Power conversion device

Abstract

The embodiment of the invention discloses a power conversion device, relates to the field of power electronics, and solves the problem of how to improve the efficiency and reliability of a switching tube in a power conversion circuit by a controller. The controller is used for controlling the first switch tube to be switched on periodically if the voltage instantaneous value is greater than or equal to zero and the current instantaneous value is greater than or equal to zero under the condition that the absolute value of the voltage instantaneous value between the bus midpoint and the alternating current end is greater than or equal to a voltage threshold value and the absolute value of the current instantaneous value of the alternating current end is greater than or equal to a current threshold value. And the third switch tube is controlled to keep a turn-off state. Or, if the voltage instantaneous value is smaller than or equal to zero and the current instantaneous value is smaller than or equal to zero, the fourth switch tube is controlled to be switched on periodically, and the second switch tube is controlled to be kept in the off state.

Description

Technical Field

[0001] The present application relates to the field of power electronics, and in particular to a power conversion device. Background Art

[0002] With the increase in the power and voltage levels of inverter circuits, multi-level inverter circuits have been widely used in new energy fields such as photovoltaics, wind power, and direct current transmission. Multi-level inverter circuits include three-level inverter circuits or five-level inverter circuits. Such multi-level inverter circuits can be referred to as power conversion circuits. Taking a three-level inverter circuit as an example, the output voltage of a three-level inverter circuit includes a positive level, a negative level, and a zero level. The types of three-level inverter circuits include active neutral point clamped (ANPC) three-level inverter circuits, diode neutral point clamped (DNPC) three-level inverter circuits, and T-type three-level inverter circuits. DNPC three-level inverter circuits can also be referred to as NPC three-level inverter circuits.

[0003] Taking a power conversion device including a controller and an ANPC three-level inverter circuit as an example, the controller controls the switching tubes in the ANPC three-level inverter circuit to alternately conduct, thereby converting DC power into AC power, or converting AC power into DC power, and can prevent a direct short circuit between the positive DC bus and the negative DC bus.

[0004] However, when a controller controls the alternating conduction of switches in an ANPC three-level inverter circuit, current can flow through the diodes connected in antiparallel to the switched-on switches, while no current may flow through the switched-on switches. The switching losses caused by the controller turning these switches on and off reduce the efficiency of the switches in the power conversion circuit. Furthermore, if a switch connected to the DC bus in the ANPC three-level inverter circuit short-circuits and fails, the controller controls the alternately switched-on switches corresponding to the shorted-out switches to conduct, shorting either the positive or negative DC bus, potentially causing a safety incident. Therefore, improving the efficiency and reliability of the switches in the power conversion circuit has become an urgent issue. Summary of the Invention

[0005] The embodiment of the present application provides a power conversion device, in which the switching loss corresponding to the switch tube in the power conversion circuit is low and the reliability is high.

[0006] In a first aspect of an embodiment of the present application, a power conversion device is provided, comprising: a positive DC bus and a negative DC bus. A positive bus capacitor and a negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, with the series connection point of the positive bus capacitor and the negative bus capacitor being the bus midpoint. A power conversion circuit comprises a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a first diode, and a second diode. The first, second, third, and fourth switching transistors are connected in series between the positive DC bus and the negative DC bus, with the cathode of the first diode connected to the series connection point of the first and second switching transistors, the anode of the second diode connected to the series connection point of the third and fourth switching transistors, the anode of the first diode and the cathode of the second diode connected to the bus midpoint, and the series connection point of the second and third switching transistors being the AC terminal of the power conversion circuit, which is used to connect to a power grid or a load. The power conversion circuit is used to convert DC power output by a photovoltaic module or energy storage battery into AC power.

[0007] The controller is configured to control the first and third switching transistors to alternately turn on, control the second switching transistor to remain on, and control the fourth switching transistor to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is greater than zero. The controller is configured to control the second and fourth switching transistors to alternately turn on, control the third switching transistor to remain on, and control the first switching transistor to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is less than zero.

[0008] The controller is further configured to, when the absolute value of the instantaneous voltage between the busbar midpoint and the AC terminal is greater than or equal to a voltage threshold, and the absolute value of the instantaneous current at the AC terminal is greater than or equal to a current threshold: if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is greater than or equal to zero, control the first switch to periodically turn on and control the third switch to remain in an off state. Alternatively, if the instantaneous voltage value is less than or equal to zero and the instantaneous current value is less than or equal to zero, control the fourth switch to periodically turn on and control the second switch to remain in an off state. Alternatively, if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is less than or equal to zero, control the third switch to periodically turn on and control the first switch to remain in an off state. Alternatively, if the instantaneous voltage value is less than or equal to zero and the instantaneous current value is greater than or equal to zero, control the second switch to periodically turn on and control the fourth switch to remain in an off state.

[0009] The instantaneous value of the current at the AC end being greater than zero means that the current flows from the AC end to the grid or the load, and the instantaneous value of the current at the AC end being less than zero means that the current flows from the grid or the load to the AC end.

[0010] In the prior art, a controller determines a driving waveform based on a modulation wave and a triangular carrier, and then controls a power conversion circuit based on the driving waveform. Due to the presence of ripple in the current at the AC end of the power conversion circuit, near the switching point between the positive half-cycle and the negative half-cycle of the modulation wave, or near the switching point between the negative half-cycle and the positive half-cycle of the modulation wave, the current at the AC end will experience multiple zero crossings, and the direction of the current at the AC end will change multiple times. During this process, the absolute value of the instantaneous voltage between the bus midpoint and the AC end and the absolute value of the instantaneous current at the AC end are both small. Based on this solution, compared to the prior art power conversion circuit drive method, taking the first and third switching transistors as an example, when the absolute value of the instantaneous voltage between the bus midpoint and the AC terminal is greater than or equal to the voltage threshold, and the absolute value of the instantaneous current at the AC terminal is greater than or equal to the current threshold, and the controller determines that the direction of the current in the power conversion circuit will not change suddenly, if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is greater than or equal to zero, the power conversion circuit is in an inverter operating state, and current flows from the AC terminal through the inductor to the grid or load. The controller controls the first switching transistor to periodically turn on and controls the third switching transistor to remain off. When the first switching transistor is off, freewheeling is provided by the first diode and the second switching transistor, thereby reducing switching losses caused by the controller controlling the turning on and off of the third switching transistor and improving the efficiency of the switching transistors in the power conversion circuit. Furthermore, if the first switching transistor shorts, because the controller controls the third switching transistor to remain off, the positive DC bus will not be directly short-circuited to the bus midpoint, thereby improving the reliability of the switching transistors in the power conversion circuit. At the same time, when the instantaneous value of the voltage between the bus midpoint and the AC end is less than the voltage threshold, and the absolute value of the instantaneous value of the current at the AC end is less than the current threshold, the controller does not control the third switch tube to turn off, so that when the direction of the current in the power conversion device suddenly changes to flow from the power grid or load through the inductor to the AC end, and the power conversion circuit is in a rectification working state or in a reactive power support state, the current can flow from the AC end through the third switch tube to the bus midpoint, and the current in the power conversion circuit will not be distorted.

[0011] In combination with the first aspect, in one implementation, the voltage threshold is 10% of the absolute value of the peak voltage between the bus midpoint and the AC terminal.

[0012] In combination with the first aspect, in one embodiment, the voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit, and the DC bus voltage is the voltage between the positive DC bus and the negative DC bus.

[0013] Based on this solution, since the greater the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit, the greater the ripple in the current at the AC end, the voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit. By adjusting the voltage threshold or the current threshold according to various parameters of the power conversion device, the efficiency and reliability of the switching tube in the power conversion circuit can be improved.

[0014] In combination with the first aspect, in one implementation, the voltage threshold or the current threshold is negatively correlated with the power factor or efficiency of the power conversion circuit.

[0015] Based on this solution, since the smaller the power factor of the power conversion circuit, the greater the reactive power and the greater the ripple, the lower the efficiency of the power conversion circuit and the greater the ripple, the voltage threshold or current threshold is negatively correlated with the power factor or efficiency of the power conversion circuit. By adjusting the voltage threshold or current threshold according to the various parameters of the power conversion device, the efficiency and reliability of the switching tube in the power conversion circuit can be improved.

[0016] In conjunction with the first aspect, in one embodiment, the controller is further configured to: after controlling the first switch to be periodically turned on, if the first switch suffers a short-circuit fault, control the third switch to remain in an off state. Alternatively, after controlling the fourth switch to be periodically turned on, if the fourth switch suffers a short-circuit fault, control the second switch to remain in an off state. Alternatively, after controlling the third switch to be periodically turned on, if the third switch suffers a short-circuit fault, control the first switch to remain in an off state. Alternatively, after controlling the second switch to be periodically turned on, if the second switch suffers a short-circuit fault, control the fourth switch to remain in an off state.

[0017] Based on this solution, a direct short circuit between the positive DC bus and the bus midpoint can be avoided, or a direct short circuit between the bus midpoint and the negative DC bus can be avoided, thereby improving the reliability of the switching tube in the power conversion circuit.

[0018] A second aspect of the embodiments of the present application provides a power conversion device comprising: a positive DC bus and a negative DC bus. A positive bus capacitor and a negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, with the series connection point of the positive and negative bus capacitors being the bus midpoint. A power conversion circuit comprises a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a fifth switching transistor, and a sixth switching transistor. The first switching transistor and the second switching transistor are connected in series between the positive DC bus and the bus midpoint, the third switching transistor and the fourth switching transistor are connected in series between the bus midpoint and the negative DC bus, the fifth switching transistor and the sixth switching transistor are connected in series between the series connection point of the first switching transistor and the second switching transistor and the series connection point of the third switching transistor and the fourth switching transistor, the second switching transistor and the third switching transistor are connected to the bus midpoint, and the series connection point of the fifth switching transistor and the sixth switching transistor is the AC terminal of the power conversion circuit, which is used to connect to a power grid or a load. The power conversion circuit is used to convert DC power output by a photovoltaic module or energy storage battery into AC power.

[0019] The controller is configured to control the first and second switching transistors to alternately turn on, control the third and fifth switching transistors to remain on, and control the fourth and sixth switching transistors to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is greater than zero. The controller is configured to control the third and fourth switching transistors to alternately turn on, control the second and sixth switching transistors to remain on, and control the first and fifth switching transistors to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is less than zero.

[0020] The controller is further configured to, when the absolute value of the instantaneous voltage between the busbar midpoint and the AC terminal is greater than or equal to a voltage threshold, and the absolute value of the instantaneous current at the AC terminal is greater than or equal to a current threshold: if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is greater than or equal to zero, control the first switch to periodically turn on and control the second switch to remain in an off state. Alternatively, if the instantaneous voltage value is less than or equal to zero and the instantaneous current value is less than or equal to zero, control the fourth switch to periodically turn on and control the third switch to remain in an off state. Alternatively, if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is less than or equal to zero, control the second switch to periodically turn on and control the first switch to remain in an off state. Alternatively, if the instantaneous voltage value is less than or equal to zero and the instantaneous current value is greater than or equal to zero, control the third switch to periodically turn on and control the fourth switch to remain in an off state.

[0021] The instantaneous value of the current at the AC end being greater than zero means that the current flows from the AC end to the grid or the load, and the instantaneous value of the current at the AC end being less than zero means that the current flows from the grid or the load to the AC end.

[0022] In combination with the second aspect, in one implementation, the voltage threshold is 10% of the absolute value of the peak voltage between the bus midpoint and the AC terminal.

[0023] In combination with the second aspect, in one embodiment, the voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit, and the DC bus voltage is the voltage between the positive DC bus and the negative DC bus.

[0024] In combination with the second aspect, in one implementation, the voltage threshold or the current threshold is negatively correlated with the power factor or efficiency of the power conversion circuit.

[0025] In conjunction with the second aspect, in one embodiment, the controller is further configured to: after controlling the first switch to be periodically turned on, if the first switch suffers a short-circuit fault, control the second switch to remain in an off state. Alternatively, after controlling the fourth switch to be periodically turned on, if the fourth switch suffers a short-circuit fault, control the third switch to remain in an off state. Alternatively, after controlling the second switch to be periodically turned on, if the second switch suffers a short-circuit fault, control the first switch to remain in an off state. Alternatively, after controlling the third switch to be periodically turned on, if the third switch suffers a short-circuit fault, control the fourth switch to remain in an off state.

[0026] According to a third aspect of the embodiments of the present application, a power conversion device is provided, comprising: a positive DC bus and a negative DC bus. A positive bus capacitor and a negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, with the series connection point of the positive bus capacitor and the negative bus capacitor being the bus midpoint. A power conversion circuit comprises a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube. The first switching tube and the fourth switching tube are connected in series between the positive DC bus and the negative DC bus, with the connection point of the first switching tube and the fourth switching tube being the AC end of the power conversion circuit, which is used to connect to a power grid or a load. The emitter or source of the second switching tube is connected to the AC end, the collector or drain of the second switching tube is connected to the collector or drain of the third switching tube, and the emitter or source of the third switching tube is connected to the bus midpoint. The power conversion circuit is used to convert DC power output by a photovoltaic module or energy storage battery into AC power.

[0027] The controller is configured to control the first and third switching transistors to alternately turn on, control the second switching transistor to remain on, and control the fourth switching transistor to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC terminal is greater than zero. The controller is configured to control the second and fourth switching transistors to alternately turn on, control the third switching transistor to remain on, and control the first switching transistor to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC terminal is less than zero.

[0028] The controller is further configured to, when the absolute value of the instantaneous voltage between the busbar midpoint and the AC terminal is greater than or equal to a voltage threshold, and the absolute value of the instantaneous current at the AC terminal is greater than or equal to a current threshold: if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is greater than or equal to zero, control the first switch to periodically turn on and control the third switch to remain in an off state. Alternatively, if the instantaneous voltage value is less than or equal to zero and the instantaneous current value is less than or equal to zero, control the fourth switch to periodically turn on and control the second switch to remain in an off state. Alternatively, if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is less than or equal to zero, control the third switch to periodically turn on and control the first switch to remain in an off state. Alternatively, if the instantaneous voltage value is less than or equal to zero and the instantaneous current value is greater than or equal to zero, control the second switch to periodically turn on and control the fourth switch to remain in an off state.

[0029] The instantaneous value of the current at the AC end being greater than zero means that the current flows from the AC end to the grid or the load, and the instantaneous value of the current at the AC end being less than zero means that the current flows from the grid or the load to the AC end.

[0030] In combination with the third aspect, in one implementation, the voltage threshold is 10% of the absolute value of the peak voltage between the bus midpoint and the AC terminal.

[0031] In combination with the third aspect, in one embodiment, the voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit, and the DC bus voltage is the voltage between the positive DC bus and the negative DC bus.

[0032] In combination with the third aspect, in one implementation, the voltage threshold or the current threshold is negatively correlated with the power factor or efficiency of the power conversion circuit.

[0033] In conjunction with the third aspect, in one embodiment, the controller is further configured to: after controlling the first switch to be periodically turned on, if the first switch suffers a short-circuit fault, control the third switch to remain in an off state. Alternatively, after controlling the fourth switch to be periodically turned on, if the fourth switch suffers a short-circuit fault, control the second switch to remain in an off state. Alternatively, after controlling the third switch to be periodically turned on, if the third switch suffers a short-circuit fault, control the first switch to remain in an off state. Alternatively, after controlling the second switch to be periodically turned on, if the second switch suffers a short-circuit fault, control the fourth switch to remain in an off state.

[0034] The beneficial effects of the second to third aspects of this application can be analyzed with reference to the beneficial effects of the first aspect, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1A schematic diagram of a circuit topology of a photovoltaic power generation system provided in an embodiment of the present application;

[0036] Figure 2 A schematic diagram of a circuit topology of a power conversion device provided in an embodiment of the present application;

[0037] Figure 3 A schematic diagram of a driving waveform of a DNPC three-level inverter circuit provided in an embodiment of the present application;

[0038] Figure 4 A schematic diagram of a circuit topology of another power conversion device provided in an embodiment of the present application;

[0039] Figure 5 A schematic diagram of a driving waveform of an ANPC three-level inverter circuit provided in an embodiment of the present application;

[0040] Figure 6 A schematic diagram of a circuit topology of another power conversion device provided in an embodiment of the present application;

[0041] Figure 7 A schematic diagram of a driving waveform of a T-shaped three-level inverter circuit provided in an embodiment of the present application;

[0042] Figure 8 A schematic diagram of driving waveforms of another DNPC three-level inverter circuit provided in an embodiment of the present application;

[0043] Figure 9 A schematic diagram of current flow in a power conversion device provided in an embodiment of the present application;

[0044] Figure 10 A schematic diagram of a circuit topology of another power conversion device provided in an embodiment of the present application;

[0045] Figure 11 A schematic diagram of driving waveforms of another ANPC three-level inverter circuit provided in an embodiment of the present application;

[0046] Figure 12 A schematic diagram of current flow in another power conversion device provided in an embodiment of the present application;

[0047] Figure 13 A schematic diagram of driving waveforms of another T-shaped three-level inverter circuit provided in an embodiment of the present application;

[0048] Figure 14 A schematic diagram of current flow in another power conversion device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0049] The following sections discuss the making and use of various embodiments in detail. However, it should be understood that many applicable inventive concepts provided herein can be implemented in a variety of specific contexts. The specific embodiments discussed are intended merely to illustrate specific ways to implement and use the present description and technology and are not intended to limit the scope of this application.

[0050] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

[0051] Various circuits or other components may be described or referred to as being "configured to" perform one or more tasks. In this case, "configured to" is used to imply structure by indicating that the circuit / component includes structure (e.g., circuitry) that performs the one or more tasks during operation. Thus, even when a specified circuit / component is not currently operational (e.g., not turned on), the circuit / component may be referred to as being configured to perform the task. Circuits / components used with the phrase "configured to" include hardware, such as circuitry that performs an operation, etc.

[0052] Before introducing the embodiments of the present application, the background technology involved in the present application is first introduced.

[0053] like Figure 1 The figure shows a schematic circuit topology diagram of a photovoltaic power generation system 100 provided in an embodiment of the present application. The photovoltaic power generation system 100 includes a photovoltaic inverter 110. The DC side of the photovoltaic inverter 110 is connected to a photovoltaic module 200, and the AC side of the photovoltaic inverter 110 is connected to a power grid or load 300. The photovoltaic module 200 is used to convert solar energy into DC power, and the photovoltaic inverter 110 is used to convert this DC power into AC power and transmit it to the power grid or load 300.

[0054] In one embodiment, reference Figure 1 The photovoltaic power generation system 100 may further include an energy storage battery 120 and a power conversion system (PCS) 130. The electrodes of the energy storage battery 120 are connected to the DC side of the energy storage converter 130, and the AC side of the energy storage converter 130 is connected to the AC side of the photovoltaic inverter 110. The energy storage converter 130 is used to convert the AC power output by the photovoltaic inverter 110 into DC power, or to convert the AC power provided by the power grid or load 300 into DC power to charge the energy storage battery 120. The energy storage converter 130 is also used to convert the DC power output by the energy storage battery 120 into AC power to provide power to the power grid or load 300.

[0055] The photovoltaic inverter 110 or the energy storage converter 130 described above can both be referred to as a power conversion device. The power conversion device can include a multi-level inverter circuit, which can be referred to as a power conversion circuit. A controller in the power conversion device can convert DC power to AC power, or vice versa, by controlling the alternating conduction of switches in the multi-level inverter circuit, and can prevent a direct short circuit between the positive DC bus and the negative DC bus. The multi-level inverter circuit can include a three-level inverter circuit, a five-level inverter circuit, or an inverter circuit with multiple levels. In the embodiments of this application, a three-level inverter circuit is used as an example for illustrative purposes.

[0056] like Figure 2 FIG. 4 is a schematic diagram of a circuit topology of a power conversion device 400 provided in an embodiment of the present application. Figure 2 The power conversion device 400 shown includes a DNPC three-level inverter circuit. The DNPC three-level inverter circuit includes a first switching transistor Q1, a second switching transistor Q2, a third switching transistor Q3, a fourth switching transistor Q4, a first diode Da, and a second diode Db. The first switching transistors Q1, Q2, Q3, and Q4 are connected in series between a positive DC bus BUS+ and a negative DC bus BUS-. The cathode of the first diode Da is connected to the series connection point between the first switching transistor Q1 and the second switching transistor Q2. The anode of the second diode Db is connected to the series connection point between the third switching transistor Q3 and the fourth switching transistor Q4. The anode of the first diode Da and the cathode of the second diode Db are connected to the bus midpoint H. The series connection point between the second switching transistor Q2 and the third switching transistor Q3 forms an AC terminal K of the DNPC three-level inverter circuit, which is used to connect to a power grid or a load 300.

[0057] Reference Figure 2 Taking the first to sixth switching tubes Q1 to Q4 as an example, the first to fourth switching tubes Q1 to Q4 may include IGBTs, and the power conversion device 400 further includes diodes D1 to D6 connected in reverse parallel to the first to fourth switching tubes Q1 to Q4 respectively.

[0058] like Figure 3 FIG. 1 is a driving waveform diagram of a DNPC three-level inverter circuit provided by an embodiment of the present application. Figure 2The power conversion device 400 may further include a controller 410. The controller 410 is configured to determine a drive waveform for the first to fourth switching transistors Q1 to Q4 based on the modulation wave and the triangular carrier wave, and to control the first to fourth switching transistors Q1 to Q4 to turn on or off based on the drive waveform. Specifically, the controller 410 is configured to control the first switching transistor Q1 and the third switching transistor Q3 to turn on alternately, control the second switching transistor Q2 to remain on, and control the fourth switching transistor Q4 to remain off, so that the instantaneous value of the voltage between the bus midpoint H and the AC terminal K is greater than zero. The controller 410 is configured to control the second switching transistor Q2 and the fourth switching transistor Q4 to turn on alternately, control the third switching transistor Q3 to remain on, and control the first switching transistor Q1 to remain off, so that the instantaneous value of the voltage between the bus midpoint H and the AC terminal K is less than zero.

[0059] However, taking the first switch tube Q1 and the third switch tube Q3 as an example, in the positive half cycle of the modulation wave, the output current of the AC terminal K is greater than zero, and the current flows from the AC terminal K through the inductor L to the power grid or the load 300. When the first switch tube Q1 and the third switch tube Q3 are alternately turned on, when the first switch tube Q1 is turned off and the third switch tube Q3 is turned on, the current may flow through the diode D3 connected in antiparallel to the third switch tube Q3 and the diode D4 connected in antiparallel to the fourth switch tube Q4, and no current may flow through the third switch tube Q3. The switching loss caused by the controller 410 controlling the turning on and off of the third switch tube Q3 will lead to a reduction in the efficiency of the switch tubes in the DNPC three-level inverter circuit. Secondly, if the first switch tube Q1 fails to short-circuit, the controller 410 controls the third switch tube Q3 to turn on, which will cause the positive DC bus BUS+ to be directly short-circuited to the bus midpoint H through the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the second diode Db, which will cause a safety accident. The reliability of the switch tubes in the DNPC three-level inverter circuit is low.

[0060] like Figure 4 FIG. 4 is a schematic diagram of a circuit topology of another power conversion device 400 provided in an embodiment of the present application. Figure 2The power conversion device 400 shown in FIG. differs in that it includes an ANPC three-level inverter circuit. This ANPC three-level inverter circuit includes a positive DC bus BUS+ and a negative DC bus BUS-, which are used to connect to the photovoltaic module 200. A positive bus capacitor C1 and a negative bus capacitor C2 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-, with the series connection point between the positive and negative bus capacitors C1 and C2 being the bus midpoint H. The ANPC three-level inverter circuit includes a first switch Q1, a second switch Q2, a third switch Q3, a fourth switch Q4, a fifth switch Q5, and a sixth switch Q6. The first switch tube Q1 and the second switch tube Q2 are connected in series between the positive DC bus BUS+ and the bus midpoint H. The third switch tube Q3 and the fourth switch tube Q4 are connected in series between the bus midpoint H and the negative DC bus BUS-. The fifth switch tube Q5 and the sixth switch tube Q6 are connected in series between the series connection point of the first switch tube Q1 and the second switch tube Q2 and the series connection point of the third switch tube Q3 and the fourth switch tube Q4. The second switch tube Q2 and the third switch tube Q3 are connected to the bus midpoint H. The series connection point of the fifth switch tube Q5 and the sixth switch tube Q6 is the AC terminal K of the ANPC three-level inverter circuit, which is used to connect to the power grid or the load 300. Figure 2 The power conversion device 400 provided in the embodiment of the present application further includes an inductor L, a first end of the inductor L is connected to the AC terminal K, and a second end of the inductor L is used to be connected to the power grid or the load 300.

[0061] Reference Figure 4 Taking the first to sixth switching tubes Q1 to Q6 as an example, the first to sixth switching tubes Q1 to Q6 may include IGBTs, and the power conversion device 400 further includes diodes D1 to D6 respectively connected in reverse parallel to the first to sixth switching tubes Q1 to Q6.

[0062] like Figure 5 FIG. 1 is a schematic diagram of a driving waveform of an ANPC three-level inverter circuit provided in an embodiment of the present application. Figure 5As shown, the controller 410 is configured to determine the drive waveforms of the first to sixth switches Q1 to Q6 based on the modulation wave and the triangular carrier wave, and to control the first to sixth switches Q1 to Q6 to be turned on or off based on the drive waveforms. Specifically, the controller 410 is configured to control the first and second switches Q1 to Q2 to be alternately turned on, control the third and fifth switches Q3 to remain on, and control the fourth and sixth switches Q4 to remain off, so that the instantaneous value of the voltage between the bus midpoint H and the AC terminal K is greater than zero. The controller 410 controls the third and fourth switches Q3 to be alternately turned on, controls the second and sixth switches Q6 to remain on, and controls the first and fifth switches Q1 to remain off, so that the instantaneous value of the voltage between the bus midpoint H and the AC terminal K is less than zero.

[0063] However, taking the first switch Q1 and the second switch Q2 as an example, during the positive half-cycle of the modulation wave, the output current at the AC terminal K is greater than zero, and the current flows from the AC terminal K through the inductor L to the power grid or load 300. When the first switch Q1 and the second switch Q2 are alternately turned on, when the first switch Q1 is turned off and the second switch Q2 is turned on, current can flow through the diode D2 connected in antiparallel to the second switch Q2, and no current may flow through the second switch Q2. The switching losses caused by the controller 410 turning the second switch Q2 on and off will reduce the efficiency of the switches in the ANPC three-level inverter circuit. Furthermore, if the first switch Q1 fails due to a short circuit, the controller 410 will turn the second switch Q2 on, causing a direct short circuit between the positive DC bus BUS+ and the bus midpoint H through the first and second switches Q1 and Q2, resulting in a safety incident. This reduces the reliability of the switches in the ANPC three-level inverter circuit.

[0064] like Figure 6 FIG. 4 is a schematic diagram of a circuit topology of another power conversion device 400 provided in an embodiment of the present application. Figure 2 or Figure 4 The difference of the power conversion device 400 is that the Figure 6 The illustrated power conversion device 400 includes a T-shaped three-level inverter circuit. The T-shaped three-level inverter circuit includes a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4. The first switch Q1 and the fourth switch Q4 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-. The connection point between the first switch Q1 and the fourth switch Q4 is an AC terminal K of the T-shaped three-level inverter circuit, which is used to connect to the power grid or load 300. The emitter or source of the second switch Q2 is connected to the AC terminal K, the collector or drain of the second switch Q2 is connected to the collector or drain of the third switch Q3, and the emitter or source of the third switch Q3 is connected to the bus midpoint H.

[0065] In one embodiment, the positions of the second switching tube Q2 and the third switching tube Q3 can be interchanged, the collector or drain of the third switching tube Q3 is connected to the AC terminal K, the emitter or source of the third switching tube Q3 is connected to the emitter or source of the second switching tube Q2, and the collector or drain of the second switching tube Q2 is connected to the bus midpoint H.

[0066] like Figure 7 The figure shows a schematic diagram of the driving waveforms of a T-shaped three-level inverter circuit provided by an embodiment of the present application. The controller 410 is used to determine the driving waveforms of the first to fourth switching transistors Q1 to Q4 based on the modulation wave and the triangular carrier, and control the first to fourth switching transistors Q1 to Q4 to turn on or off according to the driving waveforms. Specifically, the controller 410 is used to control the first switching transistor Q1 and the third switching transistor Q3 to be alternately turned on, control the second switching transistor Q2 to remain on, and control the fourth switching transistor Q4 to remain off, so that the instantaneous value of the voltage between the bus midpoint H and the AC terminal K is greater than zero. The controller 410 is also used to control the second switching transistor Q2 and the fourth switching transistor Q4 to be alternately turned on, control the third switching transistor Q3 to remain on, and control the first switching transistor Q1 to remain off, so that the instantaneous value of the voltage between the bus midpoint H and the AC terminal K is less than zero.

[0067] However, taking the first switch tube Q1 and the third switch tube Q3 as an example, in the positive half cycle of the modulation wave, the output current of the AC terminal K is greater than zero, and the current flows from the AC terminal K through the inductor L to the power grid or the load 300. When the first switch tube Q1 and the third switch tube Q3 are alternately turned on, when the first switch tube Q1 is turned off and the third switch tube Q3 is turned on, the current may flow through the diode D3 connected in antiparallel to the third switch tube Q3 and the diode D4 connected in antiparallel to the fourth switch tube Q4, and no current may flow through the third switch tube Q3. The switching loss caused by the controller 410 controlling the turning on and off of the third switch tube Q3 will lead to a reduction in the efficiency of the switch tube in the T-type three-level inverter circuit. Secondly, if the first switch tube Q1 fails to short-circuit, the controller 410 controls the third switch tube Q3 to turn on, which will cause the positive DC bus BUS+ to be directly short-circuited to the bus midpoint H through the first switch tube Q1, the second switch tube Q2 and the third switch tube, which will cause a safety accident. The reliability of the switch tubes in the T-type three-level inverter circuit is low.

[0068] In summary, the controller 410 suffers from low efficiency and poor reliability when controlling the power conversion circuit in the power conversion device 400. Based on this, an embodiment of the present application provides a power conversion device that utilizes diodes connected in reverse parallel to switching tubes for freewheeling, thereby reducing switching losses and improving the efficiency of the switching tubes in the power conversion circuit. It also prevents short circuits of the positive DC bus BUS+ or the negative DC bus BUS-, thereby improving the reliability of the switching tubes in the power conversion circuit.

[0069] The power conversion device provided in the embodiment of the present application can be an independent device. The power conversion device includes a power conversion circuit. The power conversion circuit can include a three-level inverter circuit, a five-level inverter circuit, or an inverter circuit of more levels. The embodiment of the present application is not limited to this. In the embodiment of the present application, the power conversion device includes a three-level inverter circuit. The circuit topology of the power conversion device is as described above. Figure 2 、 Figure 4 or Figure 6 The circuit topology of the power conversion device 400 shown is taken as an example for exemplary description.

[0070] The power conversion device 400 provided in the embodiment of the present application can be a photovoltaic inverter. The power conversion device 400 can replace the photovoltaic inverter 110 and be applied to the photovoltaic power generation system 100. The power conversion device 400 provided in the embodiment of the present application can also be an energy storage converter. The power conversion device 400 can replace the energy storage converter 130 and be applied to the photovoltaic power generation system 100. The detailed descriptions of the photovoltaic inverter 110 and the energy storage converter 130 mentioned above can be correspondingly referred to the power conversion device 400, and the embodiments of the present application will not be repeated here.

[0071] In one embodiment, the circuit topology of the power conversion device 400 provided in the embodiment of the present application is as follows: Figure 2 The circuit topology of the power conversion device 400 shown in FIG. Figure 8 FIG. 1 is a driving waveform diagram of another DNPC three-level inverter circuit provided in an embodiment of the present application, as shown in FIG. Figure 9 FIG. 4 is a schematic diagram showing the current flow in a power conversion device 400 provided in an embodiment of the present application.

[0072] Reference Figure 8 The controller 410 is configured to, when the absolute value of the instantaneous voltage value between the bus midpoint H and the AC terminal K is greater than or equal to the voltage threshold, and the absolute value of the instantaneous current value at the AC terminal K is greater than or equal to the current threshold, and the controller 410 determines that the direction of the current in the power conversion device 400 will not change suddenly:

[0073] If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the current flows from the AC terminal K through the inductor L to the grid or load 300, such as Figure 8 As shown in (a) of FIG. 1 , the controller 410 controls the first switch tube Q1 to be turned on periodically, and controls the third switch tube Q3 to be kept off. When the controller 410 controls the first switch tube Q1 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 9As shown by the broken line Z1 in (a), the current flows from the positive DC bus BUS+ through the first switch tube Q1 and the second switch tube Q2 to the AC terminal K. When the controller 410 controls the first switch tube Q1 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 9 As shown by the broken line Z2 in (a), the current flows from the busbar midpoint H through the first diode Da and the second switch tube Q2 to the AC terminal K for freewheeling.

[0074] Alternatively, if the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the current flows from the grid or load 300 through the inductor L to the AC terminal K, as shown in FIG. Figure 8 As shown in (b) of FIG. 1 , the controller 410 controls the fourth switch tube Q4 to be turned on periodically and controls the second switch tube Q2 to remain in the off state. When the controller 410 controls the fourth switch tube Q4 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 9 As shown by the broken line Z3 in (a), the current flows from the AC terminal K through the third switch tube Q3 and the fourth switch tube Q4 to the negative DC bus BUS-. When the controller 410 controls the fourth switch tube Q4 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 9 As shown by the broken line Z4 in (d), the current flows from the AC terminal K through the third switch tube Q3 and the second diode Db to the busbar midpoint H for freewheeling.

[0075] Alternatively, if the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the current flows from the grid or load 300 through the inductor L to the AC terminal K, as shown in FIG. Figure 8 As shown in (c) of FIG. 1 , the controller 410 controls the third switch tube Q3 to be turned on periodically and controls the first switch tube Q1 to remain in the off state. When the third switch tube Q3 is turned on, the direction of the current in the power conversion device 400 is as follows: Figure 9 As shown by the broken line X1 in (b), the current flows from the AC terminal K through the third switch tube Q3 and the second diode Db to the bus midpoint H for freewheeling. When the third switch tube Q3 is turned off, the direction of the current in the power conversion device 400 is as follows: Figure 9 As shown by the broken line X2 in (b) of FIG, current flows from the AC terminal K through the second switch Q2 and the antiparallel diode D1 connected to the first switch Q1, toward the positive DC bus BUS+. In this state, the power conversion device 400 absorbs energy (also known as reactive power support). Alternatively, the power conversion device 400 converts the AC power provided by the grid or load 300 into DC power, which is then supplied to the energy storage battery 120.

[0076] Alternatively, if the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the current flows from the AC terminal K through the inductor L to the grid or load 300, as shown in FIG. Figure 8 As shown in (d) in FIG, the controller 410 controls the second switch tube Q2 to be turned on periodically and controls the fourth switch tube Q4 to remain in the off state. When the controller 410 controls the second switch tube Q2 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 9 As shown by the broken line X3 in (b), the current flows from the busbar midpoint H through the first diode Da and the second switch tube Q2 to the AC terminal K for freewheeling. When the controller 410 controls the second switch tube Q2 to turn off, the direction of the current in the power conversion device 400 is as follows: Figure 9 As shown by the broken line X4 in (b) of FIG, current flows from the negative DC bus BUS− through the diode D4 connected in antiparallel to the fourth switch Q4 and the third switch Q3 to the AC terminal K. In this case, the power conversion device 400 absorbs energy (also known as reactive power), or the power conversion device 400 converts the AC power provided by the grid or the load 300 into DC power, which is then provided to the energy storage battery 120.

[0077] In this embodiment of the present application, the instantaneous value of the current at the AC terminal K is greater than zero, which means that the current flows from the AC terminal K to the power grid or load 300, and the instantaneous value of the current at the AC terminal K is less than zero, which means that the current flows from the power grid or load 300 to the AC terminal K.

[0078] In one implementation, the voltage threshold in the embodiment of the present application is 10% of the absolute value of the peak voltage between the bus midpoint and the AC terminal.

[0079] In one embodiment, the voltage threshold or current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion of grid-connected current (THD) of the output current of the DNPC three-level inverter circuit, or the output power of the DNPC three-level inverter circuit. The specific values of the voltage threshold and current threshold are not limited in the embodiments of the present application. The total harmonic distortion of current is the ratio of the total harmonic current effective value to the fundamental current effective value, and is often expressed as a percentage.

[0080] In one embodiment, the above-mentioned voltage threshold or current threshold, as well as the voltage threshold or current threshold in the following embodiments, are positively correlated with high and low ride-through states (high voltage ride-through state and low voltage ride-through state). Among them, high voltage ride-through (HVRT) means that when a high voltage fault occurs in the power system, the relevant equipment or power supply can remain connected to the power grid and operate normally, without being disconnected from the grid and meeting certain performance requirements to help the power grid restore stability. This high voltage ride-through can also be called high voltage fault ride-through. Low voltage ride-through (LVRT) means that when a low voltage fault occurs in the power system, the relevant equipment or power supply can remain connected to the power grid and operate normally, without being disconnected from the grid and meeting certain performance requirements to help the power grid restore stability. This low voltage ride-through can also be called low voltage fault ride-through.

[0081] In one embodiment, the voltage threshold or current threshold is negatively correlated with the power factor or efficiency of the DNPC three-level inverter circuit.

[0082] In one embodiment, the controller 410 is further configured to:

[0083] Reference Figure 8 (a) and Figure 9 In (a), after controlling the first switch Q1 to periodically turn on, if a short-circuit fault occurs in the first switch Q1, the third switch Q3 is controlled to remain off. This prevents the positive DC bus BUS+ from being short-circuited to the bus midpoint H through the first switch Q1, the second switch Q2, the third switch Q3, and the second diode Db, thereby improving the reliability of the switches in the DNPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the first switch Q1 short-circuited.

[0084] Or, refer to Figure 8 (b) and Figure 9 In step (a), after controlling the fourth switch Q4 to periodically turn on, if a short-circuit fault occurs in the fourth switch Q4, the second switch Q2 is controlled to remain off. This prevents a direct short circuit between the bus midpoint H and the negative DC bus BUS- through the first diode Da, the second switch Q2, the third switch Q3, and the fourth switch Q4, thereby improving the reliability of the switches in the DNPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the fourth switch Q4 short-circuited.

[0085] Or, refer to Figure 8 (c) and Figure 9In step (b), after controlling the third switch Q3 to periodically turn on, if a short-circuit fault occurs in the third switch Q3, the first switch Q1 is controlled to remain off. This prevents the positive DC bus BUS+ from being short-circuited to the bus midpoint H through the first switch Q1, the second switch Q2, the third switch Q3, and the second diode Db, thereby improving the reliability of the switches in the DNPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the third switch Q3 short-circuited.

[0086] Or, refer to Figure 8 (d) and Figure 9 In step (b), after controlling the second switch Q2 to periodically turn on, if a short-circuit fault occurs in the second switch Q2, the fourth switch Q4 is controlled to remain off. This prevents a direct short circuit between the bus midpoint H and the negative DC bus BUS- through the first diode Da, the second switch Q2, the third switch Q3, and the fourth switch Q4, thereby improving the reliability of the switches in the DNPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the second switch Q2 short-circuited.

[0087] In one embodiment, reference Figure 2 , taking the power conversion device 400 including a DNPC three-level inverter circuit as an example, Figure 10 FIG2 is a circuit topology diagram of another power conversion device 400 provided in an embodiment of the present application. The power conversion device 400 includes three DNPC three-level inverter circuits and three switches S. One end of the three switches S is respectively connected to the second end of the three inductors L, and the other ends of the three switches S are respectively used to connect to the three-phase AC end of the power grid or the load 300.

[0088] The controller 410 is further configured to, after controlling the switching tubes in any one of the DNPC three-level inverter circuits to be periodically turned on, control the switching tubes in the remaining DNPC three-level inverter circuits to be turned off if a short circuit fault occurs in the periodically turned-on switching tube, and control the switches S corresponding to the remaining DNPC three-level inverter circuits to be opened, thereby improving the reliability of the switching tubes in the DNPC three-level inverter circuits.

[0089] For example, refer to Figure 8 In (a), the controller 410 is used as an example to control the first switch Q1 to be periodically turned on and the third switch Q3 to be kept off. The controller 410 is further configured to, after controlling the first switch Q1 in any DNPC three-level inverter circuit to be periodically turned on, control the third switch Q3 to be kept off if a short circuit fault occurs in the first switch Q1, control all switches in the remaining DNPC three-level inverter circuits to be turned off, and control all switches K corresponding to the remaining DNPC three-level inverter circuits to be opened.

[0090] Refer to the above Figure 3 The driving waveform of the DNPC three-level inverter circuit shown in the figure, the controller 410 determines the driving waveform according to the modulation wave and the triangular carrier, and then controls the DNPC three-level inverter circuit according to the driving waveform. Since the current at the AC terminal K of the DNPC three-level inverter circuit has ripples, near the switching point between the positive half cycle and the negative half cycle of the modulation wave, or near the switching point between the negative half cycle and the positive half cycle of the modulation wave, the current at the AC terminal K will experience multiple zero crossings, and the direction of the current at the AC terminal K will change multiple times. During this process, the absolute value of the instantaneous voltage value between the bus midpoint H and the AC terminal K and the absolute value of the instantaneous current value at the AC terminal are both small. The power conversion device 400 provided in the embodiment of the present application is different from the above-mentioned Figure 3 Compared with the driving mode of the DNPC three-level inverter circuit shown in the figure, Figure 8 Taking the first switch Q1 and the second switch Q2 as an example, if the absolute value of the instantaneous voltage between the busbar midpoint H and the AC terminal K is greater than or equal to the voltage threshold, and the absolute value of the instantaneous current at the AC terminal K is greater than or equal to the current threshold, and the controller 410 determines that the direction of the current in the power conversion circuit will not change suddenly, if the instantaneous voltage value is greater than or equal to zero and the instantaneous current value is greater than or equal to zero, the power conversion circuit is in an inverter operating state, and current flows from the AC terminal K through the inductor L to the power grid or load 300. The controller 410 controls the first switch Q1 to periodically turn on and controls the third switch Q3 to remain off. When the first switch Q1 is off, freewheeling is provided by the first diode Da and the second switch Q2, thereby reducing switching losses caused by the controller 410 controlling the third switch Q3 to turn on and off, and improving the efficiency of the switches in the power conversion circuit. Furthermore, if the first switch Q1 is short-circuited, because the controller 410 controls the third switch Q3 to remain in the off state, the positive DC bus BUS+ will not be directly short-circuited to the bus midpoint H, thereby improving the reliability of the switches in the power conversion circuit. Furthermore, when the instantaneous value of the voltage between the bus midpoint H and the AC terminal K is less than the voltage threshold, and the absolute value of the instantaneous current at the AC terminal K is less than the current threshold, the controller 410 does not control the third switch Q3 to turn off. Consequently, when the current in the power conversion device 400 suddenly changes direction from the grid or load 300 to the AC terminal K through the inductor L, and the power conversion circuit is in a rectifying operating state or a reactive power support state, the current can flow from the AC terminal K through the third switch Q3 to the bus midpoint H, and the current in the power conversion circuit is not distorted.

[0091] In one embodiment, the circuit topology of the power conversion device 400 provided in the embodiment of the present application is as follows: Figure 4 The circuit topology of the power conversion device 400 shown in FIG. Figure 11FIG. 1 is a schematic diagram of driving waveforms of another ANPC three-level inverter circuit provided in an embodiment of the present application. Figure 12 FIG2 is a schematic diagram showing the current flow in another power conversion device 400 provided in an embodiment of the present application.

[0092] Reference Figure 11 The controller 410 is configured to, when the absolute value of the instantaneous voltage value between the bus midpoint H and the AC terminal K is greater than or equal to the voltage threshold, and the absolute value of the instantaneous current value at the AC terminal K is greater than or equal to the current threshold, and the controller 410 determines that the direction of the current in the power conversion device 400 will not change suddenly:

[0093] If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the current flows from the AC terminal K through the inductor L to the grid or load 300, and the ANPC three-level inverter circuit is in the inverter working state, such as Figure 11 As shown in (a) of FIG. 1 , the controller 410 controls the first switch tube Q1 to be turned on periodically and controls the second switch tube Q2 to be kept off. When the controller 410 controls the first switch tube Q1 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line Z1 in (a), the current flows from the positive DC bus BUS+ through the first switch tube Q1 and the fifth switch tube Q5 to the AC terminal K. When the controller 410 controls the first switch tube Q1 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line Z2 in (a), the current flows from the busbar midpoint H through the diode D2 connected in anti-parallel to the second switch tube Q2 and the fifth switch tube Q5 to the AC terminal K for freewheeling.

[0094] Alternatively, if the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the current flows from the grid or load 300 through the inductor L to the AC terminal K, and the ANPC three-level inverter circuit is in the inverter working state, such as Figure 11 As shown in (b) of FIG. 1 , the controller 410 controls the fourth switch tube Q4 to be turned on periodically and controls the third switch tube Q3 to remain in the off state. When the controller 410 controls the fourth switch tube Q4 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line Z3 in (a), the current flows from the AC terminal K through the sixth switch tube Q6 and the fourth switch tube Q4 to the negative DC bus BUS-. When the controller 410 controls the fourth switch tube Q4 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line Z4 in (a), the current flows from the AC terminal K through the sixth switch tube Q6 and the diode D3 connected in anti-parallel to the third switch tube Q3 to the bus midpoint H for freewheeling.

[0095] Alternatively, if the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the current flows from the grid or load 300 through the inductor L to the AC terminal K, and the ANPC three-level inverter circuit is in a rectifying working state or in a reactive power support state, such as Figure 11 As shown in (c) of FIG. 1 , the controller 410 controls the second switch tube Q2 to be turned on periodically and controls the first switch tube Q1 to remain in the off state. When the controller 410 controls the second switch tube Q2 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line X1 in (b), the current flows from the AC terminal K through the fifth switch tube Q5 and the second switch tube Q2 to the bus midpoint H for freewheeling. When the controller 410 controls the second switch tube Q2 to turn off, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line X2 in (b), the current flows from the AC terminal K through the fifth switch tube Q5 and the diode D1 connected in anti-parallel to the first switch tube Q1 to the positive DC bus BUS+.

[0096] Alternatively, if the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the current flows from the AC terminal K through the inductor L to the grid or load 300, and the ANPC three-level inverter circuit is in a rectifying working state or in a reactive power support state, such as Figure 11 As shown in (d) in FIG, the controller 410 controls the third switch tube Q3 to be turned on periodically and controls the fourth switch tube Q4 to remain in the off state. When the controller 410 controls the third switch tube Q3 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line X3 in (b), the current flows from the busbar midpoint H through the third switch tube Q3 and the sixth switch tube Q6 to the AC terminal K for freewheeling. When the controller 410 controls the third switch tube Q3 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 12 As shown by the broken line X4 in (b), the current flows from the negative DC bus BUS- through the diode D4 connected in anti-parallel to the fourth switch tube Q4 and the sixth switch tube Q6 to the AC terminal K.

[0097] In one embodiment, the positive and negative signs and the magnitude of the voltage between the bus midpoint H and the AC terminal K can be used to indicate the positive and negative signs and the magnitude of the modulated wave. The voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the ANPC three-level inverter circuit, or the output power of the ANPC three-level inverter circuit. The DC bus voltage is the voltage between the positive DC bus BUS+ and the negative DC bus BUS-. The specific values of the voltage threshold and the current threshold are not limited in the embodiments of the present application.

[0098] In one embodiment, the voltage threshold or the current threshold is negatively correlated with the power factor or efficiency of the ANPC three-level inverter circuit.

[0099] In one embodiment, the controller 410 is further configured to:

[0100] Reference Figure 11 (a) and Figure 12 In (a), after controlling the first switch Q1 to periodically turn on, if a short-circuit fault occurs in the first switch Q1, the second switch Q2 is controlled to remain off. This prevents the positive DC bus BUS+ from being short-circuited to the bus midpoint H through the first and second switches Q1, Q2, thereby improving the reliability of the switches in the ANPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the first switch Q1 short-circuited.

[0101] Or, refer to Figure 11 (b) and Figure 12 In step (a), after controlling the fourth switch Q4 to periodically turn on, if a short-circuit fault occurs in the fourth switch Q4, the third switch Q3 is controlled to remain off. This prevents a direct short circuit between the bus midpoint H and the negative DC bus BUS- through the third and fourth switches Q3 and Q4, thereby improving the reliability of the switches in the ANPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the fourth switch Q4 short-circuited.

[0102] Or, refer to Figure 11 (c) and Figure 12 In step (b), after controlling the second switch Q2 to periodically turn on, if a short-circuit fault occurs in the second switch Q2, the first switch Q1 is controlled to remain off. This prevents a direct short circuit between the positive DC bus BUS+ and the bus midpoint H through the first and second switches Q1, Q2, thereby improving the reliability of the switches in the ANPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the second switch Q2 short-circuited.

[0103] Or, refer to Figure 11 (d) and Figure 12 In step (b), after controlling the third switch Q3 to periodically turn on, if a short-circuit fault occurs in the third switch Q3, the fourth switch Q4 is controlled to remain off. This prevents a direct short circuit between the bus midpoint H and the negative DC bus BUS- through the third and fourth switches Q3 and Q4, thereby improving the reliability of the switches in the ANPC three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the third switch Q3 short-circuited.

[0104] In one embodiment, the circuit topology of the power conversion device 400 provided in the embodiment of the present application is as follows: Figure 6 The circuit topology of the power conversion device 400 shown in FIG. Figure 13 FIG. 1 is a schematic diagram of driving waveforms of another T-shaped three-level inverter circuit provided in an embodiment of the present application. Figure 14 FIG. 4 is a schematic diagram showing the current flow in another power conversion device 400 provided in an embodiment of the present application.

[0105] Reference Figure 13 The controller 410 is configured to, when the absolute value of the instantaneous voltage value between the bus midpoint H and the AC terminal K is greater than or equal to the voltage threshold, and the absolute value of the instantaneous current value at the AC terminal K is greater than or equal to the current threshold, and the controller 410 determines that the direction of the current in the power conversion device 400 will not change suddenly:

[0106] If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the current flows from the AC terminal K through the inductor L to the grid or load 300, such as Figure 13 As shown in (a) of FIG. 1 , the controller 410 controls the first switch tube Q1 to be turned on periodically, and controls the third switch tube Q3 to be kept off. When the controller 410 controls the first switch tube Q1 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line Z1 in (a), the current flows from the positive DC bus BUS+ through the first switch tube Q1 to the AC terminal K. When the controller 410 controls the first switch tube Q1 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line Z2 in (a), the current flows from the busbar midpoint H through the diode D3 connected in anti-parallel to the third switch tube Q3 and the second switch tube Q2 to the AC terminal K for freewheeling.

[0107] Alternatively, if the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the current flows from the grid or load 300 through the inductor L to the AC terminal K, as shown in FIG. Figure 13 As shown in (b) of FIG. 1 , the controller 410 controls the fourth switch tube Q4 to be turned on periodically and controls the second switch tube Q2 to remain in the off state. When the controller 410 controls the fourth switch tube Q4 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line Z3 in (a), the current flows from the AC terminal K through the fourth switch tube Q4 to the negative DC bus BUS-. When the controller 410 controls the fourth switch tube Q4 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line Z4 in (a), the current flows from the AC terminal K through the diode D2 connected in anti-parallel to the second switch tube Q2 and the third switch tube Q3 to the busbar midpoint H for freewheeling.

[0108] Alternatively, if the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the current flows from the grid or load 300 through the inductor L to the AC terminal K, as shown in FIG. Figure 13 As shown in (c) of FIG. 1 , the controller 410 controls the third switch tube Q3 to be turned on periodically and controls the first switch tube Q1 to remain in the off state. When the controller 410 controls the third switch tube Q3 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line X1 in (b), the current flows from the AC terminal K through the second switch tube Q2 and the third switch tube Q3 to the bus midpoint H for freewheeling. When the controller 410 controls the third switch tube Q3 to be turned off, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line X2 in (b), the current flows from the AC terminal K to the positive DC bus BUS+ through the diode D1 connected in anti-parallel to the first switch tube Q1.

[0109] Alternatively, if the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the current flows from the AC terminal K through the inductor L to the grid or load 300, as shown in FIG. Figure 13 As shown in (d) in FIG, the controller 410 controls the second switch tube Q2 to be turned on periodically and controls the fourth switch tube Q4 to remain in the off state. When the controller 410 controls the second switch tube Q2 to be turned on, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line X3 in (b), the current flows from the busbar midpoint H through the third switch tube Q3 and the second switch tube Q2 to the AC terminal K for freewheeling. When the controller 410 controls the second switch tube Q2 to turn off, the direction of the current in the power conversion device 400 is as follows: Figure 14 As shown by the broken line X4 in (b), the current flows from the negative DC bus BUS- through the diode D4 connected in anti-parallel to the fourth switch tube Q4 to the AC terminal K.

[0110] In one embodiment, the above-mentioned voltage threshold or current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the T-type three-level inverter circuit, or the output power of the T-type three-level inverter circuit. The specific values of the voltage threshold and the current threshold are not limited in the embodiments of the present application.

[0111] In one embodiment, the voltage threshold or current threshold is negatively correlated with the power factor or efficiency of the T-shaped three-level inverter circuit.

[0112] In one embodiment, the controller 410 is further configured to:

[0113] Reference Figure 13 (a) and Figure 14In step (a), after controlling the first switch Q1 to periodically turn on, if a short-circuit fault occurs in the first switch Q1, the third switch Q3 is controlled to remain off. This prevents a direct short circuit between the positive DC bus BUS+ and the bus midpoint H through the first switch Q1, the second switch Q2, and the third switch Q3, thereby improving the reliability of the switches in the T-type three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the first switch Q1 short-circuited.

[0114] Or, refer to Figure 13 (b) and Figure 14 In step (a), after controlling the fourth switch Q4 to periodically turn on, if a short-circuit fault occurs in the fourth switch Q4, the second switch Q2 is controlled to remain off. This prevents a direct short circuit between the bus midpoint H and the negative DC bus BUS- through the third switch Q3, the second switch Q2, and the fourth switch Q4, thereby improving the reliability of the switches in the T-type three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the fourth switch Q4 short-circuited.

[0115] Or, refer to Figure 13 (c) and Figure 14 In step (b), after controlling the third switch Q3 to periodically turn on, if a short-circuit fault occurs in the third switch Q3, the first switch Q1 is controlled to remain off. This prevents a direct short circuit between the positive DC bus BUS+ and the bus midpoint H through the first switch Q1, the second switch Q2, and the third switch Q3, thereby improving the reliability of the switches in the T-type three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the third switch Q3 short-circuited.

[0116] Or, refer to Figure 13 (d) and Figure 14 In step (b), after controlling the second switch Q2 to periodically turn on, if a short-circuit fault occurs in the second switch Q2, the fourth switch Q4 is controlled to remain off. This prevents a direct short circuit between the bus midpoint H and the negative DC bus through the third switch Q3, the second switch Q2, and the fourth switch Q4, thereby improving the reliability of the switches in the T-type three-level inverter circuit. The controller 410 is further configured to control the remaining switches to maintain the state in which the second switch Q2 short-circuited.

[0117] Based on this, Figure 1As shown, the embodiment of the present application further provides a photovoltaic power generation system 100, which includes a photovoltaic inverter 110. The DC side of the photovoltaic inverter 110 is used to connect to the photovoltaic module 200, and the AC side of the photovoltaic inverter 110 is used to connect to the power grid or load 300. The circuit topology of the photovoltaic inverter 110 is as described above. Figure 2 、 Figure 4 、 Figure 6 、 Figure 9 、 Figure 10 、 Figure 12 or Figure 14 The circuit topology of the power conversion device 400 shown in any of the figures.

[0118] In one embodiment, reference Figure 1 The photovoltaic power generation system 100 may further include an energy storage battery 120 and an energy storage converter 130 , wherein the electrodes of the energy storage battery 120 are connected to the DC side of the energy storage converter 130 , and the AC side of the energy storage converter 130 is connected to the AC side of the photovoltaic inverter 110 .

[0119] The detailed description of the power conversion device 400 and the analysis of its beneficial effects can be found in the Figure 1 In the photovoltaic power generation system 100 shown, the embodiments of the present application are not described in detail here.

[0120] The above is only a specific embodiment of the present application, but the scope of protection of this application is not limited to this. Any changes or substitutions 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 conversion device, characterized in that: include: Positive DC bus and negative DC bus; A positive bus capacitor and a negative bus capacitor, wherein the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, and the series connection point of the positive bus capacitor and the negative bus capacitor is the bus midpoint; A power conversion circuit includes a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a first diode, and a second diode. The first, second, third, and fourth switching tubes are connected in series between the positive DC bus and the negative DC bus. The cathode of the first diode is connected to the series connection point of the first and second switching tubes. The anode of the second diode is connected to the series connection point of the third and fourth switching tubes. The anode of the first diode and the cathode of the second diode are connected to the midpoint of the bus. The series connection point of the second and third switching tubes is an AC terminal of the power conversion circuit, which is used to connect to a power grid or a load. The power conversion circuit is used to convert DC power output by a photovoltaic module or energy storage battery into AC power. The controller is configured to control the first and third switching transistors to be alternately turned on, control the second switching transistor to remain turned on, and control the fourth switching transistor to remain turned off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is greater than zero; and control the second and fourth switching transistors to be alternately turned on, control the third switching transistor to remain turned on, and control the first switching transistor to remain turned off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is less than zero; The controller is further configured to, when an absolute value of an instantaneous value of a voltage between a midpoint of the busbar and the AC terminal is greater than or equal to a voltage threshold, and an absolute value of an instantaneous value of a current at the AC terminal is greater than or equal to a current threshold: If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the first switch tube is controlled to be periodically turned on, and the third switch tube is controlled to remain in an off state; or, If the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the fourth switch tube is controlled to be periodically turned on, and the second switch tube is controlled to remain in the off state; or, If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is less than or equal to zero, controlling the third switch tube to be periodically turned on, and controlling the first switch tube to remain in an off state; or, If the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, controlling the second switch tube to be periodically turned on, and controlling the fourth switch tube to remain in an off state; The instantaneous value of the current at the AC end being greater than zero means that the current flows from the AC end to the grid or load, and the instantaneous value of the current at the AC end being less than zero means that the current flows from the grid or load to the AC end.

2. The power conversion device according to claim 1, wherein: The voltage threshold is 10% of the absolute value of the peak voltage between the busbar midpoint and the AC terminal.

3. The power conversion device according to claim 1 or 2, characterized in that: The voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit, and the DC bus voltage is the voltage between the positive DC bus and the negative DC bus.

4. The power conversion device according to any one of claims 1 to 3, characterized in that: The voltage threshold or the current threshold is negatively correlated with the power factor or efficiency of the power conversion circuit.

5. The power conversion device according to any one of claims 1 to 4, characterized in that: The controller is further configured to: After controlling the first switch tube to be periodically turned on, if a short circuit fault occurs in the first switch tube, controlling the third switch tube to remain in an off state; or, After controlling the fourth switch tube to be periodically turned on, if a short circuit fault occurs in the fourth switch tube, controlling the second switch tube to remain in an off state; or, After controlling the third switch tube to be periodically turned on, if a short circuit fault occurs in the third switch tube, controlling the first switch tube to remain in an off state; or, After the second switch tube is controlled to be periodically turned on, if a short circuit fault occurs in the second switch tube, the fourth switch tube is controlled to remain in an off state.

6. A power conversion device, characterized in that: include: A positive bus capacitor and a negative bus capacitor, wherein the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, and the series connection point of the positive bus capacitor and the negative bus capacitor is the bus midpoint; A power conversion circuit includes a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a fifth switching transistor, and a sixth switching transistor. The first switching transistor and the second switching transistor are connected in series between the positive DC bus and the bus midpoint. The third switching transistor and the fourth switching transistor are connected in series between the bus midpoint and the negative DC bus. The fifth switching transistor and the sixth switching transistor are connected in series between the series connection point of the first and second switching transistors and the series connection point of the third and fourth switching transistors. The second switching transistor and the third switching transistor are connected to the bus midpoint. The series connection point of the fifth and sixth switching transistors forms an AC terminal of the power conversion circuit, which is used to connect to a power grid or a load. The power conversion circuit is used to convert DC power output by a photovoltaic module or an energy storage battery into AC power. The controller is configured to control the first and second switching transistors to be alternately turned on, control the third and fifth switching transistors to remain turned on, and control the fourth and sixth switching transistors to remain turned off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is greater than zero; and control the third and fourth switching transistors to be alternately turned on, control the second and sixth switching transistors to remain turned on, and control the first and fifth switching transistors to remain turned off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is less than zero. The controller is further configured to, when an absolute value of an instantaneous value of a voltage between a midpoint of the busbar and the AC terminal is greater than or equal to a voltage threshold, and an absolute value of an instantaneous value of a current at the AC terminal is greater than or equal to a current threshold: If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the first switch tube is controlled to be periodically turned on, and the second switch tube is controlled to remain in an off state; or, If the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the fourth switch tube is controlled to be periodically turned on, and the third switch tube is controlled to remain in the off state; or, If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the second switch tube is controlled to be turned on periodically, and the first switch tube is controlled to remain in an off state; or, If the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, controlling the third switch tube to be periodically turned on, and controlling the fourth switch tube to remain in an off state; The instantaneous value of the current at the AC end being greater than zero means that the current flows from the AC end to the grid or load, and the instantaneous value of the current at the AC end being less than zero means that the current flows from the grid or load to the AC end.

7. The power conversion device according to claim 6, characterized in that: The voltage threshold is 10% of the absolute value of the peak voltage between the busbar midpoint and the AC terminal.

8. The power conversion device according to claim 6 or 7, characterized in that: The voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit, and the DC bus voltage is the voltage between the positive DC bus and the negative DC bus.

9. The power conversion device according to any one of claims 6 to 8, characterized in that: The voltage threshold or the current threshold is negatively correlated with the power factor or efficiency of the power conversion circuit.

10. The power conversion device according to any one of claims 6 to 9, characterized in that: The controller is further configured to: After controlling the first switch tube to be periodically turned on, if a short circuit fault occurs in the first switch tube, controlling the second switch tube to remain in an off state; or, After controlling the fourth switch tube to be periodically turned on, if a short circuit fault occurs in the fourth switch tube, controlling the third switch tube to remain in an off state; or, After controlling the second switch tube to be periodically turned on, if a short circuit fault occurs in the second switch tube, controlling the first switch tube to remain in an off state; or, After the third switch tube is controlled to be periodically turned on, if a short circuit fault occurs in the third switch tube, the fourth switch tube is controlled to remain in an off state.

11. A power conversion device, characterized in that: include: Positive DC bus and negative DC bus; A positive bus capacitor and a negative bus capacitor, wherein the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, and the series connection point of the positive bus capacitor and the negative bus capacitor is the bus midpoint; A power conversion circuit includes a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube. The first switching tube and the fourth switching tube are connected in series between the positive DC bus and the negative DC bus. The connection point between the first switching tube and the fourth switching tube is an AC terminal of the power conversion circuit, and the AC terminal is used to connect to a power grid or a load. The emitter or source of the second switching tube is connected to the AC terminal, the collector or drain of the second switching tube is connected to the collector or drain of the third switching tube, and the emitter or source of the third switching tube is connected to the midpoint of the bus. The controller is configured to control the first and third switching transistors to alternately turn on, control the second switching transistor to remain on, and control the fourth switching transistor to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is greater than zero; control the second and fourth switching transistors to alternately turn on, control the third switching transistor to remain on, and control the first switching transistor to remain off, so that the instantaneous value of the voltage between the bus midpoint and the AC end is less than zero; the power conversion circuit is configured to convert direct current output by a photovoltaic module or an energy storage battery into alternating current; The controller is further configured to, when an absolute value of an instantaneous value of a voltage between a midpoint of the busbar and the AC terminal is greater than or equal to a voltage threshold, and an absolute value of an instantaneous value of a current at the AC terminal is greater than or equal to a current threshold: If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, the first switch tube is controlled to be periodically turned on, and the third switch tube is controlled to remain in an off state; or, If the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is less than or equal to zero, the fourth switch tube is controlled to be periodically turned on, and the second switch tube is controlled to remain in the off state; or, If the instantaneous value of the voltage is greater than or equal to zero, and the instantaneous value of the current is less than or equal to zero, controlling the third switch tube to be periodically turned on, and controlling the first switch tube to remain in an off state; or, If the instantaneous value of the voltage is less than or equal to zero, and the instantaneous value of the current is greater than or equal to zero, controlling the second switch tube to be periodically turned on, and controlling the fourth switch tube to remain in an off state; The instantaneous value of the current at the AC end being greater than zero means that the current flows from the AC end to the grid or load, and the instantaneous value of the current at the AC end being less than zero means that the current flows from the grid or load to the AC end.

12. The power conversion device according to claim 11, characterized in that: The voltage threshold is 10% of the absolute value of the peak voltage between the busbar midpoint and the AC terminal.

13. The power conversion device according to claim 11 or 12, characterized in that: The voltage threshold or the current threshold is positively correlated with at least one of the DC bus voltage, the total harmonic distortion rate of the output current of the power conversion circuit, or the output power of the power conversion circuit, and the DC bus voltage is the voltage between the positive DC bus and the negative DC bus.

14. The power conversion device according to any one of claims 11 to 13, characterized in that: The voltage threshold or the current threshold is negatively correlated with the power factor or efficiency of the power conversion circuit.

15. The power conversion device according to any one of claims 11 to 14, characterized in that: The controller is further configured to: After controlling the first switch tube to be periodically turned on, if a short circuit fault occurs in the first switch tube, controlling the third switch tube to remain in an off state; or, After controlling the fourth switch tube to be periodically turned on, if a short circuit fault occurs in the fourth switch tube, controlling the second switch tube to remain in an off state; or, After controlling the third switch tube to be periodically turned on, if a short circuit fault occurs in the third switch tube, controlling the first switch tube to remain in an off state; or, After the second switch tube is controlled to be periodically turned on, if a short circuit fault occurs in the second switch tube, the fourth switch tube is controlled to remain in an off state.

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