Abstract
In this paper, a two-stage battery energy storage system (BESS) is implemented to enhance the operation condition of conventional battery storage systems in a microgrid. Particularly, the designed BESS is composed of two stages, i.e., Stage I: integration of dispersed energy storage units (ESUs) using parallel DC/DC converters, and Stage II: aggregated ESUs in grid-connected operation. Different from a conventional BESS consisting of a battery management system (BMS) and power conditioning system (PCS), the developed two-stage architecture enables additional operation and control flexibility in balancing the state-of-charge (SoC) of each ESU and ensures the guaranteed small-signal stability, especially in extremely weak grid conditions. The above benefits are achieved by separating the control functions between the two stages. In Stage I, a localized power sharing scheme based on the SoC of each particular ESU is developed to manage the SoC and avoid over-charge or over-discharge issues; on the other hand, in Stage II, an additional virtual impedance loop is implemented in the grid-interactive DC/AC inverters to enhance the stability margin with multiple parallel-connected inverters integrating at the point of common coupling (PCC) simultaneously. A simulation model based on MATLAB/Simulink is established, and simulation results verify the effectiveness of the proposed BESS architecture and the corresponding control diagram.
Highlights
Given the environmental issues that are induced by the deployment of fossil fuels, renewable energy sources (RES) are widely adopted in today’s electric grids [1,2,3]
To facilitate the integration of multiple RES simultaneously, parallel power electronic interface inverters are usually employed at the same time, and sometimes microgrids can be formulated so that dispersed sources and loads can be managed and controlled in a specific region [8,9,10,11]
In order to mitigate the impacts of voltage and power fluctuations and alleviate the negative influence of intermittent sources, energy storage systems (ESS) are commonly used to assist the RES so that they can be used as a buffer to balance the power mismatch between
Summary
Given the environmental issues that are induced by the deployment of fossil fuels, renewable energy sources (RES) are widely adopted in today’s electric grids [1,2,3]. Especially in a large renewable energy farm, the interface converters are usually connected in parallel, in order to meet the requirement of distributed characteristic and increase the power rating of the inverter system. In this way, due to the parallel structure, the analyses of the resonance problem should be expanded; it is necessary to analyze the resonance.
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