Development of battery charge balancing system for electric vehicle/hybrid electric vehicle

Abstract

The use of clean and green energy is becoming more and more important in today's world. Electric vehicles (EVs) / hybrid electric vehicles (HEVs) are currently best choice for the environment as public or private transportation. Battery-packs have been employed as an energy source to provide the power to run the traction motor in electric vehicles (EVs) / hybrid electric vehicles (HEVs). Battery needs to be delivered the peak power to meet demand of the vehicle within short time. The cells of battery packs suffer from the state-of charge (SOC) and state-of-discharge (SOD) which could incur unbalancing problem due to natural phenomena such as ambient temperature, chemical degradation and internal impedance. Many conventional balancing techniques have been developed for balancing the battery cells, both in charging and discharging period with emphasizing simple control, efficient, low cost and easy to implement. This study presents an advanced battery charge balancing (BCB) system to perform the balancing of battery cells in four modes, namely: (a) charging, (b) discharging, (c) both in charging and discharging and (d) inoperative. The resonant LC network is connected with each of the cases by using switching components. In general, the inrush high spike current occurs in switching devices due to the inductor components, which could damage the switching components and increase the total system power loss. In our developed BCB, flyback snubber circuit consisting of diode and capacitor has been introduced with the inductor component in parallel. The charge balancing time has been reduced significantly by using two parallel LC series networks instead of the single LC series network. In simulation, the cell voltages were balanced in 5sec that has reduced the balancing time by 37% without considering battery internal resistance. In experimentally, battery cells voltage variations were recorded 11.27% and 9.1% in 2 minutes and 10 minutes respectively.