Research On MH-Ni Series Battery Equalization Charging Technology

Electric vehicles are considered as the green project for 21th century and the direction for future automobile development. The problem of energy storing device becomes the bottleneck in the development of it. Energy storing device equipment on electric vehicle generally use series battery stack. When batteries are connected in series, its performance and life span can't compare with single cell. Studies have shown that it's primarily caused by imbalance between cells in series battery stack. Compared to the research of battery materials, mathematical models, charging methods, the battery balance is a new research field and has a bright future in application. This imbalance can't be completely eliminated because of its objective reality; this imbalance will be intensified during using course, so its control is a dynamic process.This paper chooses Ni-MH battery stack which has been widely used electric vehicle as object and the battery voltage as equilibrium parameter. It also discusses the reasons for the extension of equalization and several existing balanced approach. For the application of large number cells on electric vehicles, a new equalization scheme-two stage equalization method is proposed, and does improvement to the traditional MIC. Then, it describes the detail design process of system, including the hardware module design principle, the circuit schematic diagram and the main modules of the detailed process of implementation. Finally, it points out the further direction of this study. This paper mainly includes the following three aspects:1. According to the chemical mechanism and charge-discharge characteristics of battery, analyzes the reasons of the series batteries'inconsistency, and points out that over charge and over discharge is the main factors which cause the extension of the inconsistency. Compares the validity and usefulness of the capacitance, voltage and SOC equilibrium parameter, and analyzes the reasonable of voltage balance.2. The basic principles of the traditional equalization methods are discussed thoroughly, summed up the advantages and disadvantages of these scheme. Improves the traditional MIC based on its fast and accurate charging. For the specific application on electric vehicle, proposes a capacitor-improved MIC two stage equalization scheme, and analyzes working principle and relevant circuit parameters respectively.3. Designed the pharos synchronal flicker system, drawed a schematic diagram of hardware modules and software and detailed design analysis is on cell voltage monitoring module.4. Carries out experiments on improved MIC and two stage equalization system, the result shows that the system is efficient and has practical value.