Abstract
The emergence of fast-switching wide-bandgap (GaN, SiC) power electronics devices has enabled motor drive systems to achieve high efficiency, power density, control bandwidth and high-level of integration. However, the fast-switching speed and high switching frequency result in an increased level of motor overvoltage at both motor terminals and stator neutral. This overvoltage increases the stress across the motor winding insulation and bearings. This paper investigates three types of motor overvoltages, i.e., differential mode (DM) (phase-to-phase) motor terminal overvoltage, common mode (CM) (phase-to-ground) motor terminal overvoltage and CM stator neutral overvoltage (motor neutral to ground). Both the high switching speed (high dv/dt) effect and the high switching frequency effect on the motor overvoltage are investigated in this paper, where the high switching frequency effect has not been fully addressed in existing literature. Significant overvoltage is observed when the switching frequency or its multiples coincide with the cable or motor anti-resonant frequency. The anti-resonant behavior in the cable and motor impedance has been used to identify the overvoltage oscillation frequency and to explain the overvoltage observations for the three types of motor overvoltages. The analysis has been tested using a 7.5kW motor setup with and without a four-core cable, driven by a SiC or a GaN three-phase inverter with a switching frequency up to 250kHz and switching speed up to 40kV/ μs. In addition, the motor bearing current, which is a main cause of bearing degradation, has also been tested and the increase of bearing current is observed due to the high frequency effect.
Highlights
With the superior characteristics and commercial availability, wide-bandgap (WBG) devices are gradually finding their applications
This paper aims to provide a timely investigation and useful reference for the impact of high-switching speed and high-switching frequency WBG motor drives on electric machines
The motor terminal overvoltage or motor neutral overvoltage becomes significantly higher if the inverter switching frequency or its multiples coincides with the cable or electric machine anti-resonant frequency, which have been experimentally demonstrated in this paper
Summary
With the superior characteristics and commercial availability, wide-bandgap (WBG) devices are gradually finding their applications. Under higher switching speeds, the overvoltage at motor terminals can reach twice of the inverter output voltage when there is a cable connected between the inverter and the motor, due to the voltage reflection phenomenon [11], [12]. With WBG device-based motor drives, the switching frequency can reach 40kHz or even 100s of kHz if needed If this high-switching frequency or its associated harmonics at multiples of the switching frequency or their sidebands coincide with the anti-resonant frequency of the cable or/and the electric machine, there is much higher overvoltage than those due to the high dv/dt (switching speed) effect.
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