A Speed Controller for a Two-Winding Induction Motor Based on Diametrical Inversion

The objective is to control the speed of a single- or two-phase induction motor using diametrical inversion (DI) of the stator voltages. DI is a particular reversal of the sequence phases characterized by replacement of the voltage phasor by another that is diametrically opposed to it and rotating in the opposite direction. Every DI is provoked by a change in the sign of the simplest switching function (speed error) of a sliding mode. These changes cause jumps of 180° of the stator voltage phasor and successive discontinuities of its angular velocity. The main and auxiliary windings are always connected, the speed-error sign decides the rotating field direction, and so, the actual rotor velocity can be reduced (braked) or increased (accelerated). The motor is fed by a rectifier associated with a three-phase inverter. The common point of the windings is connected to the inverter's middle leg, which is switched at high frequency with a duty cycle of 50%. The core of the drive command is a 16-b dsPIC device, which receives the speed-error sign and generates the appropriate pulsewidth modulated signals to the three-phase inverter. Matlab/Simulink simulation and experimental results showed a good performance of the speed controller based on the DI.