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| Analysis of the Impact of DC-Side Ripple Current on Lithium-Ion Battery Life in Energy Storage Systems and Optimal Control Strategies |
| Xia Xiangyang1, Chen Guiquan1, Liu Junxiang1, Wu Xiaozhong2, Xu Zhiqiang2,3 |
1. State Key Laboratory of Disaster Prevention & Reduction for Power Grid Changsha University of Science and Technology Changsha 410114 China;
2. State Grid Hunan Electric Power Co. Ltd Changsha 410005 China;
3. Hunan Provincial Engineering Research Centre for Scale-up Battery Energy Storage Application Technology Changsha 410007 China |
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Abstract The rapid development of “new energy + energy storage” integration has introduced numerous power electronic devices into the power system, leading to a large number of ripple currents in the DC side of energy storage systems. Current research reflected in the effective value and harmonic frequency has not reached a consensus. In addition, it is necessary to optimize the energy storage system's safe operation control strategy while considering the changing characteristics of lithium-ion battery life. Therefore, this paper analyzes the effect of ripple current on the lifetime of Li-ion batteries through theoretical analysis, model simulation, and experimental validation.
The ripple current is first decomposed into Fourier series and introduced into the expression of the lithium-ion battery life model by simplifying the variables unrelated to the harmonic components and retaining the variables in the current affected by the harmonic components. The results show that the key factor affecting the life of Li-ion batteries in the presence of ripple currents is the average current value during charging and discharging. A higher average current value in the charge and discharge states results in accelerated battery ages.
Six sets of charging and discharging currents are designed on the Li-ion battery experimental platform. The results show that the aging rate of the battery is accelerated with the increase of the average current value during the charge/discharge state. The influence of the effective current value is found to be less significant. Since the double-layer capacitor of the Li-ion battery filters out a large amount of ripple current, the effect of the effective current is notably reduced.
The following conclusions are drawn: (1) The key factor affecting the life of Li-ion batteries under ripple current is the average current value during charging and discharging, not the effective current value. Larger average current values lead to faster and more non-linear battery aging. (2) Ripple current does not increase the average current value during the charging and discharging states of the battery. Therefore, the ripple current's impact on energy storage system life can be ignored in engineering applications. It provides a basis for optimizing control strategies to ensure the safe and economic operation of the energy storage system. (3) When the grid is unbalanced, an optimized control strategy can be adopted to suppress power fluctuations on the AC side and alleviate power fluctuations on the DC side without affecting the life of lithium-ion batteries. When the light storage system is connected to the grid with constant active power, based on the battery aging characteristic curve and the grid connection of the energy storage system, a coordinated control strategy of multiple converters is proposed. This strategy extends the life of energy storage batteries and can reduce the battery aging rate by 19.8% compared with the traditional control strategy.
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Received: 20 April 2023
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2023, Vol. 38 
