A dv/dt Filter Design Based on the Voltage Reflection Theory at SiC Converter

This paper analyzes a voltage surge generation at the end of cable in an inverter-cable-high impedance load system, and the analysis is based on the voltage reflection theory. Cable parameters are estimated by using the network analyzer, and the whole system is simulated for generation of voltage surge. A 150 V unit pulse from a SiC buck converter is injected to a high impedance load through several lengths of two cables. Voltage surge in terms of the ratio of rising time to the propagation time are analyzed. In addition, the excessive voltage surge at the cable end is mitigated by adding a dv/dt filter at the converter output to increase rise time of PWM pulses. An effective dv/dt filter is proposed and verified through the experiment. Using a cable with a characteristics impedance of $Z_{c}=80.2\Omega$ and a propagation delay of $t_{d}=44.2$ ns, the dv/dt filter is able to reduce a voltage surge of 300V to 173V which corresponds to percentage reduction of 42.3%.