Analysis of non-minimum phase behavior of PEM fuel cell membrane humidification systems

A model for the transient behavior of a membrane humidifier for PEM fuel cells is developed. This humidifier uses the exhaust fuel cell cooling water to humidify the dry inlet air. This model is based on thermodynamic principles and captures temperature, relative humidity and flow variables of the humidifier. Dynamic simulations show that the humidification system exhibits a non-minimum phase behavior with one zero located in the right half plane. The physical reason why such a non-minimum phase zero exists is explained. The effects of the humidifier design parameters on the non-minimum phase zero location are studied and discussed.