Research Of Generator Side Control Strategy For Variable Speed Constant Frequency Hydropower System

Hydropower resources are important in China.The construction cost of small hydropower stations is low,which can make a beneficial supplement to the power grid and has irreplaceable advantages.In recent years,based on the requirements of ecological civilization construction,each basin needs to ensure the decentralization of ecological flow.However,the traditional hydropower unit has narrow operating conditions,low utilization rate of water resources,low power generation efficiency of the traditional "Generating electricity from stored water" operation mode,and the level of equipment automation is not high.In order to ensure efficient power generation when the ecological flow is decentralized and meet the operation requirements of multiple working conditions,it is necessary to apply the variable speed constant frequency hydropower system to small hydropower stations,and study and optimize the variable speed constant frequency hydropower system,so as to significantly improve the efficiency of power generation.Firstly,based on the variable speed constant frequency hydropower generation system,this paper constructs the mathematical model of permanent magnet synchronous motor,analyzes in detail the vector control principle and method of permanent magnet synchronous motor,the principle of flux weakening control and SVPWM technology,and constructs the overall framework of the variable speed constant frequency hydropower generation system based on permanent magnet synchronous generator,which provides a theoretical basis for the further research and optimization of the control system in the subsequent chapters.Secondly,maximum power point tracking(MPPT)technology is studied based on variable speed constant frequency power generation system.The formula of hydraulic turbine in operation is derived.The traditional P&O control method is improved to a variable step size P&O control method based on dynamic disturbance coefficient and initial velocity evaluation.The improved P&O control method is mainly divided into two stages,and can adjust the speed disturbance and search step in the whole operating range of the system in real time according to the power change to track the maximum power of the system.It can also give real-time feedback to the adjustment of each link according to the power change.At the same time,the real-time monitoring of power fluctuation is added to the control system.Finally,the sensorless control technology of permanent magnet synchronous motor in full speed domain is studied.In the middle and high speed segment of permanent magnet synchronous motor operation,based on the traditional Luenberger observer model,the gain matrix of Luenberger observer is determined through the analytical relationship,and the sensorless control system model based on Luenberger observer is built.On this basis,an improved method is proposed.By using the control method of adjusting the control cycle of Luenberger observer and external additional phase-locked loop,The error of estimation is reduced,and the accuracy and response speed of the system are improved.In view of the problems of some sensorless control methods based on back EMF in the low-speed segment of the motor,the sensorless control based on the low-speed segment of the permanent magnet synchronous motor is realized by using the pulse high-frequency voltage signal injection method and selecting the appropriate injection signal parameters.In view of the high accuracy of the two methods in their respective suitable speed range,the appropriate control strategy is selected to switch the range,and a composite observer is constructed by combining the weighted average coefficient method with the phase-locked loop to realize the full speed range sensorless control of the permanent magnet synchronous motor.