| With the increasing of the application capacity of motor drive,multi-level converters have been widely used in the field of medium and high voltage high-capacity power transmission.Modular multilevel converter(MMC)makes up for many shortcomings of traditional multilevel converter with its superior expansion,redundancy,good output characteristics and cost volume advantages.It is especially suitable for medium and high voltage applications with large capacity.The back-to-back high power converter based on MMC has a broad application prospect in the mine hoist system.This thesis mainly studies the control strategy of the MMC rectifier.Firstly,the thesis introduces the rectifier structure commonly used in the converter of mine hoist,and summarizes their respective advantages and disadvantages.Based on the application background of mine hoist,the topological structure of MMC rectifier circuit is introduced,its working principle is analyzed,and its mathematical model is established.Two modulating modes of MMC rectifier for mine hoist are analyzed,which lays a foundation for the control strategy of the rectifier.Secondly,the working principle of PWM rectifier based on MMC is analyzed,and its overall control strategy is designed.In order to maintain the voltage stability of DC bus and realize the operation of unit power factor,the voltage and current double closed-loop control strategy of MMC rectifier is designed.In order to solve the problem that the fluctuation of the capacitance voltage of the sub-modules can easily distort the output voltage and cause the circulation,the capacitance voltage of the sub-module is calculated and the influencing factors are analyzed,and the control strategy of the balance of the capacitance voltage is designed.The overall control strategy designed for MMC rectifier is simulated and analyzed in steady state and dynamic state.Finally,the suppression method of the internal circulating current harmonics in MMC rectifier is studied,the generation mechanism and characteristics of the circulating current are analyzed in detail,the amplitude of the secondary component of the circulating current is calculated,and the steady-state mathematical model of the circulation is established.A linear active disturbance rejection circulating current suppression controller based on ADRC technology is designed.The controller has the advantages of simple parameter tuning,fast response speed and good suppression effect.The proposed circulating current suppression algorithm is verified by the simulation model,and its effectiveness is fully proved by the results of simulation. |
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