Inverter system and DC side ground short circuit protection method

Abstract

The invention discloses an inverter system and a direct current side ground short circuit protection method, and relates to the technical field of electronic power, the inverter system comprises a controller, an inverter, an alternating current side device and at least one direct current side device, the at least one direct current side device is connected with a direct current input side of the inverter through a bus capacitor, the alternating current output side of the inverter is connected with alternating current side equipment; the direct current side equipment comprises a direct current conversion module and a controller, and is used for controlling the direct current conversion module to reduce the output voltage of the direct current side equipment under the condition that the direct current input side of the inverter is short-circuited to the ground so as to reduce the voltage of the direct current side equipment for charging the bus capacitor; or the direct current side equipment comprises a bypass switch and a controller, and is used for controlling the bypass switch to be closed under the condition that the direct current input side of the inverter is short-circuited to the ground, so as to disconnect the charging path of the direct current side equipment to the bus capacitor. According to the invention, the overvoltage damage of the bus capacitor can be avoided at high efficiency and low cost when the direct current side is short-circuited to the ground.

Description

Inverter system and DC side ground short circuit protection method Technical Field

[0001] This invention relates to the field of electronic power technology, and in particular to an inverter system and a method for protecting the DC side from ground short circuits. Background Technology

[0002] Currently, to meet the power generation demands of inverters, the DC-side installed capacity is very high compared to the AC-side rated capacity, resulting in a very high open-circuit voltage. If a short circuit occurs on the DC side to ground, this high open-circuit voltage will be applied to the bus capacitor, causing overvoltage damage. To address this issue, existing technologies typically use isolated inverters; however, these methods suffer from low efficiency and high cost.

[0003] Therefore, how to achieve efficient and low-cost operation while avoiding overvoltage damage to the bus capacitor during a DC-side short circuit to ground has become an urgent problem to be solved. Summary of the Invention

[0004] This invention provides an inverter system for efficiently and cost-effectively preventing overvoltage damage to the bus capacitor when the DC side is short-circuited to ground. The inverter system includes a controller, an inverter, AC-side equipment, and at least one DC-side equipment. The at least one DC-side equipment is connected to the DC input side of the inverter via the bus capacitor, and the AC output side of the inverter is connected to the AC-side equipment. The DC-side equipment includes a DC-DC conversion module. The controller is used to control the DC-DC conversion module to reduce the output voltage of the DC-side equipment when the DC input side of the inverter is short-circuited to ground, thereby reducing the voltage at which the DC-side equipment charges the bus capacitor. Alternatively, the DC-side equipment includes a bypass switch. The controller is used to control the bypass switch to close when the DC input side of the inverter is short-circuited to ground, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor.

[0005] Optionally, the controller controls the DC-DC converter module to reduce the output voltage of the DC-side equipment, including: controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment to less than a preset bus voltage protection threshold.

[0006] Optionally, the controller controls the DC-DC converter module to reduce the output voltage of the DC-side equipment to less than a preset bus voltage protection threshold, including: adjusting the duty cycle of the power switch transistor of the DC-DC converter module to reduce the output voltage of the DC-side equipment to less than the preset bus voltage protection threshold.

[0007] Optionally, the inverter system further includes an AC side switch; one end of the AC side switch is connected to the AC output side of the inverter, and the other end is connected to the AC side equipment; the controller is also used to control the DC-DC converter module to reduce the output voltage of the DC side equipment, or to control the bypass switch to close, and then control the AC side switch to open to disconnect the inverter from the AC side equipment.

[0008] Optionally, the DC-side device further includes a DC-side switch; the controller is also configured to control the DC-DC converter module to reduce the output voltage of the DC-side device, or to control the bypass switch to close, and then control the DC-side switch to turn off to disconnect the inverter from the DC-side device.

[0009] Optionally, the DC input side of the inverter is short-circuited to ground, including: the output current of the DC-DC converter module is greater than or equal to a preset first current value, and the DC side of the inverter is over-voltage or under-voltage to ground; or, the input current of the DC-DC converter module is greater than or equal to a preset second current value, and the DC side of the inverter is over-voltage or under-voltage to ground; or, the leakage current on the AC output side of the inverter is greater than or equal to a preset third current value, and the voltage of the bus capacitor is greater than or equal to a preset first voltage value; or, the leakage current on the AC output side of the inverter is greater than or equal to a preset fourth current value, and the rising slope of the bus capacitor voltage is greater than or equal to a preset slope threshold.

[0010] This invention provides a DC-side short-circuit protection method to efficiently and cost-effectively prevent overvoltage damage to the bus capacitor during a DC-side short circuit. The method is applied to an inverter system, which includes an inverter, AC-side equipment, and at least one DC-side device. The at least one DC-side device is connected to the DC input side of the inverter via a bus capacitor, and the AC output side of the inverter is connected to the AC-side equipment. The method includes: in the event of a short circuit to ground on the DC input side of the inverter, controlling the DC-DC converter module of the DC-side device to reduce the output voltage of the DC-side device, thereby reducing the voltage at which the DC-side device charges the bus capacitor; or, in the event of a short circuit to ground on the DC input side of the inverter, controlling the bypass switch of the DC-side device to close, thereby disconnecting the charging path of the DC-side device to the bus capacitor.

[0011] Optionally, controlling the DC-DC converter module of the DC-side device to reduce the output voltage of the DC-side device in order to reduce the voltage at which the DC-side device charges the bus capacitor includes: controlling the DC-DC converter module to reduce the output voltage of the DC-side device to less than a preset bus voltage protection threshold.

[0012] Optionally, controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment to below a preset bus voltage protection threshold includes: adjusting the duty cycle of the power switch transistor of the DC-DC converter module to reduce the output voltage of the DC-side equipment to below the preset bus voltage protection threshold.

[0013] Optionally, the inverter system further includes an AC side switch; after controlling the DC-DC conversion module to reduce the output voltage of the DC-side equipment, or controlling the bypass switch to close, the method further includes: controlling the AC side switch to open to disconnect the inverter from the AC side equipment.

[0014] In this embodiment of the invention, in the event of a short circuit to ground on the DC input side of the inverter, if the DC-side equipment includes a DC-DC converter module, the controller controls the DC-DC converter module to reduce the output voltage of the DC-side equipment, thereby reducing the voltage at which the DC-side equipment charges the bus capacitor; or if the DC-side equipment includes a bypass switch, the controller controls the bypass switch to close, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor. In this way, without the need for isolated inverters or similar methods, and based on existing non-isolated inverters, ground short-circuit protection control can be achieved with minimal cost increase and high efficiency, preventing overvoltage damage to the bus capacitor. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, 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.

[0016] In the accompanying drawings: Figure 1 is a structural diagram of an inverter system provided in an embodiment of the present invention; Figure 2 is a schematic diagram of the inverter system shown in Figure 1 with the negative terminal of the DC side short-circuited to ground; Figure 3 is a schematic diagram of the inverter system shown in Figure 1 with the positive terminal of the DC side short-circuited to ground; Figure 4 is a schematic diagram of the short-circuit path between the DC power supply and the DC-DC converter module provided in an embodiment of the present invention; Figure 5 is a structural diagram of another inverter system provided in an embodiment of the present invention; Figure 6 is a structural diagram of another inverter system provided in an embodiment of the present invention; Figure 7 is a schematic diagram of the inverter system shown in Figure 6 with the DC side short-circuited to ground; Figure 8 is a logic diagram for determining whether the DC side of the inverter is short-circuited to ground provided in an embodiment of the present invention; Figure 9 is a structural diagram of a photovoltaic energy storage system provided in an embodiment of the present invention; Figure 10 is a schematic diagram of the photovoltaic energy storage system shown in Figure 9 with the negative terminal of the DC side short-circuited to ground; Figure 11 is a schematic diagram of the photovoltaic energy storage system shown in Figure 9 with the DC side short-circuited to ground. Figure 12 is a schematic diagram of the short-circuit condition between the positive terminal and ground, as shown in Figure 9; Figure 13 is a schematic diagram of the voltage and current operating curves of the photovoltaic module provided in this embodiment of the invention; Figure 14 is a logic diagram for determining whether the photovoltaic module is short-circuited to ground, as shown in this embodiment of the invention; Figure 15 is a circuit diagram of a series-type PID repair module provided in this embodiment of the invention; Figure 16 is a circuit diagram of another series-type PID repair module provided in this embodiment of the invention; Figure 17 is a circuit diagram of another series-type PID repair module provided in this embodiment of the invention; Figure 18 is an application example diagram of a three-phase four-wire photovoltaic energy storage system based on T-type three-level, as shown in this embodiment of the invention; Figure 19 is an application example diagram of a three-phase three-wire photovoltaic energy storage system based on T-type three-level, as shown in this embodiment of the invention; Figure 20 is an application example diagram of a single-phase photovoltaic energy storage system provided in this embodiment of the invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0018] In the description of this specification, the terms "comprising," "including," "having," and "containing" are open-ended terms, meaning that they include but are not limited to. The terms "an embodiment," "a specific embodiment," "some embodiments," and "for example," etc., refer to specific features, structures, or characteristics described in connection with that embodiment or example that are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. The order of steps involved in the various embodiments is used to illustrate the implementation of this application, and the order of steps is not limited and can be adjusted appropriately as needed.

[0019] Research has revealed that in order to meet the power generation needs of the inverter system, the DC-side installed capacity is matched with the AC-side rated capacity of the inverter system at a very high ratio, resulting in a very high open-circuit voltage. Once the DC side is short-circuited to ground, the high open-circuit voltage will be applied to the bus capacitor, causing the bus capacitor to be damaged by overvoltage.

[0020] Taking photovoltaic systems (such as TN and TT power supply systems) as an example, once a photovoltaic module short-circuits to ground, the high open-circuit voltage of the photovoltaic module will be applied to the bus capacitor, causing overvoltage damage to the bus capacitor. Specifically, in order to provide unbalanced load carrying capacity and adapt to TN and TT power supply systems, a three-phase four-wire connection is usually adopted, with the DC bus midpoint being supplied by the N line at the AC port. Since the N line is often grounded at the near or far end, this greatly increases the difficulty of protecting the photovoltaic module from short circuit to ground in non-isolated inverters. Once a photovoltaic module short-circuits to ground, the short-circuit point of the high-voltage photovoltaic module is directly connected to the N point or the DC bus midpoint, causing the upper or lower half of the bus capacitor to overcharge to the open-circuit voltage of the photovoltaic module, resulting in damage to the bus capacitor. To solve the above problems, existing technologies usually use isolated inverters, but these methods have problems such as low efficiency and high cost, which have significant limitations.

[0021] Based on this, embodiments of the present invention provide an inverter system and a DC-side ground short-circuit protection method, which eliminates the need for an isolated inverter. Based on existing non-isolated inverters, it achieves ground short-circuit protection control when the DC side is short-circuited to ground with minimal cost increase, thus avoiding overvoltage damage to the bus capacitor.

[0022] Figure 1 is a structural diagram of an inverter system provided in an embodiment of the present invention. As shown in Figure 1, the inverter system includes a controller, an inverter, AC-side equipment, and DC-side equipment. The DC-side equipment is connected to the DC input side of the inverter through a bus capacitor, and the AC output side of the inverter is connected to the AC-side equipment.

[0023] The DC-side equipment in Figure 1 includes a DC power supply; the DC-side equipment also includes one or any combination of a DC-DC converter module, a DC-side switch, and a bypass switch. The AC-side equipment can be an AC load and / or an AC power grid.

[0024] The inverter system provided in this embodiment of the invention can be a three-phase four-wire inverter system, a three-phase three-wire inverter system, or a single-phase two-wire inverter system, depending on the power distribution configuration (Figure 1 shows a three-phase four-wire inverter system). Based on different DC power supplies, the inverter system can be a photovoltaic system, an energy storage system, or a photovoltaic energy storage system, etc.; if the inverter system is a photovoltaic system, the DC power supply is a photovoltaic module; if the inverter system is an energy storage system, the DC power supply is an energy storage module (such as an energy storage battery); if the inverter system is a photovoltaic energy storage system, the DC power supply can include photovoltaic modules and energy storage modules, and the photovoltaic modules are connected to the DC side of the inverter equipment through a DC-DC conversion module and a bus capacitor, while the energy storage module is coupled to the DC bus.

[0025] To clearly understand this scheme, the following uses the three-phase four-wire inverter system in Figure 1 as an example to explain the two operating conditions of DC side short circuit to ground.

[0026] Figure 2 is a schematic diagram of a three-phase four-wire inverter system under the condition of a short circuit to ground at the negative terminal of the DC side. As shown in Figure 2, the three-phase four-wire inverter system includes a DC side device. When the negative terminal of the DC side is short-circuited to ground, a short-circuit path to ground is formed as shown by the red arrow in Figure 2. The DC side device can form a short-circuit path to ground through the upper half bus capacitor, the neutral line N, and the short-circuit point, thereby charging the bus capacitor C1 (i.e., the upper half bus capacitor). In this way, the bus capacitor C1 is subjected to a high open-circuit voltage, which can easily cause damage.

[0027] Figure 3 is a schematic diagram of a three-phase four-wire inverter system under the condition of a short circuit to ground at the positive terminal of the DC side. As shown in Figure 3, the three-phase four-wire inverter system includes a DC side device. When the positive terminal of the DC side is short-circuited to ground, a short-circuit path to ground is formed as shown by the red arrow in Figure 3. The DC side device can form a short-circuit path to ground through the short-circuit point to ground, the neutral line N, and the lower half bus capacitor, thereby charging the bus capacitor C2 (i.e., the lower half bus capacitor). In this way, the bus capacitor C2 is subjected to a high open-circuit voltage, which can easily cause damage.

[0028] Based on the two operating conditions in Figures 1 and 2, if the DC-side equipment includes a DC-DC converter module, the controller can be used to control the DC-DC converter module to reduce the output voltage of the DC-side equipment in the event of a short circuit to ground on the DC input side of the inverter, thereby reducing the voltage at which the DC-side equipment charges the bus capacitor; or, if the DC-side equipment includes a bypass switch, the controller can be used to control the bypass switch to close in the event of a short circuit to ground on the DC input side of the inverter, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor; or, if the DC-side equipment includes a DC-side switch, the controller can be used to control the DC-side switch to open in the event of a short circuit to ground on the DC input side of the inverter, thereby cutting off the charging path of the DC-side equipment to the bus capacitor.

[0029] The following section will first explain the DC-side ground short-circuit protection method for DC-side equipment, including DC-DC converter modules.

[0030] It should be noted that in order to safely and reliably implement the DC-side short-circuit protection method for grounding provided in the embodiments of the present invention, the short-circuit current of the DC power supply should be less than or equal to the maximum current that the DC-DC converter module can withstand when designing the DC-side equipment.

[0031] In practice, when the DC input side of the inverter is short-circuited to ground, the output voltage of the DC-side equipment can be reduced to below the preset bus voltage protection threshold by controlling the DC-DC converter module. For example, by controlling the DC-DC converter module to increase the output current of the DC-side equipment, the output voltage of the DC-side equipment can be reduced to below the preset bus voltage protection threshold. That is, the voltage at which the DC-side equipment charges the bus capacitor in the short-circuit path to ground shown by the red arrow in Figure 2 or Figure 3 is reduced. In this way, the output voltage of the DC-side equipment is less than the preset bus voltage protection threshold, and the bus capacitor will not be damaged by overvoltage.

[0032] The control of the DC-DC converter module to reduce the output voltage of the DC-side equipment to below the preset bus voltage protection threshold can include two scenarios: First, the DC-DC converter module is controlled to reduce the output voltage of the DC-side equipment to 0V or approximately 0V. In this case, the DC-side equipment stops outputting power, and the short-circuit path to ground shown by the red arrow in Figure 2 or Figure 3 will change to the current path shown by the red arrow in Figure 4. This is equivalent to creating a new "short-circuit path" between the DC power supply and the DC-DC converter module, disconnecting the charging path of the DC-side equipment to the bus capacitor. Second, it is sufficient to control the DC-DC converter module to reduce the output voltage of the DC-side equipment to below the preset bus voltage protection threshold, without needing to reduce the output voltage of the DC-side equipment to 0V or approximately 0V. In this case, even if the charging path of the DC-side equipment to the bus capacitor is not disconnected, the bus capacitor will not be damaged by overvoltage.

[0033] In one embodiment, the output voltage of the DC-side device can be reduced to below a preset bus voltage protection threshold by adjusting the duty cycle of the power switch transistor in the DC-DC converter module.

[0034] In practice, the duty cycle of the power switching transistor in the DC-DC converter module can be adjusted to a preset duty cycle (e.g., the preset duty cycle can be 1) so that the output voltage of the DC-side equipment is reduced to 0V or near 0V, thereby forming a new "short circuit channel" between the DC power supply and the DC-DC converter module, and disconnecting the path for the DC-side equipment to charge the bus capacitor formed by the DC-side short circuit to ground of the inverter.

[0035] Alternatively, the duty cycle of the power switch in the DC-DC converter module can be adjusted to a preset duty cycle range (e.g., a range greater than 0.5) to ensure that the output voltage of the DC-side equipment is below a preset bus voltage protection threshold. This avoids reducing the output voltage of the DC-side equipment to 0V or near 0V, thereby lowering the voltage at which the DC-side equipment charges the bus capacitor. In this way, even if the path for charging the bus capacitor by the DC-side equipment is not disconnected, the bus capacitor will not be damaged by overvoltage.

[0036] Furthermore, the duty cycle of the power switch can be adjusted in the following ways: by adjusting the duty cycle through the closed-loop control of the DC-DC converter input current, or by gradually adjusting the duty cycle according to a preset step size, or by directly setting the duty cycle to a preset duty cycle.

[0037] Taking the DC-DC converter module as the BOOST circuit as an example, since the BOOST input has a filter capacitor, in order to quickly increase the output current of the DC power supply and reduce the output voltage of the DC-side equipment, the maximum input current capability of the BOOST needs to be configured to be 1.2 times or more of the short-circuit current capability of the DC power supply. At the same time, since the final state is that the power switch in the BOOST is always on (i.e., the duty cycle of the power switch is adjusted to 1 or near 1), a heat sink is needed to dissipate the conduction losses of the switch in a timely manner when the power switch is always on, to avoid overheating and damaging the semiconductor.

[0038] Preferably, the duty cycle can be adjusted using a current closed-loop control method or by gradually adjusting the duty cycle according to a preset step size, so that the duty cycle of the power switch in the BOOST gradually reaches 1 or close to 1. If the duty cycle of the power switch is directly set to 1, the input current overcurrent protection of the BOOST needs to be disabled to avoid conflict between the overcurrent protection and the DC-side short-circuit protection logic.

[0039] In one embodiment, the aforementioned bus voltage protection threshold can be determined based on the power distribution configuration of the inverter system.

[0040] When the inverter system is a three-phase four-wire inverter system, the bus voltage protection threshold is set based on the half bus voltage protection threshold.

[0041] When the inverter system is a three-phase three-wire inverter system, the bus voltage protection threshold is set based on the total bus voltage protection threshold and the phase voltage peak value of the AC side equipment, or based on the half bus voltage protection threshold.

[0042] When the inverter system is a single-phase two-wire inverter system, the bus voltage protection threshold is set based on the total bus voltage protection threshold.

[0043] In practice, the bus voltage protection threshold varies depending on the inverter system's power distribution configuration. For example, the bus voltage protection threshold for a three-phase four-wire inverter system can be equal to the half-bus voltage protection threshold, or it can be a value near the half-bus voltage protection threshold (e.g., minus or plus an error). For a three-phase three-wire inverter system with the AC side equipment connected to the power grid, the bus voltage protection threshold can be equal to the total bus voltage protection threshold minus the peak value of the grid phase voltage, or it can be a value near that difference (e.g., minus or plus an error). For a single-phase two-wire inverter system, the bus voltage protection threshold can be equal to the total bus voltage protection threshold, or it can be a value near the total bus voltage protection threshold (e.g., minus or plus an error).

[0044] Among them, the peak value of the grid phase voltage is a predetermined fixed value or an actual measured value, and the half bus voltage protection threshold and the total bus voltage protection threshold are protection values ​​set based on the bus capacitance.

[0045] The above-mentioned DC-side ground short-circuit protection method does not require changes to the existing inverter structure. Based on the existing non-isolated inverter, it achieves ground short-circuit protection control when the DC side is short-circuited with the lowest cost increase and high efficiency.

[0046] The following describes the method for short-circuit protection to ground on the DC side of DC-side equipment, including bypass switches.

[0047] In practice, the bypass switch is connected in parallel across the DC power supply. When the DC input side of the inverter is short-circuited to ground, the bypass switch can be controlled to close. This establishes a low-impedance path for the DC power supply, creating a closed loop between the DC power supply and the bypass switch. This diverts the charging current, disconnecting the charging path of the DC-side equipment to the bus capacitor. This changes the short-circuit path to ground shown by the red arrow in Figure 2 or Figure 3, preventing damage to the bus capacitor due to overvoltage.

[0048] In certain operating conditions, the DC-side equipment includes a DC-side switch. In the event of a short circuit to ground on the DC input side of the inverter, the charging path of the DC-side equipment to the bus capacitor can be directly disconnected by turning off the DC-side switch, and the bus capacitor will not be damaged due to overvoltage.

[0049] By using the above methods, the path for DC-side equipment to charge the bus capacitor can be blocked or the voltage for DC-side equipment to charge the bus capacitor can be reduced, thereby preventing overvoltage damage to the bus capacitor.

[0050] In one embodiment, as shown in FIG5, the inverter system may further include an AC side switch; one end of the AC side switch is connected to the AC output side of the inverter, and the other end is connected to the AC side device; the controller is further configured to control the DC-DC converter module to reduce the output voltage of the DC side device, or to control the bypass switch to close and then control the AC side switch to open, so as to disconnect the inverter from the AC side device.

[0051] In one embodiment, where the DC-side device includes a DC-side switch, the controller can also be used to control the DC-side switch to turn off after controlling the DC-side converter module to reduce the output voltage of the DC-side device, or to disconnect the inverter from the DC-side device after controlling the bypass switch to close.

[0052] In practice, after controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment, or after controlling the bypass switch to close, there is no DC voltage or charging voltage that threatens the bus capacitor on the short circuit path formed by the DC-to-ground short circuit. At this time, disconnecting the AC-side switch or the DC-side switch can avoid the risk of DC arcing.

[0053] In one embodiment, when the output voltage of the DC-side device is reduced by controlling the DC-DC converter module, if the controller detects that the voltage of the bus capacitor has dropped to a preset voltage range after the AC-side switch is opened and / or the DC-side switch is opened, the power switch in the DC-DC converter module can be turned off.

[0054] In practice, after disconnecting the AC side switch or the DC side switch, since the short circuit path formed by the DC side short circuit to ground has been broken, it is no longer necessary to maintain the short circuit channel between the DC converter module and the DC power supply, or to maintain the charging voltage of the DC power supply to the bus capacitor in the charging circuit. Therefore, the power switch of the DC converter module can be turned off after the voltage of the bus capacitor is detected to drop to the preset voltage range (safe value).

[0055] It should be noted that since the overvoltage threat to the bus capacitor is generally posed by DC-side equipment with higher output voltage, for the aforementioned inverter system, in the event of a short circuit to ground on the DC input side of the inverter, it can be first determined whether the output voltage of the DC-side equipment is greater than or equal to the preset bus voltage protection threshold. If the output voltage of the DC-side equipment is greater than or equal to the preset bus voltage protection threshold, the aforementioned DC-side short-circuit operation to ground is performed on the DC-side equipment. That is, if the DC-side equipment includes a DC-DC converter module, the controller controls the DC-DC converter module to reduce the output voltage of the DC-side equipment, thereby reducing the voltage at which the DC-side equipment charges the bus capacitor; or, if the DC-side equipment includes a bypass switch, the controller controls the bypass switch to close, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor; or, if the DC-side equipment includes a DC-side switch, the controller controls the DC-side switch to close, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor.

[0056] In this embodiment of the invention, the inverter system may further include multiple DC-side devices, which are connected in parallel and then connected to the DC input side of the inverter via a bus capacitor. Figure 6 is a structural diagram of another inverter system provided in this embodiment of the invention. As shown in Figure 6, the inverter system includes DC-side device A and DC-side device B.

[0057] In the inverter system shown in Figure 6, the structures of DC-side device A and DC-side device B are the same as those in the inverter system in Figure 1, and will not be described in detail here.

[0058] Based on the inverter system in Figure 6, when the DC side negative terminal is short-circuited to ground, a short-circuit path to ground is formed as shown by the red arrow in Figure 7. The method described in the above embodiments can be used to perform a DC-side short-circuit operation on each DC-side device when the DC input side of the inverter is short-circuited to ground. Specifically, for each DC-side device, if the DC-side device includes a DC-DC converter module, the controller can control the DC-DC converter module to reduce the output voltage of the DC-side device when the DC input side of the inverter is short-circuited to ground, thereby reducing the voltage at which the DC-side device charges the bus capacitor; or, if the DC-side device includes a bypass switch, the controller can control the bypass switch to close when the DC input side of the inverter is short-circuited to ground, thereby disconnecting the charging path of the DC-side device to the bus capacitor; or, if the DC-side device includes a DC-side switch, the controller can control the DC-side switch to open when the DC input side of the inverter is short-circuited to ground, thereby cutting off the charging path of the DC-side device to the bus capacitor.

[0059] The specific implementation process can be referred to in the above embodiments, and will not be elaborated further here.

[0060] In one embodiment, for each DC-side device, it can be further determined whether the output voltage of the DC-side device is greater than or equal to a preset bus voltage protection threshold. If the output voltage of the DC-side device is greater than or equal to the preset bus voltage protection threshold, the above-mentioned DC-side to-ground short-circuit operation is performed on the DC-side device; if the output voltage of the DC-side device is less than the preset bus voltage protection threshold, the above-mentioned operation is not performed on the DC-side device.

[0061] For example, as shown in Figure 7, if the preset bus voltage protection threshold is 420V, and the output voltage of DC-side device B is 400V, which is less than 420V, then no operation is required on DC-side device B. If the output voltage of DC-side device A is 600V, which is greater than 420V, then the DC-DC converter module of DC-side device A can be controlled to reduce the output voltage of DC-side device A, thereby reducing the voltage at which DC-side device A charges the bus capacitor C1. Alternatively, if DC-side device A includes a bypass switch, the controller can control the bypass switch of DC-side device A to close, thereby bypassing the path of DC-side device A charging the bus capacitor C1.

[0062] In this way, ground short-circuit protection is only performed on DC-side equipment whose output voltage is greater than or equal to the preset bus voltage protection threshold, which can improve system reliability and reduce costs; at the same time, it can also ensure the timeliness of DC-side ground short-circuit protection.

[0063] In one embodiment, if the output voltage of the DC-side device is less than the preset bus voltage protection threshold, the DC-side device can be stopped from switching, i.e., a wave blocking process can be adopted, thereby relieving the pressure on the bus capacitor.

[0064] In summary, the aforementioned inverter system, based on existing non-isolated inverters, can achieve ground short-circuit protection control when the DC side of the inverter is short-circuited to ground with minimal cost increase and high efficiency, thus avoiding damage to the bus capacitor due to overvoltage. Simultaneously, by reducing the voltage used by the DC side equipment to charge the bus capacitor or disconnecting the charging path of the DC side equipment to the bus capacitor before disconnecting the AC side switch, it also avoids the risk of fire or damage to the AC side switch caused by the DC side equipment's output voltage being applied across the AC side switch, or the risk of the switch failing to disconnect due to adhesion. Furthermore, it avoids the problem of slow AC side switch disconnection speed, which prevents timely protection.

[0065] In this embodiment of the invention, a short circuit to ground on the DC input side of the inverter can include: the output current of the DC-DC converter module being greater than or equal to a preset first current value, and the DC side of the inverter experiencing overvoltage or undervoltage to ground; or, the input current of the DC-DC converter module being greater than or equal to a preset second current value, and the DC side of the inverter experiencing overvoltage or undervoltage to ground; or, the leakage current on the AC output side of the inverter being greater than or equal to a preset third current value, and the voltage of the bus capacitor being greater than or equal to a preset first voltage value; or, the leakage current on the AC output side of the inverter being greater than or equal to a preset fourth current value, and the rising slope of the bus capacitor voltage being greater than or equal to a preset slope threshold.

[0066] In practice, in order to improve the accuracy of judging the DC-to-ground short-circuit fault on the inverter side, it can be judged by any of the above methods.

[0067] In one embodiment, if the rate of change of the output voltage amplitude of the DC-side device is within a preset first voltage fluctuation range, and the rate of change of the voltage amplitude of the AC-side device is within a preset second voltage fluctuation range, and the rate of change of the duty cycle of the power switch is within a preset duty cycle fluctuation range, then if the voltage of the bus capacitor is greater than or equal to a preset voltage value, it can also be determined that a short circuit to ground fault has occurred on the DC input side of the inverter.

[0068] For example, Figure 8 is an example diagram of an embodiment of the present invention for determining whether a short-circuit fault to ground has occurred on the DC input side of an inverter.

[0069] As shown in Figure 8, if the output current of the DC-DC converter module is greater than or equal to the preset first current value, the DC-DC converter module is considered to be overcurrent. If the DC side of the inverter device is overvoltage or undervoltage to ground, the DC side voltage to ground is considered to be abnormal. If the DC-DC converter module is overcurrent and the DC side voltage to ground is abnormal, the DC side of the inverter device is considered to have a strong short circuit fault to ground.

[0070] Alternatively, if the input current of the DC-DC converter module is greater than or equal to the preset second current value, the DC-DC converter module is considered to be overcurrent. If the DC side of the inverter device is overvoltage or undervoltage to ground, the DC side voltage to ground is considered to be abnormal. If the DC-DC converter module is overcurrent and the DC side voltage to ground is abnormal, the DC side of the inverter device is considered to have a strong short circuit fault to ground.

[0071] Alternatively, if the AC side leakage current of the inverter is greater than or equal to the preset third current value, the RCD leakage current is considered abnormal. If the voltage of the bus capacitor is greater than or equal to the preset first voltage value, the DC bus voltage is considered overvoltage. If the RCD leakage current is abnormal and the DC bus voltage is overvoltage, the DC side of the inverter is considered to have a weak short circuit to ground fault.

[0072] In this way, by using the above judgment method to determine whether a short-circuit fault to ground has occurred on the DC input side of the inverter, the accuracy of the judgment can be further improved, and the speed and accuracy of judging short-circuit faults to ground can be improved while minimizing false judgments.

[0073] It should be noted that the DC-side switch, bypass switch, DC-DC converter module, bus capacitor, AC-side switch, controller, etc. can also be integrated into the inverter.

[0074] This invention also provides a DC-side short-circuit protection method for the inverter system described above. The inverter system includes an inverter, AC-side equipment, and at least one DC-side equipment. The at least one DC-side equipment is connected to the DC input side of the inverter via a bus capacitor, and the AC output side of the inverter is connected to the AC-side equipment. The method includes: in the event of a short circuit to ground on the DC input side of the inverter, controlling the DC-DC converter module of the DC-side equipment to reduce the output voltage of the DC-side equipment, thereby reducing the voltage at which the DC-side equipment charges the bus capacitor; or, in the event of a short circuit to ground on the DC input side of the inverter, controlling the bypass switch of the DC-side equipment to close, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor.

[0075] In one embodiment, controlling the DC-DC converter module of the DC-side device to reduce the output voltage of the DC-side device in order to reduce the voltage at which the DC-side device charges the bus capacitor includes: controlling the DC-DC converter module to reduce the output voltage of the DC-side device to less than a preset bus voltage protection threshold.

[0076] In one embodiment, controlling the DC-DC converter module to reduce the output voltage of the DC-side device to less than a preset bus voltage protection threshold includes: adjusting the duty cycle of the power switch transistor of the DC-DC converter module to reduce the output voltage of the DC-side device to less than the preset bus voltage protection threshold.

[0077] In one embodiment, the inverter system further includes an AC-side switch; after controlling the DC-DC converter module to reduce the output voltage of the DC-side device, or controlling the bypass switch to close, the method further includes: controlling the AC-side switch to open to disconnect the inverter from the AC-side device.

[0078] Since the principle of this DC-side ground short-circuit protection method is similar to that of the inverter system described above, the implementation of this method can be found in the implementation of the inverter system, and the repeated parts will not be described again.

[0079] Taking the inverter system as an example of a photovoltaic energy storage system, Figure 9 is a structural diagram of a photovoltaic energy storage system provided in an embodiment of the present invention.

[0080] As shown in Figure 9, the photovoltaic energy storage system may include a photovoltaic module 1, an energy storage module 2, and a photovoltaic inverter 3. The input side of the photovoltaic inverter 3 is connected to the photovoltaic module 1, and the output side is connected to the AC grid; the energy storage module 2 is coupled to the DC bus of the photovoltaic inverter 3; wherein, the photovoltaic inverter 3 may include, from left to right, a DC side switch 31, a DC-DC conversion module 32, series-connected bus capacitors C1 and C2, a power conversion module 33 (i.e., the inverter shown in Figure 1), and a grid-connected relay 34 (AC side switch).

[0081] The photovoltaic energy storage system shown in Figure 9 adopts a three-phase four-wire connection. The output side of the power conversion module 33 of the photovoltaic inverter 3 is connected to the AC grid through three power cables (A, B, and C three-phase lines) and grid-connected relay 34. The DC side of the power conversion module 33 is equipped with bus capacitors C1 and C2 connected in series. The neutral line N is connected to the midpoint of the DC bus (i.e., the middle position of bus capacitors C1 and C2) and grounded to the AC grid through grid-connected relay 34. The DC conversion module 32 is a non-isolated converter, including MPPT switch Q (i.e., power switch), inductor L and rectifier diode D.

[0082] Figures 10 and 11 illustrate two operating conditions of DC-side ground short circuit in the photovoltaic energy storage system shown in Figure 9.

[0083] Figure 10 is a schematic diagram of the DC-side negative terminal short-circuited to ground in a photovoltaic energy storage system. As shown in Figure 10, when the DC-side negative terminal is short-circuited to ground, a DC-side short-circuit channel is formed as indicated by the red arrow in Figure 10. Photovoltaic module 1 can charge bus capacitor C1 through the DC bus positive line, neutral line N, and short-circuited ground line. In this way, bus capacitor C1 is subjected to a high open-circuit voltage, which can easily cause damage. In addition, if there is no blocking diode D1, a discharge channel is formed between bus capacitor C2 and ground, and bus capacitor C2 and grid-connected relay may be damaged by overload current.

[0084] Figure 11 is a schematic diagram of the DC positive terminal of the photovoltaic energy storage system being short-circuited to ground. As shown in Figure 11, when the DC positive terminal is short-circuited to ground, a DC-side short-circuit channel is formed as indicated by the red arrow in Figure 11. The photovoltaic module 1 can charge the bus capacitor C2 through the DC bus negative line, neutral line N, and short-circuited ground line. In this way, the bus capacitor C2 is subjected to a high open-circuit voltage, which can easily cause damage.

[0085] Based on the two DC-side short-circuit conditions shown in Figures 10 and 11, it is necessary to address the discharge problem of bus capacitor C2 when the DC-side negative terminal is short-circuited to ground. Furthermore, when the DC-side positive or negative terminal is short-circuited to ground, the entire unit cannot disconnect the AC grid-connected relay 34 because the DC voltage of the photovoltaic module is applied across the AC grid-connected relay 34. Forcibly disconnecting the grid-connected relay 34 would cause it to catch fire and be damaged, and it may eventually fail to disconnect due to adhesion. In addition, the grid-connected relay 34 disconnects slowly and cannot provide timely protection. Therefore, it is also necessary to address the problems of bus capacitor damage and grid-connected relay damage when the photovoltaic module is short-circuited to ground.

[0086] Based on this, as shown in Figure 9, the photovoltaic inverter provided in this embodiment of the invention further includes: a series-type PID repair module 35 and a control module 36 (i.e., a controller). The series-type PID repair module 35 may include a blocking diode D1, which is connected in series on the negative line of the DC bus between the DC conversion module 32 and the energy storage module 2 of the photovoltaic inverter 3.

[0087] The blocking diode D1 can be used to block the discharge path of the bus capacitor of the photovoltaic inverter when the DC side is short-circuited to ground; the control module 36 can be used to adjust the duty cycle of the MPPT switch of the DC-DC converter module when the DC side is short-circuited to ground, so that the output voltage of the photovoltaic module is reduced to 0V; and then control the grid-connected relay of the photovoltaic inverter to disconnect the short circuit path formed by the short circuit to ground of the photovoltaic module.

[0088] Taking the DC-side negative terminal short-circuit to ground as shown in Figure 10 as an example, in specific implementation, since the blocking diode D1 has unidirectional conduction capability, when the bus capacitor C2 discharges, the anode of the blocking diode D1 presents a negative voltage and the cathode presents a positive voltage, and the current cannot pass through the blocking diode D1, thereby blocking the discharge channel of the bus capacitor C2. However, if the photovoltaic module's positive terminal is short-circuited to ground as shown in Figure 3, since the DC-DC converter module 34 includes a rectifier diode D, the discharge current of the bus capacitor C1 cannot pass through the rectifier diode D, so a discharge channel for the bus capacitor C1 cannot be formed. In this case, there is no need to consider the discharge problem of the bus capacitor C1.

[0089] Furthermore, when the photovoltaic module is short-circuited to ground (meaning either the positive or negative terminal of the photovoltaic module is short-circuited), the control module 36 can adjust the duty cycle of the MPPT switch Q of the DC-DC converter module 32 to reduce the output voltage of the photovoltaic module to 0V, thus forming a short-circuit path between the photovoltaic module and the DC-DC converter module. This prevents the photovoltaic module from charging the bus capacitor C1 (or C2). Specifically, the short-circuit path between the photovoltaic module and the DC-DC converter module is shown by the red arrow in Figure 13. At this time, there is no DC voltage on the short-circuit path between the photovoltaic module and ground. The control module 36 controls the AC grid-connected relay 34 to disconnect, causing the DC short-circuit path formed by the short circuit to ground of the photovoltaic module to be broken. There is no need to worry about the grid-connected relay 34 being damaged by the DC voltage interruption of the photovoltaic module, thus quickly achieving protection against short circuits to ground of the photovoltaic module.

[0090] In one embodiment, the control module 36 adjusts the duty cycle of the MPPT switch of the DC-DC converter module 32. Specifically, it adjusts the duty cycle of the MPPT switch Q to 100%, thereby reducing the output voltage of the photovoltaic module to 0V.

[0091] In practical implementation, to block the charging path of the bus capacitor when the photovoltaic module is short-circuited to ground, referring to the voltage and current operating curves of the photovoltaic module shown in Figure 13, the operating point of the photovoltaic module is adjusted to clamp the photovoltaic module voltage to 0V, thus short-circuiting the photovoltaic module. Specifically, referring to points A to B in Figure 13, when the output current of photovoltaic module 1 is at its maximum value (i.e., short-circuit current), the output voltage of the photovoltaic module gradually decreases to 0V. Therefore, the duty cycle of the MPPT switch can be directly adjusted to 100%, or the duty cycle of the MPPT switch can be gradually increased to 100%, with the MPPT switch Q in a continuously conducting state, and the output voltage of photovoltaic module 1 gradually decreasing to 0V. This forms a short-circuit path for the photovoltaic module as shown by the red arrow in Figure 12. There will be no DC voltage on the short-circuit path formed by the photovoltaic module short-circuiting to ground, thereby blocking the charging of the bus capacitor when the photovoltaic module is short-circuited to ground.

[0092] It should be noted that, in order to achieve short-circuit protection for photovoltaic modules, the photovoltaic inverter design must ensure that the input current (maximum current capability of the MPPT) that the DC-DC converter module can safely handle is 1.5 times or more of the short-circuit current of the photovoltaic module, and the thermal design must at least ensure short-term high-current operation and withstand heat dissipation at 100% duty cycle. Additionally, if the duty cycle of the MPPT switch is directly adjusted to 100%, it may be necessary to disable the MPPT's overcurrent protection to avoid conflicting protection actions.

[0093] Furthermore, after the photovoltaic module short-circuit channel is formed as shown by the red arrow in Figure 12, the output voltage of photovoltaic module 1 is 0. Therefore, there will be no DC voltage on the short-circuit channel formed by the photovoltaic module's short circuit to ground. Then, the control module 36 controls the disconnection of the AC grid-connected relay, thereby causing the DC short-circuit channel formed by the photovoltaic module's short circuit to ground to be broken. In this way, by utilizing the short-circuit characteristic of the photovoltaic module, the AC relay at the AC port is disconnected without worrying about the grid-connected relay being damaged by the DC voltage from the photovoltaic module. At this time, even if the MPPT switch Q is turned off, it will not cause overvoltage damage to the bus capacitor C1 (or C2).

[0094] In this embodiment of the invention, before adjusting the duty cycle of the MPPT switch in the DC-DC converter module 33 to reduce the output voltage of the photovoltaic module to 0V, the control module 36 needs to determine whether the photovoltaic module is short-circuited to ground. Specifically, the determination of whether the photovoltaic module is short-circuited to ground can be made through the ground over / under voltage protection module and the RCD leakage current detection module as described below.

[0095] In one embodiment, as shown in FIG9, the photovoltaic inverter 3 may further include: a ground over / under voltage protection module 37; the ground over / under voltage protection module 37 is connected between the DC conversion module 32 of the photovoltaic inverter and the negative output terminal (or DC disconnect switch 31) of the photovoltaic module, and the ground over / under voltage protection module 37 includes a ground voltage detection unit 371 and an over / under voltage judgment unit 372; wherein, one side of the ground voltage detection unit 371 is grounded, and the other side is connected between the DC conversion module 32 and the negative output terminal (or DC disconnect switch 31) of the photovoltaic module.

[0096] The ground voltage detection unit 371 is used to detect the voltage between the negative output terminal of the photovoltaic module and ground; the over / under voltage judgment unit 372 is used to determine the undervoltage protection value and the overvoltage protection value of the photovoltaic module to ground based on the predetermined maximum operating voltage of the photovoltaic module and the overvoltage protection value of the bus capacitor; and to determine whether the photovoltaic module is over-voltage or under-voltage to ground based on the detected voltage between the negative output terminal of the photovoltaic module and ground, the undervoltage protection value and the overvoltage protection value of the photovoltaic module to ground; the control module 36 is also used to determine whether the DC side is short-circuited to ground based on whether the photovoltaic module is over-voltage or under-voltage to ground.

[0097] In practical implementation, the over / under voltage protection module 37 can be used to determine whether the photovoltaic module is over-voltage or under-voltage to ground, and thus determine whether there is a short circuit to ground on the DC side. Specifically, the maximum operating voltage of the photovoltaic module refers to the maximum value of the voltage of all currently operating photovoltaic modules. This can be obtained by detecting the operating voltage of multiple photovoltaic modules connected to the photovoltaic inverter, and the maximum value can be used as the maximum operating voltage of the photovoltaic module. The bus capacitor overvoltage protection value is a safety threshold set to prevent the capacitor from being damaged due to excessive voltage. Given the parameters of a bus capacitor (C1 or C2), in application, the bus capacitor overvoltage protection value can be determined as the photovoltaic module overvoltage protection value to ground; the difference between the maximum operating voltage of the photovoltaic module and the bus capacitor overvoltage protection value is determined as the photovoltaic module undervoltage protection value to ground. The control module compares the voltage between the negative output terminal of the photovoltaic module and ground with the undervoltage protection value of the photovoltaic module to determine whether the photovoltaic module is undervoltage to ground. If the photovoltaic module is undervoltage to ground, the control module can determine that the negative terminal of the photovoltaic module is short-circuited to ground. The control module also compares the voltage between the negative output terminal of the photovoltaic module and ground with the overvoltage protection value of the photovoltaic module to ground to determine whether the photovoltaic module is overvoltage to ground. If the photovoltaic module is overvoltage to ground, the control module can determine that the positive terminal of the DC side is short-circuited to ground.

[0098] In one embodiment, the photovoltaic inverter 3 may further include: an RCD leakage current detection module 38; the RCD leakage current detection module 38 is connected between the grid-connected relay 34 and the AC grid; the RCD leakage current detection module 38 is used to detect leakage current and determine whether the leakage current exceeds a preset current value; the control module 36 is also used to determine whether the DC side is short-circuited to ground based on whether the leakage current exceeds the preset current value.

[0099] In practical implementation, leakage current can also be used to determine whether there is a short circuit to ground on the DC side. Specifically, the RCD leakage current detection module detects the current difference between the phase line and the neutral line (as shown in Figure 9, lines A and N, B and N, and C and N), and determines whether the current difference exceeds a preset current value. If the current difference exceeds the preset current value, the control module determines that there is a short circuit to ground on the DC side.

[0100] In other words, in this embodiment of the invention, whether there is a short circuit to ground on the DC side can be determined based on whether the photovoltaic module is over- or under-voltage to ground, or whether the leakage current exceeds a preset current value. For example, Figure 14 is a logic diagram for determining whether there is a short circuit to ground on the DC side provided in this embodiment of the invention. The over / under-voltage protection module outputs whether the photovoltaic module is over- or under-voltage to ground, and the RCD leakage current detection module outputs whether the leakage current exceeds a preset current value. The control module determines whether there is a short circuit to ground on the DC side based on whether the photovoltaic module is over- or under-voltage to ground, or whether the leakage current exceeds a preset current value.

[0101] In this embodiment of the invention, it is also possible to determine whether the DC side is short-circuited to ground based on the ground impedance of the photovoltaic module.

[0102] In one embodiment, the photovoltaic inverter may further include: a ground impedance detection module; the ground impedance detection module is connected to the photovoltaic module; the ground impedance detection module is used to detect the ground impedance of the photovoltaic module and determine whether the ground impedance of the photovoltaic module is lower than a preset impedance value; the control module is also used to determine whether the DC side is short-circuited to ground based on whether the ground impedance of the photovoltaic module is lower than the preset impedance value.

[0103] In practice, the ground impedance detection module can be used to detect the ground impedance of the positive output terminal and the ground impedance of the negative output terminal of the photovoltaic module, and the DC side can be short-circuited to ground based on the ground impedance of the positive output terminal and the ground impedance of the negative output terminal of the photovoltaic module.

[0104] Furthermore, existing non-isolated photovoltaic inverters cannot enable simultaneous nighttime energy storage and PID repair. Using methods such as installing semiconductor blocking switches on the photovoltaic input line to provide nighttime PID capability presents challenges due to high costs. This invention also provides a series-type PID repair module to address this issue.

[0105] Figure 15 shows a circuit diagram of a series-type PID repair module provided in an embodiment of the present invention. The PID repair module includes a blocking diode D1 and a PID voltage generating circuit. The PID voltage generating circuit includes a first diode D2, a first flyback transformer T1, a first switching transistor Q1, a first relay S1, a first current-limiting resistor R1, and a first capacitor C3. The anode of the blocking diode D1 serves as the first power port 11 of the PID repair module, connected to the negative output terminal of the energy storage module 2. The cathode of the blocking diode D1 serves as the second power port 12 of the PID repair module, connected to the negative output terminal of the DC-DC converter module 32. The first end of the secondary winding of the first flyback transformer T1 is connected to the second power port 12 through the first diode D2. The second end of the secondary winding of the first flyback transformer T1 is grounded through the first relay S1 and the first current-limiting resistor R1. The first end of the primary winding of the first flyback transformer T1 is connected to the first end of the first capacitor C3. The second end of the primary winding of the first flyback transformer T1 is connected to the first end of the first switching transistor Q1. The second end of the first switching transistor Q1 is connected to the second end of the first capacitor C3. The third end of the first switching transistor Q1 is used to receive the PID repair signal sent by the control module 36.

[0106] In one embodiment, Figure 16 is a circuit diagram of another series-type PID repair module provided by the present invention. The difference between Figure 16 and Figure 15 is that the second end of the secondary winding of the first flyback transformer T1 can be connected to the first power port 11 through the first relay S1 and the first current limiting resistor R1. Other components and their connection methods are the same as those in Figure 7, and will not be described in detail here.

[0107] Based on the series-type PID repair module described in Figure 15 or Figure 16, the PID voltage generating circuit is used to control the first switching transistor Q1 to turn on when it receives the PID repair signal sent by the control module, and output a positive voltage to the second power port 12 so that the cathode of the blocking diode D1 presents a positive voltage; when the energy storage module is simultaneously performing energy storage operation, the anode of the blocking diode D1 presents a negative voltage, and the blocking diode blocks the current on the negative line of the DC bus from passing through, so that the PID repair operation of the PID repair module and the energy storage operation of the energy storage module are carried out simultaneously.

[0108] Figure 17 is a circuit diagram of another series-type PID repair module provided in an embodiment of the present invention. The PID repair module includes a blocking diode D1 and a PID voltage generating circuit. The PID voltage generating circuit includes a second diode D3, a second flyback transformer T2, a second switch Q2, a second relay S2, a third relay S3, a second current-limiting resistor R2, and a second capacitor C3. The anode of the blocking diode D1 serves as the first power port 11 of the PID repair module and is connected to the negative output terminal of the energy storage module. The cathode of the blocking diode D1 serves as the second power port 12 of the PID repair module and is connected to the negative output terminal of the DC-DC converter module. The first end of the secondary winding of the second flyback transformer T2 is connected to the second power port 12 through the second diode D2. The second end of the secondary winding of the second flyback transformer T2 is grounded through the second relay S2 and the second current-limiting resistor R2, and the second end of the secondary winding of the second flyback transformer T2 is connected to the first power port 11 through the third relay S3. The first end of the primary winding of transformer T2 is connected to the first end of the second capacitor C2, and the second end of the primary winding of the second flyback transformer T2 is connected to the first end of the second switch Q2; the second end of the second switch Q2 is connected to the second end of the second capacitor C2; the third end of the second switch Q3 is used to receive the PID repair signal sent by the control module; wherein, the PID voltage generating circuit is used to control the second switch Q2 to conduct when the PID repair signal sent by the control module is received, and to control the second relay S2 or the third relay S3 to close based on different PID repair signals, outputting a positive voltage to the second power port 12, so that the cathode of the blocking diode D1 presents a positive voltage, and when the energy storage module 2 is simultaneously performing energy storage work, the anode of the blocking diode D1 presents a negative voltage, and the blocking diode D1 blocks the current from passing through the negative line of the DC bus, so that the PID repair work of the PID repair module and the energy storage work of the energy storage module are carried out simultaneously.

[0109] In practical implementation, the series-type PID repair module shown in Figure 17 is a composite series-type PID repair module. Based on different PID repair signals, it can selectively close the second relay to form the same series-type PID repair module as in Figure 15, or close the third relay to form the same series-type PID repair module as in Figure 16. This improves the flexibility of the working method.

[0110] In practical implementation, the series-connected PID repair module shown in Figures 15-17 can use the blocking diode D1 to bear the voltage difference between the photovoltaic module and the negative bus when the voltage of the photovoltaic module needs to be increased at night for PID repair. This allows for the simultaneous operation of energy storage at night and PID repair at low cost.

[0111] In this embodiment of the invention, the control module 36 is further configured to control the first switch Q1 or the second switch Q2 of the series-type PID repair module to disconnect when the photovoltaic module is short-circuited to ground.

[0112] In practical implementation, considering that a short circuit to ground of the photovoltaic module may cause the PID repair to fail and damage the PID repair module when the PID repair module is working, in order to avoid damage to the PID repair module, the first switch Q1 or the second switch Q2 of the series-connected PID repair module is disconnected to protect the PID repair module.

[0113] In summary, the above-mentioned photovoltaic energy storage system has the following beneficial effects: 1. By introducing a series-type PID repair module, when it is necessary to raise the voltage of the photovoltaic module for PID repair at night, the blocking diode can bear the voltage difference between the photovoltaic and the negative bus, ensuring that the energy storage works at night and the PID repair is carried out simultaneously.

[0114] 2. When the photovoltaic module is short-circuited to ground, the MPPT switch of the existing DC-DC converter module is used to clamp and limit the output voltage of the photovoltaic module, so as to prevent the photovoltaic module from charging the bus capacitor if it exceeds half the bus capacitor withstand voltage, which would cause the bus capacitor to be damaged by overvoltage.

[0115] 3. When the photovoltaic module is short-circuited to ground, after clamping and limiting the output voltage of the photovoltaic module, the AC relay of the AC port is directly disconnected by taking advantage of the characteristic that the photovoltaic module is short-circuited by the MPPT switch, without worrying about the risk of the AC relay being damaged by the DC voltage of the photovoltaic module.

[0116] 4. The photovoltaic inverter provided in this embodiment of the invention solves the problems of overvoltage damage to the bus capacitor when the photovoltaic module is short-circuited to ground in a high-efficiency and low-cost manner, based on the existing non-isolated inverter.

[0117] This invention also provides a method for protecting photovoltaic modules from ground short circuits, as described in the following embodiments. Since the principle behind this method is similar to that of the photovoltaic inverter described above, its implementation can be found in the implementation of the photovoltaic inverter described above; repeated details will not be repeated.

[0118] It should be noted that the aforementioned photovoltaic inverter can be applied to three-phase four-wire photovoltaic energy storage systems, three-phase three-phase photovoltaic energy storage systems, or single-phase photovoltaic energy storage systems. For example, Figure 18 is an application example diagram of a three-phase four-wire photovoltaic energy storage system based on a T-type three-level circuit provided by an embodiment of the present invention; Figure 19 is an application example diagram of a three-phase three-wire photovoltaic energy storage system based on a T-type three-level circuit provided by an embodiment of the present invention; and Figure 20 is an application example diagram of a single-phase photovoltaic energy storage system provided by an embodiment of the present invention. The implementation principle of DC-side ground short-circuit protection in Figures 18-20 can refer to the implementation principle of the aforementioned inverter system, and will not be elaborated further here.

[0119] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0120] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more blocks of the flowchart illustrations and / or one or more blocks of the block diagrams.

[0121] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0122] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0123] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An inverter system, characterized in that, The inverter system includes a controller, an inverter, AC-side equipment, and at least one DC-side equipment. The at least one DC-side equipment is connected to the DC input side of the inverter via a bus capacitor, and the AC output side of the inverter is connected to the AC-side equipment. The DC-side equipment includes a DC-DC converter module. The controller is used to control the DC-DC converter module to reduce the output voltage of the DC-side equipment in the event of a short circuit to ground on the DC input side of the inverter, thereby reducing the voltage at which the DC-side equipment charges the bus capacitor. Alternatively, the DC-side equipment includes a bypass switch. The controller is used to control the bypass switch to close in the event of a short circuit to ground on the DC input side of the inverter, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor.

2. The inverter system as described in claim 1, characterized in that, The controller controls the DC-DC converter module to reduce the output voltage of the DC-side equipment, including: controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment to less than a preset bus voltage protection threshold.

3. The inverter system as described in claim 2, characterized in that, The controller controls the DC-DC converter module to reduce the output voltage of the DC-side equipment to less than the preset bus voltage protection threshold, including: adjusting the duty cycle of the power switch transistor of the DC-DC converter module to reduce the output voltage of the DC-side equipment to less than the preset bus voltage protection threshold.

4. The inverter system as described in claim 1, characterized in that, The inverter system also includes an AC side switch; one end of the AC side switch is connected to the AC output side of the inverter, and the other end is connected to the AC side equipment; the controller is also used to control the DC-DC converter module to reduce the output voltage of the DC side equipment, or to control the bypass switch to close, and then control the AC side switch to open to disconnect the inverter from the AC side equipment.

5. The inverter system as described in claim 1, characterized in that, The DC-side equipment also includes a DC-side switch; the controller is further configured to control the DC-side switch to turn off after controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment, or to control the bypass switch to close, so as to disconnect the inverter from the DC-side equipment.

6. The inverter system as described in claim 1, characterized in that, The DC input side of the inverter is short-circuited to ground, including: the output current of the DC-DC converter module is greater than or equal to a preset first current value, and the DC side of the inverter is over-voltage or under-voltage to ground; or, the input current of the DC-DC converter module is greater than or equal to a preset second current value, and the DC side of the inverter is over-voltage or under-voltage to ground; or, the leakage current on the AC output side of the inverter is greater than or equal to a preset third current value, and the voltage of the bus capacitor is greater than or equal to a preset first voltage value; or, the leakage current on the AC output side of the inverter is greater than or equal to a preset fourth current value, and the rising slope of the bus capacitor voltage is greater than or equal to a preset slope threshold.

7. A method for DC-side ground short-circuit protection, characterized in that, An inverter system, comprising an inverter, AC-side equipment, and at least one DC-side equipment, wherein the at least one DC-side equipment is connected to the DC input side of the inverter via a bus capacitor, and the AC output side of the inverter is connected to the AC-side equipment, the method comprising: in the event of a short circuit to ground on the DC input side of the inverter, controlling the DC-DC conversion module of the DC-side equipment to reduce the output voltage of the DC-side equipment, thereby reducing the voltage at which the DC-side equipment charges the bus capacitor; or, in the event of a short circuit to ground on the DC input side of the inverter, controlling the bypass switch of the DC-side equipment to close, thereby disconnecting the charging path of the DC-side equipment to the bus capacitor.

8. The method as described in claim 7, characterized in that, Controlling the DC-DC converter module of the DC-side equipment to reduce the output voltage of the DC-side equipment in order to reduce the voltage at which the DC-side equipment charges the bus capacitor includes: controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment to less than a preset bus voltage protection threshold.

9. The method as described in claim 8, characterized in that, Controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment to below a preset bus voltage protection threshold includes: adjusting the duty cycle of the power switching transistor of the DC-DC converter module to reduce the output voltage of the DC-side equipment to below the preset bus voltage protection threshold.

10. The method as described in claim 1, characterized in that, The inverter system also includes an AC side switch; After controlling the DC-DC converter module to reduce the output voltage of the DC-side equipment, or controlling the bypass switch to close, the method further includes: controlling the AC-side switch to open to disconnect the inverter from the AC-side equipment.

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