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This paper is concerned with the adverse effect of subharmonics generated by a pulsewidth-modulation-controlled voltage source converter supplying an ultrahigh-speed induction machine (USIM) and also with the calculation, simulation, and test of the subharmonic generation. It is mostly believed, except for a few publications, that the impact of subharmonics is negligible in most modern drives. Our finding is the contrary, i.e., it can cause significant additional losses that might lead even to breakdown in special cases like USIMs applied in systems developed for renewable and waste energy recovery. After a brief description of the system, the generation of subharmonics and the additional losses resulting from subharmonics in USIMs are discussed.