Decentralized Power Management of Multiple PV, Battery, and Droop Units in an Islanded Microgrid

In this paper, a decentralized power management strategy is proposed for multiple photovoltaic (PV), battery, and droop units in an islanded microgrid. The control strategy is developed to handle any combination of these units without modifying their control systems. This provides a more comprehensive and generalized approach to coordinate the three types of units, in comparison to the techniques in the literature that consider only two types, mainly PV and battery systems, or consider only a single unit of each type. The operation of each unit is autonomously coordinated to maintain the balance between generation and consumption, while ensuring controlled charging/discharging of the batteries in the microgrid. To achieve this coordination, the voltage and the power control loops, within each of the PV and battery units, are configured to follow the specifically designed multi-segment power/frequency (P/f) characteristic curves. These characteristics are designed to independently adapt to the microgrid operating conditions, without relying on any external communications and centralized management systems. Accordingly, the control system for each unit is able to autonomously and seamlessly switch in real-time between power control and frequency regulation based on the available PV power, the state-of-charge of the batteries, and the total load demand in the microgrid. The strategy is designed and implemented using multi-loop controllers, in contrast to the commonly adopted approach of using discrete operating modes and switching logics. The proposed strategy is validated using a microgrid simulated in PSCAD/EMTDC with detailed switching models of the power electronic converters.