battery thermal management systems btms
TRANSCRIPT
Battery Thermal Management Systems ‐
BTMS
Charging a battery electric vehicle (BEV)
Principles of a battery
Some batteries
Battery for a vehicle
Battery Type Specific energy J/kg
Specific energy Wh/kg
Energy density Wh/liter
Cell Voltage V
Lead-acid 145 000 41 100 2
Alkaline 400 000 110 320 1.2
Carbon-zinc 130 000 36 92 1.1
NiMH 340 000 95 300 1.2
NiCd 140 000 39 140 1.2
Lithium-ion 460 000 128 230 3.6
Some data for various batteries
Battery Modeling and Simulations
•Estimation of Battery Performance•Battery Design
•Thermal management
Why is thermal management needed?
• To keep the cells at a desired temperature levelToo hot: decreased battery life, decreased performance, risk of fire or explosion
• To minimize the cell‐to‐cell temperature variations• To prevent the battery from going above or below acceptable limits• To maximize the useful energy from cells and pack• To use a small amount of energy for operation
Thermal Runaway
• A condition that is caused by a battery charging current or other process which produces more internal heat than the battery can dissipate
• Early Warnings?increase in charge current at normal operation, increase in cell
temperature over the ambient temperature
Thermal Runaway of batteries
Importance of temperature
On Battery Temperature
Optimum Temperature Range
Cooling systems in EV/HEV
Battery cooling systemInverter cooling systemMotor cooling system
Electric/hybrid vehicles
Problems in the electric/electronic equipment cooling
Battery: Twork is 50-55 , Tambient is 30-40 , Thus △Tbattery-ambient = 10-25 , It is difficult to cool the battery at a low △T.
Inverter: Heat flux is 150-200 W/cm2, Tjunction is 125 .It is hard to dissipate so high heat flux and keep Tjunction<
125
Motor: Without an appropriate cooling method, the motor performance will decrease greatly.
Thus appropriate thermal management is a significant issue for electric/electronic equipment in EV/HEV.
Example of thermal management
Direct Air Cooling
Direct Liquid cooling
Cold Plate Cooling
Indirect Liquid Cooling
Example of thermal management
Example of battery location in vehicle and thermal management
Using PCM (Phase Change Material) in Battery Thermal Management
Passive thermal management-phase change materials (PCM) as coolantBattery discharge: Battery dissipates the heat to PCM. Solid PCM becomes liquid, and stays solid-liquid state.Battery charge: Battery absorbs some heat from PCM. Liquid PCM becomes solid.
Thus the function temperature of PCM should be higher than the ambient temperature.
But it is lower than the battery working temperature.
PCM is used to surround the array of cells
Battery cooling system
Battery cooling systemPassive thermal management
Passive cooling (PCM) is more useful than the active cooling (air) to keep the battery working temperature under 55 (Sabbah R, 2008)
Active cooling (air): It can not keep the battery working temperature
under 55
Passive cooling (PCM): The battery working temperature is kept under
55
Fig. 5. Cooling performance based on volume averaged cell temperature at 10 A.
Drawback of the thermal management
• Increased complexity• Added cost• Reduced Reliability• Consumption of energy for operation
Processes needing consideration
• Heat and mass transport• Charge transport• Electrode kinetics• Electrode‐electrolyte interfacial processes
Softwares for Battery Modeling
General Purpose Tools
• MATLAB• COMSOL• ANSYS
Customized tools
•Battery Design Studio
Heat Generation
where the first term is the heat generated by ohmic and other irreversible effects in the cell. The second term represents the heat generated or consumed because of the reversible entropy change due to the electrochemical reactions in the cell.