PEM fuel cell system power control based on a feedback-linearization approach

Polymer electrolyte membrane (PEM) fuel cell systems are highly efficient energy converters. Besides electrical power, low oxygen concentration cathode exhaust gas, water and heat are the byproducts if fed with pure hydrogen gas. So, this technology has become very attractive for the use on aircraft where it is investigated as replacement for the auxiliary power unit that is currently used for electrical power generation. Hence, controlling the fuel cell system for electrical power is a central topic. The electrical power output, however, is nonlinearly dependent on stack temperature, gas pressure, membrane humidity and stack current that is being drawn. This study deals with the controls of electrical power of an air and hydrogen fed self-powered fuel cell system. For controller design the nonlinear polarization curve is approximated by a linear current-voltage-characteristic. Based on a feedback-linearization approach a nonlinear control law for fuel cell system power is presented and implemented in a nonlinear fuel cell system simulation model. Even though the polarization curve is a linear approximation, the nonlinear control law leads to a fast response and zero steady state error.