222 results about "Soft switching" patented technology

The invention discloses a high-efficiency single-stage bidirectional power conversion topological structure capable of realizing full-range soft switching and a control method of the high-efficiency single-stage bidirectional power conversion topological structure. In a single-stage bidirectional power conversion topology formed by double half bridges and a switch matrix, a controlled current source connected in parallel with a primary side of a second transformer is designed; the current on a bridge arm connected with the primary side of the second transformer can be effectively changed, so that the soft switching range of a switching tube on the bridge arm in a wide power transmission range is widened, and full-range soft switching in a power frequency period can be realized in any load range; the controlled current source is designed to only work before and after the switching moment of the primary side switching tube of the second transformer, the current stress of the switching tube can be effectively reduced, and meanwhile, the loss of the additional controlled current source is very small. According to the invention, the working range of the soft switching is widened, the additional loss caused by the soft switching is greatly reduced, higher efficiency and higher power density can be realized, and the cost advantage is realized.

The invention discloses an OLTC topological structure of an electronic soft switching technology and a driving method. In the topological structure, a power supply is connected with a first transformer, the first transformer is connected with a second transformer, and the second transformer is connected with a load; a low-voltage winding of the first transformer is connected with a plurality of taps; the fixed end of the low-voltage winding of the first transformer and each tap are connected with one end of an independent mechanical switch; according to an interval connection mode, the other ends of all the mechanical switches are connected to form two series switch loops, and each series switch loop is connected with an independent electronic change-over switch to form two series circuits; the two electronic change-over switches are connected in parallel, and the second transformer is connected into a series circuit controlled by the two electronic change-over switches respectively. The mechanical switch and the electronic change-over switch are jointly used, so that short-circuit current and surge voltage cannot be generated when the electronic change-over switch performs state switching, and the quality of output voltage waveforms is improved.

The invention relates to a dual-active bridge converter backflow power and soft switching range coordinated optimization control method, which widens the soft switching range of a dual-active bridge under full power on the premise of keeping the lowest backflow power, thereby improving the converter efficiency under a high switching frequency scene. According to the scheme, an optimization mapping relation of combination of different optimization input parameters k and output shift phases is given, so that control and implementation are facilitated.

The invention discloses a trapezoidal wave current soft switching method of an interleaving DC-DC converter, which is used for a two-phase interleaving bidirectional DC-DC converter based on a coupling inductor and a multi-phase interleaving converter thereof, and is characterized in that an inductive current adopts a trapezoidal wave mode, so that the converter works in an approximate critical conduction mode; a fixed switching frequency control or hybrid control method is adopted, so that the device can work in a Buck mode and can also work in a Boost mode. The method for realizing the soft switching is characterized in that the parasitic capacitance or the external resonant capacitor of the switching tube is discharged to be zero under the resonance action of the inductor and the capacitor in the dead zone time when the upper bridge arm switch and the lower bridge arm switch are alternately switched on, so that the zero-voltage switching-on of all the switching tubes is realized. And each phase current sharing control is adopted in the multi-phase interleaving parallel topological structure. According to the invention, the problems of large current peak value and high turn-off loss of a traditional triangular wave current mode are solved, the output ripple current is reduced, a soft switching method is provided, the switching loss is reduced, and the conversion efficiency of the converter is improved.

The application provides a driving method of an inverter bridge, a driving circuit, a servo driver and a motor device. In the driving method of the inverter bridge, voltage vector output time and dead time are set, so that a power switch tube of a jth bridge arm is kept in a conduction state in two adjacent voltage vector output times before switching, the power switch tubes kept in the conduction state are changed in turn and staggeredly, in each dead time, two other power switch tubes kept in the conduction state in a previous voltage vector output time are switched off, the corresponding switching bridge arm and winding complete resonance work, the end voltage of the power switch tube to be turned on is clamped to zero potential, zero voltage conduction is realized, a soft switching mode is formed, and the switching loss is reduced and the power conversion efficiency is improved.

The invention relates to the field of power electronic converters and control, in particular to an SOP power module dead-zone effect suppression method, which comprises the following steps: acquiring the current transmission power of an SOP power module; based on the transmission power, generating a first bus voltage instruction used for controlling an AC-DC side direct current bus voltage and a second bus voltage instruction used for controlling a DC-AC side direct current bus voltage, adjusting the corresponding direct current bus voltage so as to inhibit polarity reversal of a DAB converter bridge port voltage, and according to the transmission power of the SOP power module, adjusting the polarity of the DAB converter bridge port voltage. A first bus voltage instruction and a second bus voltage instruction are generated, the first bus voltage instruction and the second bus voltage instruction are made to be unequal during light load, a bus voltage difference value is formed, and it is ensured that the direct-current bus voltages on the two sides meet the condition for restraining DAB bridge port voltage polarity reversal in the dead-zone time period by means of compensation for frequency doubling fluctuation components in the direct-current bus voltages. Current zero step is eliminated, soft switching is recovered, voltage stability under light load is improved, extra hardware or complex control is not needed, and engineering realization is simple and convenient.

The invention provides a wireless electric energy transmission system and a control method, relates to the technical field of wireless electric energy transmission, and is used for realizing soft switching irrelevant to the load weight and the coupling coefficient so as to improve the system efficiency and reduce the thermal runaway risk. The wireless power transmission system comprises an inverter, a magnetic coupling structure, a rectifier and a controller, the input end of the inverter is electrically connected with the direct-current power supply end, and the output end of the inverter is electrically connected with the input end of the magnetic coupling structure; the input end of the rectifier is electrically connected with the output end of the magnetic coupling structure; the output end of the rectifier is connected with a load; the control end of the controller is electrically connected with the control end of the inverter; and the controller is configured to collect the voltage of the input end of the magnetic coupling structure in real time, compare the voltage with a preset upper threshold voltage and a preset lower threshold voltage, and output a driving signal according to a comparison result to control the on and off of the inverter, so that the inverter realizes zero-voltage switching in a full-power range.

The invention discloses a bidirectional DC-AC converter control method considering a soft switching condition and current optimization. According to the invention, the switching loss of the converter is reduced by optimizing the phase shift angle and the switching condition of the converter, and the energy transmission efficiency is optimized by minimizing the effective value of the current, so that the performance of the whole sodium battery energy storage system is improved. Specifically, based on the relation between the excitation inductance Lm and the current effective value Iprms, the phase shift angle of the converter is accurately controlled, the current transmission efficiency is optimized, and it is ensured that the zero-voltage switching condition of a primary side bridge arm and a secondary side bridge arm can be achieved in the working process, so that the loss of the converter is remarkably reduced, and the energy conversion efficiency is improved.

The invention relates to a converter circuit and electronic equipment. The converter circuit comprises an active clamping circuit, a control circuit and a voltage stabilizing circuit, active devices in the active clamping circuit are controlled through the active clamping circuit to realize soft switching, that is, a first switching tube and a second switching tube are controlled to realize soft switching, so that the conduction loss of the first switching tube and the second switching tube is reduced, and the switching efficiency is improved. The problem that large loss is caused when the PFC converter works at high frequency due to the fact that an existing passive clamping circuit cannot achieve soft switching is solved.

The invention discloses a flexible power distribution system planning method and system based on a long-short time energy storage type soft switch. The method comprises the following steps: establishing a source-network-load-storage cooperative operation framework of a flexible power distribution system; constructing a long-short time energy storage type soft switch model, wherein the long-short time energy storage type soft switch model is formed by integrating an energy type energy storage unit and a power type energy storage unit to a direct current side of a soft switch; an integrated planning model of the flexible power distribution system is established, wherein the integrated planning model comprises configuration and operation constraints of source side, network side, load side and storage side equipment based on a collaborative operation framework, and an optimization objective function with the purpose of minimizing the total cost of the whole life cycle of the system; and solving the integrated planning model, and determining an optimal configuration capacity and an operation strategy of each device in the system. Through the introduction of the long and short time energy storage type soft switch, although the early equipment investment is increased, the total cost of the scheme is reduced in the whole planning period due to the operation benefit brought by the long and short time energy storage type soft switch.

The invention discloses an auxiliary resonance full-soft switching FSS-BUCK direct current converter which comprises an input filter capacitor C0, a main switching tube S1, an auxiliary resonance switching tube S1a, a resonant capacitor Cr1, an output filter inductor L1, a resonant inductor Lr1, a fly-wheel diode D1 and an output filter capacitor C1. The invention further discloses a control method. The control method of the FSS-BUCK direct-current converter is as simple as control of a common BUCK topology, the efficiency of a traditional BUCK topology circuit is greatly improved, the limitation of the switching frequency of a power electronic device is broken through, the power electronic device can be used in an over-limit mode, and the FSS-BUCK direct-current converter is a breakthrough key technical invention in the field of new energy in the future.

The invention provides a resonant converter parameter optimization method and system of an electric vertical take-off and landing aircraft, and relates to the technical field of aviation power electronics. The method comprises the following steps: constructing an improved equivalent circuit model containing transformer secondary side leakage inductance; deriving a voltage gain function expression of the improved equivalent circuit model and an optimization calculation formula of the excitation inductance required for realizing the soft switching; parameter optimization is carried out based on the voltage gain function expression and the excitation inductance optimization calculation formula; and building an LLC resonant converter experimental prototype according to the optimized parameters, and carrying out system verification and performance evaluation. According to the invention, the problem of performance reduction caused by neglecting secondary side leakage inductance under a high-frequency working condition in a traditional design is solved, the efficiency, the voltage stabilization precision and the power density of the converter are remarkably improved, and the high requirement of eVTOL on an airborne power supply is met.

The invention provides a multi-resonant switched capacitor efficient cooperative operation method suitable for battery active equalization, and the method comprises the steps: building a zero-voltage soft switching realization condition model of a single-module resonant unit, and determining the amplitude constraint and direction constraint of a soft switching current needed by a switching tube for realizing zero-voltage switching; based on topology, identifying current paths of the half bridges located at the top layer, the middle layer and the bottom layer in the soft switching transient process, and determining a mathematical relationship between the soft switching current of each layer of half bridge and the current of each resonant cavity; respectively establishing equivalent circuit models at switching moments for the top-layer half-bridge, the middle-layer half-bridge and the bottom-layer half-bridge, and solving to obtain each initial current value of the corresponding junction capacitor voltage at the switching moments; and substituting each initial current value obtained by solving into the established constraint condition, and drawing an operation parameter boundary of the topology capable of realizing soft switching in all working modes. According to the invention, by determining the operation boundaries of all half-bridge soft switches of the multi-resonant switched capacitor structure, the switching loss is reduced, and the operation efficiency is improved.

The invention discloses a reactive power optimization control method suitable for a series resonance dual active bridge, relates to the technical field of power electronic converter control, and solves the problem that an effective compensation scheme is not provided for an incomplete soft switching problem caused by dead time in the prior art. And the requirement of all-working-condition efficient operation in engineering application is difficult to meet. Based on triple phase shift control, the optimal phase shift angle combination is accurately solved through the power factor Lagrange function and the KKT condition, the reactive power of the primary side or the secondary side can be counteracted in a targeted manner, and the energy circulation of the resonant cavity is effectively inhibited; meanwhile, soft switching boundary analysis and critical phase compensation are combined, so that zero-voltage switching of all main switching tubes in a full-voltage gain and full-load range can be ensured, and switching loss is reduced; and a mode switching mechanism is designed in control logic to adapt to dynamic working condition response requirements, so that the energy transmission efficiency and working condition adaptability of the series resonance dual-active bridge converter are greatly improved.

The invention relates to a vehicle large screen soft switching control method and device, a vehicle and a medium, and the method comprises the steps: generating a first function enabling signal based on an operation signal of large screen soft switching under the condition that a target function corresponding to the operation signal is allowed to be executed; judging whether the target function is allowed to be executed or not based on the enabling confirmation signal, and generating a second function enabling signal when a comparison result of a judgment result and the first function enabling signal meets a preset comparison condition; sending a clock response signal to a preset control component, and if a clock feedback signal fed back by the preset control component is received in a preset time window, generating a third function enable signal; and according to the first function enable signal, the second function enable signal and the third function enable signal, triggering or forbidding execution operation on the target function. Therefore, the problem of potential safety hazards caused by unexpected opening or closing of functions due to component faults in the prior art is solved, and the function safety and the driving safety of the cabin system are improved.

This invention proposes a three-active half-bridge DC-DC converter and its control method based on device reuse, belonging to the field of power electronics technology. To address the problems of complex architecture and low transmission efficiency in existing dual-active-bridge DC-DC converters, it includes: an FSBB circuit and a TAHB circuit. The FSBB circuit includes an extended half-bridge. HB 0. Energy storage inductor L m and reused half bridge HB 1. The TAHB circuit includes a multiplexed half-bridge. HB 1. Transmission half-bridge HB 2 and transmission half-bridge HB 3. The control method includes: switching the three active half-bridge DC-DC converter to single-input dual-output mode or dual-input single-output mode according to the number of input and output ports in the bidirectional port; setting the control strategy of TAHB circuit and FSBB circuit; and triggering eight working modes in sequence according to the closed / open state of different switching transistors. In each working mode, soft switching of the switching transistor is achieved by discharging the parasitic capacitance of the body diode of the switching transistor through the inductor current, thereby completing the high-efficiency transmission of energy storage.

The invention discloses a steam pump auxiliary steam source pressure adjusting system and a control method thereof. The steam pump auxiliary steam source pressure adjusting system comprises a steam source access module, a pressure obtaining module, an adjusting execution module, an adjusting coordination unit, a steam source soft switching module and a pressure stabilizing module. According to the pressure regulating system for the auxiliary steam source of the steam pump, through the synergistic effect of the steam source access module and the pre-filling unit, the output pipeline is supplemented with pressure in advance when the main steam pressure tends to drop, sudden drop of the pressure of a downstream pipeline is effectively avoided, steam supply continuity is guaranteed, and energy consumption is reduced. The pressure acquisition module forms closed-loop feedback through a near-end pressure acquisition unit and a far-end pressure correction unit, so that the adjustment execution module can quickly adjust the output pressure of main steam and standby steam according to a real-time deviation signal, and the adjustment coordination unit dynamically distributes the opening degree through a weight balance unit to form master-slave linkage control. Therefore, the overall adjustment response speed and precision are improved.

The invention discloses a non-isolated high-gain bidirectional non-resonant linear soft switching conversion circuit, which comprises a low-voltage side module consisting of a low-voltage power supply, two inductors and two switching tubes; the clamping capacitor soft switching module is composed of an inductor, three capacitors and four switching tubes; and the high-voltage side module consists of a high-voltage power supply and a capacitor. The conversion circuit can work in a boost mode and a buck mode, power is transmitted from a low-voltage power supply to a high-voltage power supply in the boost mode, and power is transmitted from the high-voltage power supply to the low-voltage power supply in the buck mode. The inductance value of the clamping capacitor soft switching module is small, and the current of the clamping capacitor soft switching module has a linear change characteristic in a switching period. In the conversion circuit, before and after the switching tube realizes zero-voltage or zero-current soft switching, the current of the switching tube presents a linear change characteristic, no resonance peak value of voltage or current exists, and the conversion circuit has the unique advantage of non-resonance linear soft switching.

This invention relates to the field of power Internet of Things and smart distribution network monitoring technology, and discloses a smart scheduling system for highway charging resources. The system includes: a dual-end source-side three-level rectification and busbar construction module, which constructs a bipolar three-wire DC transmission busbar between two service areas; a cross-regional transmission line impedance identification and status sensing module, which calculates the distributed inductance and capacitance parameters of long cables in real time; a terminal multi-port adaptive power routing module, which physically selects the voltage level to suit vehicle demand through a switch matrix; and a distributed parameter resonance locking and drive control module, which locks the operating frequency to the line's intrinsic resonant frequency and uses distributed parameters to achieve soft switching. This invention achieves long-distance energy exchange and voltage adaptive matching through cross-regional interconnection and multi-level routing, and transforms line parasitic parameters into resonant elements, reducing transmission losses.

The application discloses a resonant switched capacitor DC / DC converter and a power supply system, comprising: N resonant switched capacitor groups, M capacitors and at least one LC series circuit; N is an integer greater than or equal to 2; M is an integer less than or equal to N; each resonant switched capacitor group comprises: a switch and a resonant circuit; the resonant circuit comprises a resonant inductor and a resonant capacitor; the LC series circuit is connected between any two resonant switched capacitor groups, that is, a circuit in which an inductor and a capacitor are connected in series. Since the resonant inductor is not sufficient to completely discharge the charge on the junction capacitor of the switch at the moment when the switch is turned off, the charge on the junction capacitor of the switch is completely discharged by increasing the inductor, that is, the current is drawn away, so that the switch realizes soft switching. When each switch truly realizes soft switching, the power consumption of the whole resonant switched capacitor DC / DC converter can be reduced, and the power conversion efficiency of the resonant switched capacitor DC / DC converter is improved.

The invention discloses a control method of a multi-level Buck-Boost converter, which belongs to the technical field of power converters, and can realize soft switching of all switching tubes and minimization of inductive current pulsation and effective value by reasonably utilizing each control degree of freedom of the converter and controlling inductive current into a pentagonal form. And an optimal working mode is adopted, and the rising and falling slopes of the inductive current are adjusted in a pseudo inductive current discontinuous mode, so that the circulation time of the negative current is reduced, and the light load efficiency of the converter is improved.

An energy efficiency optimization control method for a single-stage isolation matrix converter is proposed. This method calculates the input current vector magnitude of a three-phase single-stage isolation matrix AC-DC converter, derives the duty cycle expression, minimizes the current stress in the three-phase single-stage isolation matrix AC-DC converter, achieves soft switching, derives the full-bridge phase shift angle expression based on the per-unit value of the input current, designs a single-loop voltage control circuit, does not sample the input current, achieves unity power factor, and keeps the input current sinusoidal.

The invention provides a cascade system control method and a cascade system, the cascade system comprises a first inductor and N power modules (N is an integer greater than or equal to 2), each power module is provided with a first side and a second side, a branch formed by connecting the first sides of the N power modules in series bears a first voltage, and the second side of the N power modules bears a second voltage. The second side of each power module is subjected to a second voltage. Each power module includes a switch operating with a switching cycle. And determining the number of the power modules working in the high-frequency modulation mode according to the ratio of the first voltage to the second voltage, so that the moment when the current flowing through the switch is 0 exists in one switching period. The invention provides a soft switching solution, which can reduce the turn-on loss and is favorable for improving the power density of the cascade system. The condition that ZVS cannot be realized when the duty ratio is about 0 or 1 in a carrier cascading modulation means and the condition that ZVS cannot be realized due to ripple cancellation in a carrier phase-shifting modulation means can be avoided.

The invention discloses a wide-gain high-frequency half-bridge LLC resonant converter based on a preceding-stage Boost, and belongs to the technical field of power electronic converters. The converter adopts a two-stage structure, wherein the front stage is an independently controlled Boost circuit, and the rear stage is a half-bridge LLC resonant circuit and a double-voltage rectifying circuit. And wide voltage gain adjustment is realized by coordinating and controlling the duty ratio of the front-stage switching tube and the switching frequency of the rear-stage switching tube. A post-stage circuit works in a high-frequency state, soft switching operation is achieved, the wide gain and high efficiency are achieved, and the circuit is particularly suitable for high-power-density power supply occasions where the input voltage change range is large or the output voltage range is required to be wide.

This invention discloses a composite control method for an LLC resonant converter to improve efficiency under light load conditions. The method includes: subtracting the output voltage of the LLC resonant converter from first and second voltage reference values, and then performing PI processing to obtain first and second judgment data; when the first judgment data is greater than a first minimum threshold value, PFM control is applied to the LLC resonant converter; when the first judgment data is less than or equal to the first minimum threshold value, PWM control is initiated, and simultaneously, the second judgment data is compared with the second minimum threshold value. When the second judgment data is greater than the second minimum threshold value, the switches in the LLC resonant converter remain on; when the second judgment data is less than or equal to the second minimum threshold value, all switches are turned off. This invention employs different control schemes in stages according to load changes, enabling soft switching across the entire operating range, narrow frequency range adjustment, and small-range duty cycle variation, thereby improving efficiency under light load conditions.

This invention relates to a bipolar self-equalizing DC-DC converter based on magnetic integration and a soft-switching optimization method. It includes two full-bridge circuits, a four-winding transformer, and a voltage-balanced coupling inductor. The first full-bridge circuit outputs two voltages, which are respectively input to the first and second primary windings of the four-winding transformer. One end of the first and second secondary windings of the four-winding transformer is connected to the midpoints of the first and second arms of the second full-bridge circuit, respectively. The other ends of the first and second secondary windings of the four-winding transformer are connected to one end of the primary and secondary windings of the voltage-balanced coupling inductor, respectively. The other ends of the primary and secondary windings of the voltage-balanced coupling inductor are also connected to one end of a first load and one end of a second load. This invention enables all power semiconductor devices to achieve zero-voltage switching characteristics.

The invention relates to the technical field of DC-DC conversion, and discloses a bidirectional DC-DC converter based on zero-voltage soft switching, which comprises a high-voltage-side full-bridge circuit, the high-voltage-side full-bridge circuit is composed of four high-voltage switching tubes S1 to S4, body diodes D1 to D4 corresponding to the switching tubes and junction capacitors C1 to C4, the output end of the high-voltage-side full-bridge circuit is connected with a high-voltage-side filter capacitor Ch in parallel, and the output end of the high-voltage-side filter capacitor Ch is connected with the output end of the high-voltage-side full-bridge circuit. The voltage stabilizing circuit is used for stabilizing the voltage Uh of the high-voltage side, and the low-voltage side full-bridge circuit is composed of four low-voltage switch tubes S5-S8, body diodes D5-D8 corresponding to the switch tubes and junction capacitors C5-C8. According to the bidirectional DC-DC converter based on the zero-voltage soft switching, zero-voltage switching-on and switching-off of the full-bridge switching tubes are achieved through the resonance network, switching loss is remarkably reduced, particularly, the efficiency is improved by 5%-8% compared with a traditional hard switching under the high-frequency working condition, the rapid dynamic response characteristic is achieved, and the reliability of the converter is improved through the combination of leakage inductance of the transformer and an external resonance inductor. And in combination with phase shift control, full-range soft switching from 20% of rated load to full load is realized.

This utility model pertains to electrical engineering, specifically to step-up converter devices incorporated into backup power supply devices for high-voltage loads obtained from a low-voltage battery. The converter is designed for highly efficient conversion of energy obtained from a low-voltage source, such as a battery, into a high, stabilized voltage for powering high-voltage loads, such as inverters or loads capable of being supplied with constant voltage. The technical result of this utility model is an increase in the efficiency of the output voltage while minimizing switching losses through soft switching and operation with low currents; increased reliability; and an expansion of the device's scope of application. This technical result is achieved through a combination of essential features.The essence of the utility model is that a two-link converter with galvanic isolation is connected to a primary source (1) and to an unregulated push-pull resonant step-up converter (2) connected to a control circuit (3) configured to form symmetrical current pulses alternately flowing from a common wire to a source through its half-winding of a transformer TR1 with a frequency set by the control circuit (3), wherein the unregulated push-pull resonant step-up converter (2) is connected to a step-up stabilized converter (4) connected to a control circuit (5) configured to convert a low, unstabilized input voltage at the terminals of the primary source (1) into a stabilized high voltage at the load (6).

This invention relates to the field of multi-source coordinated control technology in distribution networks, and discloses an automatic switching method and system for multiple power sources in a distribution network. The switching method includes: dynamically modeling the transient power flow of the main power source and distributed power sources in a multi-source distribution network, and performing dynamic response analysis of topology changes; evaluating the system energy obtained from the dynamic modeling using the transient energy function method, calculating the kinetic and potential energy components before and after the switching, and determining the system energy balance state based on the comparison result of the energy difference and the critical energy threshold; and executing phased soft switching control based on the energy evaluation result, through sequential control logic of synchronization stage, power sharing stage, and switching transition stage, and performing gradual power transition between the main power source and distributed power sources according to a predictive control algorithm. This invention achieves real-time power flow reconstruction under topology changes, energy-driven switching decisions, and smooth power transition, reducing voltage fluctuations and transient impacts caused by switching.

The application discloses a control system of a pulse sequence control triangular wave current mode soft switching Buck converter, the Buck converter comprises a direct current input power supply, a first switching tube, a second switching tube, an inductor, an output capacitor and a load, the positive pole of the direct current input power supply is connected with one end of the second switching tube and one end of the inductor through the first switching tube, the other end of the inductor is connected with one end of the output capacitor and one end of the load, the other end of the output capacitor, the other end of the load and the other end of the second switching tube are connected with the negative pole of the direct current input power supply, and the control system comprises a PT controller, a voltmeter for detecting and collecting a voltage signal between the load and a current meter for collecting an inductor current, wherein the input end of the PT controller is connected with the output end of the current meter and the output end of the voltmeter, the output end of the PT controller is connected with the control end of the first switching tube and the control end of the second switching tube, and the control system can control the size of negative current and has a relatively simple structure.