Abstract-Modern tactical missile systems are required to achieve high maneuverability and sufficient stability. As a result, the flight control design of a missile system is a creative process as it considers both performance requirements and performance limitations, which are inherently conflicting. Different modern control techniques handle such conflicting demands through the adjustment of cost weighting parameters between system internal states and control signals. The adjustment processes might need trials to tune the system performance to certain level at different operating conditions. This paper involves in the formulation of an optimal design approach that achieves the required level of robustness related to open-loop design requirements and system dynamic limits while minimizing the tracking error between the reference input and the system output. The proposed approach is based on a constrained optimization technique where the design parameters are automatically adjusted to the optimum tradeoff between the overall system performance and robustness. The effectiveness and feasibility of the proposed approach are demonstrated through a numerical example for the three-loop autopilot design.Index Terms-Optimal-robust state feedback, constraint optimization, frequency domain constraint, control effort constraint.
I. INTRODUCTIONThe modern techniques such as H∞, μ-synthesis [1], optimal LQG [2] and dynamic inversion [3] are the most popular in the design of autopilot systems for several decades. While these techniques offering powerful design tools, they also suffer from certain shortcomings when put to practice. For example, these methods solve the tradeoff between design performance and robustness requirements indirectly by using weighting parameters on the internal states and the control signal of the system. Since the relation between these weightings and the resultant performance is not so clear, the selection and adjustment of these weightings and some other design parameters might be repeated at different operating conditions to meet the design requirements. Moreover, the autopilots obtained with these techniques are mostly of high order, which is may be difficult to implement.In general, the system achieves better in terms of time performance criteria as more as the tracking error minimized. However, the free minimization of tracking error may cause too high autopilot gain with an undesired frequency response. Consequently, the optimal control method should provide the Manuscript received April 10, 2016; revised June 10, 2016. The authors are with School of Automation, University of Science and Technology, Nanjing 210094, China (e-mail: mdyosf2010@yahoo.com, qlongjun@mail.njust.edu.cn, byming@mail.njust.edu.cn).optimum of the tracking performance combined with a direct incorporation of the frequency-domain criteria values and actuator limits to achieve a satisfactory robustness level. In the same sense, the minimum error between the desired and the actual open-loop crossover frequency is formed as an ...
