Due to wider band gap of silicon carbide (SiC) compared to silicon (Si), MOSFET made in SiC has considerably lower drift region resistance, which is a significant resistive component in high-voltage power devices. With low on-state resistance and its inherently low switching loss, SiC MOSFETs can offer much improved efficiency and compact size for the converter compared to those using Si devices. In this paper, we report switching performance of a new 1700-V, 50-A SiC MOSFET designed and developed by Cree, Inc. Hard-switching losses of the SiC MOSFETs with different circuit parameters and operating conditions are measured and compared with the 1700-V Si BiMOSFET and 1700-V Si IGBT, using same test set-up. Based on switching and conduction losses, the operating boundary of output power and switching frequency of these devices are found out in a dc–dc boost converter and compared. The switching $dv/dts$ and $di/dts$ of SiC MOSFET are captured and discussed in the perspective of converter design. To validate the continuous operation, three dc–dc boost converters using these devices, are designed and tested at 10 kW of power with 1 kV of output voltage and 10 kHz of switching frequency. 1700-V SiC Schottky diode is used as the blocking diode in each case. Corresponding converter efficiencies are evaluated and the junction temperature of each device is estimated. To demonstrate high switching frequency operation, the SiC MOSFET is switched upto 150 kHz within permissible junction temperature rise. A switch combination of the 1700-V SiC MOSFET and 1700-V SiC Schottky diode connected in series is also evaluated for zero voltage switching turn-ON behavior and compared with those of bipolar Si devices. Results show substantial power loss saving with the use of SiC MOSFET.

High Switching Performance of 1700-V, 50-A SiC Power MOSFET Over Si IGBT/BiMOSFET for Advanced Power Conversion Applications

This paper addresses the influences of device and circuit mismatches on paralleling the silicon carbide (SiC) MOSFETs. Comprehensive theoretical analysis and experimental validation from paralleled discrete devices to paralleled dies in multichip power modules are first presented. Then, the influence of circuit mismatch on paralleling SiC MOSFETs is investigated and experimentally evaluated for the first time. It is found that the mismatch of the switching loop stray inductance can also lead to on-state current unbalance with inductive output current, in addition to the on-state resistance of the device. It further reveals that circuit mismatches and a current coupling among the paralleled dies exist in a SiC MOSFET multichip power module, which is critical for the transient current distribution in the power module. Thus, a power module layout with an auxiliary source connection is developed to reduce such a coupling effect. Finally, simulations and experimental tests are carried out to validate the analysis and effectiveness of the developed layout.

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Influences of Device and Circuit Mismatches on Paralleling Silicon Carbide MOSFETs

SiC MOSFETs exhibit extremely fast switching characteristics, which are unfortunately accompanied by undesirable switching oscillations. In this paper, equivalent circuit models incorporating all parasitic elements are developed for the turn-ON and turn-OFF of a SiC MOSFET. Simple mathematical formulas are derived to provide the theoretical analysis of the switching oscillation phenomenon, and to guide the snubber or damping circuit design. Both circuit simulation and experimental measurement are carried out to validate these simple equivalent circuit models.

Modeling and Analysis of SiC MOSFET Switching Oscillations

Wide-bandgap (WBG) power semiconductor devices have become increasingly popular due to their superior characteristics compared to their Si counterparts. However, their fast switching speed and the ability to operate at high frequencies brought new challenges, among which the electromagnetic interference (EMI) is one of the major concerns. Many works investigated the structures of WBG power devices and their switching performance. In some cases, the conductive or radiated EMI was measured. However, the EMI-related topics, including their influence on noise sources, noise propagation paths, EMI reduction techniques, and EMC reliability issues, have not yet been systematically summarized for WBG devices. In this article, the literature on EMI research in power electronics systems with WBG devices is reviewed. Characteristics of WBG devices as EMI noise sources are reviewed. EMI propagation paths, near-field coupling, and radiated EMI are surveyed. EMI reduction techniques are categorized and reviewed. Specifically, the EMI-related reliability issues are discussed, and solutions and guidelines are presented.

A Survey of EMI Research in Power Electronics Systems With Wide-Bandgap Semiconductor Devices

Circuit-level analytical models for hard-switching, soft-switching, and $dv/ dt$ -induced false turn on of SiC MOSFETs and their experimental validation are described. The models include the high-frequency parasitic components in the circuit and enable fast, accurate simulation of the switching behavior using only datasheet parameters. To increase the accuracy of models, nonlinearities in the junction capacitances of the devices are incorporated by fitting their nonlinear curves to a simple equation. The numerical solutions of the analytical models provide more accurate prediction than an LTspice simulation with a threefold reduction in the simulation time. The analytical models are evaluated at 25 °C and 125 °C. The effect of snubber capacitors on the soft-switching waveforms is explained analytically and validated experimentally, which enables the techniques to be used to evaluate future soft-switching solutions. Finally, the $dv/ dt$ -induced false turn-on conditions are predicted analytically and validated experimentally. It was observed that consideration of nonlinearities in the junction capacitances ensures accurate prediction of false turn on, and that the small shoot-through current due to false turn on can increase the switching loss by 8% for an off-state gate bias of −2 V.

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Predicting SiC MOSFET Behavior Under Hard-Switching, Soft-Switching, and False Turn-On Conditions

This paper presents a comprehensive study on the influences of parasitic elements on the MOSFET switching performance. A circuit-level analytical model that takes MOSFET parasitic capacitances and inductances, circuit stray inductances, and reverse current of the freewheeling diode into consideration is given to evaluate the MOSFET switching characteristics. The equations derived for emulating MOSFET switching transients are assessed graphically, which, compared to results obtained merely from simulation or parametric study, can offer better insight into where the changes in switching performance lie when the parasitic elements are varied. The analysis has been successfully substantiated by the experimental results of a 400 V, 6 A test bench. A discussion on the physical meanings behind these parasitic effect phenomena is included. Knowledge about the effects of parasitic elements on the switching behavior serves as an important basis for the design guidelines of fast switching power converters.

Characterization and Experimental Assessment of the Effects of Parasitic Elements on the MOSFET Switching Performance

Inverter-fed motor drive systems are widely used in industrial applications because of their energy efficiency and flexible control of machinery using maintenance-free induction motors. As switching inverters generate fast-switching voltage pulses, the transmission-line effects of the motor cable and motor stator windings become significant, and may lead to a doubling of the supply voltage to the motor and cable, overvoltage inside the motor windings, and an increase in the common-mode current. Such phenomena cause premature failure of the motor and cable insulation. A typical protective measure is the use of a passive filter to reduce the voltage surges and alter the rise time of the voltage pulses at the motor terminals. However, most passive filters have the drawbacks of bulky size and high power loss. This paper presents an active terminal filter that can perform the same functions as the passive filters with low power dissipation. An experimental filter has been built and evaluated on a 1-hp three-phase motor drive system with different motor cable lengths. A comparative study into the performance among the commonly used RLC filter and RC filter, and the proposed filter is provided.

An Active Low-Loss Motor Terminal Filter for Overvoltage Suppression and Common-Mode Current Reduction

This paper presents an investigation into the effects of the gate drive resistance on the losses of the MOSFET-snubberdiode (MSD) configuration commonly used in many power converters. An analytical loss model that takes the circuit stray inductances, MOSFET parasitic capacitances and inductances, and reverse current characteristic of the freewheeling diode into consideration is derived to describe the interactions among the MOSFET, snubber, and freewheeling diode during the switching transients. Two possible turn-ON switching situations, determined by the gate drive part and the power part, respectively, are distinguished in the analysis. It is then used to study the effects of the stray inductances, gate drive resistance and snubber on the switching behaviors, power loss distribution, and voltage stress on the MOSFET in the entire MSD configuration. A sequence of steps will be given to illustrate how an optimal combination of the gate drive resistance and snubber capacitance is determined, in order to minimize the overall loss of the MSD configuration for a maximum permissible voltage stress on the MOSFET. The loss model and method of determining the gate drive resistance and snubber capacitance are evaluated by comparing the theoretical predictions with the experimental results of a 400V, 6A test bench. The performances of the MSD configuration with different types of freewheeling diodes will be studied.

An Investigation Into the Effects of the Gate Drive Resistance on the Losses of the MOSFET–Snubber–Diode Configuration

Overvoltage phenomenon occurs at AC motor terminal fed by pulse width modulation (PWM) inverter drives. To protect the motor against insulation damage, many passive filter networks such as RLC filter and RC filter have been developed. However, they are either physically large and generally energy inefficient or cannot alter the wavefront of the pulses at the motor terminal to improve the inter-coil and inter-turn voltage distributions in the motor. This paper presents a motor protection filter with energy recycling which can protect the motor against insulation damage and works out the drawbacks of most recent filter networks. It has very small power loss comparing with the commonly used filters. The method is based on recycling the energy gained from suppressing the motor terminal voltage back to the whole system. An experimental filter has been built and evaluated on a 1-hp three-phase motor drive system. A comparative study into the performance among the commonly-used RC filter, RLC filter and proposed filter will be provided.

H. S-H Chung

Papers

Characterization and Experimental Assessment of the Effects of Parasitic Elements on the MOSFET Switching Performance

An Active Low-Loss Motor Terminal Filter for Overvoltage Suppression and Common-Mode Current Reduction

An Investigation Into the Effects of the Gate Drive Resistance on the Losses of the MOSFET–Snubber–Diode Configuration

A very low-loss motor overvoltage suppression filter using energy recovery concept