The Research Of The Decentralized Control Method For SOC Balancing Among Desus In Microgrids

With the prevalence of the new energy revolution, replacing the fossil fuels by the renewable energy becomes significant. Microgrid is a cost-effective way to integrate the renewable energy. Due to the intermittent and stochastic characteristic of the renewable energy, distributed energy storage units(DESUs) are necessary to supply extra power during the peak load hours. In order to regulate the output powers properly, the state-of-charge(SOC) balancing should be maintained during discharging period for DESUs with the same capacity. In addition, the reactive circulating current may cause malfunction of the converters. Hence, more efforts should be made to achieve the reactive power sharing for the power converter system(PCS) of the paralleled DESUs. According to the aforementioned, this paper proposes a decentralized droop control to achieve SOC balancing and reactive power sharing for the PCS, which is in the peer-to-peer way. Furthermore, a voltage compensation term is added into the control algorithm to restore the voltage of the point of common coupling(PCC) to the acceptable range. This control method avoids the communication between the converters as well as the control layers. The droop-control-based peer-to-peer way of the proposed control method ensures the ―plug and play‖ characteristic.In the paper, the time discretization is used to analyze the transient process of the droop control, which laid the theory foundation for the proposal and analysis of the improved droop control. Based on the transient analysis of the droop control, the improved droop control strategy is proposed: SOC-based frequency droop control, ∫Qdt-V-based voltage droop control, and ∫Pdt-V-based voltage compensation control. The three methods achieve SOC balancing, the reactive power sharing, and the voltage restoration, respectively. The theoretical correctness of the proposed methods is dominantly revealed through the transient analysis. According to the proposed method, a small signal model is also built. Subsequently, the root loci in terms of the four control parameters are revealed to analyze the influence of them on the system stability and dynamic performance, which determines the control parameters. Finally, a three paralleled DESUs simulation system with different line impedances is built in PSCAD/EMTDC, which validates the effectiveness of the proposed control strategy. Moreover, the experiment is employed on the experiment platform with two paralleled inverters. Both the simulation and the experimental results demonstrate that the proposed methods can achieve the SOC balancing, the reactive power sharing, and voltage restoration.