Droop control strategy embedded with battery life prolonging considerations in DC microgrids

Abstract

This paper presents a coordinated control of battery energy storage system (BESS) in microgrid. In order to improve the service life of the battery, a droop control strategy embadded with depth of discharge (DoD) and current rate (C-rate) control is proposed. In this control scheme, all parallel batteries in the BESS are divided into charging group and discharging group to ensure that the batteries absorb or release energy at the optimal DoD. In order to guarantee that the output current of the battery does not exceed the maximum value that the battery can endure, a measure of limiting current is adopted in the droop control. Meantime, the state of charge (SoC) is taken as an adjustment amount in drop control strategy, therefore when the battery is discharged, the battery with higher SoC delivers more power, and the battery with lower SoC deliver less power. On the contrary, when the battery is charged, the battery with higher SoC absorb less power, and the battery with lower SOC absorb more power. The model of droop control system combine with DoD and C-rate control is established, and the stability of the system is analyzed. Simulation of a 6 × 50 kw parallel converter system are presented in order to validate the proposed approach.