Control And Monitoring

Extensive efforts were directed towards developing a comprehensive controls system which would successfully initiate and operate the fuel cell system. Particular attention was paid to the monitoring and shutdown capability of the controls system. The result is an inherently safe vehicle, which is simply operated.

A microprocessor based controller, manufactured by Digitronics Sixnet, was chosen as the controls hardware. The main board is complemented by a 16-channel isolated analog input board, as well as two 8-channel digital I/O boards and RTUview, a user interface consisting of an integral keyboard and display unit. The controller is programmable in C, but many of the operating parameters of the vehicle are accessible through the user interface.

The controller monitors data such as reactant temperature and pressure, cooling water temperature, cell voltage and stack current. Using this data, functions such as initiating air compressor startup, engaging the fuel cell contactor and cooling fans, and shutting down the fuel cell system are accomplished. Any shutdown not initiated by the operator is recorded in controller memory, and the reason for shutdown is displayed on the user interface.

Aside from the stacks themselves, the critical difference between the hydrogen/air systems of the Green Car and the Gatorâ„¢ lies in the respective air compressor operating strategies. The Green Car delivered a constant flow rate of air to the fuel cell stacks, whereas the Gatorâ„¢ utilizes a more efficient strategy of varying the air flow to suit the imposed load. This is achieved by linking the compressor motor and traction motor potentiometers to the accelerator pedal.

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