Pack Voltage Research Articles

A control-oriented lithium-ion battery pack model for plug-in hybrid electric vehicle cycle-life studies and system design with consideration of health management

A crucial step towards the large-scale introduction of plug-in hybrid electric vehicles (PHEVs) in the market is to reduce the cost of its battery systems. Currently, battery cycle- and calendar-life represents one of the greatest uncertainties in the total life-cycle cost of battery systems. The field of battery aging modeling and prognosis has seen progress with respect to model-based and data-driven approaches to describe the aging of battery cells. However, in real world applications cells are interconnected and aging propagates. The propagation of aging from one cell to others exhibits itself in a reduced battery system life. This paper proposes a control-oriented battery pack model that describes the propagation of aging and its effect on the life span of battery systems. The modeling approach is such that it is able to predict pack aging, thermal, and electrical dynamics under actual PHEV operation, and includes consideration of random variability of the cells, electrical topology and thermal management. The modeling approach is based on the interaction between dynamic system models of the electrical and thermal dynamics, and dynamic models of cell aging. The system-level state-of-health (SOH) is assessed based on knowledge of individual cells SOH, pack electrical topology and voltage equalization approach.

Maximum Efficiency Point Tracking Technique for <inline-formula> <tex-math notation="TeX">$LLC$</tex-math></inline-formula>-Based PEV Chargers Through Variable DC Link Control

In this paper, a variable dc link technique is proposed to track the maximum efficiency point of the LLC converter for plug-in electric vehicle battery-charging applications over a wide battery state-of-charge (SOC) range. With the proposed variable dc link control approach, the dc link voltage follows the battery pack voltage. The operating point of the LLC converter is always constrained to the proximity of the primary resonant frequency so that the circulating current in the magnetizing inductor and the turning-off currents of MOSFETs are minimized. In comparison with conventional approaches, the proposed variable dc link voltage methodology demonstrates efficiency improvement across the wide SOC range. Efficiency improvements of 2.1% at the heaviest load condition and 9.1% at the lightest load condition are demonstrated.

Electric Vehicle Battery Pack Voltage Detection Circuit and its Error Research

The circuit structure and the sampling principle of single battery voltage detecting circuit were introduced. Switching network timing of single voltage sampling was described, and voltage conditioning circuit parameters were calculated. There were some errors in the measurement results. Through the analysis of the main sources of the errors, corresponding correction strategy was given. The test results showed that experimental results after correction were more accurate and stable.

수명 예측 기법을 이용한 도시형 전기자동차 BMS 모듈 개발 및 차량 성능에 관한 실험 연구

Abstract : This study reports on the development and investigation of a BMS module using a new algorithm on the driving performance and battery life of electric vehicles. Here, the initial SOC was calculated using an open circuit voltage (OCV) method and a current integral method was later applied to the BMS module. We verified the performance of the BMS module by comparing both the results of the in-vehicle test and the BMS simulator test. Our verification test showed good agreement between the results of experiments and simulation with a small error of ± 0.8%. Here, we confirmed that the present, newly-developed BMS module not only can predict the battery life but can also monitor SOC, pack voltage, and current temperature. Key words :BMS(배터리 관리 시스템), UEV(도시형 전기자동차), OCV(개방전압), SOC(충전상태), Coulomeb counting method(전류적산법) Nomenclature 1) A : length, mmB : vehicle velocity, m/sC : temperature, °C Subscripts OCV : open collector voltageUEV : urban electric vehicle * Corresponding author, E-mail: biochan@nate.com

Adaptive state of charge estimator for lithium-ion cells series battery pack in electric vehicles

Due to cell-to-cell variations in battery pack, it is hard to model the behavior of the battery pack accurately; as a result, accurate State of Charge (SoC) estimation of battery pack remains very challenging and problematic. This paper tries to put effort on estimating the SoC of cells series lithium-ion battery pack for electric vehicles with adaptive data-driven based SoC estimator. First, a lumped parameter equivalent circuit model is developed. Second, to avoid the drawbacks of cell-to-cell variations in battery pack, a filtering approach for ensuring the performance of capacity/resistance conformity in battery pack has been proposed. The multi-cells “pack model” can be simplified by the unit model. Third, the adaptive extended Kalman filter algorithm has been used to achieve accurate SoC estimates for battery packs. Last, to analyze the robustness and the reliability of the proposed approach for cells and battery pack, the federal urban driving schedule and dynamic stress test have been conducted respectively. The results indicate that the proposed approach not only ensures higher voltage and SoC estimation accuracy for cells, but also achieves desirable prediction precision for battery pack, both the pack's voltage and SoC estimation error are less than 2%.

A New Cell Balancing Architecture for Li-ion Battery Packs Based on Cell Redundancy

AbstractLi-ion batteries are promoting the development of more and more performing electric vehicles (EVs) and hybrid EVs (HEVs). Thanks to their high energy density and increased current capabilities – which permit to use a relative light and space saving battery pack- these batteries are replacing almost all older battery chemistries in vehicle applications. Despite the advantages these cells provide, before use them in a new design, several drawbacks about safety aspects have to be considered. In fact, Li-ion battery packs require, more than other chemistry base packs, special control systems to maintain the operative conditions in a safe area and to guarantee the best performances in terms of efficiency and pack life time. One of the most challenging problems that have to be tackled by the mentioned control system is the voltage unbalance. This problem arises when more cells are connected in series with the purpose to increase the battery pack voltage. In this paper a new cell balancing architecture based on cell redundancy is proposed. This solution is especially suited to be implemented in vehicle battery management system (BMS) where cost and space reduction are the main requirements.

Directly connected series coupled HTPEM fuel cell stacks to a Li-ion battery DC bus for a fuel cell electrical vehicle

The work presented in this paper examines the use of pure hydrogen fuelled high temperature polymer electrolyte membrane (HTPEM) fuel cell stacks in an electrical car, charging a Li-ion battery pack. The car is equipped with two branches of two series coupled 1 kW fuel cell stacks which are connected directly parallel to the battery pack during operation. This enables efficient charging of the batteries for increased driving range. With no power electronics used, the fuel cell stacks follow the battery pack voltage, and charge the batteries passively. This saves the electrical and economical losses related to these components and their added system complexity. The new car battery pack consists of 23 Li-ion battery cells and the charging and discharging are monitored by a battery management system (BMS) which ensures safe operating conditions for the batteries. The direct connection of the fuel cell stacks to the batteries can only be made if the stacks are carefully dimensioned to the battery voltage. The experimental results of stationary fuel cell charging are presented, showing stable and efficient operation.

Mechanical–electrochemical modeling of Li-ion battery designed for an electric scooter

A macroscopic electrochemical–mechanical model was developed to predict the various power demands of an electric scooter and other outputs, such as the Li-ion battery pack current and voltage requirements for a randomly generated drive cycle using the Matlab-based Simulink software. The simulation results obtained were compared with the actual field test results of a commercial lead-acid battery pack used in a specific electric scooter. The simulation results appeared to give a realistic idea of the dynamic performance of a conceptual Li-ion battery pack in a typical drive pattern. These results, though, need to be validated in an actual field test.

Steady‐State Modeling of a Parallel‐Plate Electrochemical Fluorination Reactor

A steady‐state mathematical model of a parallel‐plate reactor was developed for studying the electrochemical fluorination of organic compounds dissolved in anhydrous hydrogen fluoride. The model incorporates two‐phase flow with differential material, energy, and pressure balances. Profiles of temperature, pressure, vapor volume fraction, and current density in the reactor are presented at two inlet temperatures to provide insight into the operation of the reactor. The effects of the inlet temperature, feed flow rate, and cell current on the cell pack voltage and current efficiency of the reactor are presented to determine problematic operating regions for the reactor. Optimum operating currents based on the ratio of the moles of fluorochemical produced to the input energy are also calculated.