Abstract
In order to avoid overuse of a certain battery energy storage system (BESS) and prolong the cycle life of battery in AC microgrid, an improved SoC-based droop control based on multi-agent system (MAS) is proposed for achieving State of Charge (SoC) balance of multiple BESS units. A proportional-integral (PI) adjustment item using the average SoC is added to the P -f droop to regulate the charging and discharging power of BESS, then SoC changes towards in the direction of consistency and finally reaches equalization. The dynamic average consensus algorithm is utilized to obtain the average SoC. The proposed SoC-based droop method needs not to be changed in different operating mode of BESS and can achieve SoC balance regardless of whether the capacities of different batteries are the same, which improve the applicability of this method. A complete small-signal state space model including all BESS units is built and analyzed to select the appropriate control parameters of the improved droop. The impact of communication time delay on the improved droop method for balancing SoC is investigated and the effectiveness of the proposed strategy is verified through the simulation results of different case studies.
Highlights
Aiming at reducing greenhouse gas emissions for facing the challenges of serious environmental pollution, various measures including using renewable energy sources (RESs) such as wind turbine (WT) and photovoltaic (PV) for power generation are adopted
This paper focused on balancing State of Charge (SoC) by regulating the charging and discharging power of battery energy storage system (BESS)
A proportional-integral adjustment item using average SoC is added to the nominal frequency for regulating the charging and discharging power of BESS, and the proposed method need not be changed in different operating mode compared with the adaptive droop gain methods
Summary
Aiming at reducing greenhouse gas emissions for facing the challenges of serious environmental pollution, various measures including using renewable energy sources (RESs) such as wind turbine (WT) and photovoltaic (PV) for power generation are adopted. If a frequency adjusting variable about SoC is added to the droop control, different BESS units can reasonably distribute their power outputs to make SoC changes in the direction of consistency. The improved SoC-based droop control can achieve SoC equalization rapidly and there is no need to change the control method in different operating mode of BESS. Where fj, mj and PB_j are the output frequency, droop coefficient of P-f and charging or discharging power of jth BESS unit, respectively. = SoCN , in a short period of time, or in other words, all SoCs change at the same rate with the regulating of (1) regardless of whether different battery capacities are equal once the droop coefficients are set to be inversely proportional to their capacities.
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