An Active dv/dt Filter to Combat Motor Terminal Overvoltage in SiC-Based Adjustable Speed Drives

In silicon carbide (SiC)-based adjustable speed drives, the fast-switching voltage pulses cause power cables to act like transmission lines, leading to severe overvoltage at motor terminals. This letter proposes an active dv/dt filter to mitigate the motor terminal overvoltage due to the reflected wave phenomenon in SiC-based motor drive systems. The active dv/dt filter consists of a T-type inverter and an inductor and capacitor (LC) passive filter, where the T-type inverter generates the quasi-three-level (Q3L) pulse width modulation (PWM) voltage to actively regulate the dv/dt of the voltage supplied to the adjustable speed drives. The operation mechanism of the active dv/dt filter is mathematically derived and experimentally verified. The analysis shows that when the dwell time of the Q3L PWM voltage aligns with half of the resonant period of the LC network, the dv/dt of the inverter output voltage can be actively controlled. The experimental results show that the active dv/dt filter can mitigate the overvoltage at motor terminals within 1.15 pu, compared with the conventional two-level inverter.