A Study and Design of Circulating Current and DC Current Ripple Controlling MMC

Abstract

MMC is an evolving topology which is able to handle high voltage and power ratings.Under the unbalanced condition, the main theme of controlis to decrease the negative-sequence line current. Moreover,the circulating current of a MMC contains not only double-linenegative-sequence component, which appears under the balancedcondition, but also positive- and zero-sequence double-line components. Thus the controller should be able to remove all those components of the circulating current. A proportional-resonantcontroller (PR controller) is applied to regulate the positive- andnegative-sequence components of circulating current. In addition,the zero-sequence component of circulating current is controlledby a dc current controller. The proposed control method isconfirmed in MATLAB/SimPowerSystem.