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In this article, a multi-stage optimal allocation method for battery energy storage system (BESS) in distribution networks with photovoltaic (PV) system is proposed, which is to obtain its optimal installation location, capacity, power, and investment time. This method takes the time value of money, the PV growth rate, and the load increase during the investment period into consideration. Firstly, genetic algorithm and gravity search algorithm are combined to solve a single-stage static optimal allocation problem and the BESS installation location and parameters in target year are obtained. Then, the obtained parameters are regarded as constraints and a heuristic multi-path forward dynamic programming method is used to determine the specific investment time of each equipment. Finally, a case study is used to verify the effectiveness and the

Abstract:In this paper, a hierarchical optimal operation strategy for a hybrid energy storage system (HESS) is proposed, which is suitable to be utilized in distribution networks (DNs) with high photovoltaic (PV) penetration to achieve PV power smoothing, voltage regulation and price arbitrage. Firstly, a fuzzy-logic based variable step-size control strategy for an ultracapacitor (UC) with the improvement of the lifetime of UC and tracking performance is adopted to smooth PV power fluctuations. The impact of PV forecasting errors is eliminated by adjusting the UC power in real time. Secondly, a coordinated control strategy, which includes centralized and local controls, is proposed for lithium-ion batteries. The centralized control is structured to determine the optimal battery unit for voltage regulation or price arbitrage according to lithium-ion battery performance indices. A modified lithium-ion battery aging model with better accuracy is proposed and the coupling relationship between the lifetime and the effective capacity is also considered. Additionally, the local control of the selected lithium-ion battery unit determines the charging/discharging power. A case study is used to validate the operation strategy and the results show that the lifetime equilibrium among different lithium-ion battery units can be achieved using the proposed strategy.

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