Fuel Cell Controls

The operation of fuel cells has already been described in Section 1.3.5 (Chapter 1). Here, the emphasis will be on the control of these devices. Further research is required to reduce the cost of instruments for all fuel cell systems. For example, a complex fuel cell system can require upward of 100 flow control valves. Even if the cost is only 200 for a typical low-cost commercial valve, this cost can exceed the total cost of alternative electricity generation components by a sizable margin. Transition to high-temperature fuel cells pushes the valve price up as special materials are required, yet low cost is critical for commercial viability and salability of fuel cells if they are ever to move out of the laboratory and into general use. 

Another source of problems are the thermal losses induced by instrumenting a typical high-temperature system. Thermocouple wiring and metallic capillary tubing to pressure and flow transducers can easily double the thermal losses of the system. Therefore, nonmetallic and thermally insulating sensor leads are required at reasonable costs for reliable operation at 1200°C. 

Today s costs of tens of thousands of dollars per point for using such commercial instruments as optical strain gauges and thermometry systems are totally unacceptable. 

It is essential that the cost of the control instrumentation required to operate fuel cells be reduced to the level that car manufacturers are paying for their sensors and controllers. This is essential to the commercialization of the current generation of fuel cell technology. The reduction in price must also be matched with several orders of magnitude improvement in reliability. 

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In some of the alternative energy processes, such as in fuel cell control and optimization, where the fuel gas is generated by wastewater digesters or garbage dumps, odor can indicate both the type and the concentration of these gases. These concentrations can be in the parts per billion (ppb) and parts per trillion (ppt) ranges, so extremely sensitive detectors are needed to measure them. 

The fuel cell system is controlled by a so called fuel cell control unit (FCU) in which all the algorithms are implemented. The fuel cell system controller communicates with the vehicle controller via a CAN interface and controls aU the high dynamic processes to feed the proper amount of hydrogen and air. In additimi the FCU controls all the processes like for example the start-up and the shut-down procedure and the overall water management. 

For controlling fuel-cell hybrid systems, two different types of controllers are used a fuel-cell controller and a DC- DC controller. An example of a control structure is shown in Figure 36.10. The first controller is used to control the air and fuel supply... 

Suh, K.W. and Stefanopoulou, A. (2005) Coordination of converter and fuel cell controllers. Presented at the 13th Mediterranean Conference on Control and Automation, Limassol, Cyprus, June 2005. 

Finally, a topic that has to be addressed more intensively is the link between operational aspects of fuel cells and the stability of the bipolar plates. With intelligent fuel cell control many degradation mechanisms can be avoided, but real guidelines for system-developing companies rarely exist. 

Dynamic Simulation and Fuel Cell Control System... 

Fuel cell control options with feed-forward and feedback configurations using a look-up table,... 

Rgab, O., D. L. Yu and J. B. Gomm. Polymer electrolyte membrane fuel cell control with feed-forward and feedback strategy. International Journal of Engineering, Science and Technology 2(10) 56-66, 2010. 

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