Fault Diagnosis And Control Of Wind Energy Conversion System Based On Set-valued Observer

Wind energy has received widespread attention worldwide.With the expansion of the scale of wind power,the structure of the wind energy conversion system(WECS)is becoming more and more complex.It is a complex nonlinear dynamic system with strong input uncertainty and a high degree of coupling.The random time variation of wind speed and grid parameters poses great challenges to the safe operation of the system.In addition to the harsh operating environment,faults occur frequently,and even minor faults may develop into catastrophic faults,causing significant economic losses.The realization of fault diagnosis and fault-tolerant control of the WECS can reduce equipment accident rate and maintenance costs while ensuring power conversion efficiency.It has become an indispensable solution to ensure the reliable operation of modern wind turbines and reduce maintenance costs.The WECS includes modules such as aerodynamic subsystem,pitch angle system,drive train subsystem,generator subsystem,grid-connected inverter subsystem,etc.At present,most of the researches on its fault diagnosis are carried out for one of its systems,lacking a unified platform to realize the global fault diagnosis of the system.Therefore,based on the detailed analysis of the common fault characteristics of the WECS,this paper considers the WECS with high-order,communication delay and unknown nonlinear parts,researches the design of states set-valued observer(SVO)for subsystems of the WECS using the strong positive disturbance invariance theory of discrete system and the Euler linear approximation theory,and adopts the system fault diagnosis and fault-tolerant control strategies based on SVOs.The main contributions are as follows:1.The composition of the WECS and the overall mathematical model of the WECS are elaborated.On this basis,the characteristics of 12 common faults in WECS are analyzed,the mathematical model of each fault is established and classified,and the system augmented model under fault conditions is deduced,which lays the foundation for the following researches on fault diagnosis strategies.2.Considering the state estimation problem of WECS with communication delay and unknown nonlinearity,the strong positive disturbance invariance theory of discrete system is adopted to design the SVO,and the set-induced Lyapunov function is designed to prove the convergence of the SVO.On this basis,the SVOs of the pitch angle system and the converter model are designed.For the joint system model of the drive train system and the converter,the reduced-order set-valued observer(ROSVO)is designed by using the state transfer vector and pole placement method.Considering communication delay and unknown nonlinearity of the WECS,the Taylor's first-order expansion and high-order polynomial data fitting algorithm are used to establish the linear approximate model of the WECS,and the nonlinear system Lipschitz condition is used to design the nonlinear global SVO of the WECS.The simulation results verify the state estimation performance of each subsystem's SVO and the nonlinear global SVO.3.Based on the above-designed SVOs,fault diagnosis strategies based on multiple parallel SVOs are designed for 12 common faults of the WECSs.First,a five-parallel SVOs fault diagnosis strategy corresponding to the three pitch angle systems,the drive train system and the converter one-to-one is designed.In order to reduce the risk of fault misjudgment and realize the fault location,the SVO considering delay for the pitch angle system,the ROSVO for the joint model of the drive train system and the converter model,and the nonlinear global SVO are added on this basis to establish a unified eight-parallel SVOs fault diagnosis strategy for each subsystem of the WECS.The simulations verify that the above-mentioned fault diagnosis strategy can output the fault diagnosis result including the accurate fault detection,the proper fault location and the fast fault diagnosis time.4.Aiming at the time-delay system with variable parameters,a non-fragile robust H_?state feedback controller is designed based on Linear Matrix Inequality(LMI)and matrix Schur complement.A Lyapunov function with an integral term is established to guarantee the asymptotic stability of the close-loop system and to meet the H_?performance index.Taking the multiplicative faults of the pitch angle system of WECS as the goal,the robust fault-tolerant control law and the switching SVO group driven by the fault diagnosis result are designed.Three faults of the pitch angle actuator,namely pump wear,hydraulic leakage and high air content in oil,are simulated to verify the control effect of the designed control law.