Study On The Control Strategy Of A High Power Electro-Hydrostatic Actuator

Electro-Hydrostatic Actuators(EHA)have the advantages of simple structure,high efficiency by Electro-Mechanical Actuator(EMA)and heavy-load capability by traditional Electro-Hydraulic Actuator(EH),and is a preferred technical approach to Thrust Vector Control(TVC)for future rockets.In terms of a high power EHA,one key point is its dynamic capability.The ability of conventional simple PID control algorithms is limited.Moreover,a high power EHA means the usage of high power servo motors and pumps(or monolithic Servo-Motor-Pumps,SMP),which has large rotational inertia that limits their dynamic performance.A control algorithm of “Nonlinear PID + feed-forward compensation + notch filter" was proposed.The nonlinear PID control overcomes the difficulties to balance the rapid adjustment and precision requirement simultaneously by traditional PID controls.The feed-forward compensation can effectively reduce the phase lag in the low and intermediate frequencies.The notch filter is used to suppress the load structural resonance.Meanwhile,aimed to meet the high dynamic demand of high power EHAs,a parallel dual SMP design was put forward.While the high dynamic performance is hard to achieve by one high power SMP,by using two SMPs,the power of each SMP can be smaller and thus easier to guarantee the high dynamic capability.An EHA mockup with parallel dual SMPs was designed and manufactured.An experiment system was built,where,an inertia simulation load of 1000 kg.m~2 was driven,a commercial high performance frequency inverter adopted to realize the SMP’s closed loop speed control,and digital signal processors applied to realize the actuator’s position closed-loop control.Simulations and experiments were conducted.It shows that,compared with the basic algorithm that comprises only a proportional control and a notch filter,the algorithm of "Nonlinear PID + feed-forward compensation +notch filter",with the 0.2°sinusoidal commands,the-45° phase frequency bandwidth was increased from 18.5rad/s to 22.7rad/s.Moreover,compared with an EHA with a single SMP,the EHA with double SMPs can realize even better performances.With 0.1°、0.2°、0.3° and 0.4° sinusoidal commands,the-45° phase frequency bandwidth were increased from 24.9rad/s、22.7rad/s、21.3rad/s and 20.4rad/s to 26rad/s、22.8rad/s、23.8rad/s and 24.6rad/s,respectively.The study shows that the control strategy combining "Nonlinear PID + feed-forward compensation + notch filter" and the parallel SMP design guarantee that the high dynamic capability of high power EHAs satisfy the need for future launch vehicles.