Adaptive model predictive control for constant speed regulation of an accumulator-assisted hydromotor drive under varying load conditions

Abstract

Hydraulic excavators are widely used in the construction and mining industries. However, they operate inefficiently because they dissipate a considerable amount of energy through their relief valves during cyclic operation. To address this, the article proposes a novel energy regenerative setup, which is an accumulator-assisted valve-controlled hydromotor drive system. This system captures the waste energy in the accumulators and later uses it to drive the hydromotor. The hydromotor achieves the demand speed under varying step-load conditions by adjusting the orifice area of the proportional flow control valve present at its inlet using two different control strategies: a PID controller and an Adaptive Model Predictive Controller (AMPC). A mathematical model of the proposed system is developed in MATLAB/Simulink®, and Russell’s error method and uncertainty analysis are performed to validate the simulation results against experimental data. The tests were conducted at demand speeds of 400, 600, 800, and 1000 rpm. For a demand speed of 1000 rpm and a load of 3 Nm on the hydromotor, the results show that AMPC reduces the rise time by 19.6%, overshoot by 45%, and steady-state error by 46%. Even at higher loads (10 Nm–20 Nm), AMPC maintains lower overshoot (up to 66% reduction) and steady-state error. The analysis reveals that AMPC provides better disturbance rejection and tighter speed regulation than the PID controller. Additionally, this article examines the effect of system parameters on the speed response and finds that the load torque primarily influences the rise time and steady-state error. At the same time, the runtime is influenced mainly by the initial fluid volume in the charged accumulator. Furthermore, the sensitivity analysis suggests that optimal performance can be achieved with a high initial pressure in the charged accumulator, a high initial fluid volume in the charged accumulator, low load torque, and low demand speed.