A Technique for Eliminating Common Mode Currents in Open End Induction Motor Drives

Open end induction motor drive fed from a common DC source faces the problem of Common Mode Voltages which creates flow of zero sequence currents. These currents lead to additional power loss without contributing to the torque. A new technique to eliminate such zero sequence currents is presented here. The two inverters with common DC bus are switched with Pulse Width Modulation scheme, but with a phase difference of 120 degrees. Analysis shows that the resulting dominant zero sequence voltage, a 3rd harmonic, gets shifted by 360 degrees and hence no resultant zero sequence current can flow. The proposed method is simple and can be implemented in all topologies of multilevel inverter. Detailed analysis presented shows that the DC bus utilization of the proposed topology is same as in other conventional methods. The proposed technique is experimentally validated in a 2hp, 3-phase, 415V open end induction motor drive.