Parallel Implementation of Constrained Nonlinear Model Predictive Controller for an FPGA-Based Onboard Flight Computer

Abstract

Model Predictive Control (MPC) is an established control method in various application areas. Its ability of taking constraints into account makes it interesting also for automatic flight control. However, the computational complexity of MPC schemes usually limits its application. This paper describes a simple formulation of a constrained nonlinear MPC (NMPC) approach that can be realized on small onboard computers based on Field Programmable Gate Arrays (FPGAs). In contrary to classical implementations of MPCs a computationally expensive optimization problem can be avoided while even nonlinear prediction models and constraints can be considered. This is accomplished through parallel time-domain simulations. To this end, the parallel implementation properties of FPGAs are exploited. The 3d-kinematics is proposed as prediction model for the NMPC to plan the aircraft state trajectory (position and attitude) taking constraints and obstacles into account. Simulation results with a nonlinear 6 degree of freedom simulation model verify the functionality. Feasibility of hardware synthesis of parallel predicted models for the NMPC approach on an FPGA is shown by analysis.