Linearization of Over-Modulation Region for a Dodecagonal Space Vector Structure with a Single DC Source

The main advantage of dodecagonal space vector pulse width modulation (PWM) scheme for open-end winding induction motor (OEWIM) drives includes the elimination of the fifth and seventh harmonics and suppression of eleventh and thirteenth harmonics in the motor phase voltages. However, this scheme requires two isolated DC sources or a single DC source and a capacitor with a voltage controller. In this paper, a dodecagonal space vector PWM method is proposed for a dodecagonal space vector connected with a single DC source and a capacitor fed inverter without any voltage controller, thus simplifying the circuit to a large extent. The voltage across the capacitor of the second inverter will be maintained constant without any controller using the proposed modulation method. Also, to utilize the DC source to its maximum limit and to improve the speed range of induction motor, a modulation scheme is implemented to linearize the over-modulation region. Also, there is a smooth transition from one linear region through over-modulation region to 12-step mode using the proposed modulation method. Experimental results are included to verify the proposed modulation method.