AC/DC/AC PWM converter with reduced energy storage in the DC link

The paper introduces the family of quasi-direct converters, i.e., forced-commutated ac/dc/ac converters including small energy storage devices in the dc link. In particular, the case of three-phase to three-phase quasi-direct converter is considered. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. The paper describes a simple and effective control technique which also provides high-power factor and small distortion of the supply currents. After a discussion of the general properties of quasi-direct converters, design criteria of both power and control sections are given, and experimental results of a 2-kVA prototype are reported