Research On The Control Strategy Of HVDC-light Based On Modular Multilevel Converter

HVDC-Light is one of the important researching areas of power electronicstechnology in recent years.The characteristics of modular multilevel converter(MMC) make it suitable for HVDC systems.The design of HVDC-Light system based on two level voltage sourceconverter (VSC) is relatively mature, some design ideas and methods can be used inHVDC-Light based on MMC. But because of the different topology, modularmultilevel converter has its own characteristics. Based on the difference betweenmodular multilevel converter and two level VSC in the main circuit parametersdesign and controller design, more attention is paid to the parameters design andcontroller design that is suitable for MMC. The main research contents are asfollows:(1) Study the principle of modular multilevel converter and two modulationmodes: nearest level modulation and carrier phase shift modulation, and analyze themodular multilevel converter power operating range.(2) The modular multilevel converter bridge arm current are analyzed in detail,and analyze the relationship between the bridge arm current and the energy storedin the bridge arm, Then, establish mathematical model of modular multilevelconverter based on the bridge arm current.(3) Study the design the main circuit parameters of modular multilevelconverter, including selection of the inverter ac inductance, bridge arm inductanceand capacitance of the modules.(4) Study the circulation current control strategy and voltage balance controlstrategy of MMC, simulation verification accordingly.(5) Analysis of the double loop controller that is suitable for MMC, design thewhole control system of modular multilevel converter. And the operations ofmodular multilevel converter independent inverter, rectifier and HVDC-Lightsystem connected to two ac system are simulated.