Characteristics of Ni-based ohmic contacts on n-type 4H-SiC using different annealing methods

Nickel is an excellent ohmic-contact metal on 4H-SiC.This paper discusses the formation mechanism of nickel ohmic contact on 4HSiC by assessing the electrical properties and microstructural change.Under high-temperature annealing,the phase of nickel-silicon compound can be observed with X-ray diffraction,and the contact resistance also changes.A comparative experiment was designed to use X-ray diffraction and energy-dispersive spectroscopy to clarify the difference of ohmic-contact material composition and elemental analysis between samples prepared using pulsed laser annealing and rapid thermal annealing.It is found that more Ni2Si and carbon vacancies formed at the interface in the sample prepared using pulsed laser annealing,resulting in a better ohmic-contact characteristic.

Determination of failure degree of 1.2 kV SiC MOSFETs after short-circuit test using an improved test setup

Analysis of the short-circuit characteristics of SiC metal-oxide-semiconductor field-effect transistors(MOSFETs)is very important for their practical application.This paper studies the SiC MOSFET short-circuit characteristics with an improved test setup under different conditions.A high-current Si insulated gate bipolar transistor is used as a circuit breaker in the test circuit rather than the usual short-circuit test conducted without a circuit breaker.The test platform with a circuit breaker does not influence the calculation results regarding the shortcircuitwithstand time and energy,but the SiCMOSFETwill switch off after failure in a very short time.In addition,the degree of failure will be limited and confined to a small area,such that the damage to the chip will be clearly observable,which is significant for short-circuit failure analysis.

A Review of Drive Techniques for Multiphase Machines

Multiphase machines are gaining increasing popularity because of their distinct advantages over three-phase counterparts,such as reduced per phase power rating,improved reliability and increased degrees of freedom.This paper overviews the development history of multiphase machines and drive techniques in Section II.Three kinds of drive algorithms,including Field-Oriented Control(FOC),Direct Torque Control(DTC)and Model Predictive Control(MPC),are introduced in Section III.Then two types of fault-tolerant methods are compared in Section IV,which are the Vector Space Decomposition(VSD)strategy and Optimal Current Control(OCC)method.Furthermore,different types of existing multiphase converter topologies are listed in Section V,and various kinds of multiphase PWM methods are discussed in Section VI.Finally,based on the review,developing trends of multiphase drive techniques are forecasted.

Modulation and Voltage Balancing Control of Dual Five-level ANPC Inverter for Ship Electric Propulsion Systems

Open-end winding motors are used extensively in ship electric propulsion systems,in which medium-voltage high-power inverters are a critical component.To increase the system voltage and power density,a dual five-level active neutral-point clamped(ANPC)inverter is proposed herein to drive medium-voltage open-end winding motors for ship electric propulsion.Each phase of this inverter comprises two five-level ANPC bridges and all the phases are powered by a common direct-current link.A hybrid modulation method is proposed to control this inverter.The series-connected switches in all the five-level ANPC bridges are operated at the fundamental frequency,and the other switches are controlled with a phase-shifted pulse-width modulation(PWM),which can achieve a natural balance between the neutral-point voltage and flying capacitor voltages in a carrier period.A closed-loop capacitor voltage balancing method based on adjusting the duty ratios of the PWM signals is proposed.The neutral-point voltage and flying capacitor voltages can be controlled independently and balanced without affecting the output phase voltage.Simulation and experimental results are presented to demonstrate the validity of this method.