Technique for Mitigating Voltage Ripple of DC-Link Capacitors in a Three-Level NPC Utilizing a Zigzag Transformer

In neutral point clamped (NPC) converters, the voltage ripples in each DC link capacitor are mainly influenced by the 3rd harmonic component in the neutral point of the 3-level NPC converter. These low-order harmonic voltage ripples distort the output of the converter and compromise system stability. Moreover, as the converter's output increases, the capacitor's ripple component escalates correspondingly, necessitating capacitors with a higher capacitance to maintain the reliability of the NPC converter. In this paper, a novel technique is introduced that is designed to mitigate voltage ripples in the DC link capacitor of 3-level NPC converters. By employing a zigzag transformer, the method effectively compensates for the 3rd harmonic component of the voltage in the DC link, resulting in a significant reduction of ripple. The validity and effectiveness of the proposed method are corroborated through comprehensive simulations and experiments.