Session: 10-02: Photovoltaic, Photovoltaic-Thermal, and Electrochemical Technologies II

Paper Number: 156850

156850 - The Effect of Pulse Width Modulation of Air-Cooling on Lithium-Ion Battery Thermal Behavior 

Abstract: 

Lithium-ion batteries (LIB) usage has increased over the past several years for use in applications such as electric vehicles (EVs), and, more recently, grid-scale energy storage. LIB have a preferred temperature range for operation, yet operation of these batteries generates heat. Thus, battery thermal management systems (BTMS) have been developed with different cooling strategies to maintain battery temperature within the desired range and to minimize the temperature difference across the cell, module, and pack. For EVs, BTMS should be effective, lightweight, and compact. One of the most common, cheapest, and simplest methods of cooling batteries is using ambient air driven by a fan. However, due to the low specific heat and density of air, air cooling needs high flow rates to maintain the desired battery temperatures even at low discharge rates. These high flow rates correspond to higher parasitic power consumption. A fan with constant power draw will consume parasitic power from a battery pack proportional to its operating time. Thus, as a way to reduce the power consumption, the present study examines the effect of modulating the cooling fan on-off cycle on the thermal behavior of a small pack of lithium-ion batteries during a constant current discharge. Different total fan durations were used, from 0% of discharge time (i.e. fan is off during the entire discharge) to 100% of discharge time (i.e. fan is on the entire discharge). Additionally, various cycle pulse times were explored. For the experiment, a module of four LiFePO4 cells with an individual nominal capacity of 7Ah wired in a parallel electrical configuration was used. Physically, the cells were arranged in two cells in parallel and two cells in series. The temperatures of the cells were measured using type-T, surface mount thermocouples, four thermocouples per cell. The resulting maximum cell temperature, average cell temperature, cell temperature differential and maximum module temperature difference were evaluated to determine the effectiveness of the cooling method. Results show that a similar average temperature rise can be maintained when using a 50% fan duration and a long cycle pulse time compared to when the fan is operated continuously (100% fan duration). Additionally, the temperature difference across the module is similar. However, as the cycle pulse time decreases, the temperature rise and temperature difference across the module increases. From this study it can be seen that reducing the fan duration as a percentage of the total discharge time can produce acceptable thermal behavior of the batteries, and the reduced fan time indicates a reduction in parasitic power consumption.

Presenting Author: Evan Rasset North Dakota State University

Presenting Author Biography: Evan Rasset is a graduate student at North Dakota State University currently pursuing a master's degree. He is performing research into battery thermal management systems under the advice of Dr. Adam Gladen.