Flow mismatch, strong nonlinearity, and complex disturbance are the main challenges that electro-hydrostatic actuator (EHA) control faces. This article proposes a three-port piston pump to replace the two-port piston pump in traditional EHA to solve the flow mismatch problem caused by asymmetric cylinders. Then, for the complex disturbance problem in EHA control, an extended state observer and a nonlinear disturbance observer are designed to estimate matched and mismatched disturbances, respectively. On this basis, the virtual decomposition control method is adopted. The EHA is virtually decomposed into three subsystems, and the controllers of each subsystem are designed separately to realize the high-precision nonlinear control of the EHA. Next, the stability of the proposed control method and observer is proved. Finally, the proposed three-port pump, observer, and controller are systematically verified based on the simulation model and the EHA experimental platform. Simulation and experimental results show that the proposed three-port pump solves the flow mismatch problem without increasing the weight and volume of the EHA. The designed two observers can accurately estimate the matching and mismatching disturbances during the EHA operation. By combining designed observers and the virtual decomposition control method, the accuracy and robustness of EHA control can be greatly improved.

This study proposes an accurate dead zone compensation control method for electro-hydrostatic actuators (EHAs) under low-speed conditions. Specifically, the nonlinear dead zone characteristics under low-speed conditions are summarized based on numerous EHA experiments. An adaptive compensation function (ACF) is then constructed for the dead zone. Next, this study proposes an adaptive dead zone compensation control method for EHAs by integrating the ACF with a virtual decomposition controller (VDC) based on the established EHA model. The stability of the proposed control method is also proven. Finally, the proposed control method is verified using an EHA platform. The test results show that the dead zone trajectory tracking errors of EHAs are significantly reduced when combined with the ACF. Furthermore, since most EHAs are controlled by adjusting the motor speed, the method presented in this study is simpler and easier to use than methods that employ flow compensation.

Although electro-hydrostatic actuators (EHAs) hold broad application prospects in more-electric aircraft and high-end equipment, they face a difficult trade-off between dynamic response and energy efficiency. To simultaneously enhance the dynamic response and energy efficiency of the EHA, this paper designs an innovative variable pump displacement and variable motor speed (VPVM) configuration that utilizes an electro-hydraulic servo valve for active displacement control. To address the flow mismatch problem associated with traditional asymmetric single-rod cylinders without reducing the power density of EHA, this paper also designs an innovative symmetric single-rod cylinder configuration. Based on the above two innovative configurations, this paper further develops a corresponding EHA prototype with a rated power density of 0.72 kW/kg. Simulation and experimental results demonstrate that compared to the traditional EHA with the fixed pump displacement and variable motor speed configuration (FPVM-EHA), the EHA with the proposed VPVM configuration (VPVM-EHA) not only improves energy efficiency and reduces motor heat generation under low-speed and heavy-load conditions, but also achieves a dynamic response close to that of the FPVM-EHA under fast dynamic response conditions.

This article proposes a fault-tolerant model predictive current control method with an adaptive control set (ACS-MPCC) for the five-phase permanent magnet synchronous motor (F-PMSM), which can realize high-precision fault-tolerant control of fundamental and third harmonic currents. First, virtual voltage vectors (VVs) are established based on the third harmonic voltage (THV) injection, and candidate control sets corresponding to different THV injection values are established by extending virtual VVs. Then, the deadbeat principle is introduced to adaptively select VVs and establish the ACS. According to whether VVs in the control set can meet the fundamental and third harmonic reference voltages, three cases are divided, and the calculation methods of THV injection value and the selection methods of optimal control set in different cases are proposed. Experimental results show that the proposed ACS-MPCC method can significantly reduce the computational burden brought by establishing and extending of virtual VVs and ensure the real-time control of the F-PMSM. Compared with traditional fault-tolerant methods, the ACS-MPCC method achieves high-precision fault-tolerant control of fundamental and third harmonic currents without losing dynamic performance, and reduces the torque and speed ripples of the F-PMSM.