Motion Control of Electro-Hydrostatic Actuators With Modeling and Compensation of Nonlinear Bulk Modulus

Electro-hydrostatic actuators (EHAs) have been widely utilized in the aerospace and modern manufacturing industries owing to their small installation space, high energy efficiency, and extreme force generation capability. Recently, the model-based compensation controller has been designed to enhance the control quality of hydraulic systems. Meanwhile, some modified models focusing on friction, nonlinear flow, and flow leakage have been developed to further improve the control performance. However, the nonlinear characteristic of fluid bulk modulus reflecting oil elasticity has not been considered which still limited transient control accuracy. The existing studies on modeling of bulk modulus result in models too complicated to be used in control design. So a control-oriented model needs to reflect the real nonlinear behavior of the bulk modulus while feasible for control design. In this study, a control-oriented model for the effective bulk modulus is synthesized, which is not only able to reflect the nonlinear behavior of the real-world bulk modulus but also feasible for model compensation control design. By introducing such a model into the system dynamics, a model-based motion controller is developed for EHAs. The performance of the closed-loop system is evaluated in theory and also in comparative experiments where the proposed method further improves the trajectory tracking performance, especially during transient processes.