Dai Haifeng

A new SOH prediction concept for the power lithium-ion battery used on HEVs

One of the most important tasks of the battery management system (BMS) is to estimate the battery states which mainly include the State of Charge (SOC) and State of Health (SOH). Compared with the SOC estimation technology, which progresses a lot currently, the study of SOH prediction method is in its junior state. In this paper, a SOH prediction concept was proposed. Main points of this concept include the aging process of the battery, the definition of the SOH, and prediction of the batterys healthy state etc. Aiming at the application mode of the battery packs on hybrid electric vehicles (HEVs), ageing processes of the battery were discussed and several accelerated life test results were listed. Then according to the aging process studies, a power- reflecting SOH definition was proposed. Based on these, a parameter system identification based SOH prediction method was designed. To validate the SOH prediction concept we presented, a simulation test was designed, and test result show that the concept is feasible to predict SOH online.

A Study on Lead Acid Battery and Ultra-capacitor Hybrid Energy Storage System for Hybrid City Bus

Electrochemical energy storage, especially lead acid system alone seems not to be able to meet the demand of the hybrid vehicle propulsion system due to the power density and cycle life. Ultra-capacitor pack has been introduced in the design of energy storage system to the HEV power-train, which is often combined with battery packs to form a hybrid energy system. In these kind of applications, ultra-capacitor could either be paralleled directly with battery pack or connected with battery pack through a active energy converter like DC/DC. This paper describes two kinds of hybridization of the energy storage system with ultra-capacitor and lead acid battery. By founding the model of each component in the hybrid system and with the simulation, the power enhancement and life extension of the hybrid system compared to the pure lead acid system is analyzed. Testing results show that no matter what kind of hybridization the system is, power is enhanced with a factor β, and due to the power enhancement, current demand to the battery system is lowered, which extend the batteries’ cycle life.

Battery management systems in the China-made “Start” series FCHVs

In the China-made ldquoStartrdquo series fuel cell hybrid vehicles (FCHVs), the power battery pack, which contains a series of Lithium-ion batteries, plays an important role in the dynamic system. For developing the vehicles with high performance and good reliability, the batteries have to be managed to obtain maximum performance under various operating conditions. In this paper, a battery management system (BMS) was introduced which was designed for optimizing the use of the batteries. This system was a level-based system which contains a high-level system called ldquoCentral ECUrdquo (CECU) and several low-level systems called ldquoLocal ECUrdquo (LECU). The software of the battery management system was designed based on the UC/OS-II to guarantee the real-time requirement. The system performs such several tasks including states monitoring (State of Charge, SOC and State of Health, SOH), creepage detection, cell balance, thermal management, power limitation, diagnostics etc. In the two experiments shown in the paper, results indicate that this BMS performs well in managing the power batteries used in ldquoStartrdquo series FCHVs, it could estimate the states of the battery accurately, detect the creepage and do some protect in real time, balance the cell very well and maintain the temperature of the battery pack in a satisfactory manner. Other critical functions have also been tested during the vehiclepsilas on-road testing.

Preliminary Study of a Distributed Thermal Model for a LFP Battery in COMSOL Inc. Multiphysics(MP) Software

In order to better understand the thermal behavior of high capacities and large power lithium-ion batteries for electric vehicle application, a distributed thermal model of a LFP battery is proposed. The model includes a 3-D electrode plate pair model based on porous-electrode theory and a 3-D battery model solving the temperature distribution of the battery. These models are coupled through heat generation rate and transient temperature during discharging process.