Output redefinition method for sliding mode control of nonminimum phase missile systems

In this work robust autopilot is developed for highly maneuverable nonminimum phase missile system by using sliding mode control algorithm. Nonminimum phase nature of tail controlled missiles prevents direct implementation of Sliding Mode Control algorithms. Sliding mode control methods are not suitable to implement in nonminimum phase system because of unstable zero dynamics. To overcome this difficulty a new output redefinition technique is developed. The method is based on constructing a minimum phase ideal system that behaves similar to actual system. Outputs of the actual system and ideal system are blended to generate a virtual output and with this output the system becomes minimum phase or very slightly nonminimum phase. The sliding mode control algorithm can be used to control this virtual system. Because the outputs of virtual and real systems are converging, output tracking of the virtual systems also provides output tracking for real system. Simulation results shows that proposed output redefinition technique is successful for implementing sliding mode control schemes into nonminimum phase system.