Space vector modulation techniques for current source rectifiers operating at switching frequencies up to 1 kHz

Abstract

PWM current source rectifiers (PWM-CSRs) are gradually replacing phase-controlled thyristor-based rectifiers as front-end high power supplies. Advantages include reduced line current harmonic distortion and unity power factor operation. Moreover, with the help of regenerative and resonant snubbers, a three-phase six-switches bridge configuration can now control high power levels (1.2 MVA) while operating at switching frequencies up to 1 kHz. In this range of power and switching frequencies, the switching pattern must be carefully chosen since it defines the supply current harmonic distortion which finally restricts the maximum attainable total input power factor. This paper proposes two space vector based modulating techniques for high power/low switching frequency applications (<1 kHz). The developed switching patterns feature similar performance (low harmonic distortion, minimum switching frequency, and instantaneous line current control) to that obtained with optimum off-line pattern generators (such as selective harmonic elimination). Moreover, they add the following features: (a) the selection of the switches to turn-on/off and the calculation of their on/off-times are done by solving linear algebraic equations, (b) there is no need for stored data since calculations can be implemented on-line, (c) the overmodulation region is naturally covered, including six-step operation, and (d) the short circuit pulses are generated automatically and distributed symmetrically through all the power switches, which enables an even sharing of the switching and conduction losses.