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Integration of fuel cell Auxiliary Power Units (APUs) into vehicles requires that the vehicle Electronic Control Unit (ECU) communicate with the fuel cell controller using appropriate protocol. The common communication standard used in automotive systems is the CAN protocol. Some fuel cell controllers originate from stationary power scenarios and communicate using process industry communication protocols such as MODBUS. This paper reviews the MODBUS TCP protocol and CAN protocol. It then describes the MODBUS TCP software driver development for QNX Real Time Operating System (RTOS) used in the SwRI® Rapid Prototyping Electronic Control System (RPECS). The architecture of the communication system on the vehicle and details of RPECS needed to understand the MODBUS drivers are described. Tools such as RPECS™ and EtherPeek™ (TCP/IP packet sniffing software) used during debugging are also briefly described. A new mapping method for conversion between MODBUS and CAN protocols is proposed.

This paper describes installation and testing of electrified engine accessories and fuel cell auxiliary power units for a Class-8 tractor. A 2.4 kW fuel cell APU (Auxiliary Power Unit) has been added to supply a 42 V power supply for electrification of air conditioning and water pump systems. A 42/12 V dual alternator was used to replace the OEM alternator to provide safety back-up in case of fuel cell failure. A QNX Real Time Operating System-based (RTOS) Rapid Prototype Electronic Control System (RPECS™), developed by Southwest Research Institute (SwRI™), is used for supervisory control and coordination between accessories and engine. A Controller Area Network (CAN) interface, from the engine Electronic Control Unit (ECU), and the RS232 interface, from the fuel cell controllers, provide system data and control for RPECS. Custom wiring to the hydrogen, water pump, and air conditioning systems also provide data to RPECS. The water pump system controller is autonomous.