Project 2 Thermal modeling of battery pack
Objective :
For a 10 cell series lithium ion battery model, simulate the thermal effects and compare life cycle performance at various temperatures, charge & discharge rates using MATLAB.
Theory :
Nowadays, Lithium ion battery are mostly used in electric vehicles.We must know its charge and discharge rates to operate this battery in an efficient manner and without damage. When the battery is in operation, this temperature of it must be kept in limit. We simulate the thermal effect of the cell, by knowing the temperature rise we can provide the efficient cooling to the batteries to increase the life cycle of the battery.
We will see a model on this issue and explanation as given below:
This example shows how to simulate a battery pack consisting of multiple series-connected cells in an efficient manner. It also shows how a fault can be introduced into one of the cells to see the impact on battery performance and cell temperatures. For efficiency, identical series-connected cells are not just simply modeled by connecting cell models in series. Instead a single cell is used, and the terminal voltage scaled up by the number of cells. The fault is represented by changing the parameters for the Cell 10 Fault subsystem, reducing both capacity and open-circuit voltage, and increasing the resistance values.
Circuit construction and working :
In this circuit we use Li-ion cell 1 to 10, temperature sensors, Ambient temperature block,state of charge estimation,scope, charge-discharge profile given to circuit, from & goto block, PS-simulink converter.
Cell 01 to Cell 04 Subsystem :
Cell Subsystem basically consists of a Thermal model and Lithium Cell 1RC block which calculate the Thermal effect for cells and overall calculation for the battery pack.
- This block basically consists of capacitance value table which depends on external physical signal inputs SOC and T.It is assumed that the capacitance value is varying with time, and hence the equation i=C*dv/dt holds.
- Resistance value (R) Table which depends on an external physical signal inputs SOC and T.
- Voltage value (EM) which implements the cell's main branch voltage source, and determines the value for Capacity (C) and state of charge (SoC).The defining equations depend on cell temperaure T.
Output of 1 cell is connected to SoC estimation whereas the other output is connected with AC current source for cyclic charge-discharge profile.
The peak amplitudes set to 50A for cyclic charge and discharge.A basic parameter of AC current source is as:
Other blocks which are used in Li-ion battery pack are as follows:
Temperature Sensor :
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.
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.This block is used for Ambient Temperature which can set and check the results.
Convective Heat Transfer :
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:
Q=k·A·(TA−TB)
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.
From and Goto Blocks :
The Goto block passes its input to its corresponding From Blocks.The input can be a real/complex valued signal or vector of any datatype.From and Goto blocks allow you to pass a signal from one block to another without actually connecting them.
State of Charge Estimation :
The Coulomb counting method measures the discharging current of the battery and integrates the discharging current of the battery in order to estimate the SOC.
This system takes current as input and gives SOC % as the output .A current sensor block is used and connected for SOC estimation.
Initial SOC of the battery is taken as 100%.
The example shows how to simulate a battery pack consisting of number of series connected cells in an efficinet manner.It also shoes how a fault can be introduced into one of the cells to see thhe impact on battery performance and cell temperatures.
Results :
1) Ambient Temperature 300K i.e 26.85 deg.C
2) Ambient Temperature 310K i.e 36.85 deg.C
2) Ambient Temperature 324K i.e 50.85 deg.C
RESULT EXPLANATION :
- For a 10 cell series lithium ion battery model simulate the thermal effects and compare life cycle performance at various temperatures, charge discharge rates using MATLAB.
- 01-04 cells are normal, 5th cell is faulty and 06-10 cells are normal.As we are simulating the Thermal effects we give Cyclic charge-discharge profile to the circuit.The waveforms shown above display that the plots of temperaures for the 5th cell (faulty cell) are higher than the normal cells.Due to this high rise in temperatures, the life cycle of the cell gets reduced and may also damage the cell.
- As we give the ambient temperature of 300K, the 1-4 and 6-10 cells temperatures reach 316K, while the 5th cell temperature reaches 330K i.e, 56.85 deg.C and the Drive cycle shown is cyclic charge-discharge cycle.
- In conditon 2, we give temperature of 310K, the 1-4 and 6-10 cells temperatures reach near to 326K but 5th faulty cell temperature reaches 340K i.e, 66.85 deg.C and the Drive cycle shown is cyclic charge-discharge cycle.
- In conditon 3, we give temperature of 324K, the 1-4 and 6-10 cells temperatures reach near to 340K but 5th faulty cell temperature reaches 354K i.e, 80.85 deg.C and the Drive cycle shown is cyclic charge-discharge cycle.
Conclusions :
We simulated the Thermal effects and compared at various temperatures,faulty temperature rise more than normal cell.The charge and discharge cycle is given.The high rise in temperatures can damage the cell and reduce its lifecycle and hence reduce the performance of the battery.