Load Change Case Study of an Islanded Photovoltaic-Battery Unit Controlled by Grid-Forming Droop

Abstract

Photovoltaic generation does not have the capacity to compensate imbalances between generation and load demand, which can occur in islanded operation of microgrids and cause voltage and frequency deviations. Thus, battery energy storage systems are inserted to support microgrid regulation, what constitutes the hybrid generation units. In these units, grid interface inverter is driven through a grid-forming droop control, as long as photovoltaic and battery DCDC converters are controlled to promote power balance between generation and load demand. When there is only one hybrid unit in the microgrid, battery charging limit and maximum stateof- charge must also be taken into consideration since supplying of imbalances cannot be shared; and if battery experiences one of these conditions, photovoltaic curtailment is conducted. This paper proposes to test a hybrid unit supplying variable load in islanded mode to evaluate the effectiveness of the grid forming droop control. Through accurate simulations, efficacy of this control strategy is validated for different load, PV generation, and battery conditions.