Week 7 State of charge estimation

1. Objective :-State of Charge Estimation using Simulink

SOC:- State of Charge

SOC is the level of charge in battery relative to its capacity

SOC (t)=Q(t)/Qn

Q(t)= Current capacity

Qn=Nominal Capacity

SOC =1-DOD

Type of SOC Estimation Methods :-

S.No	Methods
1	Direct Measurement
2	Book keeping estimation
3	Adaptive system
4	Hybrid method

Direct Method :-

• Open Circuit Voltage
• Terminal Voltage method
• Impedance measurement method
• Impedance Spectroscopy method

Book Keeping :-

• Coulomb Counting
• Modified Coulomb Counting

Adaptive :-

• Fuzzy logic
• kalman filter
• Extended Kalman filter

Hybrid :-

• Coulomb counting and Kalman filter combination

Coulum Counting Implimentation in Simulink

Step 1 :-Open simulink file BMS cloosloop harness board

Step 2:- Double clik on BMS ECU

Step 3:- Click SOC Estimation Algoritm

Step 4:- Click Coulomb Counting

Coulomb Counting Method:-The coulomb counting method measures the discharge current of the battery and integrate the discharge current over time in order to estimate the SOC .

Equation :-

SOC(t) = SOC(t-1) - I(t)/Qn *dt

SOC(t)= SOC at time t

SOC(t-1)= SOC at time t-1

I(t)= Current at time t

Qn = Nominal capacity of battery

dt =time intervel

Accuracy of Coulomb counting method depends on temperature ,battery history ,discharge current and cycle life

example :- After very 10 sec discharge current changes

Qn= 10 Ah

initial SOC= 100 % (i.e SOC (t-1))

now at t= 0

SOC =100 %

After 10 sec i.e SOC (t)

I(t)=20 A

SOC (t) = 100 - (20 /10) * 10

= 100- 20

=80%

DOD =100-SOC

=20%

Coulomb Counting Implimentation in BMS using Simulink :-

• The Current and the temperature are taken as input
• capacity is varied with respect to temperature in the lookup table and thus it is operated with the current input
• Then current is divided by the capacity and then integrated to get the value of the SOC of the battery

Test cases :1

Case1:-3 phases

• Driving
• Charging
• Standby

Case 2:-2 phase

• Diving
• Charging

Case 3:-Has only one phase

• Charging