Performance optimization of quasi-direct converters

The paper describes a three-phase to three-phase quasi-direct power converter, i.e. a forced commutated AC/DC/AC power converter with small energy storage devices in the DC link. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. In the paper, an effective digital control of the line current waveforms capable to work with unbalanced line and/or load voltages and providing also high power factor, is presented. After a discussion of the general properties of quasi-direct power converters, design criteria of both power and control sections are given, and experimental results of a 2 kVa prototype are reported.<>