*Article* **An Estimation of Hydraulic Power Take-off Unit Parameters for Wave Energy Converter Device Using Non-Evolutionary NLPQL and Evolutionary GA Approaches**

**Mohd Afifi Jusoh, Mohd Zamri Ibrahim \*, Muhamad Zalani Daud, Zulkifli Mohd Yusop and Aliashim Albani**

Renewable Energy & Power Research Interest Group (REPRIG), Eastern Corridor Renewable Energy Special Interest Group, Faculty of Ocean Engineering Technology and Informatics, Universiti Malaysia Terengganu, Kuala Nerus 21030, Terengganu, Malaysia; mohd.afifi.jusoh@gmail.com (M.A.J.); zalani@umt.edu.my (M.Z.D.); zul\_12521@yahoo.com (Z.M.Y.); a.albani@umt.edu.my (A.A.)

**\*** Correspondence: zam@umt.edu.my; Tel.: +60-96683328

† This paper is an extended and revised article presented at the International Conference on Sustainable Energy and Green Technology 2019 (SEGT 2019) on 11–14 December 2019 in Bangkok, Thailand.

**Abstract:** This study is concerned with the application of two major kinds of optimisation algorithms on the hydraulic power take-off (HPTO) model for the wave energy converters (WECs). In general, the HPTO unit's performance depends on the configuration of its parameters such as hydraulic cylinder size, hydraulic accumulator capacity and pre-charge pressure and hydraulic motor displacement. Conventionally, the optimal parameters of the HPTO unit need to be manually estimated by repeating setting the parameters' values during the simulation process. However, such an estimation method can easily be exposed to human error and would subsequently result in an inaccurate selection of HPTO parameters for WECs. Therefore, an effective approach of using the non-evolutionary Non-Linear Programming by Quadratic Lagrangian (NLPQL) and evolutionary Genetic Algorithm (GA) algorithms for determining the optimal HPTO parameters was explored in the present study. A simulation–optimisation of the HPTO model was performed in the MAT-LAB/Simulink environment. A complete WECs model was built using Simscape Fluids toolbox in MATLAB/Simulink. The actual specifications of hydraulic components from the manufacturer were used during the simulation study. The simulation results showed that the performance of optimal HPTO units optimised by NLPQL and GA approaches have significantly improved up to 96% and 97%, respectively, in regular wave conditions. The results also showed that both optimal HPTO units were capable of generating electricity up to 62% and 77%, respectively, of their rated capacity in irregular wave circumstances.

**Keywords:** wave energy converter; hydraulic power take-off unit; parameter estimation; genetic algorithm; non-linear programming by quadratic Lagrangian
