Nine level inverter for open end induction motor with eight switches per phase

This paper presents a nine level inverter topology with only eight switches per phase, for driving an induction motor with open end stator winding. The topology consists of two three-level, three phase inverters connected to the two ends of the induction motor. With asymmetric DC link voltages in a ratio of 3:1, an effective nine level space vector structure is realised. Modulation is done using level shifted carriers, which requires only sampled values of the three phase voltage references. Switching state redundancies are used effectively to ensure that both inverters supply real power to the load over the entire modulation range preventing overcharging of the DC links. In case of a fault in one of the inverters, the faulty inverter can by bypassed and operation is possible using the other inverter. The topology was simulated using MATLAB/Simulink and experimentally verified over the entire linear modulation range. Experimental results validating the proposed scheme are included.