Photovoltaic system insulation detection method and device, controller and photovoltaic system

Abstract

The invention provides an insulation detection method and device of a photovoltaic system, a controller and the photovoltaic system. The method comprises the following steps: detecting whether the photovoltaic system has an insulation fault; if the photovoltaic system has the insulation fault, determining the position of the insulation fault in the fault photovoltaic string according to the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string; the first electrode is any one of a direct-current bus positive electrode and a direct-current bus negative electrode; and respectively and independently controlling the positive and negative electrodes of the input end of each direct current conversion circuit to be short-circuited, and for each MPPT module, determining whether the insulation fault position is located in the MPPT module based on the change of the voltage to ground of the first electrode before and after the short circuit of the MPPT module. According to the photovoltaic system insulation fault detection method and the photovoltaic system insulation fault detection device, insulation faults from a system level to a component level can be spanned, additional devices are not needed, manpower, time and economic cost required by field troubleshooting is reduced, and the detection efficiency of the photovoltaic system insulation faults is improved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic system technology, and in particular to an insulation detection method, device, controller, and photovoltaic system for a photovoltaic system. Background Technology

[0002] Insulation testing of photovoltaic systems is a key step in ensuring the safe and stable operation of photovoltaic systems. It can effectively prevent leakage risks caused by string insulation failure, prevent short circuits and arc discharges caused by insulation degradation, reduce equipment damage such as junction box burnout and cable aging, and extend the service life of photovoltaic systems.

[0003] To detect insulation fault types at the string level in photovoltaic systems, current technologies typically require maintenance personnel to bring specialized equipment (such as insulation megohmmeters and thermal imagers) to the site to inspect each string and each component. This consumes a significant amount of manpower, time, and transportation costs, resulting in a cumbersome testing process, long testing time, and low efficiency in string-level insulation fault detection. Summary of the Invention

[0004] This invention provides an insulation detection method, device, controller, and photovoltaic system for photovoltaic systems, to solve the problem of low efficiency in string-level insulation fault detection in the prior art.

[0005] In a first aspect, embodiments of the present invention provide an insulation detection method for a photovoltaic system, applied to a photovoltaic system; the photovoltaic system includes multiple MPPT modules; each MPPT module includes a photovoltaic string and a DC-DC converter circuit; each photovoltaic string is connected to the input terminal of its corresponding DC-DC converter circuit, the positive output terminal of each DC-DC converter circuit is connected to the positive terminal of a DC bus, and the negative output terminal of each DC-DC converter circuit is connected to the negative terminal of a DC bus; the method includes: Detect whether the photovoltaic system has an insulation fault; If an insulation fault occurs in the photovoltaic system, the location of the insulation fault in the photovoltaic string is determined based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string; the first pole is either the positive pole or the negative pole of the DC bus. Each DC-DC converter circuit is individually controlled to short-circuit the positive and negative terminals of its input terminals. For each MPPT module, the location of the insulation fault is determined based on the change in the voltage of the first terminal to ground before and after the short circuit.

[0006] Secondly, embodiments of the present invention provide an insulation detection device for a photovoltaic system, which is applied to a photovoltaic system; the photovoltaic system includes multiple MPPT modules; each MPPT module includes a photovoltaic string and a DC-DC converter circuit; each photovoltaic string is connected to the input terminal of its corresponding DC-DC converter circuit, the positive output terminal of each DC-DC converter circuit is connected to the positive terminal of the DC bus, and the negative output terminal of each DC-DC converter circuit is connected to the negative terminal of the DC bus. The device includes: a system insulation fault detection module, used to detect whether an insulation fault has occurred in the photovoltaic system; An insulation fault location determination module is used to determine the location of the insulation fault in the photovoltaic string based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string if an insulation fault occurs in the photovoltaic system; the first pole is either the positive pole or the negative pole of the DC bus. The MPPT module positioning module is used to individually control the positive and negative short circuits of the input terminals of each DC-DC converter circuit, and for each MPPT module, based on the change of the first pole to ground voltage before and after the short circuit, determine whether the insulation fault location is located in that MPPT module.

[0007] Thirdly, embodiments of the present invention provide a controller, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the insulation detection method for the photovoltaic system as described in any possible implementation of the first aspect above.

[0008] Fourthly, this embodiment provides a photovoltaic system, which includes: a photovoltaic string and a controller as described in the third aspect above.

[0009] This invention provides an insulation detection method, device, controller, and photovoltaic system for photovoltaic systems. The method calculates the ratio of the voltage to ground of the first electrode to the open-circuit voltage of the string, enabling rapid estimation of the location of the insulation fault point within the faulty string. This provides maintenance personnel with a clear module-level search range, significantly reducing the scope of manual troubleshooting. Secondly, by sequentially and individually short-circuiting the input terminals of each DC-DC converter circuit and observing the changes in the system's voltage to ground, the specific faulty MPPT module can be accurately located, thus determining which photovoltaic string has failed. The combination of these two steps achieves a leap from system-level insulation faults to module-level insulation faults without requiring additional components, significantly reducing the manpower, time, and economic costs required for on-site troubleshooting and improving the detection efficiency of insulation faults in photovoltaic systems. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a schematic diagram of the specific structure of the photovoltaic system provided in the embodiment of the present invention; Figure 2 This is a flowchart illustrating the implementation of the insulation detection method for a photovoltaic system provided in this embodiment of the invention. Figure 3 This is a schematic diagram of the structure of the insulation detection device for a photovoltaic system provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the controller provided in an embodiment of the present invention. Detailed Implementation

[0012] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0013] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0014] In one embodiment, Figure 1 This embodiment shows a schematic diagram of the specific structure of the photovoltaic system provided, as follows: Figure 1 As shown, the photovoltaic system includes multiple MPPT (Maximum Power Point Tracking) modules (MPPT1 to MPPT4); each MPPT module includes a photovoltaic string and a DC-DC converter circuit (110 to 410); each photovoltaic string is connected to the input terminal of its corresponding DC-DC converter circuit, the positive output terminal of each DC-DC converter circuit is connected to the positive terminal BUS+ of the DC bus, and the negative output terminal of each DC-DC converter circuit is connected to the negative terminal BUS- of the DC bus; the positive and negative terminals of the DC bus are also connected to the positive and negative input terminals of the inverter 20, respectively.

[0015] In existing technologies, insulation fault detection for the aforementioned photovoltaic systems typically involves maintenance personnel carrying insulation resistance testers or thermal imagers for on-site inspection. These personnel require extensive experience to determine how to segment the system, where to measure, and how to interpret complex environmental thermal images. This process is not only cumbersome and inefficient, but also highly prone to misjudgments or missed detections in large, structurally similar photovoltaic arrays.

[0016] This embodiment addresses the problem of low insulation detection efficiency in existing photovoltaic systems by providing an insulation detection method. (See [link to relevant documentation]). Figure 2 The diagram illustrates the implementation flowchart of the insulation detection method for a photovoltaic system provided in this embodiment of the invention. This method is applied to the controller in the photovoltaic system, and is described in detail below: S101: Detect whether the photovoltaic system has an insulation fault.

[0017] Specifically, before performing precise location of insulation faults, this embodiment first uses the existing insulation detection function of the photovoltaic system to detect whether an insulation fault has occurred in the entire photovoltaic system. If an insulation fault has occurred, the subsequent precise location operation is performed; otherwise, no action is taken.

[0018] In one possible implementation, the photovoltaic system further includes an inverter; the input terminal of the inverter is connected to the DC bus; the specific implementation process of S101 includes: The voltage to ground of the first pole is detected by the insulation detection module of the inverter; If the difference between the voltage to ground of the first pole and the voltage of the half busbar is greater than the second preset voltage threshold, then the photovoltaic system is determined to have an insulation fault.

[0019] In this embodiment, under normal circumstances, the photovoltaic (PV) string is suspended above ground potential. Since there is no direct conductive path, both the positive terminal BUS+ and the negative terminal BUS- of the DC bus have a voltage relative to ground. The parasitic impedance of the PV modules to ground is very large and symmetrical, and the chassis ground and neutral point N potential are close. Taking BUS- as the first terminal, the voltage of BUS- to ground (i.e., the insulation voltage) is approximately half the bus voltage. When an insulation fault occurs in a PV string, the fault point (the location of the insulation fault) is grounded, forcibly clamping the potential of that point to ground potential. This forms a clear voltage divider circuit: the voltage of the PV modules above the fault point is applied between BUS+ and ground, while the voltage of the PV modules below the fault point is applied between BUS- and ground. At this time, the voltage of BUS- to ground is no longer half the bus voltage, but rather the sum of the voltages of all PV modules below the fault point. Therefore, this embodiment utilizes the existing insulation detection module (or function) in the inverter to monitor the voltage to ground of a specific terminal of the DC bus. The system compares the real-time measured voltage to ground with the theoretically fault-free half-bus voltage. If the absolute value of the difference between the two values ​​is greater than a second preset voltage threshold, an insulation fault is determined to have occurred in the photovoltaic system.

[0020] The inverter's insulation detection module is a circuit used to monitor the DC-side insulation status to ground. It is typically based on the unbalanced bridge principle or high-frequency signal injection method, and can directly or indirectly measure the voltage to ground. In an ideal, floating, symmetrically insulated, fault-free photovoltaic system, the voltages to ground of the positive and negative terminals of the DC bus are equal, both being half of the total bus voltage.

[0021] In one embodiment, this embodiment can also calculate the percentage value of the voltage to ground of the first pole deviating from the half bus voltage. If the percentage value is greater than a preset ratio, it is determined that an insulation fault has occurred in the photovoltaic system.

[0022] As can be seen from the above embodiments, this embodiment realizes the preliminary insulation detection function of the photovoltaic system through the inverter's inherent insulation detection module. Only when the deviation between the first pole-to-ground voltage and the ideal half-bus voltage exceeds a second preset voltage threshold is the subsequent complex insulation fault location process initiated. This ensures that the system only invests diagnostic resources when truly necessary, avoiding unnecessary calculations and operations. Secondly, the setting of the second preset voltage threshold can play an anti-interference role, preventing frequent triggering of the insulation fault location program due to normal, minor potential fluctuations.

[0023] S102: If an insulation fault occurs in the photovoltaic system, the location of the insulation fault in the photovoltaic string is determined according to the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string; the first pole is either the positive pole or the negative pole of the DC bus.

[0024] In this embodiment, the voltage to ground of the first pole can be either the DC bus positive pole voltage to ground or the DC bus negative pole voltage to ground. In the standby state before grid connection after the photovoltaic converter starts up, the controller first detects the open-circuit voltage between the positive and negative poles of the DC bus using a voltage sensor, and uses this as the open-circuit voltage of the photovoltaic string. Since photovoltaic modules can be equivalent to diodes, the voltage across each photovoltaic module can be considered consistent. Therefore, the open-circuit voltage of the photovoltaic string is the product of the voltage across each photovoltaic module in the string and the number of photovoltaic modules.

[0025] When an insulation fault occurs in the photovoltaic string, for example Figure 1 If an insulation fault occurs between the second and third photovoltaic modules starting from the positive output terminal in MPPT2, the voltage to ground of the first pole becomes the sum of the voltages of the photovoltaic modules between the first pole and the insulation fault point. Therefore, this embodiment can determine the percentage of the insulation fault location in the photovoltaic string based on the ratio of the voltage to ground of the first pole to the open circuit voltage of the photovoltaic string.

[0026] S103: Individually control the short circuit of the positive and negative terminals of the input terminals of each DC-DC converter circuit, and for each MPPT module, determine whether the insulation fault location is located in the MPPT module based on the change of the first pole to ground voltage before and after the short circuit.

[0027] In this embodiment, the controller can sequentially and individually short-circuit the DC-DC converter circuit in each MPPT module to short-circuit BUS+ and BUS-. At this time, BUS+ and BUS- are forced to the same potential. For the MPPT module experiencing an insulation fault, since BUS+ and BUS- are now at the same potential, the voltage of the entire photovoltaic string is applied to the photovoltaic module from BUS+ to the insulation fault location. This means that the voltage difference between the photovoltaic module and BUS- is 0. Because the insulation fault location is grounded, the potential of BUS- is also forced to ground. Therefore, when the DC-DC converter circuit in the MPPT module experiencing an insulation fault is short-circuited, the voltage of the first terminal to ground will drop to around 0V.

[0028] If the short circuit occurs in an MPPT that does not have a ground fault, although BUS+ and BUS- are pulled to the same potential, the ground potential is unaffected by this short circuit because the entire photovoltaic string is floating and has no ground fault point. Since the ground relationship of the entire floating system remains unchanged, the voltage of BUS- to ground remains the same after the short circuit, and the voltage of the first pole to ground remains unchanged.

[0029] Therefore, this embodiment can determine the MPPT module where the insulation fault is located based on the change of the first pole-to-ground voltage of each MPPT module before and after the short circuit.

[0030] As can be seen from the above embodiments, the insulation detection method provided in this embodiment can quickly estimate the approximate percentage location of the fault point in the faulty string by calculating the ratio of the voltage of the first pole to ground to the open-circuit voltage of the string. This provides maintenance personnel with a clear search range, greatly reducing the scope of manual troubleshooting. Secondly, by sequentially controlling the short circuit of the input terminals of each DC-DC converter circuit and observing the change of the system voltage to ground, the specific faulty MPPT module can be accurately located, that is, it can be determined which string has failed. The combination of these two steps realizes the leap from system-level insulation faults to module-level insulation faults, and does not rely on any additional hardware. It only reuses the DC-DC converter circuit in the existing MPPT module and applies specific software control logic to achieve module-level insulation fault detection, improving the accuracy of photovoltaic system insulation fault detection and significantly reducing the manpower, time, and economic costs required for on-site troubleshooting, thereby improving the detection efficiency of photovoltaic system insulation faults.

[0031] In one possible implementation, the first electrode is the negative electrode of the DC bus; the specific implementation process of S102 includes: Divide the voltage to ground of the negative DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string to obtain the first percentage; Starting from the negative output terminal of the photovoltaic string, the position at the first percentage of the total length of the photovoltaic string is taken as the insulation fault location.

[0032] In this embodiment, the controller divides the measured DC bus negative terminal-to-ground voltage by the total open-circuit voltage of the photovoltaic string to obtain a percentage value. Then, starting from the negative terminal on the electrical connection of the photovoltaic string, it moves along the photovoltaic string towards the positive terminal, marking the first percentage point of the total length as the location where an insulation fault is most likely to occur, i.e., the insulation fault location.

[0033] Specifically, the implementation process of S102 above may also include: Divide the voltage to ground of the negative DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string to obtain the first percentage; Multiply the first percentage by the number of photovoltaic modules in the photovoltaic string to obtain the first value; Starting from the negative output terminal of the photovoltaic string, the Nth and N+1th photovoltaic modules forward are identified as faulty photovoltaic modules, where N represents a first value.

[0034] Specifically, in this embodiment, the first percentage can be used to locate photovoltaic modules that may have insulation faults. In order to avoid false detections and missed detections, this embodiment will identify photovoltaic modules located on both sides of the first percentage as faulty photovoltaic modules. In this way, maintenance personnel only need to check these two faulty photovoltaic modules to determine the true location of the insulation fault, thereby greatly reducing the scope of insulation fault detection and improving the efficiency of insulation fault detection.

[0035] As can be seen from the above embodiments, this embodiment explicitly uses the negative terminal of the DC bus as the reference point and directly maps the ratio of the negative terminal voltage to ground to the total string voltage to the percentage of the fault location starting from the negative terminal of the string. This method can respond very sensitively to insulation faults occurring in photovoltaic strings. Furthermore, compared to vague insulation anomaly alarms, this embodiment provides a specific insulation fault location, greatly improving the accuracy of maintenance instructions. This ensures that on-site personnel can directly access the area most likely to experience an insulation fault, avoiding the time wasted by sequentially checking each photovoltaic module, and further improving the efficiency of insulation fault detection.

[0036] In one possible implementation, the first electrode is the positive terminal of the DC bus; another implementation of S102 includes: The second percentage is obtained by dividing the voltage to ground of the positive DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string. Starting from the positive output terminal of the photovoltaic string, the location at the second percentage of the total length of the photovoltaic string is taken as the insulation fault location.

[0037] In this embodiment, the controller divides the measured DC bus positive voltage to ground by the total open-circuit voltage of the photovoltaic string to obtain another percentage value. Then, starting from the positive terminal of the electrical connection of the photovoltaic string, it moves along the photovoltaic string towards the negative terminal, marking the second percentage point of the total length as the location of the insulation fault.

[0038] Specifically, the implementation process of S102 above may also include: The second percentage is obtained by dividing the voltage to ground of the negative DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string. Multiply the second percentage by the number of photovoltaic modules in the photovoltaic string to obtain the second value; Starting from the positive output terminal of the photovoltaic string, the Mth and M+1th photovoltaic modules are identified as faulty photovoltaic modules, where M represents a second value.

[0039] Specifically, in this embodiment, the second percentage can be used to locate photovoltaic modules that may have insulation faults. In order to avoid false detections and missed detections, this embodiment identifies photovoltaic modules located on both sides of the second percentage as faulty photovoltaic modules. In this way, maintenance personnel only need to check these two faulty photovoltaic modules to determine the true location of the insulation fault, thereby greatly reducing the scope of insulation fault detection and improving the efficiency of insulation fault detection.

[0040] As can be seen from the above embodiments, this embodiment provides a positive electrode detection system that is symmetrical and complementary to the aforementioned negative electrode scheme. By specifying the positive electrode of the DC bus as the measurement point and starting from the positive electrode output terminal of the photovoltaic string, the location of the fault point in the photovoltaic string is determined based on the second percentage. This method makes the location logic independent of the specific location of the fault. No matter where the fault point is in the photovoltaic string, the system can obtain a reliable percentage result by selecting the positive or negative electrode voltage as a reference. This is particularly important in complex fault or multi-point fault scenarios, enabling the entire insulation detection method to adapt to different system design preferences and operation and maintenance habits, enhancing the robustness and universality of the scheme; ensuring that no matter the measurement conditions, the system always has a stable and reliable method to estimate the fault location, fundamentally improving the success rate and practicality of the entire insulation detection method.

[0041] In one possible embodiment, another specific implementation of the above S102 includes: Obtain the voltage to ground of the negative terminal and the voltage to ground of the DC bus of the photovoltaic system; Calculate the absolute value of the difference between the voltage to ground of the positive terminal of the DC bus and the voltage of the half bus, and use it as the first voltage difference; Calculate the absolute value of the difference between the voltage to ground at the negative terminal of the DC bus and the voltage at half the bus, and use it as the second voltage difference. The voltage to ground corresponding to the larger value between the first voltage difference and the second voltage difference is selected as the voltage to ground of the first pole; Divide the voltage of the first pole to ground by the open-circuit voltage of the photovoltaic string to obtain the third percentage; If the voltage of the first pole to ground is the voltage of the positive pole to ground of the DC bus, then starting from the positive output terminal of the photovoltaic string, the position at the third percentage of the total length of the photovoltaic string is taken as the location of the insulation fault. If the voltage of the first pole to ground is the voltage of the negative pole to ground of the DC bus, then starting from the negative output terminal of the photovoltaic string, the position at the third percentage of the total length of the photovoltaic string is taken as the insulation fault location.

[0042] As can be seen from the above embodiments, this embodiment simultaneously monitors the positive and negative voltages to ground when an insulation fault occurs. A voltage that deviates more significantly from the normal value (half-bus voltage) is selected for calculation to improve the signal-to-noise ratio and calculation accuracy in high-noise environments.

[0043] In one possible implementation, the specific implementation process of individually controlling the positive and negative short circuits at the input terminals of each DC-DC converter circuit in S103 includes: The upper and lower switching transistors of any bridge arm in the first DC-DC converter circuit are simultaneously turned on, so that the positive and negative terminals of the input terminal of the first DC-DC converter circuit are short-circuited. The first DC-DC converter circuit can be any DC-DC converter circuit in the photovoltaic system.

[0044] Specifically, a bridge arm is a basic unit in a power electronic converter consisting of an upper switch and a lower switch connected in series. The connection point between the two switches is called the midpoint. If the DC-DC converter circuit is a synchronous Boost circuit, it is itself a bridge arm. In the insulation detection mode, the controller sends a high-level signal to the drivers of its upper and lower switches, bypassing the PWM generator and dead-time generator, forcing the two switches to conduct. The current path is: PV+->inductor->upper switch->lower switch->PV-, forming a short circuit at the input.

[0045] When the DC-DC converter is a full-bridge circuit, the controller can select one of the bridge arms to perform this operation. For example, controlling the upper and lower switches of the left bridge arm of the H-bridge to conduct simultaneously can also establish a short circuit between the input ports PV+ and PV-.

[0046] Specifically, the controller can first apply a very narrow pulse to the DC-DC converter circuit to monitor the rate of rise and peak value of the short-circuit current. If both are within safe limits, a wider normal diagnostic pulse is then applied to the DC-DC converter circuit. This serves as a self-calibration and safety check function to prevent damage to the switching transistors under unknown extreme conditions (such as extremely oversized components).

[0047] As can be seen from the above embodiments, this embodiment achieves the effect of short-circuiting the positive and negative terminals of the DC bus by controlling the simultaneous conduction of the upper and lower switching transistors of the same bridge arm. It cleverly utilizes the physical characteristics of existing power circuits to create the test conditions required for diagnosis, avoiding the need for additional relays or dedicated short-circuit switches for diagnostic functions. This achieves zero additional hardware cost and avoids new fault points that might be introduced by adding external components, thus improving the overall reliability of the system. Furthermore, this scheme ensures that the short-circuit action is thorough and has low impedance, thereby generating a sufficiently obvious system voltage change signal, laying the foundation for accurate subsequent judgment. Simultaneously, since the photovoltaic module itself is a current source, its short-circuit current is limited, which provides a natural safety boundary for this controlled shoot-through, making the operation safe and feasible under strict time control. Ultimately, it achieves the best balance between cost, safety, and effectiveness.

[0048] In one possible implementation, the specific implementation process of S103 includes: If the difference between the first pole voltage and the ground voltage before and after the short circuit of the first MPPT module is greater than the first preset voltage threshold, then the insulation fault location is determined to be located in the first MPPT module; the first MPPT module is any MPPT module in the photovoltaic system. If the difference between the first pole voltage to ground before and after the first MPPT module is short-circuited is not greater than the first preset voltage threshold, then it is determined that the insulation fault location is not located in the first MPPT module.

[0049] In this embodiment, after a short-circuit operation is performed on the input terminal of a certain MPPT module, the difference between the voltage of the first pole to ground instant before the short circuit occurs and during the short circuit is calculated. This difference is compared with a preset voltage threshold. If the difference is greater than the first preset voltage threshold, the MPPT module is determined to be a faulty module; otherwise, it is determined to be normal.

[0050] The first preset voltage threshold is a threshold voltage set based on system characteristics (such as noise level, measurement accuracy, and voltage fluctuations during normal operation) to distinguish between actual fault responses and noise fluctuations. This embodiment can determine a fixed first preset voltage threshold through theoretical analysis or experimentation; alternatively, it can be determined based on the total bus voltage of the current photovoltaic system, with the total bus voltage being positively correlated with the first preset voltage threshold. For example, 5% of the total bus voltage can be used as the first preset voltage threshold. When the bus voltage is high, the first preset voltage threshold is increased accordingly to accommodate potentially higher background noise; when the bus voltage is low, the first preset voltage threshold is decreased to maintain sensitivity. This method is more adaptive.

[0051] As can be seen from the above embodiments, this embodiment effectively eliminates the risk of misjudgment caused by system background noise, measurement errors, and environmental fluctuations by introducing a first preset voltage threshold as the judgment basis and comparing the difference between the first pole and ground voltage before and after the MPPT module is short-circuited. This ensures that only MPPT modules that generate sufficiently large voltage changes will be identified as fault sources, reducing the system's dependence on ideal operating conditions and enabling it to work stably and automatically in complex actual operating environments. Ultimately, this ensures high accuracy and low false alarm rate of the insulation fault location function and enhances users' trust in the diagnostic results.

[0052] In one possible implementation, the specific implementation process of S102 includes: If the voltage to ground of the first pole is greater than the minimum insulation voltage, the location of the insulation fault in the faulty photovoltaic string is determined based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string; otherwise, an insulation fault alarm message for the first pole of the faulty photovoltaic string is generated.

[0053] Specifically, when the photovoltaic module closest to BUS- is short-circuited to ground, the theoretical voltage value is the open-circuit voltage of the photovoltaic string divided by the number of photovoltaic modules in a single photovoltaic string, which yields the minimum insulation voltage.

[0054] When a photovoltaic module in a photovoltaic string fails, its first electrode voltage to ground will be greater than the minimum insulation voltage. However, when an insulation fault occurs at the positive electrode PV+ or the negative electrode PV- of the photovoltaic string, the first electrode voltage to ground will be very small, close to zero. Based on the above principle, in this embodiment, when an abnormal insulation impedance of the photovoltaic system is detected, the insulation voltage, i.e., the first electrode voltage to ground, is detected. If the first electrode voltage to ground is less than the minimum insulation voltage, it can be determined that there is a PV- to ground short circuit fault or a PV+ to ground short circuit fault. This fault does not need to be located through voltage division; the insulation fault location can be directly determined. Therefore, step S102 is not required. Furthermore, the PV- to ground short circuit fault or the PV+ to ground short circuit fault is serious, so an insulation fault alarm message needs to be generated immediately to notify the operation and maintenance personnel to handle it in a timely manner. If the first electrode voltage to ground is greater than the minimum insulation voltage, it indicates that an insulation fault has occurred at another location in the photovoltaic string, and the insulation fault location can continue to be determined based on the voltage division principle.

[0055] The minimum insulation voltage value needs to be experimentally determined to prevent false alarms of PV-insulation impedance anomalies. For example, the minimum insulation voltage value can be 50V.

[0056] As can be seen from the above embodiments, this embodiment performs a rapid pre-judgment before initiating the time-consuming percentage calculation and MPPT short-circuit location process: if the voltage of the first pole to ground is too low (not exceeding the threshold), it is directly determined to be a PV- / PV+ near-end short circuit and an alarm is triggered, without proceeding with subsequent location. This enables rapid identification and response to the most severe fault (PV- / PV+ direct short circuit), thereby optimizing system resource allocation and improving security. It also prompts maintenance personnel to take immediate action, eliminating the time delay caused by executing the complete location process, resulting in a more agile response. Simultaneously, this method can save the controller's computing resources, allowing it to serve other tasks more efficiently.

[0057] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0058] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0059] Figure 3A schematic diagram of the insulation testing device for a photovoltaic system provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 3 As shown, the insulation testing device 100 for a photovoltaic system includes: The system insulation fault detection module 110 is used to detect whether an insulation fault has occurred in the photovoltaic system. The insulation fault location determination module 120 is used to determine the location of the insulation fault in the photovoltaic string based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string if an insulation fault occurs in the photovoltaic system; the first pole is either the positive pole or the negative pole of the DC bus. MPPT module positioning module 130 is used to individually control the positive and negative terminals of the input terminals of each DC-DC converter circuit to short-circuit, and for each MPPT module, based on the change of the first terminal voltage to ground before and after the short circuit of the MPPT module, determine whether the insulation fault location is located in the MPPT module.

[0060] In one possible implementation, the first electrode is the negative electrode of the DC bus; the insulation fault location determination module 120 includes: Divide the voltage to ground of the negative DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string to obtain the first percentage; Starting from the negative output terminal of the photovoltaic string, the position at the first percentage of the total length of the photovoltaic string is taken as the insulation fault location.

[0061] In one possible implementation, the first pole is the positive pole of the DC bus; the insulation fault location determination module 120 includes: The second percentage is obtained by dividing the voltage to ground of the positive DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string. Starting from the positive output terminal of the photovoltaic string, the location at the second percentage of the total length of the photovoltaic string is taken as the insulation fault location.

[0062] In one possible implementation, the MPPT module positioning module 130 includes a short-circuit unit for: The upper and lower switching transistors of any bridge arm in the first DC-DC converter circuit are simultaneously turned on, so that the positive and negative terminals of the input terminal of the first DC-DC converter circuit are short-circuited. The first DC-DC converter circuit can be any DC-DC converter circuit in the photovoltaic system.

[0063] In one possible implementation, the MPPT module positioning module 130 includes an MPPT positioning unit for: If the difference between the first pole voltage and the ground voltage before and after the short circuit of the first MPPT module is greater than the first preset voltage threshold, then the insulation fault location is determined to be located in the first MPPT module; the first MPPT module is any MPPT module in the photovoltaic system. If the difference between the first pole voltage to ground before and after the first MPPT module is short-circuited is not greater than the first preset voltage threshold, then it is determined that the insulation fault location is not located in the first MPPT module.

[0064] In one possible implementation, the photovoltaic system further includes an inverter; the input terminal of the inverter is connected to the DC bus; the system insulation fault detection module 110 includes: The voltage to ground of the first pole is detected by the insulation detection module of the inverter; If the difference between the voltage to ground of the first pole and the voltage of the half busbar is greater than the second preset voltage threshold, then the photovoltaic system is determined to have an insulation fault.

[0065] In one possible implementation, the insulation fault location determination module 120 includes: If the voltage to ground of the first pole is greater than the minimum insulation voltage, the location of the insulation fault in the faulty photovoltaic string is determined based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string; otherwise, an insulation fault alarm message for the first pole of the faulty photovoltaic string is generated.

[0066] Figure 4 This is a schematic diagram of the controller provided in an embodiment of the present invention. Figure 4 As shown, the controller 4 in this embodiment includes a processor 40, a memory 41, and a computer program 42 stored in the memory 41 and executable on the processor 40. When the processor 40 executes the computer program 42, it implements the steps in the insulation detection method embodiments of the various photovoltaic systems described above, for example... Figure 2 Steps S101 to S103 are shown. Alternatively, when the processor 40 executes the computer program 42, it implements the functions of each module / unit in the above-described device embodiments.

[0067] For example, the computer program 42 may be divided into one or more modules / units, which are stored in the memory 41 and executed by the processor 40 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program 42 in the controller 4.

[0068] The controller 4 can be a computing device such as a desktop computer, laptop, handheld computer, or cloud server. The controller 4 may include, but is not limited to, a processor 40 and a memory 41. Those skilled in the art will understand that... Figure 4 This is merely an example of controller 4 and does not constitute a limitation on controller 4. It may include more or fewer components than shown, or combine certain components, or different components. For example, the controller may also include input / output devices, network access devices, buses, etc.

[0069] The processor 40 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0070] The memory 41 can be an internal storage unit of the controller 4, such as a hard disk or memory of the controller 4. The memory 41 can also be an external storage device of the controller 4, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the controller 4. Furthermore, the memory 41 can include both internal storage units and external storage devices of the controller 4. The memory 41 is used to store the computer program and other programs and data required by the controller. The memory 41 can also be used to temporarily store data that has been output or will be output.

[0071] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0072] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0073] Those skilled in the art will 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, or a combination of computer software and electronic hardware. 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 implementations should not be considered beyond the scope of this invention.

[0074] In the embodiments provided by this invention, it should be understood that the disclosed devices / controllers and methods can be implemented in other ways. For example, the device / controller embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0075] 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 units can be selected to achieve the purpose of this embodiment according to actual needs.

[0076] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0077] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the insulation detection method embodiments of the various photovoltaic systems described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0078] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. An insulation testing method for a photovoltaic system, characterized in that, It is applied to photovoltaic systems; the photovoltaic system includes multiple MPPT modules; each MPPT module includes a photovoltaic string and a DC-DC converter circuit; each photovoltaic string is connected to the input terminal of its corresponding DC-DC converter circuit, the positive output terminal of each DC-DC converter circuit is connected to the positive terminal of the DC bus, and the negative output terminal of each DC-DC converter circuit is connected to the negative terminal of the DC bus. The method includes: Detect whether the photovoltaic system has an insulation fault; If an insulation fault occurs in the photovoltaic system, the location of the insulation fault in the photovoltaic string is determined based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string; the first pole is either the positive pole or the negative pole of the DC bus. Each DC-DC converter circuit is individually controlled to short-circuit the positive and negative terminals of its input terminals. For each MPPT module, the location of the insulation fault is determined based on the change in the voltage of the first terminal to ground before and after the short circuit.

2. The insulation testing method for a photovoltaic system according to claim 1, characterized in that, The first electrode is the negative terminal of the DC bus; Determining the location of the insulation fault in the faulty photovoltaic string based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string includes: Divide the voltage to ground of the negative DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string to obtain the first percentage; Starting from the negative output terminal of the photovoltaic string, the position at the first percentage of the total length of the photovoltaic string is taken as the insulation fault location.

3. The insulation testing method for a photovoltaic system according to claim 1, characterized in that, The first electrode is the positive terminal of the DC bus; Determining the location of the insulation fault in the faulty photovoltaic string based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string includes: The second percentage is obtained by dividing the voltage to ground of the positive DC bus of the photovoltaic system by the open-circuit voltage of the photovoltaic string. Starting from the positive output terminal of the photovoltaic string, the location at the second percentage of the total length of the photovoltaic string is taken as the insulation fault location.

4. The insulation testing method for a photovoltaic system according to claim 1, characterized in that, The method of individually controlling the positive and negative short circuits at the input terminals of each DC-DC converter circuit includes: The upper and lower switching transistors of any bridge arm in the first DC-DC converter circuit are simultaneously turned on, so that the positive and negative terminals of the input terminal of the first DC-DC converter circuit are short-circuited. The first DC-DC converter circuit can be any DC-DC converter circuit in the photovoltaic system.

5. The insulation testing method for a photovoltaic system according to claim 1, characterized in that, For each MPPT module, determining whether the insulation fault location is located within that MPPT module based on the change in the first pole-to-ground voltage before and after a short circuit includes: If the difference between the first pole voltage and the ground voltage before and after the short circuit of the first MPPT module is greater than the first preset voltage threshold, then the insulation fault location is determined to be located in the first MPPT module; the first MPPT module is any MPPT module in the photovoltaic system. If the difference between the first pole voltage to ground before and after the first MPPT module is short-circuited is not greater than the first preset voltage threshold, then it is determined that the insulation fault location is not located in the first MPPT module.

6. The insulation testing method for a photovoltaic system according to claim 1, characterized in that, The photovoltaic system also includes an inverter; The input terminal of the inverter is connected to the DC bus; The detection of whether the photovoltaic system has an insulation fault includes: The voltage to ground of the first pole is detected by the insulation detection module of the inverter; If the difference between the voltage to ground of the first pole and the voltage of the half busbar is greater than the second preset voltage threshold, then the photovoltaic system is determined to have an insulation fault.

7. The insulation testing method for a photovoltaic system according to claim 6, characterized in that, Determining the location of the insulation fault in the faulty photovoltaic string based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string includes: If the voltage to ground of the first pole is greater than the minimum insulation voltage, the location of the insulation fault in the faulty photovoltaic string is determined based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string; otherwise, an insulation fault alarm message for the first pole of the faulty photovoltaic string is generated.

8. An insulation testing device for a photovoltaic system, characterized in that, It is applied to photovoltaic systems; the photovoltaic system includes multiple MPPT modules; each MPPT module includes a photovoltaic string and a DC-DC converter circuit; each photovoltaic string is connected to the input terminal of its corresponding DC-DC converter circuit, the positive output terminal of each DC-DC converter circuit is connected to the positive terminal of the DC bus, and the negative output terminal of each DC-DC converter circuit is connected to the negative terminal of the DC bus. The device includes: a system insulation fault detection module, used to detect whether an insulation fault has occurred in the photovoltaic system; An insulation fault location determination module is used to determine the location of the insulation fault in the photovoltaic string based on the ratio of the voltage to ground of the first pole of the photovoltaic system to the open-circuit voltage of the photovoltaic string if an insulation fault occurs in the photovoltaic system; the first pole is either the positive pole or the negative pole of the DC bus. The MPPT module positioning module is used to individually control the positive and negative short circuits of the input terminals of each DC-DC converter circuit, and for each MPPT module, based on the change of the first pole to ground voltage before and after the short circuit, determine whether the insulation fault location is located in that MPPT module.

9. A controller comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the insulation detection method for the photovoltaic system as described in any one of claims 1 to 7.

10. A photovoltaic system, characterized in that, It includes photovoltaic strings and the controller as described in claim 9.

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