CN103457258B - A kind of MTDC transmission system DC circuit breaker and control method thereof - Google Patents

Abstract

The invention proposes a DC circuit breaker for a multi-terminal DC system and its control method. The DC circuit breaker includes a lightning arrester, a main switching circuit and an auxiliary switching circuit; the lightning arrester is connected in parallel with the main switching branch; The first current breaking unit and the second current breaking unit; the first auxiliary switch circuit and the second auxiliary switch circuit with the same structure are respectively connected in parallel at both ends of the first current breaking unit and the second current breaking unit. The auxiliary switching circuit includes a thyristor-reactance series branch, a capacitor, a resistor and a valve section composed of a thyristor and a diode. The present invention breaks the direct current through zero crossing by injecting reverse current. The invention adopts semi-controlled device thyristors to form a DC circuit breaker topology, which can be applied to high-voltage and high-current occasions, and has low cost, mature technology, simple control and low loss.

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 the 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 connected to the DC system after connecting reactances at both ends; the DC circuit breaker includes a lightning arrester, a main switch branch and an auxiliary branch; the lightning arrester and the main switch The branches are connected in parallel; the improvement is that,

The main switch branch circuit includes two sets of first and second breakout units connected in series with the same structure; a first auxiliary switch circuit is arranged in parallel at both ends of the first breakout unit; A second auxiliary switch circuit is arranged in parallel at both ends of the flow unit;

The first auxiliary switch circuit includes a thyristor T13-reactance L1 series branch, a capacitor C1, a resistor R1, a thyristor T11 and a diode D1; parallel connection; the thyristor T13-reactance L1 series branch and the capacitor C1 are connected in parallel to both ends of the first valve section, and grounded through the resistor R1;

The second auxiliary switch circuit comprises a thyristor T23-reactance L2 series branch, a capacitor C2, a resistor R2, a thyristor T21 and a diode D2; Parallel connection; the thyristor T23-reactance L2 series branch and the capacitor C2 are connected in parallel to both ends of the second valve section, and grounded through the resistor R2.

Wherein, the first current breaking unit includes an isolation switch BRK1, a thyristor T1 and a thyristor T12;

The thyristor T1 and the thyristor T12 are connected in anti-parallel and connected in series with the isolating switch BRK1;

The second current breaking unit includes an isolation switch BRK2, a thyristor T2 and a thyristor T22;

The thyristor T2 and the thyristor T22 are connected in anti-parallel and connected in series with the isolation switch BRK2.

Wherein, in the first auxiliary switch circuit, the anode of the thyristor T13 is connected to the cathode of the diode D1, 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 D1 ; 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 D2, 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 D2; 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 D1, the thyristor T11 and the thyristor T13 in the first auxiliary switch circuit is more than two;

The number of the diode D2, the thyristor T21 and the thyristor T23 in the second auxiliary switch circuit is more than two.

Wherein, the cathode of the diode D1 in the first valve section is connected to the diode D2 in the second valve section, 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 circuit, and keep the thyristor T1, thyristor T2, thyristor T12, thyristor T22, thyristor T11, thyristor T21, thyristor T13 and thyristor T23 in the locked state, and the isolation switch BRK1 and isolation switch BRK2 are open state;

(2) closing the isolation switch BRK1 in the first current breaking unit, and triggering the thyristor T1 in the first current breaking unit;

(3) closing the isolation switch BRK2 in the second current breaking unit, and triggering the thyristor T2 in the second current breaking unit;

Shutdown process:

1) triggering and turning on the thyristor T13 in the first auxiliary switch circuit;

2) Turn off the isolating switch BRK1 in the first current breaking unit;

3) The arrester acts and absorbs energy;

4) Turn off the isolating switch BRK2 in the second current breaking unit.

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 circuit, and keep the thyristor T1, thyristor T2, thyristor T12, thyristor T22, thyristor T11, thyristor T21, thyristor T13 and thyristor T23 in the locked state, and the isolation switch BRK1 and isolation switch BRK2 are open state;

(2) closing the isolating switch BRK2 in the second breaking unit, and triggering the thyristor T22 in the second breaking unit;

(3) closing the isolation switch BRK1 in the first current breaking unit, and triggering the thyristor T12 in the first current breaking unit;

Shutdown process:

1) triggering and turning on the thyristor T23 in the second auxiliary switch circuit;

2) disconnect the isolating switch BRK2 in the second current breaking unit;

3) The arrester acts and absorbs energy;

4) Turn off the isolating switch BRK1 in the first breaker unit.

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 description

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 current-limiting reactors connected in series at both ends, and its structure is shown in Figure 1, including a lightning arrester, a main switch branch and an auxiliary switch circuit; Its arrester is connected in parallel with the main switch branch.

The main switch branch of this embodiment includes two sets of first and second interrupting units with the same structure; the first interrupting unit includes an isolating switch BRK1, a thyristor T1 and a thyristor T12; It is connected in series with the isolating switch BRK1; the second current breaking unit includes an isolating switch BRK2, a thyristor T2 and a thyristor T22; The first current breaking unit and the second current breaking unit are connected in series to form a main switch branch. In this embodiment, a first auxiliary switch circuit is arranged in parallel at both ends of the first current breaking unit; a second auxiliary switch circuit is arranged 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 capacitor C1, a resistor R1, a thyristor T11 and a diode D1; The current unit is connected in parallel; the thyristor T13-reactance L1 series branch and the capacitor C1 are connected in parallel to the two ends of the first valve section, and are grounded through the resistor R1.

The second auxiliary switch circuit includes thyristor T23-reactance L2 series branch, capacitor C2, resistor R2, thyristor T21 and diode D2; thyristor T21 and diode D2 are connected in antiparallel to form the second valve section, which is connected in parallel with the second current breaking unit; thyristor T23 - The series branch of the reactance L2 and the capacitor C2 are connected in parallel to the ground at both ends of the second valve section, and grounded through the resistor R2.

In Fig. 1, in two groups of valve sections, the diode D2 and the thyristor T21 are connected in antiparallel, and the diode D1 and the thyristor T11 are connected in antiparallel. The number of diodes D1 and D2, thyristors T11 and thyristors T21 in each valve section is multiple (only one is marked in the figure), and they are in series structure. The directions of the diode D1 and the diode D2 are opposite, and the directions of the thyristor T11 and the thyristor T21 are opposite.

For the first auxiliary switching circuit where the first valve section is located, the anode of the thyristor T13 is connected to the cathode of the diode D1, and its cathode is connected to the reactance L1; the other end of the reactance L1 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the diode The positive pole of D1 is connected, and the resistance R1 is grounded between the reactance L1 and the capacitor C1. R1 plays the role of current limiting, and the reactance L1 plays the role of suppressing the short-circuit current. The thyristor T13 is also composed of at least one thyristor connected in series in the same direction.

For the second auxiliary switching circuit where the second valve section is located, the anode of the thyristor T23 is connected to the cathode of the diode D2, and its cathode 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 diode The positive pole of D2 is connected, the reactance L2 and the capacitor C2 are grounded through another resistor R2, R2 acts as a current limiter, and the reactance L2 acts as a suppressor for short-circuit current. The thyristor T23 is also composed of at least one thyristor connected in series in the same direction.

Correspondingly, this embodiment proposes a control method for a DC circuit breaker used in a multi-terminal DC system. Since the structure of the circuit breaker in this embodiment is symmetrical, the breaking mechanism of bidirectional current flow is exactly the same. Only the forward direction is used for principle analysis, and the reverse direction can be By analogy, the current direction _Idc shown in Figure 1 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. This embodiment includes the following steps:

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 turning on, first close the fast isolating switch BRK1, then trigger the conduction of T1, the current passes through the D2-BRK1-T1 branch, close the fast isolating switch BRK2 after the current is stable, and then trigger the conduction of the thyristor T2, because the impedance of the branch where D2 is located is large In the T2 branch, the current will quickly transfer to the BRK2-T2-BRK1-T1 branch. After the current stabilizes, the current will pass through the BRK2-T2-BRK1-T1 branch stably. At this point, the circuit breaker is fully put into a stable operating state, and the opening process is over. .

Shutdown process:

When the circuit breaker needs to act to break the current, it triggers the conduction of T13. Due to the effect of the capacitor voltage, the capacitor C1 quickly generates a pulse current in the C1-T1-BRK1-T13-L1 circuit that is opposite to the forward current of the line, so that the thyristor T1 When the current crosses zero, since D1 is turned on to provide reverse voltage to T1, thyristor T1 is turned off. At this time, the fast mechanical isolating switch BRK1 quickly operates and opens in the case of no current; when BRK1 recovers the blocking ability, the current is completely transferred to BRK2- The T2-T13-L1-C1 branch charges the capacitor C1 at the same time, so that the voltage of the capacitor C1 changes from positive at the top and negative at the bottom to positive at the bottom, which is opposite to the direction shown in the figure. When the voltage of this branch reaches the MOV operating voltage of the arrester, the MOV operates, and the current is transferred to the branch where the MOV is located. The MOV absorbs the energy stored in the circuit and the current-limiting inductance. When the charging current of the capacitor C1 is zero, the thyristor T13 is turned off, and BRK2 Open the gate, and when the current in the arrester gradually decreases to 0, the arrester returns to the blocking state, and the current flowing through the DC 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 (6)

1. A DC circuit breaker for a multi-terminal DC system, the two ends of which are respectively connected to a reactance and then connected to the DC system; the DC circuit breaker includes a lightning arrester, a main switch branch and an auxiliary branch; the lightning arrester and the main switch branch in parallel; characterized in that, The main switch branch circuit includes two sets of first and second breakout units connected in series with the same structure; a first auxiliary switch circuit is arranged in parallel at both ends of the first breakout unit; A second auxiliary switch circuit is arranged in parallel at both ends of the flow unit; The first auxiliary switch circuit includes a thyristor T13-reactance L1 series branch, a capacitor C1, a resistor R1, a thyristor T11 and a diode D1; parallel connection; the thyristor T13-reactance L1 series branch and the capacitor C1 are connected in parallel to both ends of the first valve section, and grounded through the resistor R1; The second auxiliary switch circuit comprises a thyristor T23-reactance L2 series branch, a capacitor C2, a resistor R2, a thyristor T21 and a diode D2; Parallel connection; the thyristor T23-reactance L2 series branch and the capacitor C2 are connected in parallel to both ends of the second valve section, and grounded through the resistor R2; In the first auxiliary switch circuit, the anode of the thyristor T13 is connected to the cathode of the diode D1, 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 D1; 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 D2, 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 D2; 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. 2. The DC circuit breaker according to claim 1, wherein the first current breaking unit comprises an isolating switch BRK1, a thyristor T1 and a thyristor T12; The thyristor T1 and the thyristor T12 are connected in anti-parallel and connected in series with the isolating switch BRK1; The second current breaking unit includes an isolation switch BRK2, a thyristor T2 and a thyristor T22; The thyristor T2 and the thyristor T22 are connected in anti-parallel and connected in series with the isolation switch BRK2. 3. The DC circuit breaker according to claim 2, wherein the number of the diode D1, the thyristor T11 and the thyristor T13 in the first auxiliary switch circuit is more than two; The number of the diode D2, the thyristor T21 and the thyristor T23 in the second auxiliary switch circuit is more than two. 4. The DC circuit breaker according to any one of claims 1-3, characterized in that the cathode of the diode D1 in the first valve section is connected to the cathode of the diode D2 in the second valve section, D1, D2 The positive pole of the circuit is connected to the current limiting reactor in the line. 5. A control method for a DC circuit breaker as claimed in claim 1, characterized in that the control method comprises the steps of: Opening process: (1) Connect the DC circuit breaker to the circuit, and keep the thyristor T1, thyristor T2, thyristor T12, thyristor T22, thyristor T11, thyristor T21, thyristor T13 and thyristor T23 in the locked state, and the isolation switch BRK1 and isolation switch BRK2 are open state; (2) closing the isolating switch BRK1 in the first current breaking unit, triggering the conduction of the thyristor T1 in the first current breaking unit; (3) closing the isolating switch BRK2 in the second current breaking unit, triggering the conduction of the thyristor T2 in the second current breaking unit; Shutdown process: 1) triggering and turning on the thyristor T13 in the first auxiliary switch circuit; 2) disconnecting the isolating switch BRK1 in the first current breaking unit; 3) The arrester acts and absorbs energy; 4) Turn off the isolating switch BRK2 in the second current breaking unit. 6. A control method for the DC circuit breaker as claimed in claim 1, characterized in that the control method comprises the steps of: Opening process: (1) Connect the DC circuit breaker to the circuit, and keep the thyristor T1, thyristor T2, thyristor T12, thyristor T22, thyristor T11, thyristor T21, thyristor T13 and thyristor T23 in the locked state, and the isolation switch BRK1 and isolation switch BRK2 are open state; (2) closing the isolating switch BRK2 in the second current breaking unit, triggering the conduction of the thyristor T22 in the second current breaking unit; (3) closing the isolating switch BRK1 in the first current breaking unit, triggering the conduction of the thyristor T12 in the first current breaking unit; Shutdown process: 1) triggering and conducting the thyristor T23 in the second auxiliary switch circuit; 2) disconnecting the isolating switch BRK2 in the second current breaking unit; 3) The arrester acts and absorbs energy; 4) Turn off the isolating switch BRK1 in the first current breaking unit.