SiC MOSFET/Si IGBT (SiC/Si) hybrid switch usually selects the gate control pattern that SiC MOSFET turns on earlier and turns off later than Si IGBT, with the aim of making the hybrid switch show excellent switching characteristics of SiC MOSFET and reduce switching loss. However, when SiC MOSFET turns off, the fast slew rate of drain source voltage causes the current spike in Si IGBT due to the effects of parasitic capacitance charging and carrier recombination, which will produce additional turn-off loss, thus affecting the overall efficiency and temperature rise of the converter. Based on the double pulse test circuit of SiC/Si hybrid switch, the mathematical model of the turn-off transient process is established. The effects of the remnant carrier recombination degree of Si IGBT, the turn-off speed of SiC MOSFET and the working conditions on the turn-off current spike of hybrid switch are evaluated. Although adjusting these parameters can reduce the turn-off current spike somewhat, additional losses will be introduced. Therefore, a new method to suppress the turn-off current spike is proposed to balance the power loss and current stress.

The MOSFET synchronous rectification (SR) is widely used to reduce the conduction loss during the freewheeling period. Due to the wide band gap of silicon carbide (SiC), the intrinsic body diode of SiC MOSFET exhibits a high voltage drop. Therefore, SiC Schottky diodes (SBD) and SiC MOSFETs are usually used in reverse parallel to reduce power loss. However, the increase of equivalent junction capacitance due to the addition of an external SiC SBD could bring larger turn-on current on opposite power transistor of the phase-leg. Furthermore, as the parasitic inductance associated with layout hinders the prompt transfer of current between SiC SBD and body diode, the external SiC SBD cannot be fully utilized, and it may deteriorate the overall performance, especially at heavy load. We comprehensively compare power losses when SiC SBD are antiparallel or not, at different working conditions, including different layout compactness, load current and dead time. It’s hard to get the effect of loss reduction loss when add antiparallel SiC SBD due to the parasitic inductance induced by the layout. The results can provide a guidance to properly select SiC SBD in a phase-leg configuration under SR mode for freewheeling during the dead time.

SiC-based motor drives have the advantages of achieving higher efficiency and higher power density than traditional Si-based motor drives, and are gradually being widely used in electric power transmission. Due to different application situations such as oil field and airplane, a long cable is applied between the motor drive and three-phase motor and the distance may exceed hundreds of meters, which will cause serious voltage reflection problem, damaging working life of the motor. Meanwhile, the high slew rate of output voltage created by SiC-based motor drive deteriorates this phenomenon. In order to solve this problem, we first analyze the principle and influencing factors of voltage reflection, and establish the equivalent circuit model of the long cable. Then we put forward design method of LRC passive filter to suppress voltage reflection, and give simulation analysis. At last we built an experimental platform to verify the effectiveness of the LRC passive filter in SiC-based motor drive, and the experimental results show that the LRC passive filter with optimized parameters has good suppression effect of voltage reflection.

The four-switch buck-boost (FSBB) converter effectively reduces the average inductance current of FSBB when the input and output voltage is close to each other by using the four-mode operation, which alleviates the problem of limited duty cycle and low efficiency in the traditional control modes. However, the steady-state duty cycle mutation of FSBB with four-mode control will occur during mode switching, resulting in output voltage fluctuation. We analyzed the mechanism of duty cycle sudden change of four-mode control FSBB during mode switching, explored its influencing factors and governing laws, and proposed to use input voltage feedforward control to improve the smoothness of four-mode switching, so as to improve the response speed of output voltage when input voltage changes suddenly. The simulation results showed that after the input voltage feedforward control method was adopted, the four working modes can be switched smoothly in a wide input voltage range, the output voltage can be adjusted quickly, and the full load peak efficiency can reach 98%.

Accurate measurement of the gate-source voltage for silicon carbide (SiC) MOSFET is an essential prerequisite for correctly evaluating the reliability of driving circuit. Due to the high switching speed of SiC MOSFET, it is more sensitive to parasitic parameters of circuit, the measurement error caused by traditional test methods cannot be ignored in SiC MOSFET driving circuit. In this paper, we establish the equivalent model of driving circuit considering parasitic parameters, and analyze the difference between the gate-source voltage and test voltage at different test points. Then, the influence of the driving circuit parameters and layout compactness on the test voltage error is quantitatively analyzed. And the optimum selection method of gate-source voltage test point is proposed. The experiments based on double pulse platform were given to verify the correctness of theoretical analysis and simulation results.

In order to reduce the switching time and on-resistance of SiC MOSFET, it is usually recommended to use higher driving voltage and lower gate resistance, but this will affect the reliability of gate. Therefore, a parameter selection method which can reduce the total loss and ensure the safety of the gate is adopted in this paper. Firstly, the double pulse test circuit considering parasitic parameters has been analyzed. Then, the mathematical model of the main circuit affecting the drive circuit has been obtained. On this basis, considering the safety of the driving circuit, the parameters of the driving circuit have been selected based on the “optimal comprehensive loss” criterion under the condition of limiting the maximum gate voltage. Simulation and experimental results validate the correctness of the derived analytical model and the theoretical analysis.

发电机调压器是维持柴油机组正常运行不可缺少的重要部分,对机组的安全稳定运行起到重要作用;目前,主要存在基于晶体管式的模拟调压器以及基于微处理器的数字调压器两种;鉴于数字调压器具有传统的模拟式调压器无法比拟的优势,文章针对某型车辆柴油发电机设计了基于TMS320F28335芯片的数字电压调节器;设计了数字电压调节器的输入输出接口电路,包括模拟量调理电路、数字量调理电路、励磁主电路和励磁驱动电路等,制作功率板;采用以TMS320F28335为核心的DSP最小系统作为核心控制器,利用电压、励磁电流双环调节的方式,采用复合PID控制算法;搭建系统实验平台,对调压器进行测试,满足预期功能要求.

Generator voltage regulator is an indispensable part of maintaining the normal operation of diesel generator set, which plays an important role in the safe and stable operation of the generator set. At present, there are mainly two types of regulator named transistor-based analog voltage regulator and microprocessor-based digital voltage regulator. In view of the advantages that the digital voltage regulator has incomparable with the traditional analog voltage regulator, this paper designs a digital voltage regulator based on the TMS320F28335 chip for a certain type of vehicle diesel generator. The input and output interface circuit of the digital voltage regulator is designed, including the analog conditioning circuit, the digital conditioning circuit, the excitation main circuit and the excitation driving circuit, etc., to fabricate the power board. The software minimum control system is designed by using the DSP minimum system with TMS320F28335 as the core controller, and the voltage and excitation current double loop adjustment mode is adopted. Set up a system experiment platform to test the regulator to meet the expected functional requirements.

Enhancement gallium nitride high-electron-mobility transistors (eGaN HEMTs) have been developed with lower conduction losses and higher switching speed compared with MOSFETs. Self-commutated reverse conduction (SCRC) mechanism determines no reverse recovery phenomenon but a larger reverse conduction voltage drop of eGaN HEMTs than the body diodes in traditional Si MOSFETs or other freewheeling diodes. To reduce the large reverse conduction loss of eGaN HEMTs, the performance of different freewheeling methods for eGaN HEMTs in a phase-leg configuration is compared in this article. First, the reverse conduction mechanism and characteristics of eGaN HEMTs are analyzed. Then, four freewheeling ways for eGaN HEMTs are introduced, and the equivalent circuits are also given and analyzed. A double-pulse test platform is established to further explore the influence of the freewheeling ways on the conduction and switching characteristics. Finally, the total losses of a phase-leg configuration with different freewheeling ways based on a buck converter are analyzed and compared. This article aims to give guidance to properly select freewheeling ways for eGaN HEMTs under different operation conditions.

The recently emerging SiC devices provide a promising solution to improve power converter efficiency and power density. However the expensive cost limited the widely use of SiC device. The parallel connection of SiC MOSFET and Si IGBT is introduced in this paper to utilize the advantage of this two different kinds of devices and proposed corresponding switching strategies. The switching loss and current distribution of hybrid switch is simulated in LTspice. Performances of different switching strategies for the hybrid switch are evaluated using a simplified simulation circuit to prove the advantage of hybrid and proposed switching strategies.

The short-circuit capability of power devices is one of the key issues that related to the reliability and safety of Silicon Carbide (SiC) power devices. Firstly, two types of short-circuit faults are introduced, and mechanism of short-circuit current is analyzed in detail. Then, the influence of different circuit parameters on characteristics of SiC MOSFET under short-circuit condition is analyzed and compared. The key factors influencing the short-circuit characteristics are further revealed, providing a guidance for designing short-circuit protection circuit of SiC MOSFET to some extent.

To avoid large overvoltage when the current of the dc-link inductor is interrupted, overlap time is added to the drive signals in current source converters, which results in the extra harmonic in grid current. Waveforms of AC side current before and after added overlap time are achieved from analysis of the current commutation process. The expression of overlap current is given according to the pulse equivalent principle and the quantitative relationship between the extra harmonic of AC side current and overlap time is also given on the basis of the Fourier analysis. In addition, a method of restraining the overlap current is proposed. Finally, simulation and experiment results demonstrate the effectiveness of the proposed analysis and restraining method.

为了探究电路中寄生电容对SiC MOSFET高速开关特性的影响,采用理论分析与实验研究相结合的方法,考虑相关寄生电容,对SiC MOSFET的开关过程进行模态分析,确立各部分寄生电容的影响,进而建立高速双脉冲测试平台,对各部分寄生电容对SiC MOSFET开关特性的影响进行研究,揭示各部分寄生电容对SiC MOSFET开关特性的影响规律.实验结果表明:随着SiC MOSFET极间电容的增大,其开关速度降低、开关能量增大,开关过程中的电压、电流尖峰有所降低;与极间电容不同,CJ增大时会引起电流尖峰的增加.

Parasitic inductance has larger influence on Silicon Carbide devices with the increase of switching frequency.This limits full utilization of performance advantages of low switching losses in high frequency applications.By combining theoretical analysis with experimental parametric study,a mathematic model considering parasitic inductance is developed for the basic switching circuit of SiC MOS-FET.Main factors which affect the switching characteristics are explored.Moreover,a fast-switching double-pulse test platform is built to measure individual influence of each parasitic inductance on switching characteristics and guidelines are revealed through experimental results.Due to limits of practical layout in high-speed switching circuits of SiC devices,the matching relations are developed and an optimized layout design method of parasitic inductance is proposed under a constant length of the switching loop.The design criteria are concluded based on the impact of parasitic inductance,which provide guidelines for layout design considerations for SiC-based high-speed switching circuits.

Current sharing is a major problem for paralleling devices, which can affect the performance and reliability of devices. In this paper, the factors leading to current unbalance in paralleling silicon carbide (SiC) MOSFETs are analyzed, especially the circuit mismatch. A double pulse test circuit based on SiC MOSFET is established for testing the circuit mismatch including common source stray inductance (Ls), switching loop stray inductance (Ld) and the gate driver resistance (Rg). The experimental results verify the influences caused by circuit mismatch on the current sharing in paralleling devices.

Enhancement-mode GaN switches has been developed with up to 650 V blocking capability, fast switching, and low conduction losses in commercial devices. Self-commutated reverse conduction is a very important characteristic of enhancement-mode GaN HEFT, especially for synchronous rectification topologies. This paper introduces the new commercial enhancementmode GaN HEMT and its self-commutated reverse conduction characteristic. To compare three schemes: only an eGaN, only a SiC SBD, eGaN with an anti-parallel SiC SBD respectively, a DPT circuit is designed to analyse the influence of different schemes on switching characteristics and power losses of eGaN HEMT.

This paper presents the realization and switching patterns of hybrid switch, in which a power MOSFET and an insulated-gate bipolar transistor (IGBT) are connected in parallel. The hybrid parallel connection aims to reach optimum power device performance by providing low static and dynamic losses while improving the current capacity of SiC devices and reducing the loss of Si IGBTs based converters. Considering the different switching speeds and output characteristics of SiC and Si devices in such hybrid structure, the switching sequence should be controlled to utilize the advantage of this two different kinds of devices, hence the switching pattern of hybrid switch is proposed. Simulation results are obtained to validate this approach with respect to the static and dynamic performance. The simulations of a 4 kW Buck converter based on hybrid switch illustrates the efficiency improvement of 2.55 % compared with full Si IGBTs switch.

With the outstanding advantages of SiC MOSFET, which has lower junction capacitance, low-on-state resistor and high junction operating temperature compared to a Si devices, the converter can achieve a high-frequency and high-efficiency. This increases the power density with smaller volume of passive components and reduced cooling requirements. However, in the phase-leg configuration, high dv/dt will worsen the interference between the two devices during a switching transient (i.e., crosstalk). Unfortunately, SiC power devices are more easily affected by crosstalk than Si devices due to their intrinsic properties. To utilize the full potential of fast SiC devices, a novel and cost-effective gate assist circuit for crosstalk supression is proposed in this paper. Besides, with the increase of power density, the thermal design is increasingly becoming the key factor that affects the reliability of converters. Thus, the thermal model of the phase-shift full-bridge converter (PSFBC) is established. The simulation and experimental results are in good agreement, which testifies the accuracy of thermal model. The efficiency of 2kW PSFBC based on Si and SiC MOSFETs under different loads is also measured and compared in this paper.

电力电子器件是电力电子技术的重要基础.现有硅基电力电子器件的性能已经逼近其材料极限,很难再大幅提升硅基电力电子装置的性能.以氮化镓为代表的宽禁带半导体器件比硅器件具有更优的器件性能,成为电力电子器件的研究热点.介绍了氮化镓电力电子器件的商业化产品水平和实验室研究现状,阐述了其在典型场合中的应用,并剖析了其发展中存在的挑战.