An Energy-based Controller for HVDC Modular Multilevel Converter in Decoupled Double Synchronous Reference Frame for Voltage Oscillations Reduction
Résumé
This work consists of the presentation of a regulation strategy capable of controlling the energy stored in the Modular Multilevel Converter (MMC) in a HVDC configuration. This is achieved by regulating the positive, negative and zero sequences in dqo coordinates of the differential current using two rotating reference frames: at once and at twice the fundamental grid frequency value. Active and reactive negative sequence components of the differential current at twice the fundamental frequency are used to eliminate the oscillations of the threephased leg-energy reducing significantly the capacitor voltage oscillations, while the zero sequence component is used to regulate the total energy stored at a given reference. Meanwhile, active and reactive positive sequence components of the circulating current are used for eliminating the average energy difference between the upper and lower arms in a three-phase MMC. In order to decouple efficiently the differential current components the Double Synchronous Reference Frame (DDSRF) current control strategy is used. Finally, simulation results validate the performance of the MMC in a HVDC configuration with the proposed control. Control equations are demonstrated, and cross-coupled leg-energy terms are introduced.