Battery management system

A battery management system (BMS) is an electronic system that protects a rechargeable battery (cell or battery pack) from running outside its safe operating area, monitors its state, calculates secondary data, reports that data, controls its surroundings, authenticates it, and/or balances it.

Monitor

A BMS can track the state of the battery using several indicators, such as:

Voltage : Total voltage, individual cell voltages, or periodic tap voltages Temapture : Average temperature, coolant intake temperature, coolant output temperature, or specific cell temperatures
Coolant flow : For air or fluid cooled batteries, coolant flow is important.
Current : the amount of electricity flowing into or out of the battery.

Computation

A BMS may also calculate values based on the items listed above, such as:

Minimum and maximum cell voltages

State of charge (SOC) or depth of discharge (DOD), to show the battery's charge level State of health (SOH), a differently defined measurement of the battery's remaining capacity as a percentage of its original capacity

The amount of power available for a particular time frame given the current power usage, temperature, and other factors is referred to as the state of power (SOP).
Safety Condition (SOS)

As a charge current limit, the maximum charge current is used (CCL)As a discharge current limit, the maximum discharge current (DCL)Energy provided [kWh] since the last charge or charge cycle

A cell's internal impedance (to determine open circuit voltage)
Delivered or stored charge [Ah] (sometimes this feature is called Coulomb counter)
Total amount of energy delivered since the first use
Total amount of time spent in operation since the initial use
Number of cycles in total

Protection

A BMS may protect its battery by preventing it from operating outside its safe operating area, such as:

• Over-current (may be different in charging and discharging modes)
• Over-voltage (during charging), especially important for lead–acid and Li-ion cells
• Under-voltage (during discharging)
• Over-temperature
• Under-temperature
• Over-pressure (NiMH batteries)
• Ground fault or leakage current detection (system monitoring that the high voltage battery is electrically disconnected from any conductive object touchable to use like vehicle body)

The BMS may prevent operation outside the battery's safe operating area by:

• Including an internal switch (such as a relay or solid state device) which is opened if the battery is operated outside its safe operating area
• Requesting the devices to which the battery is connected to reduce or even terminate using the battery.
• Actively controlling the environment, such as through heaters, fans, air conditioning or liquid cooling

MAIN SYSTEM

The model is a battery management system. The controller is the BMS ECU (Battery Management System Electronic Control Unit), and the plant is the Battery Pack with Charger/Load. The output of the battery pack is fed back to the controller, and control signals are sent to the plant. Then we may go over the plant's subsystems.

Plant subsystem

The Precharge circuit connects the battery pack with the charger/load. Because the battery pack is at a higher voltage than the charger/load, when both components are directly connected by the main connector, there will be a high current inrush in the transient phase due to the very high potential difference, which will taper down as the potential on both sides equalise.This large transient current might produce a meltdown at contactors, resulting in the contactors being permanently welded. A parallel Precharge circuit prevents this from happening.And then we can go through the battery pack subsytem

Battery pack subsystem

There are two modules: battery pack 1 module and battery pack 16 module. In this case, we are selecting the battery pack. 1 module, we may then examine the battery pack 1 module's subsystem.

Battery pack 1module

This image shows the battery pack subsystem. The cells make up the cell module subsystem. The Cell Monitoring Unit measures the voltages of individual cells. This subsystem's voltage and current sensors measure the battery pack voltage and current.And we and check the cell module 1TC

Cell Module 1TC

This image shows the Battery Pack module. The cells are linked in a series. The battery block's SOC and thermal port are both enabled. If the SOC of any cell falls below 0.01 percent, the simulation is terminated. Heat is supplied to the battery cells via a thermal source that receives input from the ambient temperature.

Precharge circute

This is the precharge subsystem in the main system in here we can see that.The terminals of the battery are linked to the charger and load terminals. Between the battery and the charger/load lies a filter capacitor. A switch and a resistor control the current flow on either side of the Precharge circuit. A small current flow to the load side is permitted by the precharge circuit. This allows the load side to match the voltage level of the battery pack and avoids high current flow when the contactor is in the on conditon

Charger/load

This is the charger or load subsystem from the main system. We can plainly see that there are two subsystems present, the charger and the load, which are connected and taking the connections out.inside the charger subsystem we can see

Charger

This image shows the charger subsystem. It is made up of a Controlled Current Source, which supplies current to the battery pack and receives input from the BMS ECU.and we can go through the drive load

Drive Load

This image shows the Driver Load subsystem. Using a Controlled Current Source, this subsystem drains the battery. The BMS charge and discharge current limits are used to specify the upper and lower limits of the discharge current prescribed by the Drive Cycle.

BMS ECU subsystem

This is the BMS ECU subsystem, and it contains numerous subsystems such as current power limitations calculation, balancing logic, state machine, and bus management. And then, we can go through all of the subsystems.

Current power limit calc

In this subsystem, there are two discharge current limits and one charge current limit. The cell voltage and temperature are accepted as inputs, and the cell minimum and maximum voltage and temperature are determined using the min and max blocks.

Discharge current limit calc & Current current limit calc

Discharge current limit calc Charge current limit calc

This diagram depicts the Discharge current limit calculating block. As input, the minimum cell voltage and maximum cell temperature are used. The manufacturer's cell specification determines the under cell voltage limit. The cut-off voltage is critical during discharging.The difference between the minimum cell voltage and the cut-off voltage is calculated, and the current limit is derived using the V/R equation. This computed current ensures that the cell does not discharge below the safe depth of discharge. This discharge current limit is communicated to the load, and the battery is discharged in accordance with it.

The charge current limit calculation block works in the same way as the charge current calculation block, but it considers the maximum cell voltage from the manufacturer's specifications and tapers down the current so that the charge current is not sufficient to charge the battery beyond the maximum cell voltage.

State Machine

In this state machine, the current voltage and temperature variables are given as inputs, and the flowchart inside the block is validated, and then only the specific output may be taken out.

Balancing logic

The maximum and minimum cell voltages are taken inside, and the output is taken out by balancing the cells using the flow charge.

SOC estimation

This diagram depicts the SOC calculation block. Battery SOC is calculated using approaches such as the coulomb counting method and the Kalman Filter method.

1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results

Harness dashboard

The Harness Board is represented in the image. On this board, the simulation can be run and the BMS response validated. It mostly features two simulation variants: Variant of the test sequence: Predefined simulation circumstances in which Charging, Driving, and Balancing situations are ordered sequentially for a set amount of time. There are three test sequences, each of which is a one-of-a-kind combination of charging, driving, and balancing.Manual mode: The simulation settings can be changed while the system is running by adjusting the knob between balancing, charging, and driving.

Test 1

for the test we have to double click this block then a window will pop up

then select the test case 1 then press apply

after that we have to double click the BMS state request from the harness dash board

after clicking that a window will pop up

in ther we have to select the BMS test sequence then the subsystem will open up

from this window we can confirm that the test sequence 1 is open know double clicking that we can see the configuration of the test sequence 1

The following conditions are ordered progressively in this test sequence variant:

Driving state: The car is driven for 3000 seconds. During this time, the battery is depleted in accordance with the vehicle's pre-set energy and power requirements.

Balancing state: The battery is in standby mode for the next 1000 seconds. During this time, the BMS is activated in order to balance the cells.

Charging and balancing state: The battery is charged and balanced by the BMS over the next 5000 seconds.

Balancing state: The battery is at rest the remainder of the time, but BMS is actively balancing the cells.

The result

The BMS state plot reveals that the BMS is in driving mode for the first 3000 seconds.
The cell voltage varies with the current drawn from the load, as indicated in the pack current figure.The cell temperature figure demonstrates that the cell temperature,As the battery discharges, the temperature rises from 288 K to greater levels. Because cell 6 is the first to be exposed to ambient heat and cell 1 (yellow line) is the last cell to be exposed to convective heat transfer, cells react to convective heat transfer sequentially from cell 6 to cell 1. As a result, cell 6 heats up faster, while cell 1 heats up slowly.During this driving phase, the battery SOC drops from 80 percent to 70 percent. The charge imbalance between the cells grows as the discharge advances, and various cells end up having differing capacities at the end of the driving phase. The influence of temperature on the cells may be seen. Cells with higher SOC levels have lower SOC levels, while cells with lower SOC levels have higher SOC levels.

Balancing over the next 1000 seconds, as indicated by the BMS state plot During this time, the pack current is zero and the cell voltages are stable at 3.7 V. The temperatures of the cells are somewhat reduced, but the SOC remains constant, indicating that there is no activity.

The BMS state graphic depicts charging from 4000 to 9000 seconds. At 5000 seconds, the cells reach a peak voltage of 4.2 V, and a constant pack current of 30 A is delivered (Constant-Current Charging). When an overvoltage condition occurs while maintaining a fixed maximum voltage, the pack current is shown to taper down gradually and eventually decrease to zero (Constant voltage charging).The temperatures of the cells grow at various rates. Cell 6 reaches 317 K, while cell 1 reaches 303 K. Because cell 1 has a greater charge level, its SOC grows to 100% faster than the other cells. Other cells achieve 93 percent SOC. After cell 1 has been fully charged for 7000 seconds,The charging of the battery comes to a halt.
The BMS state plot indicates that the battery is in standby mode for the remainder of the period. The pack current is zero, and the cell voltages remain constant. Cell SOC is inactive. The cells begin to cool at the same pace.

Test 2

By the harness dash board we want to select the test two

in here we choose the test method 2 and apply

Then we have to go to the bms state request and the bms test sequence and then we can see that

so after that we can see the test sequemce 2 is selected here we have look what are the cinfiguration fot the test 2 so

in here there are two state are there which is Driving state: The battery is depleted for the first 10000 seconds because the vehicle is simulated to be driven.
Charging state: The battery is charged for the remainder of the simulation duration.

Result

This scope window displays the outcome of test 2: The simulation only lasts 8692 seconds. The SOC plot shows that only a few cells reach 100 percent depth of discharge before the driving period ends. As a result, the simulation comes to an end. Because the battery capacity does not allow for a drive period of 10000 seconds, the driving state period is reduced to 7000 seconds in the test sequence editor window.

by changing the driving from the 10000 to the 7000 we can see the result as

The modified test run yielded the following results: BMS state plot confirms driving state for 7000 seconds During this time, cell 6 reaches 315 K and cell 1 reaches 300 K from an initial temperature of 288 K. The cells' SOC falls from 80 percent to a range of 20-25 percent.The BMS status graphic depicts the charging condition from 7000 to about 8000 seconds. The cells' SOC climbs to a range of 40-50 percent. The battery clearly stops charging before the overvoltage situation is reached. Cell 6's temperature rises to 323 K, while cell 1's temperature rises to 305 K.

We can see the harness dash board it shows that

The Harness Board explains why charging was abruptly halted. The indicator: Fault state is on; this means that the BMS encountered a fault condition and had to place the battery in standby mode for safety reasons. The High-Temperature indication is also illuminated, indicating that cell 6 in the battery has reached the maximum allowed temperature.And charging was halted to prevent thermal runaway and allow the battery to cool.

Test 3

we have to choose the test 3 in the test sequence then

here we can see the third sequence is selected here so we can double click it to se the configuration of it

in here we can see there is only one step id going it is charging we can see the result of it

Result

The charging current initially rises to 30 A. Because the battery is already at 80% charge, it cannot be charged with constant current. As a result, by tapering down the current, the charge current transitions to constant volt charging. Since cell 1 is entirely charged and experiences an overvoltage condition, the battery is fully charged in 2000 seconds.

2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?

COULOMB COUNTING: Coulomb counting is used to determine or estimate the battery's current state of charge. In general, a battery's state of charge (SOC) is defined as the ratio of its current capacity (Qt) to its nominal capacity (Qn). The manufacturer specifies the nominal capacity, which is the maximum amount of charge that can be held in the battery.In order to estimate SOC, the Coulomb counting method analyses a battery's discharging current and integrates it over time. The Coulomb counting method is used to calculate the SoC(t), which is calculated using the discharging current, I(t), and previously calculated SOC values, SoC(t-1). The following equation is used to determine

`SOC(t)=(Q(t))/(Qn)`

`SOC(t)=SOC(t-1)+(I(t))/(Qn)*Deltat`

A novel methodology termed modified Coulomb counting method is developed to improve the Coulomb counting method. The corrected current is used in the modified Coulomb counting approach to increase estimation accuracy.
The corrected current is proportional to the discharging current.The corrected current and battery discharge current have a quadratic connection.

In modified Coulomb counting method, SOC is

`SOC(t)=SOC(t-1)+(Ic(t))/(Qn)Deltat`

in this simulink model we can see that inside the soc estimation the coulombs countignwill be there

Working:

The current that is leaving the cell enters the Coulomb counting block. The gain block multiplies the current by (1/3600), effectively converting it from ampere to ampere hour. As we all know, temperature has an effect on current, and this effect is accounted for utilising 1-D equations. Look up the table. The lookup table here does a 1-dimensional interpolated table lookup, including index searches. To make a, use an integrator block.Finally, the divide block characterises the effect of temperature on current. In order to estimate SOC, the Coulomb counting method analyses a battery's discharging current and integrates it over time. The integrator block handles this task. To develop a totally discrete model, the Discrete-Time integrator block is used instead of the Integrator block.