## 1 Introduction
In [17], a two-order sliding mode is designed for the parameter variable and external disturbance of the wind energy system based on doubly-fed induction generators DFIG, and the variable structure control based on the two-order derivative of the a properly chosen sliding manifold is designed to further improve the performance of the system. In [18], a class of MIMO (multiple-input multiple-output) nonlinear system's derivative and integral terminal sliding mode control is proposed to realize the limited convergence time of the more general high order MIMO system and avoid the singular problems in the design of the controller. Fault detection and isolation for induction generators based on a sliding mode observer is proposed in [19] by means of maximum power point tracking, and the induction generator closed loop via indirect rotor flux-oriented control is described. The WECS has the characteristics of being nonlinear, having strong coupling, being multivariable and so on, and is seriously disturbed by external interference. Through the sliding mode control, the WECS has strong robustness and excellent insensitivity to faults and external interference. The WECS is usually composed of a wind turbine, transmission link, generator, Alternating Current-Direct Current (AC-DC) converter and so on; there has been much research on fault diagnosis and fault-tolerant control of different links in the WECS. A Wound Rotor Induction Generator (WRIG)-based wind energy system associated with hybrid AC/DC microgrid (DCM) is introduced in [20], which runs under an islanded and utility-tied mode. The system operation and power transfer under the islanded and utility-tied mode are realized at all possible conditions, and the effectiveness of the system in the process of load changes is proved by the dynamic experimental results of various modes. For MPP (maximum power point) and no-MPP tracking operations, two different methods, the difference between the actual and simulated output power of the wind system and the predetermined angular shaft speed ratio are adopted respectively as indicators to detect the lubricant system faults in [21]. According to different operation modes, different diagnostic criteria are used to diagnose faults; although it is helpful for better detection of faults, the process design is rather complicated. An active fault-tolerant fuzzy control strategy based on multi observer switching control is proposed in [22], the T-S fuzzy modeling of WECS is carried out and sufficient conditions for robust stabilization of system are given by deriving Taylor series and linear matrix inequalities. Multi-observer switching control leads to an increase in the number of constraints, which is limited in engineering applications, and the actuator fault is not considered in it. A fault diagnosis method for the lubrication system and the converter in the wind energy system is presented in [23], and the tolerance of the supervisory controller towards a lubrication system and converter fault in the wind system is explained to satisfy the demanded power with maximum utilization. Compared with proposed robust formulation, this paper has been optimized to better solve the uncertainty of the WECS. With the increase of the scale of WECS, the number of actuators and sensors is increasing, and the probability of simultaneous faults is increasing. Previous works focused on fault diagnosis and fault tolerant control of a single actuator or sensor. Therefore, it is more practical to study the multi-fault diagnosis of WECS. In this paper, the state equation of the WECS is established in the case of the simultaneous faults of the actuator and the sensor in the WECS. Based on the SMO, a new augmented system is constructed by introducing the orthogonal transformation matrix and constructing the post filter. The sensor fault is converted into the actuator fault to diagnose, and a robust adaptive fault reconstruction observer is designed to achieve multiple fault reconstruction.