Research On Modular Multilevel Converter Inverter Control Strategy For Mine Hoist

With the rapid development of the power electrical technology,multilevel inverter has been widely applied in high power mine hoist system,but there are still many shortcomings.Modular Multilevel Converter is a new type of multilevel topological structure,MMC is compensates for many shortcomings of the traditional multilevel converter,which is especially suitable for high-power occasions.It needs back-to-back connection when it is applied to high power mine hoist system.This thesis focuses on the research of control strategy for MMC inverter.Firstly,in the application background of mine hoist,the topological structure,working state of sub-modules,mathematical model and working principle of MMC inverter are introduced.Two modulation methods of MMC inverter for mine hoist are compared and analyzed,which lays a foundation for studying the control strategy of the inverter.Secondly,the traditional MMC pre-charging method is described in detail,and the two-stage pre-charging method of MMC inverter is designed.By calculating the charging time of each stage,the charging state of the sub-module is controlled by the time node,and the capacitor voltage is charged to the voltage requirement of stable operation.The model was built in MATLAB/Simulink,and the pre-charging method was simulated and verified.Then,the fluctuation law of capacitor voltage of sub-module when MMC inverter applied to mine hoist is analyzed.The fluctuation coefficient of capacitor voltage of sub-module is obtained by calculation.The reason of capacitor voltage fluctuation of sub-module is analyzed.A control strategy for suppressing the fluctuation of capacitor voltage is studied.When the MMC inverter is operating in the low frequency domain,the capacitor voltage fluctuation can be effectively suppressed.The control strategy is verified by simulation.Finally,a three-phase MMC inverter experiment platform for simulating the operation control of mine hoist is constructed.The overall structure of the experimental platform,the control system,the composition of the sub-module unit,and the capacitance voltage detection system are introduced.The generation method of carrier phase shift PWM pulse signal is designed and verified by relevant experiments.