Photovoltaic systems and leakage current control methods for photovoltaic systems

Abstract

This application provides a photovoltaic system and a method for controlling the leakage current of the photovoltaic system. The photovoltaic system includes at least one photovoltaic module group, at least one photovoltaic inverter, a grounded metal frame, and a sampling control unit. The photovoltaic module group is mounted on the grounded metal frame, and the output terminal of the photovoltaic module group is connected to the input terminal of the photovoltaic inverter, which is connected to the power grid. The sampling control unit is coupled to both the photovoltaic module group and the photovoltaic inverter and is used to detect the leakage current value formed by the common-mode voltage of the photovoltaic inverter on the parasitic capacitance, which exists between the photovoltaic module group and the grounded metal frame. The sampling control unit is used to adjust the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the current value, which can reduce the leakage current of the photovoltaic system. It is simple to operate and highly applicable.

Description

Technical Field

[0001] This application relates to the field of electronic power technology, and in particular to a photovoltaic system and a method for controlling leakage current in a photovoltaic system. Background Technology

[0002] A photovoltaic (PV) system is a new type of power generation system that uses the photovoltaic effect of photovoltaic (PV) panels to convert solar radiation energy into electrical energy for use by the mains power grid. The PV inverter is one of the main components of a PV system. It converts the variable DC voltage generated by PV modules such as solar panels into AC power at the mains frequency and outputs this AC power to the grid. Its energy conversion efficiency and power quality directly affect the power generation efficiency of the PV system. In a PV system, there is an electrical connection between the PV array (composed of PV modules) and the load output by the PV inverter (such as the power grid). There is also a parasitic capacitance between the PV array and the grounded metal frame. When the PV inverter is working, a common-mode loop is formed between the parasitic capacitance, the PV system, and the grid. The common-mode voltage will generate a common-mode current, or leakage current, on the parasitic capacitance. The common-mode voltage is the voltage at the midpoint of the PV inverter output relative to the grounded metal frame with a fixed potential. The size of the parasitic capacitance is related to the area and material of the PV modules and the surrounding environment; as the parasitic capacitance increases, the leakage current also increases. When the leakage current exceeds the threshold, the electromagnetic field radiated by the leakage current will cause electromagnetic conduction interference, affecting the power generation efficiency of the photovoltaic system.

[0003] The inventors of this application discovered during research and practice that, in existing technologies, when the parasitic capacitance in a photovoltaic system is small, reducing the DC bus voltage of the photovoltaic inverter can decrease the losses of the power switching transistors in the inverter and improve its operating efficiency. However, when the parasitic capacitance in the photovoltaic system increases due to factors such as rain, the leakage current increases accordingly, affecting the normal operation of the photovoltaic inverter. Existing technologies, by increasing the DC bus voltage of the photovoltaic inverter to reduce the common-mode voltage to ground of the photovoltaic system, thereby reducing the effective value of the leakage current and ensuring the normal operation of the photovoltaic inverter system, result in significant fluctuations in the DC bus voltage and reduced bus utilization. Furthermore, during the adjustment of the DC bus voltage, the device losses of the photovoltaic inverter are substantial, leading to a loss of power generation in the photovoltaic system and limiting its applicability. Summary of the Invention

[0004] This application provides a photovoltaic system and a method for controlling the leakage current of a photovoltaic system, which can reduce the leakage current of the photovoltaic system while maintaining the bus utilization rate of the photovoltaic inverter in the photovoltaic system. It is simple to operate and has high applicability.

[0005] Firstly, this application provides a photovoltaic system comprising at least one photovoltaic module group, at least one photovoltaic inverter, a grounded metal frame, and a sampling control unit. The photovoltaic module group is mounted on the grounded metal frame; in other words, the grounded metal frame is a metal frame used to mount the photovoltaic modules, and this metal frame is grounded. The output terminal of the photovoltaic module group is connected to the input terminal of the photovoltaic inverter, and the output terminal of the photovoltaic inverter is connected to the power grid. The sampling control unit is coupled to both the photovoltaic module group and the photovoltaic inverter. The sampling control unit is used to detect the leakage current value formed by the common-mode voltage of the photovoltaic inverter on the parasitic capacitance. Here, the parasitic capacitance exists between the photovoltaic module group and the grounded metal frame, and the common-mode voltage of the photovoltaic inverter is the voltage of the output midpoint of the photovoltaic inverter relative to the grounded metal frame, which has a fixed potential. It is understandable that, during the operation of the photovoltaic inverter supplying power to the grid, a common-mode loop is formed between the parasitic capacitance (including the grounding metal frame-parasitic capacitance), the photovoltaic system (including the photovoltaic module group-photovoltaic inverter), and the grid. The common-mode voltage of the photovoltaic inverter's output midpoint relative to the grounding metal frame, which has a fixed potential, generates leakage current on the parasitic capacitance of this common-mode loop. The sampling control unit can be used to detect the value of this leakage current. The sampling control unit is used to adjust the injection amount of the common-mode voltage in the photovoltaic inverter's pulse width modulation signal based on the detected leakage current value to reduce the aforementioned leakage current. Here, the leakage current can be the ratio of the photovoltaic inverter's common-mode voltage (also known as the photovoltaic system's common-mode voltage to ground) to the parasitic impedance of the parasitic capacitance to ground (also known as the photovoltaic system's parasitic impedance to ground). In this application, the sampling control unit adjusts the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the leakage current value. While controlling the leakage current, it can keep the modulation ratio of the photovoltaic inverter constant, thereby keeping the bus utilization rate of the photovoltaic inverter from decreasing, minimizing the power generation loss of the photovoltaic inverter, ensuring the effect of pulse width modulation of the photovoltaic system, and is simple to operate and highly applicable.

[0006] In conjunction with the first aspect, in a first possible implementation, the aforementioned sampling control unit is used to reduce the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter when the detected leakage current value is greater than the current threshold, thereby reducing the injection amount of common-mode voltage in the pulse width modulation signal. In this application, adjusting the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter can change the injection amount of common-mode voltage in the pulse width modulation signal of the photovoltaic inverter, which is simple to operate and highly applicable. By reducing the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter, the common-mode injection amount in the pulse width modulation signal of the photovoltaic inverter can be effectively reduced. While suppressing leakage current, the photovoltaic system can still continue to operate in the current pulse width modulation strategy mode, that is, the adjustment of the common-mode injection amount does not affect the modulation ratio of the photovoltaic inverter, thus reducing the power generation loss of the photovoltaic system. Here, the pulse width modulation signal of the photovoltaic inverter can be a discontinuous pulse width modulation (DPWM) signal, a space vector pulse width modulation (SVPWM) signal, or a sinusoidal pulse width modulation (SPWM) signal, etc. The specific one can be determined according to the actual application scenario, and there are no restrictions here.

[0007] In conjunction with the first possible implementation of the first aspect, in the second possible implementation, the aforementioned sampling control unit is used to reduce the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal until the common-mode injection coefficient is 0 when the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1. In this application, for scenarios where the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1, such as when the photovoltaic inverter's pulse width modulation is SPWM, the sampling control unit can reduce the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal to 0 when it detects that the leakage current is greater than the current threshold. At this time, the injection amount of the common-mode voltage (also called the common-mode injection amount) in the photovoltaic inverter's pulse width modulation signal is minimal, the photovoltaic system operates under the condition of minimum leakage current, the operation is simple, and it does not affect the modulation ratio of the photovoltaic inverter. It can maintain the bus utilization rate of the photovoltaic inverter (the bus utilization rate is the ratio of the photovoltaic inverter's output voltage to the bus voltage) without decreasing, ensuring the power generation efficiency of the photovoltaic system, ensuring the working stability of the photovoltaic system, and having high applicability.

[0008] In conjunction with the first possible implementation of the first aspect, in the third possible implementation, the aforementioned sampling control unit is used to reduce the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal when the modulation ratio of the photovoltaic inverter is greater than 1, thereby reducing the injection amount of common-mode voltage in the pulse width modulation signal, until the common-mode injection coefficient is 0 and / or the detected leakage current value is less than or equal to the current threshold. In this application, for scenarios where the modulation ratio of the photovoltaic inverter's pulse width modulation is greater than 1, such as when the photovoltaic inverter's pulse width modulation is DPWM, the sampling control unit can also reduce the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal to 0 when the detected leakage current is greater than the current threshold. At this time, there is still a certain amount of common-mode injection in the photovoltaic inverter's pulse width modulation signal to ensure the DPWM modulation effect of the photovoltaic system. This reduces the leakage current of the photovoltaic system without affecting the modulation ratio of the photovoltaic inverter, maintaining the bus utilization rate of the photovoltaic inverter, ensuring the power generation efficiency of the photovoltaic system, ensuring the working stability of the photovoltaic system, and providing high applicability.

[0009] In conjunction with the third possible implementation of the first aspect, in the fourth possible implementation, when the modulation ratio of the photovoltaic inverter is greater than 1, the aforementioned sampling control unit is further configured to adjust the modulation ratio of the photovoltaic inverter's pulse width modulation to be less than or equal to 1 when the common-mode injection coefficient is reduced to 0 and the detected leakage current value is greater than the current threshold. In this application, when the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1, the common-mode voltage can be eliminated from the photovoltaic inverter's pulse width modulation signal. At this time, the photovoltaic system can be controlled to operate under the condition of minimum leakage current, which is simple to operate and highly applicable.

[0010] In conjunction with the fourth possible implementation of the first aspect, in the fifth possible implementation, the above-mentioned sampling control unit is also used to adjust the modulation ratio of the pulse width modulation of the photovoltaic inverter from greater than 1 to less than or equal to 1. When this adjustment is made, the modulation strategy of the pulse width modulation of the photovoltaic inverter can be directly switched. For example, the modulation strategy of the pulse width modulation of the photovoltaic inverter can be switched from DPWM to SPWM so that the modulation ratio of the pulse width modulation of the photovoltaic inverter is less than or equal to 1. The operation is simple.

[0011] In conjunction with any of the first to fifth possible embodiments of the first aspect, in the sixth possible embodiment, the photovoltaic system includes at least two photovoltaic module groups and at least two photovoltaic inverters. That is, the photovoltaic system includes multiple photovoltaic module groups and multiple photovoltaic inverters. A parasitic capacitance exists between one photovoltaic module group and the grounded metal frame. The output terminal of one photovoltaic module group is connected to the input terminal of one photovoltaic inverter. The output terminals of the multiple photovoltaic inverters are connected in parallel to the power grid. Each photovoltaic module group and the multiple photovoltaic inverters form a common-mode loop to ground. For example, suppose a photovoltaic system includes photovoltaic module group 1 and photovoltaic module group 2, photovoltaic inverter 1 and photovoltaic inverter 2. The output terminal of photovoltaic module group 1 is connected to the input terminal of photovoltaic inverter 1, the output terminal of photovoltaic module group 2 is connected to the input terminal of photovoltaic inverter 2, the output terminals of photovoltaic inverter 1 and photovoltaic inverter 2 are connected in parallel to the power grid, there is a parasitic capacitance 1 between photovoltaic module group 1 and the grounded metal frame, and there is a parasitic capacitance 2 between photovoltaic module group 2 and the grounded metal frame. Then, during the operation of the photovoltaic system, a common mode loop is formed between parasitic capacitance 1 (including grounded metal frame - parasitic capacitance 1) - photovoltaic module group 1 - photovoltaic inverter 1 - photovoltaic inverter 2 - photovoltaic module group 2 - parasitic capacitance 2 (including grounded metal frame - parasitic capacitance 2). The aforementioned sampling and control unit is used to detect the leakage current value formed on the parasitic capacitances (such as parasitic capacitance 1 and parasitic capacitance 2) of the common-mode voltage of the aforementioned multiple photovoltaic inverters (it can be understood that the output terminals of the aforementioned multiple photovoltaic inverters are connected in parallel to the grid, so the common-mode voltage of each photovoltaic inverter is the same voltage, which is the voltage between the output midpoint of the aforementioned multiple photovoltaic inverters connected in parallel and ground). Based on the aforementioned current value, the injection amount of the common-mode voltage in the pulse width modulation signal of the aforementioned multiple photovoltaic inverters is adjusted to reduce the aforementioned leakage current. Here, the pulse width modulation modulation strategy of the aforementioned multiple photovoltaic inverters can be the same modulation strategy. The aforementioned sampling and control unit can simultaneously adjust the injection amount of the common-mode voltage in the pulse width modulation signal of the aforementioned multiple photovoltaic inverters to be the same common-mode injection amount, thereby reducing the leakage current in the photovoltaic system. The operation is simple and applicable to application scenarios where multiple photovoltaic inverters are connected in parallel, with high applicability.

[0012] In conjunction with any of the first to sixth possible embodiments of the first aspect, in the seventh possible embodiment, the aforementioned sampling control unit is integrated into the photovoltaic inverter. In other words, in this application, the aforementioned sampling control unit can be a sampling control circuit or sampling control device in the photovoltaic inverter, which can be determined according to the actual application scenario and is not limited here. Detecting and / or controlling the leakage current of the photovoltaic system based on the sampling control unit eliminates the need for additional leakage current detection circuitry, simplifying operation and reducing implementation costs.

[0013] In conjunction with any of the first to seventh possible embodiments of the first aspect, in the eighth possible embodiment, the aforementioned photovoltaic inverter includes a DC / DC conversion module, an energy storage module, and a DC / AC conversion module; wherein, the input terminal of the DC / DC conversion module serves as the input terminal of the photovoltaic inverter, the output terminal of the DC / DC conversion module is connected to the input terminal of the DC / AC conversion module through the energy storage module, and the output terminal of the DC / AC conversion module serves as the output terminal of the photovoltaic inverter. In this application, the electrical energy generated by the photovoltaic effect of the photovoltaic module group can be directly input into the photovoltaic inverter, where it is boosted / rectified by the DC / DC conversion module of the photovoltaic inverter, and stored in the energy storage module. Here, the energy storage module can be composed of the bus capacitor of the photovoltaic inverter, and the output voltage of the bus capacitor can be converted into the AC voltage required by the grid through the DC / AC conversion module and output to the grid. Here, the photovoltaic inverter can be an isolated photovoltaic inverter or a non-isolated photovoltaic inverter. Correspondingly, the circuit topology of the DC / DC conversion module and the DC / AC conversion module in the photovoltaic inverter can be an isolated circuit topology or a non-isolated circuit topology. The specific topology can be determined according to the actual application scenario requirements, and there are no restrictions here.

[0014] In conjunction with any of the first to seventh possible embodiments of the first aspect, in the ninth possible embodiment, the photovoltaic inverter may be a DC / AC conversion module, and the photovoltaic system also includes an energy storage module; the output terminal of the photovoltaic module group in the photovoltaic system can be connected to the input terminal of the DC / AC conversion module through the energy storage module, and the output terminal of the DC / AC conversion module serves as the output terminal of the photovoltaic inverter. Optionally, the energy storage module may be an energy storage battery or the DC bus of the photovoltaic system, which can be determined according to the actual application scenario and is not limited here.

[0015] In conjunction with any of the first to ninth possible embodiments of the first aspect, in the tenth possible embodiment, in the above-described photovoltaic system, a photovoltaic module group includes multiple photovoltaic strings connected in parallel, and a photovoltaic string can be obtained by connecting one or more photovoltaic modules in series. Here, the parallel connection terminal of the above-described multiple photovoltaic strings serves as the output terminal of the photovoltaic module group. Optionally, the output terminal of the above-described photovoltaic module group can also be connected to the input terminal of the photovoltaic inverter through a combiner box, or connected to the input terminal of the photovoltaic inverter through a combiner box and an energy storage unit. The specific connection can be determined according to the actual application scenario and is not limited here.

[0016] Secondly, this application provides a leakage current control method for a photovoltaic system. This method is applicable to a sampling control unit in a photovoltaic system provided in any of the possible embodiments of the first to ninth aspects described above. Parasitic capacitance exists between the photovoltaic module group and the grounded metal frame. The method includes: the sampling control unit detecting the leakage current value formed on the parasitic capacitance by the common-mode voltage of the photovoltaic inverter, and adjusting the injection amount of the common-mode voltage in the pulse-width modulation signal of the photovoltaic inverter based on the detected current value to reduce the leakage current. In this application, during the process of the sampling control unit adjusting the injection amount of the common-mode voltage in the pulse-width modulation signal of the photovoltaic inverter based on the leakage current value, the modulation ratio of the photovoltaic inverter can be kept constant while controlling the leakage current. This ensures that the bus utilization rate of the photovoltaic inverter is not reduced, minimizes the power generation loss of the photovoltaic inverter, guarantees the effect of pulse-width modulation of the photovoltaic system, and is simple to operate and highly applicable.

[0017] In conjunction with the second aspect, in the first possible implementation, during the process of adjusting the injection amount of the common-mode voltage in the pulse-width modulation signal of the photovoltaic inverter based on the detected current value, if the current value is greater than the current threshold, the common-mode injection coefficient of the pulse-width modulation signal of the photovoltaic inverter can be reduced to decrease the injection amount of the common-mode voltage in the pulse-width modulation signal. In this application, the injection amount of the common-mode voltage in the pulse-width modulation signal of the photovoltaic inverter can be changed by adjusting the common-mode injection coefficient, which is simple to operate and highly applicable.

[0018] In conjunction with the first possible implementation of the second aspect, in the second possible implementation, during the process of the sampling control unit reducing the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal, if the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1, the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal can be reduced until the common-mode injection coefficient is 0. In this application, for scenarios where the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1, such as when the photovoltaic inverter's pulse width modulation is SPWM, the sampling control unit can reduce the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal to 0 when it detects that the leakage current is greater than the current threshold. At this time, the injection amount of the common-mode voltage in the photovoltaic inverter's pulse width modulation signal is minimal, the photovoltaic system operates under the condition of minimum leakage current, the operation is simple, and it does not affect the modulation ratio of the photovoltaic inverter. It can maintain the bus utilization rate of the photovoltaic inverter, ensure the power generation efficiency of the photovoltaic system, ensure the working stability of the photovoltaic system, and has high applicability.

[0019] In conjunction with the first possible implementation of the second aspect, in the third possible implementation, during the process of the sampling control unit reducing the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter, if the modulation ratio of the photovoltaic inverter is greater than 1, the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter can be reduced until the common-mode injection coefficient is 0 and / or the current value of the detected leakage current is less than or equal to the aforementioned current threshold. In this application, for scenarios where the modulation ratio of the pulse width modulation of the photovoltaic inverter is greater than 1, when the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter is reduced to 0, there is still a certain amount of common-mode injection in the pulse width modulation signal of the photovoltaic inverter to ensure the DPWM modulation effect of the photovoltaic system. This reduces the leakage current of the photovoltaic system without affecting the modulation ratio of the photovoltaic inverter, maintains the bus utilization rate of the photovoltaic inverter, ensures the power generation efficiency of the photovoltaic system, guarantees the working stability of the photovoltaic system, and has high applicability.

[0020] In conjunction with the third possible implementation of the second aspect, in the fourth possible implementation, the method further includes: if the common-mode injection coefficient decreases to 0 and the detected leakage current value is greater than the current threshold, the sampling control unit adjusts the modulation ratio of the pulse width modulation of the photovoltaic inverter to be less than or equal to 1. In this application, when the modulation ratio of the pulse width modulation of the photovoltaic inverter is less than or equal to 1, the common-mode voltage can be eliminated from the pulse width modulation signal of the photovoltaic inverter. At this time, the photovoltaic system can be controlled to operate under the condition of minimum leakage current, which is simple to operate and highly applicable.

[0021] In conjunction with the fourth possible implementation of the second aspect, in the fifth possible implementation, adjusting the modulation ratio of the pulse width modulation of the photovoltaic inverter to be less than or equal to 1 includes: switching the modulation strategy of the pulse width modulation of the photovoltaic inverter so that the modulation ratio of the pulse width modulation of the photovoltaic inverter is less than or equal to 1, which is simple to operate. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of an application scenario of the photovoltaic system provided in this application;

[0023] Figure 2 This is a schematic diagram of another application scenario of the photovoltaic system provided in this application;

[0024] Figure 3 This is a structural schematic diagram of the photovoltaic system provided in this application;

[0025] Figure 4 This is another structural schematic diagram of the photovoltaic system provided in this application;

[0026] Figure 5 This is another structural schematic diagram of the photovoltaic system provided in this application;

[0027] Figure 6 This is a schematic diagram of common-mode voltage injection in the discontinuous pulse width modulation signal provided in this application;

[0028] Figure 7 This is a waveform diagram of the pulse width modulation signal and the common-mode voltage input to the pulse width modulation signal provided in this application;

[0029] Figure 8 This is another waveform diagram of the pulse width modulation signal and the common-mode voltage input to the pulse width modulation signal provided in this application;

[0030] Figure 9 This is a flowchart illustrating the leakage current control method for the photovoltaic system provided in this application. Detailed Implementation

[0031] With advancements in industry production technology and the increasing prominence of economies of scale, the economic viability of photovoltaic power generation has continuously improved, and the industry has truly entered the era of grid parity. The number of newly installed photovoltaic capacity continues to grow rapidly. The photovoltaic system provided in this application can be a power supply system based on solar photovoltaic power generation. Solar photovoltaic power generation features no moving parts, no noise, no pollution, and high reliability, making it an excellent application prospect in communication power supply systems in remote areas. The photovoltaic system provided in this application can be used to power various types of electrical equipment, such as base station equipment, batteries, or household appliances (e.g., refrigerators, air conditioners, etc.), depending on the specific application scenario, and is not limited here. The photovoltaic inverter is one of the main components of a photovoltaic system, with a large market size and promising market prospects. The photovoltaic inverter can be used to convert the variable DC voltage generated by DC power sources such as photovoltaic solar panels (i.e., photovoltaic modules) into AC power at the mains frequency, and output this AC power to the mains grid for use by the mains grid, specifically for base station equipment, batteries, or household appliances within the mains grid. The photovoltaic system provided in this application can be adapted to different application scenarios, such as solar power supply scenarios and solar hybrid power supply scenarios. The specific application scenario can be determined according to the actual application scenario, and no restrictions are imposed here. This application uses a solar power supply scenario as an example for illustration.

[0032] See Figure 1 , Figure 1 This is a schematic diagram of an application scenario of the photovoltaic system provided in this application. In the photovoltaic system provided in this application, the output terminal of the photovoltaic array can be connected to the input terminal of a photovoltaic inverter, and the output terminal of the photovoltaic inverter is connected to the AC power grid. The inverter can convert the DC power input to the photovoltaic array into AC power and send it to the AC power grid. Figure 1In the photovoltaic system shown, the photovoltaic array can be a photovoltaic module group, and a photovoltaic module group can be composed of one or more photovoltaic modules connected in series and parallel. A photovoltaic module string can be composed of one or more photovoltaic modules connected in series. Here, the photovoltaic module can be a solar panel, a photovoltaic panel, or an energy storage battery. In other words, in... Figure 1 In the photovoltaic system shown, a photovoltaic string can be a series of one or more solar panels, photovoltaic panels, or energy storage batteries connected in series. The output current of multiple photovoltaic strings can provide DC input voltage to the photovoltaic inverter. After voltage-to-power conversion by the photovoltaic inverter, the voltage is used by electrical equipment such as batteries in the AC grid, communication base stations, or household appliances. Optionally, such as... Figure 2 As shown, Figure 2 This is a schematic diagram of another application scenario of the photovoltaic system provided in this application. The output current of multiple photovoltaic strings can be combined through a combiner box (i.e., multiple photovoltaic strings are connected in parallel to the combiner box) to provide DC input voltage to the photovoltaic inverter. After voltage-to-power conversion by the photovoltaic inverter, the voltage is used by electrical equipment such as batteries, communication base stations, or household appliances in the AC grid. Optionally, the output current of the aforementioned multiple photovoltaic strings can be combined through a combiner box (i.e., multiple photovoltaic strings are connected in parallel to the combiner box) to store energy in an energy storage battery, and then the energy storage battery provides DC input voltage to the photovoltaic inverter. After voltage-to-power conversion by the photovoltaic inverter, the voltage is used by electrical equipment such as batteries, communication base stations, or household appliances in the AC grid. Figure 1 and / or Figure 2 In the application scenario shown, photovoltaic modules can be mounted on a grounded metal frame. In other words, the grounded metal frame is a metal frame used to mount the photovoltaic modules, and this metal frame is grounded. Especially in remote areas, in rugged mountainous terrain, or near water—places with poor geographical conditions but abundant sunlight—metal frames can be used to fix and install photovoltaic modules, thereby better utilizing the photovoltaic effect of the modules to convert solar radiation energy into electrical energy. However, in… Figure 1 and / or Figure 2 In the photovoltaic system shown, there is an electrical connection between the photovoltaic array, the photovoltaic inverter, and the AC grid. Parasitic capacitance exists between the photovoltaic array and the grounded metal frame. When the photovoltaic inverter operates, a common-mode loop is formed between the parasitic capacitance, the photovoltaic array, the photovoltaic inverter, and the grid. The voltage at the output midpoint of the photovoltaic inverter relative to the grounded metal frame (i.e., the common-mode voltage) generates a common-mode current (i.e., leakage current, or the leakage current of the photovoltaic system) on the parasitic capacitance. The size of the parasitic capacitance is related to the area and material of the photovoltaic modules and the geographical environment. When the parasitic capacitance increases, the leakage current increases accordingly. The electromagnetic field generated by the leakage current radiates outwards, causing electromagnetic interference and affecting the power generation efficiency of the photovoltaic system.

[0033] The photovoltaic system provided in this application controls the leakage current of the photovoltaic system by adjusting the injection amount (or common-mode injection amount) of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter. This reduces the leakage current while maintaining the modulation ratio of the photovoltaic inverter, thus ensuring the bus utilization rate of the photovoltaic inverter is not reduced. This minimizes the power generation loss of the photovoltaic inverter, guarantees the effectiveness of the pulse width modulation of the photovoltaic system, and is simple to operate with high applicability. For ease of description, the following will use... Figure 1 The photovoltaic system in the application scenario shown is used as an example to illustrate this point.

[0034] See Figure 3 , Figure 3 This is a structural schematic diagram of the photovoltaic system provided in this application. Figure 3 The photovoltaic system shown includes photovoltaic module arrays, photovoltaic inverters, and a grounded metal frame. Figure 3 (Not shown in the image) and a sampling control unit, wherein the photovoltaic module group can be mounted on a grounded metal frame, the output terminal of the photovoltaic module group is connected to the input terminal of the photovoltaic inverter, and the output terminal of the photovoltaic inverter is connected to the power grid (i.e., the AC power grid). Please refer to [the image / reference]. Figure 4 , Figure 4 This is another structural schematic diagram of the photovoltaic system provided in this application. Optional, such as... Figure 4 As shown, the aforementioned photovoltaic inverter includes a direct current (DC) / DC conversion module, an energy storage module, and a direct current (AC) conversion module. The input terminal of the DC / DC conversion module serves as the input terminal of the photovoltaic inverter. The output terminal of the DC / DC conversion module is connected to the input terminal of the DC / AC conversion module via the energy storage module. The output terminal of the DC / AC conversion module serves as the output terminal of the photovoltaic inverter. In this application, the electrical energy generated by the photovoltaic effect of the photovoltaic module array can be directly input into the photovoltaic inverter. The DC / DC conversion module of the photovoltaic inverter performs voltage boosting / rectification and stores the electrical energy in the energy storage module. Here, the energy storage module can be composed of the photovoltaic inverter's bus capacitor. The output voltage of the bus capacitor can be converted into the AC voltage required by the grid through the DC / AC conversion module and output to the grid. Here, the photovoltaic inverter can be an isolated photovoltaic inverter or a non-isolated photovoltaic inverter. Correspondingly, the circuit topology of the DC / DC conversion module and the DC / AC conversion module in the photovoltaic inverter can be an isolated circuit topology or a non-isolated circuit topology, which can be determined according to the actual application scenario requirements and is not limited here. Optionally, the photovoltaic inverter can also be a DC / AC converter. In this case, the output terminal of the photovoltaic module group can be connected to the input terminal of the photovoltaic inverter through an energy storage module. This energy storage module can be an energy storage battery or the DC bus of the photovoltaic system, which can be determined according to the actual application scenario and is not limited here.

[0035] In some feasible implementations, Figure 3 and / or Figure 4 (For ease of description, the following will be in the format of...) Figure 3 (Taking an example for illustration, which will not be repeated below) In the photovoltaic system shown, the photovoltaic module group can be a photovoltaic array. A photovoltaic module group can be composed of one or more photovoltaic modules connected in series and parallel, and a photovoltaic module string can be obtained by connecting one or more photovoltaic modules in series. The photovoltaic module group is installed on a grounded metal frame. In other words, the grounded metal frame is the metal frame used to install the photovoltaic modules, and this metal frame is grounded. Figure 3 In the photovoltaic system shown, parasitic capacitance exists between the photovoltaic module array and the grounded metal frame. When the photovoltaic inverter operates (e.g., when the photovoltaic inverter is connected to the AC grid and provides power to the AC grid), a common-mode loop is formed between the parasitic capacitance, the photovoltaic module array, the photovoltaic inverter, and the grid. The common-mode voltage at the output midpoint of the photovoltaic inverter relative to the grounded metal frame with a fixed potential forms a leakage current on the parasitic capacitance of this common-mode loop. This leakage current can also be called the leakage current of the photovoltaic system. In other words, as... Figure 3 As shown, the common-mode voltage of the photovoltaic inverter generates leakage current in the common-mode loop. This leakage current can flow through parasitic capacitance, photovoltaic module array, photovoltaic inverter, and AC power grid. Figure 3 In the photovoltaic system shown, the sampling control unit can be coupled to the photovoltaic module group and the photovoltaic inverter respectively. The sampling control unit can be used to detect the leakage current value and adjust the injection amount of the common mode voltage of the pulse width modulation signal of the photovoltaic inverter based on the detected leakage current value to reduce the leakage current.

[0036] In some feasible implementations, the photovoltaic system described above may also include multiple photovoltaic module groups and multiple photovoltaic inverters. A parasitic capacitance exists between one photovoltaic module group and the grounded metal frame. The output terminal of one photovoltaic module group is connected to the input terminal of one photovoltaic inverter, and the output terminals of the multiple photovoltaic inverters are connected in parallel to the power grid. Optionally, the multiple photovoltaic module groups can be installed on the same grounded metal frame, or one photovoltaic module group can be installed on one grounded metal frame (in which case, the photovoltaic system may include multiple grounded metal frames). The specific implementation depends on the actual application scenario and is not limited here. See also Figure 5 , Figure 5 This is another structural schematic diagram of the photovoltaic system provided in this application. Figure 5 As shown, assume the photovoltaic system includes n photovoltaic module groups and n photovoltaic inverters. The n photovoltaic module groups can include photovoltaic module group 1, photovoltaic module group 2, ..., and photovoltaic module group n. The n photovoltaic inverters can include photovoltaic inverter 1, photovoltaic inverter 2, ..., and photovoltaic inverter n, where n is an integer greater than 1. Correspondingly, Figure 5The photovoltaic system shown may include parasitic capacitance 1, parasitic capacitance 2, ... and parasitic capacitance n. Each of the n photovoltaic module groups and the n photovoltaic inverters forms a common-mode loop with ground. For example, suppose the photovoltaic system includes photovoltaic module group 1 and photovoltaic module group 2, photovoltaic inverter 1 and photovoltaic inverter 2, wherein the output terminal of photovoltaic module group 1 is connected to the input terminal of photovoltaic inverter 1, the output terminal of photovoltaic module group 2 is connected to the input terminal of photovoltaic inverter 2, the output terminals of photovoltaic inverter 1 and photovoltaic inverter 2 are connected in parallel to the grid, there is parasitic capacitance 1 between photovoltaic module group 1 and the grounded metal frame, and there is parasitic capacitance 2 between photovoltaic module group 2 and the grounded metal frame. Then, during the operation of the photovoltaic system, a common-mode loop is formed between parasitic capacitance 1 (including grounded metal frame - parasitic capacitance 1) - photovoltaic module group 1 - photovoltaic inverter 1 - photovoltaic inverter 2 - photovoltaic module group 2 - parasitic capacitance 2 (including grounded metal frame - parasitic capacitance 2). The common-mode voltage at the output midpoint of the photovoltaic inverter relative to the grounded metal frame with a fixed potential creates leakage current on the parasitic capacitance of the common-mode loop. It can be understood that... Figure 5 In the photovoltaic system shown, the output terminals of each photovoltaic inverter are connected in parallel to the AC grid. At this time, the output midpoints of each photovoltaic inverter are at the same potential point. Therefore, the common-mode voltage of each photovoltaic inverter is the same voltage, which is the voltage between the output midpoints of the multiple photovoltaic inverters connected in parallel and ground. This common-mode voltage can generate leakage current on the parasitic capacitances (such as parasitic capacitance 1 and parasitic capacitance 2) of the common-mode loop.

[0037] In some feasible implementations, Figure 5 The photovoltaic system shown may include a sampling control unit ( Figure 5 (Not shown in the image), this sampling control unit can be the central control unit of the photovoltaic system, or a functional unit independent of the photovoltaic inverter. This sampling control unit can be coupled to each photovoltaic module group and each photovoltaic inverter, and can be used to collect data. Figure 5 The leakage current value in the common-mode loop is shown, and the injection amount of the common-mode voltage in the pulse width modulation signal of each photovoltaic inverter is adjusted based on the above current value to reduce the leakage current. Here, the pulse width modulation modulation strategy of the above multiple photovoltaic inverters can be the same modulation strategy. The above sampling control unit can simultaneously adjust the injection amount of the common-mode voltage in the pulse width modulation signal of the above multiple photovoltaic inverters to the same common-mode injection amount, thereby reducing the leakage current in the photovoltaic system. The operation is simple and applicable to application scenarios where multiple photovoltaic inverters are connected in parallel, with high applicability. Optionally, in Figure 5In the photovoltaic system shown, there can be multiple sampling control units, one of which is connected to a photovoltaic module group and a photovoltaic inverter. Optionally, the sampling control unit connected to any photovoltaic inverter can be a functional unit independent of the photovoltaic inverter itself; or it can be a functional unit within the photovoltaic inverter, meaning it can be integrated into the inverter. The specific implementation depends on the actual application scenario and is not limited here. The sampling control unit connected to any photovoltaic inverter can be used to detect the leakage current in the common-mode loop and adjust the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the current value to reduce the leakage current. It is understandable that at this time, the leakage current detected by each sampling control unit is the leakage current in the same common-mode loop. Therefore, each sampling control unit can use the same leakage current control strategy to adjust the injection amount of the common-mode voltage in the pulse width modulation signal of each photovoltaic inverter, so that the injection amount of the common-mode voltage in the pulse width modulation signal of each photovoltaic inverter is the same. This makes the common-mode voltage of the output midpoint of each photovoltaic inverter the same relative to the grounded metal frame with a fixed potential, thereby controlling the leakage current in the common-mode loop to decrease. It is simple to operate and can be applied to application scenarios where multiple photovoltaic inverters are connected in parallel, with high applicability.

[0038] In some feasible implementations, in the above-mentioned photovoltaic system (the above-mentioned Figures 1 to 5 In the photovoltaic system shown (hereinafter referred to as the above photovoltaic system), the pulse width modulation strategy of the photovoltaic inverter can be DPWM, SVPWM, or SPWM, etc., which can be determined according to the actual application scenario and is not limited here. Correspondingly, the pulse width modulation signal of the above photovoltaic inverter can be a DPWM signal, an SVPWM signal, or an SPWM signal, etc., which can be determined according to the actual application scenario and is not limited here. For ease of description, the following will use the DPWM signal as an example. The sampling control unit can adjust the injection amount of the common-mode voltage of the photovoltaic inverter's DPWM according to the real-time detected leakage current value, thereby adjusting the common-mode voltage of the photovoltaic inverter. Here, the common-mode voltage is a zero-sequence voltage, so the common-mode voltage can also be called the zero-sequence voltage. Both rectifier and inverter circuits exhibit common-mode voltage. Specifically, in terms of circuit structure, when the photovoltaic inverter is connected to the grid and the grid neutral point is connected to the reference ground, the common-mode voltage is the voltage between the inverter output point and the reference ground. However, when the grid neutral point is not grounded, the common-mode voltage is the voltage between the inverter output point and the neutral point, plus the voltage between the neutral point and the reference ground. For ease of description, the common-mode voltage will be illustrated below using the voltage at the inverter output midpoint relative to a fixed-potential grounded metal frame; hereinafter referred to as the photovoltaic inverter's common-mode voltage.

[0039] In some feasible implementations, injecting common-mode voltage into the pulse-width modulation signal of the photovoltaic (PV) inverter in a DPWM (Digital Width Modulation) system can improve the utilization rate of the PV inverter's bus voltage. The utilization rate of the PV inverter's bus capacitor can be the ratio of the PV inverter's output voltage to its bus voltage. Injecting common-mode voltage into the pulse-width modulation signal of the PV inverter can increase the PV inverter's output voltage, thereby improving the PV inverter's bus voltage utilization rate while keeping the PV inverter's bus voltage constant. See also... Figure 6 , Figure 6 This is a schematic diagram of common-mode voltage injection in a discontinuous pulse-width modulation signal provided in this application. For example... Figure 6 As shown, assuming the original modulation signal (i.e., the original modulation wave, also the original modulation voltage) in the pulse width modulation signal of the photovoltaic inverter is a three-phase sinusoidal modulation signal (i.e., a three-phase sinusoidal modulation wave, also the three-phase sinusoidal modulation voltage) U x (x = a, b, c), common-mode voltage injection is zero-sequence voltage U z The injection of the original modulation voltage and the injected zero-sequence voltage, when superimposed, yields the three-phase modulation voltage (i.e., the three-phase modulation signal, also known as the three-phase modulation wave) U. x * (x=a,b,c), the pulse width modulation signal S can be obtained by comparing the three-phase modulated wave with the triangular carrier wave. x (x = a, b, c). At this time, S... x (x = a, b, c) can be used to represent the switching states input to the three phases. After controlling the switching actions of the three phases in the photovoltaic inverter based on this pulse width modulation signal, a common-mode voltage can be obtained at the output midpoint of the photovoltaic inverter. This common-mode voltage can form leakage current in the common-mode loop of the photovoltaic system. Figure 6 In the common-mode voltage injection shown, the zero-sequence voltage U z Based on the original modulation voltage, the peak value of the triangular carrier wave can be calculated to be half the DC-side voltage value of the photovoltaic inverter. For example... Figure 6 As shown, in DPWM, the expression for the modulation wave of zero-sequence voltage injection can satisfy:

[0040] U x * =U x +U z

[0041] Among them U x * (x = a, b, c) represents the three-phase modulated wave after zero-sequence voltage injection, U x (x=a,b,c) is a three-phase sinusoidal modulation wave, U zThis refers to the injected zero-sequence voltage (i.e., common-mode voltage). Therefore, in the pulse-width modulation signal of a photovoltaic inverter, changing the amount of injected common-mode voltage (e.g., the amount of injected zero-sequence voltage) can alter the common-mode voltage of the photovoltaic inverter, thereby changing the leakage current of the photovoltaic system. In this application, all the aforementioned voltage values ​​are presented in per-unit form, and the voltage reference value is taken as half of the DC-side voltage of the photovoltaic inverter.

[0042] In some feasible implementations, the leakage current of a photovoltaic system can be expressed as the ratio of the common-mode voltage of the photovoltaic inverter (also known as the common-mode voltage to ground of the photovoltaic system) to the parasitic impedance to ground of the photovoltaic system's parasitic capacitance (also known as the parasitic impedance to ground of the photovoltaic system), which can be represented by the following simplified formula:

[0043]

[0044] Where I is the leakage current, U is the common-mode voltage to ground of the photovoltaic system, and Z is the parasitic impedance to ground of the photovoltaic system. Therefore, when the parasitic impedance to ground of the photovoltaic system remains constant, reducing the common-mode injection amount (i.e., the injection amount of zero-sequence voltage, or the injection amount of common-mode voltage) of the photovoltaic system can reduce the common-mode voltage to ground, thereby reducing the leakage current of the photovoltaic system.

[0045] In some feasible implementations, the sampling control unit can adjust the injection amount of the common-mode voltage in the pulse width modulation signal (i.e., DPWM signal) of the photovoltaic inverter based on the detected leakage current value to reduce the leakage current of the photovoltaic system. Here, while adjusting the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the leakage current value, the sampling control unit can control the leakage current while maintaining the modulation ratio of the photovoltaic inverter, thereby ensuring that the bus utilization rate of the photovoltaic inverter is not reduced, minimizing the power generation loss of the photovoltaic inverter, guaranteeing the effectiveness of the pulse width modulation of the photovoltaic system, and offering simple operation and high applicability.

[0046] Optionally, in some feasible implementations, when the sampling control unit detects that the leakage current value is greater than the current threshold, it can reduce the injection amount of the common-mode voltage in the pulse-width modulation signal of the photovoltaic inverter by decreasing the common-mode injection coefficient. Here, the sampling control unit can change the injection amount of the common-mode voltage in the pulse-width modulation signal of the photovoltaic inverter by adjusting the common-mode injection coefficient, which is simple to operate and highly applicable. See also Figure 7 , Figure 7 This is a waveform diagram of the pulse width modulation signal and the common-mode voltage input to the pulse width modulation signal provided in this application. Figure 7In the waveform diagram shown, the modulation ratio M of the pulse width modulation (PWM) of the photovoltaic inverter can be 1.05 (where 1.05 can be an experimental value, and M can also be other experimental values ​​greater than 1, which can be determined according to the actual application scenario and are not restricted here). In this case, line 1 represents the waveform of the common-mode injection amount (i.e., the injection amount of the common-mode voltage) when the common-mode injection coefficient k of the PWM signal is adjusted to 1 when the modulation ratio M is 1.05. Line 2 represents the waveform of the common-mode injection amount when the common-mode injection coefficient k of the PWM signal is adjusted to 0 when the modulation ratio M is 1.05. Line 3 represents the DPWM modulation waveform when the common-mode injection coefficient k of the PWM signal is adjusted to 0 when the modulation ratio M is 1.05 (i.e., the modulation waveform when the PWM signal is a DPWM signal). Line 4 represents the DPWM modulation waveform when the common-mode injection coefficient k of the PWM signal is adjusted to 1 when the modulation ratio M is 1.05 (i.e., the modulation waveform when the PWM signal is a DPWM signal). See also... Figure 8 , Figure 8 This is another waveform diagram of the pulse width modulation signal and the common-mode voltage input to the pulse width modulation signal provided in this application. Figure 8 In the waveform diagram shown, the modulation ratio M of the pulse width modulation (PWM) of the photovoltaic inverter can be 0.9 (where 0.9 can be an experimental value, and M can also be other experimental values ​​less than or equal to 1, which can be determined according to the actual application scenario and are not restricted here). In this case, line 1 represents the waveform of the common-mode injection amount (i.e., the injection amount of the common-mode voltage) when the common-mode injection coefficient k of the PWM signal is adjusted to 1 when the modulation ratio M is 0.9. Line 2 represents the waveform of the common-mode injection amount when the common-mode injection coefficient k of the PWM signal is adjusted to 0.3 when the modulation ratio M is 0.9. Line 3 represents the DPWM modulation waveform (i.e., the modulation waveform when the PWM signal is a DPWM signal) when the common-mode injection coefficient k of the PWM signal is adjusted to 0.3 when the modulation ratio M is 0.9. Line 4 represents the DPWM modulation waveform (i.e., the modulation waveform when the PWM signal is a DPWM signal) when the common-mode injection coefficient k of the PWM signal is adjusted to 1 when the modulation ratio M is 0.9. Figure 7 or Figure 8As shown in the waveform diagram, when the modulation ratio is the same but the common-mode injection coefficient is different, the waveform of the pulse-width modulation (PWM) signal of the photovoltaic (PV) inverter is also different. Specifically, the smaller the common-mode injection coefficient, the closer the waveform of the PWM signal is to a smooth sine curve. In other words, the smaller the common-mode injection coefficient, the closer the three-phase modulation wave after common-mode voltage injection is to the three-phase sinusoidal modulation wave before the common-mode voltage is superimposed; that is, the smaller the common-mode voltage in the PWM signal. Therefore, the sampling control unit can reduce the amount of common-mode voltage injected into the PWM signal by reducing the common-mode injection coefficient. Here, by reducing the common-mode injection coefficient of the PV inverter's PWM signal, the amount of common-mode injection in the PWM signal can be effectively reduced. While suppressing leakage current, the PV system can still continue to operate in the current PWM strategy mode. That is, the adjustment of the common-mode injection amount does not affect the modulation ratio of the PV inverter, thus reducing the power generation loss of the PV system.

[0047] In some feasible implementations, such as Figure 7 and Figure 8 As shown in the waveform diagram, when the modulation ratio and common-mode injection coefficient are different in the pulse width modulation signal of the photovoltaic inverter, the common-mode injection amount in the pulse width modulation signal of the photovoltaic inverter is also different, resulting in different waveforms of the pulse width modulation signal of the photovoltaic inverter. For example... Figure 8 As shown, for scenarios where the modulation ratio M is less than or equal to 1, the common-mode injection amount of the photovoltaic inverter decreases as the common-mode injection coefficient k decreases. It can be understood that when the common-mode injection coefficient drops to 0, the common-mode injection amount of the photovoltaic inverter is at its minimum, and the photovoltaic system operates under the condition of minimum leakage current. Specifically, the sampling control unit can reduce the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal until it reaches 0 when the detected leakage current value of the photovoltaic system is greater than the current threshold and the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1. In other words, in this application, for scenarios where the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1, such as when the photovoltaic inverter's pulse width modulation is SPWM, the sampling control unit can reduce the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal to 0 when it detects that the leakage current is greater than the current threshold. At this time, the injection amount of common-mode voltage in the pulse width modulation signal of the photovoltaic inverter (also known as common-mode injection amount) is the minimum, the photovoltaic system is in the minimum leakage current condition, the operation is simple, and it does not affect the modulation ratio of the photovoltaic inverter. It can keep the bus utilization rate of the photovoltaic inverter (the bus utilization rate is the ratio of the output voltage of the photovoltaic inverter to the bus voltage) from decreasing, which can ensure the power generation efficiency of the photovoltaic system, ensure the working stability of the photovoltaic system, and has high applicability.

[0048] In some feasible implementations, such as Figure 7 As shown, for scenarios where the modulation ratio M is greater than 1, even when the common-mode injection coefficient drops to 0, the photovoltaic inverter still has a certain amount of common-mode injection to ensure the pulse width modulation (PWM) effect. The sampling control unit can reduce the common-mode injection coefficient of the PV inverter's PWM signal when the modulation ratio is greater than 1, thereby reducing the injection of common-mode voltage into the PWM signal, until the common-mode injection coefficient is 0 and / or the detected leakage current value is less than or equal to the aforementioned current threshold. In other words, for scenarios where the PV inverter's PWM modulation modulation ratio is greater than 1, such as when the PV inverter's PWM is DPWM, the sampling control unit can also reduce the common-mode injection coefficient of the PV inverter's PWM signal to 0 when the detected leakage current is greater than the current threshold. At this time, the PV inverter's PWM signal still has a certain amount of common-mode injection to ensure the DPWM modulation effect of the PV system, reducing the leakage current of the PV system without affecting the PV inverter's modulation ratio, maintaining the PV inverter's bus utilization rate, ensuring the PV system's power generation efficiency, ensuring the PV system's operational stability, and demonstrating high applicability. Furthermore, when the modulation ratio of the photovoltaic inverter is greater than 1, if the sampling control unit detects a leakage current value greater than the aforementioned current threshold after adjusting the common-mode injection coefficient to 0, it can adjust the modulation ratio of the photovoltaic inverter's pulse width modulation to be less than or equal to 1 (for example, adjusting the photovoltaic inverter's pulse width modulation strategy to SPWM, in which case no common-mode voltage is injected into the photovoltaic inverter's pulse width modulation signal). At this time, the photovoltaic system operates under the condition of minimum leakage current. In this application, when the sampling control unit modulates the photovoltaic inverter's pulse width modulation modulation ratio to be less than or equal to 1, no common-mode voltage can be injected into the photovoltaic inverter's pulse width modulation signal. At this time, the photovoltaic system can be controlled to operate under the condition of minimum leakage current, which is simple to operate and highly applicable.

[0049] Optionally, in some feasible implementations, when the sampling control unit adjusts the modulation ratio of the photovoltaic inverter's pulse width modulation from greater than 1 to less than or equal to 1, the modulation strategy of the photovoltaic inverter's pulse width modulation can be directly switched. For example, the modulation strategy of the photovoltaic inverter's pulse width modulation can be switched from DPWM to SPWM so that the modulation ratio of the photovoltaic inverter's pulse width modulation is less than or equal to 1. At this time, no common-mode voltage is injected into the pulse width modulation signal of the photovoltaic inverter, and the photovoltaic system operates under the condition of minimum leakage current, which is simple to operate.

[0050] In this application, the sampling control unit can adjust the common-mode injection amount in the pulse width modulation signal of the photovoltaic inverter and / or the modulation ratio of the photovoltaic inverter based on the real-time detected leakage current value. By gradually reducing the common-mode injection coefficient, the common-mode injection amount in the pulse width modulation signal of the photovoltaic inverter can be smoothly adjusted, thereby achieving the purpose of adaptively adjusting the leakage current of the photovoltaic inverter. While controlling the leakage current, the modulation ratio of the photovoltaic inverter can be kept constant, thus maintaining the bus utilization rate of the photovoltaic inverter, minimizing the power generation loss of the photovoltaic inverter, ensuring the effectiveness of the pulse width modulation of the photovoltaic system, and offering simple operation and high applicability. When the modulation ratio of the photovoltaic inverter is greater than 1, if the sampling control unit still detects a leakage current value greater than the aforementioned current threshold after adjusting the common-mode injection coefficient to 0, it can adjust the modulation ratio of the photovoltaic inverter's pulse width modulation to be less than or equal to 1. At this time, no common-mode voltage is injected into the pulse width modulation signal of the photovoltaic inverter, controlling the photovoltaic system to operate under the minimum leakage current condition, further simplifying operation and enhancing applicability.

[0051] See Figure 9 , Figure 9 This is a flowchart illustrating the leakage current control method for the photovoltaic system provided in this application. The method provided in this application is applicable to the above-mentioned... Figures 1 to 5 The provided sampling control unit in the photovoltaic system, in which parasitic capacitance exists between the photovoltaic module group and the grounded metal frame, includes the following steps:

[0052] S901, the sampling control unit detects the leakage current value formed on the parasitic capacitance by the common-mode voltage of the photovoltaic inverter.

[0053] In some feasible implementations, the sampling control unit can detect the current value of the common-mode loop of the photovoltaic system in real time, so as to monitor the leakage current value formed on the parasitic capacitance by the common-mode voltage of the photovoltaic inverter in the photovoltaic system. Optionally, the sampling control unit can detect the current value in real time during the operation of the photovoltaic inverter (such as when the photovoltaic inverter is connected to the AC grid and provides power to the AC grid). Figure 3 The leakage current in the common-mode loop formed between parasitic capacitance, photovoltaic module array, photovoltaic inverter, and grid in the photovoltaic system shown is used to detect the leakage current of the photovoltaic system. The sampling control unit can also detect leakage current in real time during the operation of the photovoltaic inverter. Figure 5 The leakage current in the common-mode loop formed by each of the n photovoltaic module groups and the n photovoltaic inverters in the photovoltaic system shown is used to detect the leakage current of the photovoltaic system. For example, the sampling control unit can detect the leakage current in real time during the operation of the photovoltaic inverter. Figure 5The leakage current in the common-mode loop formed between parasitic capacitor 1 (including the grounding metal frame - parasitic capacitor 1), photovoltaic module group 1, photovoltaic inverter 1, photovoltaic inverter 2, photovoltaic module group 2, and parasitic capacitor 2 (including the grounding metal frame - parasitic capacitor 2) in the photovoltaic system shown is used to detect the leakage current of the photovoltaic system. The specific method can be determined according to the actual application scenario and is not limited here.

[0054] S902, the sampling control unit determines whether the detected leakage current value is greater than the current threshold. If the determination result is yes, then step S903 is executed.

[0055] S903, the sampling control unit reduces the injection amount of common-mode voltage in the pulse width modulation signal by decreasing the common-mode injection coefficient of the photovoltaic inverter's pulse width modulation signal.

[0056] In some feasible implementations, the sampling control unit can determine in real time whether the detected leakage current value is greater than a current threshold. If the determination result is yes, the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter can be adjusted based on the detected leakage current value to reduce the leakage current. Optionally, during the process of adjusting the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the detected current value, if the current value is greater than the current threshold, the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter can be reduced to reduce the injection amount of the common-mode voltage in the pulse width modulation signal. By adjusting the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter, the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter can be changed. This method is simple to operate and has high applicability. Furthermore, during the process of adjusting the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the leakage current value, the sampling control unit can maintain the modulation ratio of the photovoltaic inverter while controlling the leakage current. This ensures that the bus utilization rate of the photovoltaic inverter is not reduced, minimizes the power generation loss of the photovoltaic inverter, and guarantees the effect of pulse width modulation of the photovoltaic system. It is simple to operate and highly applicable.

[0057] S904, the sampling control unit determines whether the common mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter has decreased to 0. If the determination result is yes, then step S905 is executed; otherwise, step S902 is executed.

[0058] In some feasible implementations, such as Figure 7 and Figure 8As shown in the waveform diagram, when the modulation ratio and common-mode injection coefficient of the pulse width modulation (PWM) signal of the photovoltaic (PV) inverter are different, the common-mode injection amount of the PWM signal of the PV inverter is also different, resulting in different waveforms of the PWM signal. As the common-mode injection coefficient k decreases, the common-mode injection amount of the PV inverter also decreases. The sampling control unit can gradually decrease the common-mode injection coefficient of the PV inverter's PWM signal based on the detected leakage current value until the leakage current value is less than or equal to the current threshold, or the common-mode injection coefficient of the PV inverter's PWM signal decreases to 0.

[0059] S905, the sampling control unit determines whether the modulation ratio of the pulse width modulation of the photovoltaic inverter is greater than 1. If the determination result is yes, then step S906 is executed; otherwise, step S907 is executed.

[0060] S906, adjust the modulation ratio of the pulse width modulation of the photovoltaic inverter to be less than or equal to 1.

[0061] S907 ensures that the photovoltaic system operates under conditions with minimal leakage current.

[0062] In some feasible implementations, such as Figure 8 As shown, for scenarios where the modulation ratio M is less than or equal to 1, it can be understood that when the common-mode injection coefficient drops to 0, the common-mode injection of the photovoltaic inverter is at its minimum, and the photovoltaic system operates under the condition of minimum leakage current. The sampling control unit can reduce the common-mode injection coefficient of the photovoltaic inverter's pulse-width modulation signal until it reaches 0 when the detected leakage current value of the photovoltaic system is greater than the current threshold and the modulation ratio of the photovoltaic inverter's pulse-width modulation is less than or equal to 1. In other words, in this application, for scenarios where the modulation ratio of the photovoltaic inverter's pulse-width modulation is less than or equal to 1, such as when the photovoltaic inverter's pulse-width modulation is SPWM, the sampling control unit can reduce the common-mode injection coefficient of the photovoltaic inverter's pulse-width modulation signal to 0 when it detects that the leakage current is greater than the current threshold. At this time, the injection amount of common-mode voltage in the pulse width modulation signal of the photovoltaic inverter (also known as common-mode injection amount) is the minimum, the photovoltaic system is in the minimum leakage current condition, the operation is simple, and it does not affect the modulation ratio of the photovoltaic inverter. It can keep the bus utilization rate of the photovoltaic inverter (the bus utilization rate is the ratio of the output voltage of the photovoltaic inverter to the bus voltage) from decreasing, which can ensure the power generation efficiency of the photovoltaic system, ensure the working stability of the photovoltaic system, and has high applicability.

[0063] In some feasible implementations, for scenarios where the modulation ratio M is greater than 1, even after the common-mode injection coefficient drops to 0, the photovoltaic inverter still has a certain amount of common-mode injection to ensure the pulse width modulation (PWM) effect. The sampling control unit can reduce the common-mode injection coefficient of the PV inverter's PWM signal when the modulation ratio is greater than 1, thereby reducing the injection of common-mode voltage into the PWM signal, until the common-mode injection coefficient is 0 and / or the detected leakage current value is less than or equal to the aforementioned current threshold. In other words, for scenarios where the PV inverter's PWM modulation modulation has a modulation ratio greater than 1, such as when the PV inverter's PWM is DPWM, the sampling control unit can also reduce the common-mode injection coefficient of the PV inverter's PWM signal to 0 when the detected leakage current is greater than the current threshold. At this time, the PV inverter's PWM signal still has a certain amount of common-mode injection to ensure the DPWM modulation effect of the PV system, reducing the leakage current of the PV system without affecting the PV inverter's modulation ratio, maintaining the PV inverter's bus utilization rate, ensuring the PV system's power generation efficiency, ensuring the PV system's operational stability, and offering high applicability. Furthermore, when the modulation ratio of the photovoltaic inverter is greater than 1, if the sampling control unit detects a leakage current value greater than the aforementioned current threshold after adjusting the common-mode injection coefficient to 0, it can adjust the modulation ratio of the photovoltaic inverter's pulse width modulation to be less than or equal to 1. For example, it can switch the pulse width modulation strategy of the photovoltaic inverter from DPWM to SPWM to make the modulation ratio of the photovoltaic inverter's pulse width modulation less than or equal to 1. At this time, no common-mode voltage is injected into the pulse width modulation signal of the photovoltaic inverter, and the photovoltaic system operates under the condition of minimum leakage current. In this application, when the sampling control unit modulates the modulation ratio of the photovoltaic inverter's pulse width modulation to be less than or equal to 1, no common-mode voltage is injected into the photovoltaic inverter's pulse width modulation signal. At this time, the photovoltaic system can be controlled to operate under the condition of minimum leakage current, which is simple to operate and highly applicable.

[0064] In this application, the sampling control unit can adjust the common-mode injection amount in the pulse width modulation signal of the photovoltaic inverter and / or the modulation ratio of the photovoltaic inverter based on the real-time detected leakage current value. By gradually reducing the common-mode injection coefficient, the common-mode injection amount in the pulse width modulation signal of the photovoltaic inverter can be smoothly adjusted, thereby achieving the purpose of adaptively adjusting the leakage current of the photovoltaic inverter. The sampling control unit can maintain the modulation ratio of the photovoltaic inverter while controlling the leakage current, thus ensuring that the bus utilization rate of the photovoltaic inverter is not reduced, minimizing the power generation loss of the photovoltaic inverter, and ensuring the effect of pulse width modulation of the photovoltaic system. It is simple to operate and highly applicable. In application scenarios where the modulation ratio of the photovoltaic inverter is greater than 1, if the leakage current value is still detected to be greater than the above current threshold after the sampling control unit adjusts the common-mode injection coefficient to reduce it to 0, the modulation ratio of the pulse width modulation of the photovoltaic inverter can be adjusted to be less than or equal to 1. At this time, no common-mode voltage is injected into the pulse width modulation signal of the photovoltaic inverter, and the photovoltaic system can be controlled to the minimum leakage current condition. It is simple to operate and highly applicable.

Claims

1. A photovoltaic system, characterized in that, The photovoltaic system includes at least one photovoltaic module group, at least one photovoltaic inverter, a grounded metal frame, and a sampling control unit. The photovoltaic module group is mounted on the grounded metal frame, the output terminal of the photovoltaic module group is connected to the input terminal of the photovoltaic inverter, and the output terminal of the photovoltaic inverter is connected to the power grid. The sampling control unit is coupled to the photovoltaic module group and the photovoltaic inverter respectively, and is used to detect the leakage current value formed by the common mode voltage of the photovoltaic inverter on the parasitic capacitance. The parasitic capacitance exists between the photovoltaic module group and the grounded metal frame. When the leakage current value is detected to be greater than the current threshold, the common mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter is reduced while the modulation ratio of the pulse width modulation of the inverter remains unchanged, so as to reduce the injection amount of the common mode voltage in the pulse width modulation signal and reduce the leakage current. The sampling control unit is used to reduce the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter and keep the pulse width modulation modulation of the inverter unchanged when the modulation ratio of the pulse width modulation of the photovoltaic inverter is less than or equal to 1, until the common-mode injection coefficient is 0.

2. The photovoltaic system according to claim 1, characterized in that, The sampling control unit is further configured to reduce the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter and keep the modulation ratio of the pulse width modulation of the inverter unchanged when the modulation ratio of the photovoltaic inverter is greater than 1, so as to reduce the injection amount of the common-mode voltage in the pulse width modulation signal until the common-mode injection coefficient is 0 and / or the current value of the leakage current is detected to be less than or equal to the current threshold.

3. The photovoltaic system according to claim 2, characterized in that, When the modulation ratio of the photovoltaic inverter is greater than 1, the sampling control unit is further configured to adjust the modulation ratio of the pulse width modulation of the photovoltaic inverter to be less than or equal to 1 when the common mode injection coefficient decreases to 0 and the current value of the leakage current is detected to be greater than the current threshold.

4. The photovoltaic system according to claim 3, characterized in that, The sampling control unit is also used to switch the modulation strategy of the pulse width modulation of the photovoltaic inverter, so as to adjust the modulation ratio of the pulse width modulation of the photovoltaic inverter to be less than or equal to 1.

5. The photovoltaic system according to any one of claims 1-4, characterized in that, The photovoltaic system includes at least two photovoltaic module groups and at least two photovoltaic inverters. There is a parasitic capacitance between one photovoltaic module group and the grounded metal frame. The output terminal of one photovoltaic module group is connected to the input terminal of one photovoltaic inverter. The output terminals of the at least two photovoltaic inverters are connected in parallel to the power grid. Each photovoltaic module group and the at least two photovoltaic inverters form a common-mode loop to ground. The sampling control unit is used to detect the leakage current value formed by the common-mode voltage of the at least two photovoltaic inverters on the parasitic capacitance of the common-mode loop, and adjust the injection amount of the common-mode voltage in the pulse width modulation signal of the at least two photovoltaic inverters based on the current value to reduce the leakage current.

6. The photovoltaic system according to any one of claims 1-4, characterized in that, The sampling control unit is integrated into the photovoltaic inverter.

7. The photovoltaic system according to any one of claims 1-4, characterized in that, The photovoltaic inverter includes a DC / DC conversion module, an energy storage module, and a DC / AC conversion module. The input terminal of the DC / DC conversion module serves as the input terminal of the photovoltaic inverter. The output terminal of the DC / DC conversion module is connected to the input terminal of the DC / AC conversion module through the energy storage module. The output terminal of the DC / AC conversion module serves as the output terminal of the photovoltaic inverter.

8. The photovoltaic system according to any one of claims 1-4, characterized in that, The photovoltaic inverter is a DC / AC conversion module, and the photovoltaic system also includes an energy storage module. The output of the photovoltaic module group is connected to the input of the DC / AC conversion module through the energy storage module, and the output of the DC / AC conversion module serves as the output of the photovoltaic inverter.

9. The photovoltaic system according to any one of claims 1-4, characterized in that, A photovoltaic module group includes multiple photovoltaic strings connected in parallel. Each photovoltaic string is formed by connecting at least one photovoltaic module in series. The parallel connection of the multiple photovoltaic strings serves as the output terminal of the photovoltaic module group.

10. A method for controlling leakage current in a photovoltaic system, characterized in that, The method is applicable to a sampling control unit in a photovoltaic system as described in any one of claims 1-9, wherein parasitic capacitance exists between the photovoltaic module group and the grounded metal frame, and the method includes: The sampling control unit detects the leakage current value formed on the parasitic capacitor by the common-mode voltage of the photovoltaic inverter; The sampling control unit adjusts the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the current value to reduce the leakage current; The method of adjusting the injection amount of the common-mode voltage in the pulse width modulation signal of the photovoltaic inverter based on the current value includes: If the current value is greater than the current threshold, the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter is reduced while the modulation ratio of the pulse width modulation of the inverter remains unchanged, so as to reduce the injection amount of the common-mode voltage in the pulse width modulation signal and reduce the leakage current. Wherein, reducing the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter includes: If the modulation ratio of the pulse width modulation of the photovoltaic inverter is less than or equal to 1, then the common mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter is reduced while the modulation ratio of the pulse width modulation of the inverter remains unchanged until the common mode injection coefficient is 0.

11. The method according to claim 10, characterized in that, The reduction of the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter also includes: If the modulation ratio of the photovoltaic inverter is greater than 1, then the common-mode injection coefficient of the pulse width modulation signal of the photovoltaic inverter is reduced while the modulation ratio of the pulse width modulation of the inverter remains unchanged, until the common-mode injection coefficient is 0 and / or the current value of the leakage current is detected to be less than or equal to the current threshold.

12. The method according to claim 11, characterized in that If the modulation ratio of the photovoltaic inverter is greater than 1, the method further includes: If the common-mode injection coefficient decreases to 0 and the detected leakage current value is greater than the current threshold, the sampling control unit adjusts the modulation ratio of the pulse width modulation of the photovoltaic inverter to be less than or equal to 1.

13. The method according to claim 12, characterized in that, The adjustment of the modulation ratio of the pulse width modulation of the photovoltaic inverter to be less than or equal to 1 includes: Switch the pulse width modulation (PWM) strategy of the photovoltaic inverter to adjust the PWM modulation ratio of the photovoltaic inverter to be less than or equal to 1.

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