Download EVS-09-04e

Battery Charging Safety
1. Objective:
The objective is to evaluate the Battery Management System (BMS) response to failure modes during
charging. The focus of this safety performance area and proposed test procedure is on system level
failure modes associated with DC fast charging. The SAE J1772 combination connector configuration
was used as the basis of this test development acknowledging that similar test procedures will be
required to be developed for other battery/charging system configurations BMS interfaces and charging
conditions including A/C charging and hybrid system controllers.
2.
Risk areas and Safety needs:
Twenty four REESS Design Failure Modes and Effects Analysis (DFMEA) were reviewed and analyzed to
generate a list of safety risk areas that the BMS might experience during charging. This analysis
identified 5 general areas to which safety risks can occur before, during, and after DC charging. These
areas include: System Grounding, 12V BMS Network Control, High Voltage, Environmental Effects, and
Operational Disturbances. Eighteen specific test components were developed to test fault conditions in
these areas. Failure in any of these areas can result in electrical shock, unintentional system behavior,
and thermal event initiations.
3. Performance Tests and Pass/Fail Criteria:
Tests were developed to simulate each of the 18 fault conditions identified in the DFMEA. The pass/fail
performance criterion under a simulated fault condition is for the vehicle to transition to a safe system
state so as to reduce risk of harm to occupants in and around the vehicle and to the vehicle system.
Below is the list of tests to evaluate BMS and vehicle/charger system response to the 18 fault conditions
through the use of a Breakout Box. A Breakout Box is a device designed for this test which allows the
technician to introduce fault conditions between the vehicle charge coupler and the DC charger. Each
test will require specific settings of the switches on the breakout box.
A) System Grounding
1.
Ground Fault Test: This test determines the response of the BMS to a loss of or a fault
on the ground connection between the vehicle charge port and the charger.
 A ground fault can occur due to contamination (moisture, dust, etc.), an internal
failure of insulation, or breakdown of insulation of cabling due to excess
temperature or abrasion.
2.
Chassis Ground Offset Test: This test determines the response of the vehicle and charger
system to an offset on the ground connection between the vehicle charge port and the
charger.
 The ground between the charge station and the vehicle can become degraded due
to increased resistance due to poor connections or failure of a conductor. This
condition can result in communication stress (signal offset) causing partial or
complete loss of communication.
Test conditions for system grounding are applied both before a charge session is initiated and
during an active charge session.
Pass/Fail Criteria for System Grounding Tests: The vehicle is considered to pass the system
grounding tests when the charge session is prevented or aborted and the system is brought to
a safe state and a Diagnostic Trouble Code (DTC) is set.
B) Battery Management System (BMS) and 12V Network Control
3.
12V System Over-voltage Test: This test determines the response of the vehicle and
charger system to an overvoltage of the 12V system on the vehicle.
 It is possible for the 12V system on the vehicle to experience an overvoltage due to
faulty DC/DC converter or external jump starting or external charging of the 12V
battery during a DC fast charge.
4.
12V System Under-voltage Test: This test determines the response of the vehicle and
charger system to under voltage of the 12V system on the vehicle.
 This can be due to a faulty DC/DC converter, a loss of connection between the
DC/DC and the 12V battery, a faulty 12V battery or the operator leaving on a high
current draw accessory during a DC fast charge.
5.
12V System Disturbance Test: This test determines the response of the vehicle and
charger system to switching load disturbance of the 12V network during DC fast
charging.
 It is possible that a large 12V load turning on and off, such as a pump, fan, aftermarket system, or jump starting a second car, can cause disturbances in the 12V
system in the vehicle. These fluctuations, if severe enough, may cause different
modules on the vehicle to malfunction during a DC fast charge.
6.
BMS Internal Fault Detection Test: This test determines if a BMS is able to detect safety
relevant internal BMS faults.
 There are a number of internal BMS faults (generally BMS design specific) which
may cause hazardous conditions.
Pass/Fail Criteria for BMS and 12V Network Control Tests: The vehicle is considered to pass
the BMS and 12V Network Control tests if it is able to successfully complete the charge
session or the charging system disconnects bringing the system to a safe state.
C) High Voltage
7.
DC Bus Short Test: This test determines the response of the BMS and vehicle to a DC bus
short in the vehicle charge coupler.
 It is possible for the vehicle charge coupler to have a short circuit due to tampering
with the charge coupler or due to frayed insulation.
8.
DC Bus Held High Test: This test determines the response of the vehicle and DC
charging system to a vehicle DC bus being held high during disconnect, which means
that a potential high voltage is still present at the two charge connector pins.

It is possible that the DC bus is held high after disconnect if the DC bus discharge
that should occur after the charger disconnects from the vehicle is interrupted on
the bus voltage measurement does not match the actual bus voltage during the
initial connection.
Pass/Fail Criteria for the High Voltage Tests: The vehicle is considered to pass the DC Bus
Short test if the charge session does not start and is considered to pass the DC Bus Held High
Test if the charge connector cannot be removed from the vehicle coupler at the end of a
charge session.
D) Unforeseen Environmental Effects
9.
Vehicle Movement Test: This test determines the response of the vehicle and charger
system to vehicle movement during DC fast charging. if the drive away interlocks of the
vehicle system are effective during a DC fast charge.
 The operator of the vehicle could inadvertently try to drive off while the charge is
still connected or the vehicle could roll away during a DC fast charge due to faulty brake
mechanisms or driver error.
10. Vehicle Crash or Bump Test: This test determines the response of the BMS to a slow
speed (low energy) collision during a DC fast charge.
 It is possible that a low speed collision could occur to an actively charging vehicle
during fast charge since such chargers are located in public parking lots.
Pass/fail Criteria for Unforeseen Environmental Effects Tests: The vehicle is considered to pass
these tests if charging is terminated, the vehicle initiates a shutdown, and there are no
exposed energized components or subsystems.
E) Operational Disturbance – Failsafe Performance
11. Charge Operation Disturbance Test: This test determines the response of the
vehicle/charger system to a series of unexpected inputs during a DC fast charge.
 Abnormal actions by the operator can cause unexpected inputs to the vehicle or
charger system during a DC fast charge that could result in unsafe conditions.
12. Charge Connector Control Signal Disturbance Test: This test determines the response of
the vehicle/charge system to control signal disturbances between the vehicle and the
fast charger.
 Control signals such as field ground, CAN communication, pilot, and proximity
signals can degrade due to increased resistance, disturbances from the grid, excess
bus loading, and other conditions. Disturbances in the control signals in the charge
coupler connector can cause loss of control of the charge session and potentially
hazardous conditions.
13. Charge Connector Field Ground Connection Disturbance Test: This test determines the
response of the vehicle/charger system to a disturbance between the vehicle field
ground and the charger field ground connection.

14.
15.
It is possible for the field ground connection between the charger and the vehicle to
experience a disturbance during a DC fast charge due to increased resistance in the
connection, mechanical damage such as a broken wire or worn contact.
Charge Connector HV Connection Disturbance Test: This test determines the response
of the vehicle/charger system to disturbances in the HV connection between the vehicle
and the DC fast charger.
 It is possible for the HV connection between the vehicle and the charger to become
degraded or interrupted during a fast charge due to contamination of the terminals
resulting in increased resistance of the receptacle/plug interface, worn high voltage
contacts, over-temperature of the cable or terminals, or a degraded cable.
Overcharge Test: This test determines the response of the vehicle/charger system to a
simulated overcharge condition.
 It is possible that the DC charger applies more current than is requested by the
vehicle BMS due to communication failure between the vehicle and the charger or a
defective DC power supply in the charger.
Pass/fail criteria for Operational Disturbances Tests: The vehicle is considered to pass the
operational disturbances tests when the charge session is aborted and the system is brought
to a safe state.
The following are tests to evaluate vehicle/charger system response to the remaining 3 of the 18
fault conditions identified in DFMEA. These tests are not part of this proposal at this time. Our
reasons for not including these tests in the proposal are provided separately for each test below.
16.
12V System EMI/EMC Test: This test determines the response of the vehicle/charger
system to electromagnetic disturbances during a DC fast charge.
 Large electromagnetic disturbances during a DC fast charge can affect the low
voltage power system and disturb communication between vehicle components.
Pass/Fail Criteria for 12V System EMI/EMC Test: The vehicle is considered to pass the 12V
EMI/EMC Test if no DTCs are set and the DC charge session ends normally and does not stop
prematurely.
An EMI/EMC test of this magnitude will require more research before concluding this is a
potential safety hazard.
17.
Cooling Heating System Test: This test determines the response of the vehicle/charger
system to degraded or failed thermal management system in the vehicle/charger
system.
 Typically, the RESS needs to be cooled during DC fast charging because there can be
up to 200 A continuous charge current. It is possible that the vehicle’s RESS cooling
system is degraded due to loss of refrigerant, failed actuator, or other conditions
which causes the RESS to overheat during a fast charge.
Pass/Fail Criteria for Cooling Heating System Test: The vehicle is considered to pass the
Cooling Heating System Test if it is able to successfully complete the charge session without
putting the RESS into thermal runaway or the charging system disconnects bringing the
system to a safe state and DTC is set.
A cooling heating system test was not included in the proposal because more research is
required to develop practical test procedures. This test could involve multiple intrusions into
the battery pack as well as the use of triggering mechanisms to initiate a thermal event. More
research is needed to make this test representative of real world conditions and repeatable
and reproducible.
18.
Visual Inspection of Charge Port: The purpose of this inspection is to detect any
incompatibility between the charge plug and the vehicle receptacle.
 It is possible that low quality adapters or unsupported charging type may cause
damage to the connector.
This visual inspection of the charge port was not included in the proposal because a pass/fail
criterion could not be determined.
4. Test Procedures
See Appendix for Test Procedure.
5. U.S. Comment
The U.S. proposes this test procedure as a template for all charging scenarios (DC and AC) because we
understand that safety critical events can occur during charging and must be addressed. The GTR draft
proposes the external short circuit test, overcharge protection test, over-discharge protection test, and
over temperature protection test, which are relatable, but do not address the BMS functionality during
charging.