CN103441490A - Direct-current breaker used for multi-terminal direct current system and control method of direct-current breaker - Google Patents

Abstract

The invention discloses a DC circuit breaker for a multi-terminal DC system and a control method thereof. The circuit breaker includes a lightning arrester, a main switching branch and an auxiliary switching circuit; the lightning arrester is connected in parallel with the main switching branch; The units are formed in series, and an auxiliary switch circuit with the same structure is arranged in parallel at both ends of each group of cut-off units. The auxiliary switching circuits all include a thyristor-reactance series branch, a diode, a capacitor and a resistor; the diode is connected in parallel at both ends of the interrupting unit, and the thyristor-reactance series branch and the capacitor are connected in parallel to both ends of the diode and grounded through the resistor. The present invention breaks the direct current through zero crossing by injecting reverse current. The invention adopts a semi-controlled device thyristor to form a DC circuit breaker topology, can be applied to high-voltage and high-current occasions, has low cost, simple control and high scalability.

Description

A DC circuit breaker for a multi-terminal DC system and its control method

technical field

The invention belongs to the technical field of power electronics, and in particular relates to a DC circuit breaker for a multi-terminal DC system and a control method thereof.

Background technique

Multi-terminal DC transmission technology can realize multi-source power supply and multi-drop power receiving. It is a flexible, fast and economical power transmission method to meet the development needs of the electric power industry. The DC circuit breaker is a very important equipment in the multi-terminal DC transmission project. Only by using the DC circuit breaker in the multi-terminal DC system can the characteristics and advantages of the multi-terminal DC system be fully utilized. However, the DC circuit breaker withstands extremely high voltage during the process of breaking the DC current. The energy to be absorbed is particularly large, requiring fast breaking speed, high reliability, and breaking bidirectional current. At present, some scholars are studying its corresponding DC circuit breaker.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention proposes a DC circuit breaker for a multi-terminal DC system and its control method. The core is to break the DC current by superimposing the reverse current based on the current transfer principle, realizing the bidirectional breaking of the current, which is a DC circuit breaker. The development of the circuit breaker provides a new technical route.

A DC circuit breaker for a multi-terminal DC system provided by the present invention is characterized in that it includes a lightning arrester, a main switching branch and an auxiliary switching circuit; the lightning arrester is connected in parallel with the main switching branch;

The branch of the main switch is composed of two groups of first cut-off units and second cut-off units with the same structure in series; the first cut-off unit includes a series isolation switch BRK11, an AC circuit breaker BRK12 and a first thyristor valve section; The second cut-off unit includes a series connection of an isolating switch BRK21, an AC circuit breaker BRK22 and a second thyristor valve section;

A first auxiliary switch circuit is connected in parallel at both ends of the first current breaking unit; a second auxiliary switch circuit is connected in parallel at both ends of the second current breaking unit;

The first auxiliary switch circuit includes a thyristor T13-reactance L1 series branch, a diode D12, a capacitor C1 and a resistor R1; the diode D12 is connected in parallel at both ends of the first current breaking unit; the thyristor T13-reactance L1 is connected in series The branch and the capacitor C1 are connected in parallel to the two ends of the diode D12, and grounded through the resistor R1;

The second auxiliary switch circuit includes a thyristor T23-reactance L2 series branch, a diode D22, a capacitor C2 and a resistor R2; the diode D22 is connected in parallel at both ends of the second current breaking unit; the thyristor T23-reactance L2 is connected in series The branch and the capacitor C2 are connected in parallel to the two ends of the diode D22 and grounded through the resistor R2.

Wherein, the first thyristor valve section includes a thyristor T11, a thyristor T12, a diode D11 and a resistor R3; the diode D11 is connected in parallel with the thyristor T11 and the thyristor T12 after being connected in series with the resistor R3; the thyristor T11 and the thyristor T12 is an anti-parallel structure; the direction of the diode D11 is opposite to that of the diode D12;

The second thyristor valve section includes a thyristor T21, a thyristor T22, a diode D21 and a resistor R4; the diode D21 is connected in parallel with the thyristor T21 and the thyristor T22 after being connected in series with the resistor R4; the thyristor T21 and the thyristor T22 are Anti-parallel structure; the direction of the diode D21 is opposite to that of the diode D22.

Wherein, in the first auxiliary switch circuit, the anode of the thyristor T13 is connected to the cathode of the diode D12, and its cathode is connected to one end of the reactance L1; one end of the capacitor C1 is connected to the anode of the diode D12 ; The other end of the capacitor C1 is connected to the other end of the reactance L1; the reactance L1 is grounded through the resistor R1;

In the second auxiliary switch circuit, the anode of the thyristor T23 is connected to the cathode of the diode D22, and its cathode is connected to one end of the reactance L2; one end of the capacitor C2 is connected to the anode of the diode D22; The other end of the capacitor C2 is connected to the other end of the reactance L2; the reactance L2 is grounded through the resistor R2.

Wherein, the number of the diode D12 and the thyristor T13 in the first auxiliary switch circuit is more than two;

The number of the diode D22 and the thyristor T23 in the second auxiliary switch circuit is more than two.

Wherein, the cathode of the diode D1 in the first auxiliary switch circuit is connected to the diode D2 in the second auxiliary switch circuit, and the anode is connected to the current-limiting reactor in the line.

The present invention provides a control method for a DC circuit breaker for a multi-terminal DC system based on another purpose. The improvement is that the control method includes the following steps:

Opening process:

(1) Connect the DC circuit breaker to the line, and keep the thyristor T11, thyristor T12, thyristor T21, thyristor T22, thyristor T13 and thyristor T23 in the locked state, the isolation switch BRK11, the isolation switch BRK21, the AC circuit breaker BRK12 and the AC circuit breaker Device BRK22 is disconnected;

(2) Close the isolating switch BRK21 in the second current breaking unit, and then close the AC circuit breaker BRK22;

(3) triggering and turning on the thyristor T21 of the second current breaking unit;

(4) Close the isolating switch BRK11 in the first current breaking unit, then close the AC circuit breaker BRK12, and turn on the thyristor T11 in it;

Shutdown process:

① Trigger and conduct the thyristor T23 in the second auxiliary switch circuit;

② Disconnect the isolating switch BRK21;

③ The arrester absorbs energy;

④ Disconnect the AC circuit breaker BRK22, isolation switch BRK11 and AC circuit breaker BRK12.

The present invention provides a control method for a DC circuit breaker for a multi-terminal DC system based on another purpose. The improvement is that the control method includes the following steps:

Opening process:

(1) Connect the DC circuit breaker to the line, and keep the thyristor T11, thyristor T12, thyristor T21, thyristor T22, thyristor T13 and thyristor T23 in the locked state, the isolating switch BRK11, the isolating switch BRK21, the AC circuit breaker BRK12 and the AC circuit breaker BRK22 is disconnected;

(2) Close the isolating switch BRK11 in the first current breaking unit, and then close the AC circuit breaker BRK12;

(3) Triggering and turning on the thyristor T12 of the first current interruption unit;

(4) Close the isolating switch BRK21 in the second current breaking unit, then close the AC circuit breaker BRK22, and turn on the thyristor T22 in it;

Shutdown process:

① Triggering and conducting the thyristor T13 in the first auxiliary switch circuit;

② Disconnect the isolating switch BRK11;

③ The arrester absorbs energy;

④ Disconnect the AC circuit breaker BRK12, isolation switch BRK21 and AC circuit breaker BRK22.

Compared with the prior art, the beneficial effects of the present invention are:

The invention combines the ideas of forced commutation and current transfer breaking, and realizes the breaking of direct current in a large-capacity system.

The present invention adopts the semi-controlled device thyristor to form the DC circuit breaker topology, uses the semi-controlled device to replace the expensive full-controlled device, has low on-state loss, low manufacturing cost and heat dissipation requirements, and mature technology.

The invention can be applied to high-voltage and high-current occasions, has simple and compact topological structure, simple control and high expandability.

The invention uses a fast isolating switch to realize bidirectional DC current breaking in multiple working conditions, and the breaking process is fast and arc-free.

The invention utilizes the auxiliary switch circuit to realize the soft opening of the DC circuit breaker, and reduces the stress borne by the power device during the opening process.

The invention belongs to a hybrid high-voltage direct current circuit breaker, which combines the advantages of a mechanical direct current circuit breaker and a solid state direct current circuit breaker, is relatively less difficult to develop, and is suitable for various multi-terminal direct current systems.

The invention uses the circuit to charge the capacitor in the auxiliary switch circuit without additional charging equipment, thereby reducing the difficulty of electrical isolation between equipment, reducing the occupied area and cost, and being easy to realize engineering.

Description of drawings

Fig. 1 is a structural diagram of a DC circuit breaker provided by the present invention.

Fig. 2 is a schematic diagram of the waveform of the breaking fault current provided by the present invention.

Fig. 3 is a schematic diagram of the waveform of the breaking load current provided by the present invention.

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

A DC circuit breaker for a multi-terminal DC system proposed in this embodiment is connected to the power grid through a current-limiting reactor connected in series at both ends. Its structure is shown in Figure 1, including a lightning arrester, a main switch branch and an auxiliary switch circuit; , the arrester is connected in parallel with the main switch branch.

In the figure, the main switch branch includes two groups of the first current breaking unit and the second current breaking unit with the same structure. The first cut-off unit includes a series fast isolation switch BRK11, a high-voltage SF ₆ circuit breaker BRK12 and the first thyristor valve section; the first thyristor valve section includes a thyristor T11, a thyristor T12, a diode D11 and a resistor R3; the diode D11 is connected in series with the resistor R3 After that, they are respectively connected in parallel with the thyristor T11 and the thyristor T12; the thyristor T11 and the thyristor T12 are in an anti-parallel structure; the direction of the diode D11 is opposite to that of the diode D12. The second cut-off unit includes a series isolation switch BRK21, a high-voltage SF ₆ circuit breaker BRK22 and a second thyristor valve section; the second thyristor valve section includes a thyristor T21, a thyristor T22, a diode D21 and a resistor R4; after the diode D21 is connected in series with the resistor R4 They are respectively connected in parallel with the thyristor T21 and the thyristor T22; the thyristor T21 and the thyristor T22 are in an anti-parallel structure; the direction of the diode D21 is opposite to that of the diode D22.

In this embodiment, a first auxiliary switch circuit is connected in parallel at both ends of the first current breaking unit, and a second auxiliary switching circuit is connected in parallel at both ends of the second current breaking unit.

As shown in Figure 1, the first auxiliary switch circuit includes a thyristor T13-reactance L1 series branch, a diode D12, a capacitor C1 and a resistor R1; the diode D12 is connected in parallel at both ends of the first current breaking unit; the thyristor T13-reactance L1 series branch The capacitor C1 is connected in parallel with the two ends of the diode D12, and is connected to the ground through the resistor R1.

The second auxiliary switch circuit includes a thyristor T23-reactance L2 series branch, a diode D22, a capacitor C2 and a resistor R2; the diode D22 is connected in parallel at both ends of the second interrupting unit; the thyristor T23-reactance L2 series branch The capacitor C2 is connected to the two ends of the diode D22 in parallel with the ground, and is connected to the ground through the resistor R2.

In the first auxiliary switch circuit, the diode D12 includes at least two diodes in series in the same direction (only one is marked in the figure), which are connected in parallel at both ends of the first current breaking unit, and the direction is the same as that of the diode D11 in the first thyristor valve section. in the opposite direction. The thyristor T13 is also composed of at least two thyristors connected in series, the anode of the thyristor T13 is connected to the anode of the thyristor T12 in the first current breaking unit, the cathode of the thyristor T13 is connected to the reactance L1; the other end of the reactance L1 is connected to one end of the capacitor C1, and the capacitor The other end of C1 is connected to the isolating switch BRK11; between the reactance L1 and the capacitor C1 is grounded through the resistor R1, R1 acts as a current limiter, and the reactance L1 acts as a suppression of short-circuit current.

In the second auxiliary switch circuit, the diode D22 includes at least two diodes in series in the same direction (only one is marked in the figure), which are connected in parallel at both ends of the second current breaking unit, and the direction is the same as that of the diode D21 in the second thyristor valve section. in the opposite direction. The thyristor T23 is also composed of at least two thyristors in series. The anode of the thyristor T23 is connected to the isolation switch BRK21, and the cathode of the thyristor T23 is connected to the reactance L2; the other end of the reactance L2 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the second end of the capacitor C2. The anode of the thyristor T22 in the current-breaking unit is connected; the resistance R2 is grounded between the reactance L2 and the capacitor C2, and the R2 acts as a current limiting function, and the reactance L2 acts as a suppression short-circuit current.

In this embodiment, the cathode of the diode D1 in the first auxiliary switch circuit is connected to the diode D2 in the second auxiliary switch circuit, and the anode is connected to the current-limiting reactor in the line.

Correspondingly, this embodiment proposes a control method for a DC circuit breaker for a multi-terminal DC system. Since the structure of this circuit breaker is completely symmetrical and can realize two-way breaking, the principle is explained in the forward direction, and the reverse direction can be compared. The current direction I _dc is the positive direction of the current. For the different working conditions of cutting off the fault short-circuit current and cutting off the load current, the working principle of this circuit breaker is the same, so a unified description is given. The DC circuit breaker is divided into two processes of opening and closing, as follows:

Opening process:

The capacitors C1 and C2 are charged through the auxiliary switch circuits C1-R and C2-R through the circuit and kept in a constant charged state, and the voltage is stable at the rated voltage level of the system. When opening, first close the fast isolating switch BRK21, and then close the SF6 circuit breaker BRK22, then the current flows through the D12-BRK21-BRK22-D21-R2 branch, and the thyristor T21 is triggered after the current is stable. Due to the impedance of the D21-R2 branch Much larger than the T21 branch, the current will quickly transfer to the T21 branch, then close BRK11, and then close BRK12, triggering the thyristor T11, also because the BRK11-BRK12-T11 branch impedance is much smaller than the D12 branch, the current will quickly flow to the BRK11 -BRK12-T11 branch is transferred, and after stabilization, the current flows in the BRK11-BRK12-T11-BRK21-BRK22-T21 branch, so far the circuit breaker is fully put into operation, and the opening process is over.

Shutdown process:

When the DC circuit breaker needs to act to cut off the line current, T23 is triggered and turned on. Due to the effect of the capacitor voltage, the capacitor C2 quickly generates a pulse current opposite to the forward current of the line in the T21-BRK21-BRK21-T23-inductor L2 loop, so that The current in the thyristor T21 crosses zero. Since D22 is turned on to provide reverse voltage to T21, the thyristor T21 is turned off. At this time, the fast mechanical isolating switch BRK21 operates to open when there is no current. After the blocking capability is restored, BRK22 opens; After BRK21 restores its blocking ability, the current is transferred to the BRK11-BRK12-T11-T23-L2-C2 branch, and at the same time, it charges the capacitor C2. The voltage of the capacitor C2 changes from upper positive and lower negative to upper negative and lower positive, which is opposite to the direction shown in the figure. . When the voltage of this branch reaches the MOV action voltage of the arrester, the MOV will act. When the charging current of the capacitor C2 is zero, all the short-circuit current will be transferred to the MOV branch, the thyristor T23 will be turned off, and BRK11 and BRK12 will be opened. The energy stored in the flow inductance, when the branch current of the arrester gradually decreases to 0, and the arrester returns to the blocking state, the current flowing through the circuit breaker is completely broken, and the shutdown process ends.

As shown in Figure 2, it is a schematic diagram of the waveform of the breaking fault current. Through the control of the DC circuit breaker proposed in this embodiment, it can be seen from the figure that after 1.4 ms the main branch DC current is broken, the current is finally transferred to the arrester for energy dissipation.

As shown in Figure 3, it is a schematic diagram of the waveform of the breaking load current. Through the control of the DC circuit breaker proposed in this embodiment, it can be seen from the figure that after 1.3 ms the main branch DC current is broken, the current is finally transferred to the arrester for energy dissipation.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims (7)

1. A DC circuit breaker for a multi-terminal DC system, characterized in that it comprises a lightning arrester, a main switch branch and an auxiliary switch circuit; the lightning arrester is connected in parallel with the main switch branch; The branch of the main switch is composed of two groups of the same structure of the first cut-off unit and the second cut-off unit connected in series; the first cut-off unit includes a series disconnection switch BRK11, an AC circuit breaker BRK12 and a first thyristor valve section; The second cut-off unit includes a series connection of an isolating switch BRK21, an AC circuit breaker BRK22 and a second thyristor valve section; A first auxiliary switch circuit is connected in parallel at both ends of the first current breaking unit; a second auxiliary switch circuit is connected in parallel at both ends of the second current breaking unit; The first auxiliary switch circuit includes a thyristor T13-reactance L1 series branch, a diode D12, a capacitor C1 and a resistor R1; the diode D12 is connected in parallel at both ends of the first current breaking unit; the thyristor T13-reactance L1 is connected in series The branch and the capacitor C1 are connected in parallel to the two ends of the diode D12, and grounded through the resistor R1; The second auxiliary switch circuit includes a thyristor T23-reactance L2 series branch, a diode D22, a capacitor C2 and a resistor R2; the diode D22 is connected in parallel at both ends of the second current breaking unit; the thyristor T23-reactance L2 is connected in series The branch and the capacitor C2 are connected in parallel to the two ends of the diode D22 and grounded through the resistor R2. 2. The DC circuit breaker according to claim 1, wherein the first thyristor valve section comprises a thyristor T11, a thyristor T12, a diode D11 and a resistor R3; The thyristor T11 and the thyristor T12 are connected in parallel; the thyristor T11 and the thyristor T12 are in an anti-parallel structure; the direction of the diode D11 is opposite to that of the diode D12; The second thyristor valve section includes a thyristor T21, a thyristor T22, a diode D21 and a resistor R4; the diode D21 is connected in parallel with the thyristor T21 and the thyristor T22 after being connected in series with the resistor R4; the thyristor T21 and the thyristor T22 are Anti-parallel structure; the direction of the diode D21 is opposite to that of the diode D22. 3. The DC circuit breaker according to claim 1, characterized in that, in the first auxiliary switch circuit, the anode of the thyristor T13 is connected to the cathode of the diode D12, and its cathode is connected to one end of the reactance L1 connected; one end of the capacitor C1 is connected to the anode of the diode D12; the other end of the capacitor C1 is connected to the other end of the reactance L1; the reactance L1 is grounded through the resistor R1; In the second auxiliary switch circuit, the anode of the thyristor T23 is connected to the cathode of the diode D22, and its cathode is connected to one end of the reactance L2; one end of the capacitor C2 is connected to the anode of the diode D22; The other end of the capacitor C2 is connected to the other end of the reactance L2; the reactance L2 is grounded through the resistor R2. 4. The DC circuit breaker according to claim 3, wherein the number of the diode D12 and the thyristor T13 in the first auxiliary switch circuit is more than two; The number of the diode D22 and the thyristor T23 in the second auxiliary switch circuit is more than two. 5. The DC circuit breaker according to any one of claims 1-4, wherein the diode D1 in the first auxiliary switch circuit is connected to the cathode of the diode D2 in the second auxiliary switch circuit, and the anode is connected to the diode D2 in the second auxiliary switch circuit. Current limiting reactor connection in the line. 6. A control method for a DC circuit breaker for a multi-terminal DC system, characterized in that the control method comprises the following steps: Opening process: (1) Connect the DC circuit breaker to the line, and keep the thyristor T11, thyristor T12, thyristor T21, thyristor T22, thyristor T13 and thyristor T23 in the locked state, the isolation switch BRK11, the isolation switch BRK21, the AC circuit breaker BRK12 and the AC circuit breaker Device BRK22 is disconnected; (2) Close the isolating switch BRK21 in the second current breaking unit, and then close the AC circuit breaker BRK22; (3) triggering and turning on the thyristor T21 of the second current breaking unit; (4) Close the isolating switch BRK11 in the first current breaking unit, then close the AC circuit breaker BRK12, and turn on the thyristor T11 in it; Shutdown process: ① Trigger and conduct the thyristor T23 in the second auxiliary switch circuit; ② Disconnect the isolating switch BRK21; ③ The arrester absorbs energy; ④ Disconnect the AC circuit breaker BRK22, isolation switch BRK11 and AC circuit breaker BRK12. 7. A control method for a DC circuit breaker for a multi-terminal DC system, characterized in that the control method comprises the following steps: Opening process: (1) Connect the DC circuit breaker to the line, and keep the thyristor T11, thyristor T12, thyristor T21, thyristor T22, thyristor T13 and thyristor T23 in the locked state, the isolating switch BRK11, the isolating switch BRK21, the AC circuit breaker BRK12 and the AC circuit breaker BRK22 is disconnected; (2) Close the isolating switch BRK11 in the first current breaking unit, and then close the AC circuit breaker BRK12; (3) triggering and turning on the thyristor T12 of the first current breaking unit; (4) Close the isolating switch BRK21 in the second current breaking unit, then close the AC circuit breaker BRK22, and turn on the thyristor T22 in it; Shutdown process: ① Triggering and conducting the thyristor T13 in the first auxiliary switch circuit; ② Disconnect the isolating switch BRK11; ③ The arrester absorbs energy; ④ Disconnect the AC circuit breaker BRK12, isolation switch BRK21 and AC circuit breaker BRK22.

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