Integrated Design for Active Fault Diagnosis and Control: A Decomposition-Composition Method

Active fault diagnosis (AFD) designs inputs to excite the system to obtain more operation information for fault diagnosis. Since both AFD and control are required to design systems’ inputs, individually designing inputs for fault diagnosis will restrict the systems’ control performance. In order to achieve satisfactory performance for both AFD and control, this paper presents a novel set-based input design method for simultaneous AFD and control. The new method adopts a decomposition-composition idea to integrate AFD and control for better control performance during the AFD stage. Particularly, the proposed method first considers each single system mode separately and establishes an optimization problem, combining the AFD and control objectives, to design the optimal input. Then, all possible system modes are comprehensively considered to select the final input from all inputs designed under the single mode by an adaptive selection strategy. Meanwhile, the proposed method realizes AFD by maximizing the separation trend of all output sets online, without considering the strict set separation conditions. Hence, the method in this paper has a simple mathematical form and lower computational complexity. At the end, simulation results based on two different examples are presented to verify the effectiveness and portability of the proposed method. Note to Practitioners—Set-based AFD methods have two main features. The first one is that they only require the bounds of system uncertainties, such as modelling errors, process disturbances and measurement noise, and do not require their specific distributions and values. This requirement can be easily satisfied by varieties of engineering systems. The second one is that they design inputs to actively excite the system to obtain more system operation information for fault diagnosis. This feature enables AFD to achieve high fault diagnosis sensitivity and detect more faults, such as incipient faults, small faults, etc. Thus, when AFD methods are used in active fault-tolerant control (FTC) systems, the whole FTC performance can be improved. However, set-based AFD has conflicting requirements on input design with control, while there only exist few works in the literature on the integrated design of set-based AFD and control. This paper proposes a novel integrated design method for AFD and control, which can achieve satisfactory performance for both AFD and control with low computational complexity. Besides, although this paper only considers discrete linear time-invariant (LTI) systems, the proposed method can be extended to more complex systems such as linear parameter-varying (LPV) systems, linear time-varying systems, etc. Moreover, based on LPV modelling techniques, equilibrium linearization techniques, etc., the proposed method can be used for fault diagnosis and FTC of some nonlinear systems as well. Therefore, the proposed method has advantages in online fault diagnosis and FTC applications of engineering systems such as unmanned aerial vehicles, unmanned ships, driverless automobiles, space systems, robots, process industries, etc., which own values and potential to improve safety and reliability of varieties of engineering systems.