PWM method for open-end winding machines using small triangle space vectors without inverter output clamping

The open-end winding machines can be fed by two three-phase inverters. In each phase, three-level voltages are generated by an H-bridge. Three-level PWM can reduce current ripple in α-β frame by using the voltage vectors on the vertices of small triangle. For open-end winding configuration, PWM methods which use the small triangle have been implemented with space vector modulation based techniques. These techniques modulate the voltage by switching one inverter while clamping the other inverter. To distribute switching stress, the role of switching and clamping are alternated between the two inverters based on the area in α-β frame. However, the switching stress is still concentrated to one inverter in low speed because the role change depends on the electrical angle. In this paper, a PWM method which uses the small triangle without clamping the output of inverters is proposed. The method is implemented with carrier based technique. It is realized by alternating two carrier waves which have 90° phase difference depending on the polarity of the reference voltage. The experimental results show that the proposed method can reduce the α-β current ripple as well as the conventional method with clamping.