Insulation detection method for photovoltaic conversion system and related device

Abstract

The disclosure provides an insulation detection method of a photovoltaic conversion system and a related device, and relates to the technical field of insulation detection. The photovoltaic conversion system, under the condition that the anti-PID circuit is running, outputs an anti-PID current by an anti-PID power supply inside the anti-PID circuit, and switches a detection resistor inside the IMD, so that the detection current flows in the IMD; then, the control unit calculates the ground insulation impedance of the photovoltaic conversion system according to the resistance value of the detection resistor, the anti-PID current and the detection current, and thus the insulation detection can be completed while the anti-PID function is realized, so that the anti-PID function and the insulation detection function are compatible. Moreover, on the basis of the traditional anti-PID operation, only the detection resistor needs to be extended and switched, and the IMD does not need a related control power supply, so the cost is low.

Description

Technical Field

[0001] This disclosure relates to the field of insulation testing technology, and in particular to an insulation testing method and related apparatus for a photovoltaic conversion system. Background Technology

[0002] In photovoltaic (PV) conversion systems, anti-PID operation is typically achieved by adding an anti-PID (Potential Induced Degradation) circuit to the PV inverter or by directly grounding the DC side. This raises the voltage of the negative terminal of the PV string relative to ground, thereby suppressing the PID effect of the PV modules. However, during the anti-PID operation of the PV inverter, because a grounding loop exists, it is impossible to detect the system's insulation impedance to ground. This causes insulation monitoring and anti-PID to conflict, meaning only one function can be performed at a time. Summary of the Invention

[0003] In view of the above problems, this disclosure provides an insulation detection method and related device for a photovoltaic conversion system, so as to complete insulation detection while implementing the inverse PID function. The specific solution is as follows:

[0004] The first aspect of this disclosure provides a photovoltaic conversion system, including: a DC / AC conversion circuit, an inverse PID circuit, an insulation monitoring device, and a control unit; wherein...

[0005] The DC side of the DC / AC conversion circuit is used to connect to a photovoltaic power source;

[0006] The AC side of the DC / AC conversion circuit is used to connect at least one of the power grid and the load;

[0007] The anti-PID circuit is located on the DC side or AC side of the DC / AC conversion circuit, and the anti-PID circuit is configured to output an anti-PID current from the internal anti-PID power supply when the anti-PID circuit is running.

[0008] The insulation monitoring device is located on the DC side or AC side of the DC / AC conversion circuit. The insulation detection device is configured to switch the detection resistor inside the insulation detection device when the inverse PID circuit is running, so that a detection current flows through the insulation detection device.

[0009] The control unit is configured to calculate the ground insulation impedance of the photovoltaic conversion system based on the resistance value of the detection resistor, the inverse PID current, and the detection current.

[0010] In one possible implementation, the detection resistor is configured to be engaged in operation when the inverse PID circuit is running, so as to allow the detection current to flow.

[0011] In one possible implementation, the inverse PID power supply is configured to output different inverse PID currents when the inverse PID circuit is operating.

[0012] And / or, the insulation detection device is specifically configured to: when the inverse PID circuit is running, engage different detection resistors within the insulation detection device.

[0013] In one possible implementation, the control unit is specifically configured to calculate the ground insulation impedance based on the resistance value of the detection resistor, the anti-PID current, and the detection current, when at least one of the inverse PID current and the detection resistor has different values.

[0014] In one possible implementation, the photovoltaic conversion system further includes: at least one DC / DC conversion circuit;

[0015] One side of the DC / DC converter circuit is used to connect to the corresponding photovoltaic power source, and the other side of the DC / DC converter circuit is connected to the DC side of the DC / AC converter circuit.

[0016] In one possible implementation, the anti-PID circuit is connected between the DC side of the DC / AC converter circuit and ground, or between the AC side of the DC / AC converter circuit and ground.

[0017] In one possible implementation, the AC side of the DC / AC conversion circuit is connected in sequence to at least one of the power grid and the load via an AC switch and a transformer;

[0018] One end of the insulation detection device is grounded, and the other end of the insulation detection device is connected to any of the following locations: the positive terminal of the DC side of the DC / AC conversion circuit, the negative terminal of the DC side of the DC / AC conversion circuit, the neutral point of the DC side of the DC / AC conversion circuit, between the AC side of the DC / AC conversion circuit and the AC switch, between the AC switch and the low-voltage coil of the transformer, and the neutral point of the low-voltage side of the transformer.

[0019] The second aspect of this disclosure provides an insulation testing method for a photovoltaic conversion system, comprising:

[0020] When the anti-PID circuit is operating in the photovoltaic conversion system, the anti-PID power supply inside the anti-PID circuit is controlled to output an anti-PID current.

[0021] Switch the detection resistor inside the insulation detection device in the photovoltaic conversion system so that a detection current flows through the insulation detection device;

[0022] The ground insulation impedance of the photovoltaic conversion system is calculated based on the resistance value of the detection resistor, the inverse PID current, and the detection current.

[0023] In one possible implementation, switching the detection resistor inside the insulation detection device in the photovoltaic conversion system includes: controlling the detection resistor to be put into operation.

[0024] In one possible implementation, controlling the output of an anti-PID current from the anti-PID power supply inside the anti-PID circuit includes: controlling the output of different anti-PID currents from the anti-PID power supply.

[0025] And / or, switching the detection resistor inside the insulation detection device in the photovoltaic conversion system, including: switching on different detection resistors inside the insulation detection device respectively.

[0026] In one possible implementation, calculating the ground insulation impedance of the photovoltaic conversion system based on the resistance value of the detection resistor, the inverse PID current, and the detection current includes: calculating the ground insulation impedance based on the resistance value of the detection resistor, the inverse PID current, and the detection current when at least one of the inverse PID current and the detection resistor has different values.

[0027] A third aspect of this disclosure provides a controller for performing an insulation detection method for a photovoltaic conversion system as described in the second aspect or any implementation thereof.

[0028] The photovoltaic conversion system provided in this disclosure, when the anti-PID circuit is running, outputs an anti-PID current from the anti-PID power supply inside the anti-PID circuit, and switches the internal detection resistor through the IMD so that the detection current flows through the IMD; then, the control unit calculates the ground insulation impedance of the photovoltaic conversion system based on the resistance value of the detection resistor, the anti-PID current and the detection current, thereby completing the insulation detection while realizing the anti-PID function. Attached Figure Description

[0029] The features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. Throughout the drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and elements and actual parts are not necessarily drawn to scale.

[0030] Figure 1 This is a schematic diagram of a first structure of a photovoltaic conversion system provided in an embodiment of the present disclosure;

[0031] Figure 2 This is a schematic diagram of a second structure of a photovoltaic conversion system provided in an embodiment of this disclosure;

[0032] Figure 3 This is a schematic diagram of a third structure of the photovoltaic conversion system provided in the embodiments of this disclosure;

[0033] Figure 4 This is a schematic diagram of a fourth specific structure of the photovoltaic conversion system provided in the embodiments of this disclosure;

[0034] Figure 5 This is a schematic diagram of a fifth specific structure of the photovoltaic conversion system provided in the embodiments of this disclosure;

[0035] Figure 6 This is a schematic diagram of a specific structure of a photovoltaic conversion system provided in an embodiment of the present disclosure;

[0036] Figure 7 This is another specific structural schematic diagram of the photovoltaic conversion system provided in the embodiments of this disclosure;

[0037] Figure 8 A schematic diagram of yet another specific structure of the photovoltaic conversion system provided in the embodiments of this disclosure;

[0038] Figure 9 This is a flowchart of an insulation testing method for a photovoltaic conversion system provided in an embodiment of the present disclosure. Detailed Implementation

[0039] The embodiments of this disclosure are described below with reference to the accompanying drawings. The terminology used in the Description of Embodiments section of this disclosure is for illustrative purposes only and is not intended to limit the scope of this disclosure.

[0040] The embodiments of this disclosure are described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure. Those skilled in the art will understand that with the development of technology and the emergence of new scenarios, the technical solutions provided by the embodiments of this disclosure are also applicable to similar technical problems.

[0041] The terms “first,” “second,” etc., used in this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms are interchangeable where appropriate; this is merely a way of distinguishing objects with the same attributes in the description of embodiments of this disclosure. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion, so that a process, method, system, product, or apparatus that comprises a series of units is not necessarily limited to those units, but may include other units not expressly listed or inherent to those processes, methods, products, or apparatuses.

[0042] In the process of photovoltaic power generation, the photovoltaic inverter converts the energy of the photovoltaic module into a sinusoidal current with the same frequency and phase as the grid and feeds it into the grid. Due to the inherent characteristics of the photovoltaic module, a PID effect will be generated on the photovoltaic module in this process, which will gradually reduce its working performance and eventually lead to the loss of power generation capacity. Therefore, the photovoltaic inverter needs to suppress this effect during operation. Specifically, this can be achieved by adding an anti-PID circuit to the photovoltaic inverter or setting the DC side to be directly grounded.

[0043] However, during the anti-PID operation of a photovoltaic inverter, the grounding loop prevents the detection of the system's ground insulation impedance, causing a conflict between insulation monitoring and anti-PID. According to the requirements of IEC (International Electrotechnical Commission) standards, the IMD (Insulation Monitoring Device) installed on the AC side of the photovoltaic inverter needs to be able to operate 24 hours a day for AC insulation detection. Therefore, a method for AC insulation detection that can operate around the clock is needed.

[0044] Traditional solutions for 24-hour AC insulation testing rely on the time-sharing operation of an inverse PID circuit and an insulation monitoring device (IMD) to achieve pseudo-24-hour protection logic. That is, when switching to standalone inverse PID operation, the insulation protection function of the IMD is lost, and when switching to IMD for insulation testing, the inverse PID function is no longer available. Therefore, traditional solutions cannot meet IEC standard requirements.

[0045] Therefore, this disclosure provides a photovoltaic conversion system that performs insulation detection while implementing the inverse PID function. The specific solution is as follows:

[0046] like Figure 1 As shown, the photovoltaic conversion system includes: a DC / AC conversion circuit 101, an inverse PID circuit 102, an IMD circuit 103, and a control unit; wherein:

[0047] The DC side of the DC / AC conversion circuit 101 is used to directly or indirectly connect to the photovoltaic power source PV. The specific connection relationship can be found in the following description. The photovoltaic power source PV may include a photovoltaic string or at least two photovoltaic strings connected in parallel. The photovoltaic string includes a photovoltaic module or at least two photovoltaic modules connected in series.

[0048] The AC side of the DC / AC conversion circuit 101 is used to connect to at least one of the power grid and the load. In practical applications, the AC side of the DC / AC conversion circuit 101 can be connected to at least one of the power grid and the load in sequence through the AC switch 104 and the transformer 105. The load can refer to local loads or other loads besides the power grid. For specific descriptions of the power grid and the load, please refer to relevant technologies, which will not be elaborated here.

[0049] The inverse PID circuit 102 is located on the DC side or AC side of the DC / AC conversion circuit 101, and the IMD 103 is located on the DC side or AC side of the DC / AC conversion circuit 101. There is no limitation here. For details, please refer to the description below.

[0050] Furthermore, the inverse PID circuit 102 is configured such that, when the inverse PID circuit 102 is operating, an inverse PID current is output from the inverse PID power supply inside the inverse PID circuit 102. That is, the inverse PID circuit 102 includes an inverse PID power supply, the specific structure of which can be found in related technologies and is not limited here, as long as the inverse PID power supply can output a certain inverse PID current when the inverse PID circuit 102 is operating.

[0051] The IMD 103 is configured to switch the internal sensing resistor when the inverse PID circuit 102 is running, so that a sensing current flows through the IMD 103. That is, the IMD 103 includes an internal sensing resistor, the specific structure of which can be found below; when the inverse PID circuit 102 is running, the internal sensing resistor of the IMD 103 is switched, thereby allowing a certain sensing current to flow.

[0052] Since both the inverse PID circuit 102 and IMD 103 are grounded, the difference between the inverse PID current output by the inverse PID power supply and the detection current flowing through IMD 103 can be considered as the ground insulation impedance Rx flowing through the photovoltaic conversion system. Ignoring the difference in the connection positions of IMD 103 and the ground insulation impedance Rx in the photovoltaic conversion system, the voltage across IMD 103 and the voltage across the ground insulation impedance Rx can be considered approximately equal. Furthermore, the resistance value of the internal detection resistor of IMD 103 is known. Combined with the detection current, the voltage across IMD 103 can be calculated. Then, combined with the difference between the inverse PID current and the detection current, the ground insulation impedance Rx of the photovoltaic conversion system can be calculated. Therefore, the control unit can be configured to calculate the ground insulation impedance Rx of the photovoltaic conversion system based on the resistance value of the detection resistor, the inverse PID current, and the detection current.

[0053] In the photovoltaic conversion system provided in this embodiment, when the inverse PID circuit 102 is running, the inverse PID power supply inside the inverse PID circuit 102 outputs an inverse PID current, and switches the internal detection resistor through the IMD 103 so that a detection current flows through the IMD 103; then, the control unit calculates the ground insulation impedance Rx of the photovoltaic conversion system based on the resistance value of the detection resistor, the inverse PID current and the detection current, thereby completing the insulation detection while realizing the inverse PID function.

[0054] In practical applications, the inverse PID circuit 102 can be connected between the DC side of the DC / AC converter circuit 101 and ground (e.g., Figure 1 or Figure 2 (as shown in the diagram), or, the inverse PID circuit 102 can also be connected between the AC side of the DC / AC converter circuit 101 and ground (as shown in the diagram). Figure 3 or Figure 4 As shown in the image).

[0055] Additionally, IMD 103 can be connected between either side of the DC / AC converter circuit 101 and ground; for example, on the DC side of the DC / AC converter circuit 101, IMD 103 can be directly connected between the negative terminal and ground, the positive terminal and ground, or the neutral point and ground, or it can indirectly change the voltage to ground of the negative terminal, positive terminal, or neutral point through other means; on the AC side of the DC / AC converter circuit 101, IMD 103 can be connected to ground at any specific location, such as between the system inverter side and ground or between the low-voltage side neutral point of transformer 105 and ground. When the AC side of the DC / AC converter circuit 101 is connected to the power grid sequentially through AC switch 104 and transformer 105, and as... Figures 1 to 4As shown, transformer 105 includes a low-voltage coil 151 and a high-voltage coil 152; wherein, low-voltage coil 151 is the coil for connecting to the low-voltage side, specifically used to connect to the AC side of DC / AC converter circuit 101 via AC switch 104; high-voltage coil 152 is the coil for connecting to the high-voltage side, specifically used to connect to at least one of the power grid and the load; at this time, one end of IMD 103 is grounded, and the other end of IMD 103 can be connected to any of the following optional positions: the positive terminal of DC side of DC / AC converter circuit 101 (not shown), the negative terminal of DC side of DC / AC converter circuit 101 (e.g., ...). Figure 2 or Figure 4 As shown), the DC-side neutral point of the DC / AC converter circuit 101 (not shown), the AC side of the DC / AC converter circuit 101 and the AC switch 104 (not shown), and the AC switch 104 and the low-voltage coil 151 of the transformer 105 (as shown). Figure 1 or Figure 3 As shown in the figure), and the low-voltage side neutral point of transformer 105 (not shown); it can be determined according to the specific application environment, and is not limited here.

[0056] Furthermore, under the various connection relationships mentioned above, such as Figure 5 (in) Figure 2 As shown in the example based on the connection relationship shown, the photovoltaic conversion system can also be further equipped with at least one DC / DC conversion circuit 106 located before the DC / AC conversion circuit 101; one side of the DC / DC conversion circuit 106 is used to connect to the corresponding photovoltaic power source PV, and the other side of the DC / DC conversion circuit 106 is connected to the DC side of the DC / AC conversion circuit 101, thereby forming a two-stage photovoltaic conversion system; the position settings of the inverse PID circuit 102 and IMD 103 under this structure can be referred to the above description, and will not be repeated here.

[0057] In practical applications, the DC / AC conversion circuit 101, the inverse PID circuit 102, and the IMD 103 can be integrated into the photovoltaic inverter. For a two-stage photovoltaic conversion system, the DC / DC conversion circuit 106 can be independent of the photovoltaic inverter and integrated into the DC / DC converter, thus forming a distributed photovoltaic conversion system; alternatively, the DC / DC conversion circuit 106 can also be integrated into a string photovoltaic inverter, which may include one or at least two string photovoltaic inverters connected in parallel on the AC side; the choice depends on the specific application environment and is not limited here. Furthermore, each device in the photovoltaic inverter can be controlled by a corresponding inverter controller, which can be independent of the photovoltaic inverter or integrated into it; the control unit that implements the above-mentioned ground insulation impedance Rx calculation function can be independent of the inverter controller or integrated into it; the choice depends on the specific application environment and is not limited here.

[0058] Based on the above embodiments, this embodiment illustrates the specific process of calculating the ground insulation impedance Rx of the photovoltaic conversion system, for example:

[0059] The aforementioned detection resistor is configured to be engaged in operation when the inverse PID circuit 102 is running, so as to allow the detection current to flow.

[0060] like Figure 6 (in) Figure 1 As shown in the example (based on the situation illustrated), IMD 103 includes: a switch K and a sensing resistor R connected in series; the other end of the sensing resistor R is connected to any phase of the AC side of the DC / AC converter circuit 101. When the inverse PID circuit 102 is running, closing the control switch K activates the sensing resistor R. In practical applications, the sensing resistor R may include one resistor or at least two resistors connected in series, which is not limited here; the series connection order of the switch K and the sensing resistor R is not limited, this is just one possible example.

[0061] Or, such as Figure 7 (in) Figure 1As shown in the example (based on the situation illustrated), IMD 103 includes: a switch K and three sensing resistors Ra, Rb, and Rc; one end of each sensing resistor Ra, Rb, and Rc is connected to a corresponding phase of the AC side of the DC / AC converter circuit 101, and the other ends of each sensing resistor Ra, Rb, and Rc are connected in parallel and then in series with the switch K. When the inverse PID circuit 102 is running, the control switch K is closed, so that each sensing resistor Ra, Rb, and Rc is put into the running state. In practical applications, each sensing resistor Ra, Rb, and Rc may each include one resistor or at least two resistors connected in series, which is not limited here. Alternatively, the switch K can be replaced with a switch in which each sensing resistor Ra, Rb, and Rc are connected in series, which is not illustrated here, and all are within the protection scope of this disclosure.

[0062] by Figure 6 Taking the structure shown as an example, when the inverse PID circuit 102 is running, switch K is closed. After the inverse PID current output by the inverse PID power supply and the detection current on the detection resistor R are both stable, the steady-state value I of the inverse PID current is recorded respectively. PID and the steady-state value I of the detection current IMD The control unit can simply calculate the system-to-ground insulation impedance Rx using the following formula:

[0063] .

[0064] In practical applications, if the IMD 103 does not have a corresponding current sensor, the voltage Ur at the location where the IMD 103 is connected in the system can be used to calculate the current using formula I. IMD =Ur / R to deduce the steady-state value I of the detected current. IMD There are no restrictions here; it depends on the specific application environment.

[0065] for Figure 7 The structure shown is equivalent to the parallel impedance of the three sensing resistors Ra, Rb, and Rc through which the sensing current flows. Therefore, the formula for calculating the system's insulation impedance to ground, Rx, becomes:

[0066] .

[0067] This embodiment, based on traditional inverse PID operation, only requires external expansion of the aforementioned detection resistor and switching it on and off. Under ISO (Insulation System Oversight) steady-state conditions, the system's ground insulation impedance Rx can be easily calculated. Moreover, this IMD 103 does not require a related control power supply, resulting in lower cost.

[0068] In another example, the photovoltaic conversion system can also accurately calculate the ground insulation impedance Rx through ISO perturbation. Specifically, there are three possible settings:

[0069] (1) When the inverse PID power supply is running, it outputs different inverse PID currents; while the IMD103 keeps the same detection resistor connected.

[0070] (2) When the inverse PID circuit 102 is running, different detection resistors are connected inside the IMD 103 respectively; while the inverse PID power supply maintains the same inverse PID current output.

[0071] (3) Set the inverse PID power supply to output different inverse PID currents when the inverse PID circuit 102 is running; and set the IMD 103 to connect different detection resistors inside the IMD 103 when the inverse PID circuit 102 is running.

[0072] Regardless of which setting is used, the control unit can be specifically configured to calculate the ground insulation impedance Rx by solving a system of equations based on the resistance value of the detection resistor, the inverse PID current, and the detection current, when at least one of the inverse PID current and the detection resistor has different values.

[0073] Taking the case where the structure adopts the above-mentioned third setting as an example, such as Figure 8 (in) Figure 1 (As illustrated in the example shown), the IMD 103 includes two parallel branches. One branch includes a first detection resistor R1 and a first switch K1 connected in series, and the other branch includes a second detection resistor R2 and a second switch K2 connected in series. The specific calculation process for the ground insulation impedance Rx can then be:

[0074] When the inverse PID circuit 102 is running, the first switch K1 is closed, and the first detection resistor R1 is connected in the IMD 103; after the current stabilizes, the steady-state value I of the inverse PID current is recorded. PID-1 and the steady-state value I of the detection current IMD-1 As described in the above embodiments, the voltage Ur1 at the location where IMD 103 is connected in the system can also be used to calculate the voltage according to formula I. IMD-1 =Ur1 / R1 to deduce the steady-state value I of the detection current. IMD-1 At this point, the following formula can be written:

[0075] .

[0076] Wherein, ΔU is the difference between the voltage on IMD 103 and the voltage on the ground insulation impedance Rx, which depends on the location of IMD 103 in the system and its specific value is not limited.

[0077] Disconnecting the first switch K1 and closing the second switch K2 will switch IMD 103 to connect the second resistor R2; after the current stabilizes, record the steady-state value I of the inverse PID current. PID-2 and the steady-state value I of the detection current IMD-2 Alternatively, the voltage Ur2 at the location where IMD 103 is connected in the system can be used to calculate formula I. IMD-2 The steady-state value I of the detection current can be deduced by using Ur² / R². IMD-2 At this point, the following formula can be written:

[0078] .

[0079] Since the location of IMD 103 within the system remains unchanged, the value of ΔU also remains unchanged.

[0080] Combining the above two equations, we can obtain:

[0081] .

[0082] In practical applications, one of the inverse PID current and the sensing resistor can be kept constant, while the other is set as a disturbance parameter. The ground insulation impedance Rx can still be calculated using the above combined process. For example, when using the first setting above, that is, only the inverse PID current is set as the disturbance parameter, while the sensing resistor remains unchanged, then R1=R2 in the formula for calculating the ground insulation impedance Rx. When using the second setting above, that is, only the sensing resistor is set as the disturbance parameter, while the inverse PID current remains unchanged, then I in the formula for calculating the ground insulation impedance Rx PID-1 =I PID-2 That's it; the calculation process for both will not be elaborated here, and insulation detection can be completed while implementing the inverse PID function.

[0083] Another embodiment of this disclosure also provides an insulation detection method for a photovoltaic conversion system, such as... Figure 9 As shown, it includes:

[0084] S11. When the anti-PID circuit is running in the photovoltaic conversion system, control the output of the anti-PID power supply inside the anti-PID circuit to output the anti-PID current.

[0085] S12. Switch the detection resistor inside the IMD in the photovoltaic conversion system so that a detection current flows through the IMD.

[0086] S13. Calculate the ground insulation impedance of the photovoltaic conversion system based on the inverse PID current and the detection current.

[0087] The specific structure and working principle of the photovoltaic conversion system can be found in the above embodiments, and will not be repeated here.

[0088] The insulation detection method for the photovoltaic conversion system provided in this embodiment, when the inverse PID circuit is running, outputs an inverse PID current from the inverse PID power supply inside the inverse PID circuit, and switches the internal detection resistor through the IMD so that the detection current flows through the IMD; then, the control unit calculates the ground insulation impedance of the photovoltaic conversion system based on the inverse PID current and the detection current, thereby realizing the insulation detection while implementing the inverse PID function, so that the inverse PID function and the insulation detection function are compatible.

[0089] Based on the above embodiments, the insulation detection method for this photovoltaic conversion system can achieve insulation detection in different specific ways while implementing inverse PID operation. Specifically:

[0090] In one example, ISO steady-state detection can be used to perform a simple calculation of the insulation impedance to ground. In this case, switching the detection resistor inside the IMD in the photovoltaic conversion system in S12 can specifically include: controlling the detection resistor to be put into operation. And in S13, the insulation impedance to ground of the photovoltaic conversion system is calculated based on the inverse PID current and the detection current. Specifically, this can include: calculating the insulation impedance to ground based on the inverse PID current and the detection current.

[0091] In another example, ISO disturbance detection can also be used to accurately calculate the insulation impedance to ground; in this case, the anti-PID power supply inside the anti-PID control circuit in S11 outputs an anti-PID current, which may specifically include: controlling the anti-PID power supply to output different anti-PID currents; and / or, switching the detection resistor inside the IMD in the photovoltaic conversion system in S12 may specifically include: switching on different detection resistors inside the IMD respectively.

[0092] At this point, S13 calculates the ground insulation impedance of the photovoltaic conversion system based on the inverse PID current and the detection current. Specifically, it can include calculating the ground insulation impedance by solving a system of equations when at least one of the inverse PID current and the detection resistance has different values.

[0093] In practical applications, the appropriate insulation testing method can be selected based on the required accuracy of the insulation impedance to ground and the testing speed. No limitation is made here, and all are within the protection scope of this disclosure.

[0094] Another embodiment of this disclosure provides a controller for executing the insulation detection method for a photovoltaic conversion system as described in any of the above embodiments. The specific process and principle of this insulation detection method can be found in the above embodiments, and will not be repeated here.

[0095] The controller provided in this disclosure may include software to implement the insulation detection method for the photovoltaic conversion system described above. Alternatively, the controller provided in this disclosure may include hardware to implement the insulation detection method for the photovoltaic conversion system described above. Or, the controller provided in this disclosure may include both software and hardware, using a combination of software and hardware to execute the insulation detection method for the photovoltaic conversion system described above. For example, the controller may be composed of one or more of the following: ARM (Advanced RISC Machines), FPGA (Field-Programmable Gate Array), PLC (Programmable Logic Controller), DSP (Digital Signal Processor), CPU (Central Processing Unit), MCU (Microcontroller Unit), CPLD (Complex Programmable Logic Device), and ASIC (Application Specific Integrated Circuits); depending on the specific application environment, no specific limitation is made here, and all are within the protection scope of this disclosure.

[0096] In practical applications, this controller can specifically serve as the control unit of the photovoltaic conversion system described in the above embodiments to implement the insulation detection method. Furthermore, this control unit can be independent of the photovoltaic inverter controller or integrated into it, depending on the specific application environment, and all are within the scope of this disclosure.

[0097] The controller provided in this embodiment can perform insulation detection while implementing the insulation detection method of the photovoltaic conversion system, thus making the anti-PID function and the insulation detection function compatible.

[0098] Similar or identical parts between the various embodiments in this disclosure can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment solution according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0099] Those skilled in the art will also recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this disclosure.

[0100] The above description of the disclosed embodiments shows that the features described in the various embodiments of this disclosure can be substituted for or combined with each other, enabling those skilled in the art to implement or use this disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A photovoltaic conversion system, characterized in that, include: DC / AC conversion circuit, inverse PID circuit, insulation monitoring device, and control unit; among which... The DC side of the DC / AC conversion circuit is used to connect to a photovoltaic power source; The AC side of the DC / AC conversion circuit is used to connect at least one of the power grid and the load; The anti-PID circuit is located on the DC side or AC side of the DC / AC conversion circuit, and the anti-PID circuit is configured to output an anti-PID current from the internal anti-PID power supply when the anti-PID circuit is running. The insulation monitoring device is located on the DC side or AC side of the DC / AC conversion circuit. The insulation detection device is configured to switch the detection resistor inside the insulation detection device when the inverse PID circuit is running, so that a detection current flows through the insulation detection device. The control unit is configured to calculate the ground insulation impedance of the photovoltaic conversion system based on the resistance value of the detection resistor, the inverse PID current, and the detection current.

2. The photovoltaic conversion system according to claim 1, characterized in that, The detection resistor is configured to be engaged in operation when the inverse PID circuit is running, so as to allow the detection current to flow.

3. The photovoltaic conversion system according to claim 1, characterized in that, The inverse PID power supply is configured to output different inverse PID currents when the inverse PID circuit is running. And / or, the insulation detection device is specifically configured to: when the inverse PID circuit is running, engage different detection resistors within the insulation detection device.

4. The photovoltaic conversion system according to claim 3, characterized in that, The control unit is specifically configured to calculate the ground insulation impedance based on the resistance value of the detection resistor, the anti-PID current, and the detection current when at least one of the inverse PID current and the detection resistor has different values.

5. The photovoltaic conversion system according to any one of claims 1 to 4, characterized in that, The photovoltaic conversion system further includes: at least one DC / DC conversion circuit; One side of the DC / DC converter circuit is used to connect to the corresponding photovoltaic power source, and the other side of the DC / DC converter circuit is connected to the DC side of the DC / AC converter circuit.

6. The photovoltaic conversion system according to any one of claims 1 to 4, characterized in that, The inverse PID circuit is connected between the DC side of the DC / AC conversion circuit and ground, or between the AC side of the DC / AC conversion circuit and ground.

7. The photovoltaic conversion system according to any one of claims 1 to 4, characterized in that, The AC side of the DC / AC conversion circuit is connected to at least one of the power grid and the load in sequence through an AC switch and a transformer; One end of the insulation detection device is grounded, and the other end of the insulation detection device is connected to any of the following locations: the positive terminal of the DC side of the DC / AC conversion circuit, the negative terminal of the DC side of the DC / AC conversion circuit, the neutral point of the DC side of the DC / AC conversion circuit, between the AC side of the DC / AC conversion circuit and the AC switch, between the AC switch and the low-voltage coil of the transformer, and the neutral point of the low-voltage side of the transformer.

8. An insulation testing method for a photovoltaic conversion system, characterized in that, include: When the anti-PID circuit is operating in the photovoltaic conversion system, the anti-PID power supply inside the anti-PID circuit is controlled to output an anti-PID current. Switch the detection resistor inside the insulation detection device in the photovoltaic conversion system so that a detection current flows through the insulation detection device; The ground insulation impedance of the photovoltaic conversion system is calculated based on the resistance value of the detection resistor, the inverse PID current, and the detection current.

9. The insulation testing method for a photovoltaic conversion system according to claim 8, characterized in that, Switching the detection resistor inside the insulation detection device in the photovoltaic conversion system includes: controlling the detection resistor to be put into operation.

10. The insulation detection method for a photovoltaic conversion system according to claim 8, characterized in that, Controlling the output of the inverse PID current from the inverse PID power supply inside the inverse PID circuit includes: controlling the output of different inverse PID currents from the inverse PID power supply; And / or, switching the detection resistor inside the insulation detection device in the photovoltaic conversion system, including: switching on different detection resistors inside the insulation detection device respectively.

11. The insulation detection method for a photovoltaic conversion system according to claim 10, characterized in that, The ground insulation impedance of the photovoltaic conversion system is calculated based on the resistance value of the detection resistor, the inverse PID current, and the detection current, including: when at least one of the inverse PID current and the detection resistor has different values, the ground insulation impedance is calculated based on the resistance value of the detection resistor, the inverse PID current, and the detection current.

12. A controller, characterized in that, An insulation testing method for performing a photovoltaic conversion system as described in any one of claims 8 to 11.

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