Research On Control Methods And Applications Of Several Nonlinear State-constrained Systems

Due to physical conditions and safety factors,state-constrained control systems that need to meet hard constraints exist in a large number of engineering practices.Under the premise of ensuring that the state constraints are satisfied,how to improve the dynamic performance and robustness of the system is of great significance both in theory and application.In recent years,many new methods have emerged in state-constrained system control theory,but there are still many major problems to be solved.This dissertation will discuss the control methods and applications of several typical nonlinear state-constrained systems.The main findings and contributions are as follows:(1)For high-order Hessenberg nonlinear systems with output constraints,a new continuous state feedback controller is designed.At first,this dissertation introduces the adding a power integrator control design method in non-smooth control theory.Then,a new segmentation barrier Lyapunov function is designed.The barrier Lyapunov function is activated only when the output variable is close to the constraint boundary,then the control law is adjusted automatically.In other cases,the value of the barrier Lyapunov function is zero,and the closed-loop system will maintain the nominal control design,thus keeping the control performance under the nominal controller as much as possible.Finally,an improved adding a power integrator control design method is proposed by combining the standard adding a power integrator and the new segmentation barrier Lyapunov function together,and the state feedback stabilization problem for high-order Hessenberg nonlinear systems with output constraints is solved.(2)For DC-DC buck converter with current constraints,a new current-constrained controller is designed for the output voltage tracking problem.Consider the average model of the DC-DC buck converter control system.By designing the nonlinear function related to the inductor current directly as the control gain in the controller,a simple and novel current-constrained controller is presented in this dissertation.Under the proposed controller,the output voltage can track its reference signal asymptotically.At the same time,the current constraint is ensured.(3)A new composite control scheme is designed for the output voltage tracking problem of DC-DC buck converters with both current constraints and matched disturbances.On the one hand,the idea of direct penalty mechanism design is utilized by constructing a current penalty function in the controller.On the other hand,a class of high-gain disturbance observer is designed to quickly estimate the value of the matched disturbance.Finally,a new composite control design scheme is proposed.Under the composite controller,the closed-loop error system is ultimately bounded.The current constraint is also satisfied.(4)Aiming at the problem of speed control of the permanent magnet synchronous motor(PMSM)with current constraint and mismatched disturbance,a new current-constrained control scheme is designed.Considering the d-q model of the PMSM control system,the q-axis current needs to be less than a preset safety threshold,and its load uncertainty is treated as a mismatched disturbance.By using the nonlinear function directly related to q-axis current in the controller as the control gain,this dissertation designs a new current-constrained controller for PMSM such that the speed can can track its reference signal asymptotically.Under the proposed currentconstrained controller,this dissertation qualitatively and quantitatively analyzes the influence of load uncertainty on current constraints,and gives a sufficient condition for current constraint satisfaction.(5)A new current-constrained controller is proposed for the output voltage tracking problem of DC-DC boost converters with current constraints.Considering the average model of the DC-DC boost converter control system,inspired by the controller based on the passivity method,a new current-constrained controller is designed by adding the current penalty function as the control gain.Compared with the control scheme based on the invariant set theory,under the new current-constrained controller,the feasible set of initial value is significantly expanded.In the meantime,compared with the other related control schemes,the closed-loop system has better robustness against with parameter uncertainty under the current-constrained controller.