Research on the Performance Optimization of a Hydraulic PTO System for a "Dolphin 1" Oscillating-Body Wave Energy Converter

In this work, an oscillating-body wave energy converter (OBWEC) with a hydraulic power take-off (PTO) system named "Dolphin 1" is designed, in which the hydraulic PTO system is equivalent to a transfer station and plays a crucial role in ensuring the stability of the electrical energy output and the efficiency of the overall system. A corresponding mathematical model for the hydraulic PTO system has been established, the factors that influence its performance have been studied, and an algorithm for solving the optimal working pressure has been derived in this paper. Moreover, a PID control method to enable the hydraulic PTO system to automatically achieve optimal performance under different wave conditions has been designed. The results indicate that, compared with single-chamber hydraulic cylinders, double-chamber hydraulic cylinders have a wider application range and greater performance; the accumulator can stabilize the output power of the hydraulic PTO system and slightly increase it; excessively large or small hydraulic motor displacement hinders system performance; and each wave condition corresponds to a unique optimal working pressure for the hydraulic PTO system. In addition, the relationship between the optimal working pressure Pm and the pressure Ph of the wave force acting on the piston satisfies Pm2 integral t1t2Ph2dt/(t2-t1)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P_{\rm{m}}<^>2\int_{{t_1}}<^>{{t_2}} {P_{\rm{h}}<^>2{\rm{d}}t\Big/\left({{t_2} - {t_1}} \right)}$$\end{document}. Furthermore, adjusting the hydraulic motor displacement automatically via a PID controller ensures that the actual working pressure of the hydraulic PTO system consistently reaches or approaches its theoretically optimal value under various wave conditions, which is a very effective control method for enhancing the performance of the hydraulic PTO system.