Dynamic phasor modelling and operating characteristic analysis of half bridge MMC
A unified dynamic phasor model for modular multilevel converter (MMC) under the rotating frame is developed. The model takes the AC voltage in the rotating frame and the DC voltage as electrical inputs, the fundamental frequency and second harmonic modulation indices as the control inputs. By separately modelling the controller, the electrical dynamics of MMC and the dynamics of external electrical system, the proposed dynamic phasor model is able to seamlessly interconnect with models of controllers and external electrical system. The dynamic phasor model of MMC is therefore normalized. By setting the derivative terms in the dynamic phasor model to be zero, static phasor model of MMC is achieved. By linearizing the dynamic phasor model around the steady state operating point, small signal model of MMC is obtained. As a result, the proposed dynamic phasor model of MMC unifies the dynamic phasor model, static phasor model and small signal model of MMC. Based on the obtained static phasor model of MMC, an open loop circulating current suppressing control (CCSC) strategy and a method of analytically analyzing the operating characteristic of MMC are proposed. Simulations on PSCAD/EMTDC verified the accuracy of the dynamic phasor model, the efficacy of the open loop CCSC strategy and the different constraints on the PQ operation zone of a MMC.
2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC ECCE Asia)