Research On Control Strategy Of Modular Multilevel Converter

Modular Multilevel Converter(MMC)with its highly modular structure,easy expansion,high reliability and good voltage output quality advantages,suitable for application in the future high voltage level and transmission power of flexible DC power transmission occasions.With the development of high-power power electronics technology,MMC based flexible direct current transmission technology has shown a broad application prospect in the field of new energy and high-voltage direct current transmission,so the research on its related control strategy is of great significance.In this paper,MMC is studied from the modulation mode,sub module capacitor pre-charging control method,sub module capacitor voltage balance control method and so on.At the same time,the MMC pre-charging process and sub-module pressure equalization control process,which are two hot research topics,are deeply studied,and related control strategies are innovated and optimized.Among them,the MMC pre neutron module capacitance charging process in the charging phase transition when the trouble phenomenon of over current,over voltage,etc,deeply analyzes the inverter wife of charging process module,and according to the son of charging characteristics put forward a kind of module is suitable for the controlled charging phase of active balancing the ac control strategy,the capacitive voltage and DC voltage of its sub-modules can be adjusted with their respective reference values.Simulation analysis shows that the safe transition from uncontrollable charging stage to controllable charging stage can be realized under this control strategy,and the capacitor voltage and DC bus voltage are smoothly lifted.The phase circulation stabilization control link introduced in the process can improve the phase charging consistency.The whole pre-charging process is stable and efficient.MMC for traditional sorting are under the pressure control of sampling data processing such as poor efficiency and high switching loss problem,by using BFPRT algorithm to improve the conventional fast row,using some sort of sampling data,the computation,to increase efficiency of the operation,but also put forward displacement variables,the introduction of change in the past the module for selection method,given input and standby group central molecules capable of cutting condition module,reduce the device switch frequency,lower switching frequency.Simulation results show that the new strategy can improve the efficiency of data operation,reduce switching frequency and reduce switching energy loss.