Analytical modeling for harmonic analysis of line current of VSI-fed drives

The ac/dc/ac double-stage converter, frequently used nowadays to provide ac adjustable frequency and magnitude volt- ages in the adjustable-speed drives, consists of a voltage source in- verter (VSI) fed by a three-phase diode bridge rectifier; this rec- tifier generates high line current harmonics in the supply system. This paper presents a complete modelling of the VSI-fed drives, when energized by nonsinusoidal supply voltages, based on the analytical form of the current harmonics injected in the supply system; the equations of the current harmonics are obtained for both the continuous and discontinuous current modes and are de- rived by Fourier analysis of steady-state current time evolution. The high accuracy of the proposed models is demonstrated by com- parison with the results of time-domain simulation. The modelling is useful to study the effects of supply voltage distortions on cur- rent harmonics injected in the supply system, both in continuous and discontinuous mode, with a very short computing time.