A New Consideration for Validating Battery Performance at Low Ambient Temperatures

Abstract

Existing validation methods for equivalent circuit models (ECMs) do not capture the effects of operating lithium-ion cells over legislative drive cycles at low ambient temperatures. Unrealistic validation of an ECM may often lead to reduced accuracy in electric vehicle range estimation. In this study, current and power are used to illustrate the different approaches for validating ECMs when operating at low ambient temperatures (−15 • C to 25 • C). It was found that employing a current-based approach leads to under-testing of the performance of lithium-ion cells for various legislative drive cycles (NEDC; FTP75; US06; WLTP-3) compared to the actual vehicle. In terms of energy demands, this can be as much as~21% for more aggressive drive cycles but even~15% for more conservative drive cycles. In terms of peak power demands, this can range from~27% for more conservative drive cycles to~35% for more aggressive drive cycles. The research findings reported in this paper suggest that it is better to use a power-based approach (with dynamic voltage) rather than a current-based approach (with fixed voltage) to characterise and model the performance of lithium-ion cells for automotive applications, especially at low ambient temperatures. This evidence should help rationalize the approaches in a model-based design process leading to potential improvements in real-world applications for lithium-ion cells.

Research into the Impacts of Driving Cycles and Load Weight on the Operation of a Light Commercial Electric Vehicle

“…The impetus for further discussions is seen in the issue of the winter operation of electrically powered vehicles (BEV), where there are significant differences in energy consumption as compared to operation at optimal temperature conditions [55]. The differences are mainly caused by the need to heat the vehicle, or steering wheel heating and seat heating, which significantly increases electricity consumption and causes a rapid reduction in the capacity of a vehicle battery, with low temperatures alone reducing battery capacity and operating efficiency [56]. problems can be resolved with electric vehicle heating systems during charging, where the driver/operator/fleet operator sets the exact time at which a vehicle is to be heated.…”

Improving Accessible Capacity Tracking at Low Ambient Temperatures for Range Estimation of Battery Electric Vehicles

“…To compare the effects of the two thermal control approaches for model parameterisation, the cells were cycled for US06 duty cycles at different ambient temperatures. The vehicle level duty cycle was scaled down for the cells used for this study [36]. A backward facing model was used to achieve the scaling of the duty cycle, which converted the legislative speed versus time profile to a vehicle level power versus time profile [37,38].…”

System level heat pump model for investigations into thermal management of electric vehicles at low temperatures.

“…The resistor and open circuit voltage (OCV) values are scaled by the number of cells in series to produce an RC circuit which represents one string of the pack. This data was generated specifically for Xalt 40Ah cells by Yashraj Tripathy in (Tripathy et al, 2018). This type of battery model is typically seen in literature (Jaguemont et al, 2016;Ruan et al, 2014) when modelling pack size batteries for vehicle application.…”

“…This is then used to scale the Coulomb counting equation by the factor C e f f seen in Equation 6. Other examples of this adjustment to Coulomb counting can be seen in (Tripathy et al, 2018) and (Barai et al, 2016).…”