Research On Modeling And Control Strategy Of Semi-direct-drive Permanent Magnet Synchronous Wind Turbine

With the trend of energy shortage and environmental pollution becoming more and more serious,wind power generation technology has been paid more and more attention by large wind resource countries.Variable Speed Constant Frequency(VSCF)unit is the most widely used wind power generation system.Semi-direct drive permanent magnet synchronous unit combines the advantages of doubly fed induction unit and direct drive permanent magnet unit,and will be paid more and more attention in the trend of large-scale generation unit.In this paper,the control strategy of converter on generator side and grid side of semi-direct-drive permanent magnet synchronous wind turbine system is studied emphatically.In order to solve the problems of complex decoupling,PI tuning and multi-objective optimization in traditional control strategies,finite set model predictive control(FCS-MPC)has become a research hotspot in recent years.By using the discrete characteristics of PWM converter and the finite switching state characteristics,the method can effectively control the converter by compiling control program.It has good flexibility and stability,and improves the grid-connected quality of wind power generation.Firstly,this paper introduces the topological structure of semi-direct drive permanent magnet synchronous wind turbine,and establishes the basic mathematical models of wind speed model,wind turbine model,permanent magnet synchronous motor and converter in three-phase static coordinate system,two-phase static coordinate system and two-phase synchronous rotating coordinate system,which provides a theoretical basis for the analysis of control strategy.By analyzing the theory of model predictive control,the model predictive torque control and model predictive current control strategy are proposed to control the machine side converter and the grid side converter respectively.The method takes the value function as the optimization objective,traverses and calculates the system output under all switching states,and chooses the optimal switching state as the control signal to control the switching state of the converter bridge arm.Then,combined with the mathematical model of permanent magnet synchronous motor and converter,the value function of model control of machine-side converter is constructed with torque and flux as control variables,and the value function of network-side converter model control is constructed with current error.On this basis,the multi-objective coordinated control of converter is realized by two-step prediction method,adding target parameters and weight coefficients to improve the value function.Finally,the control system structure diagrams of model predictive torque control and current control of grid-side converter are established respectively,and the simulation model is established in MATLAB to realize the simulation of machine-side and grid-side converters.Through the simulation and verification of the converter control system,it is found that the application of model predictive control and its improved method in the converter control is reasonable.