Rsearch On The Integrated Control Method Of Modular Multilevel Converter

With the developing applications of power electronics in the field of HVDC, solar power and wind power, the modular multilevel converter(MMC) which has the advantages of no need of clamping devices and easy to achieve back-to-back four quadrant operation attracts more and more attention from domestic and foreign research institutions and universities. Recently the research emphasis modular multilevel converter mainly focus on: modeling and simulation, protection design and pre-charging strategy, modulation and circulation suppression etc.This paper first analyzes the research status of traditional multilevel converters and modular multilevel converter. It analyzes the system composition and working principle of MMC and proposes the integrated control method with the basic idea of decoupling the MMC system into common mode and differential mode so as to achieve the balancing control and current control when MMC working in inverter status. Then simulation results in MATLAB/Simulink verify the controllabilities of the sub-modules’ voltages and system current.In addition, a single-phase MMC hardware system of 4 sub-modules is designed and built. The central controller of the experimental prototype is based on DSP and CPLD. The voltage sample and data transmission of each sub-module is based on PIC. The results of experiments prove the correctness and effectiveness of the proposed integrated control method.