VOLTAGE SPECTRA OF TWO-PHASE PWM TECHNIQUE WITH 120° CYCLE

Abstract

This paper deals with a kind of two-phase PWMs when during each 1/3 of the period one of the motor phases is connected to the positive (or negative) dc bar and only the remaining two motor phases are switched between the dc bars. The novel accurate and the simpler approximated analytical equations of motor voltage harmonics are given and it is shown that the approximated equations provide a good precision of calculations. In comparison with three-phase PWMs this two-phase PWM - only for the same inverter commutation frequency - provides better quality of PWMs for high value of fundamental voltage. The realization of the two-phase PWM with 120° cycle is simpler than the other types of two-phase modulation but the transistor-diode load of the upper and bottom parts of the inverter bridge differs.