CN2831571Y - Short circuit fault limiter based on self on/off switching element - Google Patents

Abstract

The utility model relates to a short circuit fault limiter based on self on/off switching elements, which is a device applied to alternating voltage power supply systems to limit short circuit fault currents and the climbing rate thereof. The limiter comprises a switching circuit (1), a self on/off switching element current altering bridge (2), a bypass inductor (3) and a direct current limiting reactor (4), wherein the bypass inductor (3) is connected in parallel to both ends of the self on/off switching element current altering bridge (2), and both ends of the direct current limiting reactor (4) are connected in the self on/off switching element current altering bridge (2). The switching circuit (1) is connected in series with the self on/off switching element current altering bridge (2), the bypass inductor (3), a load (5) and a power supply (6) which are arranged outside into a return circuit; the self on/off switching element current altering bridge is connected in parallel with the bypass inductor. The limiter reduces the out-of-control time of the current-altering bridge from a half power frequency period of 10 milliseconds to no greater than 1 millisecond of circuit delay of a current detect and an executive control operation, and the current altering bridge and the direct current reactor are out of work when the inductance electric current passes zero.

Description

Short-circuit fault current limiter based on the self-on-off switching device

Technical field

The utility model is a kind of alternating voltage electric power system that is applied to, and to the device that short-circuit current and climbing thereof limit, belongs to the technical field that exchanges the flexible transmission technology.

Background technology

The increase day by day of electric power system scale, short circuit current numerical value also increase thereupon, and short trouble is also increasing to the harm of system.Solid-state short-circuit fault current limiter by the impedance parameter of quick change faulty line, is limited in the level of permission with short circuit current after detecting short trouble and taking place, with the protection power equipment, become one of key element of flexible AC transmitting system.Patent of invention " a kind of short-circuit protection circuit " (patent No.: ZL 96 123001.0), utility model patent " short circuit current limitation formula three-phase transformer " (patent No.: ZL 00 2 06596.7) and patent of invention " short-circuit fault current limiter " with by-pass inductor (patent No.: 02112334.9) propose based on half control device silicon controlled short-circuit fault current limiter, have: 1) just often, pass through direct current in the current limiting reactor, no pressure drop does not almost have power consumption; 2) during fault, current limiting reactor does not have time-delay and drops into automatically; When 3) excising, controllable silicon turn-offs when current over-zero, can not cause advantages such as overvoltage and additional vibration, patent of invention " the short-circuit fault current limiter " (patent No.: 02112334.9) particularly with by-pass inductor, effectively reducing weight, volume and the cost of device, is to solve practicality of short circuit current limitation technology and effective scheme.But because the unsteady flow bridge circuit in the above-mentioned short-circuit fault current limiter adopts controllable silicon, after short trouble takes place, the time of not controlling that has half period, do not control in the time at this, supply voltage is added on the direct current current-limiting reactor through the unsteady flow bridge circuit, thereby cause the rapid rising of short circuit current, in order to guarantee to be no more than permissible value at half period internal short-circuit electric current, the inductance value of dc inductance is very big, because it is saturated to prevent that the magnetic circuit of direct current reactor must add air gap, the volume of direct current reactor is big, weight is heavier, cost is higher.For this reason, a kind of short-circuit fault current limiter based on self-on-off switching device (as GTO, IGCT etc.) is proposed, can shorten the out-of-control time of unsteady flow bridge circuit greatly, after just shortening the short trouble generation, supply voltage is added on the direct current reactor through bridge circuit and then causes the time that short circuit current rises, the inductance value of direct current current-limiting reactor can reduce 6 times at least, thereby reduces the size of direct current reactor greatly, significantly reduces volume, weight and the cost of flow restricter.

Summary of the invention

Technical problem: the purpose of this utility model provides a kind of short-circuit fault current limiter based on the self-on-off switching device, out-of-control time with the unsteady flow bridge circuit, be reduced to the circuit delay (being not more than 1 millisecond) of current detecting and executive control operation from half power frequency period (10 milliseconds), the inductance value of direct current current-limiting reactor can be reduced more than 6 times, thereby reduce the size of direct current reactor greatly, significantly reduce volume, weight and the cost of flow restricter, can also realize that unsteady flow bridge circuit and direct current reactor deactivate after the inductive current zero passage.

Technical scheme: the short-circuit fault current limiter based on the self-on-off switching device of the present utility model comprises switching circuit, self-turn-off device unsteady flow bridge circuit, shunt inductor, direct current current-limiting reactor; Wherein shunt inductor is connected in parallel on the two ends of self-turn-off device unsteady flow bridge circuit, two of direct current current-limiting reactor terminates in the self-turn-off device unsteady flow bridge circuit, switching circuit with in parallel after self-turn-off device unsteady flow bridge circuit, shunt inductor and outside load, power supply be connected into a loop.

Its basic structure is that self-turn-off device unsteady flow bridge circuit is formed an electric bridge by self-turn-off device T1, T2, T3, T4 and constituted, switching circuit is that bidirectional triode thyristor T5 and self-turn-off device unsteady flow bridge circuit are in series, shunt inductor is the two ends that inductor L2 is connected in parallel on self-turn-off device unsteady flow bridge circuit, and the direct current current-limiting reactor is that two of reactor L1 terminates on the contact of the contact of self-turn-off device T1, T2 in the self-turn-off device unsteady flow bridge circuit and self-turn-off device T3, T4.Also can be inductor L2 is connected in parallel on self-turn-off device unsteady flow bridge circuit by coupling transformer TR1 two ends with shunt inductor.

Scheme of the present utility model can be based on the single-phase bridge flow restricter with by-pass inductor of self-turn-off device; Also can be to be applicable to the band coupling transformer of high-voltage system and the self-turn-off device single-phase bridge flow restricter of by-pass inductor; Also can be based on the three-phase grounding system bridge-type flow restricter with by-pass inductor of self-turn-off device; Also can be to be applicable to the band coupling transformer of high voltage grounding system and the self-turn-off device three-phase bridge flow restricter of by-pass inductor; Also can be based on the three-phase isolated neutral system bridge-type flow restricter with by-pass inductor of self-turn-off device; Can also be to be applicable to the band coupling transformer of high voltage isolated neutral system and the self-turn-off device three-phase bridge flow restricter of by-pass inductor.

With " based on the single-phase bridge flow restricter with by-pass inductor of self-turn-off device " scheme is example, is analyzed as follows:

When the switching tube in the bridge circuit adopts thyristor, because the characteristic that silicon control zero-cross turn-offs, driving pulse takes place, blocks from detecting short trouble, voltage is added in path on the dc inductance through rectifier bridge to cutting off the electricity supply, need the longest half power frequency period time, during this period of time the variation relation of the electric current I d in the dc inductance is shown below:

$I_d=\sqrt{2}{I}_e+{\∫}_0^{\mathrm{\π}}\frac{V_{\mathrm{am}}\sin \left(\mathrm{\ωt}\right)}{{\mathrm{\ωL}}_d}d\left(\mathrm{\ωt}\right)={\sqrt{2}I}_e+\frac{2\sqrt{2}{V}_a}{{\mathrm{\ωL}}_d}---\left(1\right)$

Institute can energy stored be directly proportional in the volume of inductance, weight and the inductance, so minimizing of inductance is exactly minimizing of its maximum energy storage, by following formula as can be known, the energy storage among the dc inductance Ld is:

$E=\frac{L_d}{2}{({\sqrt{2}I}_e+\frac{2{\sqrt{2}V}_a}{{\mathrm{\ωL}}_d})}^2---\left(2\right)$

Get the E minimum, the optimal value that can obtain the inductance of direct current reactor is:

$L_{\mathrm{aop}}=\frac{{2V}_a}{{\mathrm{\ωI}}_e}---\left(3\right)$

Under above-mentioned optimal conditions, the maximum current of process switching tube and direct current reactor is:

$I_{\mathrm{Lam}}=I_{\mathrm{SCRr}}=2{\sqrt{2}I}_e---\left(4\right)$

When the switching tube in the bridge circuit adopts turn-off device IGCT, because IGCT can realize turn-offing by gate signal, so, after detecting the short trouble generation, distribute control signal immediately, the control bridge circuit works in inverter mode, supply voltage process bridge circuit can be added in the time on the dc inductance, shorten within the delay time of testing circuit, thereby further reduce the size of direct current reactor.The key of this way is to shorten signal detection time, and effective method is to adopt fast detecting element testing dc inductance electric current, and judges in view of the above whether short trouble takes place.At present, can detect the transducer of direct current, Hall current sensor and optical current sensor are arranged, the rapidity of these two kinds of transducers is good, it is very little to detect time-delay, considers the time delay of the photoelectric switching circuit that the high voltage environment application need carries out and enough surpluses, the desirable 1mS of this delay time.Under stable state and nominal load current, under the situation about being short-circuited at the t=4.5mS place (the most abominable short circuit), bridge circuit switches to inverter mode by rectification state after 1 millisecond, inductive current increases under the supply voltage effect between 4.5 milliseconds to 5.5 milliseconds, and dc inductance electric current greatest measure is as follows:

$I_d={\sqrt{2}I}_e+{\∫}_{0.0045}^{0.0055}\frac{{\sqrt{2}V}_a\sin \left(\mathrm{\ωt}\right)}{L_d}\mathrm{dt}={\sqrt{2}I}_e+\frac{{0.4424V}_a}{{\mathrm{\ωL}}_d}---\left(5\right)$

In the case, energy stored is in the direct current reactor:

$E=\frac{L_d}{2}{(\sqrt{2}{I}_e+\frac{{0.4424V}_a}{{\mathrm{\ωL}}_d})}^2---\left(6\right)$

Get the E minimum, the optimal value that can obtain dc inductance is:

$L_{\mathrm{dop}}=\frac{{0.31287V}_a}{{\mathrm{\ωI}}_e}---\left(7\right)$

Under this optimal situation, the maximum current of flow through switching tube and direct current reactor still as the formula (4), i.e. 2  I _eThat is to say that the electric current quota of switching tube and dc inductance is constant, the inductance value of dc inductance reduces more than 6 times, thereby makes its volume, weight and cost all dwindle about 6 times.The prerequisite of above-mentioned optimization, be under high voltage environment, current detection signal need pass through the photoelectricity isolation processing, it is longer to detect time-delay, when being applied to low-voltage system, current detecting and carry out the handover operation required time postpone to be reduced to 200 delicate within, thereby with the direct current sensibility reciprocal on the basis of the above, reduce several times again.

Beneficial effect: the utility model self-turn-off device (inverse-impedance type GTO, IGCT etc.) the half control device controllable silicon in the above-mentioned existing flow restricter of replacement, thereby out-of-control time with the unsteady flow bridge circuit, be reduced to the circuit delay (being not more than 1 millisecond) of current detecting and executive control operation from half power frequency period (10 milliseconds), the inductance value of direct current current-limiting reactor can be reduced more than 6 times, thereby reduce the size of direct current reactor greatly, significantly reduce the volume of flow restricter, weight and cost, can also realize that unsteady flow bridge circuit and direct current reactor deactivate after the inductive current zero passage, failure removal is by the bidirectional triode thyristor of string in circuit, and the characteristics of zero-crossing switching guarantee that operation can not cause overvoltage and additional vibration.

Description of drawings

Fig. 1 is the utility model schematic block circuit diagram.Wherein have: switching circuit 1 self-turn-off device unsteady flow bridge circuit 2 shunt inductor 3 direct current current-limiting reactors 4 loads 5 power supplys 6.

Fig. 2 is the utility model example 1, that is: based on the circuit theory schematic diagram of the single-phase bridge flow restricter with by-pass inductor of self-turn-off device.

Fig. 3 is the utility model example 2, is applicable to the circuit theory schematic diagram of the self-turn-off device single-phase bridge flow restricter of the band coupling transformer of high-voltage system and by-pass inductor that is:.

Fig. 4 is the utility model example 3, that is: based on the circuit theory schematic diagram of the three-phase grounding system bridge-type flow restricter with by-pass inductor of self-turn-off device.

Fig. 5 is the utility model example 4, is applicable to the circuit theory schematic diagram of the self-turn-off device three-phase bridge flow restricter of the band coupling transformer of high voltage grounding system and by-pass inductor that is:.

Fig. 6 is the utility model example 5, that is: based on the circuit theory schematic diagram of the three-phase isolated neutral system bridge-type flow restricter with by-pass inductor of self-turn-off device.

Fig. 7 is the utility model example 6, is applicable to the circuit theory schematic diagram of the self-turn-off device three-phase bridge flow restricter of the band coupling transformer of high voltage isolated neutral system and by-pass inductor that is:.

Embodiment

Followingly describe embodiment of the present utility model in detail with reference to accompanying drawing.

This flow restricter comprises switching circuit 1, self-turn-off device unsteady flow bridge circuit 2, shunt inductor 3, direct current current-limiting reactor 4; Wherein shunt inductor 3 is connected in parallel on the two ends of self-turn-off device unsteady flow bridge circuit 2, two of direct current current-limiting reactor 4 terminates in the self-turn-off device unsteady flow bridge circuit 2, switching circuit 1 with in parallel after self-turn-off device unsteady flow bridge circuit 2, shunt inductor 3 and outside load 5, power supply 6 be connected into a loop.

Unsteady flow bridge circuit in this flow restricter is made of inverse-impedance type self-turn-off device such as gate turn-off thyristor GTO, integral gate commutation controllable silicon IGCT, emitter-base bandgap grading turn-off SCR ETO etc.,

Embodiment 1: as shown in Figure 2, be the single-phase bridge flow restricter based on self-turn-off device, the bridge circuit of being made up of self-turn-off device T1 ~ T4, direct current current-limiting reactor L1, by-pass inductor L2, bidirectional triode thyristor T5 etc. form.One of the negative electrode of self-turn-off device T1, T2, direct current reactor L1 terminates at together; The other end of the anode of self-turn-off device T3, T4 and direct current reactor L1 is connected together; The main electrode of the end of the negative electrode of the anode of self-turn-off device T1, self-turn-off device T4, by-pass inductor L2 and bidirectional triode thyristor T5 is connected together; Another main electrode of bidirectional triode thyristor is an exit of flow restricter; The other end of the negative electrode of the anode of self-turn-off device T2, self-turn-off device T3 and by-pass inductor L2 is connected together, and is another exit of flow restricter; Va is a power supply, and R1 is load.

Embodiment 2: as shown in Figure 3, for being used for the single-phase flow restricter with by-pass inductor and coupling transformer based on self-turn-off device of high-voltage system, the bridge circuit, direct current current-limiting reactor L1, coupling transformer TR1, by-pass inductor L2, the bidirectional triode thyristor T5 etc. that are made up of self-turn-off device T1 ~ T4 form.One of the negative electrode of self-turn-off device T1, T2, direct current reactor L1 terminates at together; The other end of the anode of self-turn-off device T3, T4 and direct current reactor L1 is connected together; One of the secondary of the negative electrode of the anode of self-turn-off device T1, self-turn-off device T4, coupling transformer TR1 terminates at together; The other end of the secondary of the negative electrode of the anode of self-turn-off device T2 and self-turn-off device T3, coupling transformer TR1 is connected together; The main electrode of one end on the former limit of coupling transformer TR1, the end of by-pass inductor L2, bidirectional triode thyristor T5 is connected together, and another main electrode of bidirectional triode thyristor T5 is an exit of flow restricter; The other end of the other end on the former limit of coupling transformer TR1 and by-pass inductor L2 is connected together, and is another exit of flow restricter.Va is a power supply, and R1 is load.

Embodiment 3: as shown in Figure 4, for being used for the flow restricter with by-pass inductor based on self-turn-off device of three-phase grounding system, the unsteady flow bridge circuit, direct current current-limiting reactor L1, by-pass inductor L2, L3, L4 and bidirectional triode thyristor T9, T10, the T11 etc. that are made up of self-turn-off device T1 ~ T8 form.In this circuit, the common point of three phase mains is untied, for sake of convenience, originally that end of being connected together of three phase mains is called reference edge.One of the negative electrode of self-turn-off device T1, T3, T5, T7 and direct current current-limiting reactor L1 terminates at together; The other end of self-turn-off device T2, T4, T6, T8 and direct current current-limiting reactor L1 is connected together; The main electrode of the end of the negative electrode of the anode of self-turn-off device T1, self-turn-off device T2, by-pass inductor L2, bidirectional triode thyristor T9 is connected together; Another main electrode of bidirectional triode thyristor T9 and a reference edge of power supply mutually link together; The main electrode of the end of the negative electrode of the anode of self-turn-off device T3, self-turn-off device T4, by-pass inductor L3, bidirectional triode thyristor T10 is connected together; Another main electrode of bidirectional triode thyristor T10 and the b reference edge of power supply mutually link together; The main electrode of the end of the negative electrode of the anode of self-turn-off device T5, self-turn-off device T6, by-pass inductor L4, bidirectional triode thyristor T11 is connected together; Another main electrode of bidirectional triode thyristor T11 and the c reference edge of power supply mutually link together; The negative electrode of the other end of by-pass inductor L2, L3, L4 and the anode of T7, self-turn-off device T8 is ground connection together; R1, R2, R3 are load.

Embodiment 4: as shown in Figure 5, for being used for the flow restricter with by-pass inductor and coupling transformer based on self-turn-off device of high voltage three-phase grounding system, unsteady flow bridge circuit, direct current current-limiting reactor L1, by-pass inductor L2, L3, L4, bidirectional triode thyristor T9, T10, T11 and the three-phase coupling transformer TR1 etc. that are made up of self-turn-off device T1 ~ T8 form.The secondary of coupling transformer TR1 connects by star connection, and the negative electrode of the common point of star connection and the anode of T7, self-turn-off device T8 is connected together; One of the negative electrode of self-turn-off device T1, T3, T5, T7 and direct current current-limiting reactor L1 terminates at together; The other end of self-turn-off device T2, T4, T6, T8 and direct current current-limiting reactor L1 is connected together; The negative electrode of a phase output terminal of coupling transformer TR1 secondary and the anode of self-turn-off device T1, self-turn-off device T2 is connected together; The negative electrode of the b phase output terminal of coupling transformer TR1 secondary and the anode of self-turn-off device T3, self-turn-off device T4 is connected together; The negative electrode of the c phase output terminal of coupling transformer TR1 secondary and the anode of self-turn-off device T5, self-turn-off device T6 is connected together; The mutually former limit of a winding correspondence of the end of by-pass inductor L2, coupling transformer TR1 and this one terminating at together of secondary star connection common point mutually connect this phase load; The mutually former limit of the b winding correspondence of the end of by-pass inductor L3, coupling transformer TR1 and this one terminating at together of secondary star connection common point mutually connect this phase load; The mutually former limit of the c winding correspondence of the end of by-pass inductor L4, coupling transformer TR1 and this one terminating at together of secondary star connection common point mutually connect this phase load; The mutually former limit of a of the other end of by-pass inductor L2, coupling transformer TR1 winding corresponding with this mutually an end of secondary output and the main electrode of bidirectional triode thyristor T9 be connected together, another main electrode of bidirectional triode thyristor T9 connects a phase power supply; The mutually former limit of the b of the other end of by-pass inductor L3, coupling transformer TR1 winding corresponding with this mutually an end of secondary output and the main electrode of bidirectional triode thyristor T10 be connected together, another main electrode of bidirectional triode thyristor T10 connects b phase power supply; The mutually former limit of the c of the other end of by-pass inductor L4, coupling transformer TR1 winding corresponding with this mutually an end of secondary output and the main electrode of bidirectional triode thyristor T11 be connected together, another main electrode of bidirectional triode thyristor T11 connects c phase power supply; R1, R2, R3 are load.

Embodiment 5: as shown in Figure 6, for being used for the bridge-type flow restricter with by-pass inductor based on self-turn-off device of three-phase isolated neutral system, the unsteady flow bridge circuit of being made up of self-turn-off device T1 ~ T6, direct current current-limiting reactor L1, by-pass inductor L2, L3, L4, bidirectional triode thyristor T7, T8, T9 etc. form.In this circuit, the common point of three phase mains is untied, for sake of convenience, originally that end of being connected together of three phase mains is called reference edge.One of the negative electrode of self-turn-off device T1, T3, T5 and direct current current-limiting reactor L1 terminates at together; The other end of self-turn-off device T2, T4, T6 and direct current current-limiting reactor L1 is connected together; The main electrode of the end of the negative electrode of the anode of self-turn-off device T1, self-turn-off device T2, by-pass inductor L2 and bidirectional triode thyristor T7 is connected together, and another main electrode of bidirectional triode thyristor T7 and a reference edge of power supply mutually are connected together; The main electrode of the end of the negative electrode of the anode of self-turn-off device T3, self-turn-off device T4, by-pass inductor L3 and bidirectional triode thyristor T8 is connected together, and another main electrode of bidirectional triode thyristor T8 and the b reference edge of power supply mutually are connected together; The main electrode of the end of the anode of T5, the negative electrode of T6, by-pass inductor L4 and bidirectional triode thyristor T9 is connected together, and another main electrode of bidirectional triode thyristor T9 and the c reference edge of power supply mutually are connected together; The other end of by-pass inductor L2, L3, L4 is connected together; R1, R2, R3 are load.

Embodiment 6: as shown in Figure 7, for being used for the flow restricter with by-pass inductor and coupling transformer based on self-turn-off device of high voltage three-phase isolated neutral system, unsteady flow bridge circuit, direct current current-limiting reactor L1, by-pass inductor L2, L3, L4 and the three-phase coupling transformer TR1 that is made up of self-turn-off device T1 ~ T6, bidirectional triode thyristor T7, T8, T9 etc. form.The secondary of coupling transformer TR1 connects by star connection; One of the negative electrode of self-turn-off device T1, T3, T5 and direct current current-limiting reactor L1 terminates at together; The other end of self-turn-off device T2, T4, T6 and direct current current-limiting reactor L1 is connected together; The negative electrode of a phase output terminal of coupling transformer TR1 secondary and the anode of T1, self-turn-off device T2 is connected together; The negative electrode of the b phase output terminal of coupling transformer TR1 secondary and the anode of self-turn-off device T3, self-turn-off device T4 is connected together; The c phase output terminal of coupling transformer TR1 secondary and the anode of T5, the negative electrode of T6 are connected together; The mutually former limit of a winding correspondence of the end of by-pass inductor L2, coupling transformer TR1 and this one terminating at together of secondary star connection common point mutually connect this phase load; The mutually former limit of the b winding correspondence of the end of by-pass inductor L3, coupling transformer TR1 and this one terminating at together of secondary star connection common point mutually connect this phase load; The mutually former limit of the c winding correspondence of the end of by-pass inductor L4, coupling transformer TR1 and this one terminating at together of secondary star connection common point mutually connect this phase load; The mutually former limit of a of the other end of by-pass inductor L2, coupling transformer TR1 winding corresponding with this mutually an end of secondary output and the main electrode of bidirectional triode thyristor T7 be connected together, another main electrode of bidirectional triode thyristor T7 connects a phase power supply; The mutually former limit of the b of the other end of by-pass inductor L3, coupling transformer TR1 winding corresponding with this mutually an end of secondary output and the main electrode of bidirectional triode thyristor T8 be connected together, another main electrode of bidirectional triode thyristor T8 connects b phase power supply; The mutually former limit of the c of the other end of by-pass inductor L4, coupling transformer TR1 winding corresponding with this mutually an end of secondary output and the main electrode of bidirectional triode thyristor T9 be connected together, another main electrode of bidirectional triode thyristor T9 connects c phase power supply.R1, R2, R3 are load.

Claims (3)

1. the short-circuit fault current limiter based on the self-on-off switching device is characterized in that this flow restricter comprises switching circuit (1), self-turn-off device unsteady flow bridge circuit (2), shunt inductor (3), direct current current-limiting reactor (4); Wherein shunt inductor (3) is connected in parallel on the two ends of self-turn-off device unsteady flow bridge circuit (2), two of direct current current-limiting reactor (4) terminates in the self-turn-off device unsteady flow bridge circuit (2), switching circuit (1) with in parallel after self-turn-off device unsteady flow bridge circuit (2), shunt inductor (3) and outside load (5), power supply (6) be connected into a loop.

2. according to claims 1 described short-circuit fault current limiter based on the self-on-off switching device, it is characterized in that self-turn-off device unsteady flow bridge circuit (2) is by self-turn-off device T1, T2, T3, T4 forms an electric bridge and constitutes, switching circuit (1) is that bidirectional triode thyristor T5 and self-turn-off device unsteady flow bridge circuit (2) are in series, shunt inductor (3) is the two ends that inductor L2 is connected in parallel on self-turn-off device unsteady flow bridge circuit (2), and direct current current-limiting reactor (4) is that two of reactor L1 terminates at the self-turn-off device T1 in the self-turn-off device unsteady flow bridge circuit (2), the contact of T2 and self-turn-off device T3, on the contact of T4.

3. according to claims 1 or 2 described short-circuit fault current limiters, it is characterized in that shunt inductor (3) is inductor L2 is connected in parallel on self-turn-off device unsteady flow bridge circuit (2) by coupling transformer TR1 two ends based on the self-on-off switching device.

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