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 waveform 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 with three different waveform templates: sinusoidal, quasisquare and rectifier compensation current. They are compared in terms of the harmonic content and distortion at the same switching frequency. The paper shows that for sinusoidal current generation, the best method is the triangular carrier, followed by the hysteresis band and the periodical sampling. However, for the other two types of reference templates, the analysis showed that, depending on external factors such as inverter inductance, type of load, or delays in the PWM switching signals, one strategy may be better than the others. The paper shows that each control 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 simulations and experimental results.