A new approach for the computation of harmonics and interharmonics produced by line-commutated AC/DC/AC converters

A new approach for modeling line-commutated ac/dc/ac conversion systems is presented and discussed. It is based on the modulation function theory taking advantage of a two-step procedure in which two different models are used. The goal is to achieve a reduction of the computational burden with respect to the time domain models and better modeling accuracy with respect to classical modulation function approaches. The proposed model constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Comparative tests validate the proposed method and demonstrate its computational efficiency and result accuracy.

I. Introduction

A great effort has been made in modeling HVdc links and high power adjustable speed drives based on line-commutated converters [1]– [7]. An important aspect of the problem is related to the modeling of ac/dc/ac conversion systems in order to achieve a detailed description and computation fastness. Various models are available to obtain the ac and the dc absorbed currents: experimental analogue, time domain and frequency domain models [4]. Each of them is characterized by a different degree of complexity in representing the ac supply-system, the converters, the dc link and ac supplied systems. Frequency domain models operate with different degrees of complexity, by using, in most cases, the modulation function approach [1]–[9]. Frequency domain models do not require heavy computational efforts and are very quick in execution.