Research On PMSG Control Strategy Based On DC Grid Connection

With the growing demand for electricity and the decreasing reserves of fossil energy around the world,wind power technology has been developed rapidly.Permanent magnet synchronous wind power generation system has the advantages of simple structure,low failure rate,and low maintenance cost,and it has become the fastest developing generator.At the same time,the wind farm DC grid-connected technology is widely used because of its advantages such as convenient control,fast adjustment speed,and suitable for long-distance transmission.Therefore,this paper takes DC grid-connected PMSG as the research object to study the system control strategy,and improve the system response speed and anti-interference ability and reduce the design difficulty of system control parameter.The specific work of this paper is as follows:(1)Research on system modeling,simulation,and experimental systemFirst,the research object is a PMSG system based on DC grid-connection,the system power generation principle is analyzed and the mathematical model is established PMSG model,and machine-side converter model.Second,the paper describes classical double-loop PI control strategy and analyzes its advantages and disadvantages.Finally,the system simulation and experiment platform is built for the effectiveness and feasibility validation of control strategy.(2)Research on a Single-loop Model Predictive Control(MPC)strategy.In this paper,a Single-loop MPC strategy is proposed to solve the problems of complex control parameter design,slow response speed,and control delay in a classical double-loop control system.First,according to the system torque equation and current equation,the second-order system equation is established.owing to some difficult measurements in the system,the integral discretization and Euler differential forward discretization methods are adopted to discretize the system integral and differential terms,and the system is reduced to a first-order system.Second,the influence of current limit term in the cost function is analyzed to ensure the safe and stable system operation within its limit range.Finally,the feasibility and effectiveness of single-loop MPC strategy are verified by the simulation and experiment platforms.The results show that the single-loop MPC strategy improves the system response speed.The rotor speed response speed increases by about 0.1 second,and active current response speed increases by 0.1 second as well.The control parameters of single-loop MPC strategy are reduced by 2/3,which reduces the design difficulty of control parameter.(3)Research on a Single-loop Sliding Mode Variable Structure Control(SMC)strategy.This paper proposes a Single-loop SMC strategy to solve some problems of classical doubleloop cascade control,such as complex design of control parameters and weak anti-interference ability.First,establish the equation with rotor speed and reactive current as the control targets.And the second-order system is reduced by the integral discretization,to avoid some difficult quantities in the measurement system.Second,the system sliding mode surface is designed,system control rate is obtained,and the system stability is verified.Finally,the effectiveness and feasibility of Single-loop SMC strategy are verified by simulation and experimental research.The results show that the proposed strategy eliminates the overshoot during system starting operation and wind speed variation,and realizes the smooth speed tracking targets.The control parameter number is reduced by 1/3 and design complexity is reduced.Compared with a classical doubleloop PI control strategy,the single-loop SMC strategy improves the system robustness and eliminates the fluctuation caused by parameter perturbation.