Research On Control Method And Application For Time-delay Systems

Strictly speaking, the control systems with time-delays are common. Since time-delay often causes performance degradation of systems, the time-delay systems has been research hot spots. And due to the delay systems are theoretically infinite dimensional systems, so the analysis and control problems for delay systems are very difficult to solve. This thesis mainly studies control methods of delay systems, and the application of the control methods. The major result and innovations of this dissertation are summarized as follows.1. Discuss how to make full use of the known input feature information, to seek the effective control method for networked control systems with disturbances. Using priori knowledge of disturbances, we present a new quasi-internal model control approach. The controller design process is divided into two steps:quasi-internal model compensator design and stabilization controller design. The quasi-internal model compensator ensures control precision of the closed-loop system. Stabilization controller guarantees stability, robustness and other performance index of the closed-loop system. Moreover, the construction approach of quasi-internal model compensator is presented. Simulation examples indicate that the quasi-internal model control approach is effective with respect to damping the external step and sinusoidal disturbances.2. The control problem for input delay systems with random disturbances is studied, and a non-delay transformation approach is proposed. In vehicle active suspension systems, for example, we study the damping controller design problem for input delay active suspension systems with random disturbances of road. First the mathematical model of the system is established, and according to the characteristics of the vehicle active suspension systems, from the perspective of practical, the mathematical model of suspension system is simplified. Then using non-delay transformation approach, the active suspension systems with input delay is converted to the system without time delay in form. Using the converted system without time-delay, the damping controller of the active suspension systems with input delay is designed. Finally from cost and ease of implementation of the controller, by constructing a state observer, we design a damping control strategy with memory and integral characteristics for the vehicle active suspension system.3. A successive approximation approach of optimal tracking control for time-delay systems with external disturbances is proposed, to avoid the difficulties to design the optimal controller by solving two-point boundary value problems with time-delay terms and time-advance terms. A state equation sequence and an adjoint vector differential equation sequence are first constructed, and the convergence of the sequences are proved to ensure the existence and uniqueness of the optimal control law. Then by finite iterations of the state equation sequence and adjoint vector differential equation sequence, the approximate solution of optimal tracking control law is obtained. Finally through the design of disturbance state observer and reference input state observer, the physically realizable problem for the optimal tracking control law is solved. An example of an industrial electric heater is given to demonstrate the efficiency of the proposed approach.4. A stabilization approach by using time-delay positive feedback proportional law for second order linear systems with open-loop unstable and vibration is presented. By using the Nyquist stability criteria, a necessary and sufficient condition is first derived that ensures the stabilizability via a delayed positive feedback proportional control law for such kinds of systems. Then according to the stabilizable condition, a graphical way shows delay-independent stability domain, delay-dependent stability domain and instability domain. Finally a design algorithm of the positive feedback delay proportion controller for the closed-loop systems with a certain stability margin is proposed.