Kim B. Larsen

Evaluation of modulation schemes for three-phase to three-phase matrix converters

This paper presents a method for evaluating different modulation schemes employed with three-phase to three-phase matrix converters. The evaluation method addresses three important modulator characteristics: the output waveform quality, the input waveform quality and the switching losses associated with the modulation schemes. The method is used to evaluate four different modulation strategies, all based on the direct space-vector modulation approach. Further, regarding the switching losses, the paper proposes a new space-vector approach by which the switching losses can be reduced by 15%-35%, depending on the output load angle. This new modulation approach is applicable whenever the output voltage reference is below half the input voltage and the output voltage quality is then superior to that of the conventional space vector modulation scheme. The functionality of the new modulation scheme is validated by both simulations and experimental results and compared to waveforms obtained by using exiting space vector modulation schemes. The output voltage of the proposed scheme turns out to be comparable to the best of the conventional schemes while the input current is more distorted.

A General Solution for Theoretical Harmonic Components of Carrier Based PWM Schemes

In this paper, a general solution for the theoretical PWM harmonic components is presented. Analytical solutions of harmonic components for all PWM schemes can be easily achieved by using it. The method is applicable irrespective of the pulse ratio between the carrier and the fundamental, and the computational requirements are essentially constant irrespective of the absolute value of the carrier frequency. Moreover, it is especially suitable for software calculation of theoretical harmonic components due to the ease of implementation. Compared with numerical integration method and conventional FFT scheme, the computation time of the proposed solution is much less. Simulation results of 5 popular PWM schemes are presented to verify the general solutions.