Stochastic Model Predictive Fault Tolerant Control For Wind Energy Conversion System

Wind energy is drawing considerable attention as an important kind of green energy.Wind Energy Conversion System(WECS)is a mechanical electrical hydraulic integrated system with complex nonlinear dynamic characteristics.As the WECS exhibits strong model uncertainties and disturbances at random wind speeds,it's difficult to control and model WECS with traditional methods.Meanwhile,WECSs have many real difficulties such as high rates of facility faults,maintenance inconvenience caused by their poor reliability,and high outage losses.Therefore,how to realize the fault-tolerant control of WECS is significant to improve the utilization rate of wind energy and reduce maintenance costs.This paper addresses the fault-tolerant control problem of a WECS with a probable actuator fault.A new stochastic model predictive control(SMPC)fault-tolerant controller with the Conditional Value at Risk(CVaR)objective function is proposed in this paper.The main research of this article is as follows:1)For the modeling of wind energy conversion systems,the Markov chain theory is introduced.Due to the influence of random wind speed,the wind energy conversion system exhibits strong random and non-linear switching characteristics.2)In order to solve the problems of WECS with system model uncertainties and disturbance,this paper proposes a SMPC method based on scenario tree.The uncertain stochastic model predictive control problem is transformed into deterministic model predictive control(MPC)problem through the method that scenario tree enumerates all the possible realization of the disturbance in prediction horizon.Finally,to meet the real-time performance of the WECS,the method of off-line calculating and online calling the controller is adopted to improve the operation speed of SMPC.3)To solve the fault tolerance control problem of WECS with actuator probability faults,this paper proposes a scenario-based SMPC controller with the CVaR objective function.CVaR can provide a balance between the performance and random failure risks of the system.With CVaR objective function,a certain risk probability is transformed into a Linear Programming(LP)problem,and the fault-tolerant control performance of WECS probabilistic failures is guaranteed.The Min-Max and Var indexes are introduced to compare with the proposed method.The comparison results suggest that the proposed method has better fault-tolerant control performance than the controller with Min-Max and Var indexes.