| Modular Multilevel Converter(MMC),as a highly modular new topology,has gradually become a research hotspot due to its characteristics of easy expansion,good output characteristics and low voltage stress.This thesis takes large-scale ships as the application background.On the basis of modeling and analysis of MMC fundamental frequency and low frequency working conditions,modulation strategy implementation and Permanent Magnet Synchronous Motor(PMSM)frequency conversion and speed regulation operation,combined with PMSM The speed sensorless control strategy proposed for the first time a method of multiplexing the high frequency signal in the low frequency stage and the switching function in the switching stage,and finally realized the MMC driven PMSM speed sensorless control strategy under the full speed range operation.This thesis first studies and analyzes the operating principle and control strategy of MMC,analyzes the mathematical model and operating principle of MMC,modulation strategy,and capacitor voltage balance control strategy.It conducts in-depth research and verification on Carrier Phase Shifting PWM(CPS-PWM)and Submodule Unified Pulse Width Modulated(SUPWM)strategies.When MMC is used as an AC motor driver,there is a problem of sharp fluctuation of capacitor voltage in low frequency condition.By analyzing the mechanism of capacitor voltage fluctuation in sub-modules,this thesis theoretically concludes the feasibility of high frequency circulation and common-mode voltage signal injection for capacitor voltage suppression.The suppression effect of double third harmonic high frequency signal injection method and square wave plus third harmonic high frequency signal injection method is analyzed and compared.At the same time,in the variable frequency speed control strategy of PMSM driven by MMC topology,the linear cutting mode of high frequency signal is adopted to ensure the smooth start and operation of the motor,so as to realize the full speed operation.Based on the normal start and operation of the motor,this thesis proposes a speed sensorless control strategy suitable for PMSM driven by MMC,and analyzes in detail the two speed sensorless speed sensorless signal injection method and sliding mode observer.In order to further simplify the system control strategy and reduce the cost,a method is designed to reuse the high frequency signals in the low frequency stage and the switching function in the switching stage.Finally,the speed sensorless control strategy of PMSM driven by MMC is realized under full speed range operation.Further,in order to realize the application of this scheme in large ships,a mathematical model is built based on basic parameters of propellers,and the speed sensorless control strategy of high-power ships driven by MMC is verified under the working condition of propeller load.Finally,based on the MMC experimental prototype platform,the operation control strategy of the fundamental frequency and low frequency conditions is verified.The experimental results show that the capacitor voltage balance control strategy and the low frequency operation control strategy based on the SUPWM modulation method are feasible. |
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