Control and power management of grid connected vented oscillating water column wave energy converter arrays

Wave energy is a vast, sustainable, and low environmental impact renewable energy source with a high degree of predictability and availability at large scale. Over the last six decades, numerous studies have been conducted, and various technologies have been developed to convert wave energy into electricity. Nevertheless, Wave Energy Conversion (WEC) is still not a widespread technology, compared to other dominant renewable energy technologies such as wind and solar. One of the contributing factors for this is the large and periodic fluctuations present in the extracted power in WEC systems. Even though intermittencies are present in the extracted power in the wind and solar generation systems, the level of fluctuations present in those systems are much smaller compared to that in wave energy. Therefore, the direct connection of a WEC system to a power grid without any power conditioning could lead to instabilities. The use of energy storage is a promising solution to absorb fluctuation and thereby ensure smooth power delivery to the grid. Battery energy storage is the most common solution recommended for similar issues in the wind and solar energy systems. Nevertheless, due to the short-term and periodic (10 -15 seconds) nature of the power pulses present in wave energy, a combination of battery and supercapacitor is recommended as the most suitable energy storage solution for WEC systems. Most studies reported in the literature on WEC systems with battery-supercapacitor hybrid energy storage have considered only a single WEC system. The effects of spatial and temporal averaging of extracted power in wave energy converter arrays on the sizing of energy storage systems have not been explored so far. Therefore, this study has attempted to fill this knowledge gap using vented oscillating water column (VOWC) wave energy converter arrays. VOWC is a novel WEC technology developed at the Australian Maritime College in collaboration with the Wave Swell Energy company in Australia. This technology produces energy only during the inhale stage resulting in large discrete power pulses. These characteristics of VOWC make control and power smoothing even more challenging compared to conventional bi-directional WEC technologies such as Wells turbines. As solutions, novel control and power management strategies have been developed to suit the characteristics of the VOWC. The efficacy of the developed control and power management solutions are validated through simulations carried out on the MATLAB/Simulink digital simulation platform. The results verify the efficacy of the proposed control strategy in tracking the setpoints efficiently with minimal overshoots and oscillations. Furthermore, the findings confirm that the proposed PMS can reduce the mismatch between supply and demand, while maintaining smooth delivery of power to the grid in single and array configurations of VOWC WECs. Moreover, further findings reveal that the required ESS capacity drops when WEC systems are placed correctly in array configurations.