Two-stage energy storage equalization system for lithium-ion battery pack

Abstract

Abstract. How to raise the efficiency of energy storage and maximize storage capacity is a core problem in current energy storage management. For that, two-stage energy storage equalization system which contains two-stage equalization topology and control strategy based on a symmetric multi-winding transformer and DC-DC (direct current-direct current) converter is proposed with bidirectional active equalization theory, in order to realize the objectives of consistent lithium-ion battery packs voltages and cells voltages inside packs by using a method of the Range. Modeling analysis demonstrates that the voltage dispersion of lithium-ion battery packs and cells inside packs can be kept within 2 percent during charging and discharging. Equalization time was 0.5 ms, which shortened equalization time of 33.3 percent compared with DC-DC converter. Therefore, the proposed two-stage lithium-ion battery equalization system can achieve maximum storage capacity between lithium-ion battery packs and cells inside packs, meanwhile efficiency of energy storage is significantly improved. IntroductionEnergy storage technology is a crucial part of six steps containing adoption-generate powertransmission-distribution-utilization of power-energy storage in power grid operation, implementing effectively management of supply side, peak shaving and load shifting, which can efficiently utilize power equipment and reduce the power cost. The development of lithium-ion battery for large-scale energy storage systems enable this technology to address high energy density, long cycle life, high standard voltage, and other factors, which are in line with the current green requirements of sustainable development. Energy storage technology is available for large-scale applications, such as electric vehicle, light railway vehicle, smart building, etc [1][2][3]. The success of these applications of energy storage will depend on how to maximize storage energy and raise the efficiency of stored energy [4], therefore, energy storage equalization technology is a key expectation at present. Many scholars have made in-depth research and design for energy storage equalization topology of the Lithium-ion battery at home and abroad. Two main categories are as follows: dissipative equalization and non-dissipative equalization. The dissipative equalization refers to dissipate redundant energy in the form of heat through the parallel resistance on both ends of the battery, and it is with advantages of simplicity, speediness, high reliability, but low energy efficiency and thermal management issues [5,6]. Non-dissipative equalization is that energy is transferred between the cells through the inductor or capacitor, which has various circuit forms: Ye Y M [7], Bruen T [8] and their fellows have proposed the combination usage of switch and capacitor to achieve energy transfer