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

Abstract

In SiC motor drives, the high-voltage slew rate (/) of switching transients results in excessive motor overvoltage, due to the reflected wave phenomenon (RWP), which stands behind the premature failure of motor winding insulation while raises electromagnetic interference (EMI) problems. This paper adopts a soft-switching inverter topology, denoted as the auxiliary resonant commutated pole inverter (ARCPI), to mitigate the motor overvoltage caused by the RWP in SiC-based cable-fed drives. The performance of the SiC motor drive system under the RWP is first investigated to determine how the motor overvoltage is affected by the / of the inverter output voltage and the cable length. Then, a SiC ARCPI with profiled output voltage slew rate is utilized as a candidate solution to mitigate the RWP in the cable-fed motor drive. The effectiveness of the presented mitigation approach is experimentally verified, where it is shown that the ARCPI can completely eliminate the motor overvoltage and improve the EMI performance at high frequency region (500 kHz onwards) due to the prolonged rise/fall time of the output voltage, compared with the conventional hard-switching inverter. Keywords-Auxiliary resonant commutated pole inverter (ARCPI), high / , motor drives, reflected wave phenomenon, SiC MOSFET, soft-switching inverter.

Impact of High Switching Speed and High Switching Frequency of Wide-Bandgap Motor Drives on Electric Machines

“…This overvoltage phenomenon has been observed for conventional Si IGBT based motor drives with long cables (tens or hundreds of meters). However, with the very fast switching of WBG devices, the cable length that can lead to overvoltage has been reduced to several meters [13]. Further, under high switching frequencies, a greater than twice of the inverter voltage can occur at the motor terminal at high modulation indices.…”

“…To avoid the shortcomings of passive filters, methods have been proposed to attenuate the dv/dt or harmonics from the source, i.e., by shaping the output voltage waveforms of the inverter. A soft-switching converter has been introduced to shape the SiC inverter output voltage to have a longer rising/falling time that can mitigate the motor terminal overvoltage [13]. It has been found that when the rising/falling time of the inverter output voltage is four times of the voltage wave propagation time along the cable, the motor terminal overvoltage can be fully attenuated.…”

Impact of Parasitic and Load Current on the Attenuation of Motor Terminal Overvoltage in SiC-Based Drives

“…The RWP is caused by high 𝑑𝑣/𝑑𝑡 voltage pulses travelling through power cables terminated by a motor that has significantly higher characteristic impedance than that of cables [7]. The resultant overvoltage depends on cable length and the rise/fall time of the inverter switching voltage [8], as depicted in Fig. 1, which shows how the motor overvoltage varies with the cable length under various switching speeds.…”

“…1, as the rise time decreases, the motor overvoltage increases at the same cable length. Also, the critical cable length, at which the motor experiences voltage doubling, decreases as the rise time is reduced [8]. Thus, the motor overvoltage is more common when fast switching (usually between 25-50 ns) SiC MOSFETs are used in inverter-fed drives where the motor voltage can be doubled with shorter cable lengths (e.g., a few meters) compared to those used in equivalently rated Si-IGBT-based counterparts [8]- [10].…”

“…Also, the critical cable length, at which the motor experiences voltage doubling, decreases as the rise time is reduced [8]. Thus, the motor overvoltage is more common when fast switching (usually between 25-50 ns) SiC MOSFETs are used in inverter-fed drives where the motor voltage can be doubled with shorter cable lengths (e.g., a few meters) compared to those used in equivalently rated Si-IGBT-based counterparts [8]- [10]. The consequent overvoltage induces undesired stress on the motor winding insulation, increasing the possibility of partial discharge while degrading the motor reliability and lifetime.…”