CN107785867A - A kind of dc circuit breaker for reducing drop-out current and its DC Line Fault processing strategy - Google Patents

Abstract

The invention discloses a DC circuit breaker capable of reducing breaking current and its DC fault handling strategy, including a normal flow branch, a cutoff branch, an energy consumption branch, a superconducting current limiter, a reactor and an isolating switch , the normal flow branch is composed of an ultra-fast mechanical switch and a load transfer switch in series, the cut-off branch is composed of a main circuit breaker, the energy consumption branch is composed of a lightning arrester, and the load transfer switch is composed of multiple sub-modules with bidirectional flow capacity connected in series and parallel , the main circuit breaker can be composed of multiple enhanced half-bridge sub-modules connected in series and parallel. The circuit breaker of the present invention uses a superconducting current limiter to suppress the rising speed and amplitude of the fault current, thereby reducing the breaking current of the circuit breaker, and the number of sub-modules of the main circuit breaker is greatly reduced, which can greatly reduce the engineering cost and operating loss. It has very strong reference significance and use value in engineering.

Description

A DC circuit breaker with reduced breaking current and its DC fault handling strategy

technical field

The invention belongs to the technical field of power electronic systems, and in particular relates to a DC circuit breaker capable of reducing breaking current and a DC fault processing strategy thereof.

Background technique

There are two basic network construction methods for DC power grids: the first network construction method uses a modular multilevel converter (MMC) plus DC circuit breaker scheme based on half-bridge sub-modules. This network construction method is suitable for any number of terminals. The second network construction method uses MMC with DC fault self-clearing capability, such as the MMC based on the full bridge sub-module, but does not require DC circuit breakers. This network construction method is suitable for small-scale networks with less than 10 terminals DC grid. When the half-bridge sub-module MMC plus DC circuit breaker is used to construct the network, the converter station is usually required to continue to operate during the DC line fault and cannot be blocked. The faulty line is quickly cut off by the DC circuit breaker. The fault handling principle is similar to that of the AC power grid. When the network construction method without DC circuit breaker is adopted, the relevant converters in the network are blocked during the DC line fault, and the fault current reaches zero and stabilizes at zero value about 10ms after the blockage, and then the faulty line is isolated through the isolation switch, and then the relevant converters Unlocking and resuming power transmission, the time from the fault to resume power transmission is generally about 20ms, and the impact on the AC power grid is usually within the tolerable range.

When the half-bridge sub-module MMC plus DC circuit breaker is used to construct the network, the DC circuit breaker becomes a key component of the DC power grid. At present, the construction scheme of high-voltage DC circuit breakers mainly focuses on three types, namely, traditional mechanical circuit breakers based on conventional switches, solid-state circuit breakers based on pure power electronic devices, and hybrid circuit breakers based on the combination of the two. Although a technically feasible high-voltage DC circuit breaker has been developed, it is difficult to be widely used in the power grid like the AC circuit breaker due to its high cost and large size. In addition, the fault current of the high-voltage large-capacity DC grid system can usually reach tens of thousands of amperes, far exceeding the breaking capacity of current DC circuit breakers. Therefore, DC circuit breakers are still the fundamental technical bottleneck in the development of DC grids.

Contents of the invention

In view of the above, the present invention provides a DC circuit breaker capable of reducing the breaking current and its DC fault handling strategy. The circuit breaker utilizes the high impedance characteristics of the superconducting current limiter in DC faults to suppress the growth rate of the fault current , reduce the breaking current of the circuit breaker, and then reduce the number of sub-modules constituting the main circuit breaker on the main transfer branch under the condition of ensuring safe operation, which can greatly reduce the performance requirements of the DC circuit breaker and reduce the project cost. Very strong reference significance and use value.

A DC circuit breaker capable of reducing the breaking current, comprising a normal flow branch, a cutoff branch, an energy consumption branch, a superconducting current limiter, a reactor and an isolating switch, a normal flow branch and a cutoff branch After the circuit is connected in parallel, one end is connected to one end of the superconducting current limiter, and the other end is connected to one end of the energy consumption branch and the DC transmission line; the other end of the superconducting current limiter is connected to one end of the isolation switch and the other end of the energy consumption branch The other end of the isolating switch is connected to one end of the reactor, and the other end of the reactor is connected to the converter station;

The normal flow branch is composed of an ultra-fast mechanical switch and a load transfer switch in series, the cut-off branch is composed of a main circuit breaker, the energy consumption branch is composed of a lightning arrester, and the main circuit breaker is composed of multiple sub-modules connected in series and parallel , the load transfer switch is composed of multiple sub-modules connected in series and parallel with bidirectional current flow capability.

Further, the sub-module of the main circuit breaker adopts an enhanced half-bridge sub-module structure.

Further, the enhanced half-bridge sub-module structure includes two IGBT tubes T1-T2 with anti-parallel diodes, two diodes D1-D2 and a capacitor C1; wherein, the emitter of the IGBT tube T1 and the cathode of the diode D1 Connected and used as one end of the sub-module, the collector of the IGBT tube T1 is connected to the collector of the IGBT tube T2 and one end of the capacitor C1, the emitter of the IGBT tube T2 is connected to the cathode of the diode D2 and used as the other end of the sub-module, the diode D1 The anode of the diode D2 is connected to the anode of the diode D2 and the other end of the capacitor C1, and the bases of the IGBT tubes T1-T2 are connected to the switch control signal provided by the external control circuit.

Further, the sub-module of the load transfer switch is composed of two IGBT tubes T3-T4 with anti-parallel diodes; wherein, the collector of the IGBT tube T3 is used as one end of the sub-module, and the emitter of the IGBT tube T3 is connected to the IGBT tube T4 The emitters are connected, the collector of IGBT tube T4 is used as the other end of the sub-module, and the bases of IGBT tubes T3~T4 are all connected to the switch control signal provided by the external control circuit.

The DC fault handling strategy of the DC circuit breaker includes the following steps:

(1) During normal operation, the isolating switch and the ultra-fast mechanical switch are closed, all the sub-modules in the load transfer switch are in the on state, and all the sub-modules in the main circuit breaker are in the off state;

(2) In the case of a short-circuit fault on the DC transmission line, when the fault current is detected, firstly apply a turn-on signal to all sub-modules in the main circuit breaker, and then apply a turn-off signal to all sub-modules in the load transfer switch after a short delay. off signal;

(3) After a short delay, turn off the ultra-fast mechanical switch; after the ultra-fast mechanical switch is completely off, set all the sub-modules in the main circuit breaker to the off state to block the fault current path, and the remaining Energy will be released through energy-consuming branches.

Compared with the prior art, the present invention has the following beneficial technical effects:

1. During steady-state operation, the DC current flows through the normal flow branch, and since the load transfer switch sub-module of the present invention has a small number, the steady-state operation loss is low.

2. Since the present invention adopts a superconducting current limiter, the change speed and peak value of the fault current are suppressed, so the breaking current of the circuit breaker can be reduced, and the number of sub-modules in the main circuit breaker can be greatly reduced, and the investment of the circuit breaker The cost is greatly reduced.

Description of drawings

Fig. 1 is a schematic diagram of the topological structure of the DC circuit breaker of the present invention.

Fig. 2 is a schematic diagram of the sub-module topology of the load transfer switch.

Figure 3 is a schematic diagram of the topology structure of the enhanced half-bridge sub-module of the main circuit breaker.

Fig. 4 is a schematic diagram of a simulation waveform of the DC circuit breaker of the present invention.

Detailed ways

In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, the DC circuit breaker that can reduce the breaking current of the present invention includes a normal current flow branch, a current interruption branch, an energy consumption branch, a superconducting current limiter, a reactor and an isolating switch. The circuit is connected in parallel with the current-breaking branch and then connected in series with the superconducting current limiter, and the whole connected in series is connected in parallel with the energy-consuming branch; the connection point between the energy-consuming branch and the superconducting current-limiter is connected with one end of the isolating switch, The other end is connected to one end of the reactor, and the other end of the reactor is connected to the converter station; the common connection point of the normal flow branch, the cut-off branch and the energy consumption branch is connected to the DC transmission line; the normal flow branch is connected to the The ultra-fast mechanical switch and the load transfer switch are composed in series, the current breaking branch is composed of the main circuit breaker, the energy consumption branch is composed of the lightning arrester, the main circuit breaker is composed of multiple sub-modules SM2 connected in series and parallel, and the load transfer switch is composed of multiple The sub-modules SM1 are connected in series and parallel. The structure of the sub-module SM1 is shown in FIG. 2 , and the structure of the sub-module SM2 is shown in FIG. 3 .

For the sub-module SM1, when all the IGBTs are turned on, the current can flow through the IGBT or its anti-parallel diode, which is recorded as the on state; when all the IGBTs are turned off, the current cannot flow, which is recorded as the off state. For the sub-module SM2, when all the IGBTs are turned on, the current flows through the IGBT, and the capacitor is bypassed, which is recorded as the on state; when all the IGBTs are turned off, the current flows through the capacitor branch, which is recorded as the off state .

The superconducting current limiter has the following three characteristics: ① It has low impedance characteristics during normal power transmission of the grid; ② It can quickly turn to high impedance characteristics when a short-circuit fault occurs in the grid, effectively limiting the short-circuit current; ③ It can automatically and timely return to a low impedance state.

The DC fault handling strategy of the DC circuit breaker of the present invention includes the following steps:

(1) Before the fault occurs, the isolating switch is closed, the ultra-fast mechanical switch is closed, all the sub-modules of the load transfer switch are in the on state, all the sub-modules of the main circuit breaker are in the off state, and the DC current flows through the normal flow branch;

(2) When a DC fault is detected, set all the sub-modules of the main circuit breaker to the on state, and then set all the sub-modules of the load transfer switch to the off state;

(3) After a short delay, turn on the ultra-fast mechanical switch;

(4) After the ultra-fast mechanical switch is completely in the off state, after a short delay, set all sub-modules of the main circuit breaker to the off state to block the fault current path.

The following uses a single-ended 400kV, 400MW test system for simulation verification, and the DC circuit breaker uses the circuit breaker shown in Figure 1.

Assuming that the test system has entered steady-state operation at t=2s, a single-pole grounding short circuit occurs at the outlet of the smoothing reactor at t=2s, the load transfer switch is turned off at t=2.003s, and the high-speed machine is at t=2.0031s The switch adds a disconnection command, the high-speed mechanical switch is fully opened at t=2.005s, and the disconnection branch is added with a shutdown command at t=2.0051s. Fig. 4 shows the variation curves of DC fault current I _dc1 , the pressure U _{breaker at both ends of the circuit breaker} and the MMC DC side voltage U _dc . It can be seen from Fig. 4 that the DC circuit breaker of the present invention has good current breaking characteristics.

The above description of the embodiments is for those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to the above-mentioned embodiments, and apply the general principles described here to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention should fall within the protection scope of the present invention.

Claims (5)

1. A DC circuit breaker capable of reducing breaking current, characterized in that: it comprises a normal flow branch, a cutoff branch, an energy consumption branch, a superconducting current limiter, a reactor and a disconnector, and the normal flow After the branch is connected in parallel with the current breaking branch, one end is connected to one end of the superconducting current limiter, and the other end is connected to one end of the energy consumption branch and the DC transmission line; the other end of the superconducting current limiter is connected to one end of the isolating switch and the power consumption The other end of the energy branch is connected, the other end of the isolating switch is connected to one end of the reactor, and the other end of the reactor is connected to the converter station; The normal flow branch is composed of an ultra-fast mechanical switch and a load transfer switch in series, the cut-off branch is composed of a main circuit breaker, the energy consumption branch is composed of a lightning arrester, and the main circuit breaker is composed of multiple sub-modules connected in series and parallel , the load transfer switch is composed of multiple sub-modules connected in series and parallel with bidirectional current flow capability. 2. The DC circuit breaker according to claim 1, characterized in that: the sub-module of the main circuit breaker adopts an enhanced half-bridge sub-module structure. 3. The DC circuit breaker according to claim 2, characterized in that: the enhanced half-bridge sub-module structure includes two IGBT tubes T1-T2 with anti-parallel diodes, two diodes D1-D2 and a capacitor C1 ; Among them, the emitter of the IGBT tube T1 is connected to the cathode of the diode D1 and is used as one end of the sub-module, the collector of the IGBT tube T1 is connected to the collector of the IGBT tube T2 and one end of the capacitor C1, and the emitter of the IGBT tube T2 is connected to the diode The cathode of D2 is connected as the other end of the sub-module, the anode of diode D1 is connected with the anode of diode D2 and the other end of capacitor C1, and the bases of IGBT tubes T1-T2 are connected to the switch control signal provided by the external control circuit. 4. The DC circuit breaker according to claim 1, characterized in that: the sub-module of the load transfer switch is composed of two IGBT tubes T3-T4 with anti-parallel diodes; wherein, the collector of the IGBT tube T3 is used as a sub-module At one end of the module, the emitter of the IGBT tube T3 is connected to the emitter of the IGBT tube T4, the collector of the IGBT tube T4 is used as the other end of the sub-module, and the bases of the IGBT tubes T3~T4 are connected to the switch control signal provided by the external control circuit . 5. The DC fault handling strategy of the DC circuit breaker according to any one of claims 1 to 4, comprising the following steps: (1) During normal operation, the isolating switch and the ultra-fast mechanical switch are closed, all the sub-modules in the load transfer switch are in the on state, and all the sub-modules in the main circuit breaker are in the off state; (2) In the case of a short-circuit fault on the DC transmission line, when the fault current is detected, firstly apply a turn-on signal to all sub-modules in the main circuit breaker, and then apply a turn-off signal to all sub-modules in the load transfer switch after a short delay. off signal; (3) After a short delay, turn off the ultra-fast mechanical switch; after the ultra-fast mechanical switch is completely off, set all the sub-modules in the main circuit breaker to the off state to block the fault current path, and the remaining Energy will be released through energy-consuming branches.