Half-wave Rectified Synchronous Motor Using Inverter Carrier - Frequency Current for Excitation

Abstract

In this paper, inverter carrier frequency component voltage induced in synchronous motor rotor circuit is explored as a source of the rotor excitation current. The triangular waves for a three phase inverter (sine-triangle-modulated) supplying the machine are suggested to be phase shifted by one-third the carrier frequency period, so that rotating magneto-motive-force (mmf) at the carrier frequency can be created. The rotating mmf, hence, can induce voltage in the rotor winding circuit. The induced voltage and the resulting current in the rotor winding, then, can be rectified to keep the excitation flux in the same direction. Furthermore, variable inverter carrier frequency is suggested to vary the excitation current magnitude for field weakening operation. Simplified expressions relating the carrier frequency component current in the stator windings, in the rotor winding and rotor position angle have been developed. Preliminary simulation results using MATLAB indicate that the inverter carrier frequency can be utilized for excitation to run the motor without brush and additional external DC power supply for excitation.