Experimental Evaluation of SiC Mosfets in Comparison to Si IGBTs in a Soft-Switching Converter

Abstract

SiC MOSFETs have shown superior characteristics to Si IGBTs, bringing in significant performance improvement such as enabling more compact, higher efficiency converters that are not feasible with conventional Si IGBTs. Currently, there is a lack of systematic and conclusive investigation into soft-switching inverters using SiC MOSFETs in comparison to Si IGBTs. This paper, therefore, presents a comparative evaluation of a softswitching inverter, i.e. the auxiliary resonant commutated pole inverter (ARCPI) using SiC MOSFETs or Si IGBTs. The switching transition, switching device current stress, neutral point ripple current, electromagnetic interference (EMI), efficiency and cost are compared on identical ARCPI setups, i.e. with the same PCBs and under identical driving conditions (gate drivers). Experimental results show that the ARCPI using SiC MOSFETs has better performance than that using Si IGBTs due to its faster switching speed. Firstly, the ARCPI using SiC MOSFETs performs full zero-voltage switching and the switching transition behaviour is more predictable. Unlike Si IGBTs, SiC MOSFETs have no turn-off tail current and forward voltage drop during switching transitions. Secondly, the ARCPI using SiC MOSFETs endures less current stress and smaller ripple current in dc-link capacitors. Thirdly, the ARCPI using SiC MOSFETs exhibits better EMI performance and higher efficiency. Specifically, a maximum 20 dBμV harmonic reduction can be achieved around 800 kHz and a 3.1% improvement in efficiency can be achieved at 6 kW.

Mitigation of Motor Overvoltage in SiC-Device-Based Drives using a Soft-Switching Inverter

“…The resultant overvoltage caused by the RWP increases the possibility of partial discharges leading to an accelerated aging of the machine winding insulation and ultimate failure of the drive system [4]. In addition, the high frequency voltage oscillations at the motor terminal raise electromagnetic interference (EMI) problems [10].…”

“…However, the motor windings still suffer from high / resulting in uneven voltage distribution across the motor turns, where the first several turns would endure higher voltage since this approach cannot flatten the voltage slew rate applied to the motor windings. Furthermore, the high / at the motor terminal will deteriorate the EMI performance, being the main source of the EMI in the ASD [10].…”

“…2) Profiled / : the output voltage fronts are smoothed in a sinusoidal manner since the inverter operates in a resonant mode [10]. Therefore, it can reduce the uneven voltage distribution across the motor windings and improve the EMI performance.…”

Opportunities, Challenges, and Potential Solutions in the Application of Fast-Switching SiC Power Devices and Converters

“…Also, compared with Si IGBTs, SiC MOSFETs have a much smaller turn-on delay and no tail current. SiC MOSFET based soft-switching converters can achieve ideal soft-switching waveforms [108]. If a shorter switching transition time is needed for SiC soft-switching converters, the required size of resonant components, such as auxiliary inductors and capacitors, can also be reduced.…”

Impact of Parasitics and Load Current on the Switching Transient Time and Motor Terminal Overvoltage in SiC-Based Drives

“…Although the fast switching speed has clear potential to reduce the switching loss and increase the switching frequency, it raises several undesired issues and technical challenges for both the inverters and motors [4][5][6]. One specific problem is the transient overvoltage across the motor terminals, known as the reflected wave phenomenon (RWP) [6].…”