A Semi-Markov Model for Control of Energy Storage in Utility Grids and Microgrids With PV Generation

Photovoltaic (PV) penetration levels in the power grid have significantly increased during the last years. However, issues such as cloud-induced intermittency in PV generation forces equipment on the electrical grid to cycle excessively, preventing PV generation from being considered as a reliable or dispatchable source of power, particularly by utilities. A semi-Markov process model is proposed to model PV power. Unlike existing models of PV power, the proposed model has a wide range of applicability across both small and large timescales. These applications include simulating PV power, short-term forecasting of PV power, design of rule-based controllers for energy storage units (ESU), and stochastic scheduling of ESU in conjunction with other resources. The model is applied to study two cases of coordinating ESU with PV generation. In the first case, the model serves to design a coordination scheme for a hybrid battery-ultracapacitor (UC) ESU where the UC serves to extend the lifetime of a lead-acid battery. In the second case, the model allows probabilistic scheduling in a standalone PV/diesel/battery-ESU microgrid. In both cases, the model improves performance in terms of either battery lifetime or fuel consumption.