Modeling and Design of Three Phase Current Regulator with Inductor over Saturation Region for DC/AC Converters

Abstract

For high performance control of three phase ac circuit, current regulation is usually used as inner loop of three phase converter control system. In conventional current regulators such as state decoupled PI controller and complex vector PI controller, inductor in three phase circuit is presumed as linear and constant, and always operating far lower than the magnetic saturation level region. However, because of three phase instantaneous current difference and nonlinear characteristics of magnetic material, inductance of each phase would not be the same among three phase and would be time varying. Moreover, because of saturation characteristics, inductors are oversized to avoid the saturation region.

This paper presents an improved current regulating strategy with a feed-forward term to compensate widely varying inductance of three phase AC inductor over magnetic saturation region. With the proposed control strategy by extracted self and mutual inductance look-up table or by estimated inductance voltage, not only inductance variation can be compensated, but also low order harmonics, especially 3rd order harmonics, are considerably reduced as well when operating over saturation current level. Experiment results are presented to verify the validation of the proposed control strategy.