BMS

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BMS Hardware/Software for Battery-Powered Vehicle
2023. 10. 02.
Asst. Prof. Mazhar Abbas
CEME
National University
whdgns0422@cnu.ac.kr
[TEKNOFEST 2024] BMS System

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Contents
 Introduction
 Configuration of the BMS
 Hardware
 Software
 Technologies trend and issue
 Advanced HW / SW
 Research issue
 Conclusion

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1 Configuration of the BMS

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BMS: Hardware-Cell, module/pack levels
 Cells
 smallest individual electrochemical unit: primary and secondary cells
 Batteries and battery packs
 made up from groups of cells
 cells can be wired together in series, in parallel, or in some combination of both

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Components of an electrochemical cell
 Electrochemical cells have the same components
 Negative and positive electrodes
 Electrolyte
 Separator
 Current collectors
a) Core of a prismatic lithium-ion battery with planar electrodes
b) Schematic of a cell assembly in the battery
Cylindrical
Pouch

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Specific energy and energy density
 Specific energy: maximum stored energy per unit weight
 Energy density: maximum stored energy per unit volume
 For a given weight, higher specific energy stores more energy
 For a given storage capacity, higher specific energy cells are lighter
 For a given volume, higher energy density stores more energy
 For a given storage capacity, higher energy density cells are smaller
 Lithium ion has higher energy density and specific energy

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Charge and discharge process
 During discharge:
 Li exits the surface of the negative-electrode particles,
 Gives up an electron, becoming Li in the electrolyte
 During charge:
 Li exits surface of positive electrode particles,
 Gives up an electron, becoming Li in the electrolyte
Schematic of the structure and working mechanism of lithium-ion batteries

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Cell nominal voltage and capacity
 Cell (nominal) voltage
 Nickel-based cells: 1.2 V (e.g., NiCad, NiMH)
 Lithium-based cells: over 3 V
 Cell (nominal) capacity
 the quantity of charge, (Ah) or (mAh)
 C rate:
 relative measure of cell electrical current
 20 Ah cell deliver 20 A (“1C”) for 1 h or 2 A (“C/10”) for about 10 h
Discharge curve at different C-rates 18650 Battery Capacity Chart

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CC/CV and CP/CV charging modes
 Cells are often first charged with either:
 constant-current (CC) or constant-power (CP)
 When maximum permitted cell voltage is reached:
 cell is held constant voltage (CV) until it is fully charged
Master BMS

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BMS functionality
Battery management system key functions
Battery
Management
System
Voltage and Current
Measurement Unit
Man-machine
Interface Module
Temperature Control
Unit
Global Clock Module
General Analogue &
Digital Inputs
Accelerating pedals
Brake pedals
Heating/Cooling
system
Voltage/Current
sensor
Safety Unit
Charging System
Unit
Balancing Control
Module
Communication
Module
Internal Power
Supply Module
General Digital
Outputs
SOC/SOH/
Failure alarm
Calibration Channel
CAN
Active/Passive
balancing
Fuse, Contactor,
Circuit breaker

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BMS architecture
 Modular battery pack suggests a hierarchical master–slave BMS
 BMS master:
 Control contactors that connect battery to load
 Monitor pack current, isolation
 Communicate with BMS slaves
 Communicate with host-application controller
 Control thermal-management
 BMS slave:
 Measure voltage of every cell within the module
 Monitor temperatures
 Balance energy stored in every cell
 Communicate every information of each cell to the
master

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BMS design requirements
 Battery-pack sensing: Voltage
 Voltage is measured using an analog-to-digital converter (ADC)
 Special chipsets: aid high-voltage BMS design and high-capacity battery packs
 Battery-pack sensing: Temperature
 To measure temperature, must convert into a voltage signal
 Can use thermocouple with amplifier, or thermistor plus voltage-divider circuit
Thermocouple-amplifier circuit Thermistor-voltage divider circuit
Analog-to-digital converter
Chipset

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BMS design requirements
 Battery-pack sensing: Current
 Shunt current sensor
 Hall-effect sensor
 Control battery-pack temperature
 Lithium-ion cells maintain operating temperature band, 10 ℃ to 40 ℃
 Air cooling may be sufficient, especially for EV (low rates)
 Liquid cooling for some aggressive P/HEV applications
Shunt current sensor
Hall-effect sensor
Air Cooler Battery Thermal Management
System (Toyota Prius)
Battery-pack with liquid cooling system

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BMS Software: Diagnostics
 Detect and log external failures that impact battery
 Detect and log internal failures that impact battery
 Monitor battery status due to normal degradation processes
Internal and external failures of a battery Battery status monitoring

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BMS state estimation techniques
Battery state-of-charge (SOC)
estimation
Battery state-of-energy (SOC)
estimation

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BMS state estimation techniques
Battery state-of-health (SOH)
estimation
Battery state-of-power (SOP)
estimation

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BMS state estimation techniques
Battery state-of-temperature (SOT)
estimation
Battery state-of-safety (SOS)
estimation

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Multi-timescale nature of battery critical states
Current
Voltage
Ambient
temperature

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Future trends of state estimation for BMS