Modelling and control of three-phase grid-connected power supply with small DC-link capacitor for electrolysers

These days electrolyzers are becoming more and more interesting due to the high demand for energy storage in form of hydrogen for renewable power generation using fuel cells. The design of a power supply for such a system is complex especially when the DC-link capacitance is reduced. By substituting the complex switching model of the power supply with a simplified one, the system dynamics can be better observed. The resonances caused by the small DC link capacitor and grid side inductance can be easier analyzed. A feed forward compensation method is proposed based on the simplified model of the system in order to minimize the effects of the DC link voltage ripple on the load voltage and current. The proposed method uses Frequency-Locked Loop (FLL) for estimating the fundamental component of the DC-link voltage ripple. Based on the reconstructed rectifier component a new feed-forward compensation signal is created, canceling in such a way the resonance introduced by the grid inductance and the DC-link capacitor from the feed-forward loop. The theoretical work has been validated through experiments on a 5 kW DC power supply used for electrolyser application.