HYBRID PWM SWITCHING STRATEGY FOR A THREE-LEVEL INVERTER FED INDUCTION MOTOR DRIVE WITH OPEN-END WINDINGS

Abstract

A dual two‐level inverter fed induction motor with open‐end windings is capable of generating a three‐level output voltage. Several, sine‐triangle and space vector pulse width modulation (PWM) switching strategies are presented for the dual‐inverter scheme either using space‐vector or carrier‐based implementation. In this paper, a hybrid PWM switching strategy for the dual‐inverter scheme is proposed employing sine‐triangle PWM (SPWM) and space vector PWM (SVPWM) for the individual inverters. SPWM is theoretically analyzed and space vector based implementation of SPWM is presented using a simple offset‐time concept. This is exploited to implement the hybrid PWM switching strategy for the dual two‐level inverter. The implementation of the hybrid PWM switching strategy proposed in this paper do not require any look‐up tables, the switching is totally automatic obviating the time‐consuming task of sector identification. The implementation of the hybrid PWM scheme requires only the three instantaneous phase reference voltages corresponding to the reference space vector. The third harmonic component in the voltage appearing across the motor phase windings in the induction motor is significantly reduced (by 50%) with the use of the proposed hybrid PWM scheme as compared to the use of the PWM scheme presented earlier. Also, the percentage weighted total harmonic distortion (%WTHD) of the output voltage is significantly reduced in the entire range of speed of the induction motor driven by the dual‐inverter scheme.