A Speed Range Extension Scheme for Scalar-Controlled Open-End Winding Induction Motor Drives

This articleproposes a new control scheme for extension of speed range of dual inverter fed induction motor drives with open-end stator windings. One of the inverters connected to one end of the stator windings is fed by a dc power source whereas the inverter connected to the other end of the windings is fed by a capacitor. The control scheme ensures that only active power required by the drive is supplied by the inverter fed by dc power source and the reactive power alone is provided by the capacitor fed inverter. The modulation index of the capacitor fed inverter is varied to provide higher voltage to the motor at higher speeds keeping the capacitor voltage constant, thereby facilitating operation above base speed without field weakening. An alternative scheme in which the capacitor voltage is allowed to vary while keeping the modulation index of the capacitor fed inverter at its maximum value is also presented in this article. The proposed schemes, based on constant v/f ratio control, are simple compared to the existing schemes. Validation of the proposed schemes is carried out under transient and steady state operating conditions by extensive simulation using PLECS software. Experimental verification is also carried out on a laboratory prototype using a digital signal controller for implementation of the control scheme.