Method and device for controlling power converter and power conversion system

Abstract

The embodiment of the invention provides a method and device for controlling a power converter, control equipment and a power conversion system. The method includes receiving an instruction to convert at least one leg of the power converter from a first switching mode to a second switching mode, an upper leg or a lower leg of the at least one leg including a first switching device and a second switching device coupled in series between a direct current bus and an alternating current phase line, the first switching device and the second switching device are in an on state in a first switching mode, and the switching device of at least one bridge arm is in an off state in a second switching mode; and in response to receiving the instruction, sending a first control signal to switch the first switching device from the on state to the off state and maintain the second switching device in the on state, the first switching device being closer to the DC bus than the second switching device. According to the embodiment of the invention, the overvoltage problem caused by non-synchronous turn-off of the switching device can be simply eliminated or relieved with low cost.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to the field of power electronics technology, and more specifically, to a method and apparatus for controlling a power converter, a control device, and a power conversion system. Background Art

[0002] A power converter such as an inverter can convert input power into appropriate output power and provide it to a load or other electrical device. The power converter generally includes a power switching device, and by controlling the on and off of the power switching device, the desired power conversion operation can be achieved.

[0003] At present, multi-level power converters (such as three-phase three-level inverters) are widely used. Multi-level technology can provide many advantages, such as reduced output harmonics, reduced switching losses, etc. However, in some operations of multi-level power converters, the asynchronous shutdown of power switching devices may cause overvoltage problems, which may damage the devices. In order to avoid this situation, switching devices with higher voltage levels can be used or the voltage input to the power converter can be reduced. However, this will lead to a significant increase in system costs or a decrease in system performance. Therefore, there is still a lack of low-cost and efficient means to solve the above problems. Summary of the invention

[0004] Based on the above problems, according to example embodiments of the present disclosure, a method and apparatus for controlling a power converter, a control device, and a power conversion system are provided.

[0005] In a first aspect of the present disclosure, a method for controlling a power converter is provided. The method includes: receiving an instruction to convert at least one bridge arm of the power converter from a first switching mode to a second switching mode, an upper bridge arm or a lower bridge arm of at least one bridge arm includes a first switching device and a second switching device coupled in series between a DC bus and an AC phase line, the first switching device and the second switching device are in an on state in the first switching mode, and the switching devices of at least one bridge arm are both in an off state in the second switching mode; and in response to receiving the instruction, sending a first control signal to switch the first switching device from an on state to an off state and maintain the second switching device in an on state, the first switching device being closer to the DC bus than the second switching device.

[0006] In some embodiments of the present disclosure, the method further includes: after sending the first control signal, sending a second control signal to switch the second switching device from an on state to an off state.

[0007] In some embodiments of the present disclosure, sending the second control signal includes: sending the second control signal in response to a predetermined time period having elapsed since the first control signal was sent.

[0008] In some embodiments of the present disclosure, receiving an instruction to convert at least one bridge arm of the power converter from a first switching mode to a second switching mode includes: receiving an instruction to convert at least one bridge arm from a pulse width modulation (PWM) mode to a free-wheeling (FW) mode.

[0009] In some embodiments of the present disclosure, receiving an instruction to convert at least one bridge arm of the power converter from a first switching mode to a second switching mode includes: receiving an instruction to convert at least one bridge arm from an active short circuit ASC mode to a free flow FW mode.

[0010] In some embodiments of the present disclosure, an upper bridge arm and a lower bridge arm of each bridge arm in at least one bridge arm each include a pair of switching devices.

[0011] In some embodiments of the present disclosure, the power converter includes a three-level inverter.

[0012] In a second aspect of the present disclosure, a device for controlling a power converter is provided. The device includes: a receiving unit configured to receive an instruction to convert at least one bridge arm of the power converter from a first switching mode to a second switching mode, an upper bridge arm or a lower bridge arm of at least one bridge arm includes a first switching device and a second switching device coupled in series between a DC bus and an AC phase line, the first switching device and the second switching device are in an on state in the first switching mode, and the switching devices of at least one bridge arm are both in an off state in the second switching mode; and a sending unit configured to send a first control signal in response to receiving the instruction to switch the first switching device from an on state to an off state and maintain the second switching device in an on state, the first switching device being closer to the DC bus than the second switching device.

[0013] In a third aspect of the present disclosure, a control device is provided. The control device is adapted to be coupled to a power converter and is configured to perform the method according to the first aspect.

[0014] In a fourth aspect of the present disclosure, a power conversion system is provided. The power conversion system comprises: a power converter; and a control device according to the third aspect, coupled to the power converter.

[0015] It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other features, advantages and aspects of the various embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, wherein:

[0017] Figure 1 A schematic block diagram of a power conversion system, a power source, and a load according to an embodiment of the present disclosure is shown.

[0018] Figure 2 A schematic circuit diagram of a power converter according to an embodiment of the present disclosure is shown.

[0019] Figures 3A to 3C A schematic circuit diagram showing the operation of a portion of the circuit of a power converter.

[0020] Figures 4A to 4C A schematic circuit diagram showing another operation process of a part of the circuit of a power converter.

[0021] Figure 5 A schematic flow chart of a method for controlling a power converter according to an embodiment of the present disclosure is shown.

[0022] Figures 6A to 6C A schematic circuit diagram showing the operation process of a partial circuit of a power converter according to an embodiment of the present disclosure.

[0023] Figures 7A to 7C A schematic circuit diagram showing another operation process of a partial circuit of a power converter according to an embodiment of the present disclosure.

[0024] Figure 8 A schematic block diagram of an apparatus for controlling a power converter according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0025] The following will describe the embodiments of the present disclosure in more detail with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as being limited to the embodiments described herein, which are instead provided for a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are only for exemplary purposes and are not intended to limit the scope of protection of the present disclosure.

[0026] In the description of the embodiments of the present disclosure, the term "including" and similar terms should be understood as open inclusion, that is, "including but not limited to". The term "based on" should be understood as "based at least in part on". The term "one embodiment / implementation" or "the embodiment / implementation" should be understood as "at least one embodiment / implementation". The terms "first", "second", etc. may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0027] The embodiment of the present disclosure provides an improved scheme for controlling a power converter. In the improved scheme, when it is necessary to turn off two switch devices of the upper bridge arm or the lower bridge arm at the same time, by first turning off the switch device close to the DC bus, it is possible to avoid the situation where the DC bus voltage is directly applied to a single switch device, thereby ensuring that the voltage applied to the single switch device is always maintained at a low level. In this way, the overvoltage problem caused by the asynchronous shutdown of the switch device can be effectively avoided, and it has the advantages of low cost and high efficiency.

[0028] Figure 1 FIG. 1 shows a schematic block diagram of a power conversion system 100, a power supply 200, and a load 300 according to an embodiment of the present disclosure. Figure 1 As shown, the power conversion system 100 is coupled between the power source 200 and the load 300 to convert the power from the power source 200 into appropriate power to provide to the load 300. As an example, the power source 200 can be an energy storage battery, a super capacitor, a utility grid, a power generation device (such as a photovoltaic power generation device or a wind power generation device), a power supply device with a power converter connected to other power sources, or any other power source of any appropriate type, and the load 300 can be a motor or any electrical device capable of receiving power.

[0029] The power conversion system 100 may include a power converter 110 and a control device 120. For example, the power converter 110 may be an inverter, and under the control of the control device 120, the DC power from the power supply 200 is converted into AC power and output to the load 300. It is understood that the power converter 110 may be other types of power conversion devices, including but not limited to rectifiers, AC-DC converters, etc. In addition, the control device 120 may be implemented in a variety of ways. For example, the control device 120 may be implemented in the form of a controller with computing and processing capabilities, in the form of an analog circuit and / or a digital circuit, or in a combination of the above multiple forms. It is understood that the power conversion system 100 may also include other devices or devices not shown in the figure. For example, the power conversion system 100 may also include a voltage and / or current sensing device, which may be a device or device separated from the power converter 110 and the control device 120, or may be integrated with the power converter 110 or the control device 120 to provide a sensing signal to the control device 120 to achieve the desired control.

[0030] In addition, the power converter 110 may include a power switch device. The power switch device can be turned on and off under the control of the control device 120, so as to achieve the required power conversion. The power switch device may include a controllable switch device and a diode connected in anti-parallel with the controllable switch device, wherein the anti-parallel diode may be a body diode of the controllable switch device, or may be an additionally provided diode. The implementation methods of power switching devices include but are not limited to insulated gate bipolar transistors (IGBT), junction field-effect transistors (JFET), bipolar junction transistors (BJT), metal-oxide-semiconductor field effect transistors (MOSFET), gate turn off thyristors (GTO), MOS controlled thyristors (MCT), integrated gate-commutated thyristors (IGCT), silicon carbide (SiC) switching devices or gallium nitride (GaN) switching devices and other power switching devices.

[0031] Figure 2A schematic circuit diagram of a power converter 110 according to an embodiment of the present disclosure is shown. As an example only, the power converter 110 may be a three-phase three-level inverter. However, it is understood that the power converter 110 may also be a power converter of other appropriate types, such as a five-level inverter or a multi-level rectifier. As an example, the power converter 110 configured as a three-phase three-level inverter includes three bridge arms SA, SB and SC corresponding to phase A, phase B and phase C, respectively. The first bridge arm SA includes an upper bridge arm composed of switching devices Sa1 and Sa2 and a lower bridge arm composed of switching devices Sa3 and Sa4, the second bridge arm SB includes an upper bridge arm composed of switching devices Sb1 and Sb2 and a lower bridge arm composed of switching devices Sb3 and Sb4, and the third bridge arm SC includes an upper bridge arm composed of switching devices Sc1 and Sc2 and a lower bridge arm composed of switching devices Sc3 and Sc4. Each bridge arm is connected to the positive terminal and the negative terminal of the DC bus at both ends, and the node between the upper bridge arm and the lower bridge arm of each bridge arm is connected to the corresponding phase line. Specifically, the node Va between the upper and lower bridge arms of the first bridge arm SA is connected to the A phase line, the node Vb between the upper and lower bridge arms of the second bridge arm SB is connected to the B phase line, and the node Vc between the upper and lower bridge arms of the third bridge arm SC is connected to the C phase line. In the first bridge arm SA, the node between the two switching devices Sa1 and Sa2 of the upper bridge arm is coupled to the two switching devices Sa3 and Sa4 of the lower bridge arm via two series-connected diodes. The upper and lower bridge arms of the second bridge arm SB and the third bridge arm SC are also coupled by diodes in a similar manner. In addition, the power converter 110 also includes bus capacitors C1 and C2 connected in series, and the node between the two capacitors C1 and C2 is coupled to the node between the two series-connected diodes of each bridge arm, thereby providing the corresponding bridge arm with a third level between the first level of the positive terminal of the DC bus and the second level of the negative terminal.

[0032] When selecting a switch device for the power converter 110, it is necessary to ensure that the switch device can withstand the maximum voltage that may occur to avoid breakdown or damage of the switch device. For example, in the case where the DC bus voltage Vdc of the power converter 110 ranges from 200V to 800V, the switch device needs to ensure that it will not be broken down or damaged when Vdc is 800V. However, if a switch device with a voltage level equal to or greater than 800V is selected, the cost of the power converter 110 will increase and the volume will increase, and if the DC bus voltage Vdc is reduced, the maximum operating condition of the power converter 110 may be affected. Advantageously, in the case where the power converter 110 is a three-level inverter, each bridge arm usually has at most two switch devices closed at the same time, so there are actually two switch devices that withstand the DC bus voltage. Therefore, in the example case where the DC bus voltage is up to 800V, the voltage level of the switch device of the power converter 110 can be selected to be equal to or greater than 400V. However, in some operating conditions, such selection of switch devices may have an overvoltage risk that causes device damage.

[0033] Figures 3A to 3C FIG. 1 is a schematic circuit diagram showing the operation process of a portion of the circuit of the power converter 110. Figure 3A As shown, the control terminals (e.g., gates) of the switch devices Sa1 and Sa2 of the upper bridge arm of the first bridge arm SA receive high-level signals and are both turned on, while the control terminals (e.g., gates) of the switch devices Sa3 and Sa4 of the lower bridge arm of the first bridge arm SA receive low-level signals and are both turned off, so the current will flow from the positive terminal PE of the DC bus through the switch devices Sa1 and Sa2 at the node Va to the A phase line. Figure 3C As shown, the first bridge arm SA of the power converter 110 will then transition to a state where all four switch devices Sa1 to Sa4 are turned off. However, during this transition process, since these switch devices are not absolutely the same, it may happen that the switch devices Sa1 and Sa2 are turned off in sequence. The probability of this happening is higher under high current conditions, because the turn-off time of switch devices such as IGBTs decreases as the current increases (decreases in an exponential and hyperbolic composite law with the current). Therefore, when the current flowing through the switch devices is large, the turn-off time of the two switch devices will be very short, making it very easy for a sequence problem to occur when turning off. More specifically, as Figure 3BAs shown, the switch device Sa2 may be turned off before the switch device Sa1. Since the current flowing through the A-phase line cannot directly become zero, the current will continue to flow from the negative terminal NE of the DC bus through the anti-parallel diodes Da3 and Da4 of the switch devices Sa3 and Sa4 to the A-phase line at the node Va. At this time, the potential of the node Va between the upper and lower bridge arms is the same as the potential of the negative terminal NE of the DC bus. In addition, since the switch device Sa1 is still in the on state, the potential of the node A1 between the switch devices Sa1 and Sa2 is the same as the potential of the positive terminal PE of the DC bus. It can be seen that the switch device Sa2 that is turned off first will be subjected to a voltage of the same magnitude as the voltage of the DC bus Vdc. As mentioned earlier, if the voltage level of the selected switch device is approximately half of Vdc, then Figure 3B The voltage borne by the switching device Sa2 in the circuit far exceeds the voltage that the switching device itself can withstand, which will cause the switching device Sa2 to be broken down.

[0034] Figures 4A to 4C FIG. 2 is a schematic circuit diagram showing another operation process of a part of the circuit of the power converter 110. Figure 4A As shown, the control ends (e.g., gates) of the switch devices Sa3 and Sa4 of the lower bridge arm of the first bridge arm SA receive high-level signals and are both turned on, while the control ends (e.g., gates) of the switch devices Sa1 and Sa2 of the upper bridge arm of the first bridge arm SA receive low-level signals and are both turned off, so the current will flow from the A phase line through the node Va, the switch devices Sa3 and Sa4 to the negative terminal NE of the DC bus. Figure 4C As shown, the first bridge arm SA of the power converter 110 will then transition to a state where all four switch devices Sa1 to Sa4 are turned off. Figures 3A to 3C In this transition process, the switch devices Sa3 and Sa4 may be turned off in sequence. Figure 4B As shown, the switch device Sa3 may be turned off before the switch device Sa4. Since the current flowing through the A phase line cannot directly become zero, the current will continue to flow from the A phase line through the node Va, the anti-parallel diodes Da2 and Da1 of the switch devices Sa2 and Sa1 to the positive terminal PE of the DC bus. At this time, the potential of the node Va between the upper and lower bridge arms is the same as the potential of the positive terminal PE of the DC bus. In addition, since the switch device Sa4 is still in the on state, the potential of the node A2 between the switch devices Sa3 and Sa4 is the same as the potential of the negative terminal NE of the DC bus. In this case, the switch device Sa3 that is turned off first will be subjected to a voltage of the same magnitude as the voltage of the DC bus Vdc. If the voltage level of the selected switch device is approximately half of Vdc, then Figure 4BThe voltage borne by the switching device Sa3 in the circuit far exceeds the voltage that the switching device itself can withstand, which will cause the switching device Sa3 to be broken down.

[0035] It can be seen that since the turn-off of the switching device cannot guarantee complete synchronization, Figure 3B and Figure 4B The condition shown in the figure may result in overvoltage, which may cause the switch device to be broken down or damaged during operation. In addition, even if the cost and volume of the power converter are not taken into consideration and a switch device with a voltage level higher than Vdc (e.g., 800V or higher) is selected, the overvoltage problem may still exist. Specifically, in some cases (e.g., the external power supply is unstable, other devices or components discharge to the DC bus), the bus voltage Vdc may increase in voltage (e.g., exceed 800V) due to the impact of the DC grid. Figure 3B and 4B In the state shown, the increased bus voltage may still cause damage to the switching device Sa2 or Sa3.

[0036] Figure 5 1 is a schematic flow chart of a method 500 for controlling a power converter 110 according to an embodiment of the present disclosure. The method 500 may be performed in Figure 1 , and is executed by the control device 120. For the purpose of discussion, reference will be made to Figure 1 and Figure 2 Method 500 is described.

[0037] In box 501, the control device 120 receives an instruction to convert at least one bridge arm of the power converter 110 from a first switching mode to a second switching mode, wherein an upper bridge arm or a lower bridge arm of the at least one bridge arm includes a first switching device and a second switching device coupled in series between a DC bus and an AC phase line, wherein the first switching device and the second switching device are in an on state in the first switching mode, and the switching devices of the at least one bridge arm are both in an off state in the second switching mode. As an example, the at least one bridge arm may be one or more bridge arms of the first bridge arm SA, the second bridge arm SB, and the third bridge arm SC. The first switching device and the second switching device may be, for example, the switching devices of the upper bridge arm of the bridge arm SA, SB, and / or SC, or the switching devices of the lower bridge arm of the bridge arm SA, SB, and / or SC.

[0038] In some embodiments, receiving an instruction to convert at least one bridge arm of the power converter 110 from a first switching mode to a second switching mode includes: receiving an instruction to convert at least one bridge arm from a pulse width modulation (PWM) mode or an active short circuit (ASC) mode to a freewheeling (FW) mode.

[0039] As an example, the first switching mode may be a PWM mode or an ASC mode, and the second switching mode may be a FW mode. Specifically, the control device 120 can control the power input to the load 300 by controlling the on and off of the switching device of the power converter 110, thereby effectively controlling the operation and stop of the motor or other types of loads. In this control process, the power converter 110 may have three switching modes, namely, a PWM mode, an ASC mode, and a FW mode. In the PWM mode, the power converter 110 may receive a PWM signal from the control device 120, and turn on and off the switching device based on the PWM signal, thereby normally controlling the operation of the motor or other types of loads. In the ASC mode, the switching devices of all lower bridge arms of the power converter 110 (i.e., Sa1, Sa2, Sb1, Sb2, Sc1, and Sc2) are turned on, or the switching devices of all upper bridge arms of the power converter 110 (i.e., Sa3, Sa4, Sb3, Sb4, Sc3, and Sc4) are turned on. Thus, when the load 300 is a motor, the stator winding of the motor can form a closed loop to avoid the impact of excessive back electromotive force generated by the rotation of the motor on the system. In FW mode, the switching devices of all bridge arms of the power converter 110 are turned off. When shutting down the motor normally or shutting down the motor due to a fault, the power converter 110 may switch from PWM mode or ASC mode to FW mode. For example, when switching from ASC mode to FW mode, all the switching devices of the upper bridge arms of the power converter 110 (i.e., Sa1, Sa2, Sb1, Sb2, Sc1, and Sc2) or all the switching devices of the lower bridge arms (i.e., Sa3, Sa4, Sb3, Sb4, Sc3, and Sc4) need to be switched from the on state to the off state. During this switching process, the switching devices may be turned off asynchronously. Figure 3B and 4B Status shown.

[0040] In block 502, in response to receiving the aforementioned instruction, the control device 120 sends a first control signal to switch the first switching device from the on state to the off state and maintain the second switching device in the on state, the first switching device being closer to the DC bus than the second switching device. Figure 3B and 4B In the overvoltage state in the circuit, the first switch device closer to the DC bus can be turned off first and the second switch device can be kept turned on. For example, in the process of switching from the ASC mode to the FW mode, for the first bridge arm SA, the switch device Sa1 close to the DC bus can be turned off first and the switch device Sa2 can be kept turned on. As a result, the turned-off switch device Sa1 will only withstand a lower voltage and will not be applied with the DC bus voltage Vdc, thereby avoiding the following Figure 3BAs shown, a DC bus voltage exceeding the withstand voltage of the switching device Sa2 appears across both ends of the switching device Sa2. Therefore, in this way, the DC bus voltage Vdc is effectively prevented from being directly applied to a single switching device, and the voltage across the single switching device is ensured to be maintained at a low level.

[0041] In some embodiments of the present disclosure, the method 500 may further include a block 503. In block 503, after sending the first control signal, the control device 120 sends a second control signal to switch the second switching device from the on state to the off state. Specifically, by means of the first control signal, the first switching device close to the DC bus has been turned off. In this case, the second switching device can be safely turned off. In this way, the power converter 110 can be safely and reliably converted from a first switching mode such as a PWM mode or an ASC mode to a second switching mode such as a FW mode. In some embodiments, in response to a predetermined time period having passed when the first control signal is sent, the control device 120 sends a second control signal. Specifically, taking into account the signal transmission delay or the turn-off delay, and ensuring that the first switching device has been reliably turned off, the predetermined time period can be pre-set, and the time elapsed after sending the first control signal can be counted (for example, a timer can be started). When the elapsed time exceeds the predetermined time period, the control device 120 can send a second control signal so that the second switching device can be safely turned off.

[0042] Figures 6A to 6C A schematic circuit diagram showing the operation process of a part of the circuit of the power converter 110 according to an embodiment of the present disclosure, and Figures 7A to 7C FIG. 1 is a schematic circuit diagram showing another operation process of a part of the circuit of the power converter 110 according to an embodiment of the present disclosure. Figures 6A to 6C and Figures 7A to 7C The process and effect of controlling the power converter 110 according to the embodiment of the present disclosure are exemplarily described.

[0043] like Fig. 6A As shown, the control terminals (e.g., gates) of the switch devices Sa1 and Sa2 of the upper bridge arm of the first bridge arm SA receive high-level signals and are both turned on, while the control terminals (e.g., gates) of the switch devices Sa3 and Sa4 of the lower bridge arm of the first bridge arm SA receive low-level signals and are both turned off, so the current will flow from the positive terminal PE of the DC bus through the switch devices Sa1 and Sa2 at the node Va to the A phase line. Figure 6C As shown, the first bridge arm SA of the power converter 110 will then transition to a state where all four switch devices Sa1 to Sa4 are turned off. Fig. 6A The status and Figure 6CBetween the states shown, the control device 120 uses the first control signal to control the switch device Sa1 to be turned off before the switch device Sa2, and during this period, the switch device Sa2 is kept turned on. Figure 6B As shown, since the current flowing through the A phase line cannot directly become zero, the current will flow from the node between the two bus capacitors C1 and C2 through the diode D1, the node A1 between the switching devices Sa1 and Sa2, the turned-on switching device Sa2 and the node Va to the A phase line. At this time, the potential of the node A1 is the same as the potential of the node between the two bus capacitors C1 and C2. Therefore, the voltage borne by the switching device Sa1 that is still in the off state is the same as the voltage across the bus capacitor C1, that is, it is only half of the bus voltage Vdc. It can be seen that the switching device Sa1 that is turned off first will only withstand a lower voltage. Figure 6C In the process, the switching device Sa2 can continue to be safely turned off.

[0044] like Fig. 7A As shown, the control terminals (e.g., gates) of the switch devices Sa3 and Sa4 of the lower bridge arm of the first bridge arm SA receive high-level signals and are both turned on, while the control terminals (e.g., gates) of the switch devices Sa1 and Sa2 of the upper bridge arm of the first bridge arm SA receive low-level signals and are both turned off, so the current will flow from the A phase line through the node Va and the turned-on switch devices Sa3 and Sa4 to the negative terminal NE of the DC bus. Figure 7C As shown, the first bridge arm SA of the power converter 110 will then transition to a state where all four switch devices Sa1 to Sa4 are turned off. Fig. 7A The status and Figure 7C Between the states shown, the control device 120 uses the first control signal to control the switch device Sa4 to be turned off before the switch device Sa3, and during this period, the switch device Sa3 is kept turned on. Figure 7B As shown, since the current flowing through the A-phase line cannot directly become zero, the current will flow from the A-phase line through the node Va, the turned-on switch device Sa3, the node A2 between the switch devices Sa3 and Sa4, and the diode D2 to the node between the two bus capacitors C1 and C2. At this time, the potential of the node A2 is the same as the potential of the node between the two bus capacitors C1 and C2. Therefore, the voltage borne by the switch device Sa4 that is still in the off state is the same as the voltage across the bus capacitor C2, that is, it is only half of the bus voltage Vdc. It can be seen that the switch device Sa4 that is turned off first will only withstand a lower voltage. Figure 7C In the process, the switching device Sa3 can continue to be safely turned off.

[0045] In this way, the power converter 110 can be safely and reliably switched from a first switching mode such as a PWM mode or an ASC mode to a second switching mode such as an FW mode without overvoltage caused by the asynchronous shutdown of the switch devices of the upper bridge arm or the lower bridge arm. In this way, the possible overvoltage problem can be eliminated at a lower cost and with simple control, and a switch device with a lower voltage level can be selected, and there is no need to reduce the bus voltage (which causes the modulation voltage to be reduced and reduces the output efficiency of the inverter) in order to avoid overvoltage, which is conducive to reducing system cost and volume and improving system efficiency.

[0046] In addition, in some cases (such as unstable external power supply and other devices or components discharging to the bus), the DC grid and the DC bus may be impacted and the voltage may increase. This overvoltage may also damage or break down the power switching device in the power converter. However, even if the bus voltage increases to twice or more of the original bus voltage, the embodiments of the present disclosure can protect or prevent the switching device from being damaged without increasing the withstand voltage range of the switching device, which effectively improves the bus voltage operating range of the power converter and enhances the robustness.

[0047] Figure 8 FIG. 8 is a schematic block diagram of an apparatus 800 for controlling a power converter 110 according to an embodiment of the present disclosure. The apparatus 800 may be implemented as Figure 1 The control device 120. Figure 8 As shown, the device 800 includes a receiving unit 810. The receiving unit 810 is configured to receive an instruction to convert at least one bridge arm of the power converter 110 from a first switching mode to a second switching mode, the upper bridge arm or the lower bridge arm of at least one bridge arm includes a first switching device and a second switching device coupled in series between a DC bus and an AC phase line, the first switching device and the second switching device are in an on state in the first switching mode, and the switching devices of at least one bridge arm are both in an off state in the second switching mode. In addition, the control device 800 also includes a sending unit 820. The sending unit 820 is configured to send a first control signal in response to receiving the aforementioned instruction to switch the first switching device from an on state to an off state and maintain the second switching device in an on state, the first switching device being closer to the DC bus than the second switching device.

[0048] In some embodiments of the present disclosure, the receiving unit 810 is further configured to receive an instruction to convert at least one bridge arm from the PWM mode or the ASC mode to the FW mode.

[0049] In some embodiments of the present disclosure, the sending unit 820 is further configured to send a second control signal to switch the second switch device from the on state to the off state after sending the first control signal. In one embodiment, the sending unit 820 is further configured to send the second control signal in response to a predetermined time period having passed since the time of sending the first control signal.

[0050] Those skilled in the art should understand that the various steps of the method disclosed above can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, optionally, they can be implemented with program codes executable by the computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present disclosure is not limited to any specific combination of hardware and software.

[0051] It should be understood that although several devices or sub-devices of the device are mentioned in the detailed description above, this division is only exemplary and not mandatory. In fact, according to an embodiment of the present disclosure, the features and functions of two or more devices described above can be embodied in one device. Conversely, the features and functions of one device described above can be further divided into multiple devices to be embodied.

[0052] The above description is only an optional embodiment of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, the present disclosure may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A method for controlling a power converter, comprising: Receiving an instruction to convert at least one bridge arm of the power converter from a first switching mode to a second switching mode, an upper bridge arm or a lower bridge arm of the at least one bridge arm comprises a first switching device and a second switching device coupled in series between a DC bus and an AC phase line, the first switching device and the second switching device are in an on state in the first switching mode, and the switching devices of the at least one bridge arm are both in an off state in the second switching mode; as well as In response to receiving the instruction, a first control signal is sent to switch the first switching device from an on state to an off state and maintain the second switching device in an on state, the first switching device being closer to the DC bus than the second switching device.

2. The method according to claim 1, further comprising: After sending the first control signal, sending a second control signal to switch the second switching device from an on state to an off state.

3. The method according to claim 2, wherein sending the second control signal comprises: In response to a predetermined time period having elapsed since the first control signal was sent, the second control signal is sent.

4. The method of claim 1 , wherein receiving an instruction to switch at least one leg of the power converter from a first switching mode to a second switching mode comprises: An instruction to convert the at least one bridge arm from a pulse width modulation (PWM) mode to a free-wheeling (FW) mode is received.

5. The method of claim 1 , wherein receiving an instruction to switch at least one leg of the power converter from a first switching mode to a second switching mode comprises: An instruction to convert the at least one bridge arm from an active short circuit ASC mode to a free-wheeling FW mode is received. 6 . The method according to claim 1 , wherein an upper bridge arm and a lower bridge arm of each bridge arm of the at least one bridge arm each comprise a pair of switching devices.

7. The method of claim 1, wherein the power converter comprises a three-level inverter.

8. An apparatus for controlling a power converter, comprising: a receiving unit configured to receive an instruction to convert at least one bridge arm of the power converter from a first switching mode to a second switching mode, wherein an upper bridge arm or a lower bridge arm of the at least one bridge arm comprises a first switching device and a second switching device coupled in series between a DC bus and an AC phase line, wherein the first switching device and the second switching device are in an on state in the first switching mode, and the switching devices of the at least one bridge arm are both in an off state in the second switching mode; as well as A sending unit is configured to send a first control signal in response to receiving the instruction to switch the first switching device from an on state to an off state and maintain the second switching device in an on state, the first switching device being closer to the DC bus than the second switching device.

9. A control device adapted to be coupled to a power converter and configured to perform the method according to any one of claims 1 to 7.

10. A power conversion system comprising: Power converters; as well as The control device of claim 9, coupled to the power converter.

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