A high-capacity compact direct current transfer switch and control method

Abstract

The application discloses a large-capacity compact direct-current transfer switch and a control method, relates to the technical field of power equipment, and comprises a long-term current passing branch, a high-frequency oscillation breaking branch and an energy consumption branch, wherein the long-term current passing branch, the high-frequency oscillation breaking branch and the energy consumption branch are connected in parallel, the long-term current passing branch is provided as a gas switch, the energy consumption branch is provided as a second zinc oxide lightning arrester MOV2, the high-frequency oscillation breaking branch comprises a temporary current passing branch and a resonance branch, and the temporary current passing branch and the resonance branch are connected in parallel; the gas switch is used as a long-term current passing switch, the vacuum trigger gap is used as a breaking arc extinguishing unit, the negative impedance characteristic of the SF6 switch is simulated through a square wave generator, the high-frequency breaking of the vacuum trigger gap is realized, the capacitance and inductance of the LC resonance branch are greatly reduced, the current breaking level of the direct-current transfer switch is improved, and the direct-current transfer switch has the advantages of low cost, small occupied area and high current breaking capacity.

Description

Technical Field

[0001] This invention relates to the field of power equipment technology, and in particular to a high-capacity compact DC-DC transfer switch and its control method. Background Technology

[0002] DC transfer switches are key equipment in ultra-high voltage direct current transmission systems. In cases of converter valve or DC line failure, DC line maintenance, or changes in system power demand, DC transfer switches need to change the system's operating mode to transfer the load current on the branch to be disconnected to the branch to be connected.

[0003] In the existing technology, high-frequency interruption is achieved by using SF6 switches. SF6 switches have strong current carrying capacity and strong insulation performance, which can meet the requirements of higher voltage levels and larger currents.

[0004] However, the dielectric recovery speed of SF6 switches is relatively slow after arcing. In order to prevent SF6 switches from undergoing re-breakdown after arc extinction, the LC resonant frequency is low and the amount of capacitors and inductors in the LC branch is large, resulting in high cost, large size and large footprint of DC-DC converter switches.

[0005] In addition, the arc voltage amplitude of SF6 switches is limited, only a few kilovolts, resulting in a low switching current level for DC transfer switches, which is difficult to meet the high-level DC engineering current requirements of the system.

[0006] Therefore, a high-capacity, compact DC-DC transfer switch and control method are provided to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a high-capacity, compact DC-DC transfer switch and its control method, which overcomes the shortcomings of the prior art, improves the current interruption capability of the DC-DC transfer switch, and reduces cost and floor space.

[0008] To achieve the above objectives, the present invention provides a high-capacity compact DC-DC transfer switch, comprising a long-term current-carrying branch, a high-frequency oscillation breaking branch, and an energy-dissipating branch. The long-term current-carrying branch, the high-frequency oscillation breaking branch, and the energy-dissipating branch are connected in parallel. The long-term current-carrying branch is configured as a gas switch, the energy-dissipating branch is configured as a second zinc oxide surge arrester MOV2, and the high-frequency oscillation breaking branch includes a temporary current-carrying branch and a resonant branch, which are connected in parallel.

[0009] Preferably, the temporary current-carrying branch includes a vacuum trigger gap and a square wave generator, with the vacuum trigger gap and the square wave generator connected in series. The resonant branch includes a reactance and a first capacitor, with the reactance and the first capacitor connected in series.

[0010] Preferably, the square wave generator includes a switching branch, a buffer branch, and a clamping branch, which are connected in parallel. The switching branch includes a first IGBT module and a second IGBT module, which are connected in parallel. The buffer branch includes a resistor and a second capacitor, which are connected in series. The clamping branch is configured as a first zinc oxide surge arrester MOV1.

[0011] Preferably, the first IGBT module includes a first diode and a first IGBT. The first diode is configured to be four, and the four first diodes are connected to the first IGBT in a bridge configuration. The two first diodes in the upper bridge arm are connected to a common cathode, and the two first diodes in the lower bridge arm are connected to a common anode. The anode of the first IGBT is connected to the common cathode point of the two first diodes in the upper bridge arm, and the cathode of the first IGBT is connected to the common anode point of the two first diodes in the lower bridge arm.

[0012] Preferably, the second IGBT module includes a second diode and a second IGBT. The second diode is configured to be four, and the four second diodes are connected to the second IGBT in a bridge configuration. The two second diodes in the upper bridge arm are connected to a common cathode, and the two second diodes in the lower bridge arm are connected to a common anode. The anode of the second IGBT is connected to the common cathode point of the two second diodes in the upper bridge arm, and the cathode of the second IGBT is connected to the common anode point of the two second diodes in the lower bridge arm.

[0013] A control method for a high-capacity, compact DC-DC transfer switch includes the following steps:

[0014] S1: During normal operation, the gas switch remains closed, the vacuum trigger gap and the square wave generator are not triggered, and the current flows through the long-term current-carrying branch.

[0015] S2: When switching current, the gas switch is opened, triggering the vacuum trigger gap, the first IGBT module and the second IGBT module. After the gas switch is opened and the arc is ignited, an arc voltage is generated, the vacuum trigger gap is broken down, and the current is forced to transfer from the long-term current-carrying branch to the temporary current-carrying branch.

[0016] S3: After the gas switch restores its insulation capability, it performs high-frequency switching on the square wave generator, and the current is transferred from the temporary flow branch to the resonant branch.

[0017] S4: The current continuously charges the first capacitor until the voltage across the second zinc oxide arrester MOV2 rises to the reference voltage, and the current is transferred from the temporary flow branch to the energy dissipation branch.

[0018] S5: The second zinc oxide surge arrester MOV2 operates, establishing a transient voltage TIV, absorbing the energy on the line to be interrupted and the energy fed into the DC conversion switch at the sending-end converter station, and the current is transferred to the next long-term current-carrying branch.

[0019] Preferably, step S3 specifically includes the following steps:

[0020] S31: Turn off the first IGBT module and the second IGBT module. The turn-off time of the first IGBT module is set to t1, and the turn-off time of the second IGBT module is set to t2.

[0021] S32: Alternately turn on the first IGBT module and the second IGBT module, with the turn-on frequency set to f. IGBT The duty cycle is set to 1 / 4;

[0022] S33: When the first IGBT module and the second IGBT module are alternately turned on, the square wave generator outputs a square wave voltage, which excites the resonant current i in the resonant branch. LC The amplitude increases, and the circulating current i flowing through the temporary flow branch and the resonant branch... oc Increase;

[0023] S34: When the current superimposed on the temporary current-carrying branch crosses zero, the vacuum trigger gap extinguishes the arc, and the current is transferred from the temporary current-carrying branch to the resonant branch.

[0024] Preferably, in step S31, the turn-off time t1 of the first IGBT module is 1 / 4 of a switching cycle, and the turn-off time t2 of the second IGBT module is 3 / 4 of a switching cycle, wherein the switching cycle is the reciprocal of the conduction frequency.

[0025] Preferably, in step S33, the amplitude of the square wave voltage is the residual voltage U of the first zinc oxide surge arrester MOV1. MOV1 The frequency f of the square wave voltage SVS Set to the on-frequency f IGBT Twice the frequency f of the square wave voltage SVS Specifically set as follows:

[0026] f SVS =2f IGBT ;

[0027] In step S34, the resonant frequency f of the resonant branch is... LC Specifically set as follows:

[0028] f LC =Nf SVS (N = 1, 2, 3...).

[0029] Therefore, the present invention employs the above-mentioned high-capacity compact DC-DC transfer switch and control method, which has the following beneficial effects:

[0030] (1) This scheme uses a gas switch as a long-term current-carrying switch, so that the load current is transferred from the long-term current-carrying switch to the temporary current-carrying branch. No additional power source or control is required. It can be achieved solely by the arc voltage of the gas switch, which has the advantages of high reliability and easy control.

[0031] (2) This scheme uses the vacuum trigger gap as the arc interruption unit, which greatly reduces the amount of capacitors and inductors used in the LC resonant branch, and has the advantages of low cost and small footprint.

[0032] (3) This scheme achieves autonomous resonance by simulating the negative impedance characteristics of the SF6 switch through a square wave generator. The current breaking level of the DC-DC conversion switch can be improved through reasonable parameter design, and it has the advantage of high current breaking capacity.

[0033] The method of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0034] Figure 1 This is a structural diagram of a high-capacity, compact DC-DC transfer switch according to the present invention;

[0035] Figure 2 This is a structural diagram of the square wave generator of the present invention;

[0036] Figure 3 This is a schematic diagram illustrating the working principle of the square wave generator of the present invention.

[0037] Figure 4 This is a schematic diagram of the dynamic characteristics of the square wave generator of the present invention;

[0038] Figure 5 This is a schematic diagram of the autonomous resonance process based on a square wave generator according to the present invention;

[0039] Figure 6 This is a flowchart of a control method for a high-capacity, compact DC-DC transfer switch according to the present invention;

[0040] Figure 7 This is a schematic diagram illustrating the working principle before current conversion in an application scenario where the MRTB circuit breaker trips to transfer current from the ground return line to the positive metal return line.

[0041] Figure 8 This is a schematic diagram illustrating the working principle of transferring current from a long-term current-carrying branch to a temporary current-carrying branch in the application scenario of MRTB tripping to transfer current on the ground return line to the positive metal return line, according to an embodiment of the present invention.

[0042] Figure 9This is a schematic diagram illustrating the working principle of high-frequency disconnection after the gas switch restores its insulation state in the application scenario of transferring the current on the ground return line to the positive metal return line during MRTB tripping in an embodiment of the present invention.

[0043] Figure 10 This is a schematic diagram illustrating the working principle of the second zinc oxide surge arrester MOV2 establishing a transient voltage in the application scenario of transferring the current on the ground return line to the positive metal return line by MRTB tripping in an embodiment of the present invention.

[0044] Figure 11 The following is a schematic diagram of the current transfer process when the MRTB transfers the current on the ground return line to the positive metal return line in an embodiment of the present invention: (a) is a schematic diagram of the transfer of system load current; (b) is a schematic diagram of the current transfer inside the large-capacity compact DC-DC converter and the voltage change of the square wave generator; and (c) is a schematic diagram of the voltage change across the second zinc oxide surge arrester MOV2.

[0045] Figure 12 This is a detailed schematic diagram of the current and voltage changes inside the high-capacity compact DC-DC converter when the MRTB transfers the current from the ground return line to the positive metal return line in an embodiment of the present invention. (a) is a schematic diagram of the changes in internal current and square wave voltage, and (b) is a schematic diagram of the changes in voltage across the second zinc oxide arrester MOV2.

[0046] Figure 13 This is a schematic diagram of the configuration of a traditional DC-DC transfer switch in an ultra-high voltage DC transmission system.

[0047] Figure 14 This is a schematic diagram of the topology of a traditional DC-DC transfer switch.

[0048] The components are: 1. Gas switch; 2. Second zinc oxide surge arrester MOV2; 3. Vacuum trigger gap; 4. Square wave generator; 5. Reactor; 6. First capacitor; 7. Resistor; 8. Second capacitor; 9. First diode; 10. First IGBT; 11. Second diode; 12. Second IGBT; 13. First zinc oxide surge arrester MOV1. Detailed Implementation

[0049] The method of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0050] Unless otherwise defined, the methodological or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0051] The terms "comprising" or "including" as used in this invention mean that the element preceding the term encompasses the element listed after the term, and do not exclude the possibility of encompassing other elements. Terms such as "inner," "outer," "upper," and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. In this invention, unless otherwise explicitly specified and limited, the term "attached" and similar terms should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two elements or the interaction relationship between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] Example

[0053] like Figure 13 and Figure 14 As shown, depending on the installation location, traditional DC transfer switches are divided into metallic circuit breaker (MRTB), earth circuit breaker (ERTB), neutral bus switch (NBS), and neutral bus grounding switch (NBGS). The metallic circuit breaker (MRTB) and earth circuit breaker (ERTB) are used to switch between earth circuit operation mode and metallic circuit operation mode, while the neutral bus switch (NBS) is mainly used to isolate the neutral bus from the converter, and the neutral bus grounding switch (NBGS) is used to quickly connect the neutral point to the substation grounding grid when the grounding electrode fails.

[0054] The traditional DC-DC transfer switch uses a self-excited oscillation method: it utilizes the negative impedance characteristics of the SF6 switch to excite the resonant current in the LC branch connected in parallel with it, so that the current superimposed on the SF6 switch generates a zero-crossing point. After the SF6 switch extinguishes its arc, the LC branch and MOV are sequentially switched into the branch to be disconnected, and a transient voltage TIV is established to transfer the current to the branch to be connected.

[0055] like Figures 1-12 As shown, the present invention provides a high-capacity compact DC transfer switch, including a long-term current-carrying branch, a high-frequency oscillation breaking branch, and an energy-dissipating branch. The long-term current-carrying branch, the high-frequency oscillation breaking branch, and the energy-dissipating branch are connected in parallel. The long-term current-carrying branch is set as a gas switch 1. During normal operation, the gas switch 1 is closed to provide a path for the load current. When switching current, the gas switch 1 is opened, and the arc voltage can reach several hundred volts, driving the current to transfer from the long-term current-carrying branch to the high-frequency oscillation breaking branch.

[0056] The energy-consuming branch is equipped with a second zinc oxide surge arrester MOV22 to limit the rise of the voltage across the DC transfer switch and to absorb the energy on the line to be disconnected and the energy fed into the DC transfer switch from the sending-end converter station.

[0057] The high-frequency oscillation interruption branch includes a temporary current-carrying branch and a resonant branch, with the temporary current-carrying branch and the resonant branch connected in parallel.

[0058] The temporary current-carrying branch includes a vacuum trigger gap 3 and a square wave generator 4, with the vacuum trigger gap 3 and the square wave generator 4 connected in series. The resonant branch includes a reactance 5 and a first capacitor 6, with the reactance 5 and the first capacitor 6 connected in series.

[0059] During normal operation, the temporary current-carrying branch is in the open state. When switching current, the vacuum trigger gap 3 and the square wave generator 4 on the temporary current-carrying branch are triggered to conduct for temporary current carrying. At the same time, the excitation effect of the square wave voltage is used to realize the high-frequency opening of the vacuum trigger gap 3, so that the resonant current i in the resonant branch is increased. LC As the current increases, it causes the current superimposed on the temporary current-carrying branch to cross zero, transferring the current from the temporary current-carrying branch to the resonant branch.

[0060] The square wave generator 4 is a controllable square wave voltage source composed of power electronic devices. The square wave generator 4 includes a switching branch, a buffer branch, and a clamping branch. The switching branch, buffer branch, and clamping branch are connected in parallel. The switching branch includes a first IGBT module and a second IGBT module. The first IGBT module and the second IGBT module are connected in parallel.

[0061] The buffer branch includes a resistor 7 and a second capacitor 8, which are used to buffer the current transferred to the clamping branch after the switch branch is turned off. The resistor 7 and the second capacitor 8 are connected in series. The clamping branch is set as a first zinc oxide surge arrester MOV113, which is used to establish a high-level voltage for the square wave generator 4.

[0062] The first IGBT module includes a first diode 9 and a first IGBT 10. There are four first diodes 9, which are connected to the first IGBT 10 in a bridge configuration. The two first diodes 9 in the upper bridge arm are connected to a common cathode, and the two first diodes 9 in the lower bridge arm are connected to a common anode. The anode of the first IGBT 10 is connected to the common cathode of the two first diodes 9 in the upper bridge arm, and the cathode of the first IGBT 10 is connected to the common anode of the two first diodes 9 in the lower bridge arm.

[0063] The second IGBT module includes a second diode 11 and a second IGBT 12. There are four second diodes 11, which are connected to the second IGBT 12 in a bridge configuration. The two second diodes 11 in the upper bridge arm are connected to a common cathode, and the two second diodes 11 in the lower bridge arm are connected to a common anode. The anode of the second IGBT 12 is connected to the common cathode of the two second diodes 11 in the upper bridge arm, and the cathode of the second IGBT 12 is connected to the common anode of the two second diodes 11 in the lower bridge arm.

[0064] The first diode 9 and the second diode 11 have bidirectional conduction capability. During normal operation, the first IGBT module and the second IGBT module are in the off state. When converting current, the first IGBT module and the second IGBT module are first fully turned on to temporarily carry current, and then the first IGBT module and the second IGBT module are turned on alternately to enable the square wave generator 4 to output a square wave voltage.

[0065] A control method for a high-capacity, compact DC-DC transfer switch includes the following steps:

[0066] S1: During normal operation, gas switch 1 remains closed, and current flows through the long-term current-carrying branch. Vacuum trigger gap 3 and square wave generator 4 are not connected. After gas switch 1 ignites, it generates an arc voltage with an amplitude of several hundred volts. Under the action of the arc voltage, vacuum trigger gap 3 is broken down and conducts current. The current in the long-term current-carrying branch is quickly transferred to the temporary current-carrying branch, and gas switch 1 extinguishes the arc.

[0067] S2: When switching current, the gas switch 1 is opened, and the vacuum trigger gap 2, the first IGBT module and the second IGBT module are started.

[0068] S3: Since the dielectric recovery speed of gas switch 1 is slow, the current cannot be interrupted immediately. Wait for a dielectric recovery time, which is set to 1ms. After the dielectric is recovered, gas switch 1 restores its insulation capability and controls square wave generator 4 to perform high-frequency interruption. The current is transferred from the temporary flow branch to the resonant branch.

[0069] Step S3 specifically includes the following steps:

[0070] S31: Turn off the first IGBT module and the second IGBT module. The turn-off time of the first IGBT module is set to t1, and the turn-off time of the second IGBT module is set to t2.

[0071] In step S31, the turn-off time t1 of the first IGBT module is 1 / 4 of a switching cycle, and the turn-off time t2 of the second IGBT module is 3 / 4 of a switching cycle. The switching cycle is the reciprocal of the conduction frequency.

[0072] In this embodiment, the turn-off time t1 of the first IGBT module is 50us, and the turn-off time t2 of the second IGBT module is 150us.

[0073] S32: Alternately turn on the first IGBT module and the second IGBT module, with the turn-on frequency set to f. IGBT The duty cycle is set to 1 / 4. In this embodiment, the conduction frequency f IGBT Set to 5kHz;

[0074] S33: When the first IGBT module and the second IGBT module are alternately turned on, the square wave generator 4 outputs a square wave voltage, which excites the resonant current i in the resonant branch. LC The amplitude increases, and the circulating current i flowing through the temporary flow branch and the resonant branch... oc Increase;

[0075] In step S33, the amplitude of the square wave voltage is the residual voltage U of the first zinc oxide surge arrester MOV113. MOV1 The frequency f of the square wave voltage SVS Set to the on-frequency f IGBT Twice the frequency f of the square wave voltage SVS Specifically set as follows:

[0076] f SVS =2f IGBT ;

[0077] S34: When the current superimposed on the temporary current-carrying branch crosses zero, the vacuum trigger gap 3 extinguishes the arc, and the current is transferred from the temporary current-carrying branch to the resonant branch.

[0078] In step S34, the resonant frequency f of the resonant branch is... LC Specifically set as follows:

[0079] f LC =Nf SVS (N = 1, 2, 3...).

[0080] In this embodiment, the frequency f of the square wave voltage SVS With resonant frequency f LC The ratio is 1, that is, N=1, and the resonant frequency f LC It is 10kHz.

[0081] S4: The current continuously charges the first capacitor 6 until the voltage U across the second zinc oxide surge arrester MOV22 is reached. MOV2 As the voltage rises to the reference voltage, the current shifts from the temporary flow branch to the energy-consuming branch.

[0082] S5: The second zinc oxide surge arrester MOV22 starts, establishes the transient voltage TIV, absorbs the energy on the line to be interrupted and the energy fed into the DC conversion switch of the sending-end converter station, and the current is transferred to the next long-term current-carrying branch.

[0083] This embodiment uses the MRTB tripping to transfer current from the ground return line to the positive metal return line as an application scenario to illustrate the current transfer process of a high-capacity compact DC transfer switch in an ultra-high voltage DC transmission system.

[0084] Before the current conversion, i.e., before time t0 = 4.0s, the high-capacity compact DC-DC transfer switch of the MRTB is in the closed state, and the ground return current i e Gas switch 1, flowing through the long-term current-carrying branch, connects the positive metal return line between the sending and receiving busbars via another DC-DC changeover switch ERTB, disconnector switch S1, and disconnector switch S2. At this time, the positive metal return line and the ground return line operate in parallel. The ground return line current i... e and positive metal loop current i p The sum equals the negative metal loop current i n ;

[0085] At t0 = 4.0s, current conversion begins, gas switch 1 opens, vacuum trigger gap 3 is triggered and started, and the first and second IGBT modules in square wave generator 4 are triggered and turned on. Under the action of arc voltage, vacuum trigger gap 3 breaks down and conducts, the ground return current is transferred to the temporary current-carrying branch, and the current i of gas switch 1... k The current i in the temporary current-carrying branch drops to 0. TCP It rose to 7.3 kA.

[0086] Because the medium recovery speed of gas switch 1 is slow, the current cannot be interrupted immediately, otherwise gas switch 1 may be severely damaged.

[0087] After waiting approximately 1 ms, at t1 = 4.001 s, gas switch 1 returns to its insulating state. First, the first IGBT module is turned off for 50 μs, then the second IGBT module is turned off for 150 μs. The first and second IGBT modules are then alternately turned on at a frequency of 5 kHz, with a duty cycle of 1 / 4. At this time, the output amplitude U of square wave generator 4... MOV1 It has a voltage of 3.8kV and an output frequency of 10kHz.

[0088] Under the excitation of a square wave voltage, the current i in the resonant branch... LC The current i in the temporary current-carrying branch gradually increases, thus causing the current i TCP The amplitude gradually increases, and at t2 = 4.00141s, its amplitude is equal to the earth loop current i. eAt this time, the current i in the temporary current-carrying branch TCP Zero crossing, vacuum trigger gap 3 extinguishes arc, ground return current i e The charge is transferred to the resonant branch to charge the first capacitor.

[0089] The first capacitor 6 continues to charge until t3 = 4.00151s, at which point the second zinc oxide surge arrester MOV22 rises to the reference voltage. After the second zinc oxide surge arrester MOV22 operates, the current i of the second zinc oxide surge arrester MOV22... MOV2 The surge arrester MOV22, transitioning from the temporary flow branch to the energy dissipation branch, establishes a transient voltage TIV of 183kV. Under the influence of this transient voltage TIV, it absorbs energy from the ground return line and the energy fed into the MRTB from the sending-end converter station. The ground return line current i e The current gradually decreases and reaches 0 at t4 = 4.63s, at which point the current conversion is complete.

[0090] Therefore, the present invention adopts the above-mentioned high-capacity compact DC-DC converter switch and control method, using a gas switch as a long-term current-carrying switch and a vacuum trigger gap as an interruption and arc-extinguishing unit. By simulating the negative impedance characteristics of the SF6 switch through a square wave generator, the high-frequency interruption of the vacuum trigger gap is realized, which greatly reduces the amount of capacitors and inductors used in the LC resonant branch and improves the current interruption level of the DC-DC converter switch. It has the advantages of low cost, small footprint, and high current interruption capability.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the method of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the method of the present invention, and these modifications or equivalent substitutions should not cause the modified method to deviate from the spirit and scope of the method of the present invention.

Claims

1. A high-capacity compact DC transfer switch, characterized by, It includes a long-term current-carrying branch, a high-frequency oscillation breaking branch, and an energy-dissipating branch. The long-term current-carrying branch, the high-frequency oscillation breaking branch, and the energy-dissipating branch are connected in parallel. The long-term current-carrying branch is set as a gas switch, and the energy-dissipating branch is set as a second zinc oxide surge arrester MOV2. The high-frequency oscillation breaking branch includes a temporary current-carrying branch and a resonant branch. The temporary current-carrying branch and the resonant branch are connected in parallel. The temporary current-carrying branch includes a vacuum trigger gap and a square wave generator, with the vacuum trigger gap and the square wave generator connected in series. The resonant branch includes a reactance and a first capacitor, with the reactance and the first capacitor connected in series. The square wave generator includes a switching branch, a buffer branch, and a clamping branch. The switching branch, buffer branch, and clamping branch are connected in parallel. The switching branch includes a first IGBT module and a second IGBT module. The first IGBT module and the second IGBT module are connected in parallel. The buffer branch includes a resistor and a second capacitor. The resistor and the second capacitor are connected in series. The clamping branch is set as a first zinc oxide surge arrester MOV1. The turn-off time t1 of the first IGBT module is 1 / 4 of a switching cycle, and the turn-off time t2 of the second IGBT module is 3 / 4 of a switching cycle. The switching cycle is the reciprocal of the conduction frequency.

2. A high-capacity compact DC transfer switch according to claim 1, characterized in that The first IGBT module includes a first diode and a first IGBT. There are four first diodes, which are connected to the first IGBT in a bridge configuration. The two first diodes in the upper bridge arm are connected to a common cathode, and the two first diodes in the lower bridge arm are connected to a common anode. The anode of the first IGBT is connected to the common cathode of the two first diodes in the upper bridge arm, and the cathode of the first IGBT is connected to the common anode of the two first diodes in the lower bridge arm.

3. A high-capacity compact DC transfer switch according to claim 2, characterized in that The second IGBT module includes a second diode and a second IGBT. There are four second diodes, which are connected to the second IGBT in a bridge configuration. The two second diodes on the upper bridge arm are connected to a common cathode, and the two second diodes on the lower bridge arm are connected to a common anode. The anode of the second IGBT is connected to the common cathode of the two second diodes on the upper bridge arm, and the cathode of the second IGBT is connected to the common anode of the two second diodes on the lower bridge arm.

4. A control method of a high-capacity compact direct current transfer switch according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: During normal operation, the gas switch remains closed, the vacuum trigger gap and the square wave generator are not triggered, and the current flows through the long-term current-carrying branch. S2: When switching current, the gas switch is opened, triggering the vacuum trigger gap, the first IGBT module and the second IGBT module. After the gas switch is opened and the arc is ignited, an arc voltage is generated, the vacuum trigger gap is broken down, and the current is forced to transfer from the long-term current-carrying branch to the temporary current-carrying branch. S3: After the gas switch restores its insulation capability, it performs high-frequency switching on the square wave generator, and the current is transferred from the temporary current-carrying branch to the resonant branch. S4: The current continuously charges the first capacitor until the voltage across the second zinc oxide arrester MOV2 rises to the reference voltage, and the current is transferred from the temporary current-carrying branch to the energy-dissipating branch. S5: The second zinc oxide surge arrester MOV2 operates, establishing a transient voltage TIV, absorbing the energy on the line to be interrupted and the energy fed into the DC conversion switch at the sending-end converter station, and the current is transferred to the next long-term current-carrying branch.

5. The control method of a high-capacity compact DC transfer switch according to claim 4, characterized by, Step S3 specifically includes the following steps: S31: Turn off the first IGBT module and the second IGBT module. The turn-off time of the first IGBT module is set to t1, and the turn-off time of the second IGBT module is set to t2. S32: alternately turn on the first IGBT module and the second IGBT module, and the turn-on frequency is set to f IGBT , and the turn-on duty ratio is set to 1 / 4; S33: when the first IGBT module and the second IGBT module are alternately turned on, the square wave generator outputs a square wave voltage, and the square wave voltage excites the resonant current of the resonant branch i LC The amplitude of the resonant current of the resonant branch increases, and the circulating current flowing through the temporary conduction branch and the resonant branch also increases i oc ​ S34: When the current superimposed on the temporary current-carrying branch crosses zero, the vacuum trigger gap extinguishes the arc, and the current is transferred from the temporary current-carrying branch to the resonant branch.

6. The control method of a high-capacity compact DC transfer switch according to claim 5, characterized by, In step S31, the turn-off time t1 of the first IGBT module is 1 / 4 of a switching cycle, and the turn-off time t2 of the second IGBT module is 3 / 4 of a switching cycle. The switching cycle is the reciprocal of the conduction frequency.

7. The control method for a high-capacity compact DC-DC transfer switch according to claim 6, characterized in that, In step S33, the amplitude of the square wave voltage is the residual voltage of the first zinc oxide surge arrester MOV1 U MOV1 The frequency of the square wave voltage is set to twice the on frequency f SVS The frequency of the square wave voltage is set to twice the on frequency f IGBT The frequency of the square wave voltage is set to twice the on frequency f SVS Specifically set to: f SVS =2 f IGBT ； In step S34, the resonant frequency of the resonant branch is... f LC Specifically set as follows: 。

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