A Novel Control Strategy of Modular Multilevel Converter Based on Instantaneous Power Theory

The rapid response characteristics of the power electronic device may aggravate the subsynchronous oscillation, which is closely related to the controller of modular multilevel converter (MMC). When a subsynchronous frequency component is fed into classical d/q decoupling controller, the output signals of the converter will include multiple component of sub-and super-synchronous frequency under such situation. In order to solve the problem that classical controller may increase power oscillation, a new controller based on instantaneous power theory is designed, without phase-lock loop and d/q coordinate transformation. Two different control strategies are simulated separately by MMC-HVDC electromagnetic model on PSCAD/EMTDC and the results show that the use of the proposed control strategy suppresses power fluctuations effectively and improves stability of HVDC system as well.