Frequency-Based Energy-Management Strategy for Stand-Alone Systems With Distributed Battery Storage

Distributed generation is an attractive solution for stand-alone ac supply systems. In such systems, the installation of two or more energy-storage units is recommended for system redundancy and may also be required when there is a consumption increase following installation. However, energy management with multiple energy-storage units has been, but vaguely analyzed in the literature and the few studies made are based on communication cables with a central supervisor. This paper proposes an energy-management strategy for a multiple-battery system which makes it possible to avoid the use of communication cables, rendering the system more cost effective and reliable. The strategy modifies the conventional droop method so that the power becomes unbalanced, allowing for the regulation of one or more battery voltages or currents, as required. Furthermore, whenever the frequency is high, the PV inverters reduce their power in order to prevent the battery from overcharge or high charging currents. On the other hand, whenever the frequency is low, then either the noncritical loads are regulated or the system stops in order to prevent the battery from overdischarge or high discharging currents. Simulation and experimental validation are performed for a system with two-battery inverters, two-PV inverters, and a number of loads.