Soft switching power circuit, submodule, MMC and flexible direct current converter valve
By introducing a soft-switching power circuit into the flexible DC converter valve, and using a saturated reactor and a buffer capacitor to control the switching on and off of the power transistor, the problem of high power transistor loss under overload is solved, and the current carrying capacity of the power transistor and the overload capacity of the flexible DC converter valve are improved.
Patent Information
- Application Number
- CN202511195795.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-26
- Publication Date
- 2025-11-28
AI Technical Summary
In existing technologies, flexible DC converter valves suffer from high power transistor losses, high temperature rise, and large turn-off overshoot under overload conditions, resulting in insufficient current carrying capacity of the power transistors and failing to meet the stability and safety requirements of the power grid.
A soft-switching power circuit is adopted, which controls the power transistor's turn-on and turn-off by using a series-connected turn-on current-limiting module and a parallel-connected turn-off voltage-limiting module. The turn-on current-limiting module uses a saturated reactor, and the turn-off voltage-limiting module uses a buffer capacitor to achieve soft turn-on and soft turn-off of the power transistor.
It reduces the turn-on and turn-off losses of the power transistor, improves the current carrying capacity of the power transistor, and enhances the overload capacity and transmission capacity of the flexible DC converter valve, thus meeting the support requirements of the power grid.
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Figure CN121036484A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of power systems, in particular to a soft-switching power circuit, a sub-module, an MMC and a flexible DC converter valve. BACKGROUND
[0002] With the expansion of the power grid scale and the increase of new energy proportion, the stability and safety of the power grid are increasingly prominent, and the voltage, frequency and damping stability margin are insufficient. In the face of the growing stability demand of the power grid, it is urgent to rely on the flexible DC flexible controllable performance to improve the overload capacity of the flexible DC and fully tap the support capacity of the flexible DC to the power grid. The flexible DC converter valve runs under overload, and the current increases, which brings problems such as large loss, high temperature rise and large turn-off overshoot, which puts higher requirements on the loss and overload capacity of the flexible DC converter valve.
[0003] The flexible DC converter valve can include a power tube, and the main factors limiting the overload capacity of the power tube are the junction temperature and the turn-off overvoltage of the power tube. When the junction temperature or the voltage exceeds the threshold that the power tube can tolerate, the power tube will fail.
[0004] In order to control the power tube, the related technology usually directly sends a drive signal to the control stage of the power tube to realize hard switching of the power tube. However, since the junction temperature fluctuation and the turn-off overvoltage of the power tube are both high, in order to ensure the stable operation of the power tube, a large junction temperature margin and voltage margin need to be left. Under the overload condition, the loss (which can include switching loss and on-state loss) of the power tube is large, which causes the junction temperature or voltage of the power tube to exceed the safety threshold, greatly reducing the current-carrying capacity of the power tube. SUMMARY
[0005] In order to solve the problem of large loss and low current-carrying capacity of the power tube in the prior art, the present application provides a soft-switching power circuit, a sub-module, an MMC and a flexible DC converter valve.
[0006] In a first aspect, the present application provides a soft-switching power circuit, which can include a power tube, a turn-on current limiting module and a turn-off voltage limiting module. The turn-on current limiting module is connected in series with the power tube, and the turn-off voltage limiting module is connected in parallel with the power tube. The turn-on current limiting module includes a saturable reactor, and the turn-off voltage limiting module includes a buffer capacitor.
[0007] The turn-on current limiting module is configured to control the soft turn-on of the power tube through the saturable reactor.
[0008] The turn-off voltage limiting module is configured to control the soft turn-off of the power tube through the buffer capacitor.
[0009] Optionally, the turn-on current limiting module can further include a first diode. The first diode is connected in antiparallel with the saturable reactor.
[0010] In some possible implementation manners, the turn-off voltage limiting module further includes a second diode and a first resistor.
[0011] The anode of the second diode and the first end of the first resistor are connected to the first pole of the power tube, the cathode of the second diode and the second end of the first resistor are connected to the first end of the buffer capacitor, and the second end of the buffer capacitor is connected to the second pole of the power tube.
[0012] In some possible implementation manners, the turn-off voltage limiting module further includes a second diode, a first resistor and a switch tube.
[0013] The anode of the second diode is connected to the first pole of the power tube, the cathode of the second diode is connected to the first end of the first resistor, and the cathode of the second diode is also connected to the first end of the buffer capacitor, the second end of the first resistor is connected to the first pole of the switch tube, and the second end of the buffer capacitor is connected to the second pole of the switch tube.
[0014] In some possible implementation manners, the turn-off voltage limiting module further includes a second diode, a third diode, a fourth diode, a feed capacitor and a resonant reactor.
[0015] The anode of the second diode and the first end of the feed capacitor are connected to the first pole of the power tube, the cathode of the second diode and the first end of the buffer capacitor are connected to the anode of the fourth diode, the second end of the buffer capacitor is connected to the second pole of the power tube, the second end of the feed capacitor and the first end of the resonant reactor are connected to the anode of the third diode, the cathode of the fourth diode is connected to the second end of the resonant reactor, and the cathode of the third diode is connected to the first end of the energy storage capacitor in the sub-module including the power tube.
[0016] In the second aspect, the application provides a sub-module, which can include a first bridge arm and a second bridge arm connected in series. The first bridge arm and / or the second bridge arm include the soft-switching power circuit provided by the first aspect and possible implementation manners thereof. It can be seen that the sub-module can be a half-bridge sub-module.
[0017] For example, the sub-module can be a full-bridge sub-module. The sub-module can further include a third bridge arm and a fourth bridge arm connected in series. The third bridge arm and / or the fourth bridge arm include the soft-switching power circuit provided by the first aspect and possible implementation manners thereof.
[0018] In some possible implementation manners, the sub-module can further include a second resistor and an energy storage capacitor. The first end of the second resistor and the first end of the energy storage capacitor are connected to the first bridge arm, and the second end of the second resistor and the second end of the energy storage capacitor are connected to the second bridge arm.
[0019] In some possible implementation manners, the sub-module can further include a second resistor and an energy storage capacitor. The first end of each of the second resistor and the energy storage capacitor is connected to the first bridge arm and the third bridge arm, and the second end of each of the second resistor and the energy storage capacitor is connected to the second bridge arm and the fourth bridge arm.
[0020] Further, the sub-module can further include a thyristor and a bypass switch. The thyristor and the bypass switch are both connected in parallel to the second bridge arm.
[0021] Optionally, the sub-module can further include a thyristor and a bypass switch. The first end of each of the thyristor and the bypass switch is connected to the first bridge arm and the second bridge arm, and the second end of each of the thyristor and the bypass switch is connected to the third bridge arm and the fourth bridge arm.
[0022] In a third aspect, the present application provides a modular multilevel converter (MMC) including the sub-module provided in the second aspect and possible implementation manners thereof. The sub-module can be a half-bridge sub-module or a full-bridge sub-module.
[0023] Of course, in addition to the sub-module, the MMC can further include other parts, which are not limited in the present application.
[0024] In a fourth aspect, the present application provides a flexible DC converter valve, which can include the modular multilevel converter (MMC) provided in the third aspect.
[0025] Of course, in addition to the MMC, the flexible DC converter valve can further include other parts, which are not limited in the present application.
[0026] Compared with the prior art, the present application has the following beneficial effects:
[0027] The soft-switching power circuit provided in the present application can include a power tube, a turn-on current limiting module and a turn-off voltage limiting module. The turn-on current limiting module is connected in series with the power tube, and the turn-off voltage limiting module is connected in parallel with the power tube. The turn-on current limiting module includes a saturable reactor, and the turn-off voltage limiting module includes a buffer capacitor. The turn-on current limiting module is configured to control the soft turn-on of the power tube through the saturable reactor. The turn-off voltage limiting module is configured to control the soft turn-off of the power tube through the buffer capacitor. The present application realizes the soft turn-on of the power tube through the saturable reactor and the soft turn-off of the power tube through the buffer capacitor, greatly reduces the turn-on loss and turn-off loss of the power tube in the process of soft turn-on and soft turn-off, and greatly improves the current-carrying capacity of the power tube.
[0028] The present application reduces the junction temperature fluctuation of the power tube through the soft-switching power circuit, so that the power tube can operate at a larger current, thereby improving the overload capacity and delivery capacity of the sub-module, that is, the overload capacity and delivery capacity of the MMC.
[0029] The application greatly reduces the overvoltage stress of the power tube in the turn-off process through the turn-off voltage limiting module, so that the MMC has strong overload capacity, and thus the flexible DC converter valve meets the demand of the power grid for support. BRIEF DESCRIPTION OF DRAWINGS
[0030] In order to more clearly illustrate the technical solutions in the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.
[0031] Figure 1 It is a schematic structural diagram of the soft-switching power circuit in the embodiment of the application;
[0032] Figure 2 It is another schematic structural diagram of the soft-switching power circuit in the embodiment of the application;
[0033] Figure 3 It is a schematic structural diagram of the turn-on current limiting module in the embodiment of the application;
[0034] Figure 4 It is a schematic structural diagram of the turn-off voltage limiting module in the embodiment of the application;
[0035] Figure 5 It is a schematic structural diagram of the turn-off voltage limiting module in the embodiment of the application;
[0036] Figure 6 It is a schematic structural diagram of the turn-off voltage limiting module in the embodiment of the application;
[0037] Figure 7 It is a schematic structural diagram of the sub-module in the embodiment of the application;
[0038] Figure 8 It is a schematic structural diagram of the sub-module in the embodiment of the application;
[0039] Figure 9 It is a schematic structural diagram of the sub-module in the embodiment of the application;
[0040] Figure 10 It is a schematic curve diagram of the current flowing through the power tube and the collector-emitter voltage of the power tube in the sub-module without using the soft-switching power circuit;
[0041] Figure 11 It is a schematic curve diagram of the current flowing through the power tube and the collector-emitter voltage of the power tube in the sub-module using the soft-switching power circuit. DETAILED DESCRIPTION
[0042] The technical solutions in the present application will be described below with reference to the drawings.
[0043] The terms "first", "second", etc. in the description, claims and drawings of the present application are only used for distinguishing purposes of description, and cannot be understood as indicating or implying relative importance, nor can be understood as indicating or implying sequence. In addition, the terms "comprise" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, comprising a series of steps or units. The method, system, product or device is not necessarily limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.
[0044] It should be understood that in the present application, "at least one" refers to one or more, and "multiple" refers to two or more. "And / or" is used to describe the association between the associated objects, which means that there can be three relationships, for example, "A and / or B" can represent three cases: only A, only B, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally represents that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions means any combination of these items, including any combination of single or multiple items. For example, at least one of a, b or c, can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.
[0045] The present application provides a soft switching power circuit, as shown in Figure 1 The soft switching power circuit 10 can include a power tube Q1 (which can be an IGBT, etc.), a turn-on current limiting module 1, and a turn-off voltage limiting module 2. The turn-on current limiting module 1 is connected in series with the power tube Q1, and the turn-off voltage limiting module 2 is connected in parallel with the power tube Q1.
[0046] Referring to Figure 2 and Figure 3 , the turn-on current limiting module 1 includes a saturable reactor L1, and referring to Figure 2 and Figure 4 , the turn-off voltage limiting module 2 includes a buffer capacitor C1.
[0047] The turn-on current limiting module 1 is configured to control the soft turn-on of the power tube Q1 through the saturable reactor L1.
[0048] The turn-off voltage limiting module 2 is configured to control the soft turn-off of the power tube Q1 through the buffer capacitor C1.
[0049] Optionally, as shown in Figure 2 and 3As shown, the turn-on current limiting module 1 can include the saturable reactor L1 and the first diode D1.
[0050] In the power tube off state, the current of the saturable reactor L1 is 0, and when the power tube starts to turn on, the current of the saturable reactor L1 starts to rise. Due to the small current, the inductance is large, which reduces the current rising rate when the power tube turns on, realizes approximate zero current turn-on in the turn-on process, reduces the turn-on loss of the power tube, and as the current increases, the saturable reactor L1 approaches saturation, and the inductance in the sub-module is approximately 0, which does not affect the on-state operation of the power tube. The first diode D1 can be used to freewheel the saturable reactor L1 and prevent oscillation.
[0051] In some possible implementation manners, as shown in Figure 2 and 4 , the turn-off voltage limiting module 2 can include the buffer capacitor C1, the second diode D2, and the first resistor R1.
[0052] The anode of the second diode D2 and the first end of the first resistor R1 are connected to the first pole (which can be the collector) of the power tube Q1, the cathode of the second diode D2 and the second end of the first resistor R1 are connected to the first end of the buffer capacitor C1, and the second end of the buffer capacitor C1 is connected to the second pole (which can be the emitter) of the power tube Q1.
[0053] In the power tube on state, the buffer capacitor C1 discharges through the first resistor R1, and the voltage of the buffer capacitor C1 is 0. When the power tube starts to turn off, due to the presence of the first resistor R1, the voltage between the collector and the emitter of the power tube is limited, the voltage rises slowly, the Miller platform ends quickly, the current of the power tube decreases rapidly, and approximate zero voltage turn-off is realized, which reduces the turn-off loss of the power tube. At the same time, due to the presence of the buffer capacitor C1, the turn-off overvoltage of the power tube can be reduced, the overvoltage stress of the power tube is reduced, and the maximum turn-off current capability of the power tube is improved.
[0054] In other possible implementation manners, as shown in Figure 5 , the turn-off voltage limiting module 2 can include the buffer capacitor C1, the second diode D2, the first resistor R1, and the switch tube S (which can be a MOS tube or the like).
[0055] The anode of the second diode D2 is connected to the first pole (which can be the collector) of the power tube Q1, the cathode of the second diode D2 is connected to the first end of the first resistor R1, and the cathode of the second diode D2 is also connected to the first end of the buffer capacitor C1. The second end of the first resistor R1 is connected to the first pole (which can be the drain) of the switch tube S, and the second end of the buffer capacitor C1 is connected to the second pole (which can be the source) of the switch tube S.
[0056] It is conceived that the switch tube S can be used to actively control the discharge of the buffer capacitor C1, and a smaller resistance value of the first resistor R1 can be used to achieve fast discharge of the buffer capacitor C1 and improve the switching frequency of the power tube.
[0057] In yet some possible implementation manners, as shown in Figure 6 FIG. 2, the turn-off voltage limiting module 2 can further include a second diode D2, a third diode D3, a fourth diode D4, a feed capacitor C2 and a resonant reactor L2 in addition to the buffer capacitor C1.
[0058] The anode of the second diode D21 and the first end of the feed capacitor C2 are both connected to the first pole (which can be a collector) of the power tube Q1, the cathode of the second diode D2 and the first end of the buffer capacitor C1 are both connected to the anode of the fourth diode D4, the second end of the buffer capacitor C1 is connected to the second pole (which can be an emitter) of the power tube Q1, the second end of the feed capacitor C2 and the first end of the resonant reactor L2 are both connected to the anode of the third diode D3, the cathode of the fourth diode D4 is connected to the second end of the resonant reactor L2, and the cathode of the third diode D3 is connected to the first end of the energy storage capacitor C3 included in the sub-module SM of the power tube Q1. Figure 8
[0059] The buffer capacitor C1 limits the rise of the collector-emitter voltage of the power tube to achieve soft turn-off of the power tube. When the power tube starts to turn off, the current charges the buffer capacitor C1 through the second diode D2, and the negative potential of the feed capacitor C2 rises accordingly. The feed capacitor C2 (which has been charged to the bus voltage during conduction) discharges through the third diode D3, and the energy is fed back to the energy storage capacitor C3 of the sub-module. When the third diode D3 is charged to the bus voltage and the feed capacitor C2 discharges to zero, the third diode D3 turns off, and then the soft turn-off process of the power tube ends.
[0060] When the power tube turns on, the third diode D3 turns off, the buffer capacitor C1, the resonant reactor L2 and the feed capacitor C2 form a resonant circuit, the voltage is applied to both ends of the resonant reactor L2, and the current charges the feed capacitor C2 from the buffer capacitor C1 through the resonant reactor L2 and the fourth diode D4. When the buffer capacitor C1 discharges to zero and the current in the resonant reactor L2 is zero, the fourth diode D4 in series is cut off, the charging of the feed capacitor C2 is completed, the resonance ends, and the feed capacitor C2 stores energy which is fed into the energy storage capacitor C3 of the sub-module when the power tube turns off. Not only is the soft switching of the power tube achieved, but also the loss of the power tube is reduced.
[0061] The embodiments of the present application also provide a sub-module. As shown in Figure 7 and Figure 8 , the sub-module can be a half-bridge sub-module. Alternatively, as shown in Figure 9 As shown, the sub-module can be a full-bridge sub-module.
[0062] The half-bridge sub-module can include a first bridge arm and a second bridge arm in series. The first bridge arm and / or the second bridge arm includes the soft-switching power circuit described above. That is, each bridge arm can include the soft-switching power circuit described above, or at least one bridge arm can include the soft-switching power circuit described above.
[0063] For example, referring to Figure 7 , the sub-module SM can include a first bridge arm 100 and a second bridge arm 200 in series. In the embodiments of the present application, the first bridge arm 100 (which can be called an upper bridge arm) can include a power tube Q2 and a diode D6 in anti-parallel. The second bridge arm 200 (which can be called a lower bridge arm) can include a soft-switching power circuit 201 (i.e., the soft-switching power circuit described above) and a diode D5, which is connected in parallel with the soft-switching power circuit 201. That is, the lower bridge arm of the sub-module SM includes the soft-switching power circuit.
[0064] Of course, the sub-module SM can further include a second resistor R2 and an energy storage capacitor C3. The first end of each of the second resistor R2 and the energy storage capacitor C3 is connected to the first bridge arm 100 (i.e., connected to the power tube Q2), and the second end of each of the second resistor R2 and the energy storage capacitor C3 is connected to the second bridge arm 200 (i.e., connected to the soft-switching power circuit 201).
[0065] Continuing to refer to Figure 7 , the sub-module SM can further include a thyristor SCR and a bypass switch S1. The thyristor SCR and the bypass switch S1 are both connected in parallel with the second bridge arm 200.
[0066] In the sub-module (half-bridge sub-module) shown in Figure 8 , the first bridge arm 100 and the second bridge arm 200 both include the soft-switching power circuit. Among them, the first bridge arm 100 includes a diode D6 and a soft-switching power circuit 101, and the second bridge arm 200 includes a diode D5 and a soft-switching power circuit 201.
[0067] Of course, referring to Figure 8 , the sub-module SM can further include a second resistor R2, an energy storage capacitor C3, a thyristor SCR, and a bypass switch S1. The first end of each of the second resistor R2 and the energy storage capacitor C3 is connected to the first bridge arm 100, and the second end of each of the second resistor R2 and the energy storage capacitor C3 is connected to the second bridge arm 200.
[0068] In other embodiments, the full-bridge sub-module can include a first bridge arm and a second bridge arm in series, and can further include a third bridge arm and a fourth bridge arm in series. At least one of the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm can include the soft-switching power circuit described above.
[0069] Referring toFigure 9 The submodule SM can have a first bridge arm 100, a second bridge arm 200, a third bridge arm 300, and a fourth bridge arm 400. In this embodiment, the first bridge arm 100 (which can be called the upper bridge arm) can include a soft-switching power circuit 101 (i.e., the soft-switching power circuit mentioned above) and a diode D6 connected in parallel. The second bridge arm 200 (which can be called the lower bridge arm) can include a soft-switching power circuit 201 (i.e., the soft-switching power circuit mentioned above) and a diode D5 connected in parallel. The third bridge arm 300 (which can be called the upper bridge arm) can include a soft-switching power circuit 301 (i.e., the soft-switching power circuit mentioned above) and a diode D7 connected in parallel. The fourth bridge arm 400 (which can be called the lower bridge arm) can include a soft-switching power circuit 401 (i.e., the soft-switching power circuit mentioned above) and a diode D8 connected in parallel. That is, all bridge arms of the submodule SM include soft-switching power circuits.
[0070] Of course, for reference Figure 9 The submodule SM may also include a second resistor R2 and an energy storage capacitor C1. The first terminals of the second resistor R2 and the energy storage capacitor C1 are connected to the first bridge arm 100 and the third bridge arm 300, and the second terminals of the second resistor R2 and the energy storage capacitor C1 are connected to the second bridge arm 200 and the fourth bridge arm 400.
[0071] Further reference Figure 9 The submodule SM also includes a thyristor SCR and a bypass switch S1. The first terminal of each of the thyristor SCR and the bypass switch S1 is connected to the first bridge arm 100 and the second bridge arm 200, and the second terminal of each of the thyristor SCR and the bypass switch S1 is connected to the third bridge arm 300 and the fourth bridge arm 400.
[0072] In the submodule that does not employ soft-switching power circuitry (i.e., implements hard switching of the power transistor), the current I flowing through the power transistor is... c With the collector-emitter voltage U of the power transistor ce (i.e., the voltage between the collector and emitter) such as Figure 10 As shown. The current I flowing through the power transistor in the sub-module of the soft-switching power circuit provided in this application (i.e., implementing soft switching of the power transistor) is... c With the collector-emitter voltage U of the power transistor ce like Figure 11 As shown. Figure 10 and Figure 11 In the process, the power transistor starts to turn on at time t1 and is turned on completely at time t2. Figure 10 Middle I c Rapid rise, I c The corresponding curve and U ce The large overlap area of the corresponding curves indicates a large turn-on loss in the power transistor. The current rise rate is limited by using a saturated reactor. Figure 11 Middle I cThe corresponding curve and U ce The corresponding curve overlap area is small, indicating that the power tube in the opening process loss is greatly reduced.
[0073] At t3, the power tube starts to turn off, and at t4, the turn-off process ends. Figure 10 I c Wait until U ce Rises to the capacitor voltage and then starts to decline, I c The corresponding curve and U ce The corresponding curve overlap area is large, and the opening process loss is large. The application can limit the voltage rise across the power tube through the buffer capacitor, Figure 11 I c Fast decline, I c The corresponding curve and U ce The corresponding curve overlap area is small, indicating that the power tube in the opening process loss is greatly reduced.
[0074] The embodiment of the application further provides a modular multilevel converter (MMC) comprising the sub-module. The sub-module can be a half-bridge sub-module or a full-bridge sub-module.
[0075] Of course, in addition to the sub-module, the MMC can also include other parts, which are not limited by the embodiment of the application.
[0076] The embodiment of the application further provides a flexible DC converter valve, which can comprise the modular multilevel converter (MMC) described above.
[0077] Of course, in addition to the MMC, the flexible DC converter valve can also include other parts, which are not limited by the embodiment of the application.
[0078] The above is only an embodiment of the application and is not used to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application are included in the scope of the claims of the application.
Claims
1. A soft-switching power circuit, characterized in that, It includes a power transistor, a turn-on current limiting module, and a turn-off voltage limiting module. The turn-on current limiting module is connected in series with the power transistor, and the turn-off voltage limiting module is connected in parallel with the power transistor. The turn-on current limiting module includes a saturated reactor, and the turn-off voltage limiting module includes a buffer capacitor. The current limiting module is used to: control the soft turn-on of the power transistor through the saturated reactor; The shutdown voltage limiting module is used to control the soft shutdown of the power transistor through the buffer capacitor.
2. The soft-switching power circuit according to claim 1, characterized in that, The current limiting module also includes a first diode; the first diode is connected in antiparallel with the saturated reactor.
3. The soft-switching power circuit according to claim 1, characterized in that, The shutdown voltage limiting module also includes a second diode and a first resistor; The anode of the second diode and the first terminal of the first resistor are both connected to the first terminal of the power transistor, the cathode of the second diode and the second terminal of the first resistor are both connected to the first terminal of the buffer capacitor, and the second terminal of the buffer capacitor is connected to the second terminal of the power transistor.
4. The soft-switching power circuit according to claim 1, characterized in that, The shutdown voltage limiting module also includes a second diode, a first resistor, and a switching transistor; The anode of the second diode is connected to the first terminal of the power transistor, the cathode of the second diode is connected to the first terminal of the first resistor, the cathode of the second diode is also connected to the first terminal of the buffer capacitor, the second terminal of the first resistor is connected to the first terminal of the switching transistor, and the second terminal of the buffer capacitor is connected to the second terminal of the switching transistor.
5. The soft-switching power circuit according to claim 1, characterized in that, The shutdown voltage limiting module also includes a second diode, a third diode, a fourth diode, a power supply capacitor, and a resonant reactor; The anode of the second diode and the first terminal of the power supply capacitor are both connected to the first terminal of the power transistor. The cathode of the second diode and the first terminal of the buffer capacitor are both connected to the anode of the fourth diode. The second terminal of the buffer capacitor is connected to the second terminal of the power transistor. The second terminal of the power supply capacitor and the first terminal of the resonant reactor are both connected to the anode of the third diode. The cathode of the fourth diode is connected to the second terminal of the resonant reactor. The cathode of the third diode is connected to the first terminal of the energy storage capacitor in the submodule including the power transistor.
6. A submodule, characterized in that, It includes a first bridge arm and a second bridge arm connected in series; the first bridge arm and / or the second bridge arm includes a soft-switching power circuit as described in any one of claims 1 to 5.
7. The submodule as described in claim 6, characterized in that, The submodule is a full-bridge submodule; The submodule further includes a third bridge arm and a fourth bridge arm connected in series; the third bridge arm and / or the fourth bridge arm includes a soft-switching power circuit as described in any one of claims 1 to 6.
8. The submodule as described in claim 6, characterized in that, The submodule also includes a second resistor and an energy storage capacitor; The first terminal of each of the second resistor and the energy storage capacitor is connected to the first bridge arm, and the second terminal of each of the second resistor and the energy storage capacitor is connected to the second bridge arm.
9. The submodule as described in claim 7, characterized in that, The submodule also includes a second resistor and an energy storage capacitor; The first terminals of the second resistor and the energy storage capacitor are connected to the first bridge arm and the third bridge arm, and the second terminals of the second resistor and the energy storage capacitor are connected to the second bridge arm and the fourth bridge arm.
10. The submodule as described in claim 6 or 7, characterized in that, The submodule also includes a thyristor and a bypass switch; both the thyristor and the bypass switch are connected in parallel with the second bridge arm.
11. The submodule as described in claim 7 or 9, characterized in that, The submodule further includes a thyristor and a bypass switch; the first terminal of each of the thyristor and the bypass switch is connected to the first bridge arm and the second bridge arm, and the second terminal of each of the thyristor and the bypass switch is connected to the third bridge arm and the fourth bridge arm.
12. A modular multilevel converter (MMC), characterized in that, Includes the submodules as described in any one of claims 6 to 11.
13. A flexible DC converter valve, characterized in that, Including the modular multilevel converter (MMC) as described in claim 12.