Project 2 Thermal modeling of battery pack
Aim:- Modelling and simulation of lithium-ion battery with temperature effects using MATLAB/Simulink
Objective:- A battery model is used to study the relationship between external characteristics and the internal states of a battery by establishing a mathematical model [12]. LIBs modelling has a significant impact on accurate estimation of SOC, safety performance and durability
Introduction:- The battery model is required to define and study voltage u, current I, SOC, temperature [8] and other battery parameter. Several literatures propose many battery models which are made of the equivalent circuit combination of capacitance and resistance.
. The Thevenin ECM is chosen because it is the best applicable when you want to get the LiFePO4 battery behaviour under charging and discharging conditions
To ensure optimum compatibility between the ECM and the electrochemical model, a 2RC Thevenin model is chosen [15]. This is because according to the electrochemical reactions, the diffusions and migration at the electrodes are assumed to be realized by paralleled resistance and capacitance parts respectively and the added resistance compensates the changes of the electrolyte
There are heat sources that are associated with LIB batteries which includes the reaction heat, reversible heat, irreversible heat, ohmic heat, and external contact resistance heat [17] . This heat has to be dissipated to the air as quick as possible otherwise it will lead to the increase of cell temperature. The battery on itself generates heat which is either reversible or irreversible heat.
The dissipated heat can be expressed as:
Where h is the equivalent heat transfer coefficient, A is the surface area of the battery, T is the battery temperature, and T∞ is the ambient temperature. This makes the heat balance equation to be obtained as follows:
Where m is the mass of the battery and c is the specific heat capacity. From Eqn. 4 we can resolve that the total heat generated from by the battery is basically influenced by resistance, current, entropy potential, the equivalent heat transfer coefficient, and battery temperature.
3. Lithium-ion battery modelling A battery model is used to study the relationship between external characteristics and the internal states of a battery by establishing a mathematical model [12]. LIBs modelling has a significant impact on accurate estimation of SOC, safety performance and durability.
MODELING AND SIMULATION
The numerical analysis proposed here consisted of a parameter estimation / validation stage, and a simulation stage. During parameter estimation, a discharge profile was iteratively simulated and its results compared with experimental data. The ECM was created using SimscapeTM blocks and SimscapeTM language. The drawing shown in Figure 4 represented the circuit diagram with a single RC block. Each of the circuit elements was a subsystem consisting of custom electrical blocks, and blocks to calculate the properties of the circuit element
Simscape Equivalent Circuit Model
The resistive circuit elements were modeled as variable resistors, as shown in Figure 4. These were modeled based on Ohm’s Law, though a minimum resistance value was used to prevent the differential equation solver from entering a bad state during parameter estimation or simulation. The real power of the resistive elements was also calculated for later use in simulation of thermal dynamics
Modeling Battery Fade
It is generally thought that lithium deposition, electrolyte decomposition, active material dissolution, phase transition inside the insertion electrode materials, and further passive film formation on the electrode and current collectors can affect up to different degrees the capacity fade of lithium-ion batteries. Quantifying these degradation processes will not only help to improve the predictive capability of battery models but also help to elucidate the mechanism of capacity fade.
- No load voltage change
The no load voltage across fundamental battery is modeled using the equation below.
V0,fade = V0 ( 1+ (dV0 * n / 100*N))
Where,
N is the reference number of discharge cycles over which we specify percent change of various battery parameters.
Main battery parameters
Since battery model is table based with temperature dependent, all the values have entered depending upon temperature and SOC.
Cyclic charge/discharge profile
An AC source has been connected to analyse the cyclic charge and discharge performance. The positive cycle will charge the battery and negative cycle will discharge the battery.
Life cycle Analysis
Figure 13 shows the Simulink model of battery pack for lifecycle analysis is shown below. From [2] and [3], we know that the terminal voltage and capacity of the battery will decrease and internal resistance will increase
.Conclusion
MATLAB library model parameters were evaluated for its life cycle and thermal effects parameters. A battery pack with 10 cells connected in series also made with a source of charging and discharging cycle.
The thermal effects of battery pack at different ambient temperatures for cycling charging/discharging has been analysed and plotted.