Device and method for adjusting serial connection number of photovoltaic strings and photovoltaic power generation system

Abstract

The invention provides a device and method for adjusting the number of photovoltaic strings connected in series and a photovoltaic power generation system, and belongs to the technical field of photovoltaic power generation, and the method comprises the steps: monitoring the environment temperature under the working condition of the photovoltaic strings based on a temperature monitoring unit, and obtaining an environment temperature signal; acquiring an output voltage signal of the photovoltaic string based on a direct-current voltage acquisition unit; the control unit generates a control signal according to the environment temperature signal, the output voltage signal and a preset voltage signal and outputs the control signal to the control end of the switch unit, and the control signal is used for controlling the switch unit to be switched on or switched off; when the switch unit is in a conducting state, the photovoltaic modules connected with the switch unit in parallel are short-circuited, so that the number of the photovoltaic strings connected in series is reduced; wherein the photovoltaic modules connected in parallel with the switch units are photovoltaic modules capable of adjusting the number of group strings; according to the scheme, the number of the photovoltaic strings connected in series can be automatically, flexibly and accurately adjusted by using the switch unit at different environment temperatures.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic power generation technology, and specifically to a photovoltaic string series quantity adjustment device, method and photovoltaic power generation system. Background Art

[0002] The number of PV strings in series is determined by the lowest temperature under the working conditions of the PV strings. The lower the lowest daytime temperature in the PV plant, the fewer PV strings in series, the lower the output voltage of the PV strings, and the lower the power generation of the PV power generation system. When the lowest temperature of the day occurs, the PV strings are in standby mode, so the lowest temperature of the PV strings under working conditions is higher than the lowest temperature of the day.

[0003] Extreme low temperature weather accounts for a small proportion of the year, and areas with abundant sunlight resources have a large temperature difference between day and night. At the same time, due to seasonal changes, the time of sunrise and sunset will also change continuously, causing the time of the lowest temperature in a day to change with the seasons. Therefore, adjusting the number of photovoltaic strings in series according to the lowest temperature will lead to a decrease in the power generation of the photovoltaic power generation system.

[0004] Therefore, how to flexibly and accurately adjust the number of photovoltaic strings in series has become a problem that needs to be solved. Summary of the invention

[0005] The purpose of the present application is to provide a photovoltaic string series quantity adjustment device, method and photovoltaic power generation system, which can solve the problem of how to flexibly and accurately adjust the number of photovoltaic strings in series in the prior art.

[0006] In a first aspect, an embodiment of the present application provides a photovoltaic string series quantity adjustment device, the device comprising: a control unit, a temperature monitoring unit, a DC voltage acquisition unit, and a switch unit;

[0007] The output end of the temperature monitoring unit is connected to the first input end of the control unit, and the temperature monitoring unit is used to monitor the ambient temperature under the working conditions of the photovoltaic string to obtain an ambient temperature signal; the input end of the DC voltage acquisition unit is connected to the DC output end of the photovoltaic string, and the output end of the DC voltage acquisition unit is connected to the second input end of the control unit, and the DC voltage acquisition unit is used to collect the output voltage signal of the photovoltaic string;

[0008] In a photovoltaic string consisting of N photovoltaic modules connected in series, a switch unit is provided at least at one location, each switch unit is connected in parallel to at least one photovoltaic module, a control end of the switch unit is connected to an output end of the control unit, and when the switch unit is in an on state, the photovoltaic modules connected in parallel therewith are short-circuited to reduce the number of photovoltaic modules connected in series; wherein the photovoltaic modules connected in parallel to the switch unit are photovoltaic modules for adjusting the number of strings.

[0009] In a first possible implementation of the first aspect, the photovoltaic assembly for adjusting the number of strings includes adjacent first photovoltaic assembly to be adjusted, second photovoltaic assembly to be adjusted, third photovoltaic assembly to be adjusted, and fourth photovoltaic assembly to be adjusted; the photovoltaic assembly for adjusting the number of strings is the second part of the photovoltaic string, and the remaining photovoltaic assemblies are the first part of the photovoltaic string. When the switch unit is in the off state, the photovoltaic assembly for adjusting the number of strings is connected to the first part of the photovoltaic string.

[0010] In a second possible implementation of the first aspect, the control unit includes: a main control module and a PWM control module; a first input end of the main control module is connected to an output end of the temperature monitoring unit, a second input end of the main control module is connected to an output end of the DC voltage acquisition unit, an output end of the main control module is connected to an input end of the PWM control module, and an output end of the PWM control module is connected to a control end of the switch unit.

[0011] In a third possible implementation of the first aspect, the control unit also includes: a limit module and a signal superposition module; the input end of the limit module is connected to the output end of the temperature monitoring unit, the output end of the limit module is connected to the first input end of the signal superposition module, the second input end of the signal superposition module is connected to the output end of the main control module, and the output end of the signal superposition module is connected to the input end of the PWM control module.

[0012] In a fourth possible implementation manner of the first aspect, the device includes: a first switch unit and a second switch unit; a control end of the first switch unit is connected to a first output end of the control unit, a first controlled end of the first switch unit is connected to a negative electrode of a first photovoltaic component to be adjusted, and a second controlled end of the first switch unit is connected to a positive electrode of a second photovoltaic component to be adjusted, and the first switch unit is used to short-circuit the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted when the first switch unit is in an on state, or to connect the first photovoltaic component to be adjusted with the second photovoltaic component to be adjusted when the first switch unit is in an off state, and to connect the third photovoltaic component to be adjusted with the fourth photovoltaic component to be adjusted;

[0013] The control end of the second switch unit is connected to the second output end of the control unit, the first controlled end of the second switch unit is connected to the negative electrode of the third photovoltaic component to be adjusted, and the second controlled end of the second switch unit is connected to the positive electrode of the fourth photovoltaic component to be adjusted. The second switch unit is used to short-circuit the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted when it is in the on state, or to connect the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted to the first part of the photovoltaic string at the same time when it is in the off state; wherein, when the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted are short-circuited, the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted are disconnected from the first part of the photovoltaic string at the same time.

[0014] In a fifth possible implementation manner of the first aspect, the first switch unit includes: a first switch device and a first diode, and the second switch unit includes: a second switch device and a second diode; a control end of the first switch device is connected to a first output end of the control unit, a first controlled end of the first switch device is connected to a negative electrode of a first photovoltaic component to be regulated, a second controlled end of the first switch device is connected to an anode of the first diode, a cathode of the first diode is connected to a positive electrode of a second photovoltaic component to be regulated, and the first diode is used to prevent current from flowing from the positive electrode of the second photovoltaic component to be regulated into the negative electrode of the first photovoltaic component to be regulated;

[0015] The control end of the second switching device is connected to the second output end of the control unit, the first controlled end of the second switching device is connected to the negative electrode of the third photovoltaic component to be regulated, the second controlled end of the second switching device is connected to the anode of the second diode, the cathode of the second diode is connected to the positive electrode of the fourth photovoltaic component to be regulated, and the second diode is used to prevent current from flowing from the positive electrode of the fourth photovoltaic component to be regulated to the negative electrode of the third photovoltaic component to be regulated.

[0016] In a sixth possible implementation of the first aspect, the device also includes a signal input unit; the input end of the signal input unit is connected to the output end of the control system, the output end of the signal input unit is connected to the third input end of the control unit, and the signal input unit is used to input a preset voltage signal output by the control system and output the preset voltage signal to the control unit.

[0017] In a seventh possible implementation manner of the first aspect, the device includes: a control unit, a temperature monitoring unit, a DC voltage acquisition unit, and a plurality of switch units; wherein the DC voltage acquisition unit includes a plurality of input terminals and a plurality of output terminals, the control unit includes a plurality of second input terminals and a plurality of output terminals, and there are a plurality of photovoltaic strings connected to the input terminal of the DC voltage acquisition unit;

[0018] The output end of the temperature monitoring unit is connected to the first input end of the control unit, and the temperature monitoring unit is used to monitor the ambient temperature under the working conditions of each photovoltaic string to obtain multiple ambient temperature signals; each input end of the DC voltage acquisition unit is connected to the DC output end of the corresponding photovoltaic string, and each output end of the DC voltage acquisition unit is connected to the corresponding second input end of the control unit, and the DC voltage acquisition unit is used to collect the output voltage signal of each photovoltaic string;

[0019] In each photovoltaic string composed of N photovoltaic components connected in series, a switch unit is provided at least at one place, each switch unit is connected in parallel to at least one photovoltaic component, a control end of each switch unit is connected to an output end corresponding to the control unit, and when each switch unit is in an on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of series connections of the corresponding photovoltaic strings; wherein the photovoltaic components connected in parallel to each switch unit are adjusted for the corresponding number of strings.

[0020] In a second aspect, an embodiment of the present application provides a photovoltaic power generation system, the system comprising: a photovoltaic string, an inverter, a box-type transformer AC device, a control system, and a photovoltaic string series quantity adjustment device of the first to sixth possible implementations in the first aspect;

[0021] The DC input end of the photovoltaic string is connected to the output end of the photovoltaic string series quantity adjustment device, and the DC output end of the photovoltaic string is connected to the power supply input end of the inverter and the first input end of the photovoltaic string series quantity adjustment device. The photovoltaic string is used to provide an output voltage signal to the photovoltaic string series quantity adjustment device and output direct current after adjusting the number of photovoltaic strings in series to the inverter;

[0022] The output end of the inverter is connected to the input end of the box-type transformer AC device. The inverter is used to invert the DC power output by the photovoltaic string into AC power and output the AC power to the box-type transformer AC device. The output end of the box-type transformer AC device is connected to the input end of the power grid. The box-type transformer AC device is used to collect and boost the AC power output by the inverter and output the boosted AC power to the power grid.

[0023] The output end of the control system is connected to the second input end of the photovoltaic string series quantity adjustment device, and the control system is used to output a preset voltage signal to the photovoltaic string series quantity adjustment device; the photovoltaic string series quantity adjustment device is used to adjust the number of photovoltaic strings in series based on the ambient temperature signal under the working conditions of the photovoltaic strings, the output voltage signal provided by the photovoltaic strings, and the preset voltage signal.

[0024] In a possible implementation of the second aspect, the system includes: a plurality of photovoltaic strings, an inverter, a box-type transformer AC device, a control system, and a photovoltaic string series quantity adjustment device in the seventh possible implementation; wherein the photovoltaic string series quantity adjustment device includes a plurality of first input terminals, a second input terminal, and a plurality of output terminals, and the inverter includes a plurality of power supply input terminals;

[0025] The DC input end of each photovoltaic string is connected to the corresponding output end of the photovoltaic string series quantity adjustment device, and the DC output end of each photovoltaic string is connected to the corresponding power supply input end of the inverter and the corresponding first input end of the photovoltaic string series quantity adjustment device. Each photovoltaic string is used to provide a corresponding output voltage signal to the photovoltaic string series quantity adjustment device and output the corresponding DC power after adjusting the number of photovoltaic strings in series to the inverter;

[0026] The output end of the inverter is connected to the input end of the box-type transformer AC device. The inverter is used to invert the DC power output by each photovoltaic string into AC power and output the AC power to the box-type transformer AC device. The output end of the box-type transformer AC device is connected to the input end of the power grid. The box-type transformer AC device is used to collect and boost the AC power output by the inverter and output the boosted AC power to the power grid.

[0027] The output end of the control system is connected to the second input end of the photovoltaic string series quantity adjustment device, and the control system is used to output a preset voltage signal to the photovoltaic string series quantity adjustment device; the photovoltaic string series quantity adjustment device is used to adjust the series quantity of each photovoltaic string based on the ambient temperature signal under the working conditions of each photovoltaic string, the output voltage signal provided by each photovoltaic string and the preset voltage signal.

[0028] In a third aspect, an embodiment of the present application provides a method for adjusting the number of photovoltaic strings connected in series, which is implemented based on the photovoltaic string connection number adjustment device in the first to sixth possible implementations of the first aspect, and the method includes:

[0029] Based on the temperature monitoring unit, the ambient temperature under the working condition of the photovoltaic string is monitored to obtain an ambient temperature signal;

[0030] The output voltage signal of the photovoltaic string is collected based on the DC voltage collection unit;

[0031] The control unit generates a control signal according to the ambient temperature signal, the output voltage signal and the preset voltage signal, and outputs a corresponding control signal to the control end of each switch unit, each control signal is used to control the corresponding switch unit to be turned on or off;

[0032] When each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of photovoltaic strings connected in series; wherein the photovoltaic components connected in parallel with each switch unit are adjusted to the corresponding number of strings.

[0033] In a possible implementation of the third aspect, the control unit includes: a main control module, a PWM control module, a limit module and a signal superposition module, the device includes: a first switch unit and a second switch unit; the string quantity adjustment photovoltaic assembly includes adjacent first photovoltaic assemblies to be adjusted, second photovoltaic assemblies to be adjusted, third photovoltaic assemblies to be adjusted and fourth photovoltaic assemblies to be adjusted, the string quantity adjustment photovoltaic assembly is the second part of the photovoltaic string, and the remaining photovoltaic assemblies are the first part of the photovoltaic string, when each switch unit is in an off state, the string quantity adjustment photovoltaic assembly is connected to the first part of the photovoltaic string; the device also includes a signal input unit; based on the control unit generating a control signal according to an ambient temperature signal, an output voltage signal and a preset voltage signal, when each switch unit is in an on state, the photovoltaic assembly connected in parallel therewith is short-circuited, and when each switch unit is in an off state, the string quantity adjustment photovoltaic assembly is connected to the first part of the photovoltaic string, including:

[0034] When the first ambient temperature is lower than the standard test temperature: based on the main control module, the first output voltage is compared with the first preset voltage input by the signal input unit to obtain a first comparison result, and a first main control signal is generated based on the first comparison result, and at the same time, a first limit signal is generated based on the limit module according to the first ambient temperature signal; based on the signal superposition module, the first main control signal and the first limit signal are logically superimposed to generate a first modulation signal; based on the PWM control module, a first drive signal is generated according to the first modulation signal, and the first drive signal is output to the control end of the first switch unit and the control end of the second switch unit; based on the PWM control module, the first switch unit is driven to turn on according to the first drive signal to short-circuit the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted, and at the same time, the second switch unit is driven to turn off according to the first drive signal to connect the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted to the first part of the photovoltaic string at the same time;

[0035] When the second ambient temperature is lower than the first ambient temperature: the control unit generates a second control signal according to the second output voltage and the first preset voltage, and outputs the second control signal to the control end of the first switch unit and the control end of the second switch unit; the control unit controls the first switch unit to be turned off according to the second control signal, and controls the second switch unit to be turned on according to the second control signal, so as to short-circuit the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted; wherein, when the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted are short-circuited, the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted are simultaneously disconnected from the first part of the photovoltaic string.

[0036] In a possible implementation of the third aspect, based on the control unit generating a control signal according to the ambient temperature signal, the output voltage signal and the preset voltage signal, when each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited, and when each switch unit is in the off state, the photovoltaic components for adjusting the number of strings are connected to the first part of the photovoltaic string, further comprising:

[0037] When the third ambient temperature is greater than the second ambient temperature: based on the main control module, the third output voltage is compared with the second preset voltage to obtain a third comparison result; if the third comparison result is that the third output voltage is less than the second preset voltage, the main control module generates a third main control signal according to the absolute value of the difference between the third output voltage and the second preset voltage, and the limit module generates a third limit signal according to the third ambient temperature signal; wherein the second preset voltage is the difference between the first preset voltage and twice the equivalent open-circuit voltage of the photovoltaic string; based on the signal superposition module, the third main control signal and the third limit signal are logically superimposed to generate a third modulation signal; based on the PWM control module, a third drive signal is generated according to the third modulation signal, and the third drive signal is output to the control end of the first switch unit and the control end of the second switch unit; based on the PWM control module, the first switch unit is driven to conduct according to the third drive signal to short-circuit the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted, and the second switch unit is driven to turn off according to the third drive signal to connect the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted to the first part of the photovoltaic string at the same time;

[0038] When the fourth ambient temperature is greater than or equal to the standard test temperature: based on the control unit, a fourth control signal is generated according to the fourth output voltage and the preset voltage, and the fourth control signal is output to the control end of the first switch unit and the control end of the second switch unit; based on the control unit, the first switch unit and the second switch unit are controlled to be turned off according to the fourth control signal, so as to connect the first photovoltaic component to be adjusted, the second photovoltaic component to be adjusted, the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted to the first part of the photovoltaic string at the same time.

[0039] In a possible implementation manner of the third aspect, the method is implemented based on the photovoltaic string series quantity adjustment device in the sixth possible implementation manner, and the method includes:

[0040] The temperature monitoring unit is used to monitor the ambient temperature under the working conditions of each photovoltaic string to obtain multiple ambient temperature signals; the DC voltage acquisition unit is used to collect the output voltage signal of each photovoltaic string; the control unit generates a control signal according to the ambient temperature signal, the output voltage signal and the preset voltage signal, and outputs the corresponding control signal to the control end of each switch unit, each control signal is used to control the corresponding switch unit to be turned on or off;

[0041] The control end of each switch unit is connected to the output end corresponding to the control unit. When each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of series connections of the corresponding photovoltaic strings; wherein the photovoltaic components connected in parallel to each switch unit are adjusted for the corresponding number of strings.

[0042] The photovoltaic string series quantity adjustment device of the present application includes: a control unit, a temperature monitoring unit, a DC voltage acquisition unit and a switch unit. The temperature monitoring unit obtains an ambient temperature signal by monitoring the ambient temperature under the working conditions of the photovoltaic string. The DC voltage acquisition unit acquires the output voltage signal of the photovoltaic string. The switch unit adjusts the series quantity of the photovoltaic string by short-circuiting the photovoltaic components connected in parallel therewith. The scheme of the present application sets a switch unit at least in one place in the photovoltaic string. The switch unit can be used to automatically, flexibly and accurately adjust the series quantity of the photovoltaic string at different ambient temperatures. It is not limited by the minimum temperature under the working conditions of the photovoltaic string and has strong ease of use and practicality.

[0043] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0045] Figure 1 It is a schematic block diagram of the overall structure of a photovoltaic string series quantity adjustment device of a photovoltaic string provided in an embodiment of the present application;

[0046] Figure 2 It is a schematic block diagram of the specific structure of a photovoltaic string series quantity adjustment device of a photovoltaic string provided in an embodiment of the present application;

[0047] Figure 3 It is a schematic block diagram of the overall structure of a photovoltaic string series quantity adjustment device for multiple photovoltaic strings provided in an embodiment of the present application;

[0048] Figure 4 is a schematic block diagram of a photovoltaic power generation system including a photovoltaic string provided in an embodiment of the present application;

[0049] Figure 5 is a schematic block diagram of a photovoltaic power generation system including a plurality of photovoltaic strings provided in an embodiment of the present application;

[0050] Figure 6It is a schematic diagram of the steps of a method for adjusting the number of photovoltaic strings connected in series in a photovoltaic string provided in an embodiment of the present application;

[0051] Figure 7 It is a schematic diagram of the steps of a method for adjusting the number of photovoltaic strings connected in series for a plurality of photovoltaic strings provided in an embodiment of the present application. DETAILED DESCRIPTION

[0052] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0053] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0054] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0055] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0056] As used in this specification and the appended claims, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to monitoring, depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is monitored" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is monitored" or "in response to monitoring [described condition or event]", depending on the context.

[0057] In addition, in the description of the present application, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0058] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0059] In the present application specification, unless otherwise specified, directional words such as "up, down, left, right" generally refer to the orientation or position relationship shown in the accompanying drawings, or the orientation or position relationship in which the invented product is usually placed when in use.

[0060] In the present application specification, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0061] With the rapid development of the current economy, the global demand for energy is increasing day by day, but the problems of fossil energy shortage and environmental pollution are gradually becoming prominent. Therefore, it is urgent to find new energy forms to replace fossil energy, which will become an important means to solve the problems of energy shortage and environmental pollution. Therefore, the use of clean, safe and pollution-free renewable energy has received more and more attention. New energy sources such as wind energy, solar energy, biomass energy, and ocean energy are constantly improving their status in the energy strategies of various countries due to their clean, safe and renewable characteristics. Among them, solar energy has relatively low cost, mature technology and high reliability. It has developed rapidly in recent years and has begun to play an important role in energy supply.

[0062] The most important form of solar energy utilization is photovoltaic power generation. For large ground-mounted photovoltaic power stations, the number of photovoltaic strings in series in the photovoltaic power generation system is mainly affected by the open circuit voltage Voc of the photovoltaic string, the open circuit voltage temperature coefficient Kv of the photovoltaic string, the maximum DC input voltage Vdcmax allowed by the inverter, and the ambient temperature t. In general design, the open circuit voltage Voc of the photovoltaic string, the open circuit voltage temperature coefficient Kv of the photovoltaic string, and the maximum DC input voltage Vdcmax allowed by the inverter can be determined according to the manufacturer's information and are fixed values, while the ambient temperature t is a variable that changes at any time, so it has become an important parameter affecting the number of photovoltaic strings in series.

[0063] The number of PV strings in series refers to the number of PV modules in series in each PV string, N, which can be calculated according to the following formula:

[0064]

[0065] Wherein, Kv represents the open circuit voltage temperature coefficient of the PV string, Kv` represents the operating voltage temperature coefficient of the PV string, N represents the number of PV modules in series (N is rounded up), t` represents the minimum temperature of the PV string under working conditions, t`` represents the maximum temperature of the PV string under working conditions, Vdcmax represents the maximum DC input voltage allowed by the inverter, Vmppt max represents the maximum MTTP (Maximum Power Point Tracking) voltage of the inverter, Voc represents the open circuit voltage of the PV string, and Vpm represents the operating voltage of the PV string (i.e., the output voltage of the PV string or the series voltage of the PV modules).

[0066] In order to achieve technical and economic optimization, ground photovoltaic power stations are generally designed with the maximum number of photovoltaic strings in series. In this case, it is only necessary to calculate according to Formula 1. Distributed photovoltaic power generation systems combined with buildings usually do not use the maximum number of photovoltaic strings in series. In this case, it is necessary to combine Formula 1 and Formula 2 to comprehensively consider and derive the range of the number of photovoltaic strings in series.

[0067] It can be seen from formula 1 that when the open circuit voltage Voc of the photovoltaic string, the open circuit voltage temperature coefficient Kv of the photovoltaic string and the maximum DC input voltage Vdcmax allowed by the inverter are fixed, the number of photovoltaic strings in series N is proportional to the ambient temperature t. Assuming that the system voltage is 1500V, that is, the maximum DC input voltage Vdcmax allowed by the inverter is 1500V, and taking the parameters of a certain brand of photovoltaic modules as a reference, under standard test conditions, the open circuit voltage Voc of the photovoltaic string is 50V, the open circuit voltage temperature coefficient Kv of the photovoltaic string is -0.0026 / ℃, and the ambient temperature t under the working conditions of the photovoltaic string is 25℃, and the number of photovoltaic strings in series N is calculated to be 30 by substituting it into formula 1. Table 1 is a table of the number of photovoltaic strings in series N at different ambient temperatures, and the number of photovoltaic strings in series N at different ambient temperatures is shown in Table 1.

[0068] From Table 1 and the characteristics of the photovoltaic modules, it can be seen that the voltage of the photovoltaic modules will decrease with the increase of the ambient temperature under the sunlight. Affected by the open-circuit voltage temperature coefficient, the open-circuit voltage of the photovoltaic string will decrease with the increase of the ambient temperature under the working conditions of the photovoltaic string. Therefore, as the ambient temperature of the photovoltaic string decreases, its open-circuit voltage will increase. In order to ensure that the inverter can work normally and continuously at the local minimum temperature, when calculating the working voltage of the photovoltaic string using the above formula, the influence of the local minimum temperature on the open-circuit voltage of the photovoltaic string should be considered. Therefore, the ambient temperature t should be the lowest temperature under the working conditions of the photovoltaic string.

[0069] Table 1

[0070]

[0071] It can be seen that the number of PV strings in series is determined by the lowest temperature under the working conditions of the PV strings. The lower the daytime lowest temperature in the PV plant, the fewer the number of PV strings in series, the lower the output voltage of the PV strings, and the lower the power generation of the PV power generation system. When the lowest temperature of the day occurs, the PV strings are in standby mode, so the lowest temperature under the working conditions of the PV strings is higher than the lowest temperature of the day.

[0072] Extreme low temperature weather accounts for a small proportion of the year, and areas with abundant sunlight resources have a large temperature difference between day and night. At the same time, due to seasonal changes, the time of sunrise and sunset will also change continuously, causing the time of the lowest temperature in a day to change with the seasons. Therefore, adjusting the number of photovoltaic strings in series according to the lowest temperature will lead to a decrease in the power generation of the photovoltaic power generation system.

[0073] The output voltage of the photovoltaic string (i.e., the input voltage of the inverter) cannot exceed the maximum DC input voltage allowed by the inverter. Limiting the output voltage of the photovoltaic string is generally achieved through the inverter. At present, there are not many solutions for adjusting the number of photovoltaic strings in series. In order to increase the number of photovoltaic strings in series, a voltage switch is set at the input end of the inverter in the prior art. When the output voltage of the photovoltaic string exceeds the maximum DC input voltage allowed by the inverter, the inverter will stop working. This usually causes the inverter to be unable to work in the rated state for a long time and fail to achieve the ideal efficiency. Therefore, how to flexibly and accurately adjust the number of photovoltaic strings in series has become a problem to be solved.

[0074] In view of the above defects, the present application provides a photovoltaic string series quantity adjustment device including: a control unit, a temperature monitoring unit, a DC voltage acquisition unit and a switch unit, wherein the temperature monitoring unit obtains an ambient temperature signal by monitoring the ambient temperature under the working conditions of the photovoltaic string, the DC voltage acquisition unit acquires the output voltage signal of the photovoltaic string, and the switch unit adjusts the series quantity of the photovoltaic string by short-circuiting the photovoltaic components connected in parallel therewith. The scheme of the present application sets a switch unit at least in one place in the photovoltaic string, and the switch unit can be used to realize automatic, flexible and accurate adjustment of the series quantity of the photovoltaic string at different ambient temperatures, which is not limited by the minimum temperature under the working conditions of the photovoltaic string, and has strong ease of use and practicality.

[0075] The overall structure of the photovoltaic string series quantity adjustment device provided in the embodiment of the present application is introduced below through specific embodiments.

[0076] See also Figure 1 , Figure 1 1 is a schematic block diagram of the overall structure of a photovoltaic string series quantity adjustment device 100 of a photovoltaic string 210 provided in an embodiment of the present application. Figure 1 As shown, the photovoltaic string series quantity adjustment device 100 includes: a control unit 110 , a temperature monitoring unit 120 , a DC voltage acquisition unit 130 , and a first switch unit 142 and a second switch unit 144 .

[0077] In one embodiment, the output end of the temperature monitoring unit 120 is connected to the first input end of the control unit 110, and the temperature monitoring unit 120 is used to obtain the ambient temperature signal T by real-time monitoring the ambient temperature under the working conditions of the photovoltaic string 210 (i.e., the ambient temperature of the photovoltaic plant), and output the ambient temperature signal T to the control unit 110. The input end of the DC voltage acquisition unit 130 is connected to the DC output end (including the positive and negative terminals BUS+ and BUS-) of the photovoltaic string 210, and the output end of the DC voltage acquisition unit 130 is connected to the second input end of the control unit 110. The DC voltage acquisition unit 130 is used to collect the output voltage signal Vdc of the photovoltaic string 210, and provide the output voltage signal Vdc to the control unit 110.

[0078] In some embodiments, the control unit 110 includes at least one output terminal. In a photovoltaic string consisting of N photovoltaic modules connected in series, a switch unit is provided at least at one location. Each switch unit is connected in parallel to at least one photovoltaic module, and a control terminal of each switch unit is connected to a corresponding output terminal of the control unit 110. When each switch unit is in a conducting state, the photovoltaic module connected in parallel therewith is short-circuited to reduce the number of photovoltaic strings connected in series. The photovoltaic modules connected in parallel to each switch unit adjust the photovoltaic modules for the corresponding number of strings.

[0079] It should be noted that, as can be seen from Table 1, the maximum number of photovoltaic strings connected in series is 30 and the minimum is 26. Therefore, N can be set to 30, and there can be 4 photovoltaic modules to be adjusted. N and the number of photovoltaic modules to be adjusted can be determined according to the specific circumstances in the actual application scenario, and are not specifically limited here. The present application scheme is introduced with N being 30 and 4 photovoltaic modules to be adjusted.

[0080] In some embodiments, the control unit 110 is used to generate control signals UK1-UKn based on the ambient temperature signal T, the output voltage signal Vdc and the preset voltage signal Vdcmax, and output the corresponding control signals UK1-UKn to the control terminals of the respective switch units. The preset voltage is the maximum DC input voltage allowed by the inverter, and each control signal UK1-UKn is used to control the corresponding switch unit to be turned on or off.

[0081] In one embodiment, in a photovoltaic string composed of 30 photovoltaic components connected in series, a first switch unit 142 may be provided at photovoltaic components A1 and A2, and the first switch unit 142 is connected in parallel to photovoltaic components A1 and A2; a second switch unit 144 may also be provided at photovoltaic components B1 and B2, and the switch unit 144 is connected in parallel to photovoltaic components B1 and B2, and the control ends of the first switch unit 142 and the second switch unit 144 are respectively connected to the output end of the control unit 110. When the first switch unit 142 and the second switch unit 144 are in the on state, the photovoltaic components A1, A2, B1 and B2 are short-circuited to reduce the number of photovoltaic strings 210 connected in series. When the photovoltaic components A1, A2, B1 and B2 are short-circuited, a part of the photovoltaic components in the photovoltaic string 210 is missing, so that the number of photovoltaic strings 210 connected in series is reduced. Among them, the photovoltaic components A1, A2, B1 and B2 are the photovoltaic components 214 for adjusting the number of strings.

[0082] In one embodiment, the first output terminal and the second output terminal of the control unit 110 are respectively connected to the control terminals of the first switch unit 142 and the second switch unit 144. The control unit 110 is used to generate control signals UK1 and UK2 based on the ambient temperature signal T, the output voltage signal Vdc, and the preset voltage signal Vdcmax, and output the control signals UK1 and UK2 to the control terminals of the first switch unit 142 and the second switch unit 144. The control signals UK1 and UK2 are respectively used to control the first switch unit 142 and the second switch unit 144 to be turned on or off.

[0083] In another embodiment, in a photovoltaic string consisting of 30 photovoltaic modules connected in series, a switch unit may be provided at each of the photovoltaic modules A1, A2, B1, and B2. Four switch units are connected in parallel to the photovoltaic modules A1, A2, B1, and B2, respectively, and the control ends of the four switch units are connected to the output ends of the control unit 110, respectively. When the four switch units are in the on state, the photovoltaic modules A1, A2, B1, and B2 are short-circuited, respectively, to reduce the number of photovoltaic modules connected in series.

[0084] In another embodiment, a switch unit is provided at one location in a photovoltaic string consisting of 30 photovoltaic modules connected in series, and the switch unit is connected in parallel to four photovoltaic modules A1, A2, B1 and B2, and the control end of the switch unit is connected to the output end of the control unit 110.

[0085] It should be noted that Figure 1 The setting method of the switch unit is only one of the ways. There can be many other setting methods. There can also be multiple photovoltaic modules for adjusting the number of strings. They can be adjacent or non-adjacent. They are not listed here one by one and can be determined according to the specific circumstances in the actual application scenario.

[0086] In this embodiment, the temperature monitoring unit 120 obtains the ambient temperature signal T by monitoring the ambient temperature under the working conditions of the photovoltaic string 210, the DC voltage acquisition unit 130 acquires the output voltage signal Vdc of the photovoltaic string 210, and the control unit 110 generates control signals UK1~UKn based on the ambient temperature signal, the output voltage signal Vdc and the preset voltage signal Vdcmax, and controls the corresponding switch units to be turned on based on the control signals UK1~UKn. Each switch unit adjusts the number of series connections of the photovoltaic string 210 by short-circuiting the photovoltaic components connected in parallel with it.

[0087] The solution of this embodiment sets a switch unit at at least one place of the photovoltaic string 210, and the switch unit can be used to automatically and flexibly adjust the number of photovoltaic strings 210 in series under different ambient temperatures, without being restricted by the minimum temperature under the working conditions of the photovoltaic string 210. Under the premise of meeting the maximum DC input voltage allowed by the inverter, the maximum number of series connections can be guaranteed, the number of inverters and photovoltaic brackets can be reduced, and the floor space of the photovoltaic plant can also be reduced, so that the investment in the photovoltaic project can be reduced. In addition, the power generation of the photovoltaic power generation system is increased, the economic performance of the photovoltaic project is improved, and it has strong ease of use and practicality.

[0088] The specific structure of the device 100 for adjusting the number of series-connected photovoltaic strings 210 provided in the embodiment of the present application is described below through a specific embodiment.

[0089] See also Figure 2 , Figure 2 1 is a schematic block diagram of the specific structure of a photovoltaic string series quantity adjustment device 100 of a photovoltaic string 210 provided in an embodiment of the present application. Figure 2 As shown, in one embodiment, the photovoltaic assembly 214 for adjusting the number of strings includes the adjacent first photovoltaic assembly A1 to be adjusted, the second photovoltaic assembly A2 to be adjusted, the third photovoltaic assembly B1 to be adjusted, and the fourth photovoltaic assembly B2 to be adjusted. The photovoltaic assembly 214 for adjusting the number of strings is the second part of the photovoltaic string 210, and the remaining photovoltaic assemblies are the first part of the photovoltaic string 210.

[0090] In one embodiment, when the first switch unit 142 and the second switch unit 144 are in the off state, the string quantity adjustment photovoltaic component 214 is connected to the first part 212 of the photovoltaic string 210 to increase the number of photovoltaic strings 210 in series after the reduction, which can also be understood as reducing the number of photovoltaic strings 210 in series. For example, the original number of photovoltaic strings 210 in series was reduced by 4, and now the number of photovoltaic strings 210 in series is reduced by 2, so the number of photovoltaic strings 210 in series is reduced by 4, but the overall number of photovoltaic strings 210 in series N is not increased. It is just that after the number of photovoltaic strings 210 in series is reduced, it is necessary to increase the photovoltaic components to be adjusted connected to the first part 212 of the photovoltaic string 210 in some cases. For example, the original number of photovoltaic components to be adjusted connected to the first part 212 of the photovoltaic string 210 is 2, and now it is necessary to increase 2 photovoltaic components to be adjusted connected to the first part 212 of the photovoltaic string 210.

[0091] In another embodiment, the plurality of photovoltaic components to be adjusted may not be adjacent, but may be separated in the photovoltaic string 210. For example, a switch unit is set at the first column of photovoltaic components in the photovoltaic string 210, a switch unit is set at the middle column of photovoltaic components, and a switch unit is set at the last column of photovoltaic components. These three columns of photovoltaic components are photovoltaic components for adjusting the number of strings and are not adjacent.

[0092] In this embodiment, a plurality of photovoltaic components to be adjusted are adjacent, and only one switch unit may be provided. Only one switch unit may be used to adjust the number of photovoltaic strings 210 in series, thereby reducing the number of switch units and simplifying the circuit structure.

[0093] Please continue to see Figure 2In one embodiment, the control unit 110 includes: a main control module 112 and a PWM control module 114. A first input end of the main control module 112 is connected to an output end of the temperature monitoring unit 120, and an ambient temperature signal T output by the temperature monitoring unit 120 is input to the control module 112. A second input end of the main control module 112 is connected to an output end of a DC voltage acquisition unit 130, and an output voltage signal Vdc acquired by the DC voltage acquisition unit 130 is input to the main control module 112. The main control module 112 is used to generate a main control signal U0 based on the ambient temperature signal T, the output voltage signal Vdc, and the preset voltage signal Vdcmax. The output end of the main control module 112 is connected to an input end of the PWM control module 114, and the main control module 112 outputs the main control signal U0 to the PWM control module 114. The first output end of the PWM control module 114 is connected to the control end of the first switch unit 142 , and the second output end of the PWM control module 114 is connected to the control end of the second switch unit 144 . The PWM control module 114 outputs the main control signal U0 to the control ends of the first switch unit 142 and the second switch unit 144 , respectively.

[0094] Please continue to see Figure 2 In one embodiment, the control unit 110 further includes: a limit module 116 and a signal superposition module 118. The input end of the limit module 116 is connected to the output end of the temperature monitoring unit 120, the ambient temperature signal T is input to the limit module 116, and the output end of the limit module 116 is connected to the first input end of the signal superposition module 118. The limit module is used to generate a limit signal 0 or 1 based on the ambient temperature signal T, and output the limit signal 0 or 1 to the signal superposition module 118. The second input end of the signal superposition module 118 is connected to the output end of the main control module 112, the main control signal U0 is input to the signal superposition module 118, and the output end of the signal superposition module 118 is connected to the input end of the PWM control module 114. The signal superposition module 118 is used to perform logical operation superposition on the ambient temperature signal T and the main control signal U0 to generate a modulation signal U1, and output the modulation signal U1 to the PWM control module 114.

[0095] Please continue to see Figure 2 In one embodiment, the PWM control module 114 is used to generate a drive signal PWM (Pulse Width Modulation) based on the modulation signal U1, and output the drive signal PWM to the control terminals of the first switch unit 142 and the second switch unit 144. The drive signal PWM is used to control the first switch unit 142 and the second switch unit 144 to be turned on or off.

[0096] Please continue to see Figure 2In one embodiment, the photovoltaic string series quantity adjustment device 100 includes: a first switch unit 142 and a second switch unit 144. The control end of the first switch unit 142 is connected to the first output end of the control unit 110, the first controlled end of the first switch unit 142 is connected to the negative pole of the first photovoltaic component A1 to be adjusted, and the second controlled end of the first switch unit 142 is connected to the positive pole of the second photovoltaic component A2 to be adjusted. The first switch unit 142 is used to short-circuit the first photovoltaic component A1 to be adjusted and the second photovoltaic component A2 to be adjusted when it is in the on state, or the first switch unit 142 is used to connect the first photovoltaic component A1 to be adjusted with the second photovoltaic component A2 to be adjusted, and connect the third photovoltaic component B1 to be adjusted with the fourth photovoltaic component B2 to be adjusted when it is in the off state.

[0097] In one embodiment, the control end of the second switch unit 144 is connected to the second output end of the control unit 110, the first controlled end of the second switch unit 144 is connected to the negative electrode of the third photovoltaic component to be adjusted B1, and the second controlled end of the second switch unit 144 is connected to the positive electrode of the fourth photovoltaic component to be adjusted B2. The second switch unit 144 is used to short-circuit the third photovoltaic component to be adjusted B1 and the fourth photovoltaic component to be adjusted B2 when it is in the on state, or the second switch unit 144 is used to connect the third photovoltaic component to be adjusted B1 and the fourth photovoltaic component to be adjusted B2 to the first part 212 of the photovoltaic string 210 at the same time when it is in the off state.

[0098] When the third photovoltaic assembly B1 and the fourth photovoltaic assembly B2 are short-circuited, the first photovoltaic assembly A1 and the second photovoltaic assembly A2 are disconnected from the first part 212 of the photovoltaic string 210 at the same time, so that the number of photovoltaic strings 210 connected in series is reduced.

[0099] Please continue to see Figure 2 In one embodiment, the first switch unit 142 includes: a first switch device VD1 and a first diode D1, and the second switch unit 144 includes: a second switch device VD2 and a second diode D2. The control end of the first switch device VD1 is connected to the first output end of the control unit 110, the first controlled end of the first switch device VD1 is connected to the cathode of the first photovoltaic component A1 to be regulated, and the second controlled end of the first switch device VD1 is connected to the anode of the first diode D1. The cathode of the first diode D1 is connected to the anode of the second photovoltaic component A2 to be regulated, and the first diode D1 is used to prevent current from flowing back, that is, from the second anode of the second photovoltaic component A2 to be regulated to the cathode of the first photovoltaic component A1 to be regulated.

[0100] In one embodiment, the control end of the second switch device VD2 is connected to the second output end of the control unit 110, the first controlled end of the second switch device VD2 is connected to the negative electrode of the third photovoltaic component to be adjusted B1, and the second controlled end of the second switch device VD2 is connected to the anode of the second diode D2. The cathode of the second diode D2 is connected to the positive electrode of the fourth photovoltaic component to be adjusted B2, and the second diode D2 is used to prevent the current from flowing back, that is, from the positive electrode of the fourth photovoltaic component to be adjusted B2 to the negative electrode of the third photovoltaic component to be adjusted B1. When the second switch device VD2 is in the on state, the third photovoltaic component to be adjusted B1 and the fourth photovoltaic component to be adjusted B2 are short-circuited. Due to the action of the second diode D2, the current cannot flow back, and the first photovoltaic component to be adjusted A1, the second photovoltaic component to be adjusted A2, the third photovoltaic component to be adjusted B1 and the fourth photovoltaic component to be adjusted B2 cannot form a loop, so they are disconnected from the first part 212 of the photovoltaic string 210, and the number of photovoltaic strings 210 in series is reduced.

[0101] Wherein, both the first switch device VD1 and the second switch device VD2 can be IGBTs, which are small in size, controllable, switchable, high in voltage resistance, highly integrated in driving circuits, and simple to control, and are preferred switch devices. The control end of the first switch device VD1 and the second switch device VD2 is the gate G, the first controlled end is the collector E, and the second controlled end is the emitter C.

[0102] Please continue to see Figure 2 In one embodiment, the photovoltaic string 210 series quantity adjustment device 100 further includes a signal input unit 150. The input end of the signal input unit 150 is connected to the output end of the control system 230, and the output end of the signal input unit 150 is connected to the third input end of the control unit 110. The signal input unit 150 is used to input fixed parameters output by the control system 230, such as a preset voltage signal Vdcmax, and output the preset voltage signal Vdcmax to the control unit 110.

[0103] See also Figure 3 , Figure 3 1 is a schematic block diagram of the overall structure of a photovoltaic string series quantity adjustment device 100 for multiple photovoltaic strings 211 to 21n provided in an embodiment of the present application. Figure 3 As shown, the photovoltaic string series quantity adjustment device 100 includes: a control unit 110, a temperature monitoring unit 120, a DC voltage acquisition unit 130, and a plurality of switch units 141-14n. The DC voltage acquisition unit 130 includes a plurality of input terminals and a plurality of output terminals, the control unit 110 includes a plurality of second input terminals and a plurality of output terminals, and there are a plurality of photovoltaic strings connected to the input terminal of the DC voltage acquisition unit 130, including photovoltaic strings 211-21n.

[0104] In one embodiment, the output end of the temperature monitoring unit 120 is connected to the first input end of the control unit 110, and the temperature monitoring unit 120 is used to monitor the ambient temperature of each photovoltaic string 211~21n under working conditions to obtain multiple ambient temperature signals T1~Tn. Each input end of the DC voltage acquisition unit 130 is connected to the DC output end [including the positive and negative terminals (BUS1+, BUS1-)~(BUSn+, BUSn-)] of the corresponding photovoltaic string 211~21n, and each output end of the DC voltage acquisition unit 130 is connected to the corresponding second input end of the control unit 110, and the DC voltage acquisition unit 130 is used to collect the output voltage signals VdcS1~VdcSn of each photovoltaic string 211~21n.

[0105] In one embodiment, each output terminal of the control unit 110 is connected to the control terminal of each switch unit 141-14n. The control unit 110 is used to generate control signals UK1-UKn based on the ambient temperature signals T1-Tn, the output voltage signals VdcS1-VdcSn and the preset voltage signal Vdcmax, and output the corresponding control signals UK1-UKn to the control terminals of each switch unit 141-14n. Each control signal UK1-UKn is used to control the corresponding switch unit 141-14n to be turned on or off.

[0106] In some embodiments, in each photovoltaic string 211-21n composed of N photovoltaic components connected in series, a switch unit is provided at least at one place. Each switch unit is connected in parallel to at least one photovoltaic component, and the control end of each switch unit is connected to the corresponding output end of the control unit 110. When each switch unit is in the on state, the photovoltaic component connected in parallel with it is short-circuited to reduce the number of series connections of the corresponding photovoltaic strings 211-21n. Among them, the photovoltaic components connected in parallel with each switch unit are adjusted for the corresponding number of strings.

[0107] In one embodiment, a photovoltaic string 211-21n composed of N photovoltaic components connected in series in positive and negative directions is provided with switch units 141-14n. Each switch unit 141, 142-14(n-1), 14n is connected in parallel to the corresponding photovoltaic components (A1 and A2), (B1 and B2)-(A1n and A2n), (B1n and B2n), and the control end of each switch unit 141, 142-14(n-1), 14n is connected to the corresponding output end of the control unit 110. When each switch unit 141, 142-14(n-1), 14n is in the on state, the corresponding photovoltaic components (A1, A2, B1 and B2)-(A1n, A2n, B1n and B2n) are short-circuited to reduce the number of series connections of the corresponding photovoltaic strings 211-21n. Among them, the photovoltaic components (A1, A2, B1 and B2) to (A1n, A2n, B1n and B2n) are photovoltaic components 21111 to 2111n for adjusting the number of strings.

[0108] It should be noted that the specific structure of the device 100 for adjusting the number of series-connected photovoltaic strings 210 of multiple photovoltaic strings is substantially the same as the specific structure of the device 100 for adjusting the number of series-connected photovoltaic strings 210 of one photovoltaic string, and will not be repeated here.

[0109] See also Figure 4 , Figure 4 is a schematic block diagram of a photovoltaic power generation system 200 including a photovoltaic string provided in an embodiment of the present application. Figure 4 As shown, the photovoltaic power generation system 200 includes: a photovoltaic string 210, an inverter 220, a control system 230, a box-type transformer AC device 240 and a photovoltaic string series quantity adjustment device 100 of a photovoltaic string 210.

[0110] In one embodiment, the DC input end (including positive and negative terminals VIN+, VIN-) of the photovoltaic string 210 is connected to the output end of the photovoltaic string 210 series quantity adjustment device 100, and the DC output end (including positive and negative terminals BUS+, BUS-) of the photovoltaic string 210 is connected to the power supply input end (including positive and negative terminals N+, N-) of the inverter 220 and the first input end of the photovoltaic string 210 series quantity adjustment device 100. The photovoltaic string 210 is used to provide an output voltage signal Vdc to the photovoltaic string 210 series quantity adjustment device 100 and output the DC power after adjusting the series quantity of the photovoltaic string 210 to the inverter 220.

[0111] In one embodiment, the output end of the inverter 220 is connected to the input end of the box-type transformer AC device 240, and the inverter 220 is used to invert the direct current output by the photovoltaic string 210 into alternating current, and output the alternating current to the box-type transformer AC device 240. Among them, the inverter can be a DC-AC converter. The input end of the box-type transformer AC device 240 is connected to the output end of the inverter 220, and the output end of the box-type transformer AC device 240 is connected to the input end of the power grid. The box-type transformer AC device 240 is used to collect and boost the alternating current output by the inverter 220, and output the boosted alternating current to the power grid.

[0112] In one embodiment, the output end of the control system 230 is connected to the second input end of the photovoltaic string 210 series connection quantity adjustment device 100, and the control system 230 is used to output a preset voltage signal Vdcmax to the photovoltaic string 210 series connection quantity adjustment device 100. The photovoltaic string 210 series connection quantity adjustment device 100 is used to adjust the number of photovoltaic strings 210 in series based on the ambient temperature signal T under the working conditions of the photovoltaic string 210, the output voltage signal Vdc provided by the photovoltaic string 210, and the preset voltage signal Vdcmax.

[0113] See also Figure 5 , Figure 5 2 is a schematic block diagram of a photovoltaic power generation system 200 including a plurality of photovoltaic strings 211 to 21n provided in an embodiment of the present application. Figure 5 As shown, the photovoltaic power generation system 200 includes: a plurality of photovoltaic strings 211 to 21n, an inverter 220, a control system 230, a box-type transformer AC device 240, and a photovoltaic string series quantity adjustment device 100 for a plurality of photovoltaic strings 211 to 21n. The photovoltaic string series quantity adjustment device 100 includes a plurality of first input terminals, a second input terminal, and a plurality of output terminals, and the inverter 220 includes a plurality of power supply input terminals [including positive and negative terminals (N1+, N1-) to (Nn+, Nn-)].

[0114] In one embodiment, the DC input end of each photovoltaic string 211-21n [including the positive and negative terminals (VIN1+, VIN1-)-(VINn+, VINn-)] is connected to the corresponding output end of the photovoltaic string series quantity adjustment device 100, and the DC output end of each photovoltaic string 211-21n [including the positive and negative terminals (BUS1+, BUS1-)-(BUSn+, BUSn-)] is connected to the corresponding power supply input end of the inverter 220 and the corresponding first input end of the photovoltaic string series quantity adjustment device 100. Each photovoltaic string 211-21n is used to provide the corresponding output voltage signal VdcS1-VdcSn to the photovoltaic string series quantity adjustment device 100 and output the corresponding DC power after adjusting the series quantity of the photovoltaic strings 211-21n to the inverter 220.

[0115] In one embodiment, the output end of the inverter 220 is connected to the input end of the box-type transformer AC device 240, and the inverter 220 is used to invert the DC power output by each photovoltaic string 211-21n into AC power, and output the AC power to the box-type transformer AC device 240. The output end of the box-type transformer AC device 240 is connected to the input end of the power grid, and the box-type transformer AC device 240 is used to collect and boost the AC power output by the inverter 220, and output the boosted AC power to the power grid.

[0116] In one embodiment, the output end of the control system 230 is connected to the second input end of the photovoltaic string series quantity adjustment device 100, and the control system 230 is used to output a preset voltage signal Vdcmax to the photovoltaic string series quantity adjustment device 100. The photovoltaic string series quantity adjustment device 100 is used to adjust the series quantity of each photovoltaic string 211-21n based on the ambient temperature signals T1-Tn under the working conditions of each photovoltaic string 211-21n, the output voltage signals VdcS1-VdcSn provided by each photovoltaic string 211-21n, and the preset voltage signal Vdcmax.

[0117] It should be noted that different product models of the inverter 220 have different numbers of MPPTs (Maximum Power Point Tracking), and the numbers of photovoltaic strings that can be connected to the inverter 220 are also different.

[0118] See also Figure 6 , Figure 6 1 is a schematic diagram of the steps of a method for adjusting the number of photovoltaic strings in series of a photovoltaic string 210 provided in an embodiment of the present application. The method is implemented based on a photovoltaic string 210 photovoltaic string series number adjustment device 100, combined with Figure 1 and Figure 6 , the method may include the following steps:

[0119] S601 , monitoring the ambient temperature of the photovoltaic string 210 under working conditions based on the temperature monitoring unit 120 to obtain an ambient temperature signal T.

[0120] In one embodiment, after the temperature monitoring unit 120 detects the ambient temperature signal T, it outputs the ambient temperature signal T to the control unit 110 .

[0121] S602 , collecting the output voltage signal Vdc of the photovoltaic string 210 based on the DC voltage collection unit 130 .

[0122] In one embodiment, after the DC voltage acquisition unit 130 acquires the output voltage signal Vdc, it provides the output voltage signal Vdc to the control unit 110 .

[0123] S603, based on the control unit, generates control signals UK1~UKn according to the ambient temperature signal T, the output voltage signal Vdc and the preset voltage signal Vdcmax, and outputs the corresponding control signals UK1~UKn to the control end of each switch unit, each control signal UK1~UKn is used to control the corresponding switch unit to be turned on or off.

[0124] In one embodiment, the control unit 110 generates control signals UK1 and UK2 according to the ambient temperature signal T, the output voltage signal Vdc and the preset voltage signal Vdcmax, and outputs the control signals UK1 and UK2 to the control ends of the first switch unit 142 and the second switch unit 144, respectively. The control signals UK1 and UK2 are respectively used to control the first switch unit 142 and the second switch unit 144 to be turned on or off.

[0125] S604, when each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of photovoltaic strings connected in series; wherein the photovoltaic components connected in parallel with each switch unit are adjusted to the corresponding number of strings.

[0126] In one embodiment, when the first switch unit 142 and the second switch unit 144 are in the on state, the photovoltaic components A1, A2, B1 and B2 are short-circuited to reduce the number of series-connected photovoltaic strings 210; wherein the photovoltaic components A1, A2, B1 and B2 are the photovoltaic components 214 for adjusting the number of strings.

[0127] Among them, Figure 2 As shown, the control unit 110 includes: a main control module 112, a PWM control module 114, a limit module 116 and a signal superposition module 118. The photovoltaic string series quantity adjustment device 100 includes: a first switch unit 142 and a second switch unit 144, the string quantity adjustment photovoltaic assembly includes adjacent first photovoltaic assembly A1 to be adjusted, second photovoltaic assembly A2 to be adjusted, third photovoltaic assembly B1 to be adjusted and fourth photovoltaic assembly B2 to be adjusted, the string quantity adjustment photovoltaic assembly 214 is the second part of the photovoltaic string 210, and the remaining photovoltaic assemblies are the first part of the photovoltaic string 210. When the first switch unit 142 and the second switch unit 144 are in the off state, the string quantity adjustment photovoltaic assembly 214 is connected to the first part 212 of the photovoltaic string 210. The photovoltaic string 210 series quantity adjustment device 100 also includes a signal input unit 150.

[0128] According to an embodiment of the present application, based on the control unit 110 generating a control signal U according to the ambient temperature signal T, the output voltage signal Vdc and the preset voltage signal Vdcmax, when each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of photovoltaic strings in series, and when each switch unit is in the off state, the photovoltaic component 214 for adjusting the number of strings is connected to the first part of the photovoltaic string 210, which may include the following steps:

[0129] It should be noted that under standard test conditions, the test temperature is 25°C and the STC (Standard Test Condition) irradiance is 1000W / m 2 , the number of series connections of the photovoltaic strings 210 is N0, at this time the first switch unit 142 and the second switch unit 144 are both in the off state, the first photovoltaic component A1 to be adjusted is connected with the second photovoltaic component A2 to be adjusted, the third photovoltaic component B1 to be adjusted is connected with the fourth photovoltaic component B2 to be adjusted, and the third photovoltaic component B1 to be adjusted and the fourth photovoltaic component B2 to be adjusted are simultaneously connected with the first part of the photovoltaic string 210.

[0130] In one embodiment, when the first ambient temperature t1 is less than the standard test temperature of 25°C: based on the main control module 112, the first output voltage Vdc1 is compared with the first preset voltage Vdc-max1 (the maximum DC voltage allowed by the inverter) input by the signal input unit 150 to obtain a first comparison result, which is the absolute value of the difference between the first output voltage Vdc1 and the first preset voltage Vdc-max1. The main control module 112 generates a first main control signal U01 based on the first comparison result, and at the same time generates a first limit signal based on the limit module 116 according to the first ambient temperature signal, and the first limit signal is a binary number 1. Based on the signal superposition module 118, the first main control signal U01 and the first limit signal are logically superimposed to generate a first modulation signal U11, and the amplitude of the first modulation signal U11 is 1. Based on the PWM control module 114, a first drive signal PWM1 (binary number 1) is generated according to the first modulation signal U11, and the first drive signal PWM1 is output to the control end of the first switch unit 142 and the control end of the second switch unit 144. Based on the PWM control module 114, the first switch unit 142 is driven to turn on according to the first drive signal PWM1 to short-circuit the first photovoltaic component A1 to be adjusted and the second photovoltaic component A2 to be adjusted, and the second switch unit 144 is driven to turn off according to the first drive signal PWM1 to simultaneously connect the third photovoltaic component B1 to be adjusted and the fourth photovoltaic component B2 to be adjusted to the first part of the photovoltaic string 210. At this time, the number of series connections of the photovoltaic string 210 is N1, and N1<N0.

[0131] In one embodiment, when the second ambient temperature t2 is less than the first ambient temperature t1: based on the control unit 110, a second control signal is generated according to the second output voltage Vdc2 and the first preset voltage Vdc-max1, and the second control signal is output to the control end of the first switch unit 142 and the control end of the second switch unit 144. Based on the control unit 110, the first switch unit 142 is controlled to be turned off according to the second control signal, and the second switch unit 144 is controlled to be turned on according to the second control signal, so as to short-circuit the third photovoltaic component B1 to be adjusted and the fourth photovoltaic component B2 to be adjusted. Wherein, when the third photovoltaic component B1 to be adjusted and the fourth photovoltaic component B2 to be adjusted are short-circuited, the first photovoltaic component A1 to be adjusted and the second photovoltaic component A2 to be adjusted are simultaneously disconnected from the first part of the photovoltaic string 210. At this time, the number of series connections of the photovoltaic string 210 is N2, and N2<N1<N0.

[0132] Specifically, when t2<t1: based on the main control module 112, the second output voltage Vdc2 is compared with the first preset voltage Vdc-max1 to obtain a second comparison result, which is the absolute value of the difference between the second output voltage Vdc2 and the first preset voltage Vdc-max1. The main control module 112 generates a second main control signal U02 based on the second comparison result, and at the same time generates a second limit signal based on the limit module 116 according to the second ambient temperature signal, and the second limit signal is a binary number 1. Based on the signal superposition module 118, the second main control signal U02 is logically superimposed with the first limit signal to generate a second modulation signal U12, and the amplitude of the second modulation signal U12 is 1. Based on the PWM control module 114, a second drive signal PWM2 (binary number 1) is generated according to the second modulation signal U12, and the second drive signal PWM2 is output to the control end of the first switch unit 142 and the control end of the second switch unit 144. Based on the control unit 110, the first switch unit 142 is driven to turn off according to the second drive signal PWM2, and the second switch unit 144 is driven to turn on according to the second drive signal PWM2, so as to short-circuit the third photovoltaic component B1 to be adjusted and the fourth photovoltaic component B2 to be adjusted. When the third photovoltaic component B1 to be adjusted and the fourth photovoltaic component B2 to be adjusted are short-circuited, the first photovoltaic component A1 to be adjusted and the second photovoltaic component A2 to be adjusted are simultaneously disconnected from the first part of the photovoltaic string 210. At this time, the number of series connections of the photovoltaic string 210 is N2, and N2<N1<N0.

[0133] According to an embodiment of the present application, based on the control unit 110 generating a control signal U according to the ambient temperature signal T, the output voltage signal Vdc and the preset voltage Vdc-max signal Vdcmax, the photovoltaic components connected in parallel with each switch unit are short-circuited when each switch unit is in the on state, and the photovoltaic components 214 for adjusting the number of strings are connected to the first part of the photovoltaic string 210 when each switch unit is in the off state, and the following steps may also be included:

[0134] In one embodiment, when the third ambient temperature t3 is greater than the second ambient temperature t2: the equivalent open circuit voltage Vdc' of the photovoltaic string 210 is reduced due to the open circuit voltage temperature coefficient Kv of the photovoltaic string 210. The third output voltage Vdc3 is compared with the second preset voltage Vdc-max2 based on the main control module 112 to obtain a third comparison result. If the third comparison result is that the third output voltage Vdc3 is less than the second preset voltage Vdc-max2 (the difference between the first preset voltage Vdc-max1 and twice the equivalent open-circuit voltage Vdc` of the photovoltaic string 210, that is, Vdc-max2=Vdc-max1-2×Vdc`, Vdc-max2 can also be understood as the minimum DC input voltage allowed by the inverter), the main control module 112 generates a third main control signal U03 based on the absolute value of the difference between the third output voltage Vdc3 and the second preset voltage Vdc-max2, and the limit module 116 generates a third limit signal based on the third ambient temperature signal, and the third limit signal is a binary number 1. The signal superposition module 118 performs a logical operation on the third main control signal U03 and the third limit signal to generate a third modulation signal U13, and the amplitude of the third modulation signal U13 is 1. The PWM control module 114 generates a third drive signal PWM3 (binary number 1) according to the third modulation signal U13, and outputs the third drive signal PWM3 to the control end of the first switch unit 142 and the control end of the second switch unit 144. The PWM control module 114 drives the first switch unit 142 to conduct according to the third drive signal PWM3 to short-circuit the first photovoltaic component A1 to be adjusted and the second photovoltaic component A2 to be adjusted, and drives the second switch unit 144 to turn off according to the third drive signal to connect the third photovoltaic component B1 to be adjusted and the fourth photovoltaic component B2 to be adjusted to the first part of the photovoltaic string 210. At this time, the number of series connections of the photovoltaic string 210 is N3, and N3=N1.

[0135] In one embodiment, when the fourth ambient temperature t4 is greater than or equal to the standard test temperature 25°C: the control unit 110 generates a fourth control signal according to the fourth output voltage Vdc4 and the second preset voltage Vdc-max2, and outputs the fourth control signal to the control end of the first switch unit 142 and the control end of the second switch unit 144. The control unit 110 controls the first switch unit 142 and the second switch unit 144 to be turned off according to the fourth control signal, so as to connect the first photovoltaic assembly A1 to be adjusted, the second photovoltaic assembly A2 to be adjusted, the third photovoltaic assembly B1 to be adjusted, and the fourth photovoltaic assembly B2 to be adjusted to the first part of the photovoltaic string 210. At this time, the number of series connections of the photovoltaic string 210 is N4, and N4=N0.

[0136] Specifically, when t4≥25°C: affected by the open-circuit voltage temperature coefficient Kv of the photovoltaic string 210, the equivalent open-circuit voltage Vdc` of the photovoltaic string 210 is reduced. Based on the main control module 112, the fourth output voltage Vdc4 is compared with the second preset voltage Vdc-max2 to obtain a fourth comparison result. If the fourth comparison result is that the fourth output voltage Vdc4 is less than the second preset voltage Vdc-max2, the fourth main control signal U04 is generated based on the absolute value of the difference between the fourth output voltage Vdc4 and the second preset voltage Vdc-max2 based on the main control module 112, and the fourth limit signal is generated based on the fourth ambient temperature signal based on the limit module 116, and the fourth limit signal is a binary number 0. Based on the signal superposition module 118, the fourth main control signal U04 and the fourth limit signal are logically superimposed to generate a fourth modulation signal U14, and the amplitude of the fourth modulation signal U14 is 0. The PWM control module 114 generates a fourth drive signal PWM4 (binary number 0) according to the fourth modulation signal U14, and outputs the fourth drive signal PWM4 to the control end of the first switch unit 142 and the control end of the second switch unit 144. The control unit 110 drives the first switch unit 142 and the second switch unit 144 to turn off according to the fourth drive signal PWM4, so as to connect the first photovoltaic component A1 to be adjusted, the second photovoltaic component A2 to be adjusted, the third photovoltaic component B1 to be adjusted, and the fourth photovoltaic component B2 to be adjusted to the first part of the photovoltaic string 210. At this time, the number of series connections of the photovoltaic string 210 is N4, and N4=N0.

[0137] See also Figure 7 , Figure 7 1 is a schematic diagram of the steps of a method for adjusting the number of photovoltaic strings connected in series of multiple photovoltaic strings 211 to 21n provided in an embodiment of the present application. The method is implemented based on a photovoltaic string connection number adjustment device 100 for multiple photovoltaic strings 211 to 21n, such as Figure 7 As shown, the method may include the following steps:

[0138] S701 , the temperature monitoring unit 120 monitors the ambient temperature of each photovoltaic string 211 ˜ 21 n under working conditions to obtain a plurality of ambient temperature signals T1 ˜Tn.

[0139] S702 , collecting output voltage signals VdcS1 -VdcSn of the photovoltaic strings 211 - 21 n based on the DC voltage collection unit 130 .

[0140] S703, based on the control unit 110, the control signals UK1~UKn are generated according to the ambient temperature signals T1~Tn, the output voltage signals VdcS1~VdcSn and the preset voltage signal Vdcmax, and the corresponding control signals UK1~UKn are output to the control end of each switch unit, and each control signal UK1~UKn is used to control the corresponding switch unit to be turned on or off.

[0141] S704, when each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of series-connected photovoltaic strings 211-21n corresponding thereto; wherein the photovoltaic components connected in parallel with each switch unit are adjusted for the corresponding number of strings.

[0142] It should be noted that the specific implementation process of the method for adjusting the number of photovoltaic strings connected in series for multiple photovoltaic strings 211 to 21 n is substantially the same as the specific implementation process of the method for adjusting the number of photovoltaic strings connected in series for one photovoltaic string 210 , and will not be repeated here.

[0143] The photovoltaic string series quantity adjustment device 100 and method provided in the embodiment of the present application can adjust the series quantity of a photovoltaic string 210, and can also adjust the series quantity of multiple photovoltaic strings 211~21n. When adjusting the series quantity of a photovoltaic string 210, the temperature monitoring unit 120 obtains the ambient temperature signal T by monitoring the ambient temperature under the working conditions of the photovoltaic string 210, and the DC voltage acquisition unit 130 acquires the output voltage signal Vdc of the photovoltaic string 210. The control unit 110 generates control signals UK1~UKn based on the ambient temperature signal T, the output voltage signal Vdc and the preset voltage signal Vdcmax, and controls the corresponding switch unit to be turned on or off based on the control signals UK1~UKn. Each switch unit adjusts the series quantity of the photovoltaic string 210 by short-circuiting the photovoltaic components connected in parallel with it. When adjusting the number of series connections of multiple photovoltaic strings 211~21n, the temperature monitoring unit 120 obtains multiple ambient temperature signals T1~Tn by monitoring the ambient temperature under the working conditions of each photovoltaic string 211~21n, and the DC voltage acquisition unit 130 acquires the output voltage signals VdcS1~VdcSn of each photovoltaic string 211~21n. The control unit 110 generates control signals UK1~UKn based on the ambient temperature signals T1~Tn, the output voltage signals VdcS1~VdcSn and the preset voltage signal Vdcmax, and controls the corresponding switch unit to be turned on or off based on each control signal UK1~UKn. Each switch unit adjusts the number of series connections of the corresponding photovoltaic strings 211~21n by connecting or disconnecting the photovoltaic components connected in parallel with it and the first part 212 of the corresponding photovoltaic string 211~21n.

[0144] The solution of the embodiment of the present application sets a switch unit in at least one place in each photovoltaic string 211~21n, and each switch unit can be used to automatically and flexibly adjust the number of series connections of the corresponding photovoltaic strings 211~21n under different ambient temperatures, without being restricted by the minimum temperature under the working conditions of the photovoltaic strings 211~21n. Under the premise of meeting the maximum DC input voltage allowed by the inverter, the maximum number of series connections can be guaranteed, the number of inverters and photovoltaic brackets is reduced, and the floor space of the photovoltaic plant is also reduced, so that the investment in the photovoltaic project is reduced. In addition, the power generation of the photovoltaic power generation system 200 is increased, the economic performance of the photovoltaic project is improved, and it has strong ease of use and practicality.

[0145] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0146] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0147] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A photovoltaic string series quantity adjustment device, characterized in that: The device comprises: a control unit, a temperature monitoring unit, a DC voltage acquisition unit and a switch unit; The output end of the temperature monitoring unit is connected to the first input end of the control unit, and the temperature monitoring unit is used to monitor the ambient temperature under the working conditions of the photovoltaic string to obtain an ambient temperature signal; The input end of the DC voltage acquisition unit is connected to the DC output end of the photovoltaic string, the output end of the DC voltage acquisition unit is connected to the second input end of the control unit, and the DC voltage acquisition unit is used to collect the output voltage signal of the photovoltaic string; In a photovoltaic string composed of N photovoltaic modules connected in series, the switch unit is provided at least at one location, each switch unit is connected in parallel to at least one photovoltaic module, the control end of the switch unit is connected to the output end of the control unit, and when the switch unit is in the on state, the photovoltaic module connected in parallel therewith is short-circuited to reduce the number of photovoltaic strings connected in series; Wherein, the photovoltaic assembly connected in parallel with the switch unit is a string quantity adjustment photovoltaic assembly.

2. The photovoltaic string series quantity adjustment device according to claim 1, characterized in that: The string quantity adjustment photovoltaic assembly includes a first photovoltaic assembly to be adjusted, a second photovoltaic assembly to be adjusted, a third photovoltaic assembly to be adjusted, and a fourth photovoltaic assembly to be adjusted that are adjacent to each other; The photovoltaic components for adjusting the number of strings are the second part of the photovoltaic strings, and the remaining photovoltaic components are the first part of the photovoltaic strings. When the switch unit is in the off state, the photovoltaic components to be adjusted are connected to the first part of the photovoltaic strings.

3. The photovoltaic string series quantity adjustment device according to claim 1, characterized in that: The control unit comprises: a main control module and a PWM control module; The first input end of the main control module is connected to the output end of the temperature monitoring unit, the second input end of the main control module is connected to the output end of the DC voltage acquisition unit, the output end of the main control module is connected to the input end of the PWM control module, and the output end of the PWM control module is connected to the control end of the switch unit.

4. The photovoltaic string series quantity adjustment device according to claim 3, characterized in that: The control unit also includes: a limit module and a signal superposition module; The input end of the limit module is connected to the output end of the temperature monitoring unit, the output end of the limit module is connected to the first input end of the signal superposition module, the second input end of the signal superposition module is connected to the output end of the main control module, and the output end of the signal superposition module is connected to the input end of the PWM control module.

5. The photovoltaic string series quantity adjustment device according to claim 2, characterized in that: The device comprises: a first switch unit and a second switch unit; The control end of the first switch unit is connected to the first output end of the control unit, the first controlled end of the first switch unit is connected to the negative electrode of the first photovoltaic component to be adjusted, and the second controlled end of the first switch unit is connected to the positive electrode of the second photovoltaic component to be adjusted. The first switch unit is used to short-circuit the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted when it is in the on state, or connect the first photovoltaic component to be adjusted with the second photovoltaic component to be adjusted, and connect the third photovoltaic component to be adjusted with the fourth photovoltaic component to be adjusted when it is in the off state; The control end of the second switch unit is connected to the second output end of the control unit, the first controlled end of the second switch unit is connected to the negative electrode of the third photovoltaic component to be adjusted, and the second controlled end of the second switch unit is connected to the positive electrode of the fourth photovoltaic component to be adjusted. The second switch unit is used to short-circuit the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted when it is in the on state, or to connect the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted to the first part of the photovoltaic string at the same time when it is in the off state; Wherein, when the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted are short-circuited, the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted are simultaneously disconnected from the first part of the photovoltaic string.

6. The photovoltaic string series quantity adjustment device according to claim 5, characterized in that: The first switch unit includes: a first switch device and a first diode, and the second switch unit includes: a second switch device and a second diode; The control end of the first switch device is connected to the first output end of the control unit, the first controlled end of the first switch device is connected to the negative electrode of the first photovoltaic component to be regulated, the second controlled end of the first switch device is connected to the anode of the first diode, the cathode of the first diode is connected to the positive electrode of the second photovoltaic component to be regulated, and the first diode is used to prevent current from flowing from the positive electrode of the second photovoltaic component to be regulated to the negative electrode of the first photovoltaic component to be regulated; The control end of the second switching device is connected to the second output end of the control unit, the first controlled end of the second switching device is connected to the negative electrode of the third photovoltaic component to be regulated, the second controlled end of the second switching device is connected to the anode of the second diode, the cathode of the second diode is connected to the positive electrode of the fourth photovoltaic component to be regulated, and the second diode is used to prevent current from flowing from the positive electrode of the fourth photovoltaic component to be regulated to the negative electrode of the third photovoltaic component to be regulated.

7. The photovoltaic string series quantity adjustment device according to claim 1, characterized in that: The device also includes a signal input unit; The input end of the signal input unit is connected to the output end of the control system, and the output end of the signal input unit is connected to the third input end of the control unit. The signal input unit is used to input a preset voltage signal output by the control system and output the preset voltage signal to the control unit.

8. The photovoltaic string series quantity adjustment device according to any one of claims 1 to 7, characterized in that: The device comprises: a control unit, a temperature monitoring unit, a DC voltage acquisition unit and a plurality of switch units; wherein the DC voltage acquisition unit comprises a plurality of input terminals and a plurality of output terminals, the control unit comprises a plurality of second input terminals and a plurality of output terminals, and a plurality of photovoltaic strings are connected to the input terminal of the DC voltage acquisition unit; The output end of the temperature monitoring unit is connected to the first input end of the control unit, and the temperature monitoring unit is used to monitor the ambient temperature under the working conditions of each photovoltaic string to obtain multiple ambient temperature signals; Each input end of the DC voltage collection unit is connected to the DC output end of the corresponding photovoltaic string, each output end of the DC voltage collection unit is connected to the second input end corresponding to the control unit, and the DC voltage collection unit is used to collect the output voltage signal of each photovoltaic string; In each photovoltaic string composed of N photovoltaic modules connected in series, the switch unit is provided at least at one place, each switch unit is connected in parallel to at least one photovoltaic module, the control end of each switch unit is connected to the output end corresponding to the control unit, and when each switch unit is in the on state, the photovoltaic module connected in parallel therewith is short-circuited to reduce the number of series connections of the corresponding photovoltaic string; The photovoltaic components connected in parallel with each switch unit are adjusted for the corresponding number of strings.

9. A photovoltaic power generation system, characterized in that: The system comprises: a photovoltaic string, an inverter, a box-type transformer AC device, a control system, and a photovoltaic string series quantity adjustment device according to any one of claims 1 to 7; The DC input end of the photovoltaic string is connected to the output end of the photovoltaic string series quantity adjustment device, and the DC output end of the photovoltaic string is connected to the power supply input end of the inverter and the first input end of the photovoltaic string series quantity adjustment device. The photovoltaic string is used to provide an output voltage signal to the photovoltaic string series quantity adjustment device and output direct current after adjusting the number of photovoltaic strings in series to the inverter; The output end of the inverter is connected to the input end of the box-type transformer AC device. The inverter is used to invert the DC power output by the photovoltaic string into AC power and output the AC power to the box-type transformer AC device. The output end of the box-type transformer AC device is connected to the input end of the power grid. The box-type transformer AC device is used to collect and boost the AC power output by the inverter, and output the boosted AC power to the power grid; The output end of the control system is connected to the second input end of the photovoltaic string series quantity adjustment device, and the control system is used to output a preset voltage signal to the photovoltaic string series quantity adjustment device; The photovoltaic string series quantity adjustment device is used to adjust the number of photovoltaic strings in series based on the ambient temperature signal under the working conditions of the photovoltaic strings, the output voltage signal provided by the photovoltaic strings and the preset voltage signal.

10. The photovoltaic power generation system according to claim 9, characterized in that: The system comprises: a plurality of photovoltaic strings, an inverter, a box-type transformer AC device, a control system and the photovoltaic string series quantity adjustment device according to claim 8; wherein the photovoltaic string series quantity adjustment device comprises a plurality of first input terminals, a second input terminal and a plurality of output terminals, and the inverter comprises a plurality of power supply input terminals; The DC input end of each photovoltaic string is connected to the corresponding output end of the photovoltaic string series quantity adjustment device, and the DC output end of each photovoltaic string is connected to the corresponding power supply input end of the inverter and the corresponding first input end of the photovoltaic string series quantity adjustment device. Each photovoltaic string is used to provide a corresponding output voltage to the photovoltaic string series quantity adjustment device and output a corresponding DC power after adjusting the number of photovoltaic strings in series to the inverter; The output end of the inverter is connected to the input end of the box-type transformer AC device. The inverter is used to invert the DC power output by each photovoltaic string into AC power and output the AC power to the box-type transformer AC device. The output end of the box-type transformer AC device is connected to the input end of the power grid. The box-type transformer AC device is used to collect and boost the AC power output by the inverter, and output the boosted AC power to the power grid; The output end of the control system is connected to the second input end of the photovoltaic string series quantity adjustment device, and the control system is used to output a preset voltage signal to the photovoltaic string series quantity adjustment device; The photovoltaic string series quantity adjustment device is used to adjust the series quantity of each photovoltaic string based on the ambient temperature signal under the working conditions of each photovoltaic string, the output voltage signal provided by each photovoltaic string and the preset voltage signal.

11. A method for adjusting the number of photovoltaic strings in series, characterized in that: The photovoltaic string series quantity adjustment device according to any one of claims 1 to 7 is implemented, and the method comprises: Based on the temperature monitoring unit, the ambient temperature under the working condition of the photovoltaic string is monitored to obtain an ambient temperature signal; The output voltage signal of the photovoltaic string is collected based on the DC voltage collection unit; A control unit generates a control signal according to the ambient temperature signal, the output voltage signal and the preset voltage signal, and outputs a corresponding control signal to a control end of each switch unit, each control signal being used to control the corresponding switch unit to be turned on or off; When each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of photovoltaic strings connected in series; wherein the photovoltaic components connected in parallel with each switch unit are adjusted to the corresponding number of strings.

12. The method for adjusting the number of photovoltaic strings in series according to claim 11, characterized in that: The control unit includes: a main control module, a PWM control module, a limit module and a signal superposition module, the device includes: a first switch unit and a second switch unit; the string quantity adjustment photovoltaic assembly includes adjacent first photovoltaic assemblies to be adjusted, second photovoltaic assemblies to be adjusted, third photovoltaic assemblies to be adjusted and fourth photovoltaic assemblies to be adjusted, the string quantity adjustment photovoltaic assembly is the second part of the photovoltaic string, and the remaining photovoltaic assemblies are the first part of the photovoltaic string, when each switch unit is in the off state, the string quantity adjustment photovoltaic assembly is connected to the first part of the photovoltaic string; the device also includes a signal input unit; based on the control unit generating a control signal according to the ambient temperature signal, the output voltage signal and the preset voltage signal, when each switch unit is in the on state, the photovoltaic assembly connected in parallel with it is short-circuited, and when each switch unit is in the off state, the string quantity adjustment photovoltaic assembly is connected to the first part of the photovoltaic string, including: When the first ambient temperature is lower than the standard test temperature: The main control module compares the first output voltage with the first preset voltage input by the signal input unit to obtain a first comparison result, and generates a first main control signal based on the first comparison result, and generates a first limit signal based on the limit module according to the first ambient temperature signal; Based on the signal superposition module, the first main control signal and the first limit signal are logically superimposed to generate a first modulation signal; Generate a first drive signal based on the PWM control module according to the first modulation signal, and output the first drive signal to the control end of the first switch unit and the control end of the second switch unit; Based on the PWM control module, the first switch unit is driven to turn on according to the first drive signal to short-circuit the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted, and the second switch unit is driven to turn off according to the first drive signal to connect the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted to the first part of the photovoltaic string at the same time; When the second ambient temperature is lower than the first ambient temperature: Based on the control unit generating a second control signal according to the second output voltage and the first preset voltage, and outputting the second control signal to the control end of the first switch unit and the control end of the second switch unit; Based on the control unit controlling the first switch unit to turn off according to the second control signal, and controlling the second switch unit to turn on according to the second control signal, so as to short-circuit the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted; Wherein, when the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted are short-circuited, the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted are simultaneously disconnected from the first part of the photovoltaic string.

13. The method for adjusting the number of photovoltaic strings in series according to claim 12, characterized in that: Based on the control unit generating a control signal according to the ambient temperature signal, the output voltage signal and the preset voltage signal, when each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited, and when each switch unit is in the off state, the photovoltaic components for adjusting the number of strings are connected to the first part of the photovoltaic strings, further comprising: When the third ambient temperature is greater than the second ambient temperature: Comparing the third output voltage with the second preset voltage based on the main control module to obtain a third comparison result; If the third comparison result is that the third output voltage is less than the second preset voltage, the main control module generates a third main control signal according to the absolute value of the difference between the third output voltage and the second preset voltage, and the limit module generates a third limit signal according to the third ambient temperature signal; wherein the second preset voltage is the difference between the first preset voltage and twice the equivalent open-circuit voltage of the photovoltaic string; Based on the signal superposition module, the third main control signal and the third limit signal are logically superimposed to generate a third modulation signal; Generate a third driving signal based on the PWM control module according to the third modulation signal, and output the third driving signal to the control end of the first switch unit and the control end of the second switch unit; Based on the PWM control module, the first switch unit is driven to turn on according to the third drive signal to short-circuit the first photovoltaic component to be adjusted and the second photovoltaic component to be adjusted, and the second switch unit is driven to turn off according to the third drive signal to connect the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted to the first part of the photovoltaic string at the same time; When the fourth ambient temperature is greater than or equal to the standard test temperature: generating a fourth control signal based on the control unit according to the fourth output voltage and the preset voltage, and outputting the fourth control signal to the control end of the first switch unit and the control end of the second switch unit; Based on the control unit controlling the first switch unit and the second switch unit to be turned off according to the fourth control signal, the first photovoltaic component to be adjusted, the second photovoltaic component to be adjusted, the third photovoltaic component to be adjusted and the fourth photovoltaic component to be adjusted are simultaneously connected to the first part of the photovoltaic string.

14. The method for adjusting the number of photovoltaic strings connected in series according to any one of claims 11 to 13, characterized in that: Based on the photovoltaic string series quantity adjustment device according to claim 8, the method comprises: Based on the temperature monitoring unit being used to monitor the ambient temperature under the working conditions of each photovoltaic string, a plurality of ambient temperature signals are obtained; Based on the DC voltage collection unit, the output voltage signal of each photovoltaic string is collected; A control unit generates a control signal according to the ambient temperature signal, the output voltage signal and the preset voltage signal, and outputs a corresponding control signal to a control end of each switch unit, each control signal being used to control the corresponding switch unit to be turned on or off; The control end of each switch unit is connected to the output end corresponding to the control unit. When each switch unit is in the on state, the photovoltaic components connected in parallel therewith are short-circuited to reduce the number of series connections of the corresponding photovoltaic strings; wherein the photovoltaic components connected in parallel to each switch unit are adjusted for the corresponding number of strings.

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