WO2020164198A1

WO2020164198A1 - Module voltage limiting method and apparatus and system using same

Info

Publication number: WO2020164198A1
Application number: PCT/CN2019/086554
Authority: WO
Inventors: 曹仁贤; 杨宗军
Original assignee: 阳光电源股份有限公司
Priority date: 2019-02-14
Filing date: 2019-05-13
Publication date: 2020-08-20
Also published as: CN111564866A

Abstract

Provided in the present invention are a module voltage limiting method and an apparatus and a system using same, comprising: by means of detecting a parameter of a photovoltaic cell string, determining whether the parameter of the photovoltaic cell string meets a voltage limiting enabling condition or a voltage limiting lifting condition; if the parameter of the photovoltaic cell string meets the voltage limiting enabling condition, then controlling at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode to thereby decrease the voltage of the photovoltaic cell string, enabling the amount of photovoltaic module series connections in the system to be increased whilst ensuring that the maximum voltage does not exceed a corresponding requirement, and reducing system costs; and if the parameter of the photovoltaic cell string meets the voltage limiting lifting condition, then controlling the photovoltaic cell working in the voltage limiting mode to return to normal output, increasing the output voltage of the photovoltaic cell string and thereby increasing the direct current voltage utilisation rate and DC/AC capacity ratio of the photovoltaic system.

Description

Method for limiting component pressure and its application device and system

This application claims the priority of a Chinese patent application filed with the Chinese Patent Office on February 14, 2019, the application number is 201910114210.6, and the invention title is "a component voltage limiting method and its application device and system", the entire content of which is by reference Incorporated in this application.

Technical field

The present invention relates to the technical field of power electronics, in particular to a component voltage limiting method and its application device and system.

Background technique

The photovoltaic power generation system is mainly composed of photovoltaic components and inverters. Several photovoltaic components are connected in series and parallel to the DC voltage into the inverter, and the inverter converts the DC voltage into AC voltage and then supplies it to the grid or load.

As the power level of the inverter continues to increase, the more photovoltaic modules are connected in the system, the lower the system cost. However, when multiple photovoltaic modules are connected in series, the maximum voltage of the system must not exceed 1500V, which limits the number of photovoltaic modules connected in series.

And because the output power of photovoltaic modules is constantly changing with voltage, as shown in Figure 1, the output voltage Vmpp corresponding to its maximum power point is generally about 80% of its open circuit voltage Voc; such as a 1500V system, when the inverter is running At this time, its DC side voltage gradually runs to about 1200V and maintains it. Therefore, actually for photovoltaic modules and inverters, the effective utilization of the system DC voltage is low, and the DC/AC capacity ratio of the photovoltaic power generation system is also low.

Summary of the invention

In view of this, the present invention provides a component voltage limiting method and its application device and system to solve the problems of the limited number of components connected in series and the low utilization rate of system DC voltage in the prior art.

In order to achieve the above objectives, the technical solutions provided by this application are as follows:

One aspect of the present invention provides a component voltage limiting method, including:

Detecting parameters of the photovoltaic cell string; the photovoltaic cell string includes a plurality of photovoltaic cells connected in series, and the photovoltaic cells are photovoltaic cells, photovoltaic substrings or photovoltaic modules;

According to the parameters of the photovoltaic cell string, determine whether the parameters of the photovoltaic cell string meet the voltage limit enable condition or the voltage limit release condition;

If the parameter of the photovoltaic cell string meets the voltage limiting enabling condition, controlling at least one photovoltaic cell in the photovoltaic cell string to work in the voltage limiting mode;

If the parameter of the photovoltaic cell string meets the voltage limit release condition, the photovoltaic cell working in the voltage limit mode is controlled to resume normal output.

Preferably, the voltage limiting mode includes: a complete short circuit mode where the output voltage is zero, and a chopping mode where voltage output is performed according to pulse width modulation PWM control.

Preferably, the parameter of the photovoltaic cell string is: the voltage or current of the photovoltaic cell string, or the voltage or current of at least one photovoltaic cell.

Preferably, the voltage limiting enabling condition is: a condition that characterizes the system DC voltage exceeding the upper limit;

The voltage limit release condition is: a condition that characterizes the system DC voltage being lower than the lower limit.

Preferably, if the parameter of the photovoltaic cell string is the voltage of the photovoltaic cell string, then:

The condition that characterizes that the DC voltage of the system exceeds the upper limit is: the voltage of the photovoltaic cell string is greater than the first preset voltage;

The condition for characterizing that the DC voltage of the system is lower than the lower limit is: the voltage of the photovoltaic cell string is less than the second preset voltage;

The first preset voltage is greater than the second preset voltage.

Preferably, if the parameter of the photovoltaic cell string is the current of the photovoltaic cell string, then:

The condition for characterizing the DC voltage of the system exceeding the upper limit is: the current of the photovoltaic cell string is less than the first preset current;

The condition for characterizing that the DC voltage of the system is lower than the lower limit is: the current of the photovoltaic cell string is greater than the second preset current;

The first preset current is less than the second preset current.

Another aspect of the present invention also provides a component voltage limiting circuit, including: a detection control unit, a switch unit and a power supply module; wherein:

The detection control unit is used to execute any one of the component pressure limiting methods described above;

The switch unit is connected in parallel with the photovoltaic cell controlled by the detection control unit, and is controlled by the detection control unit, so that the corresponding photovoltaic cell works in a voltage limiting mode or restores normal output;

The power supply module is used to supply power to the detection control unit.

Another aspect of the present invention also provides an intelligent voltage limiting device, which includes the component voltage limiting circuit as described above, and the photovoltaic cell connected to the component voltage limiting circuit is a photovoltaic component.

Another aspect of the present invention also provides a photovoltaic power generation system, including: an inverter, and at least one photovoltaic string connected to the DC side of the inverter;

The photovoltaic string includes a plurality of photovoltaic modules connected in series;

Each photovoltaic string is connected with at least one intelligent voltage limiting device as described above.

Another aspect of the present invention also provides an intelligent voltage-limiting junction box, which is characterized by comprising: a plurality of diodes, and the component voltage-limiting circuit as described above; wherein:

The photovoltaic cell connected to the component voltage limiting circuit is a photovoltaic substring;

Each of the diodes is connected in reverse parallel with the corresponding photovoltaic substring.

Another aspect of the present invention also provides an intelligent component, which is characterized by comprising: a photovoltaic component, and the above-mentioned intelligent voltage-limiting junction box.

The photovoltaic string includes a plurality of smart components connected in series;

The smart component is the above-mentioned smart component.

In the module voltage limiting method provided by the present invention, by detecting the parameters of the photovoltaic cell string, it is determined whether the parameters of the photovoltaic cell string meet the voltage limiting enabling condition or the voltage limiting release condition; if the parameters of the photovoltaic cell string meet the limit Voltage enable condition, control at least one photovoltaic cell in the photovoltaic cell string to work in the voltage limiting mode, thereby reducing the voltage of the photovoltaic cell string, so that the system can increase the series connection of photovoltaic modules while ensuring that the maximum voltage does not exceed the corresponding requirements. If the parameters of the photovoltaic cell string meet the voltage limit release condition, control the photovoltaic cell working in the voltage limit mode to resume normal output, increase the output voltage of the photovoltaic cell string, and thereby improve the photovoltaic system DC voltage utilization and DC/AC capacity ratio.

Description of the drawings

Figure 1 is a graph of output characteristics of photovoltaic modules provided in the prior art;

2 is a flowchart of a component voltage limiting method provided by an embodiment of the present invention;

3a and 3b are schematic diagrams of waveforms in the chopping mode provided by an embodiment of the present invention;

4 is a schematic structural diagram of a component voltage limiting circuit provided by an embodiment of the present invention;

5 is a schematic diagram of the structure of a controller provided by an embodiment of the present invention;

6a to 6e are respectively structural schematic diagrams of component voltage limiting circuits in five forms according to the embodiments of the present invention;

FIG. 7 is a schematic structural diagram of a photovoltaic power generation system with an independent intelligent voltage limiting device according to an embodiment of the present application;

8 is a schematic structural diagram of an intelligent voltage-limiting junction box provided by an embodiment of the present application;

Fig. 9 is a schematic diagram of a photovoltaic curve provided by an embodiment of the present invention;

Fig. 10 is a schematic structural diagram of a photovoltaic power generation system composed of smart components provided by an embodiment of the present application.

detailed description

In order to further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, and not to limit the claims of the present invention.

The present invention provides a component voltage limiting method to solve the problems of the limited number of components connected in series and low system DC voltage utilization in the prior art.

See Figure 2. The component pressure limiting method includes:

S101. Detect the parameters of the photovoltaic cell string;

A photovoltaic cell string includes a plurality of photovoltaic cells connected in series. The photovoltaic cell can refer to photovoltaic cells, photovoltaic substrings, or photovoltaic modules; among them, photovoltaic cells generally refer to the smallest photovoltaic power generation. Unit, a single photovoltaic cell can output about 0.3-0.7V; several (such as 10, 12, or 20, etc.) photovoltaic cells are connected in series through the bus belt to form a photovoltaic substring; several photovoltaic substrings are connected in series again to form Photovoltaic modules, conventionally there are 60 photovoltaic modules, 72 photovoltaic modules, half-cell modules and so on. If the photovoltaic cell refers to a photovoltaic cell or a photovoltaic substring, it means that the component voltage limiting method is applied to the inside of the photovoltaic component; if the photovoltaic cell refers to a photovoltaic component, it means that the component voltage limiting method is applied to the entire photovoltaic string.

The parameters detected in step S101 can be the corresponding parameters of the entire photovoltaic cell string, or any photovoltaic cell, such as a corresponding parameter of a representative photovoltaic cell, depending on its specific application environment. Within the scope of protection. In addition, the aforementioned parameters may be voltage or current, as long as they can reflect the output state of the photovoltaic cell string, and they are all within the protection scope of the present application.

The output status of the photovoltaic battery string includes: the output voltage of the photovoltaic battery string is high, which causes the system DC voltage to exceed the upper limit value and requires voltage limitation, such as the output status before the inverter is connected to the grid; and, causes the system DC voltage to be low At the lower limit, the state that requires boosting, such as the output state caused by the MPPT (Maximum Power Point Tracking) control after the inverter is connected to the grid.

S102: According to the parameters of the photovoltaic cell string, determine whether the parameters of the photovoltaic cell string meet the voltage limit enable condition or the voltage limit release condition;

Specifically, when the parameter of the photovoltaic cell string characterizes the system DC voltage exceeds the upper limit, it means that the parameter of the photovoltaic cell string meets the voltage limit enable condition, and step S103 will be executed at this time; when the parameter of the photovoltaic cell string characterizes the system DC voltage is low When the lower limit value is reached, it indicates that the parameters of the photovoltaic cell string meet the voltage limit release condition, and step S104 will be executed at this time.

S103. Control at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode;

Specifically, the voltage limiting mode includes: a complete short circuit mode where the output voltage is zero, and a chopping mode where voltage output is performed according to PWM (Pulse Width Modulation) control.

In the complete short-circuit mode, the output voltage of the corresponding photovoltaic cell remains at zero, thereby reducing the output voltage of the entire photovoltaic cell string. In the chopping mode, the output voltage of the corresponding photovoltaic cell is transformed according to the PWM control, so that the output voltage waveform of the entire photovoltaic cell string becomes a rectangular wave. In Figure 3a, any photovoltaic cell in the photovoltaic cell string containing 3 photovoltaic cells is controlled. In order to work in the chopping mode of the output voltage waveform, the rectangular wave can be converted into a sawtooth waveform with a certain wave with the help of the capacitor connected to the rear stage of the photovoltaic cell, as shown in Figure 3b; further, the photovoltaic module After being connected in series, the output is output to the inverter side. Because the photovoltaic modules are out of phase and the inverter side has input capacitors, the total output voltage of the photovoltaic string will be relatively smooth. Therefore, the chopper mode can also reduce the output voltage of the entire photovoltaic cell string, and the degree of adjustment can be more refined, and the corresponding photovoltaic cell can be controlled to output with a certain duty cycle. For its chopping frequency, a higher frequency higher than the preset frequency is preferred to reduce the ripple size.

It can be seen from the above that whether the corresponding photovoltaic cell works in the full short-circuit mode or the chopper mode, it can achieve a corresponding degree of short-circuit, thereby reducing the output voltage of the entire photovoltaic cell string, so that the system can ensure that the maximum voltage does not exceed the corresponding requirements. At the same time, it can increase the number of photovoltaic modules in series, expand the access of DC side modules, and reduce system costs.

S104. Control the photovoltaic cell working in the voltage limiting mode to resume normal output.

After the photovoltaic cell working in the voltage limiting mode returns to normal output, the output voltage of the entire photovoltaic cell string can be increased, so that the DC voltage utilization rate and DC/AC capacity ratio of the photovoltaic system are also effectively improved.

It can be seen from the above content that the component voltage limiting method provided in this embodiment can reduce the photovoltaic cells by controlling the corresponding photovoltaic cells to work in the voltage limiting mode when the DC voltage of the system exceeds the upper limit before the inverter is connected to the grid. The voltage of the string enables the system to increase the number of photovoltaic modules in series while ensuring that the maximum voltage does not exceed the corresponding requirements, expand the access of the DC side components, and reduce the system cost; and after the inverter is connected to the grid, the system DC voltage is lower than When the lower limit value needs to be boosted, the output voltage of the photovoltaic cell string is increased by controlling the photovoltaic cells working in the voltage limiting mode to restore the normal output, so that the DC voltage utilization rate and the DC/AC capacity ratio of the photovoltaic system are also effectively improved.

Another embodiment of the present invention provides a specific component pressure limiting method. Based on the above-mentioned embodiment and FIGS. 2 to 3b, preferably:

The voltage limit enabling condition is: the condition that the system DC voltage exceeds the upper limit; the voltage limit release condition is: the condition that the system DC voltage is lower than the lower limit. To characterize whether the DC power supply of the system exceeds the upper limit or is lower than the lower limit, it can be directly judged by the output voltage of the entire photovoltaic string, or by the output voltage of any photovoltaic module and the preset score of the photovoltaic string under the corresponding ratio. It can also be used for comparison and judgment, or indirect judgment can be realized by the current of the photovoltaic cell string.

Taking the voltage of the photovoltaic cell string as the parameter of the photovoltaic cell string as an example, the condition for characterizing the system DC voltage exceeding the upper limit is: the voltage of the photovoltaic cell string is greater than the first preset voltage; indicating that the system DC voltage is lower than the lower limit The condition of the value is: the voltage of the photovoltaic cell string is less than the second preset voltage; wherein the first preset voltage is greater than the second preset voltage.

Taking the current of the photovoltaic cell string as the parameter of the photovoltaic cell string as an example, the condition for characterizing the system DC voltage exceeding the upper limit is: the current of the photovoltaic cell string is less than the first preset current; indicating that the system DC voltage is lower than the lower limit The condition of the value is: the current of the photovoltaic cell string is greater than the second preset current; wherein the first preset current is less than the second preset current.

The rest of the principles are the same as the above embodiments, and will not be repeated here.

Another embodiment of the present invention also provides a component voltage limiting circuit. In practical applications, the component voltage limiting circuit can be connected to two ends of several photovoltaic cells, or two ends of several photovoltaic substrings, or several photovoltaic modules The ends. As shown in Figure 4, the component voltage limiting circuit includes: a detection control unit 101, a switch unit 102, and a power supply module 103; among them:

The switch unit 102 is connected in parallel with the photovoltaic cell (photovoltaic cell, photovoltaic substring or photovoltaic module) controlled by the detection control unit 101, and is controlled by the detection control unit 101 to make the corresponding photovoltaic cell work in the voltage limiting mode or restore normal output The power supply module 103 is used to supply power to the detection control unit 101; the detection control unit 101 is used to execute the component voltage limiting method described in any of the above embodiments.

Specifically, the detection control unit 101 can realize the condition judgment by judging the voltage of the photovoltaic cell string; if the voltage of the photovoltaic cell string is greater than the first preset voltage, it is judged that the parameters of the photovoltaic cell string meet the voltage limiting enabling condition; if If the voltage of the photovoltaic cell string is less than the second preset voltage, it is determined that the parameter of the photovoltaic cell string meets the voltage limit release condition; wherein, the first preset voltage is greater than the second preset voltage. The condition can also be judged by judging the current of the photovoltaic cell string; if the current of the photovoltaic cell string is less than the first preset current, it is determined that the parameters of the photovoltaic cell string meet the voltage limit enabling condition; if the current of the photovoltaic cell string is greater than The second preset current determines that the parameter of the photovoltaic cell string satisfies the voltage limit release condition; wherein, the first preset current is less than the second preset current. When the detection control unit 101 detects and judges that the parameters of the photovoltaic cell string meet the voltage limit enable condition, it controls the corresponding photovoltaic cell to work in the voltage limit mode, thereby reducing the voltage of the photovoltaic cell string, so that the system can ensure that the maximum voltage does not exceed the corresponding requirements. At the same time, it can increase the number of photovoltaic modules connected in series and reduce the system cost; when the parameters of the photovoltaic cell string meet the voltage limit release condition, control the photovoltaic cell working in the voltage limit mode to resume normal output, increase the output voltage of the photovoltaic cell string, and then increase The DC voltage utilization rate and DC/AC capacity ratio of the photovoltaic system.

Wherein, the detection control unit 101 preferably includes: a detection module and a controller. The controller can be implemented as shown in Figure 5 by using a comparator with hysteresis feedback. When the output parameters of the detection module (such as voltage Vs) exceed the corresponding upper limit (such as reference voltage Vref) to meet the voltage limit enable When conditions are met, the control switch unit 102 is always on, and when the parameters output by the detection module meet the voltage limit release condition, the control switch unit 102 is turned off; the implementation cost of this controller is low. Alternatively, the controller may also be a PWM generator or a processor. When the parameters output by the detection module meet the voltage limit enable condition, the switch unit 102 is controlled to be turned on according to PWM, and the capacitance of the power module 103 is used to make the photovoltaic battery string The output voltage changes from the rectangular wave shown in Fig. 3a to the sawtooth wave shown in Fig. 3b, and the total output of the photovoltaic cell string will be relatively smooth due to the phase error between the components and the input capacitance on the inverter side; When the parameter output by the detection module meets the voltage limit release condition, the controller will control the switch unit 102 to turn off.

In addition, the switch unit 102 may also have a variety of specific implementation forms: for example, when the photovoltaic cell controlled by the detection control unit 101 is a photovoltaic cell in a photovoltaic cell string, the switch unit 102 is a photovoltaic cell connected in parallel with the photovoltaic cell. Just switch, as shown in Figure 6a; and when the photovoltaic cell controlled by the detection control unit 101 is a photovoltaic cell connected in series in the photovoltaic cell string, the switch unit 102 can be connected in parallel with the corresponding photovoltaic cells one by one. The switch (as shown in Figure 6b) can also be a switch connected in parallel with all corresponding photovoltaic cells (as shown in Figure 6c); when the photovoltaic cells controlled by the detection control unit 101 are multiple photovoltaic cell strings that are not connected to each other In the case of photovoltaic cells, the switch unit 102 includes a plurality of switches connected in parallel with the corresponding photovoltaic cells one by one (as shown in Figure 6d); when the photovoltaic cells controlled by the detection control unit 101 are all photovoltaic cells in the photovoltaic cell string, The switch unit 102 includes a plurality of switches connected in parallel with all photovoltaic cells one by one (as shown in FIG. 6e). In addition, the above several situations can also be combined with each other, which will not be repeated here, and they all fall within the protection scope of this application.

In practical applications, the switch is preferably a controllable electronic switch, such as MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET, metal-oxide semiconductor field effect transistor), IGBT (Insulated Gate Bipolar Transistor, insulated gate double Polar transistors), triodes, or relays can all be used, depending on the application environment, and they are all within the protection scope of this application.

In addition, the power module 103 can take electricity from a photovoltaic cell string (as shown in Figure 4 and Figure 6a to Figure 6e), or it can take electricity from a part of the photovoltaic cell string (not shown), or alternatively, Take electricity from the outside (not shown in the figure); there is no specific limitation here, depending on the application environment, and all are within the protection scope of this application.

The circuit form of the power module 103 can be a commonly used LDO (low dropout regulator), a half-bridge circuit, or a flyback circuit, etc., which are not specifically limited here, depending on the application environment. Within the scope of protection of this application.

For the specific implementation process of the component voltage limiting method, refer to the foregoing embodiment, and will not be repeated here.

Another embodiment of the present invention also provides an intelligent voltage limiting device, which is applied to the photovoltaic power generation system shown in FIG. 7. A photovoltaic string of the photovoltaic power generation system includes several conventional photovoltaic modules connected in series in sequence; Some of the photovoltaic modules in the string can be equipped with the intelligent voltage-limiting device, for example, the intelligent voltage-limiting device is connected in parallel with the photovoltaic module in a one-to-one correspondence (not shown), or multiple photovoltaic modules connected in series in sequence are jointly connected to an intelligent voltage-limiting device Parallel connection (as shown in Figure 7); each photovoltaic module can also be equipped with a parallel-connected intelligent voltage limiting device (not shown).

The intelligent voltage-limiting device includes the component voltage-limiting circuit as described in any of the above embodiments. For its specific structure and principle, please refer to the above-mentioned embodiment. The photovoltaic power generation system shown in FIG. 7 is taken as an example for illustration. The voltage to the DC side of the inverter does not exceed 1500V, so before the inverter is connected to the grid, the intelligent voltage limiting device limits the output voltage of the connected photovoltaic modules so that the total output of the photovoltaic string does not exceed 1500V; After the inverter is connected to the grid, as the MPPT gradually stabilizes, the DC bus voltage of the inverter decreases to about 1200V. At this time, the intelligent voltage limiting device releases the voltage limiting function and the voltage resumes, but the total voltage is still below 1500V.

As a result, for a 1500V inverter, the PV modules connected in series on the DC side can be configured higher, such as up to 1800V, through the intelligent voltage limiting device, it is still effectively controlled within 1500V, reducing costs; and after grid connection It can also increase the system voltage from 1200V in the prior art to within 1500V, which improves the system capacity ratio.

Another embodiment of the present invention also provides a photovoltaic power generation system, as shown in FIG. 7, comprising: an inverter, and at least one photovoltaic string connected to the DC side of the inverter; the photovoltaic string includes a plurality of series Connected photovoltaic modules.

Each photovoltaic string is connected with at least one intelligent voltage limiting device as described in the above embodiment. Preferably, the number of intelligent voltage limiting devices provided in each photovoltaic string is the same and the connection method is the same, so as to ensure that each photovoltaic The output voltage of the string remains the same.

The specific structure and working principle of the intelligent pressure limiting device are the same as those in the above-mentioned embodiment, and will not be repeated here.

Another embodiment of the present invention also provides an intelligent voltage-limiting junction box, as shown in FIG. 8, comprising: a plurality of diodes, and the component voltage-limiting circuit according to any one of the above embodiments, and the component voltage-limiting circuit The connected photovoltaic cells are photovoltaic substrings, and each diode is connected in reverse parallel to the corresponding photovoltaic substring.

A conventional 60-cell photovoltaic module has a maximum open circuit voltage of about 42V in winter, and contains three photovoltaic substrings inside, and the voltage of each photovoltaic substring is 14V. The 72-cell photovoltaic modules are similar.

The power supply module 103 of the intelligent voltage-limiting junction box takes power from the entire photovoltaic assembly and supplies power to the detection control unit 101. The switch unit 102 is a controllable electronic switch, such as MOSFET, IGBT, triode, relay and other devices. In FIG. 8, the switch is connected in parallel on both sides of one photovoltaic substring as an example.

Taking voltage as the parameter of detection and judgment, then:

When the voltage of the photovoltaic module is high, for example, when it exceeds Uth1=36V, the detection control unit 101 actively controls the short circuit of the switch, which can theoretically reduce the voltage by 1/3, that is, to 24V; PV sub-string, the output voltage of the photovoltaic module is changed to 2/3V. If the switch is controlled in PWM mode to short-circuit the corresponding photovoltaic sub-string, the output voltage of the photovoltaic module will change to a sawtooth wave near 2/3V (see Figure 3a and 3b); V is the module voltage before the corresponding photovoltaic substring is short-circuited. As the voltage continues to increase to 42V, the actual port voltage will not exceed 28V. That is to say from the overall point of view, after the intelligent voltage limiting junction box is provided with a component voltage limiting circuit, the maximum output of the entire photovoltaic module is limited to Uth1=36V or less.

When the voltage of the photovoltaic module is low, for example, lower than Uth2=20V, the detection control unit 101 restores the short-circuited photovoltaic substring, and at this time the voltage theoretically restores to 30V.

It can be known from the above process that for a 1500V photovoltaic power generation system, the maximum number of components that can be connected in the original design is 1500V/42V=35 blocks, and now through the intelligent voltage limiting junction box, 1500V/36V=41 blocks can be connected , Further expand the capacity of the photovoltaic system, reduce the number of cables under the same inverter, reduce the cost, and increase the utilization rate of the inverter.

Taking current as the parameter of detection and judgment, then:

When the photovoltaic module is open, the load current is 0, and the voltage is higher at this time; once it is loaded, the voltage will be pulled down according to the photovoltaic curve (as shown in Figure 9) to form a load current. Therefore, assuming that the current is lower than Ith1 (for example, 2A), the detection control unit 101 controls the switch unit 102 to be turned on to ensure that the output voltage is low. When the current exceeds Ith2 (for example, 3A), it is considered that the inverter is already running at this time, and the bus voltage is pulled down. Therefore, the detection control unit 101 can release the switch unit 102 to restore the cell power generation. The effect achieved is the same.

Further, if the switch unit 102 is arranged on 1/6 of the photovoltaic substring, the granularity of the adjustment will be finer and the effect will be better.

The rest of the structure and principle are the same as the above-mentioned embodiment, and will not be repeated here.

Another embodiment of the present invention also provides an intelligent component, including a photovoltaic component, and the intelligent voltage-limiting junction box as described in any of the above embodiments.

A number of smart components are connected in series and parallel to the DC side of the inverter. The system structure is shown in Figure 10. The initial value of the DC voltage of the system is 1800V. Before the inverter is connected to the grid, when the voltage limiting function in the smart component is activated, the internal output of the intelligent component is limited to ensure that the DC voltage of the entire system does not exceed 1500V; when the inverter is connected to the grid After operation, as the MPPT gradually stabilizes, the system DC voltage is pulled down to about 1200V, and then the voltage limiting function of each intelligent component is released, and the system generates power normally, but the total voltage is still lower than 1500V.

The structure and principle of the intelligent voltage-limiting junction box are the same as the above-mentioned embodiments, and will not be repeated here.

Another embodiment of the present invention also provides a photovoltaic power generation system, as shown in FIG. 10, comprising: an inverter, and at least one photovoltaic string connected to the DC side of the inverter;

The photovoltaic string includes multiple smart components connected in series;

The smart component is the smart component described in the above embodiment.

The structure and principle of the smart component are the same as the above-mentioned embodiments, and will not be repeated here.

The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other.

The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown in this document, but should conform to the widest scope consistent with the principles and novel features disclosed in this document.

Claims

A component voltage limiting method, characterized in that it includes:

Detecting the parameters of the photovoltaic cell string; the photovoltaic cell string includes a plurality of photovoltaic cells connected in series, and the photovoltaic cell is a photovoltaic cell, a photovoltaic substring or a photovoltaic component;

According to the parameters of the photovoltaic cell string, determine whether the parameters of the photovoltaic cell string meet the voltage limit enable condition or the voltage limit release condition;

If the parameter of the photovoltaic cell string meets the voltage limiting enabling condition, controlling at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode;

If the parameter of the photovoltaic cell string meets the voltage limit release condition, the photovoltaic cell working in the voltage limit mode is controlled to resume normal output.
The component voltage limiting method according to claim 1, wherein the voltage limiting mode comprises: a complete short circuit mode where the output voltage is zero, and a chopping mode where the voltage is output according to pulse width modulation (PWM) control.
The module voltage limiting method according to claim 2, wherein the parameter of the photovoltaic cell string is: the voltage or current of the photovoltaic cell string, or the voltage or current of at least one photovoltaic cell.
The component voltage limiting method according to claim 3, wherein the voltage limiting enabling condition is: a condition that characterizes a system DC voltage exceeding an upper limit;

The voltage limit release condition is: a condition that characterizes the system DC voltage being lower than the lower limit.
The module voltage limiting method according to claim 4, wherein if the parameter of the photovoltaic cell string is the voltage of the photovoltaic cell string, then:

The condition that characterizes that the DC voltage of the system exceeds the upper limit is: the voltage of the photovoltaic cell string is greater than the first preset voltage;

The condition for characterizing that the DC voltage of the system is lower than the lower limit is: the voltage of the photovoltaic cell string is less than the second preset voltage;

The first preset voltage is greater than the second preset voltage.
The module voltage limiting method according to claim 4, wherein if the parameter of the photovoltaic cell string is the current of the photovoltaic cell string, then:

The condition for characterizing the DC voltage of the system exceeding the upper limit is: the current of the photovoltaic cell string is less than the first preset current;

The condition for characterizing that the DC voltage of the system is lower than the lower limit is: the current of the photovoltaic cell string is greater than the second preset current;

The first preset current is less than the second preset current.
A component voltage limiting circuit, which is characterized by comprising: a detection control unit, a switch unit and a power supply module; wherein:

The detection control unit is used to execute the component voltage limiting method according to any one of claims 1-6;

The switch unit is connected in parallel with the photovoltaic cell controlled by the detection control unit, and is controlled by the detection control unit, so that the corresponding photovoltaic cell works in a voltage limiting mode or restores normal output;

The power supply module is used to supply power to the detection control unit.
An intelligent voltage limiting device, characterized in that it comprises the component voltage limiting circuit according to claim 7, and the photovoltaic cell connected to the component voltage limiting circuit is a photovoltaic component.
A photovoltaic power generation system, characterized by comprising: an inverter, and at least one photovoltaic string connected to the DC side of the inverter;

The photovoltaic string includes a plurality of photovoltaic modules connected in series;

Each photovoltaic string is connected with at least one intelligent voltage limiting device as described above.
An intelligent voltage-limiting junction box, characterized by comprising: a plurality of diodes, and the component voltage-limiting circuit according to claim 7; wherein:

The photovoltaic cell connected to the component voltage limiting circuit is a photovoltaic substring;

Each of the diodes is connected in reverse parallel with the corresponding photovoltaic substring.
An intelligent component, characterized by comprising: a photovoltaic component, and the intelligent voltage-limiting junction box according to claim 9.
A photovoltaic power generation system, characterized by comprising: an inverter, and at least one photovoltaic string connected to the DC side of the inverter;

The photovoltaic string includes a plurality of smart components connected in series;

The smart component is the smart component of claim 11.