Avoiding over-voltages in long distance driving of induction motors

Driving induction motors through long cables implies that resonance phenomena will usually occur and submit the motor to overvoltages. This problem exists in industrial plants and also in subsea on exploitation systems. The oscillations due to the resonance are noticed in the voltage at the motor leads, along the power cable as well as in the current at the inverter output. This paper considers a system comprised of pulse width modulated voltage source inverter (PWM-VSI), long cable and induction motor. In order to outline the frequency response of the system, and identify critical frequencies, the cable electrical parameters should be estimated. Using these data the inverter switching frequency can be chosen in order to avoid the coincidence with the system resonance frequencies. As a consequence, using PWM and without additional filters, the motor voltage does not present significant overvoltages. These procedures are performed online, allowing to adjust the inverter frequency according to the system parameters changes