A low-loss bidirectional DC solid-state circuit breaker based on thyristor and control method thereof

Abstract

The present invention discloses a low-loss bidirectional DC solid-state circuit breaker based on thyristors and a control method thereof. The bidirectional DC solid-state circuit breaker is composed of a main branch, a commutation and capacitor charging branch, an energy absorption branch and a control unit. The present invention can realize the control of the commutation branch in combination with the control unit, and then use the induced current of the coupled inductor to realize the interruption and isolation of the fault current. When the bidirectional DC solid-state circuit breaker is working normally, the main branch current only passes through one semiconductor device, the conduction loss is low, the shutdown is controllable, and the reliability is high. The control algorithm of the present invention is simple, and the current can be effectively monitored and the type of short-circuit fault can be judged.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a low-loss bidirectional DC solid-state circuit breaker based on a thyristor. Background Art

[0002] With the development of distributed power sources such as photovoltaic power generation and wind power generation, DC microgrids have attracted more and more attention as a more efficient access form. Compared with AC power, DC power has better economy and broader development prospects. Moreover, in terms of power transmission, DC power transmission has the advantages of high efficiency and low loss. However, due to the lack of natural zero crossing of DC power, how to effectively achieve fault isolation of DC power grid restricts the development of DC power. At present, DC circuit breakers are an effective way to solve this problem. However, traditional DC circuit breakers have problems such as long shutdown time, complex circuit structure, arc, low reliability and anti-interference. Solid-state circuit breakers based on solid-state power electronic devices have attracted more and more attention due to their advantages such as low loss, low cost and simple structure.

[0003] Z-source solid-state circuit breakers and their derivative topological structures are currently a common type of solid-state circuit breakers. They have a simple circuit structure and do not require additional fault detection and control circuits. They can interrupt and isolate short-circuit faults. However, the performance of Z-source solid-state circuit breakers is greatly affected by factors such as load and line impedance, which restricts their application in practice. In order to enhance the reliability of circuit breakers and reduce the impact of circuit parameters on circuit breaker performance, and to meet the needs of DC microgrids for bidirectional energy flow and bidirectional fault protection, Chinese Patent (202011145187.6) and Chinese Patent (201911098557.2) proposed two bidirectional DC solid-state circuit breakers based on thyristors. These two bidirectional DC solid-state circuit breakers have the advantages of controllable shutdown, high reliability, and fast response speed. However, when the circuit is working normally, the current needs to pass through two semiconductor devices, and the conduction loss is relatively large. Y.Yang and C.Huang proposed a low-loss bidirectional DC solid-state circuit breaker in the document "A Low-Loss Z-Source Circuit Breaker for LVDC Systems, in IEEE Journal of Emerging and Selected Topics in Power Electronics, vol.9, no.3, pp.2518-2528, June 2021", but the circuit breaker is still based on the Z-source structure, with low stability and high possibility of false triggering. Summary of the invention

[0004] In view of the shortcomings of the current bidirectional DC solid-state circuit breakers, the present invention proposes a low-loss bidirectional DC solid-state circuit breaker based on thyristors, which can realize bidirectional flow of energy and bidirectional interruption and isolation of faults. The bidirectional circuit breaker has the characteristics of controllability, high stability, fast response speed, and low conduction loss.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] The thyristor-based low-loss bidirectional DC solid-state circuit breaker has a topological structure consisting of a main branch, a commutation and capacitor charging branch, an energy absorption branch and a control unit. Figure 1 The main branch is composed of a first thyristor (SCR1), a second thyristor (SCR2) and a coupled inductor primary coil (L w1 ), the commutation and capacitor charging branch consists of the first diode (D1), the second diode (D2), the third thyristor (SCR3), the fourth thyristor (SCR4), the fifth thyristor (SCR5), the sixth thyristor (SCR6), the capacitor (C), the coupled inductor secondary coil (L w2 ), resistor (R), the energy absorption branch is composed of a varistor (MOV), and the control unit is composed of a current sensor and a controller.

[0007] The invention is characterized in that: the first thyristor (SCR1) and the second thyristor (SCR2) are connected in reverse parallel to form a bidirectional current flow branch, the anode of the first thyristor (SCR1) is connected to the cathode of the second thyristor (SCR2), the cathode of the first thyristor (SCR1) is connected to the anode of the second thyristor (SCR2), the cathode of the first thyristor (SCR1) and the primary coil of the coupled inductor (L w1 ) are connected to the same end; the positive electrode of the first diode (D1) is connected to the anode of the first thyristor (SCR1), the negative electrode of the first diode (D1) is connected to the negative electrode of the second diode (D2), the positive electrode of the second diode (D2) is connected to the secondary coil of the coupled inductor (L w2 ) opposite ends are connected, the anode of the third thyristor (SCR3) is connected to the anode of the fifth thyristor (SCR5), the cathode of the third thyristor (SCR3) is connected to the anode of the fourth thyristor (SCR4), the cathode of the fourth thyristor (SCR4) is connected to the cathode of the sixth thyristor (SCR6), the anode of the sixth thyristor (SCR6) is connected to the cathode of the fifth thyristor (SCR5), and the coupled inductor secondary coil (L w2 ) is connected to the cathode of the fifth thyristor (SCR5) and the anode of the sixth thyristor (SCR6), and the secondary coil of the coupled inductor (L w2) is connected to the cathode of the third thyristor (SCR3) and the anode of the fourth thyristor (SCR4), the positive electrode of the capacitor (C) is connected to the anode of the fifth thyristor (SCR5), the negative electrode of the capacitor (C) is connected to the cathode of the sixth thyristor (SCR6), one end of the resistor (R) is connected to the negative electrode of the capacitor (C), and the other end is connected to the negative electrode of the power supply; one end of the varistor (MOV) is connected to the anode of the first thyristor (SCR1) and the positive electrode of the first diode (D1), and the other end of the varistor (MOV) is connected to the primary coil of the coupled inductor (L w1 ) opposite-name terminals and the positive electrode of the second diode (D2); the main loop current flows through the current sensor, the output end of the current sensor is connected to the controller, and the output end of the controller is connected to the gates of the first (SCR1), the second (SCR2), the third (SCR3), the fourth (SCR4), the fifth (SCR5), and the sixth thyristor (SCR6).

[0008] The low-loss bidirectional DC solid-state circuit breaker based on thyristors can realize bidirectional flow of energy and bidirectional interruption and isolation of short-circuit faults. The first thyristor (SCR1), the coupled inductor primary coil (L w1 ) constitute the main branch of the forward flow channel of the bidirectional circuit breaker energy, the first diode (D1), the fifth thyristor (SCR5), the coupled inductor secondary coil (L w2 ), the fourth thyristor (SCR4), the capacitor (C) and the resistor (R) constitute the commutation and capacitor charging branch when the energy of the bidirectional circuit breaker flows forward; the second thyristor (SCR2), the coupled inductor primary coil (L w1 ) constitute the main branch of the circuit breaker energy backward flow, the second diode (D2), the third thyristor (SCR3), the coupled inductor secondary coil (L w2 ), the sixth thyristor (SCR6), the capacitor (C), and the resistor (R) constitute the commutation and capacitor charging branch of the bidirectional circuit breaker when the energy flows backward; the varistor (MOV) is the energy absorption circuit of the bidirectional circuit breaker when the energy flows forward and backward; the current sensor and the controller are the control unit of the bidirectional circuit breaker when the energy flows forward and backward.

[0009] The control method of the low-loss bidirectional DC solid-state circuit breaker based on thyristor is characterized by comprising the following steps:

[0010] The output current is I O , set the reference current value to I ref1 ,I ref2 , I ref1 ref2 , output current and reference current I ref1 The difference is: ​

[0011] ΔI=I O -I ref1 (1)

[0012] When a fault occurs:

[0013] Step 1: When △I>0, start to continuously monitor the output current I O The size of

[0014] Step 2: When the output current I O The value is greater than I ref2 And the duration t(s) is greater than T delay , that is, I O -I ref2 >0 duration t(s)>T delay When the controller sends a trigger signal to the gate of thyristors SCR4 and SCR5 (when working in reverse: SCR3 and SCR6) to turn them on, thereby making capacitor C, SCR5, and coupled inductor secondary coil L w2 and SCR4 (when working in reverse: capacitor C, SCR3 coupled inductor secondary coil L w2 and SCR6) form a commutation circuit, thereby isolating the short-circuit fault.

[0015] When the circuit breaker is turned on again: set the minimum time interval from the circuit breaker being turned off to the circuit breaker being turned on again as T0, and the time required for the capacitor to charge is T1. Then the time interval from the circuit breaker being turned off to the circuit breaker being turned on again should be greater than the charging time of the capacitor C, that is, T0>T1.

[0016] When working in reverse, when the output current I O The value is greater than I ref2 And the duration t(s) is greater than T delay , that is, I O -I ref2 >0 duration t(s)>T delay When the controller sends a trigger signal to the gate of thyristors SCR3 and SCR6 to turn them on, the capacitor C, SCR5, and the coupled inductor secondary coil L w2 Together with SCR6, it forms a commutation circuit, thereby isolating the short-circuit fault.

[0017] When the circuit breaker is turned on again: set the minimum time interval from the circuit breaker being turned off to the circuit breaker being turned on again as T0, and the time required for the capacitor to charge is T1. Then the time interval from the circuit breaker being turned off to the circuit breaker being turned on again should be greater than the charging time of the capacitor C, that is, T0>T1.

[0018] Step 3: When a short circuit fault occurs and the circuit breaker is turned off for T0 time, the controller sends a trigger signal to the gate of thyristor SCR1 (when working in reverse: SCR2) to turn on the circuit breaker, and repeats steps 1 and 2. If the circuit breaker is turned off again, it is judged as a permanent fault and the circuit breaker is not turned on again until the fault is completely cleared. Otherwise, it is judged as a transient fault.

[0019] When working in reverse, when a short-circuit fault occurs and the circuit breaker is turned off for T0 time, the controller sends a trigger signal to the gate of thyristor SCR2 to turn on the circuit breaker and repeat steps 1 and 2. If the circuit breaker is turned off again, it is judged as a permanent fault and the circuit breaker is not turned on again until the fault is completely cleared. Otherwise, it is judged as a transient fault.

[0020] The present invention can achieve the following beneficial effects:

[0021] 1) When the bidirectional circuit breaker is operating normally, the current only flows through one thyristor, which greatly reduces the conduction loss of the system;

[0022] 2) The bidirectional circuit breaker uses a controller to detect the current, which enhances the controllability of the circuit breaker, improves the reliability of the circuit breaker, and reduces the possibility of false triggering of the circuit breaker;

[0023] 3) The bidirectional circuit breaker can realize the pre-charging of the commutation branch capacitor and realize the protection of the circuit when the circuit is energized;

[0024] 4) The bidirectional circuit breaker adds current detection and controller to realize the switching function;

[0025] 5) When the fault current is cut off, no large current will be fed back to the power supply end;

[0026] 6) The type of fault can be determined by using a re-conducting circuit breaker. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] One or more embodiments are exemplarily described by corresponding drawings, which do not limit the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements, and the drawings do not constitute a scale limitation, and wherein:

[0028] Figure 1 It is a circuit topology diagram of the present invention;

[0029] Figure 2 This is a working timing diagram of the present invention when a load short circuit fault occurs;

[0030] Figure 3 A flow chart of the control method for fault isolation;

[0031] Figure 4 A flow chart of a control method for determining the fault type during re-conduction;

[0032] Figure 5 This is a working timing diagram when the present invention is used as a switch;

[0033] Figure 6 To simulate the output current, capacitor voltage and capacitor current waveforms when the load is short-circuited;

[0034] Figure 7 The load voltage and load current waveforms are shown in the simulation when the switch function is used to cut off the power to the load. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0036] Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in this field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0037] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0038] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a kind of", "the" and the like involved in this application do not indicate a quantitative limitation and may represent the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device comprising a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices.

[0039] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] The bidirectional DC solid-state circuit breaker based on thyristor disclosed in the present invention is as follows Figure 1 As shown in FIG. 1 , the topological structure is composed of a main branch, a commutation and capacitor charging branch, an energy absorption branch and a control unit. The main branch is composed of a first thyristor (SCR1), a second thyristor (SCR2) and a coupled inductor primary coil (L w1 ), the commutation and capacitor charging branch consists of the first diode (D1), the second diode (D2), the third thyristor (SCR3), the fourth thyristor (SCR4), the fifth thyristor (SCR5), the sixth thyristor (SCR6), the capacitor (C), the coupled inductor secondary coil (L w2 ), resistor (R), the energy absorption branch is composed of a varistor (MOV), and the control unit is composed of a current sensor and a controller.

[0041] The following takes forward operation as an example to introduce the specific working principle of the low-loss bidirectional DC solid-state circuit breaker based on thyristor and the control method thereof proposed by the present invention:

[0042] When the circuit breaker energy flows forward, the first thyristor (SCR1), the coupled inductor primary coil (L w1 ) constitute the main branch of the forward flow channel of the bidirectional circuit breaker energy; the first diode (D1), the fifth thyristor (SCR5), the coupled inductor secondary coil (L w2), the fourth thyristor (SCR4), the capacitor (C) and the resistor (R) constitute the commutation and capacitor charging branch when the energy of the bidirectional circuit breaker flows forward; the varistor (MOV) is the energy absorption branch; the current sensor and the controller are the control unit. At this time, the first thyristor (SCR1) is in the on state, the second (SCR2), the third (SCR3), the fourth (SCR4), the fifth (SCR5), and the sixth thyristor (SCR6) are in the off state, and the power supply charges the capacitor (C) through the first diode (D1) so that its voltage is equal to the power supply voltage.

[0043] like Figure 2 and Figure 3 As shown, the circuit breaker isolates the short-circuit fault. When a short-circuit fault occurs in the load at time t0, the output current I O The output current I O and reference current I ref1 When the difference ΔI is greater than 0, the output current I O When the output current I O The value is greater than I ref2 And the duration t(s) is greater than T delay , that is, I O -I ref2 >0 duration greater than T delay When the controller sends a trigger signal to the gate of the fifth thyristor (SCR5) and the gate of the fourth thyristor (SCR4) to turn them on, the capacitor (C), the fifth thyristor (SCR5), and the coupled inductor secondary coil (L w2 ) and the fourth thyristor (SCR4) form a path, the capacitor (C) discharges, and an instantaneous large current passes through the fifth thyristor (SCR5) and the fourth thyristor (SCR4) and flows through the coupled inductor secondary coil (L w2 ), at this time, the primary coil of the coupled inductor (L w1 ) will generate a reverse induced current, which will reduce the current flowing through the first thyristor (SCR1) to 0 at t3. At this time, the first thyristor (SCR1) is turned off and the fault is removed. After that, the varistor (MOV) absorbs the energy stored in the coupled inductor, and the power supply charges the capacitor (C) through the first diode (D1) again, making its voltage equal to the power supply voltage, preparing for the next shutdown.

[0044] like Figure 4 As shown in the figure, when a short circuit fault occurs and the circuit breaker is turned off for T0 time, the controller sends a trigger signal to the gate of the thyristor SCR1 to turn on the circuit breaker and conduct again. Figure 2 and Figure 3According to the fault detection and isolation steps shown in , if the circuit breaker is turned off again, it is judged as a permanent fault and the circuit breaker is not turned on again until the fault is completely cleared. Otherwise, it is judged as a transient fault.

[0045] like Figure 5 As shown, the circuit breaker is used as a switch to cut off the power to the load. Before time t0, the circuit operates normally. At time t0, the controller sends a trigger signal to the gate of the fifth thyristor (SCR5) and the gate of the fourth thyristor (SCR4) to turn them on. Similarly, at this time, the capacitor (C), the fifth thyristor (SCR5), and the coupled inductor secondary coil (L w2 ) and the fourth thyristor (SCR4) form a path, the capacitor (C) discharges, and an instantaneous large current passes through the fifth thyristor (SCR5) and the fourth thyristor (SCR4) and flows through the coupled inductor secondary coil (L w2 ), at this time, the primary coil of the coupled inductor (L w1 ) will generate a reverse induced current, which will turn off the first thyristor (SCR1) and reduce the load voltage and load current to 0.

[0046] A simulation experiment is carried out in the PLECS simulation software for the example to verify the controllable bidirectional DC solid-state circuit breaker based on thyristor proposed in the present invention. Here, the forward flow of energy of the circuit breaker is taken as an example for explanation. The simulated power supply voltage is 200V, the load is 10Ω, the capacitor is 100uF, the resistor is 40Ω, and the inductance values ​​of the primary coil and the secondary coil of the coupled inductor are 900uH and 100uH respectively.

[0047] Example 1: Simulating a load short circuit fault

[0048] The simulation waveform is as follows Figure 6 As shown, a short circuit fault occurs at t=10s. At this time, the system output current and the current flowing through the first thyristor (SCR1) increase. When the current sensor recognizes that the output current meets the fault protection condition, the controller outputs a control signal to turn on the fifth thyristor (SCR5) and the fourth thyristor (SCR4). At this time, the capacitor discharges (C), the capacitor voltage decreases, and the instantaneous large current is released and flows through the coupled inductor secondary coil (L w2 ), in the coupled inductor primary coil (L w1 ) induces a large reverse current to turn off the first thyristor (SCR1), ultimately isolating the short-circuit fault. After the short-circuit fault is removed, the power supply charges the capacitor (C).

[0049] Example 2: Simulating load disconnection

[0050] The simulation waveform is as follows Figure 7As shown, the controller outputs a control signal to the gate of the fifth thyristor (SCR5) and the gate of the fourth thyristor (SCR4) to turn them on when t=10s. At this time, the capacitor (C) discharges, releasing an instantaneous large current and flowing through the coupled inductor secondary coil (L w2 ), in the coupled inductor primary coil (L w1 ) induces a large reverse current, turning off the first thyristor (SCR1), ultimately cutting off the load power.

[0051] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A low-loss bidirectional DC solid-state circuit breaker based on thyristor, characterized in that: It consists of main branch, commutation and capacitor charging branch, energy absorption branch and control unit. The main branch is composed of a first thyristor SCR1, a second thyristor SCR2 and a coupled inductor primary coil L w1 composition; The commutation and capacitor charging branch comprises a first diode D1, a second diode D2, a third thyristor SCR3, a fourth thyristor SCR4, a fifth thyristor SCR5, a sixth thyristor SCR6, a capacitor C, a coupled inductor secondary coil L w2 , resistor R; The energy absorption branch is composed of varistor MOV; The control unit consists of a current sensor and a controller; The first thyristor SCR1 and the second thyristor SCR2 are connected in reverse parallel to form a bidirectional current flow branch. The anode of the first thyristor SCR1 is connected to the cathode of the second thyristor SCR2, the cathode of the first thyristor SCR1 is connected to the anode of the second thyristor SCR2, and the cathode of the first thyristor SCR1 and the coupled inductor primary coil L are connected. w1 The positive electrode of the first diode D1 is connected to the anode of the first thyristor SCR1, the negative electrode of the first diode D1 is connected to the negative electrode of the second diode D2, and the positive electrode of the second diode D2 is connected to the primary coil of the coupled inductor L w1 The opposite ends are connected, the anode of the third thyristor SCR3 is connected to the anode of the fifth thyristor SCR5, the anode of the third thyristor SCR3 is connected to the cathode of the first diode D1 and the cathode of the second diode D2; the cathode of the third thyristor SCR3 is connected to the anode of the fourth thyristor SCR4, the cathode of the fourth thyristor SCR4 is connected to the cathode of the sixth thyristor SCR6, the anode of the sixth thyristor SCR6 is connected to the cathode of the fifth thyristor SCR5, and the coupling inductor secondary coil L w2 The same-name terminal is connected to the cathode of the fifth thyristor SCR5 and the anode of the sixth thyristor SCR6, and the coupling inductor secondary coil L w2 The opposite end is connected to the cathode of the third thyristor SCR3 and the anode of the fourth thyristor SCR4, the positive electrode of the capacitor C is connected to the anode of the fifth thyristor SCR5, the negative electrode of the capacitor C is connected to the cathode of the sixth thyristor SCR6, one end of the resistor R is connected to the negative electrode of the capacitor C, and the other end is connected to the negative electrode of the power supply; one end of the varistor MOV is connected to the anode of the first thyristor SCR1 and the positive electrode of the first diode D1, and the other end of the varistor MOV is connected to the primary coil of the coupling inductor L w1 The opposite-name end and the positive electrode of the second diode D2 are connected; the main branch current flows through the current sensor, the output end of the current sensor is connected to the controller, and the output end of the controller is connected to the gate of the first thyristor SCR1, the second thyristor SCR2, the third thyristor SCR3, the fourth thyristor SCR4, the fifth thyristor SCR5, and the sixth thyristor SCR6.

2. A low-loss bidirectional DC solid-state circuit breaker based on thyristor as claimed in claim 1, characterized in that: The first thyristor SCR1, coupled inductor primary coil L w1 The first diode D1, the fifth thyristor SCR5, the coupled inductor secondary coil L constitute the main branch of the forward flow channel of the bidirectional DC solid-state circuit breaker energy. w2 , the fourth thyristor SCR4, the capacitor C and the resistor R constitute the commutation and capacitor charging branch when the energy of the bidirectional DC solid-state circuit breaker flows forward; the second thyristor SCR2, the coupled inductor primary coil L w1 The second diode D2, the third thyristor SCR3, the coupled inductor secondary coil L constitute the main branch of the energy backward flow of the bidirectional DC solid-state circuit breaker. w2 The sixth thyristor SCR6, the capacitor C, and the resistor R constitute the commutation and capacitor charging branch when the energy of the bidirectional DC solid-state circuit breaker flows backward; the varistor MOV is the energy absorption circuit when the energy of the bidirectional DC solid-state circuit breaker flows forward and backward; the current sensor and controller are the control unit when the energy of the bidirectional DC solid-state circuit breaker flows forward and backward.

3. A control method for a low-loss bidirectional DC solid-state circuit breaker based on a thyristor according to any one of claims 1 to 2, characterized in that: The following steps are involved: The output current is I O , set the reference current value to I ref1 ,I ref2 , I ref1 ref2 , output current and reference current I ref1 The difference is:​ ΔI=I O -I ref1 When a fault occurs: Step 1: When △I>0, start to continuously monitor the output current I O The size of Step 2: When the output current I O The value is greater than I ref2 And the duration t(s) is greater than T delay When, that is, I O -I ref2 >0 duration t(s)>T delay When the controller sends a trigger signal to the gate of the fourth thyristor SCR4 and the fifth thyristor SCR5 to turn them on, the capacitor C, the fifth thyristor SCR5, and the coupled inductor secondary coil L w2 Together with the fourth thyristor SCR4, it forms a commutation circuit, thereby isolating the short-circuit fault; When the circuit breaker is turned back on: Set the minimum time interval from the circuit breaker turning off to the circuit breaker turning on again as T0, and the time required for capacitor charging as T1. Then the time interval from the circuit breaker turning off to the circuit breaker turning on again should be greater than the charging time of capacitor C, that is, T0>T1 Step 3: When a short circuit fault occurs and the circuit breaker is turned off for T0 time, the controller sends a trigger signal to the gate of the first thyristor SCR1 to turn on the circuit breaker, and repeats steps 1 and 2. If the circuit breaker is turned off again, it is judged as a permanent fault and the circuit breaker is not turned on again until the fault is completely cleared. Otherwise, it is judged as a transient fault.

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