A generalized model for harmonic analysis of natural commutation conversion systems

The proposed methodology can be defined as a deterministic approach operating in the frequency domain by means of an iterative algorithm and allows one to obtain the harmonic content of the required currents and voltages in steady state conditions as well as the time waveforms of any relevant system variable. With respect to the time domain models this one eliminates the computation time necessary for the transient behaviour determination which is not required for harmonic analysis. In comparison with the frequency domain models it presents two main characteristics: an accurate frequency model for any natural commutation static conversion structure (comparable with the time domain static converters models) and no convergence problems for the iteration process. The results of the implementation of the algorithm are reported and discussed in the case of a significant power application: the twelve pulse bridge rectifier for 3 kV DC railway traction supply. A comparison with the results achieved by a time domain method is pointed out in terms of computation time and result accuracy.