Mixed H₂/H_∞ control of direct-drive electromechanical actuator

While elimination of reducer, on one hand, makes direct-drive Electromechanical actuator (EMA) system in some ways better, on the other hand it makes designing a controller, which is to ensure the robustness of the direct-drive EMA system, even more difficult. This paper introduces the structure and principles of a missile EMA based on a limited angle torque motor (LATM). According to the problem that direct-drive EMA system is sensitive to load disturbance and parameter perturbation, a mixed H₂/H_∞, controller of the actuator is designed. Mixed H₂/H_∞ controller makes a suitable trade-off between dynamic performance and robustness. H₂ control ensures the dynamic performance of the system, while H_∞ control ensures the robustness of the system that is subjected to bounded disturbance, parameter perturbation and model indeterminacy. Simulation results for a specific numerical example show that, under load disturbance and parameter perturbation, the maximum deflection of control surface is reduced by mixed H₂/H_∞ controller to only about one seventh of that attainable by traditional PI controller; simulation results also show that mixed H₂/H_∞ controller has robustness in tracing without steady state error.