A novel direct AC-AC converter for single and two-phase asynchronous motors

The single-phase asynchronous motors are widely used in low power industrial machines, home applications and many applications where single-phase grid is used. The squirrel-cage rotor type induction motor requires auxiliary stator windings, starting capacitor and centrifuge switch in order to have high starting torque. In applications where high torques are required starting and running capacitors are used together in transient and steady-state. The single-phase asynchronous motor operates at a constant speed when connected to a fixed amplitude and frequency voltage source. Speed of an AC motor can be controlled by a voltage source inverter with variable amplitude/frequency. However, this structure has some disadvantages such as requiring a bulky DC-link capacitor and uncontrolled rectifier circuit. In addition, the power quality of the grid significantly decreases due to the uncontrolled rectifier nature. These disadvantages can be eliminated by using an AC-AC matrix converter structure. In this thesis, a two-phase AC-AC matrix converter has been designed and performed to obtain two-phase adjustable output voltage. The converter has been tested with an R-L load and a standard single-phase asynchronous motor with two-phase winding. The converter can generate two-phase output voltages with 90 degree phase-shift. As a result, the motor does not need any starting/running capacitors and a centrifuge switch. Simulation and experimental results of the output voltages and load currents have been given for various output frequency. The performance of the motor has been also demonstrated for various output frequencies. Keywords: Single-phase matrix converter, Single-phase asynchronous motor, Simulation