A Speed Range Extension Scheme for Direct Torque Controlled Open-End Winding Permanent Magnet Synchronous Motor Drives

This paper proposes a scheme for extension of speed range extension in a direct torque controlled permanent magnet synchronous motor drives with open-end stator windings fed from two inverters. One of the inverters is powered from a DC voltage source whereas a charged capacitor provides the DC voltage to the other inverter. In the proposed scheme the direct torque control is implemented by using virtual voltage vectors generated by combining the actual voltage vectors of the two inverters. A stator current oriented reference frame is used to determine the active and reactive components of the motor voltage vector. The active component is generated by the DC source fed inverter while the reactive component is provided by the capacitor fed inverter. As the speed increases, the reactive voltage drop in the motor also increases and it is fully compensated by the voltage injected from the capacitor fed inverter. The DC source fed inverter can then be fully utilized to overcome the increased back EMF at higher speeds. The proposed scheme thus facilitates the operation of the motor above the base speed without field weakening. The validation of the proposed scheme is accomplished using PLECS-Simulation software.