Research On The Control Strategy And Regulating Method Of Modular Multilevel Converter(MMC)

HVDC Light is one of the important researching areas of power electronicstechnology in recent years.The characteristics of modular multilevel convertermake it suitable for HVDC systems.In this paper，through analysising principles of MMC，the control strategies ofReactive power、active power、combined voltage、current and frequency areresearched in detail.The main aspects of this dissertation are summarized asfollows:1.This paper summarized the trend of multilevel converter by analyzingtopologies and the basic operating principle of several common used multilevelconverters.These lead to the focus of this paper--modular multilevel converter（MMC）.2.The operating principles and controlling strategies of MMC was analyzed indetail.Several modulation techniques for MMC such as carrier phase-shiftedsinusoidal pulse width modulation were analyzed,the Carrier Phase Shifting SPWM(cps-SPWM) is more suitable for MMC topology.a method for charging anddischarging capacitors in Modular Multilevel Converter (MMC) is explained.TheDC capacitor voltage balance control strategies, as well as the capacitor voltagepre-charge method were also researched in detail.3. The control strategy was also proposed.Inner loop current controller and Outer loopvoltage controller were designed in detail. MMC active power control system and MMCDC vpltage control system wre researched in detail.4.Simulation is performed to validate the control strategies of HVDC-Lightwhick consist of MMC.