Week 9 Thermal Management of battery

The importance of a cooling system

While advancements have been made in electric vehicle batteries that allow them to deliver more power and require less frequent charges, one of the biggest challenges that remain for battery safety is the ability to design an effective cooling system.

In electric cars, discharging the battery generates heat; the more rapidly you discharge a battery, the more heat it generates.

Batteries work based on the principle of a voltage differential, and at high temperatures, the electrons inside become excited which decreases the difference in voltage between the two sides of the battery. Because batteries are only manufactured to work between certain temperature extremes, they will stop working if there is no cooling system to keep it in a working range. Cooling systems need to be able to keep the battery pack in the temperature range of about 20-40 degrees Celsius, as well as keep the temperature difference within the battery pack to a minimum (no more than 5 degrees Celsius).

If there is a large internal temperature difference, it can lead to different charge and discharge rates for each cell and deteriorate the battery pack performance.

Potential thermal stability issues, such as capacity degradation, thermal runaway, and fire explosion, could occur if the battery overheats or if there is non-uniform temperature distribution in the battery pack. In the face of life-threatening safety issues, innovation is continually happening in the electric vehicle industry to improve the battery cooling system.

Which cooling system works best in Electric Vehicles?

Battery thermal management systems are still a highly researched topic, and what we know about them is going to change and develop over the coming years as engineers continue to rethink how our car engines work.

There are a few options to cool an electric car battery—with phase change material, fins, air, or a liquid coolant.

1. Phase change material absorbs heat energy by changing state from solid to liquid. While changing phase, the material can absorb large amounts of heat with little change in temperature. Phase change material cooling systems can meet the cooling requirements of the battery pack, however, the volume change that occurs during a phase change restricts its application. Also, phase change material can only absorb heat generated, not transfer it away, which means that it won’t be able to reduce overall temperature as well as other systems. Although not favorable for use in vehicles, phase change materials can be useful for improving thermal performance in buildings by reducing internal temperature fluctuations and reducing peak cooling loads.

2. Cooling fins increase surface area to increase the rate of heat transfer. Heat is transferred from the battery pack to the fin through conduction, and from the fin to the air through convection. Fins have high thermal conductivity and can achieve cooling goals, but they add a lot of additional weight to the pack. The use of fins has found a lot of success in electronics, and traditionally they have been used as an additional cooling system on internal combustion engine vehicles. Using fins to cool the electric car battery has fallen out of favor since the additional weight of the fins outweighs the cooling benefits.

3. Air cooling uses the principle of convection to transfer heat away from the battery pack. As air runs over the surface, it will carry away the heat emitted by the pack. Air cooling is simple and easy, but not very efficient and relatively crude compared to liquid cooling. Air cooling is used in earlier versions of electric cars, such as the Nissan Leaf. As electric cars are now being used more commonly, safety issues have arisen with purely air-cooled battery packs, particularly in hot climates. Other car manufacturers, such as Tesla, insist that liquid cooling is the safest method.

4. Liquid coolants have higher heat conductivity and heat capacity (ability to store heat in the form of energy in its bonds) than air, and therefore performs very effectively and own advantages like compact structure and ease of arrangement. Out of these options, liquid coolants will deliver the best performance for maintaining a battery pack in the correct temperature range and uniformity. Liquid cooling systems have their own share of safety issues related to leaking and disposal, as glycol can be dangerous for the environment if handled improperly. These systems are currently used by Tesla, Jaguar, and BMW, to name a few.

2.Create a simple simscape model with a battery and show the temparature dependance in the performance.Also connect a resistor load of 10 Ohm

Battery (Table-Based)

Description
The Battery (Table-Based) block represents a high-fidelity battery model. The block calculates no-load voltage as a function of charge level and optional temperature using lookup tables and includes several modeling options:

Self-discharge

Battery fade

Charge dynamics

Note
The block can use linear or nearest interpolation and extrapolation for all the table based parameters. For rows and columns, it follows the row-column convention, whereas rows are indexed first and, subsequently, columns.

The plot shows a battery whose performance varies with temperature and state of charge changes, as typically found on a datasheet.

Use this block to parameterize batteries with complex no-load voltage behavior from datasheets or experimental results. For a simpler representation of a battery, see the Battery block.

The Battery (Table-Based) block has four modeling variants, accessible by right-clicking the block in your block diagram and then selecting the appropriate option from the context menu, under Simscape > Block choices:

Uninstrumented | No thermal port — Basic model that does not output battery charge level and simulates at a fixed temperature. This modeling variant is the default.

Uninstrumented | Show thermal port — Model with exposed thermal port. This model does not output internal charge level of the battery.

Instrumented | No thermal port — Model with exposed charge output port. This model uses a fixed temperature throughout the simulation.

Instrumented | Show thermal port — Model that lets you output internal charge level of the battery. Both the thermal port and the charge output port are exposed.

The instrumented variants have an extra physical signal port that outputs the internal state of charge. Use this functionality to change load behavior as a function of state of charge, without the complexity of building a charge state estimator.

The thermal port variants expose a thermal port, which represents the battery thermal mass.

here we have use the Instrumented | show thermal port

Temperature Source
Constant source of thermal energy, characterized by temperature expand all in page

Description
The Temperature Source block represents an ideal source of thermal energy that is powerful enough to maintain specified temperature at its outlet regardless of the heat flow consumed by the system.

The source generates constant absolute temperature, defined by the Temperature parameter value.

Convective Heat Transfer

Description
The Convective Heat Transfer block represents a heat transfer by convection between two bodies by means of fluid motion. The transfer is governed by the Newton law of cooling and is described with the following equation:

where

Q Heat flow
k Convection heat transfer coefficient
A Surface area
TA,TB Temperatures of the bodies
Connections A and B are thermal conserving ports associated with the points between which the heat transfer by convection takes place. The block positive direction is from port A to port B. This means that the heat flow is positive if it flows from A to B.

Temperature Sensor

Description
The Temperature Sensor block represents an ideal temperature sensor, that is, a device that determines the temperature differential measured between two points without drawing any heat.

Connections A and B are thermal conserving ports that connect to the two points where temperature is being monitored. Port T is a physical signal port that outputs the temperature differential value.

The block positive direction is from port A to port B. The measured temperature is determined as T = TA – TB.

Ports
The block has the following ports:

A
Thermal conserving port associated with the sensor positive probe.

B
Thermal conserving port associated with the sensor negative probe.

T
Physical signal output port for temperature.

NOW SIMULATING THE SYSTEM WITH TEMPERATURE SOURCE AS 293K AT 0.1 m^2 AREA

here we can see that the soc of the battery has reached to 0.9 when temp. is 293k with 0.1 m^2 area.

3.Compare the resultants graph for different area of contact of heat

NOW SIMULATING THE SYSTEM WITH TEMPERATURE SOURCE AS 310K AT 1 m^2 AREA

here we can see that soc of the battery has reached to 0.8 at 310k temperature source using 1 m sq area

Outcome:- BY COMPARING BOTH THE GRAPHS WE CAN CONCLUDE THAT THE SOC OF THE SYSTEM DECREASES WHEN WE INCREASE THE AREA AND TEMPERATURE OF TEMP. SOURCE

TO AVOID THE DECREASE OF EEFICENCY OF BATTERY THERMAL MANAGMENT OF THE BATTERY AREA IS MUST IN ORDER TO MAINTAIN A GOOD STATE

OF CHARGE.