CN103457256A - Direct-current breaker used for multi-terminal direct-current system and control method thereof - Google Patents

Abstract

The invention relates to a DC circuit breaker for a multi-terminal DC system and a control method thereof. The DC circuit breaker includes a lightning arrester, a main switch branch and an auxiliary switch circuit connected in parallel in sequence; the main switch branch includes an isolating switch BRK1, a thyristor T1 and a thyristor T12. ; Thyristor T1 and thyristor T12 are anti-parallel connected and then connected in series with isolating switch BRK1; the auxiliary switch circuit includes a first auxiliary switch circuit and a second auxiliary switch circuit, with a symmetrical structure, connected in series and connected in parallel at both ends of the main switch branch, each auxiliary switch The circuits all include a thyristor-reactance series branch, a capacitor, a resistor and a valve section composed of another thyristor connected in antiparallel with a diode. The present invention breaks the direct current through zero crossing by injecting reverse current. The invention can be applied to high-voltage and high-current occasions, and has simple topological structure, low cost, fast breaking, 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 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.

The present invention provides a DC circuit breaker for a multi-terminal DC system. The DC circuit breaker includes a lightning arrester, a main switch branch and an auxiliary switch circuit connected in parallel in sequence; the improvement is that the main switch branch includes an isolating switch BRK1 , thyristor T1 and thyristor T12; said thyristor T1 and thyristor T12 are connected in anti-parallel and connected in series with said isolating switch BRK1;

The auxiliary switch circuit includes a first auxiliary switch circuit and a second auxiliary switch circuit;

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 thyristor T11 and the diode D1 are connected in antiparallel to form a first valve section; the thyristor T13 - the series branch of the reactance L1 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 includes a thyristor T23-reactance L2 series branch, a capacitor C2, a resistor R2, a thyristor T21 and a diode D2; the thyristor T21 and the diode D2 are connected in antiparallel to form a second valve section; the thyristor T23 - the series branch of the reactance L2 and the capacitor C2 are connected in parallel to both ends of the second valve section, and grounded through the resistor R2;

The first valve section is connected in parallel with the main switch branch after being connected in series with the second valve section.

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 T11, thyristor T21, thyristor T13, thyristor T23, thyristor T1 and thyristor T12 in the locked state, and the isolation switch BRK1 in the open state;

(2) Triggering and conducting the thyristor T11 in the first valve section;

(3) Turn on the thyristor T1 after closing the isolation switch BRK1;

Shutdown process:

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

2) Disconnect the isolating switch BRK1;

3) Charging the capacitor C1 of the first auxiliary switch circuit until the arrester operates and absorbs energy.

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 T11, thyristor T21, thyristor T13, thyristor T23, thyristor T1 and thyristor T12 in the locked state, and the isolation switch BRK1 in the open state;

(2) Triggering and conducting the thyristor T21 in the second valve section;

(3) Turn on the thyristor T12 after closing the isolation switch BRK1;

Shutdown process:

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

2) Disconnect the isolating switch BRK1;

3) Charging the capacitor C2 of the second auxiliary switch circuit until the arrester operates and absorbs energy.

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 invention adopts semi-controlled device thyristors to form a DC circuit breaker topology, can be applied to high-voltage and high-current occasions, and has low cost and mature technology.

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

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 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 current-limiting reactors connected in series at both ends. switch circuit.

The main switch branch in this embodiment includes a fast isolating switch BRK1, a thyristor T1 and a thyristor T12; the thyristor T1 and the thyristor T12 are connected in antiparallel to the fast isolating switch BRK1 in series to form the main switch branch.

The auxiliary switch circuit of this embodiment includes a first auxiliary switch circuit and a second auxiliary switch circuit, wherein: 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; T11 and diode D1 are connected in antiparallel to form the first valve section; the thyristor T13-reactance L1 series branch and capacitor C1 are connected in parallel to the ground at both ends of the first valve section, and are grounded through resistor R1; the second valve section and the first valve section After being connected in series, it is connected in parallel with the main switch branch; the second auxiliary switch circuit includes the thyristor T23-reactance L2 series branch, capacitor C2, resistor R2, thyristor T21 and diode D2; the thyristor T21 and diode D2 are connected in antiparallel to form the second valve section; The T23-reactance L2 series branch and the capacitor C2 are connected in parallel to the two ends of the second valve section and grounded through the resistor R2.

As shown in Fig. 1, in the 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 group of valve sections 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 one end of the reactance L1; one end of the capacitor C1 is connected to the anode of the diode D1, and the other end is connected to the other end of the reactance L1 One end is connected to and; between the reactance L1 and the capacitor C1 is grounded through the resistor R1, 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 one end of the reactance L2; one end of the capacitor C2 is connected to the anode of the diode D2, and the other end is connected to the reactance L2. The other end is connected to and; between the reactance L2 and the capacitor C2 is grounded through another resistor R2, R2 acts as a current limiter, and the reactance L2 acts as a suppression of 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 for a multi-terminal DC system. Since the structure of the circuit breaker is symmetrical, the breaking mechanism of bidirectional current flow is the same. Only the forward direction is taken for principle analysis, and the reverse direction can be compared. 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:

Capacitors C1 and C2 are charged through the auxiliary switch circuits C1-R and C2-R and kept in a constant charged state, and the voltage is stable at the system rated voltage level. When it is turned on, first trigger and conduct T11, and the current passes through the branch of the current-limiting reactor 1-D2-T11. After the current is stable, close the fast isolation switch BRK1, and then trigger and conduct the thyristor T1. Since the impedance of the branch where D2-T11 is located is much larger than In the BRK1-T1 branch, the current will quickly transfer to the BRK1-T1 branch. After the current is stable, the current will pass through the 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 DC 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 circuit of T1-BRK1--D2-T13-L1, which is opposite to the forward current of the line, so that the thyristor The current in T1 crosses zero, and the thyristor T1 is turned off. At this time, the fast isolating switch BRK1 quickly operates to open the gate in the case of no current; when the fast isolating switch BRK1 recovers the blocking capability, the current is completely transferred to the D2-T13-L1-C1 branch. , and charge the capacitor C1 at the same time, so that the voltage of the capacitor C1 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 the D2-T13-L1-C1 branch reaches the MOV action 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 the fast isolating switch BRK2 is opened. After the current in the arrester gradually decreases to 0, the arrester returns to the blocking state. At this point, 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, said DC circuit breaker comprising a lightning arrester, a main switch branch and an auxiliary switch circuit connected in parallel in sequence; it is characterized in that said main switch branch comprises a disconnector BRK1, a thyristor T1 and A thyristor T12; the thyristor T1 and the thyristor T12 are connected in antiparallel and connected in series with the isolating switch BRK1; The auxiliary switch circuit includes a first auxiliary switch circuit and a second auxiliary switch circuit; 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 thyristor T11 and the diode D1 are connected in antiparallel to form a first valve section; the thyristor T13 - the series branch of the reactance L1 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 includes a thyristor T23-reactance L2 series branch, a capacitor C2, a resistor R2, a thyristor T21 and a diode D2; the thyristor T21 and the diode D2 are connected in antiparallel to form a second valve section; the thyristor T23 - the series branch of the reactance L2 and the capacitor C2 are connected in parallel to both ends of the second valve section, and grounded through the resistor R2; The first valve section is connected in parallel with the main switch branch after being connected in series with the second valve section. 2. 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 D1, 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 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. 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 diode D1 in the first valve section is connected to the diode D2 in the second valve section with negative poles, and the positive pole is connected to the circuit breaker. The current limiting reactor connection. 5. 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 circuit, and keep the thyristor T11, thyristor T21, thyristor T13, thyristor T23, thyristor T1 and thyristor T12 in the locked state, and the isolation switch BRK1 in the open state; (2) Triggering and conducting the thyristor T11 in the first valve section; (3) Turn on the thyristor T1 after closing the isolation switch BRK1; Shutdown process: 1) triggering and turning on the thyristor T13 in the first auxiliary switch circuit; 2) Disconnect the isolating switch BRK1; 3) Charging the capacitor C1 of the first auxiliary switch circuit until the arrester operates and absorbs energy. 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 circuit, and keep the thyristor T11, thyristor T21, thyristor T13, thyristor T23, thyristor T1 and thyristor T12 in the locked state, and the isolation switch BRK1 in the open state; (2) Triggering and conducting the thyristor T21 in the second valve section; (3) Turn on the thyristor T12 after closing the isolation switch BRK1; Shutdown process: 1) triggering and turning on the thyristor T23 in the second auxiliary switch circuit; 2) Disconnect the isolating switch BRK1; 3) Charging the capacitor C2 of the second auxiliary switch circuit until the arrester operates and absorbs energy.

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