High-capacity compact direct-current change-over switch and control method

Abstract

The invention discloses a high-capacity compact direct-current change-over switch and a control method, and relates to the technical field of electrical equipment, the high-capacity compact direct-current change-over switch comprises a long-term through-flow branch, a high-frequency oscillation on-off branch and an energy consumption branch, the long-term through-flow branch, the high-frequency oscillation on-off branch and the energy consumption branch are connected in parallel, the long-term through-flow branch is set as a gas switch, and the high-frequency oscillation on-off branch is set as a gas switch. The energy consumption branch is arranged to be a second zinc oxide arrester MOV2, the high-frequency oscillation on-off branch comprises a temporary through-flow branch and a resonance branch, and the temporary through-flow branch is connected with the resonance branch in parallel; a gas switch is used as a long-term through-flow switch, a vacuum trigger gap is used as an on-off arc extinguishing unit, the negative impedance characteristic of an SF6 switch is simulated through a square-wave generator, high-frequency on-off of the vacuum trigger gap is achieved, the use amount of capacitors and inductors of an LC resonance branch is greatly reduced, the current on-off level of the direct-current change-over switch is improved, and the service life of the direct-current change-over switch is prolonged. The device has the advantages of low cost, small occupied area and high current breaking capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment, and in particular to a large-capacity compact DC conversion switch and a control method thereof. Background Art

[0002] The DC converter switch is a key device in the UHVDC transmission system. In the event of a fault in the converter valve or DC line, DC line maintenance, or changes in system power demand, the DC converter switch needs to change the system's operating mode and transfer the load current on the branch to be cut off to the branch to be passed.

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

[0004] However, the post-arc dielectric recovery speed of the SF6 switch is slow. To prevent the SF6 switch from re-breaking down after arc extinction, the LC resonant frequency is low, and the amount of LC branch capacitance and inductance is large. This results in high cost, large size, and large space for DC conversion switches.

[0005] In addition, the arc voltage amplitude of the SF6 switch is limited, only a few thousand volts, resulting in a low conversion current level of the DC conversion switch, which is difficult to meet the system requirements of high-level DC engineering current.

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

[0007] The purpose of the present invention is to provide a large-capacity compact DC conversion switch and a control method thereof, so as to overcome the deficiencies of the prior art, improve the current interruption capability of the DC conversion switch, and reduce the cost and floor space.

[0008] To achieve the above-mentioned objectives, the present invention provides a large-capacity compact DC conversion switch, including a long-term current flow branch, a high-frequency oscillation breaking branch and an energy consumption branch. The long-term current flow branch, the high-frequency oscillation breaking branch and the energy consumption branch are connected in parallel. The long-term current flow branch is set as a gas switch, and the energy consumption branch is set as a second zinc oxide lightning arrester MOV2. The high-frequency oscillation breaking branch includes a temporary current flow branch and a resonant branch. The temporary current flow branch is connected in parallel with the resonant branch.

[0009] Preferably, the temporary flow branch includes a vacuum trigger gap and a square wave generator, the vacuum trigger gap and the square wave generator are connected in series, and the resonant branch includes a reactance and a first capacitor, the reactance and the first capacitor are connected in series.

[0010] Preferably, the square wave generator includes a switching branch, a buffer branch and a clamping branch, the switching branch, the buffer branch and the 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, and the clamping branch is set as a first zinc oxide lightning arrester MOV1.

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

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

[0013] A control method for a large-capacity compact DC transfer switch comprises 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 flow 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 arcing, an arc voltage is generated, the vacuum trigger gap is broken down, and the current is forced to transfer from the long-term flow branch to the temporary flow branch.

[0016] S3: After the gas switch recovers its insulation capacity, the square wave generator is interrupted at high frequency, and the current is transferred from the temporary flow branch to the resonant branch;

[0017] S4: The current continues to charge the first capacitor until the voltage across the second zinc oxide lightning arrester MOV2 rises to the reference voltage, and the current is transferred from the temporary flow branch to the energy consumption branch;

[0018] S5: The second zinc oxide lightning arrester MOV2 operates, establishing a transient voltage TIV, absorbing the energy on the line to be disconnected and the energy fed into the DC transfer switch by 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, and the conduction frequency is set to f IGBT , the on-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 of the resonant branch. LC The amplitude of the current 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 flow branch passes through zero, the vacuum trigger gap extinguishes the arc, and the current is transferred from the temporary flow branch to the resonant branch.

[0024] Preferably, in step S31 , the off time t1 of the first IGBT module is 1 / 4 of the switching cycle, and the off time t2 of the second IGBT module is 3 / 4 of the switching cycle, where the switching cycle is the inverse 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 lightning arrester MOV1. MOV1 , the frequency of the square wave voltage f SVS Set to the conduction frequency f IGBT Twice the frequency of the square wave voltage f SVS The specific settings are:

[0026] f SVS =2f IGBT ;

[0027] In step S34, the resonant frequency f of the resonant branch is LC The specific settings are:

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

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

[0030] (1) This solution uses a gas switch as a long-term flow switch to transfer the load current from the long-term flow switch to the temporary flow branch. This process can be achieved solely by the arc voltage of the gas switch without adding an additional power source or control. It has the advantages of high reliability and easy control.

[0031] (2) This solution uses a vacuum trigger gap as the arc-breaking unit, which greatly reduces the amount of capacitance and inductance used in the LC resonant branch, and has the advantages of low cost and small footprint;

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

[0033] The method scheme of the present invention is further described in detail below through the drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0037] Figure 4 Schematic diagram of the dynamic characteristics of the square wave generator of the present invention;

[0038] Figure 5 Schematic diagram of the autonomous resonance process based on the square wave generator of the present invention;

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

[0040] Figure 7 This is a working principle diagram before current conversion in an application scenario where the MRTB is opened to transfer the current on the earth return line to the positive metal return line;

[0041] Figure 8 This is a working principle diagram of the current transfer from the long-term flow branch to the temporary flow branch in the application scenario of the embodiment of the present invention, in which the MRTB is opened to transfer the current on the earth return line to the positive metal return line;

[0042] Figure 9This is a working principle diagram of high-frequency interruption after the gas switch restores the insulation state in an application scenario where the MRTB is opened to transfer the current on the earth return line to the positive metal return line in an embodiment of the present invention;

[0043] Figure 10 This is a working principle diagram of the transient voltage established after the second zinc oxide lightning arrester MOV2 is actuated in the application scenario of the present invention, where the MRTB is opened to transfer the current on the earth return line to the positive metal return line;

[0044] Figure 11 Schematic diagram of the current transfer process when the MRTB in an embodiment of the present invention transfers the current from the earth return line to the positive metal return line. (a) is a schematic diagram of the transfer of system load current, (b) is a schematic diagram of the current transfer within the large-capacity compact DC transfer switch and the voltage change of the square wave generator, and (c) is a schematic diagram of the voltage change across the second zinc oxide lightning arrester MOV2.

[0045] Figure 12 Detailed schematic diagram of the current and voltage changes within a large-capacity compact DC transfer switch when used as an MRTB to transfer current from the earth return line to the positive metal return line in an embodiment of the present invention. (a) is a schematic diagram of the changes in the internal current and square wave voltage, and (b) is a schematic diagram of the changes in the voltage across the second zinc oxide lightning arrester MOV2.

[0046] Figure 13 This is a schematic diagram of the configuration of traditional DC transfer switches in UHVDC transmission systems;

[0047] Figure 14 This is the topological principle diagram of the traditional DC conversion switch.

[0048] Among them: 1. gas switch; 2. second zinc oxide lightning arrester MOV2; 3. vacuum trigger gap; 4. square wave generator; 5. reactance; 6. first capacitor; 7. resistor; 8. second capacitor; 9. first diode; 10. first IGBT; 11. second diode; 12. second IGBT; 13. first zinc oxide lightning arrester MOV1. DETAILED DESCRIPTION

[0049] The method scheme of the present invention is further described below through the drawings and examples.

[0050] Unless otherwise defined, technical terms or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0051] The words “include” or “comprising” and similar words used in the present invention mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of also including other elements. The orientation or position relationship indicated by the terms “inside”, “outside”, “upper”, “lower”, etc. is based on the orientation or position relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention. When the absolute position of the described object changes, the relative position relationship may also change accordingly. In the present invention, unless otherwise clearly stipulated and limited, the terms such as “attachment” should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral whole; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0052] Example

[0053] like Figure 13 and Figure 14 As shown in the figure, according to different installation locations, traditional DC transfer switches are divided into metal return line transfer circuit breakers (MRTB), earth return line transfer circuit breakers (ERTB), neutral bus switches (NBS), and neutral bus grounding switches (NBGS). The metal return line transfer circuit breakers (MRTB) and earth return line transfer circuit breakers (ERTB) are used to switch between earth return line operation mode and metal return line operation mode, while the neutral bus switch (NBS) is mainly used to isolate the neutral bus from the converter. The neutral bus grounding switch (NBGS) is used to quickly connect the neutral point to the substation grounding grid when a grounding electrode fault occurs.

[0054] The technical route of the traditional DC conversion switch is the passive self-excited oscillation route: the negative impedance characteristics of the SF6 switch are used to excite the resonant current on the LC branch connected in parallel with it, so that the current superimposed on the SF6 switch has a zero crossing point. After the SF6 switch extinguishes the arc, the LC branch and the MOV are cut into the branch to be interrupted in turn, and a transient voltage TIV is established to transfer the current to the branch to be passed.

[0055] like Figures 1-12 As shown, the present invention provides a large-capacity compact DC conversion switch, including a long-term current flow branch, a high-frequency oscillation breaking branch and an energy consumption branch. The long-term current flow branch, the high-frequency oscillation breaking branch and the energy consumption branch are connected in parallel. The long-term current flow 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 converting current, the gas switch 1 is opened, the arc voltage can reach several hundred volts, and the driving current is transferred from the long-term current flow branch to the high-frequency oscillation breaking branch.

[0056] The energy consumption branch is set as the second zinc oxide lightning arrester MOV22 to limit the voltage rise at both ends of the DC conversion switch and absorb the energy on the line to be disconnected and the energy fed into the DC conversion switch by the sending-end converter station.

[0057] The high-frequency oscillation breaking branch comprises a temporary flow-through branch and a resonance branch, and the temporary flow-through branch is connected in parallel with the resonance branch.

[0058] The temporary flow branch includes a vacuum trigger gap 3 and a square wave generator 4, which are connected in series. The resonant branch includes a reactance 5 and a first capacitor 6, which are connected in series.

[0059] During normal operation, the temporary flow branch is in the disconnected state. When switching current, the vacuum trigger gap 3 and the square wave generator 4 on the temporary flow branch are triggered to conduct for temporary flow. At the same time, the square wave voltage is used to stimulate the vacuum trigger gap 3 to open at high frequency, so that the resonant current i LC It increases continuously, causing the current superimposed on the temporary flow branch to have a zero crossing point, and transferring the current from the temporary flow 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 switch branch, a buffer branch, and a voltage clamping branch. The switch branch, the buffer branch, and the voltage clamping branch are connected in parallel. The switch 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 to a first zinc oxide lightning arrester MOV113 to establish a high level voltage of the square wave generator 4.

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

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

[0064] The first diode 9 and the second diode 11 have bidirectional conduction capabilities. 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 all turned on to temporarily pass current, and then the first IGBT module and the second IGBT module are alternately turned on to enable the square wave generator 4 to output a square wave voltage.

[0065] A control method for a large-capacity compact DC transfer switch comprises the following steps:

[0066] S1: During normal operation, the gas switch 1 remains closed, current flows through the long-term flow branch, and current does not flow through the vacuum trigger gap 3 and the square wave generator 4. After the gas switch 1 ignites an arc, an arc voltage with an amplitude of several hundred volts is generated. Under the action of the arc voltage, the vacuum trigger gap 3 is broken down and conducts current. The current in the long-term flow branch is quickly transferred to the temporary flow branch, and the 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 period of dielectric recovery time (set to 1ms). After the dielectric is restored, the gas switch 1 recovers its insulation capacity and controls the 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 off time t1 of the first IGBT module is 1 / 4 of the switching cycle, and the off time t2 of the second IGBT module is 3 / 4 of the switching cycle, where the switching cycle is the inverse of the conduction frequency;

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

[0073] S32: Alternately turn on the first IGBT module and the second IGBT module, and the conduction frequency is set to f IGBT , the conduction 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 of the resonant branch. LC The amplitude of the current 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 lightning arrester MOV113. MOV1 , the frequency of the square wave voltage f SVS Set to the conduction frequency f IGBT Twice the frequency of the square wave voltage f SVS The specific settings are:

[0076] f SVS =2f IGBT ;

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

[0078] In step S34, the resonant frequency f of the resonant branch is LC The specific settings are:

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

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

[0081] S4: The current continues to charge the first capacitor 6 until the voltage U across the second zinc oxide lightning arrester MOV22 reaches MOV2 When the voltage rises to the reference voltage, the current is transferred from the temporary flow branch to the energy consumption branch;

[0082] S5: The second zinc oxide lightning arrester MOV22 starts, establishes a transient voltage TIV, absorbs the energy on the line to be disconnected and the energy fed into the DC transfer switch by the sending-end converter station, and transfers the current to the next long-term current-carrying branch.

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

[0084] Before the current conversion, that is, before time t0 = 4.0s, the large-capacity compact DC transfer switch as MRTB is in the closed state, and the earth return current i e The positive metal return line flows through the gas switch 1 on the long-term flow branch, and is connected between the sending end bus and the receiving end bus through another DC conversion switch ERTB, disconnector S1 and disconnector S2. At this time, the positive metal return line and the earth return line are in parallel operation. The earth return line current i e and the positive metal return current i p The sum is equal to the negative metal loop current i n ;

[0085] At t0=4.0s, current conversion begins, the gas switch 1 opens, the vacuum trigger gap 3 is triggered and started, the first IGBT module and the second IGBT module in the square wave generator 4 are triggered and turned on, and under the action of the arc voltage, the vacuum trigger gap 3 is broken down and turned on, and the earth return current is transferred to the temporary flow branch. The current i of the gas switch 1 k Drops to 0, the current i of the temporary flow branch TCP Increased to 7.3kA.

[0086] Since the medium recovery speed of the gas switch 1 is slow, the current cannot be interrupted immediately, otherwise the gas switch 1 may be severely broken down;

[0087] After waiting for about 1ms, when t1=4.001s, the gas switch 1 recovers the insulation state, first turns off the first IGBT module for 50us, then turns off the second IGBT module for 150us, and turns on the first and second IGBT modules alternately at a frequency of 5kHz, with a duty cycle of 1 / 4. At this time, the output amplitude of the square wave generator 4 is U MOV1 The output voltage is 3.8kV and the output frequency is 10kHz;

[0088] Under the excitation of square wave voltage, the current i in the resonant branch is LC Gradually increases, resulting in the current i of the temporary flow branch TCP The amplitude of the earth return current i eAt this time, the current i of the temporary flow branch TCP Zero crossing, vacuum trigger gap 3 extinguishes the arc, the earth return current i e Transfer to the resonant branch to charge the first capacitor;

[0089] The first capacitor 6 continues to charge until t3 = 4.00151s, the second zinc oxide lightning arrester MOV22 rises to the reference voltage, and after the second zinc oxide lightning arrester MOV22 is actuated, the current i MOV2 Transferred from the temporary flow branch to the energy consumption branch, the second zinc oxide lightning arrester MOV22 establishes a transient voltage TIV of 183kV. Under the action of the transient voltage TIV, it absorbs the energy on the earth return line and the energy fed into the MRTB by the sending-end converter station. The earth return line current i e It gradually decreases and drops to 0 at t4=4.63s, and the current conversion is completed.

[0090] Therefore, the present invention adopts the above-mentioned large-capacity compact DC conversion switch and control method, uses a gas switch as a long-term current-carrying switch, uses a vacuum trigger gap as an arc-breaking unit, and simulates the negative impedance characteristics of the SF6 switch through a square wave generator to achieve high-frequency interruption of the vacuum trigger gap, greatly reducing the amount of capacitor and inductor used in the LC resonant branch, improving the current interruption level of the DC conversion switch, and has the advantages of low cost, small footprint, and high current interruption capacity.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the method scheme of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary method personnel in this field should understand that they can still modify or replace the method scheme of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified method scheme to deviate from the spirit and scope of the method scheme of the present invention.

Claims

1. A large-capacity compact DC transfer switch, characterized in that: It includes a long-term flow branch, a high-frequency oscillation breaking branch and an energy consumption branch. The long-term flow branch, the high-frequency oscillation breaking branch and the energy consumption branch are connected in parallel. The long-term flow branch is set as a gas switch, and the energy consumption branch is set as a second zinc oxide lightning arrester MOV2. The high-frequency oscillation breaking branch includes a temporary flow branch and a resonant branch. The temporary flow branch is connected in parallel with the resonant branch.

2. A large-capacity compact DC transfer switch according to claim 1, characterized in that: The temporary flow branch includes a vacuum trigger gap and a square wave generator, the vacuum trigger gap and the square wave generator are connected in series, the resonant branch includes a reactance and a first capacitor, the reactance and the first capacitor are connected in series.

3. A large-capacity compact DC transfer switch according to claim 2, characterized in that: The square wave generator includes a switching branch, a buffer branch and a clamping branch. The switching branch, the buffer branch and the 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 to a first zinc oxide lightning arrester MOV1.

4. A large-capacity compact DC transfer switch according to claim 3, characterized in that: The first IGBT module includes a first diode and a first IGBT. The first diodes are provided in four configurations. The four first diodes are bridge-connected to the first IGBT. The two first diodes provided in the upper bridge arm are connected to a common cathode, and the two first diodes provided 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 provided in the upper bridge arm, and the cathode of the first IGBT is connected to the common anode point of the two first diodes provided in the lower bridge arm.

5. The large-capacity compact DC transfer switch according to claim 3, characterized in that: The second IGBT module includes a second diode and a second IGBT. The second diodes are set to four. The four second diodes are bridge-connected to the second IGBT. The two second diodes set in the upper bridge arm are connected to a common cathode, and the two second diodes set 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 set in the upper bridge arm, and the cathode of the second IGBT is connected to the common anode point of the two second diodes set in the lower bridge arm.

6. A control method for a large-capacity compact DC converter switch according to any one of claims 1 to 5, characterized in that: The following steps are involved: 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 flow 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 arcing, an arc voltage is generated, the vacuum trigger gap is broken down, and the current is forced to transfer from the long-term flow branch to the temporary flow branch. S3: After the gas switch recovers its insulation capacity, the square wave generator is interrupted at high frequency, and the current is transferred from the temporary flow branch to the resonant branch; S4: The current continues to charge the first capacitor until the voltage across the second zinc oxide lightning arrester MOV2 rises to the reference voltage, and the current is transferred from the temporary flow branch to the energy consumption branch; S5: The second zinc oxide lightning arrester MOV2 operates, establishing a transient voltage TIV, absorbing the energy on the line to be disconnected and the energy fed into the DC transfer switch by the sending-end converter station, and the current is transferred to the next long-term current-carrying branch.

7. The control method of a large-capacity compact DC converter switch according to claim 6, characterized in that: 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 conduction frequency is set to f IGBT , the on-duty cycle 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, which excites the resonant current i of the resonant branch. LC The amplitude of the current increases, and the circulating current i flowing through the temporary flow branch and the resonant branch oc Increase; S34: When the current superimposed on the temporary flow branch passes through zero, the vacuum trigger gap extinguishes the arc, and the current is transferred from the temporary flow branch to the resonant branch.

8. The control method of a large-capacity compact DC converter switch according to claim 7, characterized in that: In step S31 , the off time t1 of the first IGBT module is 1 / 4 of the switching cycle, and the off time t2 of the second IGBT module is 3 / 4 of the switching cycle, where the switching cycle is the inverse of the on-frequency.

9. The control method of a large-capacity compact DC converter switch according to claim 7, characterized in that: In step S33, the amplitude of the square wave voltage is the residual voltage U of the first zinc oxide lightning arrester MOV1. MOV1 , the frequency of the square wave voltage f SVS Set to the conduction frequency f IGBT Twice the frequency of the square wave voltage f SVS The specific settings are: in SVS =2f IGBT ; In step S34, the resonant frequency f of the resonant branch is LC The specific settings are: f LC =Nf SVS (N=1,2,3...)。

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