Cuk converter with coupling short-circuit protection function

Abstract

The invention provides a Cuk converter with a coupling short-circuit protection function, which mainly solves the problem of power quality reduction caused by series connection of a circuit breaker and a load, so that the converter has a self short-circuit protection function, and the size of the whole system is reduced. On the basis of a Cuk circuit, a discharge branch composed of an inductor and a capacitor is added, the inductor on the branch is coupled with a first inductor in the Cuk circuit to form a coupled inductor module, a thyristor is added, and the anode of the thyristor is connected with the dotted terminal of the first inductor in series; according to the invention, the system volume is effectively reduced, the voltage stabilization time is increased from 0.11 second to 0.068 second, the system stabilization time is increased by 38.2%, and the electric energy output quality is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of direct current circuit breakers, and mainly relates to a circuit topology structure of a direct current converter with a Z-source circuit breaker structure. Background Art

[0002] In recent years, power electronics technology has developed rapidly, and people's lives and work have gradually become more dependent on intelligent electronic devices, and high-tech electronic devices must have reliable power supplies. From the 1980s when computer power supplies took the lead in realizing the replacement of switching power supplies, to the 1990s when switching power supplies were widely used in various electronic, electrical, communication and testing equipment, the important position of switching power supplies in today's intelligent era has been established. Compared with other power supplies, switching power supplies have greatly improved in terms of function, performance or circuit structure. Products based on switching power supplies are constantly developing in the direction of being smaller, lighter and more efficient. When the electrical technical indicators are qualified, the protection circuit affects the reliability of the product. A protection circuit with excellent performance can ensure the normal operation of the power supply in harsh environments and emergencies, and at the same time plays an important role in ensuring the safety of the entire circuit system.

[0003] DC circuit breakers artificially create a zero-crossing point of current to isolate faults and extinguish arcs. This is currently an effective DC protection method. In practical applications, circuit breakers are usually connected in series between the converter and the load. Arthur H. Chang and other experts proposed three topological structures of Z-source solid-state DC circuit breakers in "AH Chang, BR Snett, A. Avestruz, SB Leeb and JL Kirtley,"Analysis and Design of DC System Protection Using Z-Source Circuit Breaker," in IEEE Transactions on Power Electronics, vol. 31, no. 2, pp. 1036-1049, Feb. 2016, doi: 10.1109 / TPEL.2015.2415775.", which realize the detection and isolation functions of fault current. The Z-source DC circuit breaker has a simple structure and uses thyristors to realize the forced shutdown of current. Yuyang Liu et al. proposed a Boost converter with integrated short-circuit protection function in "Liu Y, Wang Y, Ding S, et al. A Boost Converter Integrated With DC Circuit Breaker [C] / / IECON 2021–47th Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2021: 1-6.", which enables it to have short-circuit protection and low-pass filtering functions without affecting the normal operation of the Boost circuit. However, the Cuk converters currently studied are mainly for power conversion, and additional series relays or circuit breakers are required to ensure the safety of the converter, which will cause the system volume to increase significantly and cannot meet system requirements. At the same time, the basic Cuk converter does not have the performance of low-pass filtering, and there are problems such as long output voltage stabilization time and poor output power quality. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art and solve the problems of the Cuk converter being large in size, lacking low-pass filtering performance, having a long output voltage stabilization time and having poor output power quality, the present invention provides a Cuk converter with a coupled short-circuit protection function.

[0005] The present invention discloses a Cuk converter with coupled short-circuit protection function, which mainly solves the problem of power quality degradation caused by the series connection of the circuit breaker with the load, so that the converter has a self-short-circuit protection function and reduces the volume of the entire system. The present invention mainly improves the following aspects of the Cuk converter:

[0006] 1. The series connection of circuit breakers in the power grid will affect the quality of power output;

[0007] 2. The traditional Cuk converter does not have short-circuit protection function;

[0008] 3. The traditional Cuk converter does not have a low-pass filtering function.

[0009] The technical solution adopted by the present invention to solve the technical problem is as follows: a Cuk converter with a coupled short-circuit protection function comprises a DC power supply, a MOSFET, a thyristor, a first diode, a third diode, a coupled inductor module, a coupled inductor primary winding, a coupled inductor secondary winding, a first capacitor, a second capacitor, a third capacitor, an inductor, a first resistor and a load resistor; the resistor, the capacitor and the inductor are all non-polar devices, the first end of the non-polar device is the input end, and the second end is the output end; the coupled inductor module is defined as a first end and a second end according to the same-name end, and the non-same-name end is a third end and a fourth end; the positive electrode of the DC power supply is connected to the anode of the thyristor; the thyristor is respectively connected to the first resistor and the coupled inductor module; the cathode of the thyristor is respectively connected to the first end of the first resistor and the first end of the coupled inductor module; the second end of the first resistor is connected to the cathode of the first diode; the anode of the first diode is respectively connected to the drain of the MOSFET, the positive electrode of the first capacitor and the third end of the coupled inductor module; the negative electrode of the first capacitor is respectively connected to the anode of the third diode and the first end of the inductor; the second end of the coupled inductor module is respectively connected to the second end of the inductor, the negative electrode of the third capacitor and the first end of the load resistor; the fourth end of the coupled inductor module is connected to the negative electrode of the second capacitor; the source of the MOSFET is respectively connected to the cathode of the third diode, the positive electrode of the second capacitor, the negative electrode of the third capacitor, the second end of the load resistor and the negative electrode of the DC power supply; the first resistor and the first diode form a first discharge branch of the primary winding of the coupled inductor module.

[0010] Furthermore, a Cuk converter with a coupled short-circuit protection function includes a second diode and a second resistor; the second end of the coupled inductor module is connected to the first end of the second resistor; the fourth end of the coupled inductor module is connected to the anode of the second diode; the second end of the second resistor is connected to the cathode of the second diode; the second resistor and the second diode form a second discharge branch of the secondary winding of the coupled inductor module.

[0011] Furthermore, the turns ratio of the primary winding of the coupled inductor to the secondary winding of the coupled inductor is 20:7.

[0012] Furthermore, a Cuk converter coupled with a short-circuit protection function includes a steady-state operating mode, a short-circuit fault instantaneous operating mode, a resonant operating mode, and an energy absorption operating mode;

[0013] The steady-state working mode is: the thyristor is kept in the on state, when the MOSFET is turned on, the primary winding of the coupled inductor is charged; when the MOSFET is turned off, the primary winding of the coupled inductor is discharged, the second capacitor is charged, and a voltage is generated across the load resistor;

[0014] The short-circuit fault instantaneous working mode is as follows: when a short-circuit fault occurs, the second capacitor discharges, generating a large fault current in a short time, and in the discharge branch including the second capacitor, the fault current flows through the secondary winding of the coupled inductor, and causes the primary winding of the coupled inductor to induce a current in the opposite direction to the steady-state working current, the induced current gradually offsets the forward steady-state current, and the current flowing through the thyristor gradually decreases, and when the forward current passing through the thyristor is less than 0, that is, when the reverse bias condition is reached, the thyristor is turned off;

[0015] The resonant working mode is: after the thyristor is turned off, the second capacitor, the third capacitor, and the secondary winding of the coupled inductor form a passive resonant circuit; the system enters a passive LC resonant working state; at this time, the second capacitor and the third capacitor finish discharging, and the secondary winding of the coupled inductor starts discharging;

[0016] The energy absorption mode is: when the secondary winding of the coupled inductor starts to discharge, part of the current flows through the energy absorption circuit composed of the second resistor and the second diode, and part of the current charges the second capacitor; the induced current of the primary winding of the coupled inductor flows through the energy absorption circuit composed of the first resistor and the first diode.

[0017] The beneficial effects of the present invention are as follows: by reusing the inductor devices existing in the basic Cuk circuit, the circuit topology introduces a circuit breaker structure based on the Cuk circuit, so that the conversion circuit has a short-circuit protection function, and the system volume is effectively reduced; while introducing the new short-circuit protection function, the original working mode is slightly affected, and its voltage conversion function is effectively guaranteed, and the output voltage fluctuation does not exceed 2% and can be ignored; the circuit topology solves the resonance problem that may exist when the circuit breaker and the converter are connected in series, and the voltage stabilization time is increased from 0.11 seconds to 0.068 seconds, and the system stabilization time is increased by 38.2%, which effectively improves the quality of power output. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the circuit topology structure of the present invention;

[0019] Figure 2The voltage waveforms at both ends of the simulated load during the full working phase and short circuit fault; (a) is the voltage waveform at both ends of the simulated load during the full working phase; (b) is the voltage waveform at both ends of the simulated load during the short circuit fault;

[0020] Figure 3 The voltage waveforms at both ends of the simulated thyristor during the full working stage and short-circuit fault are shown in Figure 2. (a) is the voltage waveform at both ends of the simulated thyristor during the full working stage; (b) is the voltage waveform at both ends of the simulated thyristor during the short-circuit fault;

[0021] Figure 4 The current waveforms of the full working phase and short-circuit fault of the primary winding of the thyristor and coupled inductor module are simulated; (a) is the current waveform of the full working phase of the primary winding of the thyristor and coupled inductor module; (b) is the current waveform of the short-circuit fault of the primary winding of the thyristor and coupled inductor module;

[0022] Figure 5 The following are the current waveforms of the full working stage and short circuit fault of the secondary winding of the simulated coupled inductor; (a) is the current waveform of the full working stage of the secondary winding of the simulated coupled inductor; (b) is the current waveform of the short circuit fault of the secondary winding of the simulated coupled inductor;

[0023] Figure 6 Output voltage waveforms of the traditional Cuk converter and the Cuk converter with coupled short-circuit protection function at different duty cycles; (a) Output voltage waveforms of the traditional Cuk converter at different duty cycles; (b) Output voltage waveforms of the Cuk converter with coupled short-circuit protection function at different duty cycles;

[0024] In the figure, 1 is a DC power supply, 2 is a thyristor, 3 is a first resistor, 4 is a first diode, 5 is a coupled inductor module, 6 is a primary winding of a coupled inductor, 7 is a secondary winding of a coupled inductor, 8 is a second resistor, 9 is a second diode, 10 is an inductor, 11 is a third capacitor, 12 is a load resistor, 13 is a MOSFET, 14 is a first capacitor, 15 is a second capacitor, 16 is a third diode, 17 is a connection point between the thyristor and the first end of the first resistor and the first end of the coupled inductor module, 18 is a connection point between the second end of the coupled inductor module and the second end of the second resistor The first end of the inductor, the second end of the inductor, the negative electrode of the third capacitor, the first end of the load resistor, 19—the connection point of the anode of the first diode and the drain of the MOSFET, the positive electrode of the first capacitor, and the third end of the coupled inductor module, 20—the connection point of the fourth end of the coupled inductor module and the anode of the second diode and the negative electrode of the second capacitor, 21—the connection point of the negative electrode of the first capacitor and the first end of the inductor, the anode of the third diode, 22—the connection point of the source of the MOSFET and the cathode of the third diode, the positive electrode of the second capacitor, the positive electrode of the third capacitor, the second end of the load resistor, and the negative electrode of the DC power supply. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0026] A Cuk converter with a coupled short-circuit protection function comprises a DC power supply, a MOSFET, a thyristor, a first diode, a second diode, a third diode, a coupled inductor module, a coupled inductor primary winding, a coupled inductor secondary winding, a first capacitor, a second capacitor, a third capacitor, an inductor, a first resistor, a second resistor and a load resistor;

[0027] The positive electrode of the DC power supply is connected to the anode of the thyristor; the thyristor is connected to the first resistor and the coupled inductor module respectively; the cathode of the thyristor is connected to the first end of the first resistor and the first end of the coupled inductor module respectively; the second end of the first resistor is connected to the cathode of the first diode; the anode of the first diode is connected to the drain of the MOSFET, the positive electrode of the first capacitor and the third end of the coupled inductor module respectively; the negative electrode of the first capacitor is connected to the anode of the third diode and the first end of the inductor respectively; the second end of the coupled inductor module is connected to the first end of the second resistor, the second end of the inductor, the negative electrode of the third capacitor and the first end of the load resistor respectively; the fourth end of the coupled inductor module is connected to the anode of the second diode and the negative electrode of the second capacitor respectively; the second end of the second resistor is connected to the cathode of the second diode; the source of the MOSFET is connected to the cathode of the third diode, the positive electrode of the second capacitor, the negative electrode of the third capacitor, the second end of the load resistor and the negative electrode of the DC power supply respectively; the first resistor and the first diode form the first discharge branch of the primary winding of the coupled inductor module;

[0028] The second resistor and the second diode form a second discharge branch of the secondary winding of the coupled inductor module. After adding the second discharge branch, the circuit low-pass filtering performance and output power quality can be improved;

[0029] The turns ratio of the primary winding of the coupled inductor to the secondary winding of the coupled inductor is 20:7; if the turns ratio of the primary winding of the coupled inductor to the secondary winding of the coupled inductor is too large, the fault current transmitted to the primary winding through the coupled inductor via the discharge branch is insufficient to turn off the thyristor; if the turns ratio of the primary winding of the coupled inductor to the secondary winding of the coupled inductor is too small, it will affect the normal operation of the Cuk converter; when the turns ratio of the primary winding of the coupled inductor to the secondary winding of the coupled inductor is 20:7, the output voltage performance of the Cuk converter with coupled short-circuit protection function is optimal;

[0030] When in use, the working process of a Cuk converter coupled with short-circuit protection function can be divided into four parts: (1) steady-state working part (2) short-circuit fault instantaneous working part (3) resonant working part and (4) energy absorption working part;

[0031] 1) Steady-state operation: When the system is working normally, the thyristor remains in the on state and works according to the Cuk circuit principle. When the MOSFET is turned on, the primary winding of the coupled inductor is charged; when the MOSFET is turned off, the primary winding of the coupled inductor is discharged, the second capacitor is charged, and a voltage is generated across the load resistor. When the switching frequency is very high, the current through the secondary winding branch of the coupled inductor can be ignored, and the discharge branch has no effect on the normal working state;

[0032] 2) Short-circuit fault instantaneous working link: When a short-circuit fault occurs, the discharge of the second capacitor generates a large fault current in a short time. In the discharge branch including the second capacitor, the fault current flows through the secondary winding of the coupled inductor and causes the primary winding of the coupled inductor to induce a current in the opposite direction to the steady-state working current. The induced current gradually offsets the forward steady-state current, and the current flowing through the thyristor gradually decreases. When the forward current passing through the thyristor is less than 0, that is, the reverse bias condition is reached, the thyristor is turned off;

[0033] 3) Resonance working link: After the thyristor is turned off, the second capacitor, the third capacitor, and the secondary winding of the coupled inductor form a passive resonant circuit. The system enters the passive LC resonant working state. At this time, the second capacitor and the third capacitor finish discharging, and the secondary winding of the coupled inductor starts discharging;

[0034] 4) Energy absorption link: When the secondary winding of the coupled inductor begins to discharge, part of the current flows through the energy absorption circuit composed of the second resistor and the second diode, and part of the current charges the second capacitor; the induced current of the primary winding of the coupled inductor flows through the energy absorption circuit composed of the first resistor and the first diode. Repeat 3.4. until the energy in the circuit is completely absorbed, achieving short-circuit protection of the circuit.

[0035] The resistors, capacitors and inductors used in the present invention are all non-polar devices, and can achieve effective functions regardless of forward or reverse connection. The first end of the non-polar device is the input end, and the second end is the output end. The present invention is described in terms of the first end and the second end; the coupled inductor module is defined as the first end and the second end according to the same-name ends, and the non-same-name ends are the third end and the fourth end; in actual application, the same-name ends and non-same-name ends of the coupled inductor module cannot be reversed, but the first and second ends of the same-name ends and the third and fourth ends of the non-same-name ends can be reversed without affecting normal use.

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0037] A Cuk converter with a coupled short-circuit protection function comprises: a direct current power supply (1), a thyristor (2), a first resistor (3), a first diode (4), a coupled inductor module (5), a coupled inductor primary winding (6), a coupled inductor secondary winding (7), a second resistor (8), a second diode (9), an inductor (10), a third capacitor (11), a load resistor (12), a MOSFET (13), a first capacitor (14), a second capacitor (15), and a third diode (16). The positive electrode of the direct current power supply (1) is connected to the anode of the thyristor (2); the cathode of the thyristor (2) is connected to the first end of the first resistor (3) and the first end of the coupled inductor module (5); the second end of the first resistor (3) is connected to the cathode of the first diode (4); the anode of the first diode (4) is connected to the drain of the MOSFET (13), the positive electrode of the first capacitor (14), and the third end of the coupled inductor module (5); the negative electrode of the first capacitor (14) is connected to the anode of the third diode (16) and the first end of the inductor (10); the second end of the coupled inductor module (5) is connected to the first end of the second resistor (8), the second end of the inductor (10), the negative electrode of the third capacitor (11), The first end of the load resistor (12) is connected; the fourth end of the coupled inductor module (5) is connected to the anode of the second diode (9) and the cathode of the second capacitor (15); the second end of the second resistor (8) is connected to the cathode of the second diode (9); the source of the MOSFET (13) is connected to the cathode of the third diode (16), the positive electrode of the second capacitor (15), the negative electrode of the third capacitor (11), the second end of the load resistor (12), and the negative electrode of the DC power supply (1); the first resistor (3) and the first diode (4) form a discharge branch of the primary winding of the coupled inductor module; and the second resistor (8) and the second diode (9) form a discharge branch of the secondary winding of the coupled inductor module.

[0038] In order to make the Cuk converter topology with a coupled short-circuit protection function have better performance, it is necessary to design suitable coupled inductor parameters. If the turns ratio of the coupled inductor primary winding (6) to the coupled inductor secondary winding (7) is too large, the fault current transmitted to the primary winding (6) through the discharge branch through the coupled inductor module (5) is insufficient to turn off the thyristor (2); if the turns ratio of the coupled inductor primary winding (6) to the coupled inductor secondary winding (7) is too small, it will affect the normal operation of the Cuk converter. Through simulation and experimental results analysis, it is concluded that the turns ratio of the coupled inductor primary winding (6) to the coupled inductor secondary winding (7) is 20:7.

[0039] The working process of the Cuk converter topology coupled with short-circuit protection function can be divided into four links: (1) steady-state working link, (2) short-circuit fault instantaneous working link, (3) resonant working link and (4) energy absorption working link.

[0040] 1. Steady-state operation: When the system is operating normally, the thyristor remains in the on state and operates according to the Cuk circuit principle. When the MOSFET (13) is turned on, the primary winding (6) of the coupled inductor is charged; when the MOSFET (13) is turned off, the primary winding (6) of the coupled inductor is discharged, the second capacitor (15) is charged, and a voltage is generated across the load resistor (12). When the switching frequency is very high, the current passing through the branch of the secondary winding (7) of the coupled inductor can be ignored, and the discharge branch has no effect on the normal operating state.

[0041] 2. Short-circuit fault instantaneous working link: When a short-circuit fault occurs, the second capacitor (15) discharges and generates a large fault current in a short time. In the discharge branch including the second capacitor (15), the fault current flows through the secondary winding (7) of the coupled inductor and causes the primary winding (6) of the coupled inductor to induce a current in the opposite direction to the steady-state working current. The induced current gradually offsets the forward steady-state current, and the current flowing through the thyristor (2) gradually decreases. When the forward current passing through the thyristor (2) is less than 0, that is, when the reverse bias condition is reached, the thyristor (2) is turned off.

[0042] 3. Resonance working link: After the thyristor (2) is turned off, the second capacitor (15), the third capacitor (11), and the coupled inductor secondary winding (7) form a passive resonant circuit. The system enters a passive LC resonant working state. At this time, the second capacitor (15) and the third capacitor (11) finish discharging, and the coupled inductor secondary winding (7) starts discharging.

[0043] 4. Energy absorption link: When the secondary winding (7) of the coupled inductor begins to discharge, part of the current flows through the energy absorption circuit composed of the second resistor (8) and the second diode (9), and part of the current charges the second capacitor (15); the induced current of the primary winding (6) of the coupled inductor flows through the energy absorption circuit composed of the first resistor (3) and the first diode (4). Repeat 3.4. until the energy in the circuit is completely absorbed, thus achieving short-circuit protection of the circuit.

[0044] A simulation experiment was conducted in the Simulink platform for the example. The voltage of the DC power supply (1) was set to 12V, the inductance of the primary winding (6) of the coupled inductor was set to 180μH, the inductance of the secondary winding (7) of the coupled inductor was set to 63μH, the first capacitor (14) was set to 220μF, the second capacitor (15) was set to 100μF, the third capacitor (11) was set to 100μF, the inductor (10) was set to 1mH, the load resistor (12) was set to 50Ω, and the short-circuit fault resistance was set to 0.2Ω. The experimental waveform is shown in the figure below. Figure 2 , Figure 3 , Figure 4 , Figure 5 shown.

[0045] In this simulation experiment, the simulated load short-circuit fault occurs at t=0.15s. When the Cuk converter topology system with coupled short-circuit protection function is operating normally, the current of the second capacitor (15) is almost zero, and the discharge branch formed by the second capacitor (15) and the coupled inductor secondary winding (7) will not affect the normal operation of the circuit. When a short-circuit fault occurs at the load end, the load current changes greatly in a very short time, and the second capacitor (15) discharges rapidly, with a maximum discharge current of up to 15.61A. The current of the thyristor (2) begins to decrease until the thyristor (2) is turned off, and this process takes about 6ms. After the thyristor (2) is turned off, the energy absorption circuit absorbs the remaining energy, and the time for the fault to be completely isolated is about 9ms. The above results verify the function of a Cuk converter topology with coupled short-circuit protection function.

Claims

1. A Cuk converter coupled with a short-circuit protection function, characterized in that: The invention comprises a direct current power supply, a MOSFET, a thyristor, a first diode, a third diode, a coupled inductor module, a coupled inductor primary winding, a coupled inductor secondary winding, a first capacitor, a second capacitor, a third capacitor, an inductor, a first resistor and a load resistor; the resistor, the capacitor and the inductor are all non-polar devices, the first end of the non-polar device is the input end, and the second end is the output end; the coupled inductor module is defined as a first end and a second end according to the same-name end, and a third end and a fourth end according to the non-same-name end; the positive electrode of the direct current power supply is connected to the anode of the thyristor; the thyristor is respectively connected to the first resistor and the coupled inductor module; the cathode of the thyristor is respectively connected to the first end of the first resistor and the first end of the coupled inductor module; The second end is connected to the cathode of the first diode; the anode of the first diode is respectively connected to the drain of the MOSFET, the positive electrode of the first capacitor and the third end of the coupled inductor module; the negative electrode of the first capacitor is respectively connected to the anode of the third diode and the first end of the inductor; the second end of the coupled inductor module is respectively connected to the second end of the inductor, the negative electrode of the third capacitor and the first end of the load resistor; the fourth end of the coupled inductor module is connected to the negative electrode of the second capacitor; the source of the MOSFET is respectively connected to the cathode of the third diode, the positive electrode of the second capacitor, the negative electrode of the third capacitor, the second end of the load resistor and the negative electrode of the DC power supply; the first resistor and the first diode form a first discharge branch of the primary winding of the coupled inductor module.

2. A Cuk converter coupled with short-circuit protection function according to claim 1, characterized in that: It includes a second diode and a second resistor; the second end of the coupled inductor module is connected to the first end of the second resistor; the fourth end of the coupled inductor module is connected to the anode of the second diode; the second end of the second resistor is connected to the cathode of the second diode; The second resistor and the second diode form a second discharge branch of the secondary winding of the coupled inductor module.

3. A Cuk converter coupled with short-circuit protection function according to claim 1, characterized in that: The turns ratio of the primary winding of the coupled inductor to the secondary winding of the coupled inductor is 20:

7.

4. The Cuk converter coupled with short-circuit protection function according to claim 1, characterized in that: Including steady-state working mode, short-circuit fault instantaneous working mode, resonant working mode and energy absorption working mode; The steady-state working mode is: the thyristor is kept in the on state, when the MOSFET is turned on, the primary winding of the coupled inductor is charged; when the MOSFET is turned off, the primary winding of the coupled inductor is discharged, the second capacitor is charged, and a voltage is generated across the load resistor; The short-circuit fault instantaneous working mode is as follows: when a short-circuit fault occurs, the second capacitor discharges, generating a large fault current in a short time, and in the discharge branch including the second capacitor, the fault current flows through the secondary winding of the coupled inductor, and causes the primary winding of the coupled inductor to induce a current in the opposite direction to the steady-state working current, the induced current gradually offsets the forward steady-state current, and the current flowing through the thyristor gradually decreases, and when the forward current passing through the thyristor is less than 0, that is, when the reverse bias condition is reached, the thyristor is turned off; The resonant working mode is: after the thyristor is turned off, the second capacitor, the third capacitor, and the secondary winding of the coupled inductor form a passive resonant circuit; the system enters a passive LC resonant working state; at this time, the second capacitor and the third capacitor finish discharging, and the secondary winding of the coupled inductor starts discharging; The energy absorption mode is: when the secondary winding of the coupled inductor starts to discharge, part of the current flows through the energy absorption circuit composed of the second resistor and the second diode, and part of the current charges the second capacitor; The induced current of the primary winding of the coupled inductor flows through an energy absorption circuit composed of a first resistor and a first diode.

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