Robust Anti-windup Design For Systems With Parametric Uncertainties

Model uncertainty and actuator saturation are two troublesome phenomena frequently encountered by control engineers.Research on actuator saturation has been carried out for many years,but its robustness has not been paid enough attention.It is necessary to incorporate the model uncertainty into the design of the anti-windup controller,which will have the significance of theoretical research and the value of practical application.This dissertation analyzes and designs a saturated system with the plant parametric uncertainty based on the stability and performance of the system.From the point of view of system stability,a design method of anti-windup compensator based on QFT for uncertain linear time invariant system is proposed.Within 3-DoF anti-windup framework,the anti-windup system is equivalent to a Lur'e system,and obtains the depth of saturation according to the upper and lower limits of the controller output signal,thus applies the practical modification of the circle criterion to determine the stability region of the uncertain system in the Nichols chart;Then on the basis of the controller and pre-filter are designed to meet the nominal performance specification of the system,adjusts compensator to make the Logarithmic magnitude-versus-phase curve of the system's linear part falls into the stable region in Nichols diagram,so as to meet the local absolute stability of uncertain saturated system.On the other hand,from the point of view of system performance,a practical method to optimize transient performance of uncertain saturated system is proposed by using general anti-windup framework.In order to ensure the stability of the system,the sufficient condition of robust absolute stability is derived as a constraint condition,meanwhile the maximum sensitivity and maximum complementary sensitivity index are also used as constraints,and the performance indicators to be optimized are selected as closed loop bandwidth which directly related to the transient performance of the system,the anti-windup compensator design problem is transformed into a maximum value problem.For this maximum value problem of multivariate functions with nonlinear constraints,the fmincon function in the MATLAB is applied to solve it.The final simulation results show the effectiveness of the proposed methods.