Research On Terminal Guidance Law Based On Sliding Mode Variable Structure

The design of guidance law is one of the key technologies to attack or intercept a target precisely. Missile guidance and control system is a multi-variable, nonlinear, time-varying system with model uncertainty. With the development of technology, the working environment of a missile is becoming more and more complex and the maneuverability of a target is becoming stronger. So the design of advanced guidance law is attracting more and more attention. At present, the commonly used methods, e.g., the proportional guidance law, are not available to intercept the target with large varying maneuver. It is hard to meet the requirement of attacking or intercepting the large maneuvering target with high precision. Therefore, this thesis is to design more effective guidance laws with stronger adaptability and robustness.In recent years, the guidance law with relative distance, relative velocity, acceleration measurement and estimation error robust has attracted more researcher’s attention. And it’s designed based on the sliding mode varibale structure control theory, which has the ability to reject to the disturbances and parameter pertubation, becoming to be highlighted to reseach.Firstly, this thesis introduces research status of guidance law and the common guidance law, and the theoretical basis of sliding mode variable structure guidance law. Combining the sliding mode variable structure with classic designed guidance law is the development trend of future guidance law. Then built the mathematical model of the guidance system and design the variable structure guidance law which satisfies miss distance, teminal rendezvous angle constraint and a new terminal guidance law of H∞ variable structure. Taking example of the design of the vertical plane, the desgn of guidance law that satisfies requirment with terminal rendezvous angle constraint is based on the mathematical model and relative motion equation. In order to realize the full-time robustness guided missile guidance law, the H∞ control will be added to the approaching moving section of sliding mode motion and use its analytical result to construct the variable structure closer tendency law, then apply the Lyapunov function to prove the stability. Comparing with the optimal guidance law, it’s confirmed that the superiority of the H∞ guidance law. In order to weaken the buffeting brought by variable structure, adjusting the guidance law with high gain continuous function instead of sign function, which ensures the speediness and robustness of the system, and reduces the buffeting by the variable structure caused with the essential discontinuity.