Control-Oriented Modeling of Purging Process and Cold Start of Proton-Exchange Membrane Fuel Cell

Abstract

The main purpose of the shutdown purge is to reduce the residual moisture inside the stack and improve the water storage capacity in the cold start process and thereby reduce icing damage. First, by establishing a fuel cell purging model integrated with a high-frequency impedance module, the relationship between the initial water content of the fuel cell stack, purging time, and gas temperature was qualitatively analyzed. Second, a constant flow shutdown purging control strategy for fuel cell stacks for vehicles was designed based on the simplified and practical purging model. Purging experiments showed that the humidity of the intake air mainly affected the degree of final purging and drying, and the initial moisture content mainly affected the total time required for purging and drying. The constant flow purging strategy adopted map-based control, which is relatively simple and can be easily controlled in real time within the specified purging time limit. After purging, the stack started successfully in the range of −10°C because the water still existed in the form of supercooled water. However, when the temperature reached −20°C, the large amount of ice hindered gas transmission, which resulted in a failure of start-up. Cyclic voltammetry results show that the freezing of supercooled water will reduce the electrochemically active area by about 5% after four cycles.