Harmonic reduction technique with a five-level inverter for four pole induction motor drive

In this paper a five-level inverter topology is presented for a four pole induction motor drive with a single DC source. In any ac motor, the winding coils which are 360° (electrical) apart will have identical voltage profiles. A conventional four pole induction machine consists of two such Identical Voltage Profile Winding Coils (IVPWCs) which are connected in series (or parallel). In the proposed method the series (or parallel) connected IVPWCs are disconnected into two parts. Each IVPWC is fed by a two two-level inverters from both the sides thereby four two-level inverters are used to generate the five-level voltage across the motor phase winding. All these four two-level inverters are connected to the same DC source with a magnitude V_dc over 4 (where V_dc is the dc bus voltage required for conventional five-level NPC inverter). Pulses for this five-level inverter configuration is generated using Unipolar phase shifted carrier PWM (UPSC PWM) technique by providing appropriate phase shift between modulating waves and carrier waves independently. Using the advantage of both IVPWCs of the induction motor stator winding and UPSC PWM the harmonics can be shifted to higher order which is close to four times compared to the harmonics with general SPWM. This circuit configuration does not require any major design modifications of the induction motor except the disconnection between the IVPWCs. The five-level inverter configuration supplying a 5hp four pole induction motor drive is tested with unipolar phase shifted carrier PWM in MATLAB(Simulink). Although the work is carried with 5hp induction motor, results are similar for large machines also.