Photovoltaic i-v curve testing system, testing method and photovoltaic device

Abstract

The application is suitable for the photovoltaic technical field, and provides a photovoltaic I-V curve testing system, a testing method and photovoltaic equipment.The photovoltaic I-V curve testing system comprises a photovoltaic module, a current collection box connected with the photovoltaic module and used for current collection of multiple photovoltaic module strings, a current collection switch arranged on each photovoltaic module string, an inverter connected with the current collection box, a detection unit and a control unit.The current collection switches on the multiple photovoltaic module strings are controlled to be closed in sequence and the output power of the inverter is adjusted when the inverter is in a grid-connected state;the current and voltage data of each photovoltaic module string in the output power variation range of the inverter are acquired;and the photovoltaic I-V curve under the grid-connected state of the inverter is obtained.Compared with the existing centralized inverter, the working state of the photovoltaic module can be accurately monitored and fine management can be performed through the testing system, and the photovoltaic module string with a fault can be quickly and accurately positioned.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic technology, and in particular relates to a photovoltaic IV curve testing system, a testing method and photovoltaic equipment. Background Art

[0002] With the continuous development of the photovoltaic industry, inverter power levels are increasing, and the cost of generating electricity per watt is further decreasing. PV owners have higher requirements for the power output and power generation costs of their PV systems. Research has shown that PV module failures in PV systems have a significant impact on the system's power generation. Therefore, accurately diagnosing PV module current mismatch faults has become a research focus in the photovoltaic industry today.

[0003] Using the PV I / V curve to determine the operating status of a PV system is a widely used method. Currently, PV systems must only connect to the grid when the PV string voltage reaches the minimum startup voltage. For string-type and distributed inverters, the upstream DC-DC module can monitor the current of each PV string and obtain a portion of the I / V curve to determine if a PV string is faulty. However, for single-stage inverter systems, such as centralized inverters, it is difficult to obtain the I / V curve for each branch string, making it difficult to accurately locate the faulty PV string. Summary of the Invention

[0004] An embodiment of the present invention provides a photovoltaic IV curve testing system, which aims to solve the problem that existing centralized inverters cannot accurately locate photovoltaic string faults.

[0005] An embodiment of the present invention is implemented as follows: a photovoltaic IV curve testing system is provided, which includes: a photovoltaic module, consisting of a plurality of photovoltaic strings; a junction box, connected to the photovoltaic module, for converging the plurality of photovoltaic strings, and a plurality of photovoltaic strings are each provided with a junction switch; an inverter, connected to the junction box; a detection unit, disposed in the junction box, connected to each photovoltaic string, for detecting the current and voltage of each photovoltaic string; a control unit, the control unit being connected to the junction box, the inverter, the detection unit and the plurality of junction switches, the control unit being configured to send control signals to the plurality of junction switches and to send adjustment signals for adjusting the output power to the inverter; receiving current and voltage data of each photovoltaic string when the output power of the inverter changes; and obtaining a photovoltaic IV curve based on the current and voltage data of each photovoltaic string; the plurality of junction switches being closed in sequence according to the received control signals; the inverter being configured to receive the adjustment signal sent by the control unit and adjust the output power of the inverter according to the adjustment signal.

[0006] Furthermore, it also includes a transformer connected to the inverter, the low-voltage side of the transformer is connected to the inverter; the inverter is internally provided with a grid-connected switch connected to the low-voltage side of the transformer.

[0007] Furthermore, it also includes a power grid connected to the transformer, the high-voltage side of the transformer is connected to the power grid; the power grid is connected to the control unit.

[0008] Furthermore, the inverter includes an inverter bridge, control logic and a filter circuit. The control logic includes a control module, which is connected to the control unit and is used to receive an adjustment signal from the control unit and control the inverter to adjust the output power.

[0009] Furthermore, the control unit is arranged on the inverter side, or on the grid side.

[0010] Furthermore, the bus switch is a mechanical switch or an electronic switch.

[0011] Furthermore, the inverter is of centralized, distributed or string type.

[0012] An embodiment of the present invention further provides a photovoltaic IV curve testing method, which includes the following steps:

[0013] When the inverter is in grid-connected state, the bus switches on multiple photovoltaic strings are controlled to close in sequence;

[0014] Adjust the output power of the inverter and obtain the current and voltage data of each photovoltaic string within the inverter output power variation range;

[0015] The photovoltaic IV curve is obtained based on the current and voltage data of each photovoltaic string.

[0016] Furthermore, after the step of obtaining a photovoltaic curve based on the voltage and current of each photovoltaic string, the method further includes: analyzing the photovoltaic curve to determine whether the photovoltaic component has a fault.

[0017] An embodiment of the present invention further provides a photovoltaic device, comprising the above-mentioned photovoltaic IV curve testing system and a processor, wherein the processor can run the above-mentioned photovoltaic IV curve testing method.

[0018] The photovoltaic IV curve testing system of the embodiment of the present invention includes: a photovoltaic module, which is composed of a plurality of photovoltaic strings; a junction box, which is connected to the photovoltaic module and is used to merge the plurality of photovoltaic strings, and the plurality of photovoltaic strings are each provided with a junction switch; an inverter, which is connected to the junction box; a detection unit, which is arranged in the junction box and is connected to each photovoltaic string, and is used to detect the current and voltage of each photovoltaic string; a control unit, which is connected to the junction box, the inverter, the detection unit and the plurality of junction switches, and is used to send control signals to the plurality of junction switches and send adjustment signals for adjusting the output power to the inverter; receiving current and voltage data of each photovoltaic string within the output power variation range of the inverter; and obtaining a photovoltaic IV curve based on the current and voltage data of each photovoltaic string; the plurality of junction switches are closed in sequence according to the received control signals; the inverter is used to receive the adjustment signal sent by the control unit and adjust the output power of the inverter according to the adjustment signal. The test system of the present invention controls the bus switches on multiple photovoltaic strings to close sequentially and adjust the inverter's output power when the inverter is in a grid-connected state. It then obtains current and voltage data for each photovoltaic string within the inverter's output power variation range. This generates a photovoltaic IV curve in the grid-connected state, which can be used to accurately determine whether a photovoltaic module has a fault or current mismatch. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 2 is a schematic structural diagram of a photovoltaic IV curve test system according to an embodiment of the present invention;

[0020] Figure 2 is a schematic diagram of a photovoltaic IV curve of a photovoltaic string according to an embodiment of the present invention;

[0021] Figure 3 Schematic diagram of photovoltaic IV curves of multiple photovoltaic strings according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] In the present invention, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," "fixed," and the like should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances. The term "and / or" as used herein includes any and all combinations of one or more of the relevant listed items.

[0024] The present invention provides a photovoltaic IV curve testing system. This system sequentially closes the bus switches on multiple photovoltaic strings while the inverter is connected to the grid, adjusting the inverter's output power. Current and voltage data for each photovoltaic string within the inverter's output power range are obtained. This generates a photovoltaic IV curve for the inverter when connected to the grid. This IV curve accurately determines whether the photovoltaic module is experiencing faults or current mismatches. Compared to existing centralized inverters, this testing system enables precise monitoring of the operating status of photovoltaic modules and enables refined management.

[0025] Example 1

[0026] like Figure 1 As shown, this embodiment provides a photovoltaic IV curve testing system, which includes: a photovoltaic module, consisting of a plurality of photovoltaic strings; a junction box, connected to the photovoltaic module, for converging the plurality of photovoltaic strings, and a junction switch is provided on each of the plurality of photovoltaic strings; an inverter, connected to the junction box; a detection unit, provided in the junction box, connected to each photovoltaic string, for detecting the current and voltage of each photovoltaic string; a control unit, connected to the junction box, the inverter, the detection unit and the plurality of junction switches, for sending control signals to the plurality of junction switches and sending adjustment signals for adjusting the output power to the inverter; receiving current and voltage data of each photovoltaic string within the output power variation range of the inverter; and obtaining a photovoltaic IV curve based on the current and voltage data of each photovoltaic string; the plurality of junction switches are closed in sequence according to the received control signals; the inverter is used to receive the adjustment signal sent by the control unit and adjust the output power of the inverter according to the adjustment signal.

[0027] In this embodiment, the detection unit is a current sensor and a voltage sensor, which are connected to each photovoltaic string and are used to measure the voltage and current of each photovoltaic string.

[0028] During the photovoltaic power generation process, the inverter is in the grid-connected state only when the voltage of the photovoltaic modules reaches the minimum starting voltage of the inverter.

[0029] Reference Figure 2 During the test, when the inverter reaches the minimum starting voltage and is in the grid-connected state, Figure 2 In the figure, Von is the minimum starting voltage for the inverter to be connected to the grid. Close the bus switches of the PV strings in sequence. When the bus switch of the first PV string is closed, the bus switches of other PV strings are in the disconnected state. At this time, adjust the output power of the inverter to further adjust the voltage and current of the PV string. The greater the output power, the smaller the voltage of the PV string, and the greater the current of the PV string. Through this process, all IV curves are scanned. The greater the voltage of the PV string, the smaller the current of the PV string. By adjusting the range of output power, the current and voltage values ​​of multiple PV strings can be obtained, from which the photovoltaic IV curve of the PV string can be obtained, such as Figure 2 The solid line portion in is shown. The bus switches of the other PV strings are closed sequentially, and the inverter output power is then adjusted as described above to further determine the voltage and current of each PV string within the regulated power range, thereby obtaining the photovoltaic IV curve for each PV string. The inverter's output power variation range can be adjusted according to a preset rate of change. The output power can be adjusted from low to high at a certain rate of increase. Alternatively, the output power can be adjusted from high to low at a preset rate of decrease. The adjustment rate can be set according to user requirements and is not specifically limited in this embodiment.

[0030] Furthermore, the bus switch is a mechanical switch or an electronic switch.

[0031] In this embodiment, the bus switch is a controllable electronic switch, which is connected to the control unit and is used to receive a control signal from the control unit. According to the control signal, when the inverter is in a grid-connected state, the bus switches are controlled to close in sequence to facilitate obtaining the voltage and current data of each photovoltaic string.

[0032] Furthermore, the test system includes a transformer T1 connected to the inverter, with the low-voltage side of transformer T1 connected to the inverter. In this embodiment, a grid-connected switch S1 is provided within the inverter, connected to the high-voltage side of transformer T1, and is configured to close when the inverter grid-connected voltage is reached, thereby placing the inverter in a grid-connected state.

[0033] Furthermore, the test system also includes a power grid connected to the transformer T1 , and the low-voltage side of the transformer T1 is connected to the power grid.

[0034] In this embodiment, the controller on the grid side is connected to the control unit. The controller obtains the photovoltaic IV curve obtained by the control unit, and monitors the operating status of the photovoltaic module according to the photovoltaic IV curve, and further determines whether there is an abnormality in the photovoltaic module or whether there is a current mismatch.

[0035] Furthermore, the inverter includes an inverter bridge, control logic and a filter circuit. The control logic includes a control module, and the control module is connected to the control unit.

[0036] In this embodiment, the control unit is located on the inverter side and, during testing, sends a regulation signal to the control module, which then adjusts the inverter's output power based on the regulation signal. The control unit receives the voltage and current of the PV strings within the output power regulation range. The detection unit directly transmits the detection data to the control unit.

[0037] In other embodiments, the control unit can be integrated into the control module of the inverter. During testing, when the inverter is in a grid-connected state, the control module directly sends a control signal to the bus switch to close the bus switches of each photovoltaic string in sequence; the control module adjusts the inverter output power according to a preset rate, and receives the voltage and current of the photovoltaic string detected by the detection unit, and obtains the photovoltaic IV curve of the photovoltaic string based on the obtained voltage and current.

[0038] Furthermore, the control unit and the detection unit are connected via an RS485 communication interface or via an optical fiber.

[0039] In this embodiment, the control unit and the detection unit are connected via an RS485 communication interface located on the combiner box and the inverter. In other embodiments, they may be connected via optical fiber, which is not specifically limited in this embodiment.

[0040] In another embodiment, the control unit can be set on the grid side, and the detection unit is connected to the controller on the grid side to transmit the detection data to the controller on the grid side. Specifically, the control unit can be set on the grid side, and the junction box and the inverter are both connected to the grid side. The test signal is sent through the control unit on the grid side, and when the inverter is in the grid-connected state, the control signal is sent to multiple junction switches, and the junction switches of each photovoltaic string are controlled to close in sequence. The adjustment signal is also sent to the control module of the inverter, and the control module of the inverter adjusts the output power of the inverter according to the adjustment signal. The controller on the grid side directly obtains the voltage and current data of each photovoltaic string under the change of the inverter output power, thereby obtaining the photovoltaic IV curves of multiple photovoltaic strings when the inverter is in the grid-connected state.

[0041] like Figure 3 It can be seen that the solid line parts of the curves a, b, c, and d in the figure are the measured photovoltaic IV curves of the four photovoltaic strings. In actual use, the photovoltaic IV curve is affected by the opening voltage, irradiance, temperature, temperature, or actual internal damage. For example Figure 3 Curves a and b in the figure represent normal operation, each with a single knee bend. Curve c, however, has multiple knee bends, indicating that curve c is abnormal. This indicates that the PV string corresponding to curve c is abnormal.

[0042] Generally, slight deviations in the open-circuit voltage and short-circuit current of a PV module are affected by factors such as irradiance and temperature. However, excessively low open-circuit voltage and short-circuit current, as seen in the D curve, or the C curve with multiple knee bends, indicate a PV module problem. Therefore, analyzing the PV IV curve can help diagnose PV string anomalies and their causes.

[0043] Furthermore, the voltage of the photovoltaic module includes photovoltaic systems of various voltage levels, for example: photovoltaic systems applicable to 1000V, 1500V, 2000V, 3000V and higher voltage levels.

[0044] The photovoltaic IV test system of this embodiment is suitable for photovoltaic modules of large, medium and small voltage levels, and can test the photovoltaic IV curves of photovoltaic modules of various voltage levels. Therefore, the operating status of photovoltaic modules of various voltage levels can be monitored and finely managed.

[0045] The photovoltaic IV curve testing system of this embodiment sequentially closes the bus switches on multiple photovoltaic strings and adjusts the inverter's output power when the inverter is connected to the grid. It then acquires current and voltage data for each photovoltaic string within the inverter's output power range. This generates a photovoltaic IV curve for the inverter when connected to the grid. This IV curve accurately determines whether the photovoltaic modules are experiencing faults or current mismatches. Compared to existing centralized inverters, this testing system enables precise monitoring of the operating status of photovoltaic modules and enables refined management.

[0046] Example 2

[0047] Based on the above embodiment 1, this embodiment provides a photovoltaic IV curve testing method, which includes the following steps:

[0048] When the inverter is in grid-connected state, the bus switches on multiple photovoltaic strings are controlled to close in sequence;

[0049] Adjust the output power of the inverter and obtain the current and voltage data of each photovoltaic string within the inverter output power variation range;

[0050] The photovoltaic IV curve is obtained based on the current and voltage data of each photovoltaic string.

[0051] In this embodiment, each photovoltaic string is provided with a current and voltage detection device for measuring the voltage and current of each photovoltaic string.

[0052] During the photovoltaic power generation process, the inverter is in the grid-connected state only when the voltage of the photovoltaic modules reaches the minimum starting voltage of the inverter.

[0053] Reference Figure 2 During the test, when the inverter reaches the minimum starting voltage and is grid-connected, the busbars of the PV strings are closed sequentially. When the busbar of the first PV string is closed, the busbars of the other PV strings are all open. At this point, the inverter's output power is adjusted to further regulate the voltage and current of the PV strings. A higher output power results in a lower voltage and a higher current. A lower output power results in a higher voltage and, similarly, a lower current. By adjusting the output power range, the current and voltage values ​​of multiple PV strings can be obtained, from which the PV IV curve for each PV string can be derived. The busbars of the other PV strings are closed sequentially, and the inverter output power is then adjusted as described above to further determine the voltage and current of each PV string within the adjustable power range, thereby obtaining the PV IV curve for each PV string. The inverter's output power range can be adjusted according to a preset rate of change, allowing output power to be adjusted from low to high at a specific rate of increase. Alternatively, the output power can be adjusted from high to low according to a preset decreasing rate. The adjustment rate can be set according to user requirements and is not specifically limited in this embodiment.

[0054] Furthermore, after the step of obtaining a photovoltaic curve according to the voltage and current of each photovoltaic string, the following steps are further included:

[0055] Analyze the photovoltaic curve to determine whether there is a fault in the photovoltaic module.

[0056] In this embodiment, the photovoltaic IV curve is affected by the opening voltage, irradiance, temperature, temperature or actual internal damage during actual application. Figure 3 Curves a and b in the figure represent normal operation, each with a single knee bend. Curve c, however, has multiple knee bends, indicating that curve c is abnormal. This indicates that the PV string corresponding to curve c is abnormal.

[0057] Generally, slight deviations in the open-circuit voltage and short-circuit current of a PV module are affected by factors such as irradiance and temperature. However, excessively low open-circuit voltage and short-circuit current, as seen in the D curve, or the C curve with multiple knee bends, indicate a PV module problem. Therefore, analyzing the PV IV curve can help diagnose PV string anomalies and their causes.

[0058] Furthermore, after the step of obtaining the photovoltaic IV curve according to the voltage and current of each photovoltaic string, the method further includes:

[0059] After the test is completed, multiple busbar switches are controlled to be in a closed state to enable the photovoltaic system to operate normally.

[0060] In this embodiment, after the test is completed, if the working status of the photovoltaic components is normal, the multiple bus switches are closed to enable the photovoltaic system to operate normally.

[0061] If any abnormality is found after analysis, the problematic PV strings need to be inspected or replaced.

[0062] The photovoltaic IV curve testing method of this embodiment includes: controlling the sequential closing of the bus switches on multiple photovoltaic strings while the inverter is in a grid-connected state; adjusting the inverter's output power and obtaining current and voltage data for each photovoltaic string within the inverter's output power range; and obtaining a photovoltaic IV curve based on the current and voltage data for each photovoltaic string. This testing method can produce a photovoltaic IV curve when the inverter is in a grid-connected state. Based on this photovoltaic IV curve, it can accurately determine whether a photovoltaic module has a fault or current mismatch. Compared to existing centralized inverters, this testing system allows for precise monitoring and refined management of the operating status of photovoltaic modules, accurately locating faulty photovoltaic strings.

[0063] Example 3

[0064] This embodiment further provides a photovoltaic device, which includes the above-mentioned test system and a processor, wherein the processor can execute the steps of the above-mentioned photovoltaic IV curve test method. The photovoltaic IV curve test method is as described above and will not be described in detail in this embodiment.

[0065] The photovoltaic device of this embodiment controls the sequential closing of the bus switches on multiple photovoltaic strings while the inverter is in a grid-connected state during photovoltaic IV curve testing; adjusts the inverter's output power and obtains current and voltage data for each photovoltaic string within the inverter's output power range; and generates a photovoltaic IV curve based on the current and voltage data for each photovoltaic string. This testing method can generate a photovoltaic IV curve when the inverter is in a grid-connected state, and based on this photovoltaic IV curve, it can accurately determine whether a photovoltaic module has a fault or current mismatch. Compared to existing centralized inverters, this testing system allows for precise monitoring and refined management of the operating status of photovoltaic modules, accurately locating faulty photovoltaic strings.

[0066] The photovoltaic IV curve testing system of the present invention sequentially closes the bus switches on multiple photovoltaic strings while the inverter is connected to the grid, adjusting the inverter's output power. It then acquires current and voltage data for each photovoltaic string within the inverter's output power range. This generates a photovoltaic IV curve for the inverter when connected to the grid. This curve accurately determines whether the photovoltaic module is experiencing faults or current mismatches. Compared to existing centralized inverters, this testing system enables precise monitoring of the operating status of photovoltaic modules and enables refined management.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A photovoltaic IV curve test system, characterized in that: The photovoltaic IV curve test system includes: Photovoltaic modules, consisting of multiple photovoltaic strings; A combiner box, connected to the photovoltaic assembly, for combining multiple photovoltaic strings, each of which is provided with a combiner switch; an inverter connected to the combiner box; The detection unit is installed in the combiner box and connected to each photovoltaic string to detect the current and voltage of each photovoltaic string; A control unit connected to the combiner box, the inverter, the detection unit and the plurality of combiner switches, The control unit is configured to send control signals to the plurality of bus switches and a regulation signal for regulating output power to the inverter when the inverter is in a grid-connected state; receive current and voltage data of each photovoltaic string when the inverter output power changes; and obtain a photovoltaic IV curve based on the current and voltage data of each photovoltaic string; The plurality of bus switches are closed in sequence according to the received control signal; The inverter is used to receive the adjustment signal sent by the control unit and adjust the output power of the inverter according to the adjustment signal; The photovoltaic IV curve testing system also includes: A transformer connected to the inverter, wherein the low-voltage side of the transformer is connected to the inverter; a grid-connected switch connected to the low-voltage side of the transformer is provided inside the inverter, and is configured to close when the inverter grid-connected voltage is reached, thereby placing the inverter in a grid-connected state; The control unit is further configured to determine whether an abnormality occurs in the photovoltaic string by analyzing whether the photovoltaic IV curve has too low an opening voltage, too low a short-circuit current, or multiple knee bends.

2. The photovoltaic IV curve test system according to claim 1, characterized in that: It also includes a power grid connected to the transformer, wherein the high voltage side of the transformer is connected to the power grid; and the power grid is connected to the control unit.

3. The photovoltaic IV curve test system according to claim 1, characterized in that: The inverter includes an inverter bridge, control logic and a filter circuit. The control logic includes a control module connected to the control unit. The control module is used to receive an adjustment signal from the control unit and control the inverter to adjust the output power.

4. The photovoltaic IV curve test system according to claim 1, characterized in that: The control unit is arranged on the inverter side or on the grid side.

5. The photovoltaic IV curve testing system according to claim 1, wherein: The merging switch is a mechanical switch or an electronic switch.

6. The photovoltaic IV curve test system according to claim 1, characterized in that: The inverter is of centralized, distributed or string type.

7. A photovoltaic IV curve testing method, characterized in that: The test method comprises the following steps: When the inverter is in grid-connected state, the bus switches on multiple photovoltaic strings are controlled to close in sequence; Adjust the output power of the inverter and obtain the current and voltage data of each photovoltaic string within the inverter output power variation range; The photovoltaic IV curve is obtained based on the current and voltage data of each photovoltaic string; By analyzing the PV IV curve to see if there is too low opening voltage, too low short-circuit current, or multiple knee bends, it can be determined whether there is any abnormality in the PV string.

8. A photovoltaic device, characterized in that: The test system comprises the test system and the processor according to any one of claims 1 to 6, wherein the processor is capable of running the test method according to claim 7.

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