Jianqiang Kang

Influence of practical complications on energy efficiency of the vehicle's lithium-ion batteries

A kind of battery pack of LiFePO4 was selected as the concrete study object. A kind of method was pointed out to define the energy efficiency of the battery, the constant current and pulse current of charge and discharge energy efficiency were analyzed. The results of analysis show that the charge and discharge energy efficiency are above 90%, and constant current and pulse current of charge and discharge energy efficiency of LiFePO4 are almost the same. Furthermore, the energy efficiency of LiFePO4 is in connection with SOC and current. This research provides technical support for selecting the type of the battery pack and optimizing the control strategy of a whole vehicle.

A study on capacity and power fading characteristics of Li(Ni1/3Co1/3Mn1/3)O2-based lithium-ion batteries

The objective of this study is to find out the factor that accounts for the capacity fading and to predict the cycle life of lithium-ion batteries by the driving cycle test. A new method, incremental polarization resistance, is elected to analyze the gradation mechanism based on incremental capacity analysis. It is summarized that the two major factors, the loss of lithium ions and the cathode fading, make the capacity loss in different stages. In the first stage, the loss of lithium ions, caused by the solid electrolyte interface (SEI) lay reaction, is the main reason for battery degradation. In the second stage, the cathode starts to decay and make the capacity loss, because of the less intercalation in cathode. In the third stage, the cathode degradation gradually outpaces the loss of Li and becomes the limit factor for the battery recession. Finally, a cycle life model was established to predict the capacity loss with cycle numbers.

Energy efficiency of a Ni-MH battery used in hybrid electric vehicles

The energy efficiency of the battery is the proportional relation between the net energy change of the battery and energy that input from the outside or output to the outside. The energy efficiency of a Ni-MH battery (40Ah) was studied by testing and theoretical analysis in order to improve the control precision of hybrid electric vehicles (HEVs) and the battery useful life. A test stand for testing the energy efficiency of the Ni-MH battery was established. The data from experiments of constant, pulse current energy efficiency performed on the Ni-MH battery were analyzed. Based on the experimental results, mathematical model of net energy of the battery was proposed by function-fitting methods, and the effects of current and state of charge (SOC) on energy efficiency were analyzed. Theoretical analysis and experimental results suggest that charge and discharge energy efficiency of Ni-MH battery are above 90% within the range of 30%–80% SOC, and the effect of current on energy efficiency is greater than that of SOC, which provide theoretical basis for selection of batteries and dynamic optimizing technology of HEV system controlling strategy.

Ternary-material lithium-ion battery SOC estimation under various ambient temperature

Ambient temperature produces great effects on battery state-of-charge (SOC) estimation, due to the unstable estimation algorithm, the weakened traceability of battery model, and variable model parameters at various temperatures, especially lower temperatures. The widely used method based on the equivalent circuit model (ECM) offline in using different algorithm, like current integral, the extended Kalman filter (EKF), or the unscented Kalman filter (UKF), can obtain an accurate SOC estimation at room temperature, but it is difficult to guarantee the high precision at lower temperatures. To address this problem, the battery model is investigated at different temperature, and an offset item is proposed to develop the observer equation in the estimated model. Then, the square root of the Sigma points Kalman filter (SR-UKF) is applied, and on the basis of the individual model parameter-temperature table and the developed model, the high accuracy of SOC estimation is achieved. Additionally, considering the burden of original parameter modification (all model parameters modified) at various temperature which will increase the product cost and computational complexity of the battery management system (BMS), the relationship between individual model parameter and the error of SOC estimation is built, which is helpful for the simplification of parameter modification. The results indicate that the proposed method based on the developed estimated model and the simplified parameter modification can achieve an accurate, stable, and efficient SOC estimation.

Research on energy efficiency of the vehicle's battery pack

The battery pack of LiFePO4 and MH-Ni were selected as the concrete study subject. This paper pointed out a kind of method to test the energy efficiency of the battery, the constant current and pulse of charge and discharge energy efficiency were analyzed. The results of analysis show the energy efficiency of battery pack is in connection with SOC and current, and the energy efficiency of LiFePO4 is higher than MH-Ni, which provide technical support for improving power characteristic of EV and HEV.