CN111564866A - Component voltage limiting method and application device and system thereof - Google Patents

Component voltage limiting method and application device and system thereof Download PDF

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Publication number
CN111564866A
CN111564866A CN201910114210.6A CN201910114210A CN111564866A CN 111564866 A CN111564866 A CN 111564866A CN 201910114210 A CN201910114210 A CN 201910114210A CN 111564866 A CN111564866 A CN 111564866A
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China
Prior art keywords
voltage
photovoltaic
photovoltaic cell
string
voltage limiting
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CN201910114210.6A
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Chinese (zh)
Inventor
曹仁贤
杨宗军
徐君
云平
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Sungrow Power Supply Co Ltd
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Sungrow Power Supply Co Ltd
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Priority to CN201910114210.6A priority Critical patent/CN111564866A/en
Publication of CN111564866A publication Critical patent/CN111564866A/en
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02SGENERATION OF ELECTRIC POWER BY CONVERSION OF INFRA-RED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30Electrical components
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02SGENERATION OF ELECTRIC POWER BY CONVERSION OF INFRA-RED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S50/00Monitoring or testing of PV systems, e.g. load balancing or fault identification
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy

Abstract

The invention provides a component voltage limiting method, an application device and a system thereof.A parameter of a photovoltaic cell string is detected to judge whether the parameter of the photovoltaic cell string meets a voltage limiting enabling condition or a voltage limiting releasing condition; if the parameters of the photovoltaic cell string meet the voltage limiting enabling conditions, controlling at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode, and further reducing the voltage of the photovoltaic cell string, so that the system can increase the number of photovoltaic modules in series while ensuring that the maximum voltage does not exceed the corresponding requirement, and the system cost is reduced; and if the parameters of the photovoltaic cell string meet the voltage limiting removal condition, controlling the photovoltaic cell working in the voltage limiting mode to recover normal output, and improving the output voltage of the photovoltaic cell string so as to improve the direct current voltage utilization rate and the DC/AC capacity ratio of the photovoltaic system.

Description

Component voltage limiting method and application device and system thereof
Technical Field
The invention relates to the technical field of power electronics, in particular to a component voltage limiting method and an application device and system thereof.
Background
The photovoltaic power generation system mainly comprises photovoltaic modules and an inverter, wherein the photovoltaic modules are connected in series and in parallel to converge direct-current voltage into the inverter, and the inverter inverts the direct-current voltage into alternating-current voltage and supplies the alternating-current voltage to a power grid or a load.
As the power level of the inverter is increased, the more photovoltaic modules are connected in the system, and the lower the system cost is. However, when a plurality of photovoltaic modules are connected in series, the maximum voltage of the system is required to be not more than 1500V, which limits the number of photovoltaic modules connected in series.
As the output power of the photovoltaic module is constantly changed with the voltage, as shown in fig. 1, the output voltage Vmpp corresponding to the maximum power point is generally about 80% of the open-circuit voltage Voc; for example, 1500V, when the inverter is operated, the dc side voltage is gradually increased to about 1200V and maintained. Therefore, for the photovoltaic module and the inverter, the effective utilization rate of the system direct-current voltage is low, and the DC/AC capacity ratio of the photovoltaic power generation system is also low.
Disclosure of Invention
The invention provides a component voltage limiting method, and an application device and a system thereof, which aim to solve the problems that the number of components connected in series is limited and the utilization rate of system direct-current voltage is low in the prior art.
In order to achieve the purpose, the technical scheme provided by the application is as follows:
one aspect of the present invention provides a method for limiting a voltage of a component, including:
detecting parameters of the photovoltaic cell string; the photovoltaic cell string comprises a plurality of photovoltaic cells connected in series, and the photovoltaic cells are photovoltaic cell sheets, photovoltaic substrings or photovoltaic modules;
judging whether the parameters of the photovoltaic cell string meet a voltage limiting enabling condition or a voltage limiting releasing condition according to the parameters of the photovoltaic cell string;
if the parameters of the photovoltaic cell string meet the voltage limiting enabling conditions, controlling at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode;
and if the parameters of the photovoltaic cell string meet the pressure limiting release condition, controlling the photovoltaic cell working in the pressure limiting mode to recover normal output.
Preferably, the voltage limiting mode includes: a dead short mode in which the output voltage is zero, and a chopping mode in which voltage output is performed in accordance with Pulse Width Modulation (PWM) control.
Preferably, the parameters of the photovoltaic cell string are as follows: a voltage or current of the string of photovoltaic cells, or a voltage or current of at least one photovoltaic cell.
Preferably, the voltage limiting enabling condition is as follows: representing the condition that the direct-current voltage of the system exceeds an upper limit value;
the pressure limiting releasing condition is as follows: and (4) representing the condition that the direct current voltage of the system is lower than a lower limit value.
Preferably, if the parameter of the photovoltaic cell string is the voltage of the photovoltaic cell string, then:
the condition that the direct-current voltage of the characterization system exceeds the upper limit value is as follows: the voltage of the photovoltaic cell string is greater than a first preset voltage;
the condition that the direct-current voltage of the characterization system is lower than the lower limit value is as follows: the voltage of the photovoltaic cell string is smaller than a 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 that the direct-current voltage of the characterization system exceeds the upper limit value is as follows: the current of the photovoltaic cell string is smaller than a first preset current;
the condition that the direct-current voltage of the characterization system is lower than the lower limit value is as follows: the current of the photovoltaic cell string is greater than a second preset current;
the first preset current is smaller than the second preset current.
In another aspect, the present invention provides a component voltage limiting circuit, including: the device comprises a detection control unit, a switch unit and a power supply module; wherein:
the detection control unit is used for executing any one of the component voltage limiting methods;
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 as to enable the corresponding photovoltaic cell to work in a voltage limiting mode or recover normal output;
the power module is used for supplying power to the detection control unit.
The invention also provides an intelligent voltage limiting device which comprises the component voltage limiting circuit, and the photovoltaic cell connected with the component voltage limiting circuit is a photovoltaic component.
In another aspect of the present invention, a photovoltaic power generation system is provided, including: an inverter and at least one photovoltaic string connected to the dc side of the inverter;
the photovoltaic string comprises a plurality of photovoltaic modules connected in series;
each photovoltaic group string is connected with at least one intelligent voltage limiting device.
In another aspect, the present invention further provides an intelligent voltage-limiting junction box, which includes: a plurality of diodes, and a component voltage limiting circuit as described above; wherein:
the photovoltaic cells connected with the component voltage limiting circuit are photovoltaic substrings;
and each diode is connected with the corresponding photovoltaic sub-string in reverse parallel.
In another aspect, the present invention further provides an intelligent component, which includes: photovoltaic module, and, as above-mentioned intelligent voltage limiting terminal box.
In another aspect of the present invention, a photovoltaic power generation system is provided, including: an inverter and at least one photovoltaic string connected to the dc side of the inverter;
the photovoltaic string comprises a plurality of intelligent assemblies connected in series;
the intelligent assembly is the intelligent assembly.
The method for limiting the voltage of the assembly provided by the invention comprises the steps of judging whether the parameters of the photovoltaic cell string meet a voltage limiting enabling condition or a voltage limiting releasing condition by detecting the parameters of the photovoltaic cell string; if the parameters of the photovoltaic cell string meet the voltage limiting enabling conditions, controlling at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode, and further reducing the voltage of the photovoltaic cell string, so that the system can increase the number of photovoltaic modules in series while ensuring that the maximum voltage does not exceed the corresponding requirement, and the system cost is reduced; and if the parameters of the photovoltaic cell string meet the voltage limiting removal condition, controlling the photovoltaic cell working in the voltage limiting mode to recover normal output, and improving the output voltage of the photovoltaic cell string so as to improve the direct current voltage utilization rate and the DC/AC capacity ratio of the photovoltaic system.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a graph of output characteristics of a photovoltaic module provided by the prior art;
FIG. 2 is a flow chart of a component voltage limiting method provided by an embodiment of the present invention;
FIGS. 3a and 3b are schematic diagrams of waveforms in a chopping mode provided by an embodiment of the present invention;
FIG. 4 is a schematic diagram of a component voltage limiting circuit according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a controller according to an embodiment of the present invention;
fig. 6a to fig. 6e are schematic structural diagrams of component voltage limiting circuits in five forms according to 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 invention;
FIG. 8 is a schematic structural diagram of an intelligent voltage-limiting junction box according to an embodiment of the present invention;
FIG. 9 is a schematic view of a photovoltaic curve provided by an embodiment of the present application;
fig. 10 is a schematic structural diagram of a photovoltaic power generation system composed of intelligent components according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The invention provides a component voltage limiting method, which aims to solve the problems that the number of components connected in series is limited and the utilization rate of system direct-current voltage is low in the prior art.
Referring to fig. 2, the method for limiting voltage of the assembly includes:
s101, detecting parameters of a photovoltaic cell string;
the photovoltaic cell string comprises a plurality of photovoltaic cells connected in series, and the photovoltaic cells can be photovoltaic cell sheets, photovoltaic sub strings or photovoltaic modules; the photovoltaic cell slice generally refers to the minimum unit of photovoltaic power generation, and a single photovoltaic cell slice can output about 0.3-0.7V; a plurality of (for example, 10, 12 or 20) photovoltaic cell slices are connected in series through a bus bar to form a photovoltaic sub-string; and the photovoltaic substrings are connected in series again to form a photovoltaic module, and the conventional photovoltaic module comprises 60 photovoltaic modules, 72 photovoltaic modules, a half-sheet module and the like. If the photovoltaic cell refers to a photovoltaic cell sheet or a photovoltaic sub-string, the component voltage limiting method is applied to the interior of the photovoltaic component; if the photovoltaic cell refers to a photovoltaic module, the module voltage limiting method is applied to the whole photovoltaic string.
The parameter detected in step S101 may be a corresponding parameter of the entire photovoltaic cell string, or may be a corresponding parameter of any photovoltaic cell, such as a photovoltaic cell having a representative meaning, and is within the protection scope of the present application depending on the specific application environment. The above parameters may be voltage, current, etc., and are within the scope of the present application as long as the output state of the photovoltaic cell string can be represented.
The output state of the photovoltaic cell string includes: the output voltage of the photovoltaic cell string is high, so that the direct-current voltage of the system exceeds an upper limit value, and a voltage-limiting state is required, such as an output state before grid connection of an inverter; and a state that the system dc voltage is lower than the lower limit value and needs to be boosted, for example, an output state caused by MPPT (Maximum Power point tracking) control following the grid connection of the inverter.
S102, judging whether the parameters of the photovoltaic cell string meet a voltage limiting enabling condition or a voltage limiting releasing condition according to the parameters of the photovoltaic cell string;
specifically, when the direct-current voltage of the parameter representation system of the photovoltaic cell string exceeds the upper limit value, it is indicated that the parameter of the photovoltaic cell string meets the voltage-limiting enabling condition, and at this time, step S103 is executed; when the direct-current voltage of the parameter representation system of the photovoltaic cell string is lower than the lower limit value, it is indicated that the parameter of the photovoltaic cell string satisfies the voltage limitation removal condition, and at this time, step S104 is executed.
S103, controlling at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode;
specifically, the voltage limiting mode includes: a dead short mode in which the output voltage is zero, and a chopping mode in which voltage output is performed in accordance with PWM (pulse width Modulation) control.
Under the complete short circuit mode, the output voltage of corresponding photovoltaic cell keeps zero, and then can reduce the output voltage of whole photovoltaic cell cluster. In the chopping mode, the output voltage of the corresponding photovoltaic cell is converted according to PWM control, so that the output voltage waveform of the whole photovoltaic cell string is formed into a rectangular waveform, fig. 3a is an output voltage waveform diagram when any one photovoltaic cell in the photovoltaic cell string including 3 photovoltaic cells is controlled to operate in the chopping mode, and the rectangular waveform can be converted into a sawtooth waveform with a certain text wave by means of a capacitor connected at the rear stage of the photovoltaic cell, as shown in fig. 3 b; further, the photovoltaic modules are connected in series and then output to the inverter side, and due to the fact that phase error exists between the photovoltaic modules and the input capacitor is arranged on the inverter side, the total output voltage of the photovoltaic module string is smooth. Therefore, the chopping mode can also play a role in reducing the output voltage of the whole photovoltaic cell string, the adjustment degree of the chopping mode can be more detailed, and the corresponding photovoltaic cell can be controlled to output at a certain duty ratio. For its chopping frequency, preferably a higher frequency than the preset frequency, the ripple magnitude can be reduced.
According to the photovoltaic module series connection method, no matter the corresponding photovoltaic cell works in the complete short circuit mode or the chopping mode, short circuit in the corresponding degree can be achieved, the output voltage of the whole photovoltaic cell string is further reduced, the maximum voltage of the system is guaranteed not to exceed the corresponding requirement, the series connection number of the photovoltaic modules can be increased, the direct current side module access is expanded, and the system cost is reduced.
And S104, controlling the photovoltaic cell working in the voltage limiting mode to recover normal output.
After the photovoltaic cell working in the voltage limiting mode recovers normal output, the output voltage of the whole photovoltaic cell string can be improved, so that the direct current voltage utilization rate and the DC/AC capacity ratio of the photovoltaic system are also effectively improved.
As can be seen from the above, the method for limiting the voltage of the assembly provided by this embodiment can reduce the voltage of the photovoltaic cell string by controlling the corresponding photovoltaic cell to operate in the voltage limiting mode when the dc voltage of the system exceeds the upper limit value and needs to be limited before the inverter is connected to the grid, so that the system can increase the number of photovoltaic assemblies connected in series, expand the access of the dc-side assembly, and reduce the system cost while ensuring that the maximum voltage does not exceed the corresponding requirement; and when the direct-current voltage of the system is lower than the lower limit value and needs to be boosted after the inverter is connected to the grid, the output voltage of the photovoltaic cell string is improved by controlling the photovoltaic cell working in the voltage limiting mode to recover the normal output, so that the direct-current 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 method for limiting voltage of an assembly, based on the above embodiments and fig. 2 to 3b, preferably:
the voltage limiting enabling conditions are as follows: representing the condition that the direct-current voltage of the system exceeds an upper limit value; the pressure limit releasing condition is as follows: and (4) representing the condition that the direct current voltage of the system is lower than a lower limit value. Whether the direct-current power supply of the characterization system exceeds the upper limit value or is lower than the lower limit value or not can be directly judged through the output voltage of the whole photovoltaic group string, can also be compared and judged through the output voltage of any photovoltaic module and the preset partial voltage of the photovoltaic group string in the corresponding proportion, or can also be indirectly judged through the current of the photovoltaic cell string.
Taking the voltage of the photovoltaic cell string as an example for explanation, the condition that the direct-current voltage of the characterization system exceeds the upper limit value is as follows: the voltage of the photovoltaic cell string is greater than a first preset voltage; the condition for representing that the direct-current voltage of the system is lower than the lower limit value is as follows: the voltage of the photovoltaic cell string is smaller than a second preset voltage; the first preset voltage is greater than the second preset voltage.
Taking the current of the photovoltaic cell string as an example for explanation, the condition that the direct-current voltage of the characterization system exceeds the upper limit value is as follows: the current of the photovoltaic cell string is smaller than a first preset current; the condition for representing that the direct-current voltage of the system is lower than the lower limit value is as follows: the current of the photovoltaic cell string is greater than a second preset current; the first preset current is smaller than the second preset current.
The rest of the principle is the same as the above embodiments, and is not described in detail here.
In practical application, the component voltage limiting circuit can be connected to two ends of a plurality of photovoltaic cell pieces, or two ends of a plurality of photovoltaic substrings, or two ends of a plurality of photovoltaic components. As shown in fig. 4, the component voltage limiting circuit includes: a detection control unit 101, a switch unit 102, and a power supply module 103; wherein:
the switch unit 102 is connected in parallel with the photovoltaic cells (photovoltaic cell slices, photovoltaic substrings or photovoltaic modules) controlled by the detection control unit 101 and is controlled by the detection control unit 101, so that the corresponding photovoltaic cells work in a voltage limiting mode or recover normal output; the power module 103 is used for supplying power to the detection control unit 101; the detection control unit 101 is configured to execute the component voltage limiting method according to any of the above embodiments.
Specifically, the detection control unit 101 may implement 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, judging that the parameters of the photovoltaic cell string meet the voltage limiting enabling condition; if the voltage of the photovoltaic cell string is smaller than a second preset voltage, judging that the parameter of the photovoltaic cell string meets a voltage limiting release condition; the first preset voltage is greater than the second preset voltage. Condition judgment can also be realized by judging the current of the photovoltaic cell string; if the current of the photovoltaic cell string is smaller than a first preset current, judging that the parameter of the photovoltaic cell string meets a voltage limiting enabling condition; if the current of the photovoltaic cell string is larger than a second preset current, judging that the parameter of the photovoltaic cell string meets a voltage limiting release condition; the first preset current is smaller than the second preset current. When the detection control unit 101 detects and judges that the parameters of the photovoltaic cell strings meet the voltage limiting enabling conditions, the corresponding photovoltaic cells are controlled to work in a voltage limiting mode, and further the voltage of the photovoltaic cell strings is reduced, so that the system can increase the number of the photovoltaic modules in series while ensuring that the maximum voltage does not exceed the corresponding requirement, and the system cost is reduced; when the parameters of the photovoltaic cell string meet the voltage limiting release condition, the photovoltaic cell working in the voltage limiting mode is controlled to recover normal output, the output voltage of the photovoltaic cell string is improved, and the direct current voltage utilization rate and the DC/AC capacity ratio of the photovoltaic system are further improved.
Among them, the detection control unit 101 preferably includes: a detection module and a controller. The controller may be implemented by using a comparator with hysteresis loop feedback as shown in fig. 5, wherein the switch unit 102 is controlled to be normally on when a parameter (such as a voltage Vs) output by the detection module exceeds a corresponding upper limit value (such as a reference voltage Vref) and further meets a voltage limiting enabling condition, and the switch unit 102 is controlled to be off when the parameter output by the detection module meets a voltage limiting releasing condition; such a controller is less expensive to implement. Alternatively, the controller may also be a PWM generator or a processor, when the parameter output by the detection module satisfies the voltage limiting enable condition, the switch unit 102 is controlled to be turned on according to PWM, the output voltage of the photovoltaic cell string is changed from the rectangular wave shown in fig. 3a to the sawtooth wave shown in fig. 3b by the capacitor of the power module 103, and the total output of the photovoltaic cell string is relatively smooth due to the phase error between the components and the input capacitor on the inverter side; and the controller turns off the control switch unit 102 when the parameter output by the detection module satisfies the voltage limitation release condition.
Moreover, the switch unit 102 may also have a plurality of specific implementation forms: for example, when the photovoltaic cell controlled by the detection control unit 101 is one photovoltaic cell in a photovoltaic cell string, the switch unit 102 is only a switch connected in parallel with the photovoltaic cell, as shown in fig. 6 a; when the photovoltaic cells controlled by the detection control unit 101 are photovoltaic cells partially connected in series in sequence in the string of photovoltaic cells, the switch unit 102 may be a plurality of switches connected in parallel with corresponding photovoltaic cells one by one (as shown in fig. 6 b), or may be a switch connected in parallel with all corresponding photovoltaic cells (as shown in fig. 6 c); when the photovoltaic cells controlled by the detection control unit 101 are a plurality of photovoltaic cells that are not connected to each other in the photovoltaic cell string, the switch unit 102 includes a plurality of switches (as shown in fig. 6 d) connected in parallel with the corresponding photovoltaic cells one by one; when the photovoltaic cells controlled by the detection control unit 101 are all photovoltaic cells in the string of photovoltaic cells, the switch unit 102 includes a plurality of switches connected in parallel with all the photovoltaic cells one by one (as shown in fig. 6 e). In addition, the above situations can be combined with each other, and are not described herein any more, and all of them belong to the scope of protection of the present application.
In practical applications, the switch is preferably a controllable electronic switch, such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a triode, a relay, or the like, and all of them are within the protection scope of the present application, depending on the application environment.
In addition, the power module 103 may take power from the photovoltaic cell string (as shown in fig. 4 and 6a to 6 e), or may take power from a part of the photovoltaic cell string (not shown), or may take power from the outside (not shown); it is not specifically limited herein, and is within the scope of the present application depending on the application environment.
The circuit form of the power module 103 may be a conventional LDO (low dropout regulator), a half-bridge circuit, or a flyback circuit, and the like, which is not specifically limited herein and is within the protection scope of the present application depending on the application environment.
For a specific implementation process of the component voltage limiting method, reference may be made to the above embodiments, and details are not repeated here.
Another embodiment of the present invention further provides an intelligent voltage limiting device, which is applied to the photovoltaic power generation system shown in fig. 7, wherein one photovoltaic string of the photovoltaic power generation system includes a plurality of conventional photovoltaic modules connected in series in sequence; some photovoltaic modules in the photovoltaic string may be equipped with the intelligent voltage limiting device, for example, the intelligent voltage limiting device and the photovoltaic modules are connected in parallel in one-to-one correspondence (not shown), or a plurality of photovoltaic modules connected in series in sequence are connected in parallel with one intelligent voltage limiting device (as shown in fig. 7); each photovoltaic module may also be equipped with a parallel connection of intelligent voltage limiting devices (not shown).
The intelligent voltage limiting device comprises the component voltage limiting circuit according to any one of the embodiments, and the specific structure and principle of the intelligent voltage limiting device can be described by referring to the embodiments and taking the photovoltaic power generation system shown in fig. 7 as an example, because the voltage input to the direct current side of the inverter by the photovoltaic string is required to be not more than 1500V, before the inverter is connected to the grid, the intelligent voltage limiting device limits the output voltage of the connected photovoltaic component, so that the total output of the photovoltaic string is not more than 1500V; and after the inverter is connected to the grid, the voltage of the direct-current side bus of the inverter is reduced to about 1200V along with the slow stabilization of the MPPT, at the moment, the intelligent voltage limiting device removes the voltage limiting function, the voltage is restored again, and the total voltage is still lower than 1500V.
As a result, for a 1500V inverter, the photovoltaic modules connected in series on the dc side can be configured higher, for example, up to 1800V, and the intelligent voltage limiting device is still effectively controlled within 1500V, thereby reducing the cost; and the system voltage can be increased to 1500V from 1200V in the prior art after grid connection, so that the system capacity ratio is improved.
Another embodiment of the present invention further provides a photovoltaic power generation system, as shown in fig. 7, including: 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 group string is connected with at least one intelligent voltage limiting device as described in the above embodiments, and preferably, the number of the intelligent voltage limiting devices arranged in each photovoltaic group string is the same, and the connection modes are the same, so that the output voltages of the photovoltaic group strings are ensured to be the same in a simple manner.
The specific structure and working principle of the intelligent voltage limiting device are the same as those of the above embodiments, and are not described in detail here.
Another embodiment of the present invention further provides an intelligent voltage-limiting junction box, as shown in fig. 8, including: a plurality of diodes, and, as in any of the above embodiments, the module voltage limiting circuit, the photovoltaic cells connected to the module voltage limiting circuit are photovoltaic substrings, and each diode is connected in reverse parallel with a corresponding photovoltaic substring.
The conventional photovoltaic module with 60 battery slices has an open-circuit voltage of about 42V at most in winter, and three photovoltaic sub-strings are contained in the conventional photovoltaic module, wherein the voltage of each photovoltaic sub-string is 14V. The photovoltaic module of 72 battery pieces is similar.
The power module 103 of the intelligent voltage limiting junction box takes power from the whole photovoltaic module and supplies power to the detection control unit 101. The switch unit 102 is a controllable electronic switch, such as a MOSFET, an IGBT, a triode, a relay, and the like, and fig. 8 shows the switch connected in parallel to two sides of one of the photovoltaic sub-strings.
And taking the voltage as a parameter for detection and judgment, then:
when the voltage of the photovoltaic module is high, for example, 36V is exceeded by Uth1, the detection control unit 101 actively controls the switch to be short-circuited, and theoretically, the voltage of 1/3 can be reduced, that is, reduced to 24V; if the switch is controlled to short the corresponding photovoltaic sub-string in a normal manner, the output voltage of the photovoltaic module is changed to 2/3V, and if the switch is controlled to short the corresponding photovoltaic sub-string in a PWM mode, the output voltage of the photovoltaic module is changed to a sawtooth wave around 2/3V (see fig. 3a and 3 b); and V is the voltage of the assembly before the corresponding photovoltaic sub-string is short-circuited. As the voltage is increased to 42V, the actual port voltage does not exceed 28V. In other words, when the intelligent voltage limiting junction box is provided with the module voltage limiting circuit, the maximum output of the whole photovoltaic module is limited to be below Uth 1-36V.
When the voltage of the photovoltaic module is low, for example, 20V below Uth2, the detection control unit 101 recovers the short-circuited photovoltaic sub-string, and the voltage is theoretically recovered to 30V.
From the above process, it can be known that, for a 1500V photovoltaic power generation system, the maximum number of components that can be accessed by the original design is 1500V/42V 35 blocks, and at present, 1500V/36V 41 blocks can be accessed by the intelligent voltage limiting junction box, so that the capacity of the photovoltaic system is further expanded, cables are reduced under the same inverter, the cost is reduced, and the utilization rate of the inverter is improved.
Taking the current as a parameter for detection and judgment, then:
when the photovoltaic module is in an open circuit, the load current is 0, and the voltage is higher; once loaded, the voltage is pulled down according to the photovoltaic curve (as shown in fig. 9), resulting in a load current. Therefore, assuming that the current is lower than Ith1 (such as 2A), the detection control unit 101 controls the switch unit 102 to be turned on, ensuring that the output voltage is low. When the current exceeds Ith2 (e.g., 3A), the inverter is considered to be operated at this time, pulling the bus voltage low, so that the detection control unit 101 can release the switch unit 102, and the cell power generation is resumed. The same effect is achieved.
Further, if the switch unit 102 is arranged on the photovoltaic sub-string of 1/6, the regulated granularity is finer and the regulation effect is better.
The rest of the structure and the principle are the same as those of the above embodiments, and are not described in detail here.
Another embodiment of the present invention further provides an intelligent component, including: photovoltaic module, and, as in any one of the above embodiments, intelligent voltage limiting terminal box.
A plurality of intelligent components are connected in series and in parallel and then are merged into the direct current side of the inverter, and the system structure is shown in fig. 10. The initial value of the system direct-current voltage is 1800V, before the inverter is connected to the grid, when the voltage limiting function in the intelligent assembly is started, partial output in the intelligent assembly is limited, and the direct-current voltage of the whole system is ensured not to exceed 1500V; after the inverter is in grid-connected operation, the direct current voltage of the system is reduced to about 1200V along with the slow stabilization of MPPT, then the voltage limiting function of each intelligent component is removed, the system normally generates power, but the total voltage is still lower than 1500V.
The structure and principle of the intelligent voltage-limiting junction box are the same as those of the above embodiments, and are not described in detail here.
Another embodiment of the present invention also provides a photovoltaic power generation system, as shown in fig. 10, including: an inverter, and at least one photovoltaic string connected to the dc side of the inverter;
the photovoltaic string comprises a plurality of intelligent assemblies connected in series;
the intelligent assembly is the intelligent assembly described in the above embodiments.
The structure and principle of the intelligent assembly are the same as those of the above embodiments, and are not described in detail here.
The embodiments of the invention are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments can be referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims (12)

1. A method of limiting voltage for an assembly, comprising:
detecting parameters of the photovoltaic cell string; the photovoltaic cell string comprises a plurality of photovoltaic cells connected in series, and the photovoltaic cells are photovoltaic cell sheets, photovoltaic substrings or photovoltaic modules;
judging whether the parameters of the photovoltaic cell string meet a voltage limiting enabling condition or a voltage limiting releasing condition according to the parameters of the photovoltaic cell string;
if the parameters of the photovoltaic cell string meet the voltage limiting enabling conditions, controlling at least one photovoltaic cell in the photovoltaic cell string to work in a voltage limiting mode;
and if the parameters of the photovoltaic cell string meet the pressure limiting release condition, controlling the photovoltaic cell working in the pressure limiting mode to recover normal output.
2. The component voltage limiting method of claim 1, wherein the voltage limiting mode comprises: a dead short mode in which the output voltage is zero, and a chopping mode in which voltage output is performed in accordance with Pulse Width Modulation (PWM) control.
3. The method for limiting voltage of an assembly according to claim 2, characterized in that the parameters of the string of photovoltaic cells are: a voltage or current of the string of photovoltaic cells, or a voltage or current of at least one photovoltaic cell.
4. The component voltage limiting method of claim 3 wherein the voltage limiting enabling condition is: representing the condition that the direct-current voltage of the system exceeds an upper limit value;
the pressure limiting releasing condition is as follows: and (4) representing the condition that the direct current voltage of the system is lower than a lower limit value.
5. The component voltage limiting method of claim 4, wherein if the parameter of the string of photovoltaic cells is a voltage of the string of photovoltaic cells, then:
the condition that the direct-current voltage of the characterization system exceeds the upper limit value is as follows: the voltage of the photovoltaic cell string is greater than a first preset voltage;
the condition that the direct-current voltage of the characterization system is lower than the lower limit value is as follows: the voltage of the photovoltaic cell string is smaller than a second preset voltage;
the first preset voltage is greater than the second preset voltage.
6. The component voltage limiting method of claim 4, wherein if the parameter of the string of photovoltaic cells is a current of the string of photovoltaic cells, then:
the condition that the direct-current voltage of the characterization system exceeds the upper limit value is as follows: the current of the photovoltaic cell string is smaller than a first preset current;
the condition that the direct-current voltage of the characterization system is lower than the lower limit value is as follows: the current of the photovoltaic cell string is greater than a second preset current;
the first preset current is smaller than the second preset current.
7. A component voltage limiting circuit, comprising: the device comprises a detection control unit, a switch unit and a power supply module; wherein:
the detection control unit is used for executing the component voltage limiting method of any one of claims 1 to 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 as to enable the corresponding photovoltaic cell to work in a voltage limiting mode or recover normal output;
the power module is used for supplying power to the detection control unit.
8. An intelligent voltage limiting device, characterized by comprising the component voltage limiting circuit according to claim 7, and the photovoltaic cell connected by the component voltage limiting circuit is a photovoltaic component.
9. A photovoltaic power generation system, comprising: an inverter and at least one photovoltaic string connected to the dc side of the inverter;
the photovoltaic string comprises a plurality of photovoltaic modules connected in series;
each photovoltaic group string is connected with at least one intelligent voltage limiting device.
10. An intelligent voltage limiting junction box, comprising: a plurality of diodes, and, the component voltage limiting circuit of claim 7; wherein:
the photovoltaic cells connected with the component voltage limiting circuit are photovoltaic substrings;
and each diode is connected with the corresponding photovoltaic sub-string in reverse parallel.
11. An intelligent component, comprising: a photovoltaic module, and the intelligent voltage limiting junction box of claim 9.
12. A photovoltaic power generation system, comprising: an inverter and at least one photovoltaic string connected to the dc side of the inverter;
the photovoltaic string comprises a plurality of intelligent assemblies connected in series;
the intelligent component is the intelligent component of claim 11.
CN201910114210.6A 2019-02-14 2019-02-14 Component voltage limiting method and application device and system thereof Pending CN111564866A (en)

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WO2015183840A1 (en) * 2014-05-27 2015-12-03 Sunpower Corporation Photovoltaic system protection
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