The purpose of the Voltage Monitoring System (VMS) is to measure the individual voltage of a cell, or a group of cells of a fuel cell stack. A single VMS-module can monitor 40 voltages within a maximum input voltage range of 150 Volt DC. VMS-modules can be placed in series; a total voltage range of 500 Volt DC (optionally >500 Volt DC) is thereby covered. A group of cells may consist of maximum 4 cells (depends on gain setting ADC of VMS-board).
Each VMS-module contains a microprocessor, which measures and checks the 40 voltages with a sample rate of 2 samples per second. In case one of the voltages is out of a safe range a relay contact is opened which can be used to control or shut down the fuel processor, or disconnect the fuel cell stack from the load i.e. the power consumer.
The system contains a CAN-interface via which a master-control unit is able to communicate which each individual VMS-board. The master is able read the individual cell voltages in real time, and is also able to set the alarm levels. The functionality of the VMS-module can be adapted by reprogramming the on-board microprocessor.
See also: ECN-TS&C - Fuel cell voltage monitoring system