Research On Control Of Helicopter With Saturation

Helicopter has been widely used in military and civilian in recent years, for its special flight capability, such as hover in air, vertical take off and sticking to ground. However, due to the complexity of helicopter flight dynamics, helicopter is open-loop unstable, highly coupled in shafts and significant perturbation with system parameter. Therefore, an excellent flight control system is required to assist the driver complete flight mission. And actuator saturation is a problem can not be ignored in helicopter control system design, for actuator saturation will affect helicopter flight performance, ever lead to response divergence. In this paper, with consideration of actuator saturation, two-step anti-windup control and direct anti-windup control of helicopter was studied.Firstly, all envelope linear model of helicopter was established. After analysis of motion and modeling characters of helicopter, according to motion equations and trim parameters of UH-60 Black Hawk helicopter, the linear model of helicopter was established in some representative forward speed. Analysis of mode and open-loop control response of helicopter was made by this model.Then, two-step anti-windup control of helicopter based on Linear Matrix Inequality (LMI) was studied. A two-step anti-windup control approach was proposed, which can be applied to open-loop unstable systems such as helicopter. Conservation of anti-windup compensator was reduced by loop transformation and multiplier theory. L₂ stability of the proposed anti-windup control system was proved, and anti-windup problem was equivalent to corresponding LMI. First step, without consideration of saturation constraints, H∞loop shaping inner and outer loop controller was given. The inner loop achieved all attitude control and channels decoupling, while the outer loop realized velocity tracking. Second step, with consideration of saturation constraints, the design of anti-windup compensator was proposed to reduce close-loop performance degradation caused by saturation. Then, attitude and velocity excellent control of helicopter was achieved.Finally, direct anti-windup control of helicopter was studied. Anti-windup adaptive controller of helicopter based on neural network and pseudo-control hedging was proposed. The single hidden layer neural network with robust term were used to compensate inversion error, for dynamic inversion is sensitive to inversion error such as un-modeled error and parameter uncertainty, and system asymptotic stability was proved based on Lyapunov method. And with consideration of actuator saturation, isolation of adaptive element and actuator saturation is achieved by pseudo-control hedging. Then, the proposed anti-windup adaptive control method was applied to control of helicopter pitch angle, and system performance was analyzed. Control of helicopter three attitudes and velocity were also studied.