A new model of line commutated AC/DC/AC conversion systems is presented and discussed. It is based on the inclusion of the modulation function approach inside the Iterative Harmonic and Interharmonic Analysis algorithm. The new model allows to perform the evaluation of waveform distortion taking into account comprehensive representations of both supplying and load systems and overcoming their convergence problems and long times of execution. Numerical tests validate the proposed method and demonstrate its result accuracy and computational efficiency in comparison with time domain simulations. © 2004 IEEE.