BMS_Modelling_Project_PPT.pptx

Integrated Simulation Technologies Pvt. Ltd.
Pune, India
www.integratedsimtech.com
subir.mandal@integratedsimtech.com
+91-9763909935
Name - Chandrakant Jadhav
Li ion Cell & BMS algorithms Modeling
02-Nov-2022

2 | Integrated Simulation Technologies Pvt. Ltd. | 06-Apr-2020 |
Content
 Battery Technical Specification
 BMS Function
 MATLAB Script Introduction
 Simulink blocks used
 Modeling Introduction
 Equivalent Circuit modeling
 Nomenclature
 BMS Model Flow chart
 BMS NMC Cell Model
 Discharge Results
 Charge Results

Li-ion cell & BMS modeling
Motivation, Objective and Task
Motivation:
To develop Battery Management System Algorithm for single Li-ion cell using
MATLAB Simulink. To monitoring the battery parameter.
 Over voltage protection.
 Under Voltage protection.
 Charging and Discharging management.
 Cell temperature.
 Monitoring.
Objective: Modeling li ion cell & BMS Modeling and analyzing battery parameters
 MATLAB Script.
 Cell model in Simulink.
 BMS model in Simulink.
Task:

Li ion cell and BMS Modeling
Battery Technical Specification (1/5)
 Cell, modules, and packs –
 Hybrid and electric vehicles have a high voltage battery pack that consists of individual modules and cells organized
in series and parallel.
 A cell is the smallest, packaged form a battery can take and is generally on the order of one to six volts.
 A module consists of several cells generally connected in either series or parallel. A battery pack is then assembled
by connecting modules together, again either in series or parallel.
 C- Rate –
 In describing batteries, discharge current is often expressed as a C-rate in order to normalize against battery
capacity, which is often very different between batteries.
 A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity.
 A 1C rate means that the discharge current will discharge the entire battery in 1 hour.
 For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of 100 Amps. A 5C rate for this
battery would be 500 Amps, and a C/2 rate would be 50 Amps.
State of Charge (SOC)(%) –
 An expression of the present battery capacity as a percentage of maximum capacity.
 SOC is generally calculated using current integration to determine the change in battery capacity over time

 Depth of Discharge (DOD) (%) –
 The percentage of battery capacity that has been discharged expressed as a percentage of maximum capacity.
 A discharge to at least 80 % DOD is referred to as a deep discharge.
 Terminal Voltage (V) –
 The voltage between the battery terminals with load applied.
 Terminal voltage varies with SOC and discharge/charge current.
 Internal Resistance -
 The resistance within the battery, generally different for charging and discharging, also dependent on the battery
state of charge. As internal resistance increases, the battery efficiency decreases and thermal stability is reduced as
more of the charging energy is converted into heat.
 Nominal Voltage (V)
 The reported or reference voltage of the battery, also sometimes thought of as the "normal” voltage of the battery.
Battery Technical Specification(2/5)

 Cycle Life (number for a specific DOD)
 The number of discharge-charge cycles the battery can experience before it fails to meet specific performance criteria.
 Cycle life is estimated for specific charge and discharge conditions.
 The actual operating life of the battery is affected by the rate and depth of cycles and by other conditions such as
temperature and humidity.
 The higher the DOD, the lower the cycle life.
 Specific Energy (Wh/kg)
 The nominal battery energy per unit mass, sometimes referred to as the gravimetric energy density.
 Specific energy is a characteristic of the battery chemistry and packaging.
 Along with the energy consumption of the vehicle, it determines the battery weight required to achieve a given electric
range.
Battery technical Specification (4/5)

 Capacity or Nominal Capacity (Ah for a specific C-rate)
 The coulometric capacity, the total Amp-hours available when the battery is discharged at a certain discharge
current (specified as a C-rate) from 100 percent state-of-charge to the cut-off voltage.
 Capacity is calculated by multiplying the discharge current (in Amps) by the discharge time (in hours) and decreases
with increasing C-rate.
 Energy or Nominal Energy (Wh (for a specific C-rate))
 The “energy capacity” of the battery, the total Watt-hours available when the battery is discharged at a certain
discharge current (specified as a C-rate) from 100 percent state-of-charge to the cut-off voltage.
 Energy is calculated by multiplying the discharge power (in Watts) by the discharge time (in hours). Like capacity,
energy decreases with increasing C-rate.
 Cut-off Voltage –
 The minimum allowable voltage. It is this voltage that generally defines the “empty” state of the battery.
Li ion Cell and BMS Algorithms

Li ion cell BMS Modeling
Battey management system (BMS) Function
 Monitoring the Battery pack Voltage
 Current
 Cell Temperature
 Maintain the Safety and reliability of battery.
 To Control the State of Charge.
 For balancing the cell and operating the temperature.
 Need for modeling and battery management system modeling and Simulation
 Immediate evaluations with capability checks
 Observing the behavior of cells.
 Safe and reliable Environment.
 Efficient conduct the transferring the design to the hardware
modeling and battery management system modeling

 Power Density (W/L) –
 The maximum available power per unit volume.
 Specific power is a characteristic of the battery chemistry and packaging.
 It determines the battery size required to achieve a given performance target.
 Maximum Continuous Discharge Current –
 The maximum current at which the battery can be discharged continuously.
 This limit is usually defined by the battery manufacturer in order to prevent excessive discharge rates that would
damage the battery or reduce its capacity.
 Along with the maximum continuous power of the motor, this defines the top sustainable speed and acceleration
of the vehicle.

BMS Function

MATLAB Script
 First run
Cell script &Script.m
 Generate graphical
Reprentation

Simulink Blocks used in Model
1) Scope
2) Multiply divide
3) From workspace
4) Subtraction
5) To workspace
6) Gain
7) GOTO
8) Logical
9) From
10) lookup table
11) Signal builder
12) Subsystem
13) Bus creator
14) Integral
15) Bus selector In and Out Port
16) Relation
17) Constant
18) Addition block
19) Lamp
20) Saturation

Equivalent circuit model (1/3)

Nomenclature (2/3)

Methods to find unknown parameters (3/3)

 Li ion single cell battery Specification used in BMS Modeling.
Initial conditions

BMS Model Flow Chart

Li ion cell and BMS algorithms Modeling
Discharge Model parameters calculation
 State of charge Estimation

State of charge Estimation
SOC(T) = SOC (T-1) +/- Int (Idt/C*3600)

Coulomb counting Method
 The coulomb counting method, also known as ampere hour counting and current integration, is the most common
technique for calculating the SOC.
 This method employs battery current readings mathematically integrated over the usage period to calculate SOC
values given by
SOC(T) = SOC (T-1) +/- Int (Idt/C*3600)
SOC (T-1) = initial State of charge
I = current
C = Capacity
 Equation Charging Case = +
 Equation Discharging Case = -
 The coulomb counting method then calculates the remaining capacity simply by accumulating the charge transferred in
or out of the battery.
 The accuracy of this method resorts primarily to a precise measurement of the battery current and accurate estimation
of the initial SOC.

 With a pre known capacity, which might be memorized or initially estimated by the operating conditions, the
SOC of a battery can be calculated by integrating the charging and discharging currents over the operating
periods.
 However, the releasable charge is always less than the stored charge in the charging and discharging cycle.
 In the equation to find of cell 1-D lookup table is used in which charge capacity are mention. It is multiplied by
3600 and is send to divide block.
 The valve of current is integrated with respect to time and its send to divide block. The valve form the divide
block is will be subtracted form 1 and we get SOC of cell.
.
Coulomb counting Method

Open circuit Voltage Estimation
 The voltage between the battery terminals with no load applied. The open-circuit voltage depends on the battery
state of charge, increasing with state of charge.
OCV = Em (SOC, Temp)
 Open circuit Voltage is the function of SOC and temperature. A 2-D lookup table is taken for in which the
temperature and SOC values are input the output will be based on SOC and Temperature.

Internal resistance R0 And Power loss P0 Estimation(1/3)
 Subsystem model

 Internal resistance = R0
 Discharge voltage = Vd
 Power loss due to R0 = P0
 Internal resistance (R0) of the cell will be calculated using a 2-D lookup table for which SOC and temp are input
the internal Resistance and the value of current will be multiply to get the voltage.
 The power loss will be now be calculated by multiply voltage and the current value.

Internal Resistance (R1) and Power loss (P1) Estimation (1/2)
 Subsystem model

Internal resistance (R1) of the cell will be calculated using a 2-D lookup table for which SOC and temp are input
the internal Resistance (R1) and the value of current@R1 will be multiply to get the voltage at R1 The power loss
will be now be calculated by multiply voltage at R1 and the current at R1 value.
Internal Resistance(R1) and Power loss(P1) Estimation (2/2)

Capacitance Estimation(1/2)
 Subsystem Model

 To estimate the capacitance of the used a 2-D lookup table for which SOC and Temperature are the input.
 And to calculate Discharge Capacitance used SOC and temperature at discharge condition.
Capacitance Estimation(2/2)

Temperature Estimation(1/3)
 Subsystem model

Cell mass = m
Specific heat = Cp
Power loss = P Loss
Cell area = A
Amb Temperature = Tamb
Heat transfer coefficient = h

 Temperature estimation will during discharging.
 The initial cell temperature is measured.
 A subtracted block is used and and final temperature is subtracted from the initial temperature this valve is
multiply heat transfer coefficient and cell area.
 Add block used to add the gain block value and power loss valve the sum is pass to another gain block where
it’s divided by cell mass and Specific heat the valve form gain block is integrated with respect to time and final
cell temperature is calculated this temp is send as feed back to the subtract block at the beginning.

Terminal Voltage Estimation
 Subsystem model

Terminal Voltage Estimation(2/4)

 To Estimation the terminal voltage first calculates discharge voltage at R0 and R1 And its subtracted form the open
circuit voltage.
Vt = Vocv - Vd@R0 - Vd@R1
 Terminal voltage = Vt
 Open circuit voltage = Vocv
 To find Find out discharge voltage at R0 and R1.
Vd@R0 = I@R0*R0
Vd@R1 = I@R1*R
 To find out Current at R0:
 Addition Block to add current at R1 and Current at C1
 To find discharge voltage at C1:
 The current at R1 is subtracted input discharge current and its integrated with respect to time.
 This valve is divided from capacitance (C1) and we get the Vd@C1 value.
Terminal Voltage Estimation(2/4)

State of energy Estimation(1/3)
 Subsystem Model

 State of energy – The ratio of remaining energy to total energy.
Amount of energy at particular time.
SOC(t) = SOE(t0) + Int( Power dt/En)
 Nominal energy of the cell (En) = Nominal cell voltage * nominal cell capacity
 Cell voltage and cell current are multiplied and then divided by (1/3600).
 We get the value of power by doing so the value of power is integrated with respective time to get the value of
remaining energy.
 Initial charge capacity value is multiplied by nominal voltage value of the cell to get the nominal energy of the cell in
Wh.

Discharge BMS Model

Discharge BMS logic

Discharge BMS logic
 There are three input -
 Terminal voltage
 Current
 Temperature
 No fault = 0
 Fault = 1
 Logical operator and logical or gate to is used to check the condition.

 Terminal voltage:
 If terminal voltage is less than or equel to 2.7V the operator returns 1, else 0.
 Cut off voltage = 2.7V
 Terminal voltage = 4.2V
 Discharge current logic –
 Temperature upper limit = 333K
 Temperature lower limit = 253K
 If discharge current is greater than or equal to 300A the Operator returns 1else 0. Or gate is connected to this output
Signal which returns or gate value. The value of this input are taken into another or gate output is taken as discharge
trigger.

Discharge BMS logic
 Feed discharge Current –
 The Switch block is used to determine the feed discharge current the switch condition is taken as not equal to
zero.(not equal to zero).
 The discharge trigger is taken as switch control signal. If the condition is satisfied 0 is taken as the output else
discharge current will be feed discharge current.

BMS NMC MODEL

Discharge BMS Results(1/4)

 Input Current – The in put for current is taken NEDC Drive cycle.
 Input Discharge current – The positive side of the current is filtered using a saturation block and is used in as input
discharge coolant.
 Feed Discharge current
 The current which is drawn by the motor during the current input.
 Open circuit Voltage
 The max OCV of the battery is the voltage at the starting of the cycle when soc is 100% and no load is connected.
We can see the voltage has declared to 2.7 at the end of cycle. We have also set minimum voltage at 2.7.
 Terminal Voltage
 It is the voltage which depends on the load &SOC of the cell. Its started at 4.2 at the start of
 Cycle when cell is at 100% its fluctuation with respective load &SOC by the end of cycle it reached 3.9.

 State of charge –
 Soc was 100% at the start of the cycle and its reached 80% at the end of the cycle.
 State of Energy –
 SOE was at 100% at the start of the cycle and it decrease to 82at the end of the cycle.
 Temperature –
 Temperature of the cell will increase due to exothermic chemical reaction. It was at 253K at the start of the cycle and
increase up to 305K at the end of the cycle.
 Discharge trigger –
 The trigger indicates any fault that overs in a cell when trigger = 1, it means faults is trigger it 0 there is no fault trigger
hence the plot has no fluctuation.
 R0 and R1 –
 They are the internal resistance of the equivalent circuit. The plot R0 is increasing from 8.5*10^ (-3) Ω and
touches 8.77*10^ (-3) at the end of the cycle.
 The plot R1 is difficult from that of R0 because R1is in parallel with a capacity C1.
 The value of start from 1.7*10^ (-3) Ω and touches up to 1.64*10^ (-3) at the end of the cycle.

 Power loss due to R0&R1-
 These are the P-losses at R0&R1. The power loss is larger due to R0.
 It start with 0 Watt at the start of the cycle and it reaches up to 60 watt at one point and reaches 0 watt at the end of the
cycle.
 Since the R0 value is higher the Power loss due to R1 is also higher.
 Power loss due to R1is considerably smaller than power loss due to R0.
 It starts at 0 watt reaches a 3.5 maximum of 3.5 watt and settle down at 1.2 watt at the end of the cycle.
 Capacitance –
 The capacitance C1 is connected in parallel with R1.
 It starts at 2.4*10^4 F and decrease up to 2.1*10^(4) by the end of the cycle it reaches up to 3.7*10^4.
 Total power loss –
 The total power loss of the equivalence circuit is shown here.
 It starts form 0 watt and fluctuation in the same way as of power loss in R0 and reaches 0 again at the end of the cycle.
 Current across R1-
 The value will be 0 at the start of the cycle and it fluctuate with respect to the change in input drive cycle and reaches 27A
at the end of the cycle.

Charge BMS Results

BMS_Modelling_Project_PPT.pptx

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