Integrative Sizing/Real-Time Energy Management of a Hybrid Supercapacitor/Undersea Energy Storage System for Grid Integration of Wave Energy Conversion Systems

Grid-connected operation of an offshore renewable energy source (RES), comprising a wave energy converter (WEC), a hybrid supercapacitor (SC)/undersea energy storage system (HESS), and a set of power electronics converters (PECs), is investigated. Since the HESS components feature distinctive power and energy characteristics, the effect of the operating point on their storage capacity must be considered. Thus, an integrative sizing and real-time energy management strategy (EMS) based on reinforcement learning (RL) is proposed. Effectiveness of the sizing approach is examined by comparing the power and energy capacity of the HESS components under the proposed method and when they are sized individually. A similar WEC output power profile is used and it is assumed that the storage components, as hybrid or individually, counteract the power fluctuations. To verify the adaptability of the RL-based EMS (RLEMS), different power profiles are used in the learning and testing phases. Real-time implementation feasibility is validated through real-time simulations. The obtained results confirm that the power and energy capacity of the HESS components are significantly reduced when EMS is considered in the sizing stage. Further, the WEC output power could be regulated by the RLEMS, even in the presence of serious imbalances between harvested and dispatched wave energies.