Project 2
PROJECT 2
CALCULATION OF HEAT GENERATION AND SOC OF A BATTERY
AIM:
- The objectives are
- To find maximum heat generation in the battery
- To find SOC of the battery at 2*104 second of the battery operation
HEAT GENERATION IN THE BATTERY:
- The heat generation source in a battery are
- C rate
- Cell temp
- Ambient temp
- SOC
- Internal resistance
- Number ofcycles used
- Cell electrochemistry
- Heat generation formula:
- The heat generated in a battery (Q)can be calculated by adding joules heat and entropy heat
Q = Qjoules + Qentropy
- Where Qjoules -joules heat
- Qentropy - entropy heat
- Joules heat:
- The joules heat can be calculated as
Qjoules = I(Uocv-Vt)
- Where Uocv-open circuit voltage
- Ut-voltage at time t
- we know
R=Uocv-Vt/I
- The joules heat equation can be rewritten as
Qjoules = t*R*I^2
- Where,R-battery resistance
- I-batttery current
- t-time
- Entropy heat:
- It defined as rateof change of Open circit voltage with respect to temperature
- It function of temperature and SOC
- It expressed in mV/K
- Entropy heat calculated as
Qentropy = I*T (dUocv/dT)
- Where,I-battery current
- T-temperature
- Uocv-open circuit voltage
CALCULATION:
Parameters:
- Battery resistance = 2mohms
- Maximum batterycurrent = 1.0304
- Time t = 1 s
Equation:
- The maximum heat generated Q =Qjoules + Qentropy
- Where Qjoules = I^2*R*t
- According to given condition
- Qentropy = 2*Qjoules
Solution:
- The Joules heat can be calculated as
Qjoules = I^2*R*t
Qjoules = (1.0304)^2*(0.002*1)
Qjoules = (1.06172416)*(0.002)
Qjoules = 0.002123 Joules
- The entropy heat can be calculated as
Qentropy = 2*Qjoules
Qentropy = 2*0.002123
Qentropy = 0.004246 Joules
- The maximum heat generated can be calculated as
Q =Qjoules + Qentropy
Q = 0.002123 +0.004246
Q = 0.006369
Q = 6.369 milli joules
SOC OF THE BATTERY:
- SOC is the State of charge of the battery
- SOC can be callculated as
SOC = Available capacity /Maximum capacity of battery
- SOC at given time can be calculated as
SOC(t) = SOC(0) + 100 *(Q/Qmax)
- SOC(0)- Initial state of charge
- Q-Availabe charge (Q=current *time)
- Qmax - Maximum capacity of battery
- SOC estimation techniques:
- Voltage translation SOC method:
- Battery open circuit voltage is determined to find SOC
- The SOC level repreented uing LED lights
- It easy to implement but high error rate
- Used in application like battery bank,torchlight,trimmer
- Coulomb counting method:
- SOC measured by the current flowing in & out through battery
- Z(t) =Z(0) -1/Cn(n*∫i(t)dt)
- Where,Z(0)-Initial SOC
- Cn-Battery nominalcapacity
- n-coulomb efficiency
- i(t) -intaneous cell current
- t-time
- Its have high accuracy ,but error rate increases as life cycle increases
- Combination of voltage translation & coulomb counting method:
- This type of SOC estimation reduce the error rate
- Voltage translation method ued to calibrate whilevehicle is in teady tate
- Coulomb counting used to determine SOC while vehicle moving
- It have higher accuracy ,but the calibration done periodically the error rate same as coulomb counting method
SIMULINK MODEL:
MODEL REPORT:
- The battery parameters choosen as follows,nominal battery voltage = 7.2V
- Signal builder used to provide the current input to battery through controlled current source
- The signal obtained by importing drive cycle from given excel sheet
- The output of the battery connected to scope block for further analysis
RESULT:
- The current and SOC of the battery for given time period is shown below
- The model simulating for 210 seconds to find SOC level at 208 seconds
- The SOC at 208 seconds of battery operation obtained as 98.99 %
CONCLUSION:
- The maximum heat generated obtained as 6.369 milli joules
- The SOC of battery at 208 seconds obtained as 98.99%