MULTI CARRIER BASED GENERALIZED PWM TECHNIQUE FOR REDUCTION OF COMMON MODE VOLTAGE
P Rama Mohan
This paper presents a multi carrier based generalized PWM algorithm for the reduction of common mode voltage in voltage source inverter fed induction motor drives. The generalized PWM algorithm is developed based on the concept of offset time. By using the magnitude test, the maximum and minimum time values are calculated at each sampling period from which generalized expression for offset time is derived. By varying a constant in offset time expressions, various PWM techniques like continuous and discontinues PWM techniques can be derived. As the single carrier based continuous and discontinuous PWM techniques generate large variations in common mode voltage, a multi carrier approach is presented in this paper. Based on the slope of reference voltages, suitable carrier signal will be selected. Moreover, by phase shifting the reference voltage signals by 120 degrees, a family of active zero state PWM (AZSPWM) techniques have been proposed in this paper. To evaluate the performance of these PWM techniques, experimental studies have been caried out on v/f controlled induction motor drives by using the dSPACE 1104 kit. From the experimental results it an be concluded that the proposed PWM techniques give superior performance in terms of common mode voltage when compared with the space vector PWM technique.
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