A multi-port DC conversion switch based on controllable negative pressure source

Abstract

This invention discloses a multi-port DC converter switch based on a controllable negative voltage source, belonging to the field of power equipment technology. It comprises X (X = 5 or 3) main branches, a commutation branch, and X sets of controllable conduction switches. The main branches are composed of flow-through vacuum switches, while the commutation branch consists of a controllable negative voltage source connected in series with a square-wave resonant DC circuit breaker. The five main branches on the sending end are connected to the sending-end positive rectifier, etc., while the three main branches on the receiving end are connected to the receiving-end positive rectifier, etc., all of which are connected to the commutation branch via controllable conduction switches. The controllable negative voltage source consists of a dual thyristor branch and a negative voltage source in parallel, and the square-wave resonant DC circuit breaker includes a temporary flow-through branch. This switch replaces SF6 switches with vacuum switches, improving environmental performance. It shares the commutation branch and lightning arrester, reducing the use of expensive equipment and lowering costs. A controllable square-wave voltage source is used to excite high-frequency oscillation in the LC branch, reducing component size. It also enables rapid current transfer in different directions, improving system response speed.

Description

Technical Field

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

[0002] In conventional DC transmission systems, in situations such as converter valve or DC line failures, DC line maintenance, and changes in system power demand, the DC converter switch and disconnector must work together to switch the system operating mode to ensure system stability, safety, and efficiency.

[0003] like Figure 1 As shown, the DC transfer switch is a two-port switch consisting of a flow branch, a commutation branch, and an energy absorption branch. The flow branch consists of a mechanical switch; the commutation branch is formed by an LC oscillating circuit; and the energy absorption branch is composed of a lightning arrester group. The DC transfer switch operates as follows: In response to a trip signal, the mechanical switch contacts separate, generating an arc between the contacts, and the arc resistance exhibits a nonlinear change. Due to the negative impedance of the arc, the oscillating current in the LC circuit diverges and oscillates. When the sum of the load current and the oscillating current superimposed on the flow branch passes through zero, the arc in the mechanical switch extinguishes, and the load current transfers to the commutation branch. The load current charges capacitor C. When the voltage across the lightning arrester rises to its operating voltage, the arrester activates to absorb energy and establish a transient voltage, transferring the load current to the energy absorption branch. The lightning arrester absorbs the energy, reducing the load current to zero, and current conversion is complete.

[0004] Since the DC transfer switch is a two-port switch, and the conventional DC transmission system has multiple necessary operating mode switching requirements, it is necessary to install multiple DC transfer switches in the conventional DC transmission system to meet different operating mode switching requirements. Figure 2 As shown in the figure, depending on the lines connected to the ports, the DC transfer switches in UHVDC transmission projects are subdivided into metal return transfer switches MRTB, earth return transfer switches ERTB, neutral bus switches NBS and neutral bus grounding switches NBGS.

[0005] The MRTB's ports are connected to the sending neutral busbar and the sending grounding electrode. Its primary function is to transfer the load current from the lower-impedance earth return to the higher-impedance positive / negative metallic return, completing the switch from single-pole earth return to single-pole metallic return operation. The ERTB's ports are connected to the sending neutral busbar and the positive and negative metallic return lines. Its primary function is to transfer the load current from the positive / negative metallic return to the earth return, completing the switch from single-pole metallic return to single-pole earth return operation. The NBS1 ports are connected to the sending neutral busbar and the sending positive rectifier, the NBS2 ports are connected to the sending neutral busbar and the sending negative inverter, the NBS3 ports are connected to the receiving neutral busbar and the receiving positive rectifier, and the NBS4 ports are connected to the receiving neutral busbar and the receiving negative inverter. The main functions of NBS1, NBS2, NBS3, and NBS4 are: after the converter is locked, the NBS opens to switch from bipolar operation to unipolar earth return operation. The ports of NBGS1 are connected to the neutral busbar and the sending-end grounding grid, respectively; the ports of NBGS2 are connected to the neutral busbar and the receiving-end grounding grid, respectively. The main function of the NBGS is to close when a grounding line fault occurs, providing a grounding point for the DC system, allowing unbalanced positive and negative currents to flow through the grounding grid.

[0006] In summary, traditional DC transmission systems rely on two-port DC transfer switches (such as metal return transfer switches (MRTBs) and earth return transfer switches (ERTBs)) to switch operating modes. These switches often use sulfur hexafluoride (SF6) gas as the arc extinguishing medium, which presents the following problems:

[0007] Poor environmental protection: SF6 is a strong greenhouse gas and will cause great harm to the environment if leaked;

[0008] Bulky equipment: The traditional LC resonant circuit has a low frequency (<5kHz), requiring large-capacity capacitors and reactors, resulting in a bulky device.

[0009] High cost: Multiple independent two-port switches are required to meet different switching requirements, and the lightning arrester needs to absorb a large amount of energy, which is expensive.

[0010] Existing DC transfer switches from manufacturers like ABB rely on the negative resistance of the SF6 arc to transfer current, but their dielectric recovery speed is limited, making it difficult to meet high-frequency demands. Furthermore, the lack of multi-port switches necessitates the configuration of multiple independent switches, which occupies a large area and is complex to control. Summary of the Invention

[0011] The purpose of the present invention is to provide a multi-port DC conversion switch based on a controllable negative pressure source, which solves the problems of bulky equipment, high cost and poor environmental protection in the prior art by sharing a commutation branch and a controllable conduction switch.

[0012] To achieve the above objectives, the present invention provides a multi-port DC transfer switch based on a controllable negative pressure source, comprising X main branches, a commutation branch, and X groups of controllable conduction switches, where X = 5 or 3. Each of the X main branches is composed of a flow-through vacuum switch, and the commutation branch is composed of a controllable negative pressure source and a square wave resonant DC circuit breaker connected in series.

[0013] Preferably, the multi-port DC transfer switch at the sending end of a conventional DC transmission system has five main branches. Of the five main branches, main branches 1, 2, 3, 4, and 5 respectively electrically connect the sending-end positive rectifier, the sending-end grounding electrode wire, the sending-end grounding grid, the positive / negative metal return wires, and the sending-end negative inverter to the sending-end neutral busbar. The commutation branch is connected to the sending-end neutral busbar. The remote busbar ends of the five main branches are each connected to the remote busbar end of the commutation branch via a set of controllable conduction switches.

[0014] Preferably, the multi-port DC transfer switch at the receiving end of a conventional DC power transmission system has three main branches. Of the three main branches, main branch A, main branch B, and main branch C respectively electrically connect the receiving end positive rectifier, the receiving end grounding grid, and the receiving end negative inverter to the receiving end neutral busbar. The commutation branch is connected to the receiving end neutral busbar. The remote busbar ends of each of the three main branches are connected to the remote busbar end of the commutation branch via a set of controllable conduction switches.

[0015] Preferably, the controllable negative voltage source includes two dual thyristor branches connected in parallel and one negative voltage source. When the main branch current needs to be transferred, the negative voltage source is switched into the commutation branch by triggering the thyristor to realize the transfer of load current. The first dual thyristor branch is composed of thyristor VT1 and thyristor VT2 connected in series with a common cathode, and the second dual thyristor branch is composed of thyristor VT3 and thyristor VT4 connected in series with a common anode; the anode of the thyristor VT1 is connected to the cathode of the thyristor VT3, and a terminal is led out from the connection, which is the near bus terminal of the controllable negative voltage source; the anode of the thyristor VT2 is connected to the cathode of the thyristor VT4, and a terminal is led out from the connection, which is the far bus terminal of the controllable negative voltage source; the negative voltage source is composed of a pre-charge container and a diode assembly connected in reverse parallel, and the function of the diode assembly is to provide a path for the load current after the current is transferred to the commutation branch; the negative electrode of the pre-charge container is connected to the common cathode point of the first dual thyristor branch, and the positive electrode of the pre-charge container is connected to the common anode point of the second dual thyristor branch.

[0016] Preferably, the square wave resonant DC circuit breaker comprises a temporary current-passing branch, an LC branch and an MOV branch connected in parallel;

[0017] The temporary flow branch is composed of a commutation vacuum switch and a controllable square wave voltage source in series, which is used to transfer the load current of the main branch; the LC branch is composed of an inductor and a capacitor in series, which is used to generate an oscillating current to make the current on the temporary flow branch pass through zero; the MOV branch is composed of a metal zinc oxide lightning arrester, which is used to absorb energy and establish a transient voltage to transfer the load current to other main branches.

[0018] Preferably, the controllable square wave voltage source is composed of a trigger branch, a clamping branch and a buffer branch in parallel. The trigger branch is composed of n switch branches (n=1,2,3…) in parallel, so that the trigger branch can continuously switch between the on state and the off state at a certain frequency; the buffer branch is composed of a resistor and a capacitor in series. When the trigger branch is turned off, the load current is transferred to the buffer branch to charge the capacitor, so that the voltage at both ends of the clamping branch rises rapidly to the arrester action voltage; the clamping branch is composed of a metal zinc oxide arrester. When the trigger branch is turned off, the clamping branch can maintain the output voltage of the controllable square wave voltage source equal to the residual voltage of the arrester; the i-th switch branch (i=1,2,3…,n) is composed of two IGBT components with common emitters in series, and the IGBT near the bus end is an IGBT. fi , the IGBT at the far bus end is IGBT bi , each IGBT component is connected in reverse parallel with a diode to achieve bidirectional current flow in the trigger branch; all IGBTs near the bus end of the n switch branches are IGBTs f , all IGBTs at the far bus end are IGBTs b .

[0019] Preferably, the controllable conduction switch can be composed of a thyristor assembly. When the thyristor assembly is used to connect the main branch 2, the main branch 3, the main branch 4 and the commutation branch, a bidirectional conduction structure needs to be adopted; when the thyristor assembly is used to connect the main branch 1, the main branch 5 and the commutation branch, only a unidirectional conduction structure needs to be adopted; when the thyristor assembly is used to connect the main branch B and the commutation branch, a bidirectional conduction structure needs to be adopted; when the thyristor assembly is used to connect the main branch A, the main branch C and the commutation branch, only a unidirectional conduction structure needs to be adopted. The bidirectional conduction structure is composed of two thyristor assemblies connected in reverse parallel, the thyristor assembly whose conduction direction is consistent with the direction of the current flowing out of the neutral busbar of the sending / receiving end through the commutation branch is a forward thyristor assembly, and the thyristor assembly whose conduction direction is opposite to the direction of the current flowing out of the neutral busbar of the sending / receiving end through the commutation branch is a reverse thyristor assembly; the unidirectional conduction structure is one thyristor assembly, the thyristor assembly connected to the main branch 1 and the main branch C is a forward thyristor assembly, and the thyristor assembly connected to the main branch 5 and the main branch A is a reverse thyristor assembly.

[0020] Preferably, the controllable conduction switch can be composed of a vacuum trigger gap. When the vacuum trigger gap is used to connect the main branch 2, the main branch 3, the main branch 4 and the commutation branch, a bidirectional conduction structure needs to be adopted; when the vacuum trigger gap is used to connect the main branch 1, the main branch 5 and the commutation branch, only a unidirectional conduction structure needs to be adopted; when the vacuum trigger gap is used to connect the main branch B and the commutation branch, a bidirectional conduction structure needs to be adopted; when the vacuum trigger gap is used to connect the main branch A, the main branch C and the commutation branch, only a unidirectional conduction structure needs to be adopted. The bidirectional conductive structure is composed of two vacuum trigger gaps connected in reverse parallel. The vacuum trigger gap whose conductive direction is consistent with the current direction flowing out of the neutral busbar of the sending / receiving end through the commutation branch is a forward vacuum trigger gap, and the vacuum trigger gap whose conductive direction is opposite to the current direction flowing out of the neutral busbar of the sending / receiving end through the commutation branch is a reverse vacuum trigger gap. The unidirectional conductive structure is composed of one vacuum trigger gap. The vacuum trigger gaps connecting the main branch 1 and the main branch C are the forward vacuum trigger gaps, and the vacuum trigger gaps connecting the main branch 5 and the main branch A are the reverse vacuum trigger gaps.

[0021] Therefore, the present invention adopts a multi-port DC conversion switch based on a controllable negative pressure source with the above structure, which has the following beneficial effects:

[0022] The present invention uses a shared commutation branch and a controllable conduction switch to transfer the load current of multiple main branches and use a square wave resonant DC circuit breaker to quickly transfer the load current to other main branches to complete the operation mode switch, thereby reducing the use of high-priced equipment such as high-voltage capacitors and metal lightning arresters, and greatly reducing the cost of the DC conversion switch. The controllable negative pressure source is cut into the commutation branch, which greatly increases the speed of load current transfer to the commutation branch, reduces the performance requirements of the main branch current-carrying vacuum switch, and reduces the cost of the DC conversion switch. The vacuum switch is used instead of the sulfur hexafluoride switch as the main switch of the square wave resonant DC circuit breaker, which has the advantage of being green and environmentally friendly. The controllable square wave voltage source is used to cause the oscillating current of the LC branch to diverge and oscillate, further reducing the cost of the high-voltage capacitor and high-voltage reactor.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the topological structure of an existing DC conversion switch;

[0025] Figure 2 A schematic diagram of a DC transfer switch configuration scheme in an existing conventional DC transmission system;

[0026] Figure 3A schematic diagram of the topological structure of a multi-port DC transfer switch based on a controllable negative pressure source according to an embodiment of the present invention and its connection to the sending / receiving end lines of a conventional DC transmission system;

[0027] Figure 4 This is a schematic diagram of the connection of commutation branch lines according to an embodiment of the present invention;

[0028] Figure 5 FIG. 1 is a schematic diagram of the circuit connection of a controllable square wave voltage source SWO according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0030] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" 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 object being described changes, the relative positional relationship may also change accordingly.

[0031] Example 1

[0032] like Figure 3 As shown, a topology of a multi-port DC conversion switch based on a controllable negative pressure source and its connection method in a conventional DC transmission system.

[0033] The sending-end multi-port DC converter consists of five main branches, a commutation branch, and a controllable conduction switch. Main branches 1, 2, 3, 4, and 5 are sequentially connected to the positive rectifier, grounding electrode, grounding grid, positive / negative metal return wires, negative inverter, and the sending-end neutral busbar. Each of the five main branches consists of a flow-through vacuum switch. The commutation branch is connected to the main branch via the busbar at one end and via a controllable conduction switch at the other end (in this embodiment, the controllable conduction switch is a thyristor assembly). Since the current directions of the grounding electrode, grounding grid, and positive / negative metal return lines are not unique, the controllable conduction switches connecting main branch 2, main branch 3, and main branch 4 are composed of two thyristor assemblies connected in reverse parallel; since the current of the positive rectifier is always a forward current (flowing out of the busbar), the controllable conduction switch connected to main branch 1 is a forward conduction switch; since the current of the negative inverter is always a reverse current (flowing to the busbar), the controllable conduction switch connected to main branch 5 is a reverse conduction switch.

[0034] like Figure 4 As shown in Figure 1, the commutation branch consists of a controllable negative voltage source and a square wave resonant DC circuit breaker. The controllable negative voltage source consists of a pre-charge capacitor C2, a pass diode V t The commutation branch is composed of four thyristor assemblies, of which thyristors VT1 and VT3 are the thyristor assemblies near the busbar end, and thyristors VT2 and VT4 are the thyristor assemblies far from the busbar end. If the commutation branch needs to conduct forward current, thyristors VT1 and VT4 are triggered to cut the negative voltage source into the commutation branch; if the commutation branch needs to conduct reverse current, thyristors VT2 and VT3 are triggered to cut the negative voltage source into the commutation branch.

[0035] like Figure 4 As shown in Figure 1, the square-wave resonant DC circuit breaker consists of a temporary current-passing branch, an LC branch, and an MOV branch. The temporary current-passing branch includes a commutation vacuum switch (VCB) and a controllable square-wave voltage source (SWO); the LC branch includes a high-voltage capacitor (C1) and a high-voltage reactor (L); and the MOV branch includes a lightning arrester (MOV1).

[0036] The working process of the square wave resonant DC circuit breaker is as follows: the load current flows through the temporary flow branch, the VCB is opened, and the contacts begin to separate. Then, according to the direction of the load current, the controllable square wave voltage source is selectively triggered so that the square wave voltage and the LC resonant frequency meet the same frequency / multiplied frequency relationship. An oscillating current begins to generate in the LC branch and gradually diverges. The oscillating current is superimposed on the temporary flow branch to extinguish the arc between the VCB contacts. The load current is transferred to the LC branch to charge capacitor C1. The voltage across the MOV branch gradually increases. When the voltage across the two ends rises to the operating voltage of MOV1, MOV1 operates to establish a transient voltage, absorbs energy, and the load current is transferred to other main branches.

[0037] like Figure 5As shown in Figure 1, the controllable square wave voltage source SWO consists of a trigger branch, a clamping branch, and a buffer branch. The trigger branch is composed of n switch branches connected in parallel, and each switch branch is an IGBT. fi and IGBT bi Composition (i=1,2,3,…,n), and IGBT fi The diode V is connected in reverse parallel fi , IGBT bi The diode V is connected in reverse parallel bi The clamping branch is composed of the arrester MOV1; the buffer branch is composed of the resistor R and the capacitor C3.

[0038] The working principle of the controllable square wave voltage source SWO is to control the opening and closing of the IGBT by the same frequency / divided frequency control method, so that the output voltage of the square wave voltage source is U SWO The frequency of the LC branch meets the frequency multiplication relationship with the resonant frequency of the LC branch. When the IGBT is turned on, the load current flows through the trigger branch. U SWO When the IGBT is turned off, the load current is transferred to the buffer branch to charge the capacitor C3, and the voltage across the clamping branch rises. When it rises to the action voltage of MOV1, MOV1 is actuated, and the output voltage of the square wave voltage source is U SWO Rising to the residual pressure of MOV1 U E .

[0039] When the trigger branch consists of one switch branch, the frequency-co-frequency / frequency-divided control method is achieved by reducing the switching frequency of the IGBT. The specific implementation method is: first turn off IGBT1 and keep it in the off state for 2N-1 half-waves of the capacitor voltage, wait for the capacitor voltage to reach the Nth forward peak, turn on IGBT1 and keep it in the on state for 1 half-wave, wait for the capacitor voltage to drop from the forward voltage peak to the reverse voltage peak, turn off IGBT1 again, and cycle into the process of turning off IGBT1 for 2N-1 half-waves and turning on IGBT1 for 1 half-wave.

[0040] Example 2

[0041] like Figure 3As shown, the receiving-end multi-port DC converter includes three main branches, a commutation branch, and a controllable conduction switch. Main branches A, B, and C are sequentially connected to the positive inverter, the grounding grid, the negative inverter, and the receiving-end neutral busbar. Each of the three main branches consists of a flow-through vacuum switch. The commutation branch is connected to the main branch via the busbar at one end and to the controllable conduction switch at the other end (in this embodiment, the controllable conduction switch is composed of a thyristor assembly). Because the current direction of the grounding grid is not unique, the controllable conduction switch connecting main branch B consists of two thyristor assemblies connected in anti-parallel. Since the current of the positive inverter is always in the reverse direction (flowing toward the busbar), the controllable conduction switch connected to main branch A is a reverse-conducting switch. Since the current of the negative inverter is always in the forward direction (flowing out of the busbar), the controllable conduction switch connected to main branch C is a forward-conducting switch. Its working principle is similar to that of the sending end, and efficient current transfer is achieved through a controllable negative pressure source and a square wave resonant DC circuit breaker.

[0042] Therefore, the present invention adopts the above-mentioned structure of a multi-port DC converter switch based on a controllable negative pressure source, replacing SF6 switches with vacuum switches, eliminating greenhouse gas emissions and conforming to the trend of green energy. Sharing the commutation branch and lightning arrester reduces the number of core components such as high-voltage capacitors and reactors, reducing equipment costs. A controlled square wave voltage source excites high-frequency oscillations in the LC branch, significantly reducing the size of the capacitors and inductors. Through a controllable negative pressure source and frequency-coordinated / frequency-multiplied control methods, rapid current transfer in different directions is achieved, improving system response speed.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A multi-port DC converter switch based on a controllable negative pressure source, characterized in that: The invention comprises X main branches, a commutation branch and X groups of controllable conduction switches, wherein X=5 or 3, each of the X main branches is composed of a flow-through vacuum switch, and the commutation branch is composed of a controllable negative pressure source and a square wave resonant DC circuit breaker connected in series; The multi-port DC transfer switch at the sending end of a conventional DC transmission system comprises five main branches, which are respectively connected to a sending-end positive rectifier, a sending-end grounding electrode line, a sending-end grounding grid, positive / negative metal return lines, a sending-end negative inverter, and a sending-end neutral busbar; the commutation branch is connected to the sending-end neutral busbar; the remote busbar ends of the five main branches are each connected to the remote busbar end of the commutation branch via a set of controllable conduction switches; The multi-port DC conversion switch at the receiving end of a conventional DC transmission system includes three main branches, which are respectively connected to the receiving end positive rectifier, the receiving end grounding grid, the receiving end negative inverter and the receiving end neutral bus; the commutation branch is connected to the receiving end neutral bus; the remote bus ends of the three main branches are connected to the remote bus ends of the commutation branch through controllable conduction switches.

2. The multi-port DC conversion switch based on a controllable negative pressure source according to claim 1, characterized in that: The controllable negative pressure source includes two dual thyristor branches connected in parallel and a negative pressure source; One of the dual thyristor branches is a thyristor 、 The other dual thyristor branch is composed of a common cathode in series, and a thyristor 、 Common anode series composition; The negative pressure source is composed of a pre-charge container and a diode assembly connected in reverse parallel, the negative electrode of the pre-charge container is connected to the common cathode point of the first dual thyristor branch, and the positive electrode is connected to the common anode point of the second dual thyristor branch.

3. The multi-port DC conversion switch based on a controllable negative pressure source according to claim 1, characterized in that: The square wave resonant DC circuit breaker includes a temporary current-passing branch, an LC branch and an MOV branch connected in parallel; The temporary flow branch is connected in series with a commutation vacuum switch and a controllable square wave voltage source; The LC branch is connected in series with a reactor and a capacitor; The MOV branch is composed of a metal zinc oxide arrester.

4. The multi-port DC conversion switch based on a controllable negative pressure source according to claim 1, characterized in that: The controllable conduction switch is a thyristor assembly or a vacuum trigger gap; When the current direction of the main branch is not unique, a bidirectional conduction structure is adopted, that is, two thyristor components or vacuum trigger gaps are connected in reverse parallel; When the current direction of the main branch is unique, a unidirectional conduction structure is adopted, that is, a single thyristor component or a vacuum trigger gap.

5. The multi-port DC conversion switch based on a controllable negative pressure source according to claim 3, characterized in that: The controllable square wave voltage source comprises a trigger branch, a clamping branch and a buffer branch connected in parallel; The trigger branch is composed of n switch branches connected in parallel, where n is a positive real number; The buffer branch is composed of a resistor and a capacitor in series; The clamping branch is composed of a metal zinc oxide arrester.

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