Contactor Control #
The battery management system (BMS) controls the set of internal high-voltage contactors [HIGH VOLTAGE CONTACTORS MISSING LINK] (High Voltage Contactors) through which the power is delivered to connected loads. The battery pack has no direct control over the amount of power it delivers. The battery system relies on the vehicle control unit (VCU) to control load demand and stay within the safe operating limits. If the limitations are not observed, faults may be triggered and, in extreme cases, contactors opened during operation.
The BMS carries out contactor diagnostics before and during the power-up and power-down operations, and reports the status to the VCU. The BMS also monitors the health of the contactors based on the weighted running counter make/break current and potential across the contactors.
Pre-Charge #
Hibernium® battery packs are equipped with a pre-charge functionality, that enables safe connection of the battery pack to load. The BMS controls the pre-charge contactor and pre-charge process automatically. Please refer to the High Voltage Pre-Charge page for more information.
High-voltage interlock loop (HVIL) monitoring #
In order to prevent high voltage DC arcing, all high voltage connectors contain HVIL sense pins. The purpose of these sense pine is to create a HVIL. This loop is a break-first connection that will signal to the BMS that a connector or service disconnect has been removed before the actual power contacts are broken. This enables the BMS to request the VCU to immediately remove all electrical load on the system in advance of an emergency shutdown procedure.
Refer to the HVIL page for more information.
State Of Charge (SOC) calculation #
The Coulomb counting method is used to update cell minimum, maximum and average SOC during runtime.
The Pack SOC to VCU is Cell Max SOC, if Cell Max SOC > 90%. Pack SOC to VCU is Cell Min SOC, if the Cell Min SOC < 10%. Otherwise, Cell Average SOC is used.
The BMS reports below faults to VCU on CAN in case the cell is over charged or over discharged.
State Of Health (SOH) estimation #
SOH is calculated using capacity correction map for the actual pack current throughput.
Isolation monitoring #
Isolation measurements are conducted between both the HV+ pole to Chassis and the HV- pole to Chassis. The actual value of Isolation resistance at which an Isolation Error is flagged depends on the Pack Voltage, with an error flagged before the isolation resistance reaches the minimum error threshold of 750 Ohm/V where Voltage ‘V’ is the maximum Pack Voltage.
The absolute minimum isolation resistance error threshold is 400 kOhm.
The valid resistance range is 200 kOhm (below 200 kΩ considered as 0 ohm) to 12 MOhm (above 12 MOhm considered as 12 MOhm).
If needed, Isolation Leakage Monitoring function can be disabled with a CANSignal VCU_Cmd:: VCU_ISODisableCmd.
It is recommended to have only one component per High Voltage (HV) system to check the isolation or else multiple components could raise false alarms due to overlapping Isolation resistance circuit(s).
Temperature monitoring #
The BMS continuously monitors the cell temperature and reports any alarms and faults detected.
The temperature is measured with a frequency of 1Hz at four cells on the outlet side of each module that correspond to the cells at the end of the cooling/heating duct. These cells represent the highest cell temperatures in cooling mode and the lowest cell temperatures in heating mode.
The BMS requests the VCU to start heating when then mininum temperature is below 15°C and to stop heating if the minimum temperature reaches 20°C.
The BMS requests the VCU to start cooling when then maximum temperature reaches 28°C and stops cooling if the max temperature decreases to 25°C.
When no cooling or heating is requested, it is recommended to run the coolant at a low flow rate with the water temperature target set to 20°C.
Cell Voltage monitoring #
The BMS continuously (every 100msec) monitors the cell voltage and reports any alarms and faults detected.
- The BMS reports below warning and error faults to the VCU on the CAN in case the cell voltage approaches or operates in unsafe zone.
- For details on fault criteria and reaction, refer to the Faults page.
Pack Voltage monitoring #
The BMS continuously (every 100ms) monitors the pack voltage and thus ensures the operation of the pack in a safe zone.
- The BMS reports below warning and error faults to the VCU on the CAN in case the pack voltage approaches or operates in an unsafe zone.
- For details on fault criteria and reaction, refer to the Faults page.
Cell balancing #
Cell balancing (CB) occurs only when the BMS is in an active state and when cell voltage is above 3.2V to avoid over-discharge. CB starts when cell voltage difference is higher than 25mV and stops when the difference drops to below 10mv. CB will pause if there are any critical faults. Refer to Faults and Fault list reaction information for more information.
CAN BUS-OFF Recovery #
If CAN1 or CAN3 gets BUS-OFF due to any reason (eg: wrong connections, EMI etc), the BMS will try to recover the CAN network by reinitializing the CAN chip firstly in 100ms. If it persists, re-initialization happens every 3s. On recovery, the confirmation time is 500ms.
The status of the CAN1 & 3 BUS is sent on CAN signal BMS_Sts::BMS_CAN1_BusSts and BMS_Sts::BMS_CAN3_BusSts respectively.
