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BMS Functionality
1. Objective/Purpose:
The objective is to evaluate the Battery Management System (BMS) response to a variety of failure and abuse conditions
that may be experienced during normal operation of the vehicle and that, if not properly controlled, could lead to
hazardous conditions.
2. Risk areas and Safety needs:
The BMS is one of the most safety critical components in both hybrid and electric vehicle REESS. It manages the vehicle
REESS within its operational boundaries while in use (including during charging) by monitoring the battery’s state,
controlling its environment, and performing other operations. The BMS manages the frequent electrical charging of the
REESS both through external Electric Vehicle Supply Equipment (EVSE) and through regeneration during operation.
Failure of the BMS to control parameters, such as conditions resulting in over-current and over-voltage overcharging,
could lead to dangerous situations for the occupants of the vehicle. Overcharging is generally considered one of the most
hazardous failure modes for lithium-ion REESS and may result in lithium-ion cell thermal runaway. External charging or
in-vehicle charging of the battery in extremely high or low temperature conditions could initiate a temperature and voltage
imbalance, and, if appropriate steps are not taken by the BMS, may lead to thermal runaway. In addition, it has been
recognized that over-discharging could lead to undesirable aging, electrolyte leakage, swelling, or even violent failure, if
not managed. Therefore, it is paramount to ensure that the BMS is up to the task of performing properly, even under
extreme conditions like over-current and over-voltage overcharging, extreme temperature conditions (high and low), and
over-discharge conditions, in order to ensure that the battery, and the vehicle itself, is protected from damage and that
vehicle occupants are not exposed to hazardous conditions.
3. Performance Tests and Pass/Fail Criteria:
In order to evaluate how the BMS responds when avoiding potential abuse conditions during normal operation,
a sequence of tests is performed to simulate fault conditions that are possible during normal operation. The test
procedure is applicable to all REESS-equipped HEV, PHEV, and EV vehicles. In this sequential testing, the
REESS is subjected to the following conditions (in sequence of exposure):
I.
II.
III.
IV.
V.
Over-Discharge (Drive Mode and Charge Mode)
Low Temperature (Failed Heating System Simulation)
High Temperature (Failed Cooling System Simulation)
Over-Current Overcharge
Over-Voltage Overcharge
The above tests, representing commonly experienced single point failure modes, were placed in a sequence so as to reduce
the number of required test articles and to reveal and exacerbate a range of potential failure modes. In direct comparison
to many standard tests, the loads described in the sequential testing for BMS functionality are relatively benign. A
description of each of the tests in the sequence, along with their performance criteria, is presented below.
A. Over-Discharge – Over-discharge may cause damage to cell electrodes, which may compromise the cell safety
and stability during subsequent charge cycles. This test will verify the BMS’s ability to properly shut down the
discharge of cells if they are about to exceed normal operating parameters, as set by the manufacturer.
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DRAFT – DELIBERATIVE
B.
C.
D.
E.
a. Pass/Fail Criteria –
i. BMS should shut down cell discharge before exceeding the manufacturer’s recommended normal
operation range.
Low temperature – This test will verify the BMS’s ability to limit or even prevent operation at temperatures
below the battery cells’ capabilities, as low temperatures (lower than manufacturer set low operating temperature)
can lead to thermal runaway.
a. Pass/Fail Criteria –
i. This test should not result in a hazardous situation.
ii. The temperature of the pack during operation should exceed -40 C. (preliminary consideration)
iii. The BMS must initiate normal charge termination of the battery pack when the manufacturer’s
charging and discharging requirements for the low temperature operating conditions are
exceeded.
High temperature – This test will verify the BMS’s ability to limit or even prevent operation at temperatures
above the battery cells’ capabilities, as high temperatures (higher than manufacturer set high operating
temperature) can lead to thermal runaway.
a. Pass/Fail Criteria –
i. This test should not result in a hazardous situation.
ii. The temperature of the pack during operation should not exceed 70 C. (preliminary consideration)
iii. The BMS must initiate normal charge termination of the battery pack when the manufacturer’s
charging and discharging requirements for the specified high temperature operating conditions
are exceeded.
Over-current overcharging - This test will verify the BMS’s ability to limit or even prevent operation when the
REESS is exposed to over-current overcharging conditions.
a. Pass/Fail Criteria –
i. If the over-current overcharging exceeds the manufacturer’s specified maximum voltage or
overcharging condition, the BMS must initiate the automatic disconnect in the REESS.
ii. The maximum allowable SOC of Li-Ion based REESS shall never exceed 130% of nominal SOC.
Over-voltage overcharging - This test will verify the BMS’s ability to limit or even prevent operation when the
REESS is exposed to over-voltage overcharging situations.
a. Pass/Fail Criteria –
i. If the over-voltage overcharging exceeds the manufacturer’s specified maximum voltage or
overcharging condition, BMS must initiate the automatic disconnect in the RESS.
ii. The maximum allowable SOC of Li-Ion based REESS shall never exceed 130% of the nominal
SOC.
4. Test procedures: See the appendix for test procedures.
a.
b.
c.
d.
For over-voltage overcharging procedure, see section 6.4.6 of the test procedure in the appendix.
For over-current overcharging procedure, see section 6.4.5 of the test procedure in the appendix.
For over-temperature procedure, see section 6.2.10 of the test procedure in the appendix.
For over-discharge procedure, see section 6.2.9 of the test procedure in the appendix.
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