Optimisation of Direct Battery Thermal Management for EVs Operating in Low-Temperature Climates

Abstract

Electric vehicles (EVs) experience a range reduction at low temperatures caused by the impact of cabin heating and a reduction in lithium ion performance. Heat pump equipped vehicles have been shown to reduce heating ventilation and air conditioning (HVAC) consumption and improve low ambient temperature range. Heating the electric battery, to improve its low temperature performance, leads to a reduction in heat availability for the cabin. In this paper, dynamic programming is used to find the optimal battery heating trajectory which can optimise the vehicle’s control for either cabin comfort or battery performance and, therefore, range. Using the strategy proposed in this research, a 6.2% increase in range compared to no battery heating and 5.5% increase in thermal comfort compared to full battery heating was achieved at an ambient temperature at −7 °C.

Battery Thermal Management System for Electric Vehicles: A Brief Review

“…High thermal conductivity, mostly applied for high cooling demand [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. complexity, high cost, heavy, must store the fluid, viscosity, potential leaks, additives for anti-freeze & Boiling [2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

“…Many temperature ranges recommended for the use of lithium ion batteries are found in the literature, but, only a range between 15 °C and 35 °C is desired [5]. Some battery suppliers define four temperature ranges [1][2][3][4][5][6][7][8][9][10][11][12][13][14]: (1) (0-10 °C) decreased battery capacity and pulse performance, (2) (20-30 °C) optimal range, (3) (30-40 °C) faster self-discharge, and (4) (40-60 °C) irreversible reactions, with 60 °C being the upper safety limit under normal operating conditions. Another important point is the temperature uniformity between the battery cells in which the temperature difference must be less than 5 °C [4][5][6][7][8].Tete et al [4] revealed that at high temperatures, lithium-ion battery cells lost more than 60% of their initial energy after 800 cycles at 50 °C and lost 70% after 500 cycles at 55 °C.…”

“…Some battery suppliers define four temperature ranges [1][2][3][4][5][6][7][8][9][10][11][12][13][14]: (1) (0-10 °C) decreased battery capacity and pulse performance, (2) (20-30 °C) optimal range, (3) (30-40 °C) faster self-discharge, and (4) (40-60 °C) irreversible reactions, with 60 °C being the upper safety limit under normal operating conditions. Another important point is the temperature uniformity between the battery cells in which the temperature difference must be less than 5 °C [4][5][6][7][8].Tete et al [4] revealed that at high temperatures, lithium-ion battery cells lost more than 60% of their initial energy after 800 cycles at 50 °C and lost 70% after 500 cycles at 55 °C. In another example, they reported that the life cycle of a lithium-ion battery at 45 °C is approximately 3323 cycles, and that this value is reduced to 1037 cycles at a temperature of 60 °C.…”

“…Currently, the temperature control of batteries in electric vehicles is done through the use of the battery thermal management system (BTMS). This system is responsible for ensuring that the battery works in the proper temperature range and keeps the temperature between the cells as homogeneously as possible [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

Experimental Study on Heating Performances of Integrated Battery and HVAC System with Serial and Parallel Circuits for Electric Vehicle

“…Further, Jeff et al proposed an optimal strategy for tradeoff heating between battery and cabin. The optimal strategy enables 6.2% of improvement in range for no battery heating and 5.5% of improvement in cabin comfort for full battery heating [32].…”