Voltage peaks of low voltage induction motors due to PWM inverter supply

In industrial variable speed drives, the supply of low voltage induction motors by IGBT-PWM inverters through screened cables may cause dangerous over-voltage surges at the motors terminals. These voltage peaks of about twice the de link voltage, with a short rise time of about 200 nsec, increase the armature insulation stress and may damage the motor insulation. The prsent study provides a theoretical approach to this matter and is completed by tests performed on two 3 and 7.5 kW drives, with different cable lengths. Its target is to define the properties of these voltage peaks, their dependency on the installation parameters, and to present two measures to reduce the voltage gradient du/dt or the peak voltages at the motor terminals in order to raise motor lifetime of such a.c motors.