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Improvement of Output Voltage Waveform in Dual Inverter Fed Open-winding Induction Motor at Low Speed Area

This paper proposes an improvement method of the output voltage waveform in dual inverter fed open-winding induction motor focusing of low speed operation. The system consists of two isolated DC power supplies, an open-end winding induction motor, and two voltage source inverters which are respectively connected to the opposite terminals of the open-end winding with unequal DC link voltages. In the proposed control method, the use of the voltage difference output from the inverters constituting the dual inverter lowers the peak voltage at low speed conditions. For realization of the proposed method, this paper proposes the commutation sequence of PWM pattern considering the dead-time of the dual inverter. The proposed method is verified experimentally by driving the dual inverter fed open-winding induction motor. Experimental results confirm that the harmonic component of the output voltage, which is related to the switching frequency (10 kHz), reduces from 1.03 to 0.74 by the proposed method at the motor speed of 300 rpm and the load torque of 0.48 Nm. Furthermore, the proposed method clarifies that the motor loss is reduced by 0.5 W at 300 rpm and 0.2 Nm as compared with the conventional method.