided with an energy storage capacitor for supplying power to a processor configured with the photovoltaic module, and the energy storage capacitor is charged from the anode of the photovoltaic module through a diode in one-way transmission.

6. The method of claim 1, wherein:

a control switch is coupled between the first output end of the first stage switching module and the second output end of the last stage switching module in the series-connected multi-stage switching modules;

the mode of implementing transient short circuit to the cascade voltage that the battery string group provided does:

the control switch is turned on and then turned off rapidly.

7. The method of claim 6, wherein:

the control switch is switched on for an indication time and then is rapidly switched off; thereby to obtain

And when the variable quantity of the preset index is detected to meet the preset change condition and the duration time of the transient short-circuit event is the same as the indication time, the photovoltaic module to be switched executes the mode switching.