Elimination of subharmonics in spectra of output voltage of drive inverters with space-vector PWM

Abstract

The paper describes methods and techniques of synchronized space-vector pulsewidth modulation (PWM), providing symmetry (quarter-wave symmetry and/or half-wave symmetry) of the output voltage waveforms of modulated voltage source inverters for adjustable speed drives. In this case spectra of symmetrical output voltage of inverters do not contain subharmonics (of the fundamental frequency), which are very undesirable in motor drives, especially in systems with low switching frequency of inverters. Both standard approach and novel space-vector-based approach can be used for elaboration of algorithms of synchronized modulation of drive inverters. It has been shown, that novel methods and techniques of synchronized PWM provide symmetry of the output voltage of inverters (and cancellation of subharmonics from voltage spectra) at both undermodulation and overmodulation control modes of drive inverters, and for any ratio (integer or fractional) between the switching frequency and fundamental frequency.