Modulation and control methods to reduce zero sequence current in open-end winding motors

Abstract

In this paper three modulation and control methods that aim to limit zero sequence current in a dual inverter fed open-end winding electrical motor are compared. When a single DC source is used in such an application, zero sequence current can circulate through the motor windings. The zero sequence current is generated by instantaneous common-mode voltage pulses from the two inverters feeding the motor. This circulating current will not only generate harmonic content in the load current, but also the current amplitude will rise, leading to unnecessary losses in the inverters and the motor. Generally a zero common-mode voltage modulation method intended for three-level inverters is applied. However, asymmetry in the switching instants is caused by dead times. Several approaches including dead time compensation, closed loop and feed forward control methods are studied to suppress the unwanted circulating current.