Showing papers on "Isolation transformer published in 2021"

High-Speed Electromagnetic Transient (EMT) Equivalent Modelling of Power Electronic Transformers

Abstract: The high-speed accurate electromagnetic transient (EMT) simulation of the power electronic transformers (PET) has become a challenge, due to the microsecond-range time steps and the large number of high-frequency semiconductor switches and isolating transformers. Taking the input-series-output-parallel (ISOP) connected cascaded H-bridge (CHB) type dual active bridge (DAB) based PET as an example, this paper proposes a general high-speed equivalent EMT modelling method of PET. First, the isolating transformer within each DAB is discretized into two-port Norton circuits. Second, each CHB-DAB is equivalent to two single-port circuits by eliminating the internal nodes. And the input-side is represented by a Thevenin circuit and the output-side is represented by a Norton circuit. Third, all the CHB-DABs are equivalent to a two-port circuit with all the internal node information preserved. Fourth, the implementation of PET blocking is also considered for startup and fault protective actions. Fifth, the stability of the proposed discrete decoupling method of the PET is verified that it does not introduce specific limitation on the simulation step size. Finally, the developed PET models on PSCAD/EMTDC are shown to be two orders of magnitude faster than the currently available fully-detailed models with negligible loss of accuracy.

Low-Frequency Selection Switch Based Cell-to-Cell Battery Voltage Equalizer With Reduced Switch Count

Abstract: A selection switch based cell-to-cell voltage equalizer requires only one dual-port dc–dc converter shared by all the cells. A cell-to-cell voltage equalizer is proposed that utilizes a capacitively level-shifted Cuk converter and low-frequency cell selection switches. The absence of isolation transformer and diodes in the equalizer leads to high efficiency, and the use of low-frequency selection switches significantly reduces the cost of the drive circuits. A low-frequency cell selection network is proposed using bipolar voltage buses, where the switch count is almost half, compared to the existing low-frequency cell-to-cell equalizers for the case of a large number of cells. A novel approach for cell voltage recovery compensation is proposed, which reduces the number of operations of the selection switches and the equalization time. The proposed equalizer is implemented with relays and verified with an eight-cell Li-ion stack. The developed prototype shows the efficiency of over 90% and good voltage balancing performance during charging, discharging, and varying load conditions. Experimental results also show about one order of magnitude reduction in the number of relay switchings and a significant reduction in equalization time using the proposed voltage compensation.

Design and Experimental Analysis of 166 kW Medium-Voltage Medium-Frequency Air-Core Transformer for 1:1-DCX Applications

Abstract: The galvanic isolation of solid-state transformers (SSTs) is typically realized with a medium-frequency (MF) magnetic-core transformer (MCT). Previous demonstrations indicate that achieving highly power dense and lightweight MCTs imposes several challenges on the design because of stringent requirements related to insulation and cooling. This work investigates the achievable efficiency of an optimized 166kW / 7 kV air-core transformer (ACT), which is a core part of a DC Transformer (DCX), i.e., an unregulated DC-DC SST with a voltage scaling defined by the transformer turns ratio. The ACT features relatively low complexity of the construction, comparably high coupling values, and high efficiency. Modeling, optimization, and construction of the realized ACT are explained and guidelines regarding insulation, cooling, and shielding of the magnetic stray flux are discussed in detail. Furthermore, the prototype is experimentally validated to demonstrate its full functionality. In the investigated DCX, which is based on a series resonant converter (SRC) topology, the realized ACT is found to achieve a full-load efficiency of 99.5% and an unprecedented gravimetric power density of 16.5 kW/kg. With the use of 10 kV SiC MOSFETs, the complete DCX is estimated to reach an efficiency of 99% at 166kW output power.

Principle of Flexible Ground-Fault Arc Suppression Device Based on Zero-Sequence Voltage Regulation

Abstract: Single-line-to-ground (SLG) fault arcs cause the intermittent over-voltages, leading to short circuits within large-scale area. In this paper, a flexible arc suppression device is proposed, which adopts a zigzag grounding transformer, multi-terminal breakers and an isolation transformer to regulate zero-sequence voltage. Principle of zero-sequence voltage regulation (ZVR) and arc suppression method is presented. By carefully choosing the secondary side voltages of grounding transformer as the input of isolation transformer, the zero-sequence voltage is nearly constrained to the opposite of faulty phase supply voltage, and the ground-fault current is limited to a very small value. This device has high adaptability for low-resistance ground fault as it doesn’t adopt any electronic apparatus. A 10kV prototype was established and multiple fault conditions were experimented to verify the effectiveness of the proposed ZVR device and its arc suppression principle.

Three-Phase UPQC Topology Based on Quadruple-Active-Bridge

Abstract: In this study, a three-phase unified power quality conditioner (UPQC) topology based on a quadruple-active-bridge (QAB) is presented as an attractive solution to power quality issues. It is composed of three single-phase series converters, a three-phase shunt converter and a QAB converter located at the common DC-link. Since the bulky low frequency isolation transformers are replaced by the high frequency ones in QAB, it leads to higher power density, reduced weight and volume. The QAB converter could function as an energy router to provide multiple DC-link voltage access ports in the UPQC, which increase the flexibility of the UPQC. Finally, the MATLAB/Simulink simulation results and hardware-in-the-loop testing verify the correctness and effectiveness of the proposed topology and control method.

Novel Five-Level ANPC Bidirectional Converter for Power Quality Enhancement during G2V/V2G Operation of Cascaded EV Charger

Abstract: This paper presents a novel single-phase (SP) active-neutral point clamped (ANPC) five-level bidirectional converter (FLBC) for enhancing the power quality (PQ) during the grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operation of an electric vehicle (EV) charger connected in series. This EV charger is based on a dual-active half-bridge DC-DC converter (DAHBC) with a high frequency isolation transformer. Unlike the comparable ANPC topologies found in literature, the proposed one has two more switches, i.e., ten instead of eight. However, with the addition of these components, the proposed multilevel converter not only becomes capable of properly balancing the voltage of the DC-link split capacitors under various step-changing conditions but it achieves a better efficiency, a lower stress of the switching devices and a more even distribution of the power losses. The resulting grid-tied ANPC-SPFLBC and DAHBC are accurately controlled with a cascaded control strategy and a single-phase shift (SPS) control technique, respectively. The simulation results obtained with MATLAB-SimPowerSystems as well as the experimental results obtained in laboratory validate the proposed ANPC-SPFLBC for a set of exhaustive tests in both V2G and G2V modes. A detailed power quality analysis carried out with a Fluke 43B alike demonstrates the good performance of the proposed topology.

Integrated On-Board EV Battery Chargers: New Perspectives and Challenges for Safety Improvement

Abstract: Thanks to the heavy reduction of cost and volume, integrated On-Board Chargers (OBCs) represent an effective solution to provide a versatile and powerful charging system on board of electric and plug-in electric vehicles, combining the charging function with the traction drivetrain. Such integration foresees the use of the traction motor windings as reactive elements and the traction inverter as AC/DC converter. However, this integration brings several challenges on the table. At first, shaft torque production must be avoided to reduce the losses and mechanical stress. A second challenge is to improve the filtering capability of the motor windings in order to meet the grid standards in terms of current distortion and power factor correction. At last, the most critical issue is to meet the safety standards in terms of leakage current, since it represents a risk to human operators and could also hamper the smooth operation of the charger. Therefore, this paper aims at giving a comprehensive review of the challenges in designing integrated chargers. After reviewing the architectures available in literature, an exemplifying structure of integrated OBC will be analysed in terms of leakage current generation and compliance with the relevant standards, along with an introduction to those solutions which use the machine as isolation transformer. Conclusions are given on the prospect for making integrated on-board chargers safer and more reliable.

Resonant Grounded Isolation Transformers to Prevent Ignitions From Powerline Faults

Abstract: Methods and research for preventing utility-caused wildfires have significantly advanced in the past few decades, including development of criteria on reduction of energy release in an electrical fault to mitigate the probability of ignitions. Technologies to minimize energy release during electrical faults and achieve these ignition benefits are being applied at the substation level. However, the benefits can be targeted to a high-risk area by resonant grounding an isolation transformer on a distribution circuit. By doing this it is possible to reduce single line to ground fault current beyond the transformer to a level unlikely to ignite fires. This system was constructed and shown capable of reducing the power into a phase-to-ground fault by a factor of more than 10,000 and detect ground faults smaller than 0.5 A. This allowed it to meet the ignition criteria mandated for distribution network fire safety in the Australian state of Victoria. It was also tested for typical ignition scenarios such as downed phase conductors and phase conductors contacting with a tree branch. In all cases the probability of ignition was reduced by 90% or more.

High-Voltage Insulation Design of Coreless, Planar PCB Transformers for Multi-MHz Power Supplies

Abstract: This article investigates the insulation design for printed, planar, coreless, and high-frequency transformers with high isolation-voltage. By using finite element analysis on 2-D axial-symmetry, the transformer circuit parameters and electric field distribution are modeled and estimated. Several transformers are designed for an operating frequency of 6.78 MHz. The high frequency, coreless design allows for using thicker insulation material while ensuring a high transformer efficiency. The inclusion of the coupling capacitance in the design optimization results in several design solutions with the same figure of merit, but with different footprint and isolation voltages. Moreover, high electric fields are identified around the sharp edges of the printed circuit board (PCB) windings. Finally, the electrical and isolation performance is verified experimentally. The measured electrical properties are close to the simulated values, validating the chosen model. Breakdown tests demonstrate the feasibility of isolation voltage levels up to several tens of kilovolts. The majority of breakdowns occurs at the outer edge of the PCB winding that was identified as a high-field area. Additionally, a concept for grading the electric field of PCB windings is also proposed. Based on the results, the design aspects are discussed in detail for planar, high-frequency isolation transformers with medium-voltage isolation level.

A New Hybrid Dual Active Bridge Modular Multilevel Based DC–DC Converter for HVDC Networks

Abstract: Multi-terminal high voltage DC transmission currently represents a leading technology in long-distance power transmission systems. Among the main technical challenges facing such technology, DC fault isolation, permitting different grounding schemes, providing interoperability, and high DC voltage stepping between different HVDC networks, and allowing high-speed power reversal without power interruption especially when connecting the pre-existing voltage source converters (VSC) and line commutated converters (LCC)-based HVDC networks. This paper introduces a new modular multilevel converter (MMC) based front-to-front DC-DC converter to interconnect two different types (LCC/VSC) of HVDC networks. The proposed topology comprises a voltage source MMC (VS-MMC) and a current source MMC (CS-MMC), while both are coupled via an AC link including the isolating transformer. The proposed topology can successfully provide an uninterruptible bi-directional power flow, high DC voltage stepping with a DC fault blocking capability, and low number of semiconductors due to the usage of only half-bridge SMs. The system design is provided with a detailed mathematical analysis. Furthermore, two active power control methodologies are proposed and compared. The first control technique is simpler and entails lower passive elements, while the second technique ensures a zero reactive power over the full range of active power flow. Furthermore, Losses analysis and comparison are provided between the two proposed control techniques. Finally, Control-Hardware-in-the-Loop (CHiL) test validation is employed to confirm the validity of the proposed system under healthy as well as different fault scenarios.

A Two-stage Standard On-Board Electric Vehicle Charger with Minimum Switch Count

Abstract: A novel two-stage standard battery charger with minimum switch count is presented in this paper for electric vehicle charging application. The first stage is responsible for AC to DC conversion with power factor correction operation that consists of two switches and two diodes. The second stage is a DC-DC converter having a half bridge LLC resonant circuit along with an isolation transformer. The complete charger consists of only four switches and four diodes, which is minimum among the reported literatures. It’s operation and control strategy are presented in this paper. A 470 W scaled down laboratory prototype is built to verify the proof of concept. The proposed charger is tested to charge a battery set of 24 V, 30 Ah using CC-CV logic with a maximum efficiency of 97.5%. The prototype is also tested with resistive load at its ratted power and dynamics results are captured. A TMS320F28335 DSP board is used to implement the control scheme.

Unbalanced Load Modeling and Control in Microgrid with Isolation Transformer

Abstract: Renewables and energy storage rely heavily on power electronics. The control of power electronics in a microgrid with renewables and energy storages become more challenging under unbalanced load operation condition. The unbalance in current magnitude and phase will cause ripples in normal dq0 conversion, further causing voltage unbalance in the power converter current control loop. In this paper, a simulation test microgrid is studied as a good representation of a practical microgrid with local ancillary single loads. The double second-order generalized integrator-phase lock loop (DSOGI-PLL) technique for frequency and phase angle detection is modified to address the unbalanced current issue due to local single-phase load connected through an isolation transformer. The proposed method is verified through software simulation in both grid-connected and islanded modes. From the result, the modified DSOGI method proves to be a viable technique for improving power converter current control loop performance under single load or unbalanced load.

A Method for Detecting DC Bias in Transformer of Dual Active Bridge DC-DC Converter

Abstract: A potential concern with the isolation transformer in a dual active bridge DC-DC converter (DAB) unit is the DC bias of magnetization. With the influence of DC bias, the loss of the transformer increases, and the lifespan decreases. However, it is difficult to accurately measure the small DC component mixed in a large (>10A peak), high-frequency AC current, which makes it difficult to eliminate DC bias. A novel sensor is proposed to solve this problem. The proposed sensor is based on the principle of single-core fluxgate and current transformer. Compared with an ordinary Hall effect sensor, the proposed sensor significantly improves the DC current measurement accuracy and sensitivity. This paper presents the working principle and basic structure of the sensor, and the experimental result that measuring the small DC component mixed in a large, high-frequency AC current is also be demonstrated.

A Current-fed High Gain Multilevel DC-DC Converter for BESS Grid Integration Applications

Abstract: This paper presents a new high gain, multilevel, bidirectional DC-DC converter for interfacing battery energy storage systems (BESS) with the distribution grid. The proposed topology employs a current-fed structure on the low-voltage (LV) BESS side to obtain high voltage gain during battery-to-grid mode of operation without requiring a large turns ratio isolation transformer. The high-voltage (HV) side of the converter is a voltage-doubler network comprising two half-bridge circuits with an intermediary bidirectional switch that re-configures the two bridges in series connection to enhance the boost ratio. A seamless commutation of the transformer leakage inductor current is ensured by the phase-shift modulation of HV side devices. The modulating duty cycle of the intermediary bidirectional devices generates a multilevel voltage of twice the switching frequency at the grid-side dc link, which significantly reduces the filter size. The presented modulation strategy ensures zero current switching (ZCS) of the LV devices and zero voltage switching (ZVS) of the HV devices to achieve a high power conversion efficiency. Design and operation of the proposed converter is explained with modal analysis, and further verified by detailed simulation results.

A Multiport Converter for More Electric Aircraft with Hybrid AC-DC Electric Power System

Abstract: More electric aircraft (MEA) use a heterogeneous combination of AC and DC power generation units and loads. As a result, the electric power system (EPS) of MEA is designed based on a combination of AC and DC voltages at different levels to increase the design's flexibility and improve energy efficiency. However, one of the main drawbacks of such architecture is that many power electronic converters are required to interface different voltage types, which increases system cost, size, and weight. This paper proposes a new multi-port converter to interface an AC distribution system to a high-voltage non-isolated, low-voltage isolated DC system. The isolated system is supplied through the high-frequency isolation transformer designed to operate at a fixed frequency. The proposed converter replaces two conventional AC-DC and DC-DC converters with only six active switches. Furthermore, the converter is operated by a well-known control method without adding complexity to the design procedure. The proposed converter's feasibility is verified with the simulation results obtained from a MATLAB/ Simulink model.

Design of single-phase online uninterruptible power supply based on STM32

Abstract: According to the principle of UPS, an AC sine wave online uninterruptible power supply based on STM32 is designed. The system adopts mains power, outputs corresponding DC power through isolation transformer, autotransformer and rectifier module, and then connects to single-phase full-bridge inverter circuit after boosting through booster module to supply stable AC voltage to the load, which significantly improves the load regulation rate, The voltage sampling module collects the output voltage of the boost circuit in real time and feeds it back to the single-chip microcomputer, and uses PID algorithm to realize the voltage closed-loop control, which improves the reliability of the uninterruptible power supply system. The system has functions such as overcurrent protection, instant power switching, and battery undervoltage alarm.

Coupling Characteristics of Electromagnetic Disturbance of On-Site Electronic Device Power Port in Substations and Its Suppression

Abstract: The switching operations of circuit breakers and disconnectors in substations can generate very fast transients, including transient earth voltage rise and intense electromagnetic radiation, causing severe disturbance of on-site electronic devices in substations and seriously affecting the development of smart power equipment. The power supply of an on-site electronic device provides a path along which the disturbance couples with the device. In this article, we investigated the coupling mechanism and measures to suppress this disturbance. We found that, for most on-site electronic devices, their power supply includes a power line that connects the exterior and interior of the shielding box, greatly reducing the shielding effectiveness and inducing disturbance from the outside to the inside. This article proposes a shielding–crossing isolation transformer as the power supply of which the primary winding is outside and the secondary winding is inside of the shielding box, without a power line across the shielding box. This arrangement proved to deliver the high performance in terms of eliminating disturbance from the power supply. This article provides an understanding of the mechanism according to which the electromagnetic disturbance couples through the power supply. A method to determine the electromagnetic compatibility of on-site electronic devices in a substation is also proposed.

Design and Simulation of Airfield Lighting System Using 8 Luminaire in Airfield Lighting Laboratory at Politeknik Penerbangan Surabaya

Abstract: Airfield lighting system (ALS) provides visual reference to aircrafts during airport operation. In ALS equipment, constant current regulator (CCR) feed a luminaire circuit supplied through isolation transformer. Luminaire circuits are a large number of lamps which organized in serial circuit and connected to CCR that supply energy to the lamps. Modeling the component is needed to simulate ALS including of constant current regulator, underground cables, isolation transformer, and lamps. This simulation is usefull to study ALS behaviour and predict their response to electrical systems and future technological changes. This paper present circuit design and simulation of ALS using power simulator (Psim) software. The simulation results are observed in maximum brightness condition of the CCR. The CCR measurement results for this condition are 6.63 Ampere current output and 5kV voltage output. It has been observed that the designed system has been succesfully implemented to airfield lighting system circuit according to the component specification.

Switching power supply device

Abstract: To make it possible to accurately perform protection against abnormality even though a circuit configuration is simple.SOLUTION: A switching power supply device 100 comprises a converter 102, a control unit 9, a switching circuit 20, an isolation transformer 21, a first rectification circuit 22, a second rectification circuit 23, and an overheat detection circuit 29. When a switching element of the switching circuit 20 shifts into an overheat state, the overheat detection circuit 29 detects it and outputs a stop signal S4 for stopping switching operation of the switching circuit 20. On the basis of a result obtained by comparing a variation in output voltage of the first rectification circuit 22 connected to a main winding of the isolation transformer 21 with a variation in output voltage of the second rectification circuit 23 connected to an auxiliary winding of the isolation transformer 21, the control unit 9 determines that a short circuit has occurred in output of the converter 102 or that output voltage of the converter 102 has been low and, depending on the determination result, executes control for output short circuit protection or output low voltage protection.SELECTED DRAWING: Figure 1

Fast testing platform for the isolation transformer

Abstract: This work shows a program created in a Labview environment to verify the correct functioning and regulatory compliance of isolation transformers and isolation transformers for medical use. The transformer tests will be divided into acceptance tests and type tests. For each type of test, the program will be able to provide information for correct testing and to speed up the test path.The guided test procedure will accompany the author up to the automatic printing of the test reports. Finally, considerations will be made on which tests to perform on already installed transformers that require recertification.

Magnetic flux control in an urban distribution network based on load optimisation

Abstract: This paper proposes a control method for eliminating direct current (DC) flux from the isolation transformer of a customer service device to avoid magnetic saturation. The method is characterised b...

Analysis and design of efficient SiC-based load-resonant converter with advanced features for arc welding applications

Abstract: This letter presents a novel and efficient SiC-based harmonic-current-assisted LCC load-resonant converter for arc welding applications. A higher OCV, required for arc strike, can be obtained by using the harmonic gain of the resonant network at no-load condition. Resonant elements have been designed to reduce the input DC voltage to about half compared to that in a quasi-resonant converter. This reduces the core losses of the isolation transformer. The efficiency of the converter is further increased by ensuring ZVS operation of the switching devices, irrespective of load variations. The self inductance of the lead wires make the selection of the resonant elements an interesting exercise. A Finite element (FE) based simulation is used to determine the leakage inductance. The converter is fabricated in the laboratory and the experiments are conducted up to 1.0 kW load. Excellent mutual agreement between simulated and experimental results upholds the accuracy of the FE modelling and estimation of the lead inductances with the preciseness of the experimental set-up.

Solid-state transformer

Abstract: A solid-state transformer, comprising a plurality of power units (100). Each power unit (100) comprises a high-voltage side module (110), a low-voltage side module (120), and an isolation transformer (130). The isolation transformer (130) comprises a high-voltage winding (131), a low-voltage winding (132), and an iron core (133). The high-voltage winding (131) is wound on the iron core (133) and connected to the high-voltage side module (110). The low-voltage winding (132) is wound on the iron core (133) and connected to the low-voltage side module (120). The iron core (133) is in near equipotential connection to the high-voltage side module (110) or the low-voltage side module (120) by means of a conductive medium to fix the floating potential of the iron core (133).

X-ray generator, power supply, and method for manufacturing x-ray generator

Abstract: This X-ray generator comprises a power supply unit for applying a voltage to an electron gun. The power supply unit has: a first controller; a booster; an isolation transformer including a primary coil electrically connected to the first controller, a secondary coil electrically connected to the booster, and a support member for supporting the secondary coil; and a sealing member for sealing the booster and the isolation transformer. The support member is made of a first insulating resin material, and the sealing member is made of a second insulating resin material. The absolute value of the difference between the relative permittivity of the first insulating resin material and the relative permittivity of the second insulating resin material is 25% or less of the relative permittivity of the second insulating resin material.

Semiconductor drive circuit

Abstract: The invention provides a semiconductor driving circuit. A signal processing module is used for converting a PWM signal of any frequency into a first high-frequency signal and a second high-frequency signal; an isolation transformer is used for converting the first high-frequency signal and the second high-frequency signal into a third high-frequency signal; a rectifying module is used for converting the third high-frequency signal into positive voltage and negative voltage; a push-pull module is used for converting the third high-frequency signal into a gate driving signal to drive the IGBT module; a detection module is used for detecting fault information of the IGBT module; and the isolation transformer is also used for transmitting the fault information to the fault processing module soas to output a corresponding fault signal. That is to say, the semiconductor drive circuit achieves the purpose that the power supply signal, the PWM signal and the fault signal are transmitted through one isolation transformer, the circuit structure is simplified to a great extent, and the circuit cost is reduced.

Design and Implementation of Linear Power Supply for Wireless Electromagnetic Wave MWD System

Abstract: Considering the requirements of the wireless electromagnetic wave MWD system for reliability, stability and purity of the external power supply, as well as the system's demand for multiple power supply inputs, this paper proposed research and design of a multi-output flameproof and intrinsically safe linear power supply. The circuit design adopted a high-efficiency isolation transformer, a highly integrated low-dropout output current and a linear voltage regulator chip with adjustable output voltage to form linear power supply circuit with high stability, big current, and low ripple. The test results show that the linear power supply circuit has the good characteristics of high reliability, high stability, low ripple noise, and meets the actual use requirements of the wireless electromagnetic wave MWD system.

A True Bipolar Bidirectional DC Transformer

Abstract: DC transformer is an important equipment in DC distribution network, and the DC transformer with true bipolar characteristics has complex structure, large volume and high cost. In view of these problems, this paper proposes a topology of true bipolar DC transformer which can be realized with only four switches, and adopts non isolated structure to avoid some adverse effects caused by the introduction of isolation transformer. This paper introduces the basic working principle of the proposed topology, analyzes the working characteristics of the converter under different working modes, adopts voltage source PWM control, and builds a simulation model in MATLAB. The simulation results verify the voltage output capability of the proposed topology and the feasibility of its structure.

Single-stage isolation type three-phase AC/DC rectifier with wide-range soft switching

Abstract: The invention discloses a single-stage isolation type three-phase AC/DC rectifier with wide-range soft switching. The single-stage isolation type three-phase AC/DC rectifier comprises a three-phase full-bridge rectification circuit with third harmonic injection, a single-phase full-bridge circuit with a positive bus provided with a clamping capacitor, a single-phase full-bridge circuit with a negative bus provided with a clamping capacitor, an isolation transformer of the positive bus single-phase full-bridge circuit, an isolation transformer of the negative bus single-phase full-bridge circuit and a current doubling rectification circuit. A current source type AC/DC structure is adopted, rectification output in a buck mode is achieved, and compared with an existing single-stage isolationtype three-phase AC/DC rectifier, the phase-shifting full-bridge converter with the clamping capacitor is adopted, the asymmetric isolation transformer is adopted, soft switching of a power tube in awide range is achieved in an auxiliary mode, and transmission loss of a circuit is reduced.