A five-level inverter topology for four pole induction motor drive with single DC link

In this paper an optimized five-level inverter topology is proposed for a four pole induction motor drive. This topology has developed by using the advantage of two identical voltage profile winding coils per phase in a four pole induction motor. The identical voltage profile winding coils are disconnected and each part of the winding is fed with two two-level inverters from both sides. Thereby four two-level inverters are used to generate five voltage levels on induction motor phase windings. All two-level inverters are fed with single DC link with the magnitude V_dc / 4 (where V_dc is the dc-bus voltage required for a conventional NPC five-level inverter). Because of the common DC link for all the two-level inverters, common mode currents will find a path through the motor phase windings due to the lack of isolated neutral. To minimize the common mode currents a Sine-Triangle Pulse Width Modulation is used in the proposed topology. Thereby the first dominant harmonics and triplen harmonics shifted near to the switching frequency, which will have a less impact on the motor phase currents. Since the dominant harmonics are less in the proposed topology, it gives almost sinusoidal output voltage which will improve the efficiency of the drive system. The proposed topology does not require any major design modifications of induction motor. The proposed topology is simulated in MATLAB (Simulink) with (5HP) four pole induction motor with sine triangle PWM.