Power converter

Abstract

The application provides a power converter, and belongs to the technical field of power electronics. The power converter provided by the application adopts an ANPC topology. In the process of shutting down the power converter, if the voltage at the AC end of the power converter is greater than a first threshold value, the power converter can conduct a third switch tube or a fifth switch tube. Thus, not only can the sixth switch tube be prevented from being damaged by overvoltage, but also the power grid can be effectively prevented from short circuiting. In the process of shutting down the power converter, if the voltage at the AC end is less than a second threshold value, the power converter can conduct a second switch tube or a sixth switch tube. Thus, not only can the fifth switch tube be prevented from being damaged by overvoltage, but also the power grid can be effectively prevented from short circuiting.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a power converter. Background Technology

[0002] Active-neutral-point-clamped (ANPC) is a common power conversion topology. A power converter using an ANPC topology includes at least one phase arm, with each phase inverter arm comprising six switches T1 through T6. Switches T1 through T4 are connected in series between the positive and negative DC terminals of the power converter, while switches T5 and T6 are connected in series and in parallel across switches T2 and T3. The series connection node between switches T5 and T6 serves as the AC terminal of the power converter, used to output AC power.

[0003] During the positive half-cycle of the AC voltage at the power converter, switches T5 and T6 conduct alternately, while switches T1 and T3 remain on, and switches T2 and T4 remain off. During the negative half-cycle of the AC voltage at the power converter, switches T5 and T6 conduct alternately, while switches T2 and T4 remain on, and switches T1 and T3 remain off.

[0004] During the power converter shutdown process, after all switches are turned off and the AC current freewheels to zero, a reverse current will be generated due to junction capacitance and loop inductance oscillation. This reverse current will freewheel through the reverse diodes of switches T5 and T1, or through the reverse diodes of switches T6 and T4. When the reverse current freewheels, there is a risk of overvoltage damage to switches T6 or T5. Summary of the Invention

[0005] This application provides a power converter that can solve the technical problem that some switching transistors are at risk of overvoltage damage during the power converter shutdown process.

[0006] In a first aspect, a power converter is provided, comprising: a DC terminal, an AC terminal, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, and a controller. The first, second, third, and fourth switches are connected in series between the positive and negative terminals of the DC terminal. The fifth and sixth switches are connected in series between a first node and a second node, and the series connection between the fifth and sixth switches is connected to the AC terminal. The first node is the series connection between the first and second switches, and the second node is the series connection between the third and fourth switches. The controller is used to: during the power converter shutdown process, if the voltage at the AC terminal is greater than a first threshold, control the third or fifth switch to turn on and control all other switches to turn off; if the voltage at the AC terminal is less than a second threshold, control the second or sixth switch to turn on and control all other switches to turn off. The first threshold is greater than 0, and the second threshold is less than 0.

[0007] The solution provided in this application turns on the third or fifth switch when the AC voltage is greater than a first threshold during the power converter shutdown process. This not only prevents overvoltage damage to the sixth switch but also effectively avoids a short circuit in the power grid. Conversely, turning on the second or sixth switch when the AC voltage is less than a second threshold not only prevents overvoltage damage to the fifth switch but also effectively avoids a short circuit in the power grid.

[0008] In one possible implementation, the controller is further configured to: in the event of a power converter failure, during the power converter shutdown process, if the AC terminal voltage is greater than 0 and less than or equal to a first threshold, control the third or fifth switch to turn on and control all other switches to turn off; and if the AC terminal voltage is greater than or equal to a second threshold and less than 0, control the second or sixth switch to turn on and control all other switches to turn off. The power converter failure may include at least one of the following: overvoltage, overcurrent, and overtemperature.

[0009] In the event of a power converter failure, it is essential to ensure the power converter is shut down promptly to prevent the fault from spreading. Accordingly, if the controller detects that the AC terminal voltage is greater than or equal to the second threshold and less than or equal to the first threshold, it can directly execute the corresponding blocking procedure based on the detected AC terminal voltage polarity, without waiting for the voltage to be greater than the first threshold or less than the second threshold before executing the blocking procedure.

[0010] In one possible implementation, if the voltage at the AC terminal is greater than 0 and less than or equal to the first threshold, the third switch is turned on, and if the voltage at the AC terminal is greater than or equal to the second threshold and less than 0, the second switch is turned on. The controller is further configured to: control both the second and third switches to turn on during the process of the AC terminal voltage crossing zero.

[0011] After the AC voltage crosses zero, i.e., after the voltage polarity changes, the controller needs to synchronously switch the conducting transistors. Since both turning on and off the transistors require a certain amount of time, directly switching the on / off state of the transistors could result in all transistors being turned off, leading to overvoltage damage to some high-frequency transistors. In the solution provided in this application, the controller effectively avoids the fault condition of all transistors being turned off by controlling both the second and third transistors to be turned on during the AC voltage crossing process.

[0012] In one possible implementation, if the voltage at the AC terminal is greater than 0 and less than or equal to the first threshold, the fifth switch is turned on, and if the voltage at the AC terminal is greater than or equal to the second threshold and less than 0, the sixth switch is turned on. The controller is further configured to: control both the fifth and sixth switches to turn on during the process of the AC terminal voltage crossing zero.

[0013] In the solution provided in this application, the controller can effectively avoid the fault condition where all switches are turned off by controlling both the fifth and sixth switches to be turned on during the zero-crossing process of the AC voltage.

[0014] In one possible implementation, the controller is further configured to: during the power converter shutdown process, if the AC terminal voltage is greater than or equal to a second threshold and less than or equal to a first threshold, then after the AC terminal voltage is greater than the first threshold, control the third or fifth switch to turn on and control all other switches to turn off; or, after the AC terminal voltage is less than the second threshold, control the second or sixth switch to turn on and control all other switches to turn off.

[0015] In this embodiment, when the power converter is normally powered off, if the voltage at the AC terminal is greater than or equal to a second threshold and less than or equal to a first threshold, the controller can first generate a waveform normally. Furthermore, the controller can perform waveform blocking according to the waveform blocking timing provided in this application after detecting that the voltage at the AC terminal is greater than the first threshold or less than the second threshold. Therefore, on the one hand, it can effectively avoid voltage polarity judgment errors caused by sampling errors, and on the other hand, it can ensure that the shutdown process is completed before the voltage polarity at the AC terminal changes, thereby effectively reducing the complexity of the controller's control logic during the shutdown process.

[0016] In one possible implementation, the controller is further configured to: control all six switches (from the first to the sixth) to turn off when the absolute value of the current at the AC terminal is less than a current threshold. The current threshold is a value close to 0.

[0017] Since the AC current is close to zero when the controller shuts down all the switching transistors, it can ensure that no current flows through any of the switching transistors, thus effectively preventing overvoltage damage to the switching transistors.

[0018] In one possible implementation, the controller is further configured to: control all six switching transistors to turn off when the absolute value of the current at the AC terminal is less than a current threshold and the voltage at the AC terminal is greater than a first threshold or less than a second threshold.

[0019] This effectively avoids misjudgments caused by current sampling errors, ensuring that the current at the AC end has completely decayed to 0 before all switching transistors are blocked, thus completing the shutdown process.

[0020] In one possible implementation, the first threshold is greater than or equal to 30 volts (V), and the second threshold is less than or equal to -30V.

[0021] By designing a larger first threshold and a smaller second threshold, voltage polarity judgment errors caused by voltage sampling errors and / or AC voltage fluctuations can be effectively avoided, thus effectively preventing power grid short circuits. Furthermore, it effectively ensures that the shutdown process is completed before the AC voltage polarity switches, thereby significantly reducing the complexity of the controller's control logic during shutdown.

[0022] In one possible implementation, the first, second, third, and fourth switching transistors are all insulated-gate bipolar transistors (IGBTs), while the fifth and sixth switching transistors are metal-oxide-semiconductor field-effect transistors (MOSFETs), or simply MOS transistors. That is, the power frequency transistors in the power converter can all be IGBTs, and the high-frequency transistors can all be MOS transistors. For example, high-frequency transistors can be silicon carbide (SiC) MOS transistors.

[0023] This ensures that the power frequency transistors in the power converter have low conduction losses and low cost, while the high frequency transistors have fast switching speeds and low switching losses.

[0024] Secondly, another power converter is provided, comprising: a DC terminal, an AC terminal, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, and a controller. The first, second, third, and fourth switches are connected in series between the positive and negative terminals of the DC terminal. The fifth and sixth switches are connected in series between a first node and a second node, with the series connection between the fifth and sixth switches connected to the AC terminal. The first node is the series connection between the first and second switches, and the second node is the series connection between the third and fourth switches. The controller is used to: during the power converter shutdown process, if the voltage polarity of the AC terminal is positive, control the third or fifth switch to turn on and control the other switches to turn off; if the voltage polarity of the AC terminal is negative, control the second or sixth switch to turn on and control the other switches to turn off.

[0025] In one possible implementation, if the voltage polarity of the AC terminal is positive, the third switch is turned on, and if the voltage polarity of the AC terminal is negative, the second switch is turned on. The controller is further configured to: control both the second and third switches to be turned on during the switching of the voltage polarity of the AC terminal.

[0026] In one possible implementation, if the voltage polarity of the AC terminal is positive, the fifth switch is turned on, and if the voltage polarity of the AC terminal is negative, the sixth switch is turned on. The controller is also used to control both the fifth and sixth switches to be turned on during the switching of the voltage polarity of the AC terminal.

[0027] The power converter provided in the second aspect above has essentially the same implementation method and technical effect as the power converter provided in the first aspect above, and will not be described again here.

[0028] In summary, this application provides a power converter. This power converter employs an ANPC topology. During the power converter's shutdown process, if the voltage at the AC terminal of the power converter is greater than a first threshold, the power converter can turn on either the third or fifth switch. This not only prevents overvoltage damage to the sixth switch but also effectively avoids a short circuit in the power grid. During the power converter's shutdown process, if the voltage at the AC terminal is less than a second threshold, the power converter can turn on either the second or sixth switch. This not only prevents overvoltage damage to the fifth switch but also effectively avoids a short circuit in the power grid. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of an NPC topology and an ANPC topology provided in an embodiment of this application; Figure 2 This is a schematic diagram of the driving timing of each switch in an ANPC topology provided in an embodiment of this application; Figure 3 This is a schematic diagram of the current path during power-off current freewheeling and reverse current flow of a power converter, as provided in an embodiment of this application. Figure 4 This is a schematic diagram illustrating a short circuit in the power grid caused by the conduction of switching transistors T2 and T3 in a power converter, as provided in an embodiment of this application. Figure 5 This is a schematic diagram of the structure of a power converter provided in an embodiment of this application; Figure 6 This is a schematic diagram of another power converter provided in an embodiment of this application; Figure 7 This is a schematic diagram of a shutdown process when the voltage at the AC terminal is in the positive half-cycle, as provided in an embodiment of this application. Figure 8 This is a schematic diagram of another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the positive half-cycle; Figure 9 This is a schematic diagram of a shutdown process when the voltage at the AC terminal is in the negative half-cycle, as provided in an embodiment of this application. Figure 10 This is a schematic diagram of another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the negative half-cycle; Figure 11 This is a schematic diagram of another shutdown process provided in the embodiments of this application when the voltage at the AC terminal is in the positive half-cycle; Figure 12 This is a schematic diagram of another shutdown process provided in the embodiments of this application when the voltage at the AC terminal is in the positive half-cycle; Figure 13 This is a schematic diagram of another shutdown process provided in the embodiments of this application when the voltage at the AC terminal is in the negative half-cycle; Figure 14 This is a schematic diagram of another shutdown process provided in the embodiments of this application when the voltage at the AC terminal is in the negative half-cycle. Detailed Implementation

[0030] The power converter provided in the embodiments of this application is described in detail below with reference to the accompanying drawings.

[0031] Three-level power converters (such as inverters) have advantages over traditional two-level power converters, including lower harmonic distortion and lower device voltage requirements, and are therefore widely used. ANPC (Automatic Point-Clamped) is a common three-level power conversion topology. ANPC is a new inverter topology developed based on the traditional neutral-point-clamped (NPC) topology. Figure 1 As shown, the core improvement of the ANPC topology compared to the NPC topology is that it uses controllable active switching devices (T2 and T3) to replace the original passive clamping diodes, thereby giving the ANPC topology a higher degree of control freedom.

[0032] like Figure 1 As shown, the ANPC topology includes six switching transistors T1 to T6. Transistors T1 to T4 are connected in series between the positive (DC+) and negative (DC-) terminals of the DC converter. Transistors T5 and T6 are connected in series and in parallel across transistors T2 and T3. The series connection point between transistors T5 and T6 is connected to the AC terminal X of the power converter. The AC terminal X is also called the output terminal, and the voltage at AC terminal X is called the output voltage of the power converter. Typically, transistors T1, T5, and T2 are referred to as the outer transistor, inner transistor, and clamping transistor of the upper half-arm, respectively, while transistors T4, T6, and T3 are referred to as the outer transistor, inner transistor, and clamping transistor of the lower half-arm, respectively.

[0033] ANPC topology typically uses a 2-fast-transistor, 4-slow-transistor driving method. For example... Figure 2 As shown, when the power factor (PF) equals 1, this driving method includes: during the positive half-cycle of the output voltage, switches T1 and T3 remain on, switches T2 and T4 remain off, and switches T5 and T6 alternately turn on; during the negative half-cycle of the output voltage, switches T2 and T4 remain on, switches T1 and T3 remain off, and switches T5 and T6 alternately turn on. (Reference) Figure 2 It can also be seen that during the positive half-cycle of the output voltage, when switch T5 is on, the output level is positive (P) with a magnitude of U / 2; when switch T6 is on, the output level is 0. During the negative half-cycle of the output voltage, when switch T5 is on, the output level is 0; when switch T6 is on, the output level is negative (N) with a magnitude of -U / 2. Here, U is the voltage between the positive DC+ and negative DC- terminals.

[0034] In the above modulation method, the switching frequencies of transistors T1 to T4 are all at the power frequency; therefore, transistors T1 to T4 are also called slow transistors or power frequency transistors. Switches T5 and T6 have high switching frequencies; therefore, transistors T5 and T6 are also called fast transistors or high frequency transistors. The power frequency transistors can be IGBTs, which have slower switching speeds, lower conduction losses, and lower costs, while the high frequency transistors can be MOSFETs, which have faster switching speeds and lower switching losses, to achieve a comprehensive optimization of efficiency and cost. The MOSFET has a body diode, also called a parasitic diode, and a diode is connected in parallel between the emitter and collector of the IGBT. These body diodes and parallel diodes provide a freewheeling path for the inductor current in the power converter.

[0035] Typically, in ANPC power converters, the selection of switching transistors is based on cost and performance considerations, choosing transistors with a withstand voltage slightly higher than half the bus voltage (i.e., U / 2). However, in certain specific cases, the full bus voltage U may be applied across the high-frequency transistor. For example, refer to... Figure 3 When the power converter is powered off, after the switching transistors T1 through T6 are all blocked, the inductor current at the AC terminal of the power converter will freewheel through the parallel diode of switching transistor T4 and the body diode of switching transistor T6. Blocking the switching transistors means stopping the output of drive signals to the switching transistors in the power converter, keeping the transistors in the off state. This drive signal can be a pulse width modulation (PWM) signal, also known as a PWM wave.

[0036] After the inductor current freewheels to zero, a reverse current will be generated due to the junction capacitance and the oscillation of the loop inductance. For example... Figure 3 As shown, the reverse current will freewheel through the body diode of switch T5 and the parallel diode of switch T1. At this time, switches T6 and T4 bear the full bus voltage U, and there is a dynamic voltage divider between them. Since switch T6 is usually a MOSFET with a small junction capacitance, the voltage across switch T6 after the dynamic voltage divider will be much higher than half the bus voltage. For example, in some scenarios, switch T6 may bear the full bus voltage. Based on the above analysis, it can be seen that during the shutdown process, after the inductor freewheels to 0 and reverses, switch T6 may be damaged due to overvoltage. Switch T5 also has the same problem, which will not be discussed further here.

[0037] To address the aforementioned overvoltage issue, some embodiments connect capacitors in parallel across switching transistors T5 and T6. This ensures that the internal transistor voltage after dynamic voltage division is lower than that of the external transistor, and the internal transistor voltage is clamped to half the bus voltage by the diodes connected in parallel across switching transistors T2 and T3, thus preventing internal transistor overvoltage. However, for a hybrid topology where switching transistors T1-T4 use IGBTs and switching transistors T5 and T6 use SiCMOS, the significant differences between IGBTs and SiCMOS devices necessitate a larger capacitance value for the parallel capacitors. Excessively large parallel capacitor values ​​not only limit the switching speed of SiCMOS but also reduce the efficiency of the power converter due to frequent charge-discharge losses.

[0038] In other embodiments, during power-off blocking, switches T2 and T3 remain on to clamp the voltages of switches T5 and T6 to within half the bus voltage. However, for scenarios where the power converter includes three-phase bridge arms, such as... Figure 4 As shown by the dashed arrows, when the switching transistors T2 and T3 in different bridge arms are both turned on in the off state, different phase lines of the power grid will form a short circuit path through the turned-on switching transistors and the parallel diodes of the switching transistors, thus causing the power grid to be short-circuited.

[0039] This application provides a power converter, which can be a photovoltaic power converter, a power conversion system (PCS), an on-board charger, or a main drive power converter for electric vehicles, etc. The power converter provided in this application not only avoids overvoltage damage to the switching transistors during shutdown but also effectively prevents grid short circuits. Figure 5 As shown, the power converter provided in this embodiment includes a DC terminal (DC+, DC-), an AC terminal X, a first switch T1, a second switch T2, a third switch T3, a fourth switch T4, a fifth switch T5, a sixth switch T6, and a controller 10. The DC terminal (DC+, DC-) is used to connect to a DC power source, and the AC terminal X is used to connect to the power grid or a load. The power converter converts DC power from the DC power source into AC power for output. In some scenarios, the power converter is also used to convert AC power from the AC terminal into DC power to charge the DC power source. The DC power source can be a photovoltaic module or an energy storage battery, etc. The DC terminal (DC+, DC-) can be connected to the DC power source via a DC bus. Accordingly, the positive terminal DC+ of the DC terminal is connected to the positive DC bus BUS+, and the negative terminal DC- of the DC terminal is connected to the negative DC bus BUS-.

[0040] Continue to refer to Figure 5 The first switch T1, the second switch T2, the third switch T3, and the fourth switch T4 are connected in series between the positive terminal DC+ and the negative terminal DC-. The fifth switch T5 and the sixth switch T6 are connected in series between the first node P1 and the second node P2, and the series connection node between the fifth switch T5 and the sixth switch T6 is connected to the AC terminal X. Specifically, the first node P1 is the series connection node between the first switch T1 and the second switch T2, and the second node P2 is the series connection node between the third switch T3 and the fourth switch T4.

[0041] The power converter provided in this application embodiment adopts an ANPC topology. Furthermore, the power converter provided in this application embodiment may include at least one phase arm, for example, Figure 5 The diagram schematically illustrates one phase arm. Or, as... Figure 6 As shown, the power converter can also include three-phase bridge arms: phase A, phase B, and phase C. Each phase inverter bridge arm includes a first switch T1 to a sixth switch T6, and the series connection node between the fifth switch T5 and the sixth switch T6 in each phase bridge arm is the output terminal of the bridge arm, which is connected to the AC terminal of the power converter.

[0042] In this embodiment, the controller 10 controls the switching timing of the first switch T1 to the sixth switch T6. Specifically, during the positive half-cycle of the AC terminal X voltage, the controller 10 controls the first switch T1 and the third switch T3 to remain on, controls the second switch T2 and the fourth switch T4 to remain off, and controls the fifth switch T5 and the sixth switch T6 to alternately turn on according to a switching frequency (also known as high frequency). During the negative half-cycle of the AC terminal X voltage, the controller 10 controls the second switch T2 and the fourth switch T4 to remain on, controls the first switch T1 and the third switch T3 to remain off, and controls the fifth switch T5 and the sixth switch T6 to alternately turn on according to a switching frequency.

[0043] The controller 10 is also used to: during the power converter shutdown process, if the voltage at AC terminal X is greater than a first threshold, control the third switch T3 or the fifth switch T5 to turn on, and control all other switches to turn off; if the voltage at AC terminal X is less than a second threshold, control the second switch T2 or the sixth switch T6 to turn on, and control all other switches to turn off. The first threshold is greater than 0, and the second threshold is less than 0. A voltage at AC terminal X greater than the first threshold indicates that the voltage at AC terminal X is in the positive half-cycle, i.e., the voltage polarity is positive; a voltage at AC terminal X less than the second threshold indicates that the voltage at AC terminal X is in the negative half-cycle, i.e., the voltage polarity is negative.

[0044] In this embodiment, the power converter shutdown process can refer to the period before all switches in the power converter are turned off, that is, the period before the drive signals of all switches are 0. For example, the shutdown process can refer to the period from turning off all high-frequency switches (i.e., the fifth switch T5 and the sixth switch T6) to turning off all switches. Alternatively, the shutdown process can refer to the period from turning off the first switch T1 or the fourth switch T4 to turning off all switches.

[0045] Understandably, in traditional solutions, when the power converter is powered off, the controller shuts down each switch according to a preset blocking sequence. Specifically, when the AC voltage is in the positive half-cycle, the controller sequentially shuts down the high-frequency transistor (the fifth switch T5 or the sixth switch), the first switch T1, and the third switch T3 according to the preset blocking sequence. When the AC voltage is in the negative half-cycle, the controller sequentially shuts down the high-frequency transistor (the fifth switch T5 or the sixth switch), the second switch T2, and the fourth switch T4 according to the preset blocking sequence. In this embodiment, when the power converter is powered off, the controller 10 can block each switch according to an improved blocking sequence. When the voltage at AC terminal X is greater than the first threshold, the improved blocking timing includes: turning off the high-frequency transistor and the first switch T1, turning on the third switch T3, and keeping the other off switches off; or, turning off the first switch T1 and the third switch T3, and if the sixth switch T6 is on, turning off the sixth switch T6, turning on the fifth switch T5, and keeping the other off switches off. When the voltage at AC terminal X is less than the second threshold, the improved blocking timing includes: turning off the high-frequency transistor and the fourth switch T4, turning on the second switch T2, and keeping the other off switches off; or, turning off the second switch T2 and the fourth switch T4, and if the fifth switch T5 is on, turning off the fifth switch T5, turning on the sixth switch T6, and keeping the other off switches off.

[0046] Figure 7 This is a schematic diagram of a shutdown process when the AC terminal voltage is in the positive half-cycle, as provided in an embodiment of this application. Figure 7 The scenario shown is an inverter scenario. In this embodiment, the current flowing out of the bridge arm of the AC terminal is defined as positive, and the current flowing into the bridge arm as negative, and the voltage and current directions are the same for an inverter scenario, while the voltage and current directions are opposite for a rectification scenario. Figure 7 As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is greater than the first threshold, the controller 10 can keep the third switch T3 on after turning off other switches. At this time, the current flowing from the bridge arm to the AC terminal freewheels through the on-state third switch T3 and the body diode of the sixth switch T6. After the current freewheels to 0, the reverse current freewheels through the body diode of the fifth switch T5 and the parallel diode of the first switch T1. At this time, since the third switch T3 is still on, the voltage across the sixth switch T6 can be clamped to half the bus voltage, thereby effectively preventing the sixth switch T6 from being damaged by overvoltage. Furthermore, since the second switch T2 is off at this time, the short-circuit path of the power grid can be cut off, preventing a short circuit in the power grid.

[0047] Figure 8 This is a schematic diagram of another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the positive half-cycle, and Figure 8 The scenario shown is a rectification scenario. For example... Figure 8 As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is greater than the first threshold, the controller 10 can control the third switch T3 to remain on after turning off other switches. At this time, the current flowing into the bridge arm from the AC terminal freewheels through the body diode of the fifth switch T5 and the parallel diode of the first switch T1. During the freewheeling process, since the third switch T3 is on, the voltage across the sixth switch T6 can be clamped to half the bus voltage, thus effectively preventing the sixth switch T6 from being damaged by overvoltage. After the freewheeling current reaches 0, since the third switch T3 remains on, the reverse current freewheels through the on-state third switch T3 and the body diode of the sixth switch T6. At this time, the voltage across the first switch T1 and the fifth switch T5 is half the bus voltage, thus effectively preventing the fifth switch T5 from being damaged by overvoltage. Furthermore, since the second switch T2 is off during the above process, the short-circuit path of the power grid can be cut off, preventing a short circuit in the power grid.

[0048] Figure 9 This is a schematic diagram of a shutdown process when the AC terminal voltage is in the negative half-cycle, as provided in an embodiment of this application. Figure 9 The scenario shown is an inverter scenario. For example... Figure 9 As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is less than the second threshold, the controller 10 can keep the second switch T2 on after turning off other switches. At this time, the current flowing into the bridge arm from the AC terminal freewheels through the body diode of the fifth switch T5 and the on-state second switch T2. After the freewheeling current reaches 0, the reverse current freewheels through the parallel diode of the fourth switch T4 and the body diode of the sixth switch T6. At this time, since the second switch T2 remains on, the voltage across the fifth switch T5 can be clamped to half the bus voltage, thereby effectively preventing overvoltage damage to the fifth switch T5. Furthermore, since the third switch T3 is off at this time, the short-circuit path to the power grid can be cut off, preventing a short circuit in the power grid.

[0049] Figure 10 This is a schematic diagram of another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the negative half-cycle, and Figure 10 The scenario shown is a rectification scenario. For example... Figure 10As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is less than the second threshold, the controller 10 can keep the second switch T2 on after turning off other switches. At this time, the current flowing from the bridge arm to the AC terminal freewheels through the parallel diode of the fourth switch T4 and the body diode of the sixth switch T6. During the freewheeling process, since the second switch T2 is on, the voltage across the fifth switch T5 can be clamped to half the bus voltage, thus effectively preventing the fifth switch T5 from being damaged by overvoltage. After the freewheeling current reaches 0, the reverse current freewheels through the body diode of the fifth switch T5 and the on-state second switch T2. At this time, the voltage across the fourth switch T4 and the sixth switch T6 is half the bus voltage, thus effectively preventing the sixth switch T6 from being damaged by overvoltage. Furthermore, since the third switch T3 is off during the above process, the short-circuit path of the power grid can be cut off, preventing a short circuit in the power grid.

[0050] Figure 11 This is a schematic diagram of another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the positive half-cycle, and Figure 11 The scenario shown is an inverter scenario. For example... Figure 11 As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is greater than the first threshold, the controller 10 can control the fifth switch T5 to remain on after turning off other switches. At this time, the current flowing from the bridge arm to the AC terminal freewheels through the parallel diode of the second switch T2 and the on-state fifth switch T5. Before the current freewheels, the third switch T3 switches from the on state to the off state, and when the third switch T3 is on, the current flows out of the bridge arm through the body diodes of the third switch T3 and the sixth switch T6. The fourth switch T4 resumes voltage bearing, and the voltage across the fourth switch T4 is half the bus voltage. During the freewheeling phase, the third switch T3 is off, and after the fifth switch T5 is on, the voltage across the sixth switch T6 and the fourth switch T4 is half the bus voltage. After the freewheeling current reaches zero, the reverse current continues through the conducting fifth switch T5 and the parallel diode of the first switch T1. At this time, the voltage across the sixth switch T6 and the fourth switch T4 is the bus voltage. Since the fourth switch T4 has recovered its voltage before the freewheeling phase, it effectively avoids the voltage across the sixth switch T6 being much greater than half the bus voltage due to the difference in reverse recovery characteristics or charge removal characteristics between the two switches during the freewheeling and reverse current oscillation phases. Furthermore, since the second switch T2 and the third switch T3 are both turned off during the shutdown process, the short-circuit path to the power grid is cut off, preventing a short circuit in the power grid.

[0051] Figure 12 This is a schematic diagram of another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the positive half-cycle, and Figure 12 The scenario shown is a rectification scenario. For example... Figure 12 As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is greater than the first threshold, the controller 10 can control the fifth switch T5 to remain on after turning off other switches. At this time, the AC terminal current flows through the on-state fifth switch T5 and the parallel diode of the first switch T1, and the voltage across the sixth switch T6 and the fourth switch T4 is the bus voltage. Before shutdown, the first switch T1 and the third switch T3 are on, and the rectified current flows from the AC terminal through the fifth switch T5 and the first switch T1 into the positive DC bus BUS+. The voltage across the sixth switch T6 and the fourth switch T4 is the bus voltage. Since the third switch T3 is on, the voltage across the sixth switch T6 and the fourth switch T4 can be clamped to half the bus voltage. Based on this, during the shutdown process, after the third switch T3 is turned off, the sixth switch T6 and the fourth switch T4 can evenly share the bus voltage, thereby effectively avoiding overvoltage damage to the sixth switch T6. Continue to refer to Figure 12 After the freewheeling current reaches zero, since the fifth switch T5 remains on, the reverse current flows through the parallel diode of the second switch T2 and the on-state fifth switch T5. At this time, the voltage across the sixth switch T6 and the fourth switch T4 is half the bus voltage, thus effectively preventing overvoltage damage to the sixth switch T6. Furthermore, since the second switch T2 and the third switch T3 are both off during the above process, the short-circuit path to the power grid is cut off, preventing a short circuit in the power grid.

[0052] Figure 13 This is a schematic diagram of another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the negative half-cycle, and Figure 13 The scenario shown is an inverter scenario. For example... Figure 13As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is less than the second threshold, the controller 10 can control the sixth switch T6 to remain on after turning off other switches. At this time, the AC terminal current freewheels through the parallel diode of the on-state sixth switch T6 and the third switch T3. Before the freewheeling phase, when the second switch T2 is on, the current flows into the bridge arm through the body diode of the fifth switch T5 and the second switch T2, the first switch T1 resumes voltage bearing, and the voltage across the first switch T1 is half the bus voltage. During the freewheeling phase, the second switch T2 is off, and after the sixth switch T6 is on, the voltage across the first switch T1 and the fifth switch T5 is half the bus voltage. After the freewheeling current reaches 0, the reverse current freewheels through the parallel diode of the fourth switch T4 and the sixth switch T6, and the voltage across the first switch T1 and the fifth switch T5 is the bus voltage. However, since the first switch T1 has already recovered its voltage before the freewheeling phase, it can effectively prevent overvoltage damage to the fifth switch T5 due to differences in reverse recovery characteristics or charge removal characteristics between the first switch T1 and the fifth switch T5 during the freewheeling phase and the current reverse oscillation phase. Furthermore, since the second switch T2 and the third switch T3 are both turned off during the shutdown process, the short-circuit path to the power grid can be cut off, preventing a short circuit in the power grid.

[0053] Figure 14 This is a schematic diagram illustrating another shutdown process provided in an embodiment of this application when the voltage at the AC terminal is in the negative half-cycle. Figure 14 The scenario shown is a rectification scenario. For example... Figure 14 As shown, during the power converter shutdown process, assuming the controller 10 detects that the AC terminal voltage is less than the second threshold, the controller 10 can control the sixth switch T6 to remain on after turning off other switches. At this time, the AC terminal current flows through the parallel diode of the fourth switch T4 and the freewheeling current of the sixth switch T6. Before shutdown, the second switch T2 and the fourth switch T4 are on, and the rectified current flows from the negative DC bus BUS- through the body diodes of the fourth switch T4 and the sixth switch to the AC terminal. The voltage across the first switch T1 and the fifth switch T5 is the bus voltage. Since the second switch T2 is on, the voltage across the first switch T1 and the voltage across the fifth switch T5 can be clamped to half the bus voltage. Based on this, during the shutdown process, after the second switch T2 and the fourth switch T4 are turned off, the first switch T1 and the fifth switch T5 can evenly share the bus voltage, thereby effectively preventing the fifth switch T5 from being damaged by overvoltage. (Continue to refer to...) Figure 14After the freewheeling current reaches zero, since the sixth switch T6 remains on, the reverse current flows through the parallel diode of the third switch T3 and the on-state sixth switch T6. At this time, the voltage across the first switch T1 and the fifth switch T5 is half the bus voltage, thus effectively preventing overvoltage damage to the fifth switch T5. Furthermore, since the second switch T2 and the third switch T3 are both off during the above process, the short-circuit path to the power grid is cut off, preventing a short circuit in the power grid.

[0054] Based on the above Figures 7 to 12 As shown in the shutdown sequence, during the power converter shutdown process, if the AC terminal voltage is greater than the first threshold, the third switch T3 or the fifth switch T5 is turned on; if the AC terminal voltage is less than the second threshold, the second switch T2 or the sixth switch T6 is turned on. This not only effectively prevents overvoltage damage to the fifth switch T5 and the sixth switch T6, but also effectively prevents short circuits in the power grid. Furthermore, the solution provided in this application embodiment does not require parallel capacitors across the second switch T2 and the third switch T3. This not only avoids increasing the structural complexity and hardware cost of the power converter, but also avoids the parallel capacitors affecting the start-up speed of the high-frequency transistors and the efficiency of the power converter.

[0055] In one possible implementation, such as Figure 5 and Figure 6 As shown, the power converter also includes DC bus capacitors C1 and C2. DC bus capacitors C1 and C2 are connected in series between the positive (DC+) and negative (DC-) terminals of the DC line, and the series connection point between C1 and C2 is the bus midpoint N. The series connection point between the second switch T2 and the third switch T3 in each phase arm is also connected to this bus midpoint N.

[0056] In one possible implementation, such as Figure 6 As shown, the power converter also includes a filter inductor Lf and a filter capacitor Cf connected to the AC terminals. The output of each phase arm is connected to the power grid or load via the filter inductor Lf, one end of the filter capacitor Cf is connected to the filter inductor Lf, and the other end of the filter capacitor Cf is connected to the bus midpoint N.

[0057] In this embodiment, the voltage at the AC terminal of the power converter can refer to the capacitor voltage of the filter capacitor Cf, or it can refer to the grid voltage. For example, the controller 10 also includes a voltage sampling circuit that can sample the capacitor voltage of the filter capacitor Cf momentarily before the power converter is turned off, or sample the grid voltage between the grid and the bus midpoint N. The controller 10 can then perform blocking according to the sampled voltage magnitude and the corresponding improved blocking timing.

[0058] In one possible implementation, the first switch T1, the second switch T2, the third switch T3, and the fourth switch T4 are all IGBTs, and the fifth switch T5 and the sixth switch T6 are all MOSFETs, for example, all SiCMOS. That is, the power frequency transistors in the power converter can all be IGBTs, and the high-frequency transistors can all be MOSFETs. This ensures low conduction losses and low cost for the first to fourth switches T1 and T4, and fast switching speeds and low switching losses for the fifth and sixth switches T5 and T6. As mentioned earlier, in a hybrid topology using IGBTs and MOSFETs, the high-frequency transistors are at risk of overvoltage during shutdown due to differences in the reverse recovery characteristics of different types of switches. In this embodiment, because the controller can use an improved blocking timing during shutdown, overvoltage of the high-frequency transistors can be effectively avoided.

[0059] In one possible implementation, the first threshold is greater than or equal to 30V, and the second threshold is less than or equal to -30V. For example, the first threshold can be 30V or 50V, and the second threshold can be -30V or -50V.

[0060] By designing a larger first threshold and a smaller second threshold, voltage polarity judgment errors caused by voltage sampling errors and / or AC voltage fluctuations can be effectively avoided, thereby effectively preventing grid short circuits. Furthermore, during the power converter shutdown process, if the AC voltage polarity changes, the controller needs to adjust the conducting transistors according to the changed voltage polarity, leading to high complexity in the shutdown control logic. In this embodiment, by designing a larger first threshold and a smaller second threshold, the shutdown process can be effectively ensured to be completed before the AC voltage polarity changes, thereby effectively reducing the complexity of the controller's control logic during the shutdown process.

[0061] In one possible implementation, the controller 10 is further configured to: control all of the first switch T1 to the sixth switch T6 to turn off when the absolute value of the current at the AC terminal is less than a current threshold.

[0062] The AC current can be the current flowing through the filter inductor Lf. Furthermore, the current threshold can be a value close to 0. This ensures that during the shutdown process, all switches are turned off only when the freewheeling current is close to 0 (e.g., equal to 0), thus ending the shutdown process. Since the AC current is close to 0 when the controller 10 turns off all switches, it ensures that no current flows through any of the switches, effectively preventing overvoltage damage to the switches.

[0063] For example, during the shutdown process when the AC voltage is in the positive half-cycle, such as... Figure 7 and Figure 8 As shown, controller 10 can turn off the third switch T3 when the current at the AC terminal decays to 0, thereby completing the wave blocking. Or, as... Figure 11 and Figure 12 As shown, controller 10 can turn off the fifth switch T5 when the current at the AC terminal decays to 0, thereby completing the wave blocking. During the shutdown process when the voltage at the AC terminal is in the negative half-cycle, as... Figure 9 and Figure 10 As shown, controller 10 can turn off the second switch T2 when the current at the AC terminal decays to 0, thereby completing the wave blocking. Alternatively, as... Figure 13 and Figure 14 As shown, the controller 10 can turn off the sixth switch T6 when the current at the AC terminal decays to 0, thereby completing the wave blocking.

[0064] In one possible implementation, the controller 10 is further configured to: control all of the first switch T1 to the sixth switch T6 to be turned off when the absolute value of the current at the AC terminal is less than the current threshold and the voltage at the AC terminal is greater than the first threshold or less than the second threshold.

[0065] It is understandable that the controller 10 has a certain sampling error when sampling the current at the AC terminal. Therefore, when the controller 10 detects that the absolute value of the current at the AC terminal is less than the current threshold, the absolute value of the actual current at the AC terminal may be greater than or equal to that current threshold. To avoid misjudgment caused by current sampling error, the controller 10 can block the waveform only when the voltage at the AC terminal is greater than the first threshold or less than the second threshold. For example, in a fault shutdown scenario, when the controller 10 detects that the voltage at the AC terminal is greater than the first threshold or less than the second threshold, it can ensure that the current at the AC terminal has completely decayed to 0. At this time, blocking the waveform for all switching transistors and completing the shutdown process can effectively improve the reliability of the shutdown waveform blocking.

[0066] In one possible implementation, the controller 10 is further configured to: during the power converter shutdown process, if the voltage at the AC terminal is greater than a first threshold, control the third switch T3 and the fifth switch T5 to both turn on, and control the other switches to both turn off; if the voltage at the AC terminal is less than a second threshold, control the second switch T2 and the sixth switch T6 to both turn on, and control the other switches to both turn off.

[0067] In one possible implementation, under the scenario of normal operation of the power converter, the controller 10 is further configured to: during the power converter shutdown process, if the voltage at the AC terminal is greater than or equal to the second threshold and less than or equal to the first threshold, then after the voltage at the AC terminal is greater than the first threshold, control the third switch T3 or the fifth switch T5 to turn on and control all other switches to turn off; or, after the voltage at the AC terminal is less than the second threshold, control the second switch T2 or the sixth switch T6 to turn on and control all other switches to turn off.

[0068] In this embodiment, when the power converter is normally powered off, if the voltage at the AC terminal is greater than or equal to the second threshold and less than or equal to the first threshold, the controller 10 can first transmit the signal normally, that is, the controller 10 can continue to provide drive signals to each switching transistor according to the original transmission sequence. Furthermore, after detecting that the voltage at the AC terminal is greater than the first threshold or less than the second threshold, the controller 10 then performs signal blocking according to the improved signal blocking sequence described above. Therefore, on the one hand, it can effectively avoid voltage polarity judgment errors caused by sampling errors, and on the other hand, it can ensure that the shutdown process is completed before the voltage polarity at the AC terminal changes, thereby effectively reducing the complexity of the controller's control logic during the shutdown process.

[0069] In one possible implementation, in the event of a power converter failure, the controller 10 is further configured to: during the power converter shutdown process, if the AC terminal voltage is greater than 0 and less than or equal to a first threshold, control the third switch T3 or the fifth switch T5 to turn on, and control all other switches to turn off; if the AC terminal voltage is greater than or equal to a second threshold and less than 0, control the second switch T2 or the sixth switch T6 to turn on, and control all other switches to turn off. The power converter failure includes at least one of the following: overvoltage, overcurrent, and overtemperature.

[0070] In the event of a power converter failure, timely shutdown of the power converter is crucial to prevent the fault from spreading. Accordingly, if the controller 10 detects that the AC terminal voltage is greater than or equal to a second threshold and less than or equal to a first threshold, it can directly execute the corresponding blocking process based on the detected AC terminal voltage polarity, without waiting for the voltage to be greater than the first threshold or less than the second threshold before executing the blocking process. Specifically, if the AC terminal voltage is greater than 0 and less than or equal to the first threshold, the controller 10 can perform blocking according to the improved blocking timing corresponding to a voltage greater than the first threshold; if the AC terminal voltage is greater than or equal to the second threshold and less than 0, the controller 10 can perform blocking according to the improved blocking timing corresponding to a voltage less than the second threshold. That is, during the positive half-cycle of the AC terminal voltage, the controller 10 can control the third switch T3 or the fifth switch T5 to conduct during the shutdown blocking process; during the negative half-cycle of the AC terminal voltage, the controller 10 can control the second switch T2 or the sixth switch T6 to conduct during the shutdown blocking process.

[0071] In one possible implementation, during the power converter fault shutdown process, when the AC terminal voltage is greater than 0 and less than or equal to a first threshold, the controller 10 controls the third switch T3 to turn on, and when the AC terminal voltage is greater than or equal to a second threshold and less than 0, the controller 10 controls the second switch T2 to turn on. In this implementation, the controller 10 is also used to: control both the second switch T2 and the third switch T3 to turn on during the AC terminal voltage zero crossing process. That is, during the AC terminal voltage switching from the positive half-cycle to the negative half-cycle, the controller 10 can shut down according to the timing sequence of turning on T3→turning on T2 and T3→turning on T2; during the AC terminal voltage switching from the negative half-cycle to the positive half-cycle, the controller 10 can shut down according to the timing sequence of turning on T2→turning on T2 and T3→turning on T3.

[0072] The process of voltage zero crossing may include the moment of voltage zero crossing, a first zero-crossing period before voltage zero crossing, and / or a second zero-crossing period after voltage zero crossing. The durations of the first and second zero-crossing periods may be equal or unequal, and this application does not limit this.

[0073] As mentioned earlier, after the AC voltage crosses zero, i.e., after the voltage polarity changes, the controller 10 needs to synchronously switch the conducting transistors. For example, it needs to synchronously switch the on / off states of the second switch T2 and the third switch T3. Since both turning on and off the transistors require a certain amount of time, if the on / off states of the transistors are switched directly, one switch may be off while the other is not yet on. That is, if the on / off states of the transistors are switched directly, all transistors may be off, leading to overvoltage damage to some high-frequency transistors. In this embodiment, the controller 10 effectively avoids the fault condition where all transistors are off by controlling both the second switch T2 and the third switch T3 to be on during the AC voltage crossing process.

[0074] In one possible implementation, during the power converter fault shutdown process, when the AC terminal voltage is greater than 0 and less than or equal to a first threshold, the controller 10 controls the fifth switch T5 to turn on, and when the AC terminal voltage is greater than or equal to a second threshold and less than 0, the controller 10 controls the sixth switch T6 to turn on. In this implementation, the controller 10 is further configured to: control both the fifth switch T5 and the sixth switch T6 to turn on during the AC terminal voltage zero-crossing process. That is, during the AC terminal voltage switching from the positive half-cycle to the negative half-cycle, the controller 10 can shut down according to the sequence of turning on T5 → turning on T5 and T6 → turning on T6; during the AC terminal voltage switching from the negative half-cycle to the positive half-cycle, the controller 10 can shut down according to the sequence of turning on T6 → turning on T5 and T6 → turning on T5.

[0075] As can be seen from the above analysis, during the zero-crossing process of the AC voltage, the controller 10 can effectively avoid the fault condition where all switches are turned off by controlling both the fifth switch T5 and the sixth switch T6 to be turned on.

[0076] In one possible implementation, during the power converter fault shutdown process, when the AC terminal voltage is greater than 0 and less than or equal to a first threshold, the controller 10 controls the fifth switch T5 to turn on, and when the AC terminal voltage is greater than or equal to a second threshold and less than 0, the controller 10 controls the second switch T2 to turn on. In this implementation, the controller 10 is further configured to: control both the second switch T2 and the fifth switch T5 to turn on during the AC terminal voltage zero crossing process. That is, during the AC terminal voltage switching from the positive half-cycle to the negative half-cycle, the controller 10 can shut down according to the timing sequence of turning on T5→turning on T2 and T5→turning on T2; during the AC terminal voltage switching from the negative half-cycle to the positive half-cycle, the controller 10 can shut down according to the timing sequence of turning on T2→turning on T2 and T5→turning on T5.

[0077] In one possible implementation, during the power converter fault shutdown process, when the AC terminal voltage is greater than 0 and less than or equal to a first threshold, the controller 10 controls the third switch T3 to turn on, and when the AC terminal voltage is greater than or equal to a second threshold and less than 0, the controller 10 controls the sixth switch T6 to turn on. In this implementation, the controller 10 is also used to: control both the third switch T3 and the sixth switch T6 to turn on during the AC terminal voltage zero crossing process. That is, during the AC terminal voltage switching from the positive half-cycle to the negative half-cycle, the controller 10 can shut down according to the timing sequence of T3 → T6 and T3 → T6; during the AC terminal voltage switching from the negative half-cycle to the positive half-cycle, the controller 10 can shut down according to the timing sequence of T6 → T6 and T3 → T3.

[0078] In summary, this application provides a power converter employing an ANPC topology. During shutdown, the power converter can maintain the second or third switch, or the fifth or sixth switch, on during the final step of the blocking process, depending on the AC terminal voltage. Specifically, if the AC terminal voltage is greater than a first threshold, the power converter can turn on the third or fifth switch. This not only prevents overvoltage damage to the sixth switch but also effectively avoids a short circuit in the power grid. If the AC terminal voltage is less than a second threshold, the power converter can turn on the second or sixth switch. This not only prevents overvoltage damage to the fifth switch but also effectively avoids a short circuit in the power grid.

[0079] This application also provides another power converter, such as... Figure 5 As shown, the power converter includes: (DC+, DC-), AC terminal X, a first switch T1, a second switch T2, a third switch T3, a fourth switch T4, a fifth switch T5, a sixth switch T6, and a controller 10. The first switch T1, second switch T2, third switch T3, and fourth switch T4 are connected in series between the positive terminal DC+ and the negative terminal DC- of the DC terminal. The fifth switch T5 and the sixth switch T6 are connected in series between a first node P1 and a second node P2, and the series connection point between the fifth switch T5 and the sixth switch T6 is connected to the AC terminal X. Specifically, the first node P1 is the series connection point between the first switch T1 and the second switch T2, and the second node P2 is the series connection point between the third switch T3 and the fourth switch T4.

[0080] The controller 10 is used to: during the power converter shutdown process, if the voltage polarity of AC terminal X is positive, control the third switch T3 or the fifth switch T5 to turn on, and control all other switches to turn off; if the voltage polarity of AC terminal X is negative, control the second switch T2 or the sixth switch T6 to turn on, and control all other switches to turn off.

[0081] The power converter provided in this application embodiment can perform wave blocking according to the corresponding improved wave blocking timing sequence without distinguishing between normal shutdown and fault shutdown when it is powered off, without having to distinguish between normal shutdown and fault shutdown.

[0082] In one possible implementation, if the voltage polarity of AC terminal X switches during the power converter shutdown process, the controller 10 can control the switching transistors before and after the switching to conduct simultaneously during the zero-crossing process of AC terminal X. For example, if the third switching transistor T3 conducts when the voltage polarity of AC terminal X is positive, and the second switching transistor T2 conducts when the voltage polarity of AC terminal X is negative, then during the switching process of the voltage polarity of AC terminal X, i.e., during the zero-crossing process of AC terminal X, the controller 10 can control both the second switching transistor T2 and the third switching transistor T3 to conduct. Alternatively, if the fifth switching transistor T5 conducts when the voltage polarity of AC terminal X is positive, and the sixth switching transistor T6 conducts when the voltage polarity of AC terminal X is negative, then during the switching process of the voltage polarity of AC terminal X, the controller 10 can control both the fifth switching transistor T5 and the sixth switching transistor T6 to conduct.

[0083] In one possible implementation, the controller is further configured to: control all six switches (from the first to the sixth) to turn off when the absolute value of the current at the AC terminal is less than a current threshold. The current threshold is a value close to 0.

[0084] The power converters provided in the above embodiments have essentially the same implementation methods and technical effects as the power converters described in the foregoing embodiments. Therefore, for the sake of brevity, the implementation methods and technical effects of the power converters will not be described again here.

[0085] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0086] In the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0087] The above description is merely an optional implementation of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power converter, characterized in that, The power converter includes: a DC terminal, an AC terminal, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, and a controller; The first switch, the second switch, the third switch, and the fourth switch are connected in series between the positive and negative terminals of the DC terminal. The fifth switch and the sixth switch are connected in series between the first node and the second node, and the series node between the fifth switch and the sixth switch is connected to the AC terminal. The first node is the series node between the first switch and the second switch, and the second node is the series node between the third switch and the fourth switch. The controller is configured to: during the power converter shutdown process, if the voltage at the AC terminal is greater than a first threshold, control the third or fifth switch to turn on and control all other switches to turn off; if the voltage at the AC terminal is less than a second threshold, control the second or sixth switch to turn on and control all other switches to turn off. Wherein, the first threshold is greater than 0, and the second threshold is less than 0.

2. The power converter according to claim 1, characterized in that, The controller is further configured to: in the scenario of power converter failure, during the power converter shutdown process, if the voltage at the AC terminal is greater than 0 and less than or equal to the first threshold, control the third or fifth switch to turn on and control all other switches to turn off; if the voltage at the AC terminal is greater than or equal to the second threshold and less than 0, control the second or sixth switch to turn on and control all other switches to turn off.

3. The power converter according to claim 2, characterized in that, If the voltage at the AC terminal is greater than 0 and less than or equal to the first threshold, the third switch is turned on, and if the voltage at the AC terminal is greater than or equal to the second threshold and less than 0, the second switch is turned on. Then the controller is further configured to: control both the second switch and the third switch to be turned on during the process of the voltage at the AC terminal crossing zero.

4. The power converter according to claim 2, characterized in that, If the voltage at the AC terminal is greater than 0 and less than or equal to the first threshold, the fifth switch is turned on, and if the voltage at the AC terminal is greater than or equal to the second threshold and less than 0, the sixth switch is turned on. The controller is further configured to: control both the fifth and sixth switches to be turned on during the process of the voltage at the AC terminal crossing zero.

5. The power converter according to claim 1, characterized in that, The controller is further configured to: during the shutdown process of the power converter, if the voltage at the AC terminal is greater than or equal to the second threshold and less than or equal to the first threshold, then after the voltage at the AC terminal is greater than the first threshold, control the third switch or the fifth switch to turn on and control all other switches to turn off; or, after the voltage at the AC terminal is less than the second threshold, control the second switch or the sixth switch to turn on and control all other switches to turn off.

6. The power converter according to any one of claims 1 to 5, characterized in that, The controller is also configured to: control all of the first to sixth switching transistors to turn off when the absolute value of the current at the AC terminal is less than a current threshold.

7. The power converter according to claim 6, characterized in that, The controller is further configured to: control all of the first to sixth switches to turn off when the absolute value of the current at the AC terminal is less than a current threshold and the voltage at the AC terminal is greater than the first threshold or less than the second threshold.

8. The power converter according to any one of claims 1 to 7, characterized in that, The first threshold is greater than or equal to 30 volts (V), and the second threshold is less than or equal to -30 V.

9. The power converter according to any one of claims 1 to 8, characterized in that, The first, second, third, and fourth switching transistors are all insulated gate bipolar transistors (IGBTs), and the fifth and sixth switching transistors are metal-oxide-semiconductor field-effect transistors (MOSFETs).

10. A power converter, characterized in that, The power converter includes: a DC terminal, an AC terminal, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, and a controller; The first, second, third, and fourth switching transistors are connected in series between the positive and negative terminals of the DC terminal. The fifth and sixth switching transistors are connected in series between a first node and a second node, and the series connection node between the fifth and sixth switching transistors is connected to the AC terminal. The first node is the series connection node between the first and second switching transistors, and the second node is the series connection node between the third and fourth switching transistors. The controller is configured to: during the power converter shutdown process, if the voltage polarity of the AC terminal is positive, control the third or fifth switch to turn on and control all other switches to turn off; if the voltage polarity of the AC terminal is negative, control the second or sixth switch to turn on and control all other switches to turn off.

11. The power converter according to claim 10, characterized in that, If the voltage polarity of the AC terminal is positive, the third switch is turned on, and if the voltage polarity of the AC terminal is negative, the second switch is turned on. Then the controller is further configured to: control both the second switch and the third switch to be turned on during the switching of the voltage polarity of the AC terminal.

12. The power converter according to claim 10, characterized in that, If the voltage polarity of the AC terminal is positive, the fifth switch is turned on, and if the voltage polarity of the AC terminal is negative, the sixth switch is turned on. The controller is further configured to: control both the fifth and sixth switches to be turned on during the switching of the voltage polarity of the AC terminal.

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