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Research Papers

A Controllable Membrane-Type Humidifier for Fuel Cell Applications—Part II: Controller Design, Analysis and Implementation

[+] Author and Article Information
Denise A. McKay1

Picker Engineering Program, Smith College, Northampton, MA 01063dmckay@smith.edu

Anna G. Stefanopoulou, Jeffrey Cook

Fuel Cell Control Laboratory, University of Michigan, Ann Arbor, MI 48109

1

Corresponding author.

J. Fuel Cell Sci. Technol 8(1), 011004 (Nov 01, 2010) (12 pages) doi:10.1115/1.4001020 History: Received September 29, 2009; Revised November 17, 2009; Published November 01, 2010; Online November 01, 2010

A membrane-based gas humidification apparatus was employed to actively manage the amount of water vapor entrained in the reactant gas supplied to a fuel cell stack. The humidification system utilizes a gas bypass and a series of heaters to achieve accurate and fast humidity and temperature control. A change in fuel cell load induces a reactant mass flow rate disturbance to this humidification system. If not well regulated, this disturbance creates undesirable condensation and evaporation dynamics, both to the humidification system and the fuel cell stack. Therefore, controllers were devised, tuned, and employed for temperature reference tracking and disturbance rejection. Two heater controller types were explored: on-off (thermostatic) and variable (proportional integral), to examine the ability of the feedback system to achieve the control objectives with minimal hardware and software complexities. The coordination of the heaters and the bypass valve is challenging during fast transients due to the different time scales, the actuator constraints, and the sensor responsiveness.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Overview of the control architecture for the external humidification system. Dashed lines indicate input temperatures to the controller C.

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Figure 2

Humidification system control architecture

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Figure 3

Thermostatic control signal versus temperature error

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Figure 4

Schematic comparing an unshifted versus a shifted relay with hysteresis

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Figure 5

Simulation of the temperature oscillations induced in the nonlinear water circulation system with relay feedback

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Figure 6

Influence of the mixer error bound on the simulated nonlinear mixer outlet temperature limit cycle for a relay feedback system

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Figure 7

Sequential process used to tune the bypass and mixer thermostatic error bounds

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Figure 8

Experimental humidifier air outlet closed loop temperature response to a reference step, comparing PI and thermostatic control

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Figure 9

Experimental bypass air outlet closed loop temperature response to a reference step, comparing PI and thermostatic control

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Figure 10

Experimental mixer air outlet closed loop temperature response to a reference step, comparing PI and thermostatic control

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Figure 11

Mixer gas outlet relative humidity response to a step in the reference temperature, comparing PI and thermostatic control

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Figure 12

Humidifier air outlet temperature response to disturbances using PI control

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Figure 13

Bypass air outlet response to disturbances using PI control

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Figure 14

Mixer outlet response to disturbances using PI control

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