An Improved Equalization and Energy Support Strategy for Battery-Powered Electric Motor Drives

This article proposes an improved lithium-ion (Li-ion) battery management system (BMS) that provides cell-to-cell equalization and energy support with adjustable current according to each cell operating conditions, for demanding battery-powered electric motor drive applications, such as electric vehicles (EVs). Specifically, the equalization current is decided by seeking an optimal balance between the cell equalization speed, the energy loss of the equalization dc-dc converter, and the residual available energy according to the priorities that the designer of the equalization system has imposed. The support current is determined according to the energy demand during the motor drive dynamic and each cell energy capability so as, to support the weak cells and, thus, to be satisfactorily manage the dynamic situations. Both the equalization and energy support systems are reinforced by an auxiliary energy storage (AES) unit that is utilized to temporarily store/recover electric energy to/from any cell of the main battery pack. The equalization current algorithm is implemented by utilizing the genetic algorithm (GA) technique, while the support current is decided by a system of proportional-integral (PI) controllers. The effectiveness and functionality of the suggested BMS strategy are experimentally verified and several experimental results are given to demonstrate the operating improvements.