SCALAR BASED CMV REDUCTION METHOD FOR AN EVEN LEVEL INVERTER USING OPEN-END WINDING INDUCTION MOTOR DRIVE

Common mode voltage (CMV) generated by pulse width modulated (PWM) inverters can cause shaft voltage and bearing current, which result in permanent bearing failure in drives. This common mode voltage can be eliminated from odd level inverters by switching using only zero CMV states. But inverters which have an even number of levels have no switching states with zero CMV. Complete elimination of CMV is possible only by using higher level inverter switching states to realize a lower level CMV eliminated scheme, which demands more hardware cost. In this paper carrier based methods are investigated to reduce CMV for even level inverters without using additional hardware. The scalar method proposed in this paper utilizes the choice of different carrier signals to achieve lowest CMV, by keeping the quality of output voltage. Both the modulating signals and carrier signals are phase shifted in this method. From the implementation point of view, scalar method is easy compared to space vector based method by its simple computation. The proposed method is simulated by MATLAB/Simulink and experimentally validated for a four level inverter realized by Open-End Winding (OEW) configuration of induction motor. A 4-level output voltage can be generated by driving OEW induction motor, from both ends with two 2-level inverters. These two inverters are driven by asymmetrical dc link voltages in the ratio of 2:1.