Research On Modeling,Control And Modulation Of Modular Hybrid MMC

Modular Multilevel Converter(MMC)is the preferred topology of flexible HVDC technology because of its Modular Multilevel Converter’s high output waveform quality,flexible control mode,and high reliability.It is widely used in renewable energy gridconnection and weak grid/passive network power supply.Compared with traditional half-bridge MMCS,modular hybrid MMCS have DC fault handling capability,which has become a research hotspot.The bridge arm of a modular hybrid MMC consists of a Half-bridge Submodule(HBSM)and a Full-bridge Submodule(FBSM).Since the FBSM can output negative levels,the converter can operate in an overmodulated state.However,the control and modulation strategies of traditional half-bridge MMCS cannot be applied to modular hybrid MMCS under overmodulated operating conditions.Therefore,the modeling,control and modulation techniques of modular hybrid MMC are studied in this paper,and a prototype of modular hybrid MMC physical experiment is built.This paper first introduces the topology of modular hybrid MMC,and analyzes the working status of HBSM and FBSM.Considering the dynamic charge-discharge characteristics of the submodules,the mean value model of the bridge arm in the three-phase static coordinate system is derived,and the state space model of the hybrid MMC module in the symmetric condition is established based on the synchronous rotating coordinate system.Then,an improved control strategy based on hybrid MMC modules is proposed and the overall control architecture is built.Considering the overmodulation operation condition,an improved modulation strategy suitable for modular hybrid MMC is proposed,and the feasibility of this strategy is verified by the simulation model built in PSCAD.Finally,a modular hybrid MMC physical experiment prototype is designed and built independently.The complete control system is designed based on field programmable gate array(FPGA).The system can take full advantage of FPGA parallelization to reduce the control cycle and significantly improve the real-time performance of prototype controller.On this basis,the algorithm of capacitor voltage sorting of submodules based on FPGA and the signal transmission process are improved,which shortenes the cycle of capacitor voltage sorting and improves the accuracy of data transmission.By comparing the experimental results with the simulation results,the effectiveness of the proposed modulation strategy is verified.