A Joint Fault-Tolerant and Fault Diagnosis Strategy for Multiple Actuator Faults of Full-Vehicle Active Suspension Systems

In this paper, a joint fault-tolerant and fault diagnosis strategy is proposed for handling multiple actuator faults in full-vehicle active suspension systems. Different from traditional methods where fault detection and isolation must precede the fault-tolerant control to provide the latter with certain fault information, our proposed scheme performs both jointly over the whole operation process with guaranteed suspension performance. For the fault-tolerant control, we develop high gain filters under a fast timescale to estimate the variations of the integrated control inputs caused by actuator faults, and the equivalent fault-free parts of the integrated control inputs are selected as the target control variables. In such a decomposition, we are able to determine the control law of each actuator without using the information of the faulty actuators. Under the framework of the fault-tolerant algorithm, we construct a bank of adaptive fault diagnosis observers to online identify the force constants of the actuators, where information of the heave, pitch, and roll motions are all utilized to ensure persistent excitation and enhance identification accuracy. In particular, actuator faults can be detected via the estimation of the force constants, in which both the location and severity of the actuator faults can be further identified. Subsequently, control commands are reassigned to alleviate the use of faulty actuators and thus protect them from further damage. The effectiveness of our proposed method is validated via extensive simulation results. <italic>Note to Practitioners</italic>&#x2014;Satisfactory performance of vehicle active suspension systems is founded upon good reliability and safety of the suspension systems, which motivates us to conduct deep research into fault diagnosis and fault-tolerant problems to improve the significant system reliability. In this paper, a joint fault-tolerant and fault diagnosis (joint FTFD) scheme is proposed for addressing multiple actuator faults of full-vehicle active suspension systems. The proposed method can be used to guarantee suspension performance over the whole operation period even if multiple actuator faults occur, and the location and severity of the actuator faults can be identified at the same time. Different from the traditional methods where fault diagnosis precedes the fault-tolerant control to provide certain fault information, in the proposed joint FTFD scheme, fault diagnosis is carried out under the always-on fault-tolerant framework to ensure system reliability and performance over the whole operation process. The multi-timescale technique is used to compensate for actuator failure and achieve fault-tolerant control. Under the fault-tolerant framework, actuator faults can be detected and both the location and severity of the faults are decided via monitoring the online identification results of the motor force constants. However, one limitation of the proposed method is the influence of sensor noise on high gain filters in real world application, which might degrade fault-tolerant performance. For the future research, one significant work is to carry out real vehicle tests to promote the proposed algorithm to practical application. Also, fault diagnosis and fault-tolerant control for suspension sensor faults is another valuable topic which deserves our efforts. Given that the proposed fault-tolerant framework is independent on a particular control system or a specific type of nominal controller, the fault-tolerant design idea can be transplanted to a broad range of systems besides addressing suspension actuator faults.