Performance evaluation of SiC MOSFETs with long power cable and induction motor

Silicon Carbide (SiC) MOSFETs, as wide-bandgap semiconductor device, has capability to switch at much higher frequency in comparison with their silicon (Si) counterparts. Industrial motor drive is usually connected to induction motor with long shielded cable. This long shielded cable introduces parasitics such as stray inductance and capacitance to the system, which affects SiC MOSFETs performance for inverter side and reflected wave transient overvoltage on motor terminals. In this paper, switching performance of SiC MOSFETs is systematically studied under different length of cables with both inductor load and induction motor load. Compared with standard DPT, turn on and turn off current ringing decays slower with longer cable which leads to 20% higher switching loss. Long cable also contributes to longer turn off time at low current. Furthermore, a theoretical reflected wave model with SiC MOSFETs based inverter is presented to estimate motor terminal voltage. A much higher dv/dt caused by SiC MOSFETs fast switching results in more strict requirements for both motor and cable selection. The test shows motor transient voltage achieved twice DC bus voltage with 100ft cable under single pulse condition. If pulse width modulation (PWM) is not adjusted properly, motor voltage may shoot up to 3∼4 times DC bus voltage. The potential solutions for switching performance improvement and reflected wave are also discussed and provided in this paper.