Design and simulation of a non-linear, discontinuous, flight control system using rate actuated inverse dynamics

This paper presents the novel nonlinear controller design method of Rate Actuated Inverse Dynamics (RAID). The RAID controller design uses a novel Variable Structure Control (VSC) based anti-windup method to ensure that the actuator does not become overdriven when rate or deflection limits are reached. This allows the actuator to remain on both rate and deflection limits without the system becoming unstable. This is demonstrated in a non-linear simulation of a missile body rate autopilot using a multivariable controller designed using RAID methods and, for comparison, a controller designed using Robust Inverse Dynamics Estimation (RIDE). The simulation is performed with an advanced solver which uses a discontinuity detection mechanism to ensure that errors do not occur during the simulation due to the presence of multiple discontinuities. The results show that using a smaller actuator, with reduced rate limits, is not possible with the RIDE design. Conversely, the RAID design demonstrates excellent performance, despite the actuator limiting in both deflection and rate of deflection. This illustrates the possibility of using smaller, less powerful actuators without sacrificing system stability.