Modular Multilevel Converter leg-energy controller in rotating reference frame for voltage oscillations reduction

Abstract

This work consists of the presentation of a regulation strategy capable of controlling the energy stored in the DC capacitors of the upper and lower arms of a Modular Multilevel Converter (MMC) for each phase. This is achieved by regulating the positive, negative and zero sequences in dqo coordinates of the differential current using a rotating reference frame at twice the fundamental value. Active and reactive components of the differential current are used to eliminate the oscillations of the three-phased leg-energy which reduces significantly the capacitor voltage oscillations, while the zero sequence component is used to regulate the whole system energy at a given value. All feed-forwards equations are demonstrated, and cross-coupled leg-energy terms are introduced.