Modeling And Control Of Electromechanical Actuation System In Airplane Electric Braking

Electric braking is a new brake concept along with the development of more/all aircraft. Compared with the traditional hydraulic braking system, electrical braking system has advantages of small volume, light weight, high safety, and good dynamic response. Electromechanical actuation system is the key subsystem responsible for the generation of braking force, which is mainly composed of electromechanical actuator controller(EMAC) and electromechanical actuator(EMA). In this paper, the modeling and control method of electromechanical actuation system were studied.At first, this paper presented the working principle of the EMAC and EMA. Considering the working status of electromechanical actuation system, the operation state of BLDCM in the airplane braking was studied. It is concluded that the motor works in various modes in the whole process, including light load, forward variable load, short time regenerative braking and reverse running and experiences first, three and four quadrant.According to the working principle, the mathematical model of BLDCM, gear, and ball screw was built and the relationship between braking force and piston displacement was derived by fitting the experimental data. Based on the classical static + viscous + coulomb friction model, and the brake force introduced as variables, the friction torque model of EMA was built. Then the system simulation model was constructed in Matlab/Simulink environment. The comparison between the simulation results and the measured data verified the effectiveness of the model. At the same time, further research proved that in the open-loop case, brake force generated by EMA has the hysteresis characteristics, and electromechanical actuation system is nonlinear.With PI control algorithm, the control performance of three control structure including braking force single close-loop, braking force + current double close-loop and braking force + velocity + current triple close-loop was studied respectively through simulation. The results showed that the PI control algorithm was able to satisfy the dynamic response and steady accuracy, and the control performance of triple loop control structure was better than that of single and double loop control. To optimize the control precision under adjustment of the small amplitude of the brake force, a friction torque compensation control method was proposed based on static +coulomb friction model. The compensation torque had same amplitude as, but opposite polarity to the static and coulomb friction torque in EMA. As a result, the nonlinear component in the friction torque was cancelled, which improved the control precision of the brake force and reduced the speed dead zone in the force servo control.Given the actual technical requirements, and using digital signal processor(DSP) and complex programmable logic device(CPLD) as the control core, the design of hardware circuit and software was presented. The test platform for the electromechanical actuation system was set up to verify the control performance of system. The experimental results showed that the braking force is capable of acting quickly and accurately to the command, and satisfy the performance demand of braking system.