MPPT control of hydraulic power take-off for wave energy converter on artificial breakwater

Abstract

Wave energy is a renewable energy source that is green, clean and has huge reserves. In order to develop wave energy resources, an oscillating buoyWave Energy Converter (WEC) device based on the artificial breakwater is presented in this paper. In order to effectively vent the gas in the hydraulic PTO and to improve the active control capability of the PTO system to guarantee the safety performance of the system under high sea conditions, a hydraulic PTO with an active control circuit is designed. Additionally, for the Power Take-Off (PTO) system, there is a optimal damping point under different sea conditions for PTO system, so the PTO can be controlled by the Maximum-Power-Point-Tracking (MPPT) control algorithms to improve the generated power of the system. At present, the MPPT control algorithms for wave energy are mainly used to control the load of generator. However, a fixed-load storage battery is used for the load of the generator in this paper. Additionally, an MPPT control taken at a hydraulic PTO system is executed to improve the power generated by hydraulic PTO under different sea conditions effectively in this paper. The MPPT control based on the hydraulic system is conducted by controlling the displacement of hydraulic motor to achieve the optimal damping point tracking control. The control flow of the MPPT algorithm is provided. The variable step hill-climbing method is used in MPPT control algorithm in which the big step can reduce the time of tracking and the small step can increase the accuracy of MPPT control algorithm. Due to the slow stability of the hydraulic system, a filter method for hydraulic PTO power is used. In addition, the hydraulic PTO system and MPPT control are verified to be feasible with the simulation. Additionally, MPPT control based on hydraulic variable motor is easier to carry out in practical applications than the traditional control of resistance. Finally, the simulation results demonstrate that it is an effective power control strategy for hydraulic PTO system to improve the generated power.