Time average approach for the calculation of quasi-subharmonics of PWM technique in ultra high speed AC motor supply

The paper is concerned with a novel method for the calculation of the so called quasi-subharmonics generated by PWM controlled VSC supplying ultrahigh speed induction machine. It is generally believed that the impact of subharmonics is negligible in most modern drives. Our finding is that on the contrary, it can cause serious malfunction and breakdown in special cases like ultrahigh speed induction machines (USIM) applied in systems developed for renewable and waste energy recovery. The time average method is described and used for the determination of quasi-subharmonics. The results are verified by simulations and laboratory tests.