Bidirectional Multi‐Input and Multi‐Output Energy Equalization Circuit for the Li‐Ion Battery String Based on the Game Theory

Abstract

Energy inconsistency among Li-ion battery cells widely exists in energy storage systems, which contributes to the continuous deterioration of the system durability and overall performance. Researchers have proposed various kinds of battery energy equalizers to reduce such inconsistency. Among them, the inductor equalizer is a predominant type in fast equalization applications. However, it requires relatively more complex control than other types of equalizers. In order to reduce the control complexity of inductor equalizers, a bidirectional multi-input and multi-output energy equalization circuit based on the game theory is proposed in the present work. The proposed equalizer has the modularized circuit topology and the mutually independent working principle. A static game model is developed and exploited for the mathematical description and control analysis of an energy equalization circuit comprised of these equalizers. The feasible control of each equalizer was obtained by solving a series of linear equations for the Nash Equilibrium of the model among the states of charge of the battery cells. The complexity of equations grows linearly with the cell number. The equivalent simulation model for the four-cell equalization is established in the PISM software, where the operational data and simulation results justify the static game model and verify the control validation, respectively. It is concluded that the proposed inductor equalizer is suitable for large-scale battery strings in energy storage systems, electrical vehicles, and new energy power generation applications.

Performance and comparison of equalization methods for lithium ion batteries in series

“…This provides a good reference value for extended equalization methods, such as Ref. 32. It is also helpful for technical personnel to choose the appropriate equalization method in applications.…”

Series‐connected battery equalization system: A systematic review on variables, topologies, and modular methods

“…Based on game theory, another paper compares the equilibrium process of the circuit to a full-information static game and establishes a mathematical model describing the correspondence between the duty cycle of each switch in the equilibrium unit and the energy change of every single battery. 62 Solve the Nash equilibrium solution of the game model to obtain the optimal control scheme of the equilibrium circuit. The equalization process in Reference 63 is matrixed so that each equalizer can operate synchronously, which reduces the extra equalization loss caused by energy circulation compared with the natural equalization method.…”

The control and evaluation method of the cascaded buck–boost converter for equalization on battery strings

“…7 Further development in the control of the topology is implemented to simplify the process and reduce the power loss on the switches. [8][9][10] Besides, a systemic evaluation method is presented in Shan et al, 11 in which various topologies could be evaluated by their average efficiency under the same situation. Another practical balancing strategy is proposed to mitigate the problem of the inconsistent battery capacity of lithium batteries in new energy vehicles in reference.…”