Design of Hybrid PWM Algorithm for the Reduction of Common Mode Voltage in Direct Torque Controlled Induction Motor Drives

Abstract

This paper presents a novel hybrid pulse width modulation (HPWM) technique for the reduction of common mode voltage (CMV) in direct torque controlled induction motor drives based on the concept of imaginary switching times. In the proposed approach, different active zero state PWM (AZPWM) sequences are considered in which the actual switching times are calculated based on the instantaneous values of phase voltages. Moreover AZPWM sequences utilize active voltage vectors for composing the reference voltage vector instead of using zero voltage vectors. But these sequences suffer from steady state ripples. To reduce the ripples in steady state, a HPWM technique is developed in which stator flux ripple analysis is done for all the AZPWM sequences in terms of actual switching times, dc link voltage (Vdc), sampling time period (Ts). To validate the proposed PWM algorithm, numerical simulation studies have been carried out using MATLAB-Simulink and results are presented and compared.