Zero-sum Differential Games Guidance Law Accounting for Impact-Angle-Constrained Using Adaptive Dynamic Programming

To intercept a maneuvering target with a predetermined impact angle, a computational intelligence guidance law was proposed in this paper. Based on the theory of two-player zero-sum differential games, this problem is resolved efficiently by solving the Hamilton-Jacobi-Isaacs (HJI) equation. The Nash equilibrium solution of HJI equation can be solved with a policy iteration (PI) algorithm. Instead of using the offline PI algorithm, an online PI algorithm is introduced, in which the disturbance and control policies can be updated simultaneously. It can be proved that the online PI algorithm is a replacement for Newton's iterative algorithm, the convergence of which is ensured by Kantorovich's theorem. In the scenario of missiles intercepting targets, an adaptive critic structure based on a neural network (NN) is proposed to implement the online PI algorithm. Only one critic NN approximator is used in the PI algorithm to calculate a value function and the approximate Nash equilibrium solution. It is not necessary to acquire the exact internal dynamics information of nonlinear systems on the basis of online data sampling. The effectiveness of the computational intelligence guidance law is proven by simulation results.