Power converter and detection method

Abstract

Provided in the present embodiment are a power converter and a detection method. The power converter comprises an inverter circuit, filter capacitors, and a plurality of first switches which are in one-to-one correspondence with three-phase inverter bridge arms and an N-line of the inverter circuit. One end of each filter capacitor is connected to a first phase inverter bridge arm, and the other end thereof is connected to the N-line. The first phase inverter bridge arm among the three-phase inverter bridge arms is connected to a power grid after being connected to the filter capacitors and the corresponding first switch. The N-line is connected to an alternating current power receiving apparatus after being connected to the filter capacitors and the corresponding first switch. By controlling the first switches corresponding to the first phase inverter bridge arm and the N-line to be on / off, under the condition of different connection states between the N-line and the power grid, the phase voltage of the first phase has different voltage changes. At this moment, on the basis of an amplitude difference between the phase voltage output from the first phase and the phase voltages output from the other two phases, whether the N-line is disconnected from the power grid can be determined. The present embodiment can achieve high-precision detection of the connection state of the N-line while reducing device costs.

Description

A power converter and a detection method

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on January 31, 2024, with application number 202410144755.2 and application name “A Power Converter and Detection Method”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of power supply processing technology, and in particular to a power converter and a detection method. Background Art

[0003] In photovoltaic power supply and energy storage power supply applications, power converters are required to convert the direct current (DC) from photovoltaic panels or energy storage modules into alternating current (AC) for transmission to the power grid. To achieve this DC / AC conversion, these power converters require an integrated inverter circuit. The inverter circuit typically utilizes a three-phase inverter bridge arm design. However, in scenarios where unbalanced loads are being supplied, the inverter circuit must have a neutral (N) line to handle the load for unbalanced control. In this case, an N line is typically added to direct the current from the inverter circuit back to the power source, ensuring the safety and stability of the power converter. If the N line is disconnected from the grid—that is, if it drops out—the current in the inverter circuit cannot flow back properly. This can cause the voltage in the inverter circuit to rise, potentially damaging the power converter's circuit boards, which can pose a risk to the converter or personnel.

[0004] One existing solution involves connecting pull-up resistors of varying resistance between each phase of the power converter's three-phase output and the neutral line. These pull-up resistors offset the three-phase voltages, and the resulting changes in the three-phase voltages can be used to determine if the neutral line is disconnected. However, this solution requires multiple resistors to detect disconnected coupling wires, resulting in high device cost and significant impact on detection accuracy due to other factors. Summary of the Invention

[0005] The embodiments of the present application provide a power converter and a detection method, which achieve high-precision detection of whether the N line is disconnected while reducing device costs.

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

[0007] In a first aspect, embodiments of the present application provide a power converter comprising a bus capacitor, an inverter circuit, a filter circuit, a switch assembly, and a control circuit. The input of the inverter circuit is configured to connect a positive DC bus and a negative DC bus, which are configured to connect to a DC power supply. The bus capacitor is connected between the positive DC bus and the negative DC bus. The inverter circuit comprises three-phase inverter bridge arms and an N line, with the N line connected to the midpoint of the bus capacitor. The inverter circuit is connected to the switch assembly via a filter circuit. The filter circuit comprises three filter capacitors, each connected between the output of a corresponding inverter bridge arm and the N line. The switch assembly is located between the filter circuit and the power grid and comprises a plurality of first switches, each of which is connected in a one-to-one correspondence to each of the three-phase inverter bridge arms and the N line. The control circuit is configured to control the closing of a target switch during startup of the power converter. The target switch comprises a first switch corresponding to a first-phase inverter bridge arm of the three-phase inverter bridge arms and a first switch corresponding to the N line. The first-phase inverter bridge arm is any of the three-phase inverter bridge arms. When the difference between the phase voltage of the first phase output of the power converter and the phase voltages of the other two phase outputs is greater than or equal to a first threshold, an alarm message is issued to indicate that the N line is disconnected from the grid, or the power converter is controlled to shut down. The first phase output of the power converter is the output of the first phase inverter bridge arm after passing through the filter circuit, and the other two phase outputs are the outputs of the other two phase inverter bridge arms after passing through the filter circuit. The output end of the three-phase inverter bridge arm is the output end of the bridge arm before passing through the filter circuit.

[0008] The amplitude of the phase voltage generally refers to the effective value of the phase voltage or the peak value within the control cycle. Since under normal circumstances, the phase voltages of the three-phase output of the power converter generally have the same amplitude except for a 60° phase difference between each other, the difference between the amplitude of the phase voltage output of the first phase and the phase voltage output of the other two phases is greater than or equal to the first threshold. This can be understood as the difference between the amplitude of the phase voltage output of the first phase and the amplitude of the phase voltage output of any of the other two phases being greater than or equal to the first threshold, or the difference between the amplitude of the phase voltage output of the first phase and the amplitude of the phase voltage output of the other two phases being greater than or equal to the first threshold.

[0009] In the traditional power converter design, a filter circuit for performing AC filtering processing is designed on the AC output side of the inverter circuit, and a switch component is designed between the AC output side of the inverter circuit and the power grid to ensure the working safety of the power converter. In an embodiment of the present application, during the power converter power-on startup process, the target switch of the existing switch component (for example, a first switch connected to the three-phase inverter bridge arm and the N line in a one-to-one correspondence) can be controlled to close. When the N line is not disconnected from the power grid, the closure of the target switch can form a loop between the first phase inverter bridge arm and the corresponding filter capacitor, the power grid and the N line. When the first phase inverter bridge arm, the filter capacitor corresponding to the first phase inverter bridge arm, the power grid and the N line form a loop, the filter capacitor will pull the phase voltage of the first phase output of the power converter (the phase voltage of the first phase output is the phase voltage of the output of the first phase inverter bridge arm after the filter circuit). Therefore, when the N line is not disconnected from the power grid, the loop can be formed normally. At this time, the filter capacitor, as part of the filter circuit, can normally realize the function of filtering and will not affect the phase voltage of the first phase output, so that the three-phase voltage remains relatively balanced. When the N line is disconnected from the grid, the closing of the target switch cannot form a loop between the first-phase inverter bridge arm and the corresponding filter capacitor, the grid and the N line. At this time, the filter capacitor cannot serve as a normal filter device, but as a biasing device to bias the phase voltage output by the first phase. At this time, the phase voltage output by the first phase is significantly different from the phase voltages output by the other two phases. Therefore, the control circuit can detect whether the N line is disconnected from the grid based on whether the difference between the phase voltage output by the first phase and the phase voltages output by the other two phases is greater than or equal to a preset first threshold. After detecting that the N line is disconnected, an alarm message can be output, and the power converter can also be controlled to shut down. In the above detection method, there is no need to additionally set up a biasing device for biasing the phase voltage, which saves device costs. At the same time, when the filter capacitor is used as a bias-pulling device, its bias-pulling ability will not be affected by other devices in the filter circuit. On the basis of maintaining a stable bias-pulling ability, the phase voltage after biasing in actual conditions tends to the phase voltage after biasing in ideal conditions, and the value of the preset first threshold is related to the phase voltage after biasing in ideal conditions. Therefore, the embodiment of the present application can improve the detection accuracy while reducing costs.

[0010] Illustratively, the DC power source may be a photovoltaic power generation device (eg, a photovoltaic array), a wind power generation device, a hydropower generation device, an energy storage device, or the like.

[0011] Exemplarily, power converter startup refers to the process of connecting the power converter to the device's operating power supply and then powering it on. During the power converter startup process, the control circuit within it is also powered on. After the control circuit is powered on, a self-test process is performed to detect various operating status information of the power converter to ensure the operating stability and safety of the power converter. For example, a test is performed to determine whether the N line is disconnected from the power grid. This is required to ensure that the subsequent DC / AC conversion circuit can operate. The power converter startup process involved in this application refers to the process in which the power converter performs a self-test after being powered on.

[0012] In some possible implementations, the switch assembly further includes a plurality of second switches, the plurality of second switches being connected in series with the plurality of first switches in a one-to-one correspondence, the three-phase inverter bridge arm and the N line being respectively used to connect to the power grid through the one-to-one corresponding first switch and second switch, each first switch being located between the filter circuit and the corresponding second switch; and the target switch further includes a plurality of second switches. Controlling the target switch to close comprises: first controlling the plurality of second switches to close, and then controlling the first switch corresponding to the first-phase inverter bridge arm and the first switch corresponding to the N line to close. In an embodiment of the present application, in order to ensure the operational safety of the power converter, a multi-stage switch may be provided for protection. For example, taking the power converter as an inverter, the first switch may be a relay in the inverter close to the inverter circuit side, and the second switch may be a relay in the inverter close to the power grid side, etc. When the switch assembly includes a multi-stage component, the switch on the power grid side may be closed first, and then the switch on the inverter side may be closed.

[0013] In one example, when controlling the corresponding first switch to close, the first switch corresponding to the first phase inverter bridge arm may be controlled first, and then the first switch corresponding to the N line may be controlled to close, so as to improve the safety of detection.

[0014] In some possible implementations, the control circuit is further configured to: before controlling the target switch to close, control the inverter circuit to generate an open-loop wave. After controlling the target switch to close, control the inverter circuit to stop generating an open-loop wave. In the embodiment of the present application, by controlling the inverter circuit to generate an open-loop wave before closing the target switch and controlling the inverter circuit to stop generating an open-loop wave after closing the target switch, the inverter circuit can generate an open-loop wave for only a short period of time. The resulting wave signal size meets detection requirements, and detection safety issues caused by excessively large wave signals are avoided.

[0015] In some possible implementations, the control circuit is further configured to: detect whether the target switch is closed before obtaining the phase voltage of the first phase output of the power converter. In an embodiment of the present application, before obtaining the phase voltage for final detection, it is also possible to re-verify whether the target switch is closed. After verifying that the target switch is closed, the final detection confirmation process is performed. By providing a re-verification operation, the security of the detection process can be improved, avoiding safety issues caused by performing detection when the target switch is fully or partially not closed.

[0016] Exemplarily, the power converter further includes a sampling circuit; the sampling circuit is connected to the switch assembly and the control circuit. The sampling circuit is configured to obtain a voltage across each target switch. The control circuit is specifically configured to determine that the switch is closed when the difference between the voltages across any target switch is less than a preset threshold. In embodiments of the present application, a sampling circuit is typically provided in the power converter to detect, among other things, the operating status of various circuit components in the power converter. The sampling circuit samples the input and output voltages of each target switch. The control circuit can determine whether the corresponding switch is closed based on the voltage information obtained by the sampling circuit. When a switch is closed, electrical signals can flow normally; in this case, the difference between the input and output voltages of the switch is small. When a switch is closed, electrical signals cannot flow normally; in this case, the voltage at the input of the switch is significantly greater than the voltage at the output of the switch. Therefore, when the difference between the input and output voltages of a switch is less than a preset threshold, the control circuit can verify that the switch is closed.

[0017] In some possible implementations, the control circuit is further configured to control the target switch to turn off after determining that the N line is disconnected from the power grid. In this embodiment of the present application, after the detection is completed and the N line is confirmed to be disconnected from the power grid, it indicates that the disconnection of the N line poses a safety hazard to the power converter. Because the target switch has been previously controlled to be closed for detection, the target switch can also be controlled to turn off to ensure the safety of the power converter and personnel.

[0018] In a second aspect, embodiments of the present application further provide a detection method, which is applied to a power converter comprising a bus capacitor, an inverter circuit, a filter circuit, a switch assembly, and a control circuit. The inverter circuit has an input terminal connected to a positive DC bus and a negative DC bus, which are connected to a DC power supply. The bus capacitor is connected between the positive DC bus and the negative DC bus. The inverter circuit comprises a three-phase inverter bridge arm and an N line, which is connected to the midpoint of the bus capacitor. The inverter circuit is connected to the switch assembly via a filter circuit. The filter circuit comprises three filter capacitors, each connected between the output terminal of a corresponding inverter bridge arm and the N line. The switch assembly is located between the filter circuit and the power grid and comprises a plurality of first switches, each of which is connected to the three-phase inverter bridge arm and the N line in a one-to-one correspondence. The method comprises: during power-on startup of the power converter, controlling a target switch to close. The target switch comprises a first switch corresponding to a first inverter bridge arm of the three-phase inverter bridge arm and a first switch corresponding to the N line. The first-phase inverter bridge arm is any one of the three-phase inverter bridge arms. When the difference between the amplitude of the phase voltage of the first-phase output of the power converter and the phase voltages of the other two-phase outputs is greater than or equal to a first threshold, an alarm message is issued to indicate that the N line is disconnected from the grid, or the power converter is controlled to shut down. The first-phase output of the power converter is the output of the first-phase inverter bridge arm after passing through the filtering circuit, and the other two-phase outputs are the outputs of the other two-phase inverter bridge arms after passing through the filtering circuit.

[0019] In some possible implementations, the switch assembly further includes multiple second switches, each of which is connected in series with the multiple first switches in a one-to-one correspondence. The three-phase inverter bridge arm and the N line are respectively used to connect to the power grid via the one-to-one corresponding first and second switches, with each first switch positioned between the filter circuit and the corresponding second switch. The target switch further includes multiple second switches; controlling the target switch to close includes first controlling the multiple second switches to close, and then controlling the first switch corresponding to the first-phase inverter bridge arm and the first switch corresponding to the N line to close.

[0020] In some possible implementations, the method further includes: controlling the inverter circuit to perform open-loop ripple generation before controlling the target switch to be closed, and controlling the inverter circuit to stop open-loop ripple generation after controlling the target switch to be closed.

[0021] In some possible implementations, the method further includes: before acquiring the phase voltage corresponding to the three-phase inverter bridge arm, detecting whether the target switch is closed.

[0022] In some possible embodiments, the power converter further includes a sampling circuit. The sampling circuit is connected to the switch assembly. Detecting whether the target switch is closed includes: obtaining a voltage across each of the target switches based on sampling by the sampling circuit. If the difference between the voltages across any of the target switches is less than a preset threshold, the switch is determined to be closed.

[0023] In some possible implementations, the method further includes: after determining that the N line is disconnected from the grid, controlling the target switch to turn off.

[0024] Regarding the technical principles and beneficial effects of the above-mentioned second aspect, please refer to the relevant description of the above-mentioned first aspect, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a schematic structural diagram of a photovoltaic system provided in an embodiment of the present application;

[0026] FIG2 is a schematic structural diagram of an uninterruptible power supply system provided in an embodiment of the present application;

[0027] FIG3 is a structural diagram of a power converter according to an embodiment of the present application;

[0028] FIG4 is a schematic structural diagram of a power converter of the prior art provided by an embodiment of the present application;

[0029] FIG5 is a schematic diagram showing the time variation of the corresponding phase voltage before and after the N line is disconnected from the grid according to a prior art embodiment of the present application;

[0030] FIG6 is a schematic structural diagram of a power converter provided in an embodiment of the present application;

[0031] FIG7 is a schematic structural diagram of another power converter provided in an embodiment of the present application;

[0032] FIG8 is a schematic structural diagram of another power converter provided in an embodiment of the present application;

[0033] FIG9 is a schematic diagram of a flow chart of a detection method provided in an embodiment of the present application;

[0034] FIG10 is a schematic diagram of a target switch of a power converter controlled by an embodiment of the present application after closing;

[0035] FIG11 is a schematic diagram of a flow chart of another detection method provided in an embodiment of the present application;

[0036] FIG12 is a flow chart of another detection method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0037] It should be noted that the terms "first", "second", etc. involved in the embodiments of the present application are only used to distinguish features of the same type and cannot be understood as indicating relative importance, quantity, order, etc.

[0038] The terms "exemplary" or "for example" in the embodiments of this application are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0039] The terms "coupling" and "connection" involved in the embodiments of this application should be understood in a broad sense. For example, they may refer to a physical direct connection, or an indirect connection achieved through electronic devices, such as a connection achieved through resistors, inductors, capacitors or other electronic devices.

[0040] Power converters are common devices in power supply systems. They are suitable for devices with three-phase, four-leg topologies, such as inverters and power conversion systems (PCSs). Depending on the power supply system, they can be used in various application scenarios, such as photovoltaic power supply, energy storage power supply, hydropower generation, and wind power generation, providing AC power to the grid and loads.

[0041] Figure 1 illustrates an exemplary application scenario for a photovoltaic system. As shown in Figure 1 , a photovoltaic system 1000A may include a photovoltaic array 100A, a power converter 200A, and a power grid 300 / AC load 400. A photovoltaic array 100A may be formed by connecting one or more photovoltaic modules 110A. The power converter 200A includes an inverter circuit 10A (i.e., a DC / AC conversion circuit). The DC power generated by the photovoltaic array 100A is converted into AC power by the inverter circuit 10A of the power converter 200A and then transmitted to the power grid 300 / AC load 400. In some photovoltaic-storage integration scenarios, the photovoltaic system may also include an energy storage device 500. The power converter 200A also includes a DC transformer circuit 20A (i.e., a DC / DC conversion circuit). The energy storage device 500 may be connected to the DC transformer circuit 20A. The electrical energy generated by the photovoltaic array 100A is then converted by the DC transformer circuit 20A into AC power, which is then used to charge the energy storage device 500. When the power generated by the photovoltaic array 100A is insufficient to power the grid 300 / AC load 400, the power stored in the energy storage device 500 can be transmitted to the grid 300 / AC load 400 via the DC transformer circuit 20A and the inverter circuit 10A within the power converter 200A. For details about power converters in hydropower and wind power scenarios, refer to the description of photovoltaic power scenarios and are not repeated here.

[0042] FIG2 exemplarily shows a schematic diagram of an application scenario in which a power storage converter (PCS) is used for power supply. In the PCS power supply scenario, the PCS provided in this application can be a power converter 200B, which is respectively connected to the power grid 300, the energy storage device 500 and the AC load 400. The PCS is also called a bidirectional converter, which includes an inverter circuit 10B (i.e., a DC / AC conversion circuit) and a rectifier circuit 30B (i.e., an AC / DC conversion circuit). The PCS can convert DC into AC based on the inverter circuit 10B, or convert AC into DC based on the rectifier circuit 30B. For example, the bidirectional converter can obtain AC power from the power grid 300 and convert it into DC power through the rectifier circuit 30B to charge the energy storage device 500. The DC power stored in the energy storage device 500 can also be converted into AC power through the DC transformer circuit 20B after DC conversion processing, and then converted into AC power through the inverter circuit 10B, and the converted power is transmitted to the necessary AC load 400 or the power grid 300. Furthermore, the energy storage device 500 can also supply power to the DC load 600 .

[0043] In the photovoltaic-storage fusion scenario, the energy storage device 500 can also obtain direct current from the photovoltaic array 100 for charging.

[0044] The power converter 200B may further include a DC transformer circuit 20B (i.e., a DC / DC conversion circuit), and the energy storage device 500 may be connected to the DC transformer circuit 20B. The electric energy generated by the grid 300 or the photovoltaic array 100 may be boosted or bucked by the DC transformer circuit 20B to charge the energy storage device 500.

[0045] It can be understood that the above is only an example of the application scenarios of the power converter provided by this application, and is not an exhaustive list. This application does not limit the application scenarios.

[0046] In order to meet the power supply scenario of unbalanced load, the embodiment of the present application provides a power converter. As shown in FIG3, the inverter circuit 10 of the power converter 200 adopts a three-phase four-bridge arm circuit design, that is, on the basis of the three-phase three-bridge arm (for example, phase A, phase B and phase C) of the inverter circuit, a fourth bridge arm is added as the N-phase bridge arm (also known as the N line). The N line can generate a zero-sequence voltage when the load is unbalanced, thereby achieving control of the unbalanced load. The positive DC input terminal and the negative DC input terminal of the power converter 200 are respectively connected to the positive DC bus DCL+ and the negative DC bus DCL-. The positive DC bus DCL+ and the negative DC bus DCL- are used to connect a DC power supply (for example, the photovoltaic array 100A shown in FIG1 or the energy storage device 500 shown in FIG1 and FIG2). A bus capacitor Cdc is connected between the positive DC bus DCL+ and the negative DC bus DCL-. Specifically, two identical bus capacitors Cdc can be used, and the N line is connected to the connection point of the two bus capacitors Cdc, that is, the midpoint. The current in the inverter circuit 10 is led back to the power supply through the N line, thereby ensuring the safety and stability of the power converter 200. However, in actual applications, the N line may be disconnected from the power grid 300, that is, the N line is disconnected. When the N line is disconnected from the inverter circuit 10, the current in the inverter circuit 10 cannot flow back normally. When the inverter circuit 10 starts working (for example, starts to input DC power and converts DC power to AC power) or is working, the voltage in the inverter circuit 10 will increase, causing damage to the circuit board of the power converter 200, causing harm to the power converter or the human body.

[0047] In one possible embodiment, the detection of whether the connection between the N line and the power grid 300 is disconnected can be achieved based on the pull-out resistor. As shown in Figure 4, the power converter 200 includes a bus capacitor Cdc, an inverter circuit 10, a filter circuit 20, a control circuit 40 and a plurality of pull-out resistors R1. The positive DC input terminal and the negative DC input terminal of the inverter circuit 10 are respectively connected to the positive DC bus DCL+ and the negative DC bus DCL-. The positive DC bus DCL+ and the negative DC bus DCL- are used to connect a DC power supply (such as the photovoltaic array 100A shown in Figure 1 or the internal energy storage device 20B shown in Figure 2). The bus capacitor Cdc is connected between the positive DC bus DCL+ and the negative DC bus DCL-. The N line is connected to the midpoint of the bus capacitor Cdc. The three-phase inverter bridge arm end and the N line of the inverter circuit 10 are respectively connected to the power grid 300 or the load 400 through the filter circuit 20. Multiple pull-off resistors R1 correspond one-to-one to the three-phase inverter bridge arm terminals. A first end of each pull-off resistor R1 is connected to a corresponding inverter bridge arm terminal of one of the three-phase inverter bridge arm terminals, and a second end of each pull-off resistor R1 is connected to the N line. The control circuit 40 is configured to determine whether the N line is disconnected based on the difference between the three-phase voltages of the power converter 200.

[0048] In the prior art, as shown in FIG4 , the control circuit 40 is connected to the inverter circuit 10, and the working state of the inverter circuit 10 can be controlled by a control signal. The inverter circuit 10 obtains DC power from the DC power supply through the DC bus, and after inverting the DC power, outputs AC power from the three-phase inverter bridge arm end of the inverter circuit 10. The current in the inverter circuit 10 can be led back to the DC power supply side through the N line to ensure the safety and stability of the device. When the N line is disconnected, the voltage in the circuit will increase, which may pose a safety hazard to the device or even the human body. In the embodiment of FIG4 , three pull-up resistors R1 can be set in the filter circuit 20. The resistance values ​​of the three pull-up resistors R1 are different. Each pull-up resistor R1 corresponds to the inverter bridge arm end of one phase in the three-phase inverter bridge arm end, and each phase inverter bridge arm end is coupled to the N line through the corresponding pull-up resistor R1. As shown in Figure 5 (a), the voltage at the three-phase inverter bridge arm ends varies over time when the N-wire coupling wire is intact. It can be seen that the voltage amplitudes of the phase voltages between the three-phase inverter bridge arm ends tend to be balanced and stable. As shown in Figure 5 (b), the voltage at the three-phase inverter bridge arm ends varies over time when the N-wire coupling wire is disconnected. It can be seen that due to the presence of multiple pull-off resistors R1, the phase voltages are pulled off after the N-wire coupling wire is disconnected, and the signal amplitudes between the three phase voltages corresponding to the three-phase inverter bridge arm ends have a certain voltage difference. The control circuit 40 can determine whether the N-wire coupling wire is disconnected based on the phase voltage changes, thereby ensuring the safety and stability of the power converter 200. However, in the prior art shown in Figure 4, multiple pull-off resistors R1 are required, which increases device cost. Furthermore, a filter circuit 20 is typically provided between the first inverter circuit 11A and the power grid 300 or the load 400. This filter circuit 20 affects the pull-off capability of the pull-off resistor R1, thereby reducing detection accuracy.

[0049] In order to achieve high-precision detection of whether the N line is disconnected while reducing device costs, in some possible implementations, detection of the N line disconnection can be achieved based on switch control. As shown in Figure 6, the power converter 200 includes a bus capacitor Cdc, an inverter circuit 10, a filter circuit 20, a switch component 30, and a control circuit 40. The positive DC input terminal and the negative DC input terminal of the inverter circuit 10 are respectively connected to the positive DC bus DCL+ and the negative DC bus DCL-. The positive DC bus DCL+ and the negative DC bus DCL- are used to connect to a DC power source (such as the photovoltaic array 100A shown in Figure 1 or the energy storage device 500 shown in Figure 2). The bus capacitor Cdc is connected between the positive DC bus DCL+ and the negative DC bus DCL-. The N line is connected to the midpoint of the bus capacitor Cdc. The inverter circuit 10 is connected to the switch component 30 via the filter circuit 20. The filter circuit 20 includes three filter capacitors C, each of which is connected between the output terminal of the corresponding inverter bridge arm and the N line. The switch assembly 30 is located between the filter circuit 20 and the power grid 300 and includes a plurality of first switches S1, each of which is connected to a three-phase inverter bridge arm end and an N line in a one-to-one correspondence. The control circuit 40 is used to control the target switch to close during the startup of the power converter. The target switch includes the first switch S1 corresponding to the first phase inverter bridge arm in the three-phase inverter bridge arm and the first switch S1 corresponding to the N line. The first phase inverter bridge arm is any one of the three-phase inverter bridge arms. When the difference between the phase voltage of the first phase output and the phase voltages of the other two phase outputs is greater than or equal to a first threshold, an alarm message is issued to indicate that the connection between the N line and the power grid 300 is disconnected, or the power converter 200 is controlled to shut down. The first phase output of the power converter is the output of the first phase inverter bridge arm after passing through the filter circuit 20, and the other two phase outputs are the outputs of the other two phase inverter bridge arms after passing through the filter circuit 20.

[0050] For example, powering up the power converter 200 means that the power converter 200 is connected to the device's operating power supply and then powered on and started. During the power converter 200 startup process, relevant tests may be performed to ensure the operational safety of the power converter 200. For example, a test may be performed to determine whether the N line is disconnected from the power grid 300.

[0051] Exemplarily, the filter circuit 20 may further include three filter inductors L, and the three filter inductors L are connected in series with the three-phase inverter bridge arms in a one-to-one correspondence.

[0052] In an embodiment of the present application, in order to ensure the power supply safety and reliability of the power converter 200, a switch component 30 is usually set at the three-phase inverter bridge arm end and the N line of the power converter 200. For example, as shown in Figure 6, a first switch S1 is correspondingly provided between each phase inverter bridge arm end of the three-phase inverter bridge arm end and the N line. Therefore, compared with the prior art shown in Figure 4, in the embodiment shown in Figure 6, it is not necessary to additionally set a biasing device for biasing the phase voltage (such as the biasing resistor R1 in Figure 4), and the existing filter device can be used as a biasing device to detect whether the N line is disconnected. The specific detection method is: in the stage of power-on startup of the power converter 200, by closing the first switch S1 corresponding to the first phase inverter bridge arm in the three-phase inverter bridge arm and the first switch S1 corresponding to the N line. After adopting the embodiment shown in Figure 6, after the first switch S1 corresponding to the first phase inverter bridge arm is closed, if the N line is not disconnected, a loop can be formed between the first phase bridge arm end, the power grid 300 and the N line. At this time, the filter capacitor C performs the filtering process normally and will not have a significant impact on the voltage value of the phase voltage. If the N line is disconnected, a loop cannot be formed between the first phase bridge arm end, the power grid 300 and the N line. At this time, the filter capacitor C cannot form a normal filtering structure, but acts as a pull-bias device lapped at the first phase bridge arm end. After the pull-bias of the phase voltage is achieved based on the corresponding filter capacitor C, the schematic diagram of the change of the phase voltage of the three phases of the power converter over time can refer to the schematic diagram corresponding to Figure (b) of Figure 5 above. It can be seen from Figure (b) of Figure 5 that after the N line falls off, the first phase output voltage of the power converter is greatly reduced by the pull-bias effect of the filter capacitor C, so that the phase voltage output of the first phase is significantly lower than the phase voltage output of the other two phases. Therefore, after detecting that the difference between the phase voltage output by the first phase and the phase voltage output by the other two phases is greater than or equal to the preset first threshold value, the control circuit 40 can determine that the connection between the N line and the power grid 300 is disconnected. The embodiment of the present application reuses the existing filter device (i.e., filter capacitor C) in the filter circuit 20 as a device for pulling the phase voltage, and realizes the pulling of the phase voltage of a phase in the three phases by switch control. The detection of whether the N line is disconnected can be achieved by the difference between the three phase voltages. Compared to the prior art of Figure 4, the embodiment of Figure 6 does not need to additionally set a pulling device, which reduces the cost of the device. At the same time, when using filter capacitor C as a pulling device, it will not be affected by the filter circuit 20. On the basis of maintaining a stable pulling ability, the phase voltage after pulling in the actual situation is close to the phase voltage after pulling in the ideal situation, because the value of the preset first threshold value is related to the phase voltage after pulling in the ideal situation, which makes the detection accuracy of the embodiment of Figure 6 much higher than the prior art shown in Figure 4.

[0053] In some possible implementations, as shown in FIG7 , the switch assembly 30 may further include a plurality of second switches S2, each of which is connected in series with the plurality of first switches S1 in a one-to-one correspondence. The three-phase inverter bridge arm and the N line are respectively used to connect to the power grid 300 through the one-to-one corresponding first switch S1 and second switch S2, and each first switch S1 is located between the filter circuit 20 and the corresponding second switch S2. In the embodiment of the present application, in order to ensure the operating safety of the power converter 200, in actual applications, multiple groups of switches can be provided in the switch assembly 30 to respectively ensure the safety of the inverter circuit 10 side and the power grid 300 side. In this case, the first switch S1 can be used as a switching device on the inverter circuit 10 side, and the second switch S can be used as a switching device on the power converter 200 with respect to the power grid 300 side. In this case, if the N line needs to be detected, the target switches that need to be closed during the detection also need to include the aforementioned plurality of second switches S2.

[0054] For example, the plurality of first switches S1 may be inverter-side relays, and the plurality of second switches S2 may be grid-side relays.

[0055] In some possible implementations, as shown in FIG8 , the power converter 200 further includes a sampling circuit 50 , which is connected to the switch assembly 30 and the control circuit 40 , respectively. The sampling circuit 50 is configured to sample and obtain the voltage across each target switch, i.e., the input voltage and the output voltage. The control circuit 40 can then determine whether each switch is closed based on the difference in voltage across the switch.

[0056] Exemplarily, the sampling circuit 50 is also connected to the filter circuit 20. The sampling circuit 50 can also be used to obtain the phase voltage of the three-phase output of the power converter 200 (i.e., the voltage at the output of the filter circuit 20). The control circuit 40 can obtain the phase voltage of the three-phase output from the sampling circuit 50 and determine whether the N line is disconnected based on the obtained phase voltage.

[0057] Based on the second processing circuit 100B shown in FIG. 6 , FIG. 7 and FIG. 8 , the detection method including the operations of steps S200 to S300 shown in FIG. 9 below may be executed:

[0058] S200 : During the startup process of the power converter 200 , the target switch is controlled to be closed.

[0059] In some possible implementations, the control circuit 40 starts detecting whether the N-line coupling wire is disconnected in response to power-on of the power converter 200. In this case, in step S200, an inverter bridge arm of any one of the three-phase inverter bridge arms can be used as the first-phase inverter bridge arm.

[0060] For example, when the N line of the power converter 200 is not disconnected from the grid 300, closing the target switch can form a loop between the first-phase inverter bridge arm and the corresponding filter capacitor C, the grid 300 and the N line. At this time, the filter capacitor C performs filtering and will not affect the phase voltage output by the first phase, that is, the amplitudes of the phase voltages output by the first phase and the other two phases are similar.

[0061] For example, when the N line of the power converter 200 is disconnected from the power grid 300, closing the target switch cannot form a loop between the first phase inverter bridge arm and the corresponding filter capacitor C, the power grid 300 and the N line. At this time, the filter capacitor C cannot perform filtering, and the filter capacitor C connected to the first phase inverter bridge arm will act as a biasing device to bias the phase voltage output of the first phase, so that the difference in amplitude between the phase voltage output of the first phase and the phase voltages output by the other two phases is greater than or equal to the first threshold.

[0062] For example, as shown in FIG10 , when the switch assembly 30 provided in the power converter 200 includes a plurality of first switches S1 on the inverter circuit 10 side, taking the A-phase inverter bridge arm as the first-phase inverter bridge arm as an example, in response to the inverter circuit 10 starting to work, the control circuit 40 can control the first switch S1 corresponding to the A-phase inverter bridge arm and the first switch S1 corresponding to the N line to close. At this time, if the N line is disconnected from the power grid 300, the phase voltage of the A-phase output of the power converter 200 can be pulled off based on the corresponding filter capacitor C between the A-phase inverter bridge arm and the N line. For a schematic diagram of the specific effect after pulling off, please refer to FIG5 (b).

[0063] For example, when the switch assembly 30 provided in the power converter 200 further includes a plurality of second switches S on the grid side as shown in FIG8 , during the detection of the N line, the target switches to be closed also include a plurality of second switches S2. In this case, S200 may be specifically based on the sub-operations of steps S210 to S220 shown in FIG11 :

[0064] S210 , during the startup process of the power converter 200 , controlling the plurality of second switches S2 to be closed.

[0065] S220 , controlling the first switch S1 corresponding to the first phase inverter bridge arm and the first switch S1 corresponding to the N line to be closed.

[0066] In the embodiment shown in FIG11 of the present application, taking the A-phase inverter bridge arm as the first-phase inverter bridge arm as an example, in order to ensure the safety of detection, when it is necessary to control the first switch S1 and the second switch S2 to be closed, the switch on the grid side can be controlled to be closed first (i.e., multiple second switches S2), and then the first switch S1 corresponding to the first-phase inverter bridge arm (i.e., the A-phase inverter bridge arm) and the first switch S1 corresponding to the N line can be controlled to be closed. For example, when controlling the corresponding first switch S1 to be closed, the first switch S1 corresponding to the first-phase inverter bridge arm can also be controlled first, and then the first switch S1 corresponding to the N line can be controlled to be closed. Regarding the technical principles and beneficial effects of the B-phase inverter bridge arm or the C-phase inverter bridge arm as the first-phase inverter bridge arm, reference can be made to the above-mentioned description of the A-phase inverter bridge arm as the first-phase inverter bridge arm, which will not be repeated here.

[0067] S300 , detecting whether the connection between the N line and the power grid 300 is disconnected.

[0068] In some possible implementations, as shown in FIG10 , the sampling circuit 50 provided in the power converter 200 samples the phase voltages of the three-phase outputs. The control circuit 40 determines whether the N line is disconnected from the power grid 300 based on the difference in amplitude between the phase voltage of the first phase output and the phase voltages of the other two phases. A schematic diagram of the effect of deflecting the phase voltage of the first phase output using the filter capacitor C can refer to the voltage change schematic diagram of the phase voltage after deflection in the prior art corresponding to FIG4 . As shown in FIG5 (b), when the phase voltage of the first phase output is deflected, the difference in amplitude between its phase voltage and the phase voltages of the other two phases increases. By detecting whether the difference in the phase voltages is greater than or equal to a preset first threshold, it is possible to determine whether the N line is disconnected. When it is detected that the difference in amplitude between the phase voltage of the first phase output and the phase voltages of the other two phases is greater than or equal to the first threshold, it is determined that the N line is disconnected from the power grid 300.

[0069] In one example, to ensure reliability and safety when detecting the N line, before sampling the phase voltages for N line detection using the sampling circuit 50, the sampling circuit 50 can also be used to verify whether each target switch is closed. For example, as shown in FIG10 , verification is performed on the first switch S1 corresponding to the first phase inverter bridge arm and the first switch S1 corresponding to the N line. Alternatively, verification can be performed on the first switch S1 corresponding to the first phase inverter bridge arm, the first switch S1 corresponding to the N line, and multiple second switches S2. Specifically, the sampling circuit 50 can obtain the voltage across the switch to be verified, i.e., the voltage between the input and output terminals, and determine whether the switch to be verified is closed based on the voltage between the input and output terminals. After confirming that all switches in the target switch are closed, the phase voltages are sampled to detect whether the N line is disconnected from the power grid 300. For example, for any target switch, when the difference between the corresponding voltages across the terminals is less than a preset threshold, the control circuit 40 can determine that the switch is closed. In the embodiment of the present application, when the switch is closed, a current transmission path is formed. When current flows through a certain switch, the voltage difference between the input and output ends of the switch is small (generally the voltage drop parameter value of the switch device). If the switch is turned off, the current cannot flow from the input end of the switch to the output end of the switch. At this time, the voltage difference between the input and output ends of the switch is large. Therefore, the sampling circuit 50 samples the voltage values ​​of the input and output ends of each switch in the target switch, and the control circuit 40 can determine whether the switch is closed based on the voltage difference between the input and output ends of the switch.

[0070] In some possible implementations, after determining that the N line is disconnected from the power grid 300 , the control circuit 40 may output relevant alarm indication information, where the alarm indication information is used to indicate that there is a disconnection fault on the N line.

[0071] In some possible implementations, after determining that the N line is disconnected from the grid 300 , the control circuit 40 may control the power converter 200 to shut down, so as to ensure the safety of the power converter 200 .

[0072] In some possible implementations, the detection method shown in FIG. 9 and FIG. 11 may further include the operations of step S100 and step S300 shown in FIG. 12 :

[0073] S100 , during the startup process of the power converter 200 , the inverter circuit 10 is controlled to generate an open-loop waveform.

[0074] In some possible implementations, before executing the operation of step S200 shown in FIG. 9 , the control circuit 40 may control the inverter circuit 10 to perform open-loop ringing (OLR) during the power-on startup process of the power converter 200 .

[0075] S200: Control the target switch to be closed. Specifically, step S200 includes the following sub-steps:

[0076] S210 , controlling the plurality of second switches S2 to be closed.

[0077] S220 , controlling the first switch S1 corresponding to the first phase inverter bridge arm and the first switch S1 corresponding to the N line to be closed.

[0078] S230 , controlling the inverter circuit 10 to stop open-loop wave generation.

[0079] In step S200 shown in FIG. 12 of the present application, multiple second switches S2 are first controlled to close, and then the first switches S1 corresponding to the first-phase inverter bridge arm and the first switch S1 corresponding to the N line are controlled to close. After all target switches are closed, the inverter circuit 10 is controlled to stop open-loop pulsation. Open-loop pulsation is disabled by stopping outputting the first pulsation control signal to the second inverter circuit. For example, the control circuit 40 can control the conduction state of the switches in the inverter circuit 10 based on pulse width modulation (PWM), thereby controlling the open-loop pulsation of the inverter circuit 10. In this embodiment, after the power converter 200 is powered on and started, open-loop pulsation is performed before the target switches are closed and then stopped after the target switches are closed, based on open-loop pulsation control. The duration of open-loop pulsation is within a certain range, which can control the signal size of the pulsation signal, making the pulsation signal of the inverter circuit 10 small. When the detection requirements are met, it can be ensured that the pulsation signal required for detection does not cause safety and stability issues for the power converter 200.

[0080] S300 , detecting whether the connection between the N line and the power grid 300 is disconnected.

[0081] For the description of the relevant technical principles and technical effects of other operations of step S200 and step S300 in the embodiment shown in Figure 12, reference can be made to the relevant descriptions in the embodiments shown in Figures 8 and 9 above, and no further details will be given here.

[0082] In some possible implementations, based on the embodiments shown in Figures 9, 11, and 12, the detection method further includes the operation of step S400: after determining that the connection between the N line and the power grid 300 is disconnected, controlling the target switch to turn off. In this embodiment of the present application, after determining that the connection between the N line and the power grid 300 is disconnected according to step S300, the control circuit 40 can control all target switches to turn off. By controlling all target switches to turn off, this embodiment of the present application can avoid safety hazards such as the potential for target switches to be turned on when the N line is disconnected from the power grid 300.

[0083] The control circuit involved in the embodiments of the present application may be a chip. For example, it may be a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a system on chip (SoC), a central processing unit (CPU), a network processor (NP), a digital signal processor (DSP), a microcontroller unit (MCU), a programmable logic device (PLD), or other integrated chips.

[0084] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0085] Those skilled in the art will appreciate that the modules and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0086] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and modules described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0087] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the modules is merely a logical function division. In actual implementation, there may be other division methods, such as multiple modules or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0088] The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules, that is, they may be located on a single device or distributed across multiple devices. Some or all of the modules may be selected to achieve the purpose of this embodiment based on actual needs.

[0089] In addition, the functional modules in the various embodiments of the present application may be integrated into one device, or each module may exist physically separately, or two or more modules may be integrated into one device.

[0090] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using a software program, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When loading and executing computer program instructions on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website, computer, server or data center by wired (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.) mode to another website, computer, server or data center. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that contains one or more media that can be integrated. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a DVD), or a semiconductor medium (eg, a solid state disk (SSD)).

[0091] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A power converter, characterized in that: Including bus capacitor, inverter circuit, filter circuit, switch component and control circuit; The input end of the inverter circuit is used to connect a positive DC bus and a negative DC bus, and the positive DC bus and the negative DC bus are used to connect to a DC power supply; the bus capacitor is connected between the positive DC bus and the negative DC bus; The inverter circuit includes a three-phase inverter bridge arm and an N line, and the N line is connected to the midpoint of the bus capacitor; The inverter circuit is connected to the switch component through the filter circuit; The filter circuit includes three filter capacitors, each of which is connected between the output end of a corresponding phase inverter bridge arm and the N line; The switch assembly is located between the filter circuit and the power grid, and includes a plurality of first switches, each of which is connected to the three-phase inverter bridge arm and the N line in a one-to-one correspondence; The control circuit is used to: During the startup of the power converter, controlling the target switch to be closed; the target switch includes a first switch corresponding to a first-phase inverter bridge arm in the three-phase inverter bridge arm and a first switch corresponding to the N line; the first-phase inverter bridge arm is any one of the three-phase inverter bridge arms; When it is obtained that the difference between the amplitudes of the phase voltage of the first-phase output of the power converter and the phase voltages of the other two-phase outputs is greater than or equal to a first threshold, an alarm message is issued to prompt that the connection between the N line and the power grid is disconnected, or the power converter is controlled to shut down; wherein, the first-phase output of the power converter is the output of the first-phase inverter bridge arm after passing through the filter circuit, and the other two-phase outputs are the outputs of the other two-phase inverter bridge arms after passing through the filter circuit.

2. The power converter according to claim 1, wherein: The switch assembly further includes a plurality of second switches, the plurality of second switches being connected in series with the plurality of first switches in a one-to-one correspondence, the three-phase inverter bridge arm and the N line being respectively used to connect to the power grid through the one-to-one corresponding first switches and second switches, each first switch being located between the filter circuit and the corresponding second switch; The target switch further includes the plurality of second switches; The controlling target switch to be closed includes: First, the plurality of second switches are controlled to be closed, and then the first switch corresponding to the first phase inverter bridge arm and the first switch corresponding to the N line are controlled to be closed.

3. The power converter according to claim 1 or 2, characterized in that: The control circuit is further configured to: Before the control target switch is closed, controlling the inverter circuit to generate an open loop wave; After the control target switch is closed, the inverter circuit is controlled to stop open-loop ripple generation.

4. The power converter according to any one of claims 1 to 3, characterized in that: The control circuit is further configured to: Before obtaining the phase voltage of the first phase output of the power converter, it is detected whether the target switch is closed.

5. The power converter according to claim 4, characterized in that The power converter further includes a sampling circuit; the sampling circuit is connected to the switch component and the control circuit respectively; The sampling circuit is used to: obtain the voltage across each of the target switches; The control circuit is specifically configured to: determine that any target switch is closed when the voltage difference between both ends of the target switch is less than a preset threshold.

6. The power converter according to any one of claims 1 to 5, characterized in that: The control circuit is further configured to: After determining that the N line is disconnected from the power grid, the target switch is controlled to be turned off.

7. A detection method, characterized in that: The invention is applied to a power converter, the power converter comprising a bus capacitor, an inverter circuit, a filter circuit, a switch assembly and a control circuit; wherein the input end of the inverter circuit is used to connect a positive DC bus and a negative DC bus, and the positive DC bus and the negative DC bus are used to connect a DC power supply; the bus capacitor is connected between the positive DC bus and the negative DC bus; the inverter circuit comprises a three-phase inverter bridge arm and an N line, and the N line is connected to the midpoint of the bus capacitor; the inverter circuit is connected to the switch assembly via the filter circuit; the filter circuit comprises three filter capacitors, each of which is connected between the output end of a corresponding one-phase inverter bridge arm and the N line; the switch assembly is located between the filter circuit and the power grid, and comprises a plurality of first switches, and the plurality of first switches are respectively connected to the three-phase inverter bridge arm and the N line in a one-to-one correspondence; the method comprises: During the startup of the power converter, controlling the target switch to be closed; the target switch includes a first switch corresponding to a first-phase inverter bridge arm in the three-phase inverter bridge arm and a first switch corresponding to the N line; the first-phase inverter bridge arm is any one of the three-phase inverter bridge arms; When it is obtained that the difference between the amplitudes of the phase voltage of the first-phase output of the power converter and the phase voltages of the other two-phase outputs is greater than or equal to a first threshold, an alarm message is issued to prompt that the connection between the N line and the power grid is disconnected, or the power converter is controlled to shut down; wherein, the first-phase output of the power converter is the output of the first-phase inverter bridge arm after passing through the filter circuit, and the other two-phase outputs are the outputs of the other two-phase inverter bridge arms after passing through the filter circuit.

8. The detection method according to claim 7, characterized in that The switch assembly further includes a plurality of second switches, the plurality of second switches being connected in series with the plurality of first switches in a one-to-one correspondence, the three-phase inverter bridge arm and the N line being respectively used to connect to the power grid through the one-to-one corresponding first switches and second switches, each first switch being located between the filter circuit and the corresponding second switch; The target switch further includes the plurality of second switches; The controlling target switch to be closed includes: First, the plurality of second switches are controlled to be closed, and then the first switch corresponding to the first phase inverter bridge arm and the first switch corresponding to the N line are controlled to be closed.

9. The detection method according to claim 7 or 8, characterized in that The method further comprises: Before the control target switch is closed, controlling the inverter circuit to generate an open loop wave; After the control target switch is closed, the inverter circuit is controlled to stop open-loop ripple generation.

10. The detection method according to any one of claims 7 to 9, characterized in that: The method further comprises: Before obtaining the phase voltage of the first phase output of the power converter, it is detected whether the target switch is closed.

11. The detection method according to claim 10, characterized in that: The power converter further includes a sampling circuit; the sampling circuit is connected to the switch component; and the detecting whether the target switch is closed includes: Acquiring the voltage across each of the target switches by sampling based on the sampling circuit; When the voltage difference between both ends of any target switch is less than a preset threshold, it is determined that the switch is closed.

12. The detection method according to any one of claims 7 to 11, characterized in that: The detection method further comprises: After determining that the N line is disconnected from the power grid, the target switch is controlled to be turned off.

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