Voltage, frequency, and phase-difference angle control of PWM inverters-fed two-phase induction motors

A phase-difference angle (PDA) controlled pulsewidth-modulated (PWM) inverter is proposed for a two-phase induction motor adjustable speed drive. Output waveforms are fixed over the whole operating range of the motor. The motor torque is controlled not by the modulation of the phase voltage, but by the PDA. Based on the selected harmonic elimination (SHE) PWM technique, the commutation angles of the output voltage are calculated. Several characteristics of the two-phase induction motor driven by the PDA inverter are analyzed. A hybrid PWM inverter is also proposed to compensate for the degradation of the efficiency at small PDA. Not only the PDA but also the voltage amplitude and frequency are used as the parameters for controlling the torque of the motor in the hybrid inverter. The speed characteristics of the two-phase induction motor driven by the hybrid PWM inverter are more flexible than when the motor is driven by the conventional PWM inverter, which requires adjustable communication angles