Abstract
This paper presents a new droop control method to reduce battery degradation costs in islanded direct current (DC) microgrids for multiple battery energy storage systems (BESSs). BESSs may have varying installation costs and battery cycle life characteristics depending on battery type, energy capacity, and maximum output power. These differences cause different battery degradation costs among BESSs despite exchanging the same amount of energy. To autonomously reduce the total battery degradation cost, an incremental cost (IC) of a BESS is used as a criterion for determining the state-of-charge level of BESSs and is calculated based on the battery cycle life curve containing the battery degradation information. By adopting an IC–voltage droop control, the BESSs can maintain an operating point of equal IC, an optimal point for cost minimization. Subsequently, small-signal stability analysis is performed using the state-space model of the proposed method. The case study validates that the proposed method can reduce the total battery degradation cost with a small-signal stable operation in islanded DC microgrids.
Highlights
Advances in power electronics have led to increased production of direct current (DC) systems as DC systems have greater energy conversion efficiencies [1]–[4]
Because the voltage deviation is equal at two battery energy storage systems (BESSs), the power deviation is inversely proportional to the droop slope mP,i
The incremental cost (IC) of a BESS was defined from the battery cycle life curve to identify the increment of degradation cost with respect to the current SoC level
Summary
Advances in power electronics have led to increased production of direct current (DC) systems as DC systems have greater energy conversion efficiencies [1]–[4]. A control method for BESSs that considers the battery degradation cost can improve the economics of an islanded microgrid. A new droop control method for BESSs in islanded DC microgrids is proposed to reduce the total battery degradation cost. This droop control method enables the coordination of multiple BESSs and can determine the steadystate SoC level in a decentralized manner. BESSs may have varying installation costs and battery cycle life characteristics depending on battery type, energy capacity, and maximum output power.
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