Photovoltaic inverter and control method thereof

Abstract

The invention discloses a photovoltaic inverter and a control method thereof, relates to the technical field of energy, and is used for accurately detecting parallel impedance to ground of a photovoltaic array and the photovoltaic inverter so as to control safe grid connection of the photovoltaic inverter according to the parallel impedance to ground. The photovoltaic inverter comprises a Boost circuit, a first resistor, a second resistor, a DC bus positive electrode, a DC bus negative electrode, an inverter circuit and a controller. A controller in the photovoltaic inverter is used for controlling an output voltage of an optimizer array to be reduced under the condition that a preset condition is met, and the preset condition comprises at least one of the following conditions: a difference value between a negative bus voltage and a bus voltage is greater than or equal to a preset threshold value, or the output voltage of the optimizer array is greater than the bus voltage; the bus voltage is an absolute value of a voltage difference value between the DC bus positive electrode and the DC bus negative electrode, and the negative bus voltage is an absolute value of a voltage difference value between the protection ground wire and the DC bus negative electrode.

Description

Technical Field

[0001] The present application relates to the field of energy technology, and in particular to a photovoltaic inverter and a control method thereof. Background Art

[0002] PV inverters are used to convert the variable DC power generated by PV panels into stable AC power at the mains frequency. They are a crucial component in PV power generation systems. String PV power generation systems are widely used because they effectively account for the individual differences of each PV panel and prevent shadowing and hot-spot effects during operation. To ensure safe grid connection, the shunt impedance of the PV array and PV inverter to ground can be tested to determine if there are any insulation faults or safety hazards in the PV array. This shunt impedance can be considered the PV array's insulation resistance to ground.

[0003] Currently, a single-relay insulation impedance detection solution can be used to calculate the insulation resistance of a PV array to ground. However, some string-type PV power generation systems also include an optimizer array connected to the PV array. In this case, due to limitations in hardware circuits and calculation methods, it is impossible to accurately detect the insulation resistance of the string PV array to ground, thus making it impossible to ensure the grid-connected safety of the PV inverter.

[0004] Based on this, how to accurately detect the parallel impedance of the photovoltaic array and photovoltaic inverter to the ground, and control the photovoltaic inverter to be safely connected to the grid based on the parallel impedance to the ground, has become an urgent problem that needs to be solved. Summary of the Invention

[0005] The present application provides a photovoltaic inverter and a control method thereof, which are used to accurately detect the parallel impedance to ground of a photovoltaic array and a photovoltaic inverter, so as to control the photovoltaic inverter to be safely connected to the grid according to the parallel impedance to ground.

[0006] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions:

[0007] In a first aspect, a photovoltaic inverter is provided, comprising a boost circuit, a first resistor, a second resistor, a positive DC bus, a negative DC bus, an inverter circuit, and a controller. The boost circuit has an input terminal connected to an optimizer array, a positive output terminal connected to the positive DC bus, and a negative output terminal connected to the negative DC bus. The first resistor is connected between the positive DC bus and a protective ground, and the second resistor is connected between the protective ground and the negative DC bus. The inverter circuit has an input terminal connected to the positive DC bus and a negative DC bus, respectively, and an output terminal connected to a power grid. The controller is configured to control the output voltage of the optimizer array to decrease when a preset condition is met, the preset condition comprising at least one of the following: a difference between the negative bus voltage and the bus voltage is greater than or equal to a preset threshold, or the output voltage of the optimizer array is greater than the bus voltage. The bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus.

[0008] In the above technical solution, the controller can sample the negative bus voltage and bus voltage before the insulation impedance test, and based on the obtained negative bus voltage and bus voltage, when the difference between the negative bus voltage and the bus voltage is greater than or equal to a preset threshold, or the output voltage of the optimizer array is greater than the bus voltage, control the output voltage of the optimizer array to be reduced. Afterwards, based on the reduced output voltage of the optimizer array, the International Organization for Standardization (ISO) insulation impedance test is performed. This allows the ISO insulation impedance test to be performed on complex scenarios including the optimizer array in the photovoltaic power generation system with the optimal hardware circuit design cost, i.e., using fewer circuit components. Compared with the prior art, where the detection judgment logic assumes that there is no case where the negative bus voltage is greater than the bus voltage, the present application can accurately detect the parallel impedance of the photovoltaic array and the photovoltaic inverter to ground by adjusting the output voltage of the optimizer array when the photovoltaic array is connected to the optimizer array, thereby ensuring the accuracy and reliability of the insulation impedance test, thereby improving the grid-connected safety and reliability of the photovoltaic inverter.

[0009] In combination with the first aspect, in one implementation, the controller is specifically used to: when the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold, output a first control signal, and the first control signal is used to instruct the voltage regulation coefficient of the optimizer array to be reduced so that the difference between the negative bus voltage and the bus voltage is less than the preset threshold.

[0010] Based on the above solution, the controller outputs a first control signal to the optimizer array for controlling the voltage regulation coefficient of the optimizer array. This can control the reduction in the output voltage of the optimizer array to reduce the difference between the negative bus voltage and the bus voltage. Based on the output voltage of the optimizer array after voltage reduction, ISO insulation impedance testing is performed. This allows accurate detection of the parallel impedance to ground of the photovoltaic array and photovoltaic inverter, ensuring the accuracy and reliability of the insulation impedance testing, thereby improving the grid-connected safety and reliability of the photovoltaic inverter.

[0011] In combination with the first aspect, in one implementation, the controller is also used to: control the output end of the inverter circuit to disconnect from the power grid when the voltage regulation coefficient is less than a preset coefficient and the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold.

[0012] Based on the above solution, after the controller controls the voltage regulation coefficient of the optimizer array to be reduced to a preset coefficient, if the difference between the negative bus voltage and the bus voltage is still greater than or equal to the preset threshold, it indicates that the current voltage is abnormal and normal ISO insulation impedance testing cannot be performed. The controller can control the inverter circuit to disconnect from the grid to ensure the grid connection safety and reliability of the grid-connected inverter.

[0013] In combination with the first aspect, in one implementation, the controller is specifically used to: when the output voltage of the optimizer array is greater than the bus voltage, output a second control signal, the second control signal being used to instruct the output voltage of the optimizer array to be reduced to less than or equal to the bus voltage.

[0014] Based on the above solution, when the output voltage of the optimizer array is high, for example, the output voltage of the optimizer array is greater than the bus voltage, the controller outputs a second control signal to the optimizer array to control the output voltage of the optimizer array to be less than or equal to the bus voltage. The controller then performs ISO insulation impedance testing based on the output voltage of the optimizer array after voltage reduction, thereby accurately detecting the parallel impedance to ground of the photovoltaic array and the photovoltaic inverter, ensuring the accuracy and reliability of the insulation impedance testing, and thereby improving the grid-connected safety and reliability of the photovoltaic inverter.

[0015] In combination with the first aspect, in one implementation, the controller is further configured to control the optimizer array to output a reduced output voltage to the photovoltaic inverter after a preset time period.

[0016] Based on the above solution, after the controller controls the output voltage of the optimizer array to be reduced, it controls the optimizer array to delay outputting the reduced output voltage to the photovoltaic inverter. This can avoid the controller sampling an abnormal output voltage when sampling the output voltage of the optimizer array, thereby improving the fault tolerance of the ISO insulation impedance detection to a certain extent and improving the grid-connected safety and reliability of the photovoltaic inverter.

[0017] In conjunction with the first aspect, in one implementation, the photovoltaic inverter further includes a third resistor and a first switch connected in parallel; the third resistor and the first resistor are connected in series between the positive pole of the DC bus and the protective ground, or the third resistor and the second resistor are connected in series between the protective ground and the negative pole of the DC bus. The controller is further configured to: when the output voltage of the optimizer array is less than or equal to the bus voltage, or when the difference between the negative bus voltage and the bus voltage is less than a preset threshold, control the first switch to open to obtain a first negative bus voltage; and after obtaining the first negative bus voltage, control the first switch to close to obtain a second negative bus voltage.

[0018] Based on the above scheme, when the output voltage of the optimizer array is less than or equal to the bus voltage, or the difference between the negative bus voltage and the bus voltage is less than a preset threshold, the controller can normally perform ISO insulation impedance testing. The controller controls the first switch to open to obtain the bus voltage and the first negative bus voltage. After obtaining the first negative bus voltage, the controller is further configured to control the first switch to close to obtain a second negative bus voltage between the protective ground wire and the negative pole of the DC bus. The controller determines the insulation impedance of the photovoltaic array to ground based on the resistance value of the first resistor, the resistance value of the second resistor, the resistance value of the third resistor, the bus voltage, the first negative bus voltage, and the second negative bus voltage. This can also be considered as the parallel impedance to ground of the photovoltaic array and the photovoltaic inverter. Based on the detected parallel impedance to ground, the controller can control the inverter circuit to connect to the grid or not. For example, when the parallel impedance to ground meets the grid connection standard, the controller controls the inverter circuit to connect to the grid. When the parallel impedance to ground does not meet the grid connection standard, the controller controls the inverter circuit to not connect to the grid, thereby improving the grid connection safety and reliability of the photovoltaic inverter.

[0019] In conjunction with the first aspect, in one implementation, the controller is further configured to: control the output end of the inverter circuit to establish a connection with the power grid when the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a ratio threshold, wherein the positive bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the protective ground. The controller is further configured to: control the output end of the inverter circuit to disconnect from the power grid when the ratio of the negative bus voltage to the positive bus voltage is less than the ratio threshold.

[0020] Based on the above scheme, the parallel impedance of the photovoltaic inverter and the photovoltaic array to the ground can be equivalent to the ratio of the negative bus voltage to the positive bus voltage. The controller can control whether the photovoltaic inverter is connected to the grid or not according to the ratio and the proportional threshold, or control whether the photovoltaic inverter is grid-connected or not, thereby improving the grid-connected safety and reliability of the photovoltaic inverter.

[0021] In a second aspect, a photovoltaic inverter control method is provided, which is applied to the photovoltaic inverter. The method includes: controlling the output voltage of an optimizer array to decrease when a preset condition is met. The preset condition includes at least one of the following: the difference between the negative bus voltage and the bus voltage is greater than or equal to a preset threshold, or the output voltage of the optimizer array is greater than the bus voltage; wherein the bus voltage is the absolute value of the voltage difference between the positive and negative poles of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground and the negative pole of the DC bus. The photovoltaic inverter includes a boost circuit, wherein the boost circuit has an input terminal connected to the optimizer array, a positive output terminal of the boost circuit is connected to the positive pole of the DC bus, a negative output terminal of the boost circuit is connected to the negative pole of the DC bus, a first resistor is connected between the positive pole of the DC bus and the protective ground, a second resistor is connected between the protective ground and the negative pole of the DC bus, an input terminal of an inverter circuit is connected to the positive and negative poles of the DC bus, and an output terminal of the inverter circuit is connected to a power grid or a load.

[0022] In combination with the second aspect, in one implementation, when the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold, the method further includes: outputting a first control signal, the first control signal being used to instruct the voltage regulation coefficient of the optimizer array to be reduced so that the difference between the negative bus voltage and the bus voltage is less than the preset threshold.

[0023] In combination with the second aspect, in one implementation, when the voltage regulation coefficient is less than a preset coefficient and the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold, the method further includes: controlling the output end of the inverter circuit to disconnect from the power grid.

[0024] In combination with the second aspect, in one implementation, when the output voltage of the optimizer array is greater than the bus voltage, the method further includes: outputting a second control signal, the second control signal being used to instruct the output voltage of the optimizer array to be reduced to less than or equal to the bus voltage.

[0025] In combination with the second aspect, in one implementation, the method further includes: controlling the optimizer array to output a reduced output voltage to the photovoltaic inverter after a preset time period.

[0026] In conjunction with the second aspect, in one implementation, the photovoltaic inverter further includes a third resistor and a first switch connected in parallel. The third resistor and the first resistor are connected in series between the positive pole of the DC bus and the protective ground, or the third resistor and the second resistor are connected in series between the protective ground and the negative pole of the DC bus. When the output voltage of the optimizer array is less than or equal to the bus voltage, or the difference between the negative bus voltage and the bus voltage is less than a preset threshold, the method further includes: when the difference between the negative bus voltage and the bus voltage is less than the preset threshold, controlling the first switch to open to obtain a first negative bus voltage; and after obtaining the first negative bus voltage, controlling the first switch to close to obtain a second negative bus voltage.

[0027] In conjunction with the second aspect, in one implementation, the method further includes: controlling the output end of the inverter circuit to establish a connection with the power grid when the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a ratio threshold, wherein the positive bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the protective ground line; and controlling the output end of the inverter circuit to disconnect from the power grid when the ratio of the negative bus voltage to the positive bus voltage is less than the ratio threshold.

[0028] In a third aspect, a photovoltaic power generation system is provided, comprising an optimizer array and a photovoltaic inverter, wherein the input of the optimizer array is connected to the photovoltaic array, the output of the optimizer array is connected to the input of the photovoltaic inverter, and the photovoltaic inverter comprises a boost circuit, a first resistor, a second resistor, a positive DC bus, a negative DC bus, an inverter circuit, and a controller. The input of the boost circuit is connected to the output of the optimizer array, the positive output of the boost circuit is connected to the positive DC bus, the negative output of the boost circuit is connected to the negative DC bus, the first resistor is connected between the positive DC bus and a protective ground, the second resistor is connected between the protective ground and the negative DC bus, the input of the inverter circuit is connected to the positive DC bus and the negative DC bus, respectively, and the output of the inverter circuit is connected to a power grid. The controller is configured to control the output voltage of the optimizer array to decrease when a preset condition is satisfied, wherein the preset condition includes at least one of the following: a difference between the negative bus voltage and the bus voltage is greater than or equal to a preset threshold, or the output voltage of the optimizer array is greater than the bus voltage. The bus voltage is the absolute value of the voltage difference between the positive and negative poles of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground and the negative pole of the DC bus.

[0029] The description of the second and third aspects in this application can refer to the detailed description of the first aspect; and the beneficial effects of the second and third aspects can refer to the analysis of the beneficial effects of the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of an application scenario of a photovoltaic power generation system;

[0031] Figure 2 An equivalent circuit diagram for detecting the insulation impedance to ground of a photovoltaic inverter;

[0032] Figure 3 A schematic diagram of an application scenario of a photovoltaic power generation system provided in an embodiment of the present application;

[0033] Figure 4 An equivalent circuit diagram of a photovoltaic inverter for detecting insulation impedance to ground provided in an embodiment of the present application;

[0034] Figure 5 An equivalent circuit diagram of another photovoltaic inverter for detecting insulation impedance to ground provided in an embodiment of the present application;

[0035] Figure 6 An equivalent circuit diagram of another photovoltaic inverter provided in an embodiment of the present application;

[0036] Figure 7 An equivalent circuit diagram of another photovoltaic inverter provided in an embodiment of the present application;

[0037] Figure 8 A flowchart of an insulation impedance detection method provided in an embodiment of the present application;

[0038] Figure 9 A flowchart of another insulation impedance detection method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0039] The following will discuss in detail the making and use of various embodiments. However, it should be understood that many applicable inventive concepts provided herein can be implemented in a variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to implement and use the present application and technology and do not limit the scope of this application.

[0040] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

[0041] Various circuits or other components may be described or referred to as being "configured to" perform one or more tasks. In this case, "configured to" is used to imply structure by indicating that the circuit / component includes structure (e.g., circuitry) that performs the one or more tasks during operation. Thus, even when a specified circuit / component is not currently operational (e.g., not turned on), the circuit / component may be referred to as being configured to perform the task. Circuits / components used with the phrase "configured to" include hardware, such as circuitry that performs an operation, etc.

[0042] The embodiments of the present application use words such as "first" and "second" to distinguish objects with similar names, functions or effects. Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity and execution order.

[0043] In this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be construed as preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0044] Before introducing the embodiments of the present application, the background technology involved in the present application is first introduced.

[0045] like Figure 1 Figure 1 is a schematic diagram of an application scenario for a photovoltaic power generation system. The photovoltaic power generation system includes a photovoltaic inverter 100. The input end of the photovoltaic inverter 100 is used to connect to a photovoltaic array 200, and the output end of the photovoltaic inverter 100 is used to connect to a power grid 300. The photovoltaic array 200 includes at least one photovoltaic module. When the photovoltaic array 200 includes multiple photovoltaic modules, the multiple photovoltaic modules can be connected in series or in parallel, or some of the multiple photovoltaic modules can be connected in series and the remaining photovoltaic modules can be connected in parallel.

[0046] The photovoltaic inverter 100 is used to convert the variable direct current (DC) generated by photovoltaic modules into AC power at a stable mains frequency. It is a key component of a photovoltaic power generation system. String photovoltaic power generation systems are widely used because they effectively account for the individual differences of each photovoltaic module and prevent shadowing and hot spot effects during operation. The hot spot effect refers to the phenomenon that, under certain conditions, shaded photovoltaic cells in a photovoltaic module act as a load, consuming the energy generated by other normally operating photovoltaic cells. This energy consumption generates heat in these shaded photovoltaic cells.

[0047] In practical applications, the supports of photovoltaic modules are typically metal frames, which are directly exposed to the outdoors and are easily affected by inclement weather. This can cause the insulation of the photovoltaic modules to deteriorate over time, leading to safety hazards such as leakage. Therefore, it is necessary to regularly perform ISO insulation impedance testing on the photovoltaic modules using the photovoltaic inverter 100 to determine the insulation resistance of the photovoltaic modules to ground. This can help promptly detect insulation faults and safety hazards in the photovoltaic modules and ensure the electrical safety of the photovoltaic power generation system.

[0048] The following combination Figure 2 The equivalent circuit of the photovoltaic inverter 100 shown in the figure detects the insulation impedance to ground, and introduces the ISO insulation impedance detection method. Figure 2 FIG. 1 shows only the topology structure related to ISO insulation impedance detection in the photovoltaic inverter 100 .

[0049] like Figure 2 As shown, the photovoltaic inverter 100 includes a first resistor R1, a second resistor R2, a third resistor R3, and a resistor R SAM1 And the first switch K1. The first resistor R1 and the third resistor R3 are connected in series between the DC bus positive electrode BUS+ and the protective ground line PE of the photovoltaic inverter 100, and the second resistor R2 is connected between the protective ground line PE and the negative DC bus BUS- of the photovoltaic inverter 100. The first switch K1 is connected in parallel with the third resistor R3. Resistor R SAM1 It is connected between the protective ground wire PE and the negative DC bus BUS-, and represents the insulation impedance to ground of the photovoltaic inverter 100. For example, the switch K1 may be a relay.

[0050] See Figure 2 The fifth resistor R5, the sixth resistor R6, the seventh resistor R7 and the eighth resistor R8 can be regarded as Figure 1 The insulation resistance of photovoltaic array 200 to ground is shown in FIG. For ease of description, the photovoltaic array 200 is described as including a first photovoltaic module and a second photovoltaic module. For example, the fifth resistor R5 and the sixth resistor R6 can be considered the insulation resistance of the first photovoltaic module to ground, and the seventh resistor R7 and the eighth resistor R8 can be considered the insulation resistance of the second photovoltaic module to ground.

[0051] The photovoltaic inverter 100 further includes a diode D1 and a diode D2, wherein the diode D1 is used to limit the current generated by the first photovoltaic module to be transmitted unidirectionally to the positive DC bus BUS+, and the diode D2 is used to limit the current generated by the second photovoltaic module to be transmitted unidirectionally to the positive DC bus BUS+.

[0052] In the solution provided in the embodiment of the present application, the insulation resistance of the photovoltaic array 200 to ground can be detected by the first resistor R1 , the second resistor R2 , the third resistor R3 , and the first switch K1 .

[0053] Specifically, when the first switch K1 is disconnected, according to the voltage equation and Kirchhoff's current law, the resistances of the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, and the eighth resistor R8 satisfy the following relationship:

[0054]

[0055] When the first switch K1 is closed, the third resistor R3 is short-circuited. According to the voltage equation and Kirchhoff's current law, the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, the eighth resistor R8 and the resistor R SAM1 The resistance value satisfies the following relationship:

[0056]

[0057] Among them, U PVA is the output voltage of the first photovoltaic module, U PVB is the output voltage of the second photovoltaic module, U BUS The voltage between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS- is the voltage between the first voltage U1 and the DC bus negative electrode BUS- when the first switch K1 is disconnected. The second voltage U2 is the voltage between the protective ground wire PE and the DC bus negative electrode BUS- when the first switch K1 is closed. R1 to R3, R SAM1 , R5 to R8 represent the resistance value of each resistor, and “ / / ” indicates calculation according to the resistor parallel formula.

[0058] Combining the above two relationships (1) and (2), we can get the resistance R SAM1 , the sum of the reciprocals of the fifth resistor R5 to the eighth resistor R8 satisfies the following relationship:

[0059]

[0060] According to the relationship (3), R5, R6, R7, R8 and R SAM1 The sum of the reciprocals of , that is, the reciprocal of the parallel impedance R100 to ground of the photovoltaic array 200 and the photovoltaic inverter 100, wherein the parallel impedance to ground refers to the sum of the insulation resistance to ground of the first photovoltaic component in the photovoltaic array 200, the insulation resistance to ground of the second photovoltaic component, and the insulation resistance to ground of the photovoltaic inverter 100 in parallel.

[0061] It can be seen that in the photovoltaic inverter 100, the controller can change the resistance value between the DC bus positive electrode BUS+ and the protective ground wire PE by controlling the first switch K1 to be closed or turned off, thereby obtaining the voltage between the protective ground wire PE and the DC bus negative electrode BUS- in different states based on different resistance values. Finally, the bus voltage U BUS , the first voltage U1, the second voltage U2, and the resistance values of the first resistor R1 to the third resistor R3 are combined to calculate the parallel impedance to ground of the photovoltaic array 200 and the photovoltaic inverter 100. This parallel impedance to ground can also be regarded as the insulation impedance to ground of the photovoltaic array 200. When the insulation impedance to ground meets the requirements of the International Electrotechnical Commission (IEC) 62109-2 grid-connection standard for the insulation impedance to ground of the photovoltaic array 200, the controller controls the photovoltaic inverter 100 to connect to the grid. When the insulation impedance to ground does not meet the requirements of the IEC 62109-2 grid-connection standard for the insulation impedance to ground of the photovoltaic array 200, the controller controls the photovoltaic inverter 100 to not connect to the grid, thereby ensuring the grid connection safety of the photovoltaic inverter 100.

[0062] Figure 3 A schematic diagram of an application scenario of a photovoltaic power generation system 400 provided in an embodiment of the present application. Figure 4 for Figure 3 The equivalent circuit diagram of the photovoltaic inverter 410 detecting the insulation impedance to the ground. Figure 3 As shown, the photovoltaic power generation system 400 includes an optimizer array 420 and a photovoltaic inverter 410. The input end of the optimizer array 420 is used to connect to the photovoltaic array 200, the output end of the optimizer array 420 is connected to the input end of the photovoltaic inverter 410, and the output end of the photovoltaic inverter 410 is used to connect to the power grid 300. Among them, the optimizer is used to perform fine management and optimization on the output of the photovoltaic module to improve the power generation efficiency, reliability and stability of the photovoltaic power generation system 400. For example, the optimizer can adjust the output voltage of the photovoltaic module according to the needs of the photovoltaic power generation system 400 to keep it within a stable range, thereby providing a stable input voltage for the photovoltaic inverter 410 and ensuring the stable operation of the photovoltaic power generation system 400. The photovoltaic inverter 410 is used to provide AC power to the power grid 300 after converting the DC power output by the optimizer. Among them, Figure 3 In the description, the photovoltaic array 200 includes N photovoltaic modules and the optimizer array 420 includes N optimizers. The N photovoltaic modules are connected to the N optimizers in a one-to-one correspondence.

[0063] like Figure 3As shown, among the N optimizers, the positive output terminal of optimizer 1 is connected to the positive pole BUS+ of the DC bus of the photovoltaic inverter 410, the negative output terminal of optimizer 1 is connected to the positive output terminal of optimizer 2, the negative output terminal of optimizer 2 is connected to the positive output terminal of optimizer 3, and so on. The negative output terminal of optimizer N-2 is connected to the positive output terminal of optimizer N-1, the negative output terminal of optimizer N-1 is connected to the positive output terminal of optimizer N, and the negative output terminal of optimizer N is connected to the negative pole BUS- of the DC bus of the photovoltaic inverter 410.

[0064] See Figure 3 The resistance Riso connected between the photovoltaic array 200 and the protective ground wire PE is the parallel impedance of the photovoltaic array 200 and the photovoltaic inverter 410 to the ground mentioned above, and can also be regarded as the insulation impedance of the photovoltaic array 200 to the ground. Figure 4 As shown, the resistor RisoX connected between the protective ground wire PE and the negative electrode of the DC bus BUS- is the system internal resistance of the photovoltaic inverter 410.

[0065] In such Figure 3 and Figure 4 In the scenario shown, when the photovoltaic power generation system 400 includes the optimizer array 420, the output voltage of the photovoltaic components will be increased to a certain extent, causing the voltage between the protective ground wire PE and the negative pole BUS- of the DC bus of the photovoltaic inverter 410 to be greater than the voltage between the positive pole BUS+ and the negative pole BUS- of the DC bus of the photovoltaic inverter 410. As a result, the insulation resistance of the photovoltaic array 200 to the ground cannot be accurately detected, resulting in the grid-connected security of the photovoltaic inverter 410 not being guaranteed.

[0066] The following Figure 3 and Figure 4 As an example, combining the following scenario Figure 5 The equivalent circuit of the photovoltaic inverter 410 for detecting the insulation impedance to ground is shown to explain why the insulation impedance to ground of the photovoltaic array 200 cannot be accurately detected. Figure 5 Only the topology structure related to ISO insulation impedance detection in the photovoltaic inverter 410 is shown, and the photovoltaic array 200 including the first photovoltaic component PV1 and the second photovoltaic component PV2 is taken as an example for description.

[0067] like Figure 5 As shown, the photovoltaic inverter 410 includes a first resistor R1, a second resistor R2, a third resistor R3, and a resistor R SAM2 And the first switch K1. The connection relationship of the components in the photovoltaic inverter 410 can be referred to Figure 5 The description related to the above text will not be repeated here.

[0068] See Figure 5The insulation resistance of the first photovoltaic module PV1 and the insulation resistance of the second photovoltaic module PV2 to ground are equivalent to the impedance between the protective ground wire PE and the negative DC bus electrode BUS-. The insulation resistance of the first photovoltaic module PV1 to ground is represented by resistor Riso1, the insulation resistance of the second photovoltaic module PV2 to ground is represented by resistor Riso2, and the system internal resistance of the photovoltaic inverter 410 is represented by resistor RisoX. The voltage between the protective ground wire PE and the negative DC bus electrode BUS- is represented by Upe.

[0069] like Figure 5 , also showing the flow directions of currents Ib, Iy, Ig, I1, I2, and I3. Current Ib is the current flowing through the first resistor R1 and the third resistor R3, and current Iy is the current flowing through the second resistor R2. Current Ig is the current flowing into the node N1, which is the sum of currents I1, I2, and I3. Current I1 is the current flowing through the resistor Riso1, current I2 is the current flowing through the resistor Riso2, and current I3 is the current flowing through the resistor RisoX.

[0070] Specifically, when the first switch K1 is disconnected, according to the voltage equation and Kirchhoff's current law, the current Ig satisfies the following relationship:

[0071]

[0072] When the first switch K1 is closed, the third resistor R3 is short-circuited. According to the voltage equation and Kirchhoff's current law, Ig satisfies the following relationship:

[0073]

[0074] Wherein, Upv1 is the output voltage of the first PV module, Upv2 is the output voltage of the second PV module, Ig1 is the current flowing into the node N1 when the first switch K1 is off, Upe1 is the voltage when the first switch K1 is off, Ig2 is the current flowing into the node N1 when the first switch K1 is on, and Upe2 is the voltage when the first switch K1 is off. Riso1, Riso2, and RisoX represent the resistance values of the respective resistors.

[0075] Subtracting the above two relations (4) and (5), we can get the following relation:

[0076]

[0077] After subtracting the reciprocal of the system internal resistance RisoX of the photovoltaic inverter 410, the above equation (6) is the reciprocal of the parallel connection of the insulation resistance Riso1 of the first photovoltaic module PV1 and the insulation resistance Riso2 of the second photovoltaic module PV2, which is also the reciprocal of the insulation resistance Riso of the photovoltaic array 200. At the same time, equation (6) also confirms that there is no relationship between the insulation resistance of the photovoltaic array 200 and the absolute value of the output voltage of the photovoltaic array 200.

[0078] In such Figure 3 In the illustrated application scenario of the photovoltaic power generation system 400, when the photovoltaic module voltage is high, the voltage Upe (or common-mode voltage) between the protective ground wire PE and the negative DC bus BUS- is greater than or equal to the voltage between the positive DC bus BUS+ and the negative DC bus BUS- of the photovoltaic inverter 410 (i.e., the BUS voltage). In this scenario, the value of the current Ib is negative, meaning that the current Ib may reverse, which may result in a situation where Ig2 is less than Ig1, meaning that the current after the first switch K1 is closed is less than the current before the first switch K1 is closed. However, in the existing ISO insulation impedance detection logic, it is assumed that the scenario of ΔIg=Ig2-Ig1<0 does not exist, that is, the current after the first switch K1 is closed must be greater than the current before the first switch K1 is closed. If this scenario is assumed to not exist, the photovoltaic inverter cannot complete the insulation impedance detection when Ig2<Ig1. The photovoltaic inverter 410 may output an incorrect insulation impedance value and cannot detect the true and reliable insulation impedance of the photovoltaic array 300 to the ground, and the grid-connected security of the photovoltaic inverter 410 cannot be guaranteed.

[0079] To solve this problem, an embodiment of the present application provides a photovoltaic inverter 410, which can regulate the output voltage of the optimizer array 420 before performing ISO insulation impedance testing, thereby solving the problem of the inability to accurately detect the parallel impedance to ground of the photovoltaic array 200 and the photovoltaic inverter 410 in complex scenarios, and controlling the photovoltaic inverter 410 to be safely connected to the grid based on the parallel impedance to ground, thereby improving the grid-connected safety and reliability of the photovoltaic inverter 410.

[0080] The technical solutions in the embodiments of the present application will be introduced below in conjunction with the drawings in the embodiments of the present application.

[0081] like Figure 6 FIG2 is an equivalent circuit diagram of a photovoltaic inverter 410 provided in an embodiment of the present application. The photovoltaic inverter 410 includes a boost circuit 411, a first resistor R1, a second resistor R2, a DC bus positive electrode BUS+, a DC bus negative electrode BUS-, an inverter circuit 412, and a controller 413.

[0082] The input end of the boost circuit 411 is used to connect to the optimizer array 420, the positive output end of the boost circuit 411 is connected to the positive pole BUS+ of the DC bus, and the negative output end of the boost circuit 411 is connected to the negative pole BUS- of the DC bus. The first resistor R1 is connected between the positive pole BUS+ of the DC bus and the protective ground line PE, and the second resistor R2 is connected between the protective ground line PE and the negative pole BUS- of the DC bus. The two input ends of the inverter circuit 412 are respectively connected to the positive pole BUS+ and the negative pole BUS- of the DC bus, and the output end of the inverter circuit 412 is used to connect to the power grid 300.

[0083] The circuit topology of the Boost circuit 411 can refer to the circuit topology of the Boost circuit in the related art, and the circuit topology of the inverter circuit 412 can refer to the circuit topology of the inverter circuit in the related art, which will not be described in detail in the embodiment of the present application.

[0084] Reference Figure 6 The resistance Riso is used to represent the parallel impedance of the photovoltaic array 200 and the photovoltaic inverter 410 to the ground, which can also be regarded as the insulation impedance of the photovoltaic array 200 to the ground. The resistance Riso is connected between the photovoltaic array 200 and the protective ground wire PE. Figure 6 As shown, the resistor RisoX connected between the protective ground wire PE and the DC bus negative electrode BUS- is the system internal resistance of the photovoltaic inverter 410. The first resistor R1 and the second resistor R2 are used to detect the parallel impedance of the photovoltaic inverter 410 and the photovoltaic array 200 to the ground.

[0085] Before performing ISO insulation impedance testing, the controller 413 is used to obtain the negative bus voltage and the bus voltage. BUS It is the absolute value of the voltage difference between the DC bus positive pole BUS+ and the DC bus negative pole BUS-. The negative bus voltage Upe is the absolute value of the voltage difference between the protective ground wire PE and the DC bus negative pole BUS-. The negative bus voltage Upe can also be called the common mode voltage Upe.

[0086] The controller 413 obtains the bus voltage U BUS The specific process of generating the negative bus voltage Upe can be referred to the relevant technology, and the embodiments of the present application will not be repeated here.

[0087] In one embodiment, after obtaining the negative bus voltage Upe and the bus voltage U BUS Afterwards, the controller 413 is further configured to control the output voltage of the optimizer array 420 to decrease when a preset condition is met. The preset condition includes at least one of the following: the negative bus voltage Upe is equal to the bus voltage U BUS The difference between the two is greater than or equal to the preset threshold, or the output voltage of the optimizer array 420 is greater than the bus voltage U BUSFor example, the controller 413 may output a control signal to the optimizer array 420 when a preset condition is met. The control signal may be used to instruct the optimizer array 420 to reduce the output voltage.

[0088] The preset threshold is the negative bus voltage Upe and the bus voltage U BUS The preset threshold is related to the impedance and detection accuracy of the photovoltaic power generation system 400. The higher the preset threshold, the higher the detection accuracy. The embodiment of the present application does not limit the specific value of the preset threshold. For example, the preset threshold can be 10V, that is, when Upe-U BUS ≥10V, the controller 413 outputs a control signal to the optimizer array 420 to instruct the optimizer array 420 to reduce the output voltage so that Upe-U BUS <10V. The preset threshold can also be 20V, that is, when Upe-U BUS ≥20V, the controller 413 outputs a control signal to the optimizer array 420 to instruct the optimizer array 420 to reduce the output voltage so that Upe-U BUS <20V. The preset threshold can also be 0V, that is, when Upe-U BUS ≥0, the controller 413 outputs a control signal to the optimizer array 420 to instruct the optimizer array 420 to reduce the output voltage so that Upe < U BUS .

[0089] When the negative bus voltage Upe is equal to the bus voltage U BUS If the voltage difference after subtraction is greater than or equal to the preset threshold, it means that the current voltage is abnormal and the parallel impedance of the photovoltaic array 200 and the photovoltaic inverter 410 to the ground cannot be accurately detected. It is necessary to first reduce the negative bus voltage Upe and the bus voltage U BUS The difference between the negative bus voltage Upe and the bus voltage U BUS When the difference between them is less than the preset threshold, it indicates that the output voltage of the current optimizer array 420 is normal and the ISO insulation resistance test can be performed normally.

[0090] In one embodiment, when the negative bus voltage Upe is equal to the bus voltage U BUS When the difference between the negative bus voltage Upe and the bus voltage U BUS The difference between them is less than the preset threshold.

[0091] After receiving the first control signal, the optimizer array 420 reduces the voltage regulation coefficient based on the instruction of the first control signal to reduce the amplitude of the output voltage, so that the negative bus voltage Upe of the photovoltaic inverter 410 is equal to the bus voltage U BUS The difference between the two decreases until it is less than a preset threshold. After receiving the output voltage reduced by the optimizer, the photovoltaic inverter 410 can use the aforementioned detection logic to perform ISO insulation impedance detection on the parallel impedance to ground of the photovoltaic array 200 and the photovoltaic inverter 410, thereby avoiding detection failures to a certain extent.

[0092] For example, after receiving the first control signal, the optimizer array 420 reduces the voltage regulation coefficient from 1 to 0.7 based on the instruction of the first control signal, that is, the output voltage of the optimizer array 420 is reduced to 70% of the original output voltage. BUS If the difference between the negative bus voltage Upe and the bus voltage U BUS The difference between the values is still greater than or equal to the preset threshold, and the controller 413 again outputs the first control signal to the optimizer array 420. After receiving the first control signal, the optimizer array 420 can control the voltage regulation coefficient of the optimizer array 420 to be reduced from 0.7 to 0.5, and the output voltage of the optimizer array 420 is reduced to 50% of the original output voltage.

[0093] In this way, by controlling the voltage regulation coefficient of the optimizer array 420, the output voltage drop of the optimizer array 420 can be controlled to reduce the difference between the negative bus voltage and the bus voltage, thereby improving the accuracy and reliability of ISO insulation resistance detection.

[0094] In one embodiment, the controller 413 is further configured to: BUS When the difference between the two values is greater than or equal to the preset threshold, the output end of the inverter circuit 412 is controlled to be disconnected from the power grid.

[0095] The above preset coefficient is the limit voltage regulation coefficient of the optimizer array 420. For example, the preset coefficient can be 0.5, that is, when the controller 413 controls the voltage regulation coefficient of the optimizer array 420 to be reduced to 0.5, if the negative bus voltage Upe is equal to the bus voltage U BUS If the difference between the two values is still greater than or equal to the preset threshold, it indicates that the current voltage is abnormal and normal ISO insulation impedance detection cannot be performed. The controller 413 can control the inverter circuit 412 to disconnect from the grid and issue an alarm message to ensure the grid-connected safety and reliability of the grid-connected inverter.

[0096] In another embodiment, the controller 413 is further configured to: BUS In the case of , the second control signal is output, the second control signal is used to instruct the output voltage of the optimizer array 420 to be reduced to less than or equal to the bus voltage U BUS .

[0097] For example, the controller 413 may also obtain the bus voltage U BUS Afterwards, the second control signal is directly output to the optimizer array 420 to control the output voltage of the optimizer array 420 to decrease. In this case, the controller 413 does not need to compare the negative bus voltage Upe with the bus voltage U BUS The difference between the two values is calculated. When it is determined that the photovoltaic power generation system 400 includes the optimizer array 420, the output voltage of the optimizer array 420 can be directly controlled to decrease until the output voltage of the optimizer array 420 is less than or equal to the bus voltage U BUS The photovoltaic inverter 410 receives the output voltage reduced by the optimizer array 420 and can use the aforementioned detection logic to perform ISO insulation impedance detection on the parallel impedance to ground of the photovoltaic array 200 and the photovoltaic inverter 410, thereby avoiding detection failure to a certain extent.

[0098] Specifically, the controller 413 obtains the negative bus voltage Upe and the bus voltage U BUS , it can not only be used as a benchmark to determine whether the output voltage of the optimizer array 420 needs to be adjusted to minimize the failure of ISO insulation resistance detection. It can also be used to obtain the negative bus voltage Upe and bus voltage U BUS Then, the parallel impedance to the ground of the photovoltaic array 200 and the photovoltaic inverter 410 is calculated, so as to control the photovoltaic inverter 410 to be connected to the grid or not according to the parallel impedance to the ground.

[0099] In the photovoltaic inverter 410 provided in the embodiment of the present application, the controller 413 can detect the negative bus voltage Upe and the bus voltage U before the insulation impedance detection. BUS Sampling is performed to obtain the negative bus voltage Upe and bus voltage U BUS Based on the negative bus voltage Upe and bus voltage U BUS The difference between the two is greater than or equal to the preset threshold, or the output voltage of the optimizer array 420 is greater than the bus voltage U BUSIn the case of a voltage drop, a control signal is output to the optimizer array 420 to control the output voltage of the optimizer array 420 to decrease. Afterwards, the ISO insulation impedance test is performed based on the output voltage of the optimizer array 420 after the voltage drop. This allows the ISO insulation impedance test to be performed on complex scenarios including the optimizer array 420 in the photovoltaic power generation system 400 while optimizing the hardware circuit design cost, i.e., using fewer circuit components. In contrast to the prior art, the detection judgment logic assumes that there is no negative bus voltage Upe greater than the bus voltage U BUS Compared with the situation where the photovoltaic array 200 is connected to the optimizer array 420, the present application can accurately detect the parallel impedance of the photovoltaic array 200 and the photovoltaic inverter 410 to the ground by adjusting the output voltage of the optimizer array 420, thereby ensuring the accuracy and reliability of the insulation impedance detection, thereby improving the grid-connected safety and reliability of the photovoltaic inverter 410.

[0100] In one embodiment, the controller 413 is further configured to control the optimizer array 420 to output a reduced output voltage to the photovoltaic inverter 410 after a preset period of time.

[0101] The preset duration is the duration for which the optimizer array 420 delays outputting the output voltage after reducing the output voltage. This preset duration is related to the communication link between the photovoltaic inverter 410 and the optimizer array 420, the execution speed of the controller 413, and the execution speed of the controller 413 in the optimizer array 420. The embodiments of the present application do not limit the specific value of the preset duration. For example, the preset duration can be 10 seconds, that is, after reducing the output voltage, the optimizer array 420 delays outputting the reduced output voltage to the photovoltaic inverter 410 for 10 seconds. Alternatively, the preset duration can be 20 seconds, that is, after reducing the output voltage, the optimizer array 420 delays outputting the reduced output voltage to the photovoltaic output for 20 seconds.

[0102] Therefore, since the optimizer array 420 requires corresponding processing time when executing the output voltage reduction process, the controller 413 controls the optimizer array 420 to delay outputting the reduced output voltage to the photovoltaic inverter 410 after controlling the output voltage of the optimizer array 420 to be reduced. This can avoid the controller 413 sampling an abnormal output voltage when sampling the output voltage of the optimizer array 420, thereby improving the fault tolerance of the ISO insulation impedance detection to a certain extent and improving the grid-connected safety and reliability of the photovoltaic inverter 410.

[0103] In one embodiment, if Figure 7 As shown, the photovoltaic inverter 410 further includes a third resistor R3 and a first switch K1 connected in parallel. Figure 7As shown in (a) of FIG. 1 , the third resistor R3 and the first resistor R1 are connected in series between the DC bus positive electrode BUS+ and the protective ground line PE, or, as shown in FIG. Figure 7 As shown in (b), the third resistor R3 and the second resistor R2 are connected in series between the protective ground wire PE and the negative electrode of the DC bus BUS-.

[0104] Optionally, the type of the first switch K1 includes a relay, an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor. The embodiment of the present application does not limit the specific type of the first switch K1. The embodiment of the present application uses the first switch K1 as a relay as an example for illustrative description.

[0105] The controller 413 is further configured to: BUS , or negative bus voltage Upe and bus voltage U BUS When the difference between them is less than a preset threshold, the first switch K1 is controlled to be disconnected to obtain the first negative bus voltage Upe1. After obtaining the first negative bus voltage Upe1, the first switch K1 is controlled to be closed to obtain the second negative bus voltage Upe2.

[0106] Specifically, when the output voltage of the optimizer array 420 is less than or equal to the bus voltage U BUS , or negative bus voltage Upe and bus voltage U BUS When the difference between the two values is less than the preset threshold, the controller 413 can perform the ISO insulation impedance test normally. The controller 413 controls the first switch K1 to be disconnected, and obtains the bus voltage U BUS , and the first negative bus voltage Upe1. After obtaining the first negative bus voltage Upe1, the controller 413 is further used to control the first switch K1 to be in a closed state to obtain the second negative bus voltage Upe2 between the protective ground wire PEPE and the DC bus negative electrode BUS-BUS-, the resistance value of the first resistor R1, the resistance value of the second resistor R2, the resistance value of the third resistor R3, the bus voltage U BUS , the first negative bus voltage Upe1 and the second negative bus voltage Upe2 are used to determine the insulation resistance Riso of the photovoltaic array 200 to ground, which can also be regarded as the parallel impedance to ground of the photovoltaic array 200 and the photovoltaic inverter 410. The photovoltaic inverter 410 can adopt the above Figure 2 The related method of calculating the parallel impedance to ground is to calculate the parallel impedance to ground of the photovoltaic array 200 and the photovoltaic inverter 410. The specific process can refer to the specific process of using a single relay to perform insulation impedance detection in the related art, and the embodiments of the present application will not be repeated here.

[0107] In one embodiment, the controller 413 is further configured to control the output end of the inverter circuit 412 to establish a connection with the power grid when the ratio of the negative bus voltage Upe to the positive bus voltage is greater than or equal to a proportional threshold, where the positive bus voltage is the absolute value of the voltage difference between the DC bus positive electrode BUS+ and the protective ground line PE. The controller 413 is further configured to control the output end of the inverter circuit 412 to disconnect from the power grid when the ratio of the negative bus voltage Upe to the positive bus voltage is less than a proportional threshold. This proportional threshold is related to the insulation impedance requirements corresponding to the photovoltaic inverter 410 in the grid-connected standard, and the embodiments of the present application do not limit the specific value of the proportional threshold.

[0108] For example, the ratio of the negative bus voltage Upe to the positive bus voltage can be equivalent to the parallel impedance of the photovoltaic inverter 410 and the photovoltaic array 200 to the ground. The controller 413 can control the photovoltaic inverter 410 to be connected to the grid or not based on the ratio and the proportional threshold, thereby improving the safety of the photovoltaic inverter 410.

[0109] The following combination Figure 8 and Figure 9 The flowchart shown in Figure 7 Taking the circuit topology shown in as an example, the insulation impedance detection method provided by the embodiment of the present application is described in detail.

[0110] like Figure 8 As shown, an insulation impedance detection method provided in an embodiment of the present application includes detection steps S601 to S607 and S611 to S616. S601 to S607 are steps for performing insulation impedance detection without voltage regulation, and S611 to S616 are steps for performing insulation impedance detection when voltage is abnormal. Exemplarily, the detection steps can be implemented by the aforementioned controller 413 and the controller in the optimizer array 420.

[0111] S601: Determine whether the difference between the negative bus voltage and the bus voltage is less than a preset threshold. If so, the common-mode voltage Upe is normal, and step S602 can proceed normally. Otherwise, the common-mode voltage Upe is abnormal, requiring voltage regulation of the optimizer array 420, and step 611 can be executed.

[0112] S602-S604: Control the first switch K1 to be open, obtain the first negative bus voltage, control the first switch K1 to be closed, obtain the second negative bus voltage, and calculate the insulation resistance to ground based on the first negative bus voltage, the second negative bus voltage, the bus voltage and the relevant resistance value.

[0113] S605: Determine whether the test is successful. If the controller 413 outputs the insulation resistance value normally, the test is considered successful and step S606 is executed; if the controller 413 cannot output the insulation resistance value normally, the test is considered abnormal and step S607 is executed.

[0114] S606: Subsequent processing: After outputting the insulation resistance value, if the resistance value meets the grid connection requirement, the controller 413 controls the inverter circuit 412 to establish a connection with the grid 300; if the resistance value does not meet the grid connection requirement, the controller 413 controls the inverter circuit 412 to disconnect from the grid 300.

[0115] S607: Detection failure. Exemplarily, if the number of detection failures is less than n times, steps S602 to S604 are executed again. If the number of detection failures is greater than or equal to n times, the controller 413 controls the inverter circuit 412 to disconnect from the power grid 300 and issues an alarm message. The alarm message may be the first alarm message ID0. The first alarm message ID0 is used to indicate that the number of detection failures has exceeded a threshold number when the detection voltage is normal. Wherein, n represents the threshold value of detection failure. For example, n can be 4. When the number of detection failures exceeds 4 times, the controller 413 controls the inverter circuit 412 to disconnect from the power grid 300 and issues an alarm message.

[0116] S611: Voltage adjustment: reduce the voltage adjustment coefficient of the optimizer array 420 to m1. For example, m1 represents the first voltage adjustment coefficient of the optimizer array 420, for example, m1=0.7.

[0117] S612: Determine whether the difference between the negative bus voltage and the bus voltage is less than a preset threshold. If so, it indicates that the common-mode voltage Upe is normal, and step S615 is executed. Otherwise, it indicates that the common-mode voltage Upe is abnormal and needs to be adjusted again, and step S613 is executed.

[0118] S613: Voltage adjustment: reduce the voltage adjustment coefficient of the optimizer array 420 to m2, where m2 represents the second voltage adjustment coefficient of the optimizer array 420, and m2<m1, for example, m2=0.5.

[0119] S614: Determine whether the difference between the negative bus voltage and the bus voltage is less than a preset threshold. If it is less than the preset threshold, it indicates that the common-mode voltage Upe is normal, and step S615 is executed. Otherwise, it indicates that the common-mode voltage Upe is abnormal. If the voltage regulation coefficient of the optimizer array 420 has been adjusted to the limit, and the common-mode voltage Upe is still abnormal, normal ISO insulation impedance testing cannot be performed. The controller 413 can control the inverter circuit 412 to disconnect from the power grid 300 and issue an alarm message. This alarm message can be the second alarm message ID1, which is used to indicate that the current voltage regulation coefficient of the optimizer array 420 is close to the voltage regulation limit of the optimizer array 420 and that normal voltage cannot be detected.

[0120] S615: Exit voltage regulation. At this point, it indicates that the output voltage of the optimizer array 420 has dropped to an appropriate amplitude, and the detection step can be performed normally. For specific detection steps, see S602 to S605.

[0121] S616: Restoring the voltage regulation coefficient. After determining that the test is successful, indicating that the insulation resistance test has been completed, the controller 413 can also output a voltage regulation coefficient restoration signal to the optimizer array 420 to control the output voltage of the optimizer array 420 to return to the voltage before the test.

[0122] like Figure 9 As shown, another insulation impedance detection method provided by an embodiment of the present application includes steps S701 to S708.

[0123] S701: Control the output voltage of the optimizer array 420 to decrease. Exemplarily, the controller 413 outputs a second control signal to the optimizer array 420 to control the output voltage of the optimizer array 420 to be less than or equal to the bus voltage.

[0124] S702-S704: Control the first switch K1 to be open, obtain the first negative bus voltage, control the first switch K1 to be closed, obtain the second negative bus voltage, and calculate the insulation resistance to ground based on the first negative bus voltage, the second negative bus voltage, the bus voltage and the relevant resistance value.

[0125] S705: Determine whether the test is successful. If the controller 413 outputs the insulation resistance value normally, the test is considered successful, and steps S706 and S707 are executed; if the controller 413 cannot output the insulation resistance value normally, the test is considered abnormal, and step S708 is executed.

[0126] S706: Restore the output voltage of the optimizer array 420. After determining that the detection is successful, the controller 413 is further configured to output a control signal for restoring the output voltage to the optimizer array 420, so as to control the output voltage of the optimizer array 420 to return to the voltage before the detection.

[0127] S707: Subsequent processing: After outputting the insulation resistance value, if the resistance value meets the grid connection requirement, the controller 413 controls the inverter circuit 412 to establish a connection with the grid 300; if the resistance value does not meet the grid connection requirement, the controller 413 controls the inverter circuit 412 to disconnect from the grid 300.

[0128] S708: Detection failure. Exemplarily, if the number of detection failures is less than n times, steps S602 to S604 are executed again. If the number of detection failures is greater than or equal to n times, the controller 413 controls the inverter circuit 412 to disconnect from the power grid 300 and issues an alarm message. The alarm message may be the first alarm message ID0. The first alarm message ID0 is used to indicate that when the detection voltage is normal, the number of detection failures has exceeded the threshold number. Wherein, n represents the threshold value of detection failure. For example, n can be 4. When the number of detection failures exceeds 4 times, the controller 413 controls the inverter circuit 412 to disconnect from the power grid 300 and issues an alarm message.

[0129] The present invention also provides a method for controlling a photovoltaic inverter. The method can be applied to the above-mentioned Figure 6 or Figure 7 In the photovoltaic inverter 410 shown, the method includes the following steps:

[0130] S901: When a preset condition is met, control the output voltage of the optimizer array to decrease, the preset condition including at least one of the following: the negative bus voltage Upe and the bus voltage U BUS The difference between the two is greater than or equal to the preset threshold, or the output voltage of the optimizer array is greater than the bus voltage U BUS . Among them, the bus voltage U BUS It is the absolute value of the voltage difference between the DC bus positive pole BUS+ and the DC bus negative pole BUS-. The negative bus voltage Upe is the absolute value of the voltage difference between the protective ground wire PE and the DC bus negative pole BUS-.

[0131] Illustratively, before S901 , the method further includes S900 .

[0132] S900: Get negative bus voltage U BUS and bus voltage Upe.

[0133] The above bus voltage U is obtained BUS The specific process of generating the negative bus voltage Upe can be referred to the relevant technology, and the embodiments of the present application will not be repeated here.

[0134] The embodiment of the present application also provides a photovoltaic power generation system. The circuit topology of the photovoltaic power generation system can be as follows: Figure 3The circuit topology of the photovoltaic power generation system 400 shown in FIG. 4 includes an optimizer array 420 and a photovoltaic inverter 410. The input end of the optimizer array 420 is used to connect to the photovoltaic array 200. The output end of the optimizer array 420 is connected to the input end of the photovoltaic inverter 410. The output end of the photovoltaic inverter 410 is used to connect to the power grid 300. Figure 3 In the embodiment of the present application, the optimizer array 420 includes N optimizers and the photovoltaic array 200 includes N photovoltaic modules. The photovoltaic inverter 410 can be as follows: Figure 6 and Figure 7 The photovoltaic inverter shown in any of the accompanying drawings.

[0135] The above detailed description of the photovoltaic inverter 410 and the analysis of its beneficial effects can be correspondingly referred to the control method of the photovoltaic inverter 410 and the photovoltaic power generation system 400 , and will not be further elaborated herein in the embodiments of the present application.

[0136] Finally, it should be noted that the above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A photovoltaic inverter, characterized in that: The photovoltaic inverter includes a boost circuit, a first resistor, a second resistor, a DC bus positive electrode, a DC bus negative electrode, an inverter circuit and a controller; The input end of the Boost circuit is used to connect to the optimizer array, the positive output end of the Boost circuit is connected to the positive pole of the DC bus, the negative output end of the Boost circuit is connected to the negative pole of the DC bus, the first resistor is connected between the positive pole of the DC bus and the protective ground wire, the second resistor is connected between the protective ground wire and the negative pole of the DC bus, the input end of the inverter circuit is respectively connected to the positive pole of the DC bus and the negative pole of the DC bus, and the output end of the inverter circuit is used to connect to the power grid; The controller is configured to control the output voltage of the optimizer array to decrease when a preset condition is met, where the preset condition includes at least one of the following: a difference between the negative bus voltage and the bus voltage is greater than or equal to a preset threshold, or the output voltage of the optimizer array is greater than the bus voltage; wherein the bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus.

2. The photovoltaic inverter according to claim 1, characterized in that: The controller is specifically configured to output a first control signal when the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold, wherein the first control signal is configured to instruct the optimizer array to reduce a voltage regulation coefficient so that the difference between the negative bus voltage and the bus voltage is less than the preset threshold.

3. The photovoltaic inverter according to claim 2, characterized in that: The controller is further configured to control the output end of the inverter circuit to be disconnected from the power grid when the voltage regulation coefficient is less than a preset coefficient and the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold.

4. The photovoltaic inverter according to claim 1, characterized in that: The controller is specifically configured to output a second control signal when the output voltage of the optimizer array is greater than the bus voltage, wherein the second control signal is configured to instruct the output voltage of the optimizer array to decrease to less than or equal to the bus voltage.

5. The photovoltaic inverter according to any one of claims 1 to 4, characterized in that: The controller is further configured to control the optimizer array to output a reduced output voltage to the photovoltaic inverter after a preset time period.

6. The photovoltaic inverter according to any one of claims 1 to 5, characterized in that: The photovoltaic inverter further includes a third resistor and a first switch connected in parallel; the third resistor and the first resistor are connected in series between the positive pole of the DC bus and the protective ground wire, or the third resistor and the second resistor are connected in series between the protective ground wire and the negative pole of the DC bus; The controller is further configured to control the first switch to be disconnected to obtain a first negative bus voltage when the output voltage of the optimizer array is less than or equal to the bus voltage, or when the difference between the negative bus voltage and the bus voltage is less than the preset threshold; The controller is further configured to control the first switch to close after obtaining the first negative bus voltage, so as to obtain a second negative bus voltage.

7. The photovoltaic inverter according to claim 6, characterized in that: The controller is further configured to control the output end of the inverter circuit to establish a connection with the power grid when a ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a ratio threshold, wherein the positive bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the protective ground line; The controller is further configured to control the output end of the inverter circuit to be disconnected from the power grid when the ratio of the negative bus voltage to the positive bus voltage is less than the ratio threshold.

8. A control method for a photovoltaic inverter, characterized in that: Applied to a photovoltaic inverter, the method includes: When a preset condition is met, the output voltage of the optimizer array is controlled to decrease, wherein the preset condition includes at least one of the following: the difference between the negative bus voltage and the bus voltage is greater than or equal to a preset threshold, or the output voltage of the optimizer array is greater than the bus voltage; wherein the bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus; The photovoltaic inverter includes a Boost circuit, wherein the input end of the Boost circuit is used to connect to the optimizer array, the positive output end of the Boost circuit is connected to the positive pole of the DC bus, the negative output end of the Boost circuit is connected to the negative pole of the DC bus, a first resistor is connected between the positive pole of the DC bus and the protective ground wire, a second resistor is connected between the protective ground wire and the negative pole of the DC bus, the input end of the inverter circuit is respectively connected to the positive pole of the DC bus and the negative pole of the DC bus, and the output end of the inverter circuit is used to connect to the power grid.

9. The control method according to claim 8, characterized in that: In a case where the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold, the method further includes: A first control signal is output, where the first control signal is used to instruct the voltage regulation coefficient of the optimizer array to decrease so that the difference between the negative bus voltage and the bus voltage is less than the preset threshold.

10. The control method according to claim 9, characterized in that: When the voltage regulation coefficient is less than a preset coefficient and the difference between the negative bus voltage and the bus voltage is greater than or equal to the preset threshold, the method further includes: The output end of the inverter circuit is controlled to be disconnected from the power grid.

11. The control method according to claim 8, characterized in that: In a case where the output voltage of the optimizer array is greater than the bus voltage, the method further comprises: A second control signal is output, where the second control signal is used to instruct the output voltage of the optimizer array to decrease to less than or equal to the bus voltage.

12. The control method according to any one of claims 8 to 11, characterized in that: The method further comprises: The optimizer array is controlled to output a reduced output voltage to the photovoltaic inverter after a preset time period.

13. The control method according to any one of claims 8 to 12, characterized in that: The photovoltaic inverter further includes a third resistor and a first switch connected in parallel; the third resistor and the first resistor are connected in series between the positive pole of the DC bus and the protective ground wire, or the third resistor and the second resistor are connected in series between the protective ground wire and the negative pole of the DC bus; When the output voltage of the optimizer array is less than or equal to the bus voltage, or the difference between the negative bus voltage and the bus voltage is less than the preset threshold, the method further includes: When the difference between the negative bus voltage and the bus voltage is less than the preset threshold, controlling the first switch to be disconnected to obtain a first negative bus voltage; After obtaining the first negative bus voltage, the first switch is controlled to be closed to obtain a second negative bus voltage.

14. The control method according to claim 13, characterized in that: The method further comprises: When the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a ratio threshold, controlling the output end of the inverter circuit to establish a connection with the power grid, wherein the positive bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the protective ground wire; When the ratio of the negative bus voltage to the positive bus voltage is less than the ratio threshold, the output end of the inverter circuit is controlled to be disconnected from the power grid.

15. A photovoltaic power generation system, characterized in that: The photovoltaic power generation system includes an optimizer array and a photovoltaic inverter, wherein the input end of the optimizer array is used to connect to the photovoltaic array, the output end of the optimizer array is connected to the input end of the photovoltaic inverter, and the photovoltaic inverter includes a Boost circuit, a first resistor, a second resistor, a DC bus positive pole, a DC bus negative pole, an inverter circuit and a controller; The input end of the Boost circuit is connected to the output end of the optimizer array, the positive output end of the Boost circuit is connected to the positive pole of the DC bus, the negative output end of the Boost circuit is connected to the negative pole of the DC bus, the first resistor is connected between the positive pole of the DC bus and a protective ground wire, the second resistor is connected between the protective ground wire and the negative pole of the DC bus, the input end of the inverter circuit is respectively connected to the positive pole of the DC bus and the negative pole of the DC bus, and the output end of the inverter circuit is used to connect to the power grid; The controller is configured to control the output voltage of the optimizer array to decrease when a preset condition is met, where the preset condition includes at least one of the following: a difference between the negative bus voltage and the bus voltage is greater than or equal to a preset threshold, or the output voltage of the optimizer array is greater than the bus voltage; wherein the bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus.

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