Modelling and performance enhancement of the fluid coupling interface for hydraulic pressure energy harvesting by superposition of the static mean pressure and pressure fluctuations

The monitoring and control of hydraulic systems in an autonomous and battery-free manner is receiving increasing attention to improve both safety and performance. In this regard, the conversion of pressure ripples within a hydraulic system into electric energy using hydraulic pressure energy harvesting (HPEH) is attractive due to the high energy intensity associated with dynamic pressure fluctuations. In this paper, a new theoretical model of the fluid to mechanical interface is established based on a central piezoelectric stack subject to a superimposed dynamic pressure fluctuation and a mean static pressure. A lumped-parameter model of the electromechanical coupling system is employed to study the overall harvesting performance of the system, and the force–deflection behavior of a circular edge-clamped plate with a lumped mass and a superimposed excitation is determined. The influence of static pressure on harvesting performance is explored in detail, where the mean static pressure introduces a softening nonlinearity to the harvester which decreases the power output and harvesting bandwidth. To reduce the negative impact of static pressure on power output, an optimized structure based on a quasi-zero stiffness (QZS) disc spring is proposed. The nonlinear restoring force of the circular plate interface on a central piezoelectric stack and disc spring is determined and the electromechanical coupling equations of the quasi-zero stiffness hydraulic pressure energy harvesting (QZS-HPEH) structure is established. Our theoretical analysis shows that the power output is improved using the novel QZS-HPEH structure, in particular at the high static loads presented in hydraulic systems. Experimental validation is performed, where good agreement is observed between model results and experimental measurements. The proposed model and experimental validation provide important new insights into the optimization of power output and application of HPEH devices in practical hydraulic systems.