Multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation

Abstract

The present invention discloses a multi-terminal hybrid high-voltage direct current circuit breaker based on capacitor commutation, comprising a main circuit breaker unit, a capacitor commutation unit and an energy absorption unit, wherein the main circuit breaker unit comprises a plurality of circuit breaker circuits, wherein the plurality of circuit breaker circuits are correspondingly connected in series on a plurality of transmission lines in a multi-terminal direct current transmission system, and each circuit breaker circuit is used to disconnect the fault current on the transmission line where it is located; the capacitor commutation unit is connected in parallel to the plurality of circuit breaker circuits, and is used to provide a low-voltage branch circuit for the circuit breaker circuit on the transmission line where a short circuit fault occurs to ensure its normal disconnection, and to cut off the fault current by using the self-shutdown function; the energy absorption unit is connected in parallel to the capacitor commutation unit, and is used to absorb energy and limit overvoltage. The multi-terminal hybrid high-voltage direct current circuit breaker based on capacitor commutation provided by the present invention utilizes a capacitor commutation unit to realize the clearing of multi-line fault currents, which can effectively reduce the reuse of semiconductor devices and has certain economy.

Description

Technical Field

[0001] The present invention belongs to the technical field of direct current circuit breakers, and more specifically, relates to a multi-terminal hybrid high-voltage direct current circuit breaker based on capacitor commutation. Background Art

[0002] DC power transmission can improve the utilization efficiency of renewable energy power generation and has been widely used in countries around the world. With the continuous expansion of the DC power grid, many key issues need to be solved, one of which is the DC short-circuit fault. At the same time, the interconnection degree of the power grid increases, and the number of transmission lines connected to the same transmission bus increases. Configuring a DC circuit breaker for each line alone will lead to excessively high costs for the transmission system. Therefore, it is necessary to develop an economical DC circuit breaker that can cut off multiple transmission line faults. Summary of the invention

[0003] In view of the defects of the prior art, the object of the present invention is to provide a multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation which can cut off multiple transmission line faults and has low cost.

[0004] To achieve the above object, the present invention provides a multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation, comprising a main circuit breaker unit, a capacitor commutation unit and an energy absorption unit, wherein:

[0005] The main circuit breaker unit comprises a plurality of circuit breaker circuits, wherein the plurality of circuit breaker circuits are connected in series to a plurality of transmission lines in the multi-terminal DC power transmission system, and each circuit breaker circuit is used to disconnect the fault current on the transmission line where it is located;

[0006] The capacitor conversion unit is connected in parallel to the plurality of circuit breaker circuits, and is used to provide a low-voltage branch circuit for the circuit breaker circuit on the transmission line where a short circuit fault occurs to ensure its normal breaking, and to cut off the fault current by using the self-shutdown function;

[0007] The energy absorption unit is connected in parallel to the capacitor conversion unit and is used for absorbing energy and limiting overvoltage.

[0008] In one embodiment, each of the circuit breaker circuits includes an ultra-fast mechanical switch and a load transfer switch connected in series, wherein the load transfer switch includes two IGBT tubes connected in reverse series, and each of the IGBT tubes is connected in reverse parallel with a diode.

[0009] In one embodiment, the capacitor commutation unit includes a capacitor commutation circuit and a plurality of diode bridges symmetrically anti-series connected at both ends of the capacitor commutation circuit, and the capacitor commutation circuit is connected in parallel to a plurality of circuit breaker circuits through the plurality of diode bridges; the capacitor commutation circuit includes an auxiliary lightning arrester branch, a commutation capacitor branch and two thyristor branches connected in symmetrical parallel, and the two thyristor branches each include a thyristor connected in series and a first mechanical switch; the auxiliary lightning arrester branch includes an auxiliary lightning arrester and a second mechanical switch connected in series, and the auxiliary lightning arrester branch is connected in series between the cathodes of the two thyristors; the commutation capacitor branch includes a commutation capacitor and a commutation inductor connected in series, and the commutation capacitor branch is connected in parallel to the auxiliary lightning arrester branch.

[0010] In one of the embodiments, the energy absorption unit includes a main lightning arrester, and the main lightning arrester is connected in parallel to both ends of the capacitor commutation circuit.

[0011] In one of the embodiments, when a short circuit fault is detected in a multi-terminal power transmission system, the fault current is controlled to be transferred to one of the thyristor branches, and at the same time, the load transfer switch on the transmission line where the short circuit fault occurs is turned off and the ultra-fast mechanical switch is started to open; after the ultra-fast mechanical switch is opened, the fault current is controlled to be transferred to the commutation capacitor branch; when the polarity of the commutation capacitor voltage in the commutation capacitor branch is reversed, the fault current is transferred to the main lightning arrester; when the current flowing through the main lightning arrester is reduced to zero, the auxiliary lightning arrester branch is triggered to limit the commutation capacitor voltage to a set value; one of the thyristor branches is turned off, and when one of the thyristor branches is turned off, the other thyristor branch is triggered to prepare for the next fault.

[0012] In general, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0013] (1) With the continuous development of flexible DC transmission networks, the scale of the grid continues to increase, and the number of transmission lines on the same bus will increase. The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation provided by the present invention can realize the clearing and reclosing functions of multi-line fault currents using only one capacitor commutation unit, which can effectively reduce the reuse of semiconductor devices and has certain economic efficiency.

[0014] (2) The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation provided by the present invention rationally utilizes the characteristic of charging the commutation capacitor on the power supply side, which can solve the problem of needing to equip the pre-energy storage capacitor with a charging circuit, and effectively reduce the overall size and cost of the circuit breaker.

[0015] (3) The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation provided by the present invention can effectively reduce the opening pressure of the mechanical switch and the energy absorption pressure of the lightning arrester. The cost of the internal components of the circuit breaker is relatively low, which has certain economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A principle block diagram of a multi-terminal hybrid high-voltage DC circuit breaker provided by the present invention;

[0017] Figure 2 A specific circuit diagram of a multi-terminal hybrid high-voltage DC circuit breaker in an embodiment provided by the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] Figure 1 : is a principle block diagram of a multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation provided by the present invention, such as Figure 1 As shown, it includes a main circuit breaker unit 100, a capacitor conversion unit 200 and an energy absorption unit 300. Among them, the main circuit breaker unit 100 includes a plurality of circuit breaker circuits, and the plurality of circuit breaker circuits are correspondingly connected in series on a plurality of transmission lines in a multi-terminal DC transmission system, and each circuit breaker circuit is used to disconnect the fault current on the transmission line where it is located; the capacitor conversion unit 200 is connected in parallel to the plurality of circuit breaker circuits, and is used to provide a low-voltage branch circuit for the circuit breaker circuit on the transmission line where a short circuit fault occurs to ensure its normal disconnection, and to cut off the fault current by using the self-shutdown function; the energy absorption unit 300 is connected in parallel to the capacitor conversion unit 200, and is used to absorb energy and limit overvoltage.

[0020] In a specific embodiment, the multi-terminal hybrid high-voltage direct current circuit breaker provided by the present invention includes a main circuit breaker unit 100, a capacitor conversion unit 200 and an energy absorption unit 300, and the main circuit breaker unit 100, the capacitor conversion unit 200 and the energy absorption unit 300 are all connected in parallel. Among them, the main circuit breaker unit 100 includes a plurality of circuit breaker circuits, each of which may include an ultra-fast mechanical switch UFD and a load transfer switch LCS connected in series, and the load transfer switch LCS includes two IGBT tubes connected in reverse series, and each IGBT tube is connected in reverse parallel with a diode. The capacitor commutation unit 200 includes a capacitor commutation circuit and a plurality of diode bridges symmetrically connected in anti-series at both ends of the capacitor commutation circuit. The capacitor commutation circuit is connected in parallel to a plurality of circuit breaker circuits through the plurality of diode bridges. The capacitor commutation circuit includes an auxiliary lightning arrester branch, a commutation capacitor branch, and two thyristor branches connected in parallel symmetrically. The two thyristor branches each include a thyristor connected in series and a first mechanical switch, wherein one thyristor branch includes a thyristor T2 and a mechanical switch S2, and the other thyristor branch includes a thyristor T1 and a mechanical switch S1. The auxiliary lightning arrester branch includes an auxiliary lightning arrester MOV1 and a second mechanical switch S connected in series, and the auxiliary lightning arrester branch is connected in series between the cathodes of the two thyristors. The commutation capacitor branch includes a commutation capacitor C and a commutation inductor L connected in series, and the commutation capacitor branch is connected in parallel to the auxiliary lightning arrester branch. The energy absorption unit 300 includes a main lightning arrester MOV, which is connected in parallel to both ends of the capacitor commutation circuit.

[0021] With respect to the multi-terminal hybrid high-voltage direct current circuit breaker topology structure provided above, the control method provided by the present invention is as follows: when a short circuit fault is detected in the multi-terminal power transmission system, the fault current is controlled to be transferred to one of the thyristor branches, and at the same time, the load transfer switch on the faulty transmission line is turned off and the ultra-fast mechanical switch is started to open; after the ultra-fast mechanical switch is opened, the fault current is controlled to be transferred to the commutation capacitor branch; when the polarity of the commutation capacitor voltage in the commutation capacitor branch is reversed, the fault current is transferred to the main lightning arrester MOV; when the current flowing through the main lightning arrester MOV is reduced to zero, the auxiliary lightning arrester branch MOV1 is triggered to limit the voltage of the commutation capacitor C to a set value; one of the thyristor branches is turned off, and when one of the thyristor branches is turned off, the other thyristor branch is triggered to prepare for the next fault.

[0022] In order to more clearly illustrate the solution of the present invention, taking a multi-terminal power transmission system including three power transmission lines as an example, the topological structure of the hybrid high-voltage DC circuit breaker provided by the present invention and the control method thereof are described in detail.

[0023] Figure 2 The specific circuit diagram of the hybrid high-voltage DC circuit breaker applied to three transmission lines is shown in FIG. Figure 2As shown, the main circuit breaker unit 100 includes ultra-fast mechanical switches UFD1~UFD3 and load transfer switches LCS1~LCS3, which are used to disconnect fault currents. The load transfer switches on each transmission line provide current zero-crossing points for the ultra-fast mechanical switches to ensure that the ultra-fast mechanical switches can disconnect at zero current. (2) The capacitor commutation unit 200 includes thyristors T1, T2, diodes D1~D6, commutation capacitor C, commutation inductor L, auxiliary lightning arrester MOV1 and mechanical switches S1, S2, S, which provide a low-impedance parallel branch for the main circuit breaker unit 100 during the disconnection period, ensuring that the main circuit breaker unit 100 does not need to withstand high voltage during the disconnection period. Since the semiconductor devices of the capacitor commutation unit 200 adopt a symmetrical connection structure, the capacitor commutation unit 200 can assist in cutting off the fault current regardless of the change of the voltage polarity of the commutation capacitor C; due to the symmetry and anti-series structure of the diode bridge, the diode bridge can be used to block the connection between the fault line and the non-fault line, ensuring that one capacitor commutation unit 200 can achieve fault clearing of multiple fault circuits. (3) The energy absorption unit 300 is composed of a main lightning arrester MOV, which is used to absorb energy and limit overvoltage. The circuit breaker circuits on the n transmission lines of the circuit breaker topology share a set of capacitor conversion units 200 and energy absorption units 300, which can effectively reduce the total cost of the circuit breaker of the transmission system and has certain economic advantages.

[0024] Specifically, the control method of the hybrid high-voltage DC circuit breaker applied to the three transmission lines provided above is as follows:

[0025] (1) When the multi-terminal DC transmission system operates normally, the thyristors T1, T2 and the mechanical switches S1, S are in the off state, and the mechanical switch S2 is in the on state.

[0026] (2) Assuming that a short-circuit fault occurs on the load 1 side, the fault current of transmission line 1 flows from left to right. Cutting off the circuit breaker circuit of transmission line 1 can isolate the fault. When the system determines that a short-circuit fault has occurred, it sends a turn-on signal to thyristor T2, and then immediately sends a turn-off signal to LCS1 and starts to open UFD1. The current is transferred from the branch where LCS1 and UFD1 are located to the branch where thyristor T2 and mechanical switch S2 are located. The current of the non-fault line is blocked by the diode bridge of the capacitor commutation unit. Therefore, during the operation of the capacitor commutation unit, the non-fault line will not affect the capacitor commutation unit.

[0027] (3) During the opening stage of the ultra-fast mechanical switch UFD1, the fault current is cut off by LCS1 to provide a current zero point for the opening of UFD1, and the thyristor T2 is turned on to provide a parallel low-impedance branch for the opening of UFD1 and LCS1, ensuring that UFD1 and LCS1 do not need to withstand high voltage during this stage. Therefore, during this stage, UFD1 can be opened smoothly under zero current and low withstand voltage.

[0028] (4) When UFD1 is disconnected to a certain opening distance, a turn-on command is issued to thyristor T1. Thyristor T2 begins to bear the reverse voltage of the commutation capacitor. The current flowing through thyristor T2 gradually transfers to the branch where thyristor T1, commutation capacitor C and commutation inductor L are located. Then the current of thyristor T2 passes through zero and is turned off. The power supply side continues to charge the commutation capacitor. The voltage polarity of the commutation capacitor changes from positive at the bottom and negative at the top to positive at the top and negative at the bottom, and reaches the arrester energy absorption voltage. At this time, the main arrester MOV is put into operation, begins to absorb energy and limit overvoltage, and the fault current is transferred from T1 to MOV. Then the current of thyristor T1 passes through zero and is turned off. The capacitor commutation unit exits operation. After a period of time, the current flowing through the main arrester MOV decreases to zero, and the MOV energy absorption ends.

[0029] (5) Then, a closing command is sent to the mechanical switch S, and the auxiliary lightning arrester MOV1 begins to absorb the energy stored in the commutation capacitor and limits the voltage of the commutation capacitor C to the set value. Then, an opening command is sent to the mechanical switch S, and the mechanical switch S opens at zero current.

[0030] (6) Then, an opening command is issued to the mechanical switch S2. At this time, the thyristors T1, T2, and the mechanical switch S1 are all in the off state. The mechanical switch S2 can be slowly opened at zero current and zero withstand voltage. After the mechanical switch S2 is successfully opened, a closing command is issued to the mechanical switch S1. When the mechanical switch S1 is successfully closed, the circuit breaker has met all the conditions for breaking the fault again, and can meet the system reclosing requirements. Since the time from the first disconnection of the fault current by the circuit breaker of the DC power grid to the reclosing of the circuit breaker is generally about 300ms, the action time of the internal components of the circuit breaker plus the action time of the mechanical switch during the fault is less than 300ms, and this solution is sufficient to meet the system reclosing requirements.

[0031] (7) If a short circuit occurs again (or the fault does not disappear after reclosing), the polarity of the commutation capacitor voltage will change. According to the symmetry of the semiconductor devices in the capacitor commutation unit, the operation sequence of thyristors T1 and T2 will be reversed, and the operation sequence of mechanical switches S1 and S2 will be reversed. The operation sequence of other components of the circuit breaker remains unchanged, which will not affect the circuit breaker's ability to interrupt the fault current again.

[0032] Similarly, it can be known that the topological structure and the principle of the control method of the multi-terminal hybrid high-voltage DC circuit breaker will not be described in detail in this embodiment.

[0033] Compared with the traditional DC circuit breaker, the multi-terminal hybrid high-voltage DC circuit breaker provided by the present invention has the following advantages: (1) Small capacitance and low cost. The thyristors T1, T2 and the mechanical switches S1, S2 are symmetrically connected. No matter how the voltage polarity of the commutation capacitor changes, a single capacitor can be used to realize the fault current disconnection and reclosing functions of multiple ports; the commutation capacitor is put into operation only after the UFD reaches a sufficient opening distance. At this time, the UFD can already withstand a certain voltage, and there is no need to use a large commutation capacitor to reduce the voltage required for the main circuit breaker to break. (2) Although the commutation capacitor C is an energy storage capacitor, there is no need to equip the commutation capacitor with a charging circuit. The main reasons are as follows: the circuit breaker structure utilizes the characteristic that the power supply side charges the commutation capacitor during the operation of the capacitor commutation unit, making the power supply side equivalent to the charging circuit of the commutation capacitor. The capacitor commutation unit operates once, and the voltage polarity of the commutation capacitor changes once; the symmetrical design of the capacitor commutation unit ensures that the change in the voltage polarity of the commutation capacitor will not affect the circuit breaker to cut off the fault current again. (3) The load transfer switch LCS does not need to use a large number of IGBTs in series, and the normal operation loss of the circuit breaker is small. UFD1 of the main circuit breaker does not need to withstand high voltage before the switch reaches a sufficient opening distance. When UFD1 reaches a sufficient opening distance, the voltage across the main circuit breaker can be tolerated by UFD1, ensuring that LCS1 does not need to withstand high voltage after disconnection. Therefore, the load transfer switch LCS1 does not need to use a large number of IGBTs in series, which not only reduces the voltage balancing difficulty and cost of the load transfer switch LCS1, but also effectively reduces the operating loss of the circuit breaker itself during normal operation of the system. (4) The circuit breaker topology can meet the system reclosing requirements. Whether the circuit breaker can realize the reclosing function mainly depends on whether its internal devices can recover in a short time after the circuit breaker is operated. The devices with longer operating time in the circuit breaker topology proposed in this paper mainly include lightning arresters and mechanical switches. The arrester energy absorption time is in the order of 10ms, and the action time of mechanical switches S, S1, and S2 is also in the order of 10ms. For the DC power grid's requirement of reclosing in hundreds of milliseconds, the internal components of the circuit breaker are sufficient to recover to the required state and meet the system's reclosing requirements. (5) Through a capacitor phase-changing unit and an energy absorption unit, the fault current of n ports can be cut off and the arrester energy absorption can be limited, which greatly reduces the cost of the circuit breaker of the entire transmission system, in line with the development trend of large-scale interconnection of DC power grids. (6) Only two sets of thyristors are used to cut off the fault current and break the fault current again after reclosing. The amount of semiconductor devices used is relatively small and the cost is low. (7) Although the DC circuit breaker topology uses three sets of mechanical breakers S, S1, and S2, the mechanical switch S is turned off at zero current, and there is no need to equip the break with a current zero-crossing circuit; the mechanical switches S1 and S2 are both opened at zero current and zero withstand voltage, the opening pressure is very small, and the residual action time of the mechanical breakers S, S1, and S2 is relatively long, so the action speed of the three sets of mechanical breakers is not too high. Overall, the cost of this type of mechanical break is relatively low.

[0034] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0035] (1) With the continuous development of flexible DC transmission networks, the scale of the grid continues to increase, and the number of transmission lines on the same bus will increase. The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation provided by the present invention can realize the clearing and reclosing functions of multi-line fault currents using only one capacitor commutation unit, which can effectively reduce the reuse of semiconductor devices and has certain economic efficiency.

[0036] (2) The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation provided by the present invention rationally utilizes the characteristic of charging the commutation capacitor on the power supply side, which can solve the problem of needing to equip the pre-energy storage capacitor with a charging circuit, and effectively reduce the overall size and cost of the circuit breaker.

[0037] (3) The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation provided by the present invention can effectively reduce the opening pressure of the mechanical switch and the energy absorption pressure of the lightning arrester. The cost of the internal components of the circuit breaker is relatively low, which has certain economic advantages.

[0038] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation, characterized in that: It includes a main circuit breaker unit, a capacitor conversion unit and an energy absorption unit, wherein: The main circuit breaker unit comprises a plurality of circuit breaker circuits, wherein the plurality of circuit breaker circuits are connected in series to a plurality of transmission lines in the multi-terminal DC power transmission system, and each circuit breaker circuit is used to disconnect the fault current on the transmission line where it is located; The capacitor commutation unit is connected in parallel to the plurality of circuit breaker circuits, and is used to provide a low-voltage branch for the circuit breaker circuit on the transmission line where a short circuit fault occurs to ensure its normal disconnection, and to cut off the fault current by using the self-shutdown function; the capacitor commutation unit comprises a capacitor commutation circuit and a plurality of diode bridges symmetrically connected in anti-series at both ends of the capacitor commutation circuit, and the capacitor commutation circuit is connected in parallel to the plurality of circuit breaker circuits through the plurality of diode bridges; the capacitor commutation circuit comprises an auxiliary lightning arrester branch, a commutation capacitor branch and two thyristor branches connected in parallel symmetrically, and the two thyristor branches each comprise a thyristor connected in series and a first mechanical switch; the auxiliary lightning arrester branch comprises an auxiliary lightning arrester connected in series and a second mechanical switch, and the auxiliary lightning arrester branch is connected in series between the cathodes of the two thyristors; the commutation capacitor branch comprises a commutation capacitor and a commutation inductor connected in series, and the commutation capacitor branch is connected in parallel to the auxiliary lightning arrester branch; The energy absorption unit is connected in parallel to the capacitor conversion unit and is used for absorbing energy and limiting overvoltage.

2. The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation according to claim 1, characterized in that: Each of the circuit breaker circuits includes an ultra-fast mechanical switch and a load transfer switch connected in series. The load transfer switch includes two IGBT tubes connected in reverse series, and a diode is connected in reverse parallel to each of the IGBT tubes.

3. The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation according to claim 1, characterized in that: The energy absorption unit comprises a main lightning arrester, and the main lightning arrester is connected in parallel to both ends of the capacitor commutation circuit.

4. The multi-terminal hybrid high-voltage DC circuit breaker based on capacitor commutation according to claim 3, characterized in that: When a short-circuit fault is detected in the multi-terminal power transmission system, the fault current is controlled to be transferred to one of the thyristor branches, and at the same time, the load transfer switch on the transmission line where the short-circuit fault occurs is turned off and the ultra-fast mechanical switch starts to open; after the ultra-fast mechanical switch is opened, the fault current is controlled to be transferred to the commutation capacitor branch; When the polarity of the commutation capacitor voltage in the commutation capacitor branch is reversed, the fault current is transferred to the main lightning arrester; When the current flowing through the main lightning arrester drops to zero, the auxiliary lightning arrester branch is triggered to limit the commutation capacitor voltage to a set value; one of the thyristor branches is turned off, and after one of the thyristor branches is turned off, another thyristor branch is triggered to prepare for the next fault.

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