PRACTICAL EVALUATION OF DIFFERENT MODULATION TECHNIQUES FOR CURRENT-CONTROLLED VOLTAGE-SOURCE INVERTERS

The quality of the current waveform generated by a current-controlled, voltage source inverter, depends basically on three factors: (a) the switching frequency of the PWM modulator; (b) the type of current wave form being generated; and (c) the modulation method used. In the paper , three modulation methods, whose characteristics are their simplicity , are analysed: periodical sampling control, hysteresis band control, and triangular carrier control. These three methods have been tested w ith three different waveform templates: sinusoidal, quasisquare and re ctifier compensation current. They are compared in terms of the harmon ic content and distortion at the same switching frequency. The paper s hows that for sinusoidal current generation, the best method is the tr iangular carrier, followed by the hysteresis band and the periodical s ampling. However, for the other two types of reference templates, the analysis showed that, depending on external factors such as inverter i nductance, type of load, or delays in the PWM switching signals, one s trategy may be better than the others. The paper shows that each contr ol method is affected in a different way by the switching time delays present in the driving circuitry and in the power semiconductors. The results are analysed and compared, with the help of computer simulatio ns and experimental results.