Multi-Objective Hierarchical Stochastic Control Of Wind Farm Considering Wake Effects

The wake effect in wind farms reduces the effective wind speed and exacerbates the random fluctuations in wind speed caused by the increased intensity of wind turbulence.Therefore,in the aspect of wind farm,the active power dispatch commands from the grid should be reasonably allocated to decrease fluctuation of the output power of the wind farm in response to the grid dispatch commands caused by the wake effect and to minimize the fatigue load of the whole farm.In the aspect of wind turbine,appropriate active power control strategies should be adopted to track the output power of the wind turbine to the single power distribution instruction from the wind farm,and to partially suppress the influence of random wind speed fluctuations caused by wake effect on the fatigue load of a single wind turbine.Optimization control from these two aspects can comprehensively improve the sustainable power guarantee ability and safety of wind farm,and reduce the impact of fatigue load on wind turbine’s component loss and shortening its service life,so as to improve the economic operation of wind farms.Therefore,it is of great practical significance to study the multi-objective stochastic hierarchical control of wind farm considering wake effect.This paper summarizes the research status of relevant fields in recent years,and carries out relevant research on hierarchical control of wind power plants.The specific content is as follows:(1)A wind farm dynamic wake model considering time delay has been established.This model can not only reflect the coupling relationship between the control variables(pitch angle,yaw angle,generator torque,etc.)of the upstream wind turbine and the output power of the downstream wind turbine,but also reflect the impact of the inflow wind speed angle on the effective wind speed of each wind turbine.It also reflects the main time delay dynamic characteristics of the wake.Thus.the model provides a model basis for the subsequent optimization control of wind farms.(2)In the aspect of wind farm,aiming at the problem that the output power of wind farm fluctuates frequently due to wake effect and the fatigue load of the whole field is intensified.a multi-objective active power optimization allocation strategy for wind farms based on nonlinear model predictive control is proposed.A multi-objective optimization problem is established to minimize the tracking error of wind farm output power to grid dispatching instructions and minimize the fatigue load of the whole field.By solving this problem,the optimal allocation of power grid dispatching instructions is realized.By comparing with the traditional variable proportional power distribution strategy,the proposed effectively improves the reliability and security of sustainable power guarantee for wind farm.(3)In the aspect of wind turbine,aiming at the problems that the output power of the wind turbine will fluctuate due to the random wind speed fluctuation caused by the wake effect and the fatigue load of the turbine actuator increases,a multi-objective stochastic model predictive control strategy of wind turbine based on affine disturbance feedback is proposed.The random wind speed disturbance is introduced into the controller design by affine disturbance feedback.A multi-objective optimization problem is established by minimizing the tracking error of the output power of a single unit to the power distribution instruction and minimizing the fatigue load of the unit actuator.The stochastic optimization theory is used to solve the problem and the control variable of the wind turbine is obtained.By comparing the proposed model predictive control strategy with the traditional model predictive control strategy,it is verified that the proposed strategy can effectively improve the economy and safety of the operation of wind turbine.