Online insulation condition monitoring of ac machines using ultra-fast inverter switching transition based on new semi-conductor materials

In modern propulsion applications of tractions drives, voltage source inverter-fed three phase AC machines are preferred due to their flexibility and high dynamic torque properties. However, the fast switching of the inverter (high dv/dt rates) causes increased stress for the motor windings and leads to insulation degradation. Thus, insulation condition monitoring is getting more and more important to ensure reliability. The proposed online insulation monitoring method is able to detect incipient insulation defects by evaluation of the motor current’s transient response on voltage pulses injected by inverter switching. Experimental results are presented to prove the method’s performance in case of application of voltage source inverters with very high dv/dt rates as will appear for, e.g., inverters equipped by SiC semi-conductors.