Optimal Design of Output Filter for Low Switching Frequency Multi Level Inverter Based Medium Voltage Induction Motor Drive

The use of variable-speed electric drives has gained increasing importance due to their enhanced technical performance. To address issues like current ripple, additional motor and cables losses, electromagnetic interference, overvoltage on the stator windings, and acoustic noise of PWM controlled variable-speed electric drives and achieve suitable voltage quality at the motor terminals, the use of a sine wave output filter has become a practical industrial solution. This paper presents the optimal design of a sine wave filter for a medium voltage (MV) induction motor powered by a low switching frequency multilevel inverter. The design process considers resonance and stability issues, and determines the optimal filter structure and components by minimizing the weighted sum of the objective function components. The proposed method utilizes genetic algorithms and component modeling, incorporating objective functions such as voltage total harmonic distortion (THD), current THD, and filter components cost. Constraints, including the voltage drop across the inductor and losses due to damping resistance, are also considered in the optimal filter configuration. The sine wave filter is designed with a reduced ratio of switching frequency to filter resonance frequency $\left(r_{f}\right)$, resulting in a higher resonant frequency of filter and therefore smaller inductance and capacitance, and ultimately better voltage quality for the motor across all operating frequencies. Analysis and simulations have been conducted to validate the proposed design.