Finite-time adaptive dynamic surface control for energy recovery loading systems based on command filter

This paper develops an energy-recovery loading system for hydraulic pump performance evaluation. In the proposed architecture, the hydraulic energy discharged from the tested pump is converted into electrical energy through a hydraulic motor-generator unit and fed back through the power conversion unit, thereby reducing the energy dissipation and thermal accumulation caused by conventional relief-valve loading. To achieve accurate pressure regulation under hydraulic nonlinearities, mechanical transmission losses, and parametric uncertainties, a finite-time adaptive dynamic surface control method based on command filter and fractional-order sliding mode control is proposed. The command filter avoids repeated differentiation of virtual control laws, the compensation signal reduces the influence of filter errors, and the adaptive laws estimate uncertain hydraulic parameters online. Meanwhile, the fractional-order sliding mode term improves disturbance attenuation under dynamic loading conditions. Lyapunov analysis proves that the pressure tracking error converges to a small neighborhood of zero within finite time. Comparative simulations with IMIWO-PID and ABSC show that the proposed method achieves faster convergence, smaller tracking error, and stronger suppression of pressure ripple. In the dynamic pressure tracking simulation, the tracking error is generally below 0.2 MPa after the initial transient process. Experimental results on the developed energy-recovery loading platform further demonstrate that the proposed controller provides faster pressure regulation than HRVC and maintains the dynamic tracking error generally within about 1 MPa. These results indicate that the proposed method provides an energy-efficient and practically feasible solution for high-power hydraulic pump testing.