Control strategy of switching regulators for fuel‐cell power applications

It is often assumed that the input voltage source of a switch‐mode power supply is constant or shows negligible small variations. However, the last assumption is no longer valid when a fuel‐cell stack is used as input source. A fuel‐cell stack is characterised by low and unregulated DC output voltage, in addition, this voltage decreases in a non‐linear fashion when the demanded current increases; henceforth, a suitable controller is required to cope the aforementioned issues. In this study, an average current‐mode controller is designed using a combined model for a fuel‐cell stack and a boost converter; moreover, a selection procedure for the controller gains ensuring system stability and output voltage regulation is developed. The proposed energy system uses a fuel‐cell power module (polymer electrolyte membrane fuel cells) and a boost converter delivering a power of 900 W. Experimental results confirm the proposed controller performance for output voltage regulation via closed‐loop gain measurements and step load changes. In addition, a comparison between open‐ and closed‐loop measurements is made, where the controller robustness is tested for large load variations and fuel‐cell stack output voltage changes as well.