Battery Pack Control Module (BPCM)

DESCRIPTION 

Courtesy of CHRYSLER GROUP, LLC

The Battery Pack Control Module (BPCM) is integral to the larger High Voltage Battery. If the BPCM is found to be damaged, ineffective or inoperative, then the High Voltage Battery must be replaced.

Below the access panel are non-serviceable fuses, the service disconnect and the High Voltage System Test Module (HVSTM). The HVSTM is used to test to make sure that the HV system has been powered down and ready for service.

OPERATION 

The BPCM is utilized to provide battery management and system functionality in conjunction with the Cell Supervision Circuits (CSCs) which are also located within the High Voltage Battery Pack. The CSCs monitor and balance the individual battery cells and communicate cell voltage and temperature information to the BPCM via a CAN communication bus internal to the battery pack. The BPCM communicates with the vehicle via CAN-C and various input signals.

The main functions of the BPCM are as follows:

• High voltage bus pre-charge contactor control
• Battery pack current sensing
• Battery Pack voltage sensing
• Isolation breakdown detection between the high voltage system and vehicle chassis
• CAN communication
• Fault detection and reporting
• High Voltage Interlock (HVIL) power source

The BPCM monitors the high voltage battery for the following:

• Min/Max/Avg cell voltages at open circuit and under load and cell identification number
• Min/Max/Avg cell temperatures and cell identification number
• Battery System Voltage and Current
• Inlet/Outlet battery temperatures
• Isolation Detection
• Battery State-of-Health - capacity and resistance
• Battery Conditioning and Overvoltage/Undervoltage

CONTACTORS 

The 12-Volt system, connects and disconnects the high voltage battery from the remainder of the high voltage system through heavy-duty relays called contactors. There is a positive and negative contactor connected to the positive and negative side of the high voltage battery.

There is also a pre-charge contactor to control in-rush current during the pre-charge routine.

These contactors are normally open and must have reliable 12-Volt power to keep them closed. If the 12-Volt supply to the high voltage battery is intermittent, this may cause the contactors to open momentarily and then close. This can cause an arc across the contactor surfaces that can weld closed the contactor. If this happens, the 12-Volt system cannot control the high voltage system and the high voltage system remains energized. Contactor failures set a DTC and illuminate the MIL.

The BPCM can open the contactors for the following reasons:

• The BPCM transmits threshold and max/min allowable values for cell voltage and temperature for which, if exceeded in a calibrated time, the BPCM shall open the contactors.
• The BPCM shall open contactors when component protection limits are being violated.
• The BPCM shall open contactors when an impact has been detected.
• The BPCM shall open contactors when a High Voltage Interlock (HVIL) problem is detected.

PRE-CHARGE COMPONENTS 

Pre-charge components control voltage and current applied to the high voltage system. The initial application of current or in-rush of current, could damage the high voltage system if not controlled. To control the current application, a large resister is used when the high voltage system is initially powered up.

The pre-charge components consist of the pre-charge resister, a pre-charge contactor and the required wiring to connect the components. The negative contactor is used during the pre-charge routine.

To perform the pre-charge routine, the BPCM commands the pre-charge contactor and the negative contactor to close. The pre-charge resistor is in series on the circuit with the pre-charge contactor so this controls the power applied to the high voltage system.

After the pre-charge and negative contactors close and apply partial voltage to the system, the BPCM commands the positive contactor to close. This creates a circuit with very little resistance compared to the pre-charge circuit. After the positive contactor has closed, the BPCM opens the pre-charge contactor. The high voltage system is now fully enabled and ready for operation.

HIGH VOLTAGE INTERLOCK CIRCUIT (HVIL) 

The HVIL circuit helps prevent access to high voltage. The BPCM provides an output current across the HVIL circuit and monitors the return current to verify the integrity of the HVIL circuit. Both the current drivers and return current can be read with the scan tool.

The BPCM contains the current drivers that provide the source current for the HVIL circuit. The HVIL circuit routes in series from the BPCM through the HVIL connectors at the high voltage components.

The BPCM can detect an open circuit, short to ground and short to power failures on the HVIL circuit. A distinct DTC sets for each type of failure.

The HVIL circuit is diagnosed by measuring resistance across segments of the circuit. By measuring segments, the fault is narrowed down to a specific section of the circuit.