A new strategy for differential overvoltages and common-mode currents determination in PWM induction motor drives

Abstract

The analysis of the transient overvoltages in a PWM motor drive system comprises a wide frequency range, which starts with the low values corresponding to the motor speed, includes the switching harmonics, which can reach up to few hundreds of kHz, and also the cable resonant frequency, which value can be in the MHz range, depending on the cable length. In this context, this work presents a time domain methodology for cable modeling able to represent the cable parameters variation due to skin effect in this broad range of frequencies. Three different methods for cable parameter estimation are also studied and compared in order to be used as an effective tool in the analysis, since frequency-dependent parameter cable models typically require cable parameters in different frequencies as input data for their determination. Since measurements are often unavailable, parameter estimation is strongly desirable. The frequency-dependent cable earth-return model is also included, allowing the computation of the zero-sequence currents generated by the common-mode voltage produced by the inverter. Simulations using the proposed methodology are conducted and the obtained results are compared with measurements, showing good agreement