Explicit Model Predictive Direct Force and Pitch-Roll-Yaw Torques Control for Hexacopters

High-performance control of hexacopters' force and roll, pitch, and yaw torques is the basis for achieving excellent trajectory tracking. However, the conventional method indirectly controls the force and torques by controlling six permanent magnet synchronous motors' speeds, resulting in poor dynamic performance and steady-state deviation when pneumatic parameters mismatch. Dedicated to achieving highdynamic and high-accuracy control of force and torques, an explicit model predictive (EMP) cascade-free direct force and torque control method is proposed. Firstly, analyzing the working principle of hexacopters, and defining the system-level variables force current and torque currents, whereby a new structure for direct closed-loop control of force and torques is proposed. Then, the low-dimension linear robust predictive model for the force and torques is constructed, based on which an EMP controller is designed to uniformly replace the traditional cascaded control allocation module and six proportional-integral speed controllers. The EMP controller generates the optimal current commands directly from the force and torque commands, realizing direct control without the speed loop. The proposed method successfully applies the explicit model prediction algorithm to complex, high-order, nonlinear hexacopters, optimizes force and torques' dynamic performance and steady-state accuracy, and improves the robustness to pneumatic parameters. Finally, the proposed method's feasibility is verified by simulation experiments.