Design and Implementation of a Charge Equalization Using Positive/Negative Pulse Charger

Abstract

The power for an electric vehicle (EV) is usually supplied by a series-connected battery strings. The life expectancy of the batteries will affect the economical development of EV that leading to the public acceptance. Conventionally, the charging and discharging processes are conducted on the whole battery strings that will experience an unbalance charging due to the distinct characteristics of each battery in the battery strings. An unbalance charging not only can seriously reduce the life expectancy of battery, it also will result in insufficient usage of electric power. In order to resolve the problem stated above, the development of a battery equalization charger becomes an important research topic. With the aid of battery equalization charger, each battery will experience a balance charging process and obtain the equally energy charging regardless the different characteristic of each battery. In this paper, an equalization charger based on positive/negative pulse technology is proposed. The positive pulse current is utilized to charge the whole battery strings and the negative pulse current will extract some energy from the battery strings that will store in the energy storage components. According to the energy distribution among the batteries, a transformer utilizes the energy from the energy storage components to redistribute the energy within the batteries that is leading to the balance charging process. The proposed equalization charger is composed of a DC-to-DC converter and a multi-winding transformer. This simple structure of proposed equalization charger comes with a simple circuitry and provides the benefit of a low cost devise. An experiment test is conducted based on the same operational conditions on battery strings with or without the equalization charger. The results show that the proposed equalization charger can achieve the effectiveness of equalized charging, provide a better charging performance, and effectively control the battery temperature. This provides an effective way to extend the life expectancy of battery strings.