Inverter switching frequency prediction in DTC of induction motor drive for an EV drivetrain

Abstract

In electric vehicle a drivetrain is an essential element. The dynamic performance and efficiency are two main indices for an electric vehicle drivetrain. In this work, a direct torque control based induction motor drivetrain is considered. The direct torque control of an induction machine offers a simple structure with the high dynamic performance. In direct torque control strategy, the inverter operates at variable switching frequency due to hysteresis controller. Therefore, the losses of the inverter vary in large extent due to variable switching frequency. Hence, an empirical relation is derived to predict the inverter switching frequency variation. This relation is beneficial to analyze the inverter and drivetrain performance at desired operating conditions. However, the switching frequency depends on drive control parameters such as the magnitude of hysteresis bands, reference torque, and flux. To validate the proposed method, an experiment is performed in the laboratory, and it is observed that the estimated switching frequency matches with offline calculated switching frequency at various operating conditions.