05
Designing the Next Generation of Battery Management Systems for Transport Applications
Tom Bruen
Objectives
BMS considerations
WMG, University of Warwick
a) Assess the various cell imbalance factors
• Nonlinear cell dynamics
b) Investigate and analyse cell balancing techniques
• SOC not directly
BMS Criteria
c) Develop control algorithms for cell balancing
• Reliability
• Complexity
• Balancing Time
e) Specify HW and SW for a production BMS
• Cost
• Flexibility
• Efficiency
Project scope
• Electric city car through to hybrid SUV
• EV, HEV, PHEV applications
resistor to prevent
• Various drive cycles/ usage conditions
overcharging cell
• Battery pack configurations
• Balancing series and parallel cells
• Simple
• Ideally, all cells would be at the
same SOC at any point
• Excess energy utilised
Method
• Greater level of control
Resistive
Inductive
Topology
Cell Bypass
through cell balancing
CATAPULT Conference
International Digital Laboratory
14th Nov. 2013
Transformer
Cell Bypass
Cell-cell
Cell-pack
Pack-cell
Cell-packcell
• HW/ SW complexity
• Efficiency
Imbalance occurs through variability in characteristics.
Accounting for characteristics in the cell model is also essential for accurate monitoring and control.
Characteristics are a function of:
• Impedance
• Temperature
• This reduction can be achieved
Shunting
Cell Characteristics
• Pack (dis)charging is limited by the
more energy throughput
Capacitive
• Wasted energy
• Capacity
• Reducing SOC variation allows for
Shift charge between cells
to minimise imbalance
• In reality SOCs and capacities vary
weakest cell
switching
drive cycles
Active
Why cells require balancing
single charge
• Irregular, unpredictable
Passive
• Cheap
• Thermal management
• Aim to get maximum range from a
• EMC for high frequency
Cell Balancing Techniques
Bypass current through
• Several types of cell chemistry
tuning
observable
d) Validate system using desktop and HIL simulations
• Calibration and model
• Self-discharge rate
• Age
• SOC
• Current draw
• Form Factor
Contact address: c.m.shepherd@warwick.ac.uk