Abstract
With the increased penetration of the photovoltaic (PV) energy, the power system stability problem becomes an issue, as the output power of PV plants has unpredictable fluctuations. To maintain the power stability of the PV plants, battery energy storages (BESs) play an important role due to their fast and accurate response speed. However, it is challenging that the BES with multiple sub-modules responds well to the PV power fluctuations resulting from the various influence factors, such as defects, faults, and partial shading. Therefore, a bi-level control strategy is proposed in this paper, aiming at minimizing the operation cost of BES in maintaining power stability. The control strategy consists of the PV power fluctuations identification block and the mitigation block. In specific, the identification block can output the power fluctuation of a PV system by the PV power fluctuation identification technique. The technique is developed based on the characteristics of PV-string current under electrical faults and partial shading conditions. Meanwhile, the mitigation block can manage the multiple battery sub-modules with different regulation characteristics to meet the power fluctuations. At last, the promising results are obtained by MATLAB\Simulink with the coordinated operation of those two blocks, including the precise condition of the PV system and the optimal power output of each battery sub-module. Therefore, a comprehensive bi-level control strategy is developed to regulate the operation of battery sub-modules for PV-BES systems.
Highlights
To reduce the greenhouse gas emissions, replacing the fossil energy generation with renewable energies has become an inevitable trend in the modern power grid
A bi-level control strategy is developed to minimize the operational cost of battery energy storages (BESs) for power stability of a PV-BES system
It consists of PV power-fluctuations identification block and mitigation block
Summary
To reduce the greenhouse gas emissions, replacing the fossil energy generation with renewable energies has become an inevitable trend in the modern power grid. Different from defects and faults, the power fluctuations of PV plants caused by the partial shading should be identified by the control strategy, and mitigated by BESs. To identify the partial shading, it is necessary to monitor the operation condition and output power of the PV plants. It is challenging to control battery sub-modules with different rated power, capacity, ramping rate, and real-time SoC in responding power fluctuations. 2) A PV power fluctuation mitigation technique is developed based on the regulation characteristics of BES including rated power, rated capacity, ramping rate and real-time SoC. The equivalent model of the PV-BES system including the bi-level control strategy for BES are shown as Figure 1, consists of PV plants, BES with several sub-modules, and DC-DC converter.
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