Modeling and Control of Three-Phase Grid-Connected Power Supply With a Small DC-Link Capacitor for Electrolyzers

Abstract

In this paper, a new feed forward dc-link voltage compensation method is proposed. The target applications are the converters built with diode bridge frontends, small capacitance in the dc-link which feeds a dc/dc converter used for electrolysis. The compensation method can be tuned in a way to minimize the grid side total harmonic distortion (THD) and partial weighted harmonic distortion (PWHD): thus, the converter can comply with the standards with less filtering at the grid side. In order to design the controllers and perform stability analysis, average model has been derived. However, the performance of the proposed control method is a trade-off between the size of the line filter, the value of the line current THD and PWHD, and the amplitude of the load current ripple. The theoretical work has been validated through experiments on a 5 kW dc power supply used for an electrolyzer. In the experiments, the THD of the grid current can be reduced from 30.5% to 29.5% (without filter and including compensation) and 28.5% (with filter and compensation), and the PWHD from 50% to 38.9% by applying the proposed method and also keeping the load current peak-to-peak ripple under 10% of its nominal value.