Study On Fault Detection And Robust Control For Linear Switched Systems

With the development of the industrial technology,the safety and reliability of con-trol systems have been paid more and more attention.Thus,the study on fault detection becomes a key issue in the field of automatic control.On the other hand,switched systems are of great significance in theoretical research due to their wide applications in power systems,turbofan engine,traffic control systems.Since the switching behavior between the subsystems of the switched systems always occurs and effects the performance of the systems,the process of fault detection,which is to obtain the maximal faulty sensitivity for the switched systems,becomes very complex.So far,the problem of fault detection for switched systems have not yet been fully considered,which motivates us to shorten such a gap.This thesis investigates the problems of fault detection and control for several classes of switched systems.The main theoretical results are as follows.(1)For the problem of fault detection for discrete-time switched systems is inves-tigated,the state-dependent switching approach is first used.By constructing the state-dependent switching law and fault detection filters,the overall system is with the fault de-tection performance in the finite-frequency domain,which upgrades the fault sensitivity of the system.Meanwhile,noting the fact that the state of the system is often unmeasur-able,the proposed switching law uses only the state of the fault detection filters.Thus,the switching and detection strategies are both valid.(2)Based on the results in the previous subsection,the problem of simultaneous fault detection and robust control for switched systems is studied.Under the proposed switching law,the controller/detectors generate the switching,control and detection sig-nals simultaneously.This leads to less overall complexity and also extends the existing open-loop control results to the closed-loop control ones.More importantly,by analyzing the switching regions of the state,we prove the state-dependent switching approach can lead to better fault detection performance compared with the time-dependent switching one.(3)To deal with the problem of fault detection for switched systems with sensor stuck even outage faults,the existing method is to consider the relation between the residuals and fault directly.Obviously,when the amplitude is very small or zero(the outage case),the method leads to bad fault detection.To overcome the drawback,the servo input with finite-frequency is introduced to update the fault sensitivity.Further,by using the state-dependent switching law and multi-model approach,the generated residual is sensitive to the servo input in faulty cases and robust against them in fault-free case.This means the relation between residual and small stuck including outage faults is not considered,which guarantees the stuck and outage faults can be detected.(4)The fault detection problem for a class of uncertain switched systems with time-varying delays is investigated.In the time-dependent switching framework,fault detection filters are with varying gains are designed.Compared with the existing previous fixed ones,the proposed one can improve the fault sensitivity of the systems.In addition,in special case,the proposed filters can be converted into the existing ones,which means our result is more general.Finally,the mode-dependent average dwell time switching approach is used,which leads to more degree of freedom in the switching law design.Thus,the switched systems are with less conservatism.(5)The issue of simultaneous robust control and fault detection problem for continuous-time switched systems is studied.To avoid too frequent switching,a known dwell time constraint is introduced.Then,by design a state-dependent switching law which obeys the dwell time,the switching frequency is limited.Next,time-varying output-feedback-based controller/detectors are constructed,which guarantees the closed-loop switched system is asymptotically stable and also with the robust and detection performances.Thus,the proposed switching strategy have the advantages of both slow switching and state-dependent switching.(6)In this subsection,the l2-gain analysis and control problems for saturated switched systems are considered.First,a minimal dwell time constraint is introduced,which restricts the switching frequency.Next,some time-varying regions are constructed to characterize the saturation of the switched systems.Then,using nonlinear parameter-varying output feedback controller,the states of the system starting from the origin will remain inside a time-varying ellipsoid and the closed-loop system is with the l2-gain.In addition,the resulting ellipsoid is also proven to be between two time-invariant ellipsoids,which is helpful for us to estimate the capacity of the disturbance tolerance.The conclusions and perspectives are presented in the end of the thesis.