Selective harmonic elimination in a microprocessor based single-phase AC chopper with four quadrant switch realizations

A single-phase bi-directional A.C. power control circuit using power MOSFET embedded discrete component four quadrant switch (4QSW) realizations that operate in a high-frequency chopping mode is presented. In this time-ratio controller the symmetrical multipulse modulation (SMM) technique is adopted, wherein, several equidistant pulses per half cycle (M) are used. Microprocessor based gate drive circuits are used for triggering the 4QSWs at the appropriate instants. It is shown that the lower order harmonics are substantially reduced in this method compared to phase control scheme, certain harmonics, even being eliminated for certain values of M. Theoretical and experimental data are presented.