Effects of DC-Link Capacitance on Output Voltage Quality and Power Delivery in a Three-Phase Diode Rectifier

Abstract

This study investigates the effects of DC-link capacitance on output voltage quality and load power delivery in a three-phase diode rectifier circuit. A MATLAB/Simulink model using Simscape Electrical was developed, consisting of a balanced three-phase AC source, a diode bridge rectifier, a DC-link capacitor with equivalent series resistance, and a 20 Ω resistive load. Four capacitance values, namely 470 µF, 1000 µF, 2200 µF, and 22000 µF, were evaluated under identical operating conditions. The DC-link voltage and load current were recorded to analyze the start-up response, steady-state voltage ripple, average DC-link voltage, average load power, and power fluctuation. The results show that increasing capacitance substantially improved voltage quality. The peak-to-peak voltage ripple decreased from 3.75 V at 470 µF to 0.13 V at 22000 µF, while the ripple percentage decreased from 12.75% to 0.42%. The average DC-link voltage increased from 29.39 V to 31.25 V. In addition, the average load power increased from 43.25 W to 48.83 W, whereas the peak-to-peak power fluctuation decreased from 11.28 W to 0.41 W. The results indicate that larger DC-link capacitance mainly improves output-voltage and load-power stability, while the improvement in average voltage and power becomes smaller at very high capacitance values.