Control method of multi-port direct-current change-over switch based on controllable negative pressure source

Abstract

The invention discloses a control method of a multi-port direct current change-over switch based on a controllable negative voltage source, and belongs to the technical field of power system control. Before current conversion, the through-flow vacuum switch and the commutation vacuum switch are switched on, and other assemblies are switched off. When the current of the main branch to be cut off is in the forward direction, the through-flow vacuum switch is switched off, and the thyristors VT1 and VT4 and the forward conduction assembly are triggered to enable the current to flow to the commutation branch; and opening the commutation vacuum switch, adjusting the controllable square wave voltage source by using the same frequency / frequency division control method, so that the current is transferred to the LC branch, and finally, the current is transferred to other main branches through the action of the MOV. And when the current is reverse, the VT2, the VT3 and the reverse conducting assembly are triggered, and the subsequent steps are similar. The same frequency / frequency division control method is realized by controlling the switching frequency of the IGBT, and the methods are different when the number of the trigger branches is one or more. The control method is simple, current in different directions can be rapidly transferred, and the control methods of the sending end and the receiving end are consistent.

Description

Technical Field

[0001] The present invention relates to the technical field of power system control, and in particular to a control method for a multi-port DC conversion switch based on a controllable negative pressure source. Background Art

[0002] With the rapid development of high-voltage direct current transmission technology, the power system has put forward higher requirements for the flexibility, reliability and efficiency of operation mode switching. Traditional two-port DC conversion switches (such as MRTB and ERTB) rely on the coordinated work of mechanical switches and LC oscillation circuits to achieve current transfer, but there are the following prominent problems: Limitations of control strategies: Traditional control methods rely on the negative resistance characteristics of arc to excite LC oscillations. The current transfer speed is slow and the oscillation frequency cannot be actively adjusted, making it difficult to adapt to high-frequency requirements.

[0003] Lack of multi-port coordinated control: Existing multi-port switching requires multiple independent switches to operate in sequence and lacks a unified control strategy, which can easily lead to control timing mismatch and cause overvoltage or current shock.

[0004] Insufficient dynamic response capability: The resonant frequency of the traditional LC circuit is fixed and cannot be dynamically adjusted according to the system operating conditions, resulting in low energy absorption efficiency and excessive burden on the lightning arrester.

[0005] Low level of intelligence: Lack of real-time monitoring and adaptive control functions makes it difficult to meet the development needs of intelligent and digital modern power grids.

[0006] In addition, with the advancement of the "dual carbon" goal, the ban trend of SF6 gas is becoming increasingly obvious, and environmentally friendly arc extinguishing technology is urgently needed to replace it. Although the existing vacuum switches are green and environmentally friendly, their control strategies under high-frequency current transfer and complex working conditions are still immature, which restricts their widespread application in DC conversion switches. Summary of the invention

[0007] The purpose of the present invention is to provide a control method for a multi-port DC conversion switch based on a controllable negative pressure source, which realizes rapid current transfer and efficient energy management by dynamically adjusting the output frequency of a square wave voltage source.

[0008] To achieve the above object, the present invention provides a control method for a multi-port DC conversion switch based on a controllable negative pressure source. When the current of the main branch to be disconnected is a positive current (flowing from the busbar to the main branch), the control method of the multi-port DC conversion switch comprises the following steps: S1. Before conversion, the through-current vacuum switch and the commutation vacuum switch are both in the closed state, and the controllable square wave voltage source, the controllable negative pressure source, the controllable conduction switch, etc. are all in the off state; S2: When the current needs to be converted, the vacuum switch is opened and the thyristor VT in the controllable negative pressure source is triggered.1 and thyristor VT 4 , connect the negative pressure source to the commutation branch, and at the same time trigger the positive thyristor assembly or positive vacuum trigger gap connected to the main branch to be disconnected, forcing the current to transfer to the commutation branch, and the current vacuum switch extinguishes the arc; S3, the open gate commutation vacuum switch, controls the IGBT near the bus terminal in the controllable square wave voltage source through the same frequency / divided frequency control method f , so that the square wave voltage source output voltage U SWO The frequency of and the resonant frequency of the LC branch satisfy the same frequency / multiple frequency relationship, the excitation current is further transferred from the commutation vacuum switch to the LC branch, and the commutation vacuum switch extinguishes the arc; S4, the load current charges the capacitor of the LC branch, and the voltage across the MOV branch gradually rises to the MOV action voltage; S5, MOV operates, creates transient voltage, absorbs energy, and transfers load current to other main branches.

[0009] Preferably, when the current of the main branch to be disconnected is a reverse current (flowing from the main branch to the bus), the steps of the control method of the multi-port DC conversion switch are: S1. Before conversion, the through-current vacuum switch and the commutation vacuum switch are both in the closed state, and the controllable square wave voltage source, the controllable negative pressure source, the controllable conduction switch, etc. are all in the off state; S2: When the current needs to be converted, the vacuum switch is opened and the thyristor VT in the controllable negative pressure source is triggered. 2 and thyristor VT 3 , connect the negative pressure source to the commutation branch, and at the same time trigger the reverse thyristor assembly or reverse vacuum trigger gap connected to the main branch to be disconnected, forcing the current to transfer to the commutation branch, and the through-current vacuum switch extinguishes the arc; S3, the open gate commutation vacuum switch, controls the far bus terminal IGBT in the controllable square wave voltage source through the same frequency / divided frequency control method b , so that the square wave voltage source output voltage U SWO The frequency of and the resonant frequency of the LC branch satisfy the same frequency / multiple frequency relationship, the excitation current is further transferred from the commutation vacuum switch to the LC branch, and the commutation vacuum switch extinguishes the arc; S4, the load current charges the capacitor of the LC branch, and the voltage across the MOV branch gradually rises to the MOV action voltage; S5, MOV operates, creates transient voltage, absorbs energy, and transfers load current to other main branches.

[0010] Preferably, the controllable square wave voltage source is controlled by turning on and off the IGBT in the controllable square wave generator. U SWOThe frequency of and the resonant frequency of the LC branch satisfy the same frequency / multiple frequency relationship, that is, (N=1,2,3…).

[0011] Preferably, when the trigger branch is composed of one switch branch, the switching frequency of the IGBT itself is used to realize ,Right now , N can be any positive integer. The specific implementation method is: first turn off the IGBT 1 Make U swo Output high level and keep off state for 2N-1 capacitor voltage half-waves, wait for the capacitor voltage to reach the Nth positive peak value, and then turn on the IGBT 1 Make U swo Output low level and keep the on state for 1 half wave, wait for the capacitor voltage to drop from the forward voltage peak to the reverse voltage peak, and then turn off the IGBT again. 1 Make U swo Output high level, cycle into IGBT 1 The process of turning off 2N-1 half waves and turning on 1 half wave. The positive peak value of the capacitor voltage refers to when the capacitor terminal connected to the positive pole of the square wave voltage source is positive; the reverse peak value of the capacitor voltage refers to when the capacitor terminal connected to the positive pole of the square wave voltage source is negative.

[0012] Preferably, when the trigger branch is composed of n (n=2, 3, 4...) parallel switch branches, the cross triggering of multiple parallel IGBTs can be realized. , and the switching frequency of a single IGBT and the LC resonant frequency meet The specific implementation method is: first, turn off all IGBTs so that U swo Output high level, wait for the capacitor voltage to reach the positive peak, turn on the first branch IGBT 1 Make U swo Output low level, keep the on state for one capacitor voltage half wave, wait for the capacitor voltage to decrease from the forward voltage peak to the reverse voltage peak, and turn off the IGBT 1 Make U swo Output high level, wait for the capacitor voltage to reach the positive peak, turn on the second branch IGBT 2 Make U swo Output low level, keep the on state for 1 half wave, wait for the capacitor voltage to decrease from the forward voltage peak to the reverse voltage peak, and turn off the IGBT 2 Make U swoOutput high level. During the IGBT control cycle, each IGBT is triggered to conduct half a cycle in sequence to achieve , and the switching frequency of a single IGBT and the LC resonant frequency meet The forward peak value of the capacitor voltage refers to when the capacitor terminal connected to the positive electrode of the square wave voltage source is positive; the reverse peak value of the capacitor voltage refers to when the capacitor terminal connected to the positive electrode of the square wave voltage source is negative.

[0013] Therefore, the present invention adopts a control method of a multi-port DC conversion switch based on a controllable negative pressure source with the above structure, which has the following beneficial effects: The present invention has the advantage of a simple control method. It only needs to selectively control the controllable conduction switch, the controllable negative pressure source and the controllable square wave voltage source according to the current direction of the main branch to be disconnected, so that the main branch current in any direction can be transferred to the conversion branch and finally transferred to other main branches. The control method of the multi-port DC conversion switch installed at the sending end or the receiving end is consistent.

[0014] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a control flow chart of a multi-port DC conversion switch based on a controllable negative pressure source according to an embodiment of the present invention; Figure 2 Schematic diagram of the implementation principle of the controllable square wave voltage source control method according to an embodiment of the present invention (n=1, N=2); Figure 3 Schematic diagram of the implementation principle of the controllable square wave voltage source control method according to an embodiment of the present invention (n=2, N=1); Figure 4 It is a current schematic diagram of a conventional DC system operating in a negative pole-earth return line operation mode before the multi-port DC conversion switch based on the controllable negative pressure source in the embodiment of the present invention is actuated; Figure 5 This is a schematic diagram of an embodiment of the present invention in which a ground return line and a positive metal return line are connected in parallel during the operation of a multi-port DC conversion switch based on a controllable negative pressure source; Figure 6 It is a schematic diagram of the earth return line current flowing through the sending-end commutation branch during the operation of the multi-port DC conversion switch based on the controllable negative pressure source in an embodiment of the present invention; Figure 7 It is a schematic diagram of the gradual transfer of the earth return line current to the positive metal return line during the operation of the multi-port DC conversion switch based on the controllable negative pressure source in an embodiment of the present invention; Figure 8In the process of the multi-port DC conversion switch operation based on the controllable negative pressure source in the embodiment of the present invention, the square wave resonant DC circuit breaker establishes a transient voltage U tr Schematic diagram of the process; Fig. 9 It is a schematic diagram of the earth return line current being completely transferred to the positive metal return line after the multi-port DC conversion switch based on the controllable negative pressure source according to the embodiment of the present invention is actuated; Fig.10 It is a schematic diagram of an intermediate state in the switching process when the multi-port DC conversion switch based on the controllable negative pressure source switches the negative electrode-earth return line operation mode to the negative electrode-metal return line operation mode in an embodiment of the present invention; Fig.11 The present invention is a schematic diagram of an intermediate state when a square wave resonant DC circuit breaker is disconnected when a negative pole-earth return line operation mode is switched to a negative pole-metal return line operation mode in a multi-port DC conversion switch based on a controllable negative pressure source in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0017] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] Example like Figure 1 The present invention provides a control method for a multi-port DC conversion switch based on a controllable negative pressure source. Assuming that the load current of the main branch x needs to be transferred to the main branch y through the multi-port DC conversion switch, the steps of the method are: S1, before switching, the vacuum switch K x , the commutation vacuum switch VCB is in a closed state, the controllable square wave voltage source, the controllable negative pressure source, the controllable conduction switch, etc. are in an off state; S2. When current conversion is required, close the vacuum switch K y, open gate through-current vacuum switch K x , at this time, the main branch x and the main branch y are running in parallel; S3, determine the current direction of the main branch x, if it is a positive current (the current is from the busbar to the main branch x), then trigger the thyristor VT 1 and VT 4 Cut the negative pressure source into the commutation branch to trigger the IGBT f1 The temporary current branch is forward-conducted, and the forward thyristor assembly connected to the main branch x is triggered at the same time, forcing the current to transfer to the commutation branch, and the current vacuum switch extinguishes the arc; if it is a reverse current (the current is from the main branch x to the busbar), the thyristor VT is triggered 2 and VT 3 Cut the negative pressure source into the commutation branch to trigger the IGBT b1 The temporary current-carrying branch is reversely conducted, and the reverse thyristor assembly connected to the main branch x is triggered at the same time, forcing the current to transfer to the commutation branch, and the current-carrying vacuum switch extinguishes the arc; S4, open the gate to commutate the vacuum switch VCB, and control the IGBT through the same frequency / divided frequency control method fi or IGBT bi The opening and closing of the controllable square wave voltage source makes the controllable square wave voltage source output a square wave voltage with the same frequency or a multiple of the LC resonant frequency, and the excitation current is further transferred from the commutation vacuum switch to the LC branch, and the commutation vacuum switch extinguishes the arc; S5, the load current is transferred to the LC branch to the capacitor C 1 Charging, the voltage at both ends of the MOV branch gradually rises, and the voltage at both ends rises to MOV 1 When the operating voltage of MOV 1 The action establishes transient voltage, absorbs energy, and the load current begins to transfer to the main branch y.

[0019] In order to further illustrate the operation process of the present invention, Figure 6 Taking the switching from the negative pole-earth return line operation mode to the negative pole-metal return line operation mode as an example, the current transfer process when the multi-port DC conversion switch is in operation is explained.

[0020] like Figure 2 As shown in the figure, the implementation process of the frequency-same / frequency-divided control method is explained by taking n=1 and N=2 as an example. VCB is the control signal of the commutation vacuum switch VCB, S VCB When it is in the close state, it means that VCB receives the closing signal. VCB When it is in the open state, it means that VCB receives the trip signal. IGBT1 For IGBT 1 The control signal, S IGBT1 When it is in the on state, it means IGBT 1 Receive the conduction signal, S IGBT1When it is in the off state, it means that the IGBT 1 Receive shutdown signal. U SWO is the square wave voltage output by the square wave voltage source SWO, U E for U SWO The amplitude of . f IGBT1 is the switching frequency of IGBT1, and the square wave voltage U SWO The frequencies are equal. U C1 is the capacitance C 1 The voltage across the terminals, i LC is the current in the LC branch, and the frequency of the two is f LC .time t 0 Previously, the commutation vacuum switch VCB was opened and the IGBT 1 At time t0, the IGBT is in the on state. 1 Turn off and keep turning off 3 half waves, square wave voltage U SWO Rise to U E , capacitor voltage U C1 It rises to the first positive peak during the first half-wave, and maintains constant amplitude oscillation during the second and third half-waves. Considering the line loss, the second positive peak is slightly lower than the first positive peak. At the second positive peak, the IGBT 1 Turn on and continue to conduct 1 half wave, square wave voltage U SWO Wait for the capacitor voltage to drop to zero. U C1 When the forward voltage peak decreases to the reverse voltage peak, the IGBT is turned off again. 1 , after one half wave, the capacitor voltage U C1 When the off state continues to the third half wave, the capacitor voltage U C1 It rises to the fourth forward peak. Considering the line loss, the fourth forward peak is slightly lower than the third forward peak. The IGBT is turned on again at the fourth peak. 1 , cycle into the IGBT 1 The process of turning off 3 half waves and turning on 1 half wave. U C1 The oscillating current i LCThe amplitude of gradually increases, causing the current in the temporary current-carrying branch to pass through zero, and the commutation vacuum switch VCB to extinguish.

[0021] like Figure 3 As shown in the figure, the implementation process of the frequency-same / frequency-divided control method is explained by taking n=2 and N=1 as an example. VCB is the control signal of the commutation vacuum switch VCB, S VCB When it is in the close state, it means that VCB receives the closing signal. VCB When it is in the open state, it means that VCB receives the trip signal. IGBT1 For IGBT 1 The control signal, S IGBT1 When it is in the on state, it means IGBT 1 Receive the conduction signal, S IGBT1 When it is in the off state, it means that the IGBT 1 Receive shutdown signal. IGBT2 For IGBT 2 The control signal, S IGBT2 When it is in the on state, it means IGBT 2 Receive the conduction signal, S IGBT2 When it is in the off state, it means that the IGBT 2 Receive shutdown signal. U SWO is the square wave voltage output by the square wave voltage source SWO, U E for U SWO The amplitude of . f IGBT1 is the switching frequency of IGBT1, and the square wave voltage U SWO The frequencies are equal. U C1 is the capacitance C 1 The voltage across the terminals, i LC is the current in the LC branch, and the frequency of the two is f LC .time t 0 Previously, the commutation vacuum switch VCB was opened and the IGBT 1 is in the on state. t 0 When the IGBT is turned off 1 And continue for 1 half wave, the square wave voltage source output voltage U E , capacitor voltage U C1 When the first positive peak occurs, the IGBT is turned on. 1And continue for 1 half wave, the square wave voltage source output voltage is zero, and then drops to the first reverse peak, at which time the IGBT is turned off. 1 And continue for 3 half waves. Capacitor voltage U C1 When it rises to the second positive peak, the IGBT is turned on 2 and lasts for one half wave, the capacitor voltage U C1 Drops to the reverse peak value, at which time the IGBT is turned off 2 And continue for 3 half waves. Capacitor voltage U C1 When it rises to the third positive peak, the IGBT is turned on 1 And continue for 1 half wave, and then turn off for 3 half waves. 1 and IGBT 2 At the forward peak, it conducts one half wave and turns off three half waves. U C1 The oscillating current i LC The amplitude of gradually increases, causing the current in the temporary current-carrying branch to pass through zero, and the commutation vacuum switch VCB to extinguish.

[0022] Compared with the case where the trigger branch consists of 1 switch branch, the same frequency / divided frequency control method when the trigger branch consists of n (n=2,3,4...) parallel switch branches has more technical advantages. By reducing the switching frequency of the IGBT and cross-triggering the IGBT, , without changing the IGBT trigger frequency, the divergence speed of the resonant current is accelerated.

[0023] like Figure 4 As shown, the system operates in the negative pole-earth return line operation mode, and the earth return line current The main branch 2 flowing through the sending-end multi-port DC conversion switch, the negative metal return line current Flows through the main branch 5 of the multi-port DC conversion switch at the sending end and the main branch C of the multi-port DC conversion switch at the receiving end. 2 , K 5 , K C The commutation vacuum switches VCB and VCB are both in the closed state, and the through-current vacuum switch K 1 , K 3 , K 4 , K A , K B All are in the open state, and the controllable conduction switch, controllable negative pressure source and controllable square wave voltage source of the multi-port DC conversion switch at the sending / receiving end are all in the off state. R n , L nRepresents the equivalent resistance and equivalent inductance of the positive metal loop, R p , L p Represents the equivalent resistance and equivalent inductance of the negative metal loop, R e , L e represents the equivalent resistance and equivalent inductance of the grounding electrode line, k1, k2, k3 and k4 are isolation switches for current transfer, and VT1, VT2, VT3 and VT4 are thyristor components that control the conduction direction of the negative voltage source. 2 is the negative pressure source, U C2 is the voltage of the negative voltage source. Vt is the diode that provides the current path. SWO is the controllable square wave voltage source, inductor L and capacitor C 1 It forms the LC branch of the square wave resonant DC circuit breaker and the MOV lightning arrester 1 It forms a lightning arrester branch.

[0024] like Figure 5 As shown, in response to the operating mode switching command, the vacuum switch K 4 Close the switch, main branch 2 and main branch 4 run in parallel, the earth return current Positive metal return current The sum is equal to the negative metal return current .

[0025] like Figure 6 As shown, the open-circuit vacuum switch K 2 , due to the main branch 2 current It is a positive current, so it triggers the VT in the controllable negative pressure source at the same time. 1 and VT 4 Switch the negative pressure source to the commutation branch and trigger the IGBT in the controllable square wave power supply f1 The positive thyristor assembly connected to the main branch 2 provides a path for the load current. Under the action of the negative voltage source, a circulating current is generated between the main branch 2 and the commutation branch. , the current in the commutation branch increases rapidly, and the current in the main branch 2 Rapidly decrease to zero, through the vacuum switch K 2 The arc is extinguished and the earth return current flows through the sending end commutation branch.

[0026] like Figure 7 As shown, the through-flow vacuum switch K 2 After the arc is extinguished, the controllable negative pressure source is composed of the diode component V t After the vacuum switch VCB is opened and the controllable square wave voltage source is triggered to generate a square wave voltage source with the same frequency as the LC resonant frequency, the square wave resonant DC circuit breaker establishes a transient voltage U tr, the current in the commutation branch is gradually transferred to the main branch 4, that is, the current in the earth return line is gradually transferred to the positive metal return line.

[0027] like Figure 8 As shown, the square wave resonant DC circuit breaker establishes a transient voltage U tr The process is as follows: First, under the action of the square wave voltage of the same frequency, the resonant current The amplitude gradually increases. When the current superimposed on the commutation vacuum switch VCB passes through zero, VCB extinguishes the arc and the commutation branch current is transferred to the LC branch. Then, the current To capacitor C 1 Charging, when the arrester MOV 1 When the current at both ends rises to the operating voltage, the MOV 1 Action, commutation branch current Transferred to the MOV branch, the MOV absorbs energy and creates a transient voltage U tr , commutation branch current Gradually decreases to zero.

[0028] like Fig. 9 As shown, the earth return line current is completely transferred to the positive metal return line, and the VT in the controllable negative pressure source 1 and VT 4 The forward thyristor assembly connected to the main branch returns to the off state, and the operation mode switching is completed.

[0029] like Fig.10 As shown, in t 0 =4.0s ago, negative metal return line current =5kA, positive metal return current =0.4kA, main branch 2 current =4.6kA, at this time the earth return line and the positive metal return line run in parallel.

[0030] t 0 When the DC converter at the sending end responds to the operation mode switching instruction, the vacuum switch K is opened and the current is passed. 2 And trigger the thyristor VT in the controllable negative voltage source 1 and VT 4 Cut the negative pressure source into the commutation branch and trigger the IGBT in the controllable square wave power supply f1 The forward thyristor assembly connected to the main branch 2 provides a path for the load current, such as Fig.11 As shown, the current i 2 Drops to zero, the commutation branch current rises to the level of the earth return current.

[0031] like Fig.11 As shown, in t 1 =4.00095s, open the commutation vacuum switch VCB and turn off the IGBT f1 , so that the square wave voltage source output voltage U E , subsequent cross-triggering of IGBT f1 and IGBT f2 , so that the square wave voltage source outputs a voltage wave with a frequency of 10kHz, which is the same as the resonant frequency of the LC branch. Under the action of the square wave, the LC branch current amplitude The value gradually increases. When the temporary current branch current When the commutation vacuum switch VCB extinguishes the arc, the commutation branch current Transfer to LC branch.

[0032] Current To charge the capacitor, When the voltage across the arrester reaches the operating voltage, the commutation branch current Gradually transferred to MOV branch, arrester MOV 1 A transient voltage of 148 kV is established, forcing the earth return current to transfer to the positive metal return. Fig.10 As shown, the commutation branch current Gradually decreases, the positive metal return current Gradually rising, When the commutation branch current Drop to zero, controllable VT in negative pressure source 1 and VT 4 The forward thyristor assembly connected to the main branch returns to the off state, and the operation mode switching is completed. Therefore, the present invention adopts the above-mentioned control method of a multi-port DC conversion switch based on a controllable negative pressure source, which has the advantage of a simple control method. It only needs to selectively control the controllable conduction switch, the controllable negative pressure source and the controllable square wave voltage source according to the current direction of the main branch to be disconnected, so that the main branch current in any direction can be transferred to the conversion branch and finally transferred to other main branches. The control method of the multi-port DC conversion switch installed at the sending end or the receiving end is consistent.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A control method for a multi-port DC conversion switch based on a controllable negative pressure source, characterized in that: When the current of the main branch to be disconnected is a forward current, the following steps are included: S1. Before conversion, the through-current vacuum switch and the commutation vacuum switch are both in the closed state, and the controllable square wave voltage source, the controllable negative pressure source, and the controllable conduction switch are all in the off state; S2, open the vacuum switch, trigger the thyristors VT1 and VT4 in the controllable negative pressure source, and trigger the forward conducting component connected to the main branch to be disconnected, forcing the current to transfer to the commutation branch; S3, opening the gate to commutate the vacuum switch, and controlling the frequency of the controllable square wave voltage source to meet the same frequency or multiple frequency relationship with the resonant frequency of the LC branch through the same frequency / multiple frequency control method, and transferring the excitation current to the LC branch; S4, the load current charges the capacitor of the LC branch, and the voltage across the MOV branch gradually rises to the MOV action voltage; S5, MOV operates, creates transient voltage, and transfers the load current to other main branches.

2. The control method of a multi-port DC conversion switch based on a controllable negative pressure source according to claim 1, characterized in that: When the current of the main branch to be disconnected is a reverse current, the following steps are included: S1. Before conversion, the through-current vacuum switch and the commutation vacuum switch are both in the closed state, and the controllable square wave voltage source, the controllable negative pressure source, and the controllable conduction switch are all in the off state; S2, open the vacuum switch, trigger the thyristors VT2 and VT3 in the controllable negative pressure source, and trigger the reverse conduction component connected to the main branch to be disconnected, forcing the current to transfer to the commutation branch; S3, opening the gate to commutate the vacuum switch, and controlling the frequency of the controllable square wave voltage source to meet the same frequency or multiple frequency relationship with the resonant frequency of the LC branch through the same frequency / multiple frequency control method, and transferring the excitation current to the LC branch; S4, the load current charges the capacitor of the LC branch, and the voltage across the MOV branch gradually rises to the MOV action voltage; S5, MOV operates, creates transient voltage, and transfers the load current to other main branches.

3. A control method for a multi-port DC conversion switch based on a controllable negative pressure source according to claim 1 or 2, characterized in that: The same frequency / divided frequency control method is implemented by controlling the IGBT switching frequency in the controllable square wave voltage source, satisfying: ； in, .

4. The control method of a multi-port DC conversion switch based on a controllable negative pressure source according to claim 3, characterized in that: When the trigger branch consists of one switch branch, the frequency relationship is realized by the switching frequency of the IGBT itself. The specific steps are: Turn off IGBT1 and maintain 2N-1 capacitor voltage half waves; When the capacitor voltage reaches the Nth positive peak, IGBT1 is turned on and maintained for one half wave; The above shutdown and conduction process is repeated to form a periodic square wave output.

5. The control method of a multi-port DC conversion switch based on a controllable negative pressure source according to claim 3, characterized in that: When the trigger branch is composed of n parallel switch branches, n ≥ 2, the frequency relationship is achieved by cross-triggering multiple IGBTs. The specific steps are: Turn off all IGBTs in sequence and wait for the capacitor voltage to reach the positive peak; Trigger the IGBT of each branch to conduct half a cycle in sequence; The switching frequency and LC resonant frequency of a single IGBT satisfy: 。

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