Project 2
Aim - study of Li-ion battery system using matlab & simulink
objective - 1) The max heat generation of the battery
2)The SOC of the battery at 2 *104second of the battery operation
Theory -
A] Heat generation :
Large battery packs are used in electric vehicles. Heat is generated when the battery pack is being used. Therefore, it is necessary to predict battery heat generation. Operating temperature of lithium-ion battery is an important factor influencing the performance of electric vehicles. During charging and discharging process, battery temperature varies due to internal heat generation, calling for analysis of battery heat generation rate. The generated heat consists of Joule heat and reaction heat, and both are affected by various factors, including temperature, battery aging effect, state of charge (SOC), and operation current. In this article, a series of experiments based on a power-type lithium manganese oxide/graphite battery was implemented under different conditions.
The parameters for Joule heat and reaction heat are determined, and the Joule heat, reaction heat as well as total heat generation rate is detailed and analyzed considering the influence of temperature, aging, SOC, and current. In order to validate the accuracy of heat generation rate, a lumped battery heat transfer model is applied to calculate the temperature variation, and the estimated temperature variation shows good correspondence with experimental results under different currents and aging conditions. Due to its simplicity, the temperature variation estimation method is suitable for real time applications.
What factors affect the generated heat in a battery?
The generated heat consists of Joule heat and reaction heat, and both are affected by various factors, including temperature, battery aging effect, state of charge (SOC), and operation current.
Controlling heat build up in EVs:
Battery thermal management is a huge challenge in electric vehicles. In addition to increasing the risk of fire, high temperatures can have a direct influence on range. By efficiently controlling EV temperature levels, battery range can be maximized. Just like internal-combustion engine vehicles, when an electric power train works harder, it gets hotter. Therefore, EVs require effective, efficient and durable cooling systems. Heat management can have a major impact on not only the components within a vehicle, but also its overall performance.
Battery Thermal Runaway in Electric Vehicles:
Thermal runaway begins when the heat generated within a battery exceeds the amount of heat that is dissipated to its surroundings.
What causes the battery to overheat which leads to thermal runaway?
1. Ambient Temperature
2. Age of the Battery
3. Float Charging Voltage
4. Overcharging
Approaches to Minimize Thermal Runaway
The reduction of the Thermal Runway hazard can be fulfilled on three levels-
1. First: improve the intrinsic safety of anti-TR properties by material modification;
2. Second: set passive defense against the practical abuse conditions and develop an early warning
algorithm before TR;
3. Third: postpone or inhibit the secondary hazard, such as Thermal Runway propagation, to win
sufficient time for the passenger to escape from the EV after the accident.
SOC % (State Of Charge) of a Battery pack:
The SOC is the measurement of the amount of charge remaining on a battery. It represents the ratio of the current capacity of the battery to its nominal capacity after a period of use or long-term shelving, which also indicates the maximum amount of power that can be stored in the battery. The SOC is calculated as a percentage: when it’s at 0, it means the battery is completely discharged. When the SOC is at 100, it means the battery is completely full.
Absolute Charge State
There is also what’s called an absolute charge state, which is a reference value calculated from the fixed capacity value when the cell is manufactured. The absolute SOC of a new fully charged battery is 100% while an aged battery, even if fully charged, cannot reach 100% in different charge and dis-charge situations.
Influencing Factors
Most SOC estimations require precise data measurements, whether it is the chemistry of the cell (type of electrolyte), its operating conditions, or the variables of the cell (voltage, current), etc., thus being suitable only in the laboratory and not in real applications. The SOC of a battery is a combination of voltage, charge/discharge current and internal resistance parameters to estimate its size. These parameters are also affected by a variety of uncertainties such as battery aging, temperature changes and usage status.
Accurate SOC estimations reflect important information, such as battery performance, remaining battery life, etc., which ultimately leads to efficient management and utilization of battery power and energy. In addition, SOC estimation can be used to regulate battery life degradation, explosions or fires due to battery over-discharge and overcharge, as well as aging and permanent damage to the battery cell structure. Therefore, the SOC indicator on a BMS is vital for user convenience, as well as the efficiency, safety and life of the battery.
Calculations:
1) To find the maximum heat generation of the battery.
Given ;
Battery resistance = 0.5 mohm
Entropic factor = 2
delta time = 0.1
Currrent = -0.896.....(maximum current)
formula :
Maximum heat generated = joule heat + Entropic heat
joule heat = i^2r*t
joule heat = (-0.896) ^2*0.5 * 2*60
joule heat = 48 mJ
Maximum heat generated = 48 mJ + 2mJ
Maximum heat generated = 50 mJ
2) The SOC of the battery at 2 *104second of the battery operation
the SOC of the battery pack can be calculated by using simulink & matlab.
simulink model :
component use:
signal builder block :
In this simulation we are using Drive cycle source signal builder to estimate the SOC of a battery pack for 2*104 sec of time.
excel data:
controlled current source :
Converts the Simulink input signal into an equivalent current source. The generated current is driven by the input signal of the block.
series branch R:
it opposes the flow of cuurent
Li-ion battery :
Implements a generic battery model for most popular battery types. Temperature and aging (due to cycling) effects can be specified for Lithium-Ion battery type.
bus selector:
This block accepts a bus as input which can be created from a Bus Creator, Bus Selector or a block that defines its output using a bus object. The left listbox shows the elements in the input bus. Use the Select button to select the output elements. The right listbox shows the selections. Use the Up, Down, or Remove button to reorder the selections. Check 'Output as virtual bus' to output a single bus.
scope :
it is use for to display the SOC , voltage & current ofthe battery .
powergui:
Set simulation type, simulation parameters, and preferences.
output of scope :
The SOC of the battery at 2 *104second of the battery operation is 99.99%.
conclusion :
from the above experiment we learned the how the maximum heat generate of the battery by using the joule heat & entropic heat. also, we learned how the SOC of the battery can be found by using simulink matlab.