Direct torque control of induction motor based on advanced discontinuous PWM algorithm for reduced current ripple

Abstract

In recent years several discontinuous pulse width modulation (DPWM) methods are reported to improve the performance of AC drives at high modulation indices. It is proved that the performance of the popular PWM methods is modulation index dependent and no single DPWM method provides satisfactory performance over the entire high modulation range. Two popular existing DPWM methods renowned with the names DPWMMIN, DPWMMAX clamp each phase for 120° duration in every cycle of its fundamental voltage. It is observed that only the zero state is different in these two sequences. In this paper, it is proposed that, utilizing these two DPWM sequences and by changing the zero state at any spatial angle γ, where γ is between 0° and 60°, an infinite number of DPWM sequences including the existing DPWM methods and advanced DPWM (ADPWM) methods can be generated which are categorized as “continual clamping” and “split clamping” sequences. Using these ADPWM techniques an optimal split clamping sequence-based DTC of induction motor is proposed. With the proposed DTC method it is shown that steady state line current distortion at higher line side voltages is reduced significantly compared with the CDTC as well as conventional SVPWM (CSVPWM)-based DTC.