불연속 전압 변조 방법 적용 범위에 따른 태양광 NPC 인버터의 DC-link 커패시터 신뢰성 분석

The voltage modulation method has a significant effect on the performance of 3-level neutral-point clamped (NPC) inverters such as efficiency and output quality. Discontinuous pulse width modulation (DPWM) has been proposed to improve efficiency by reducing the switching loss of power devices. In previous research, the output quality, power loss, and reliability of the power device were considered when the DPWM method was applied. However, the influence of the DPWM on the reliability of DC-link capacitors, one of the reliability-critical components, has not been investigated. In this paper, the effect of DPWM on the reliability of DC-link capacitors is studied in the NPC inverter. Considering the mission profile of the photovoltaic (PV) system, the accumulated damage of DC-link capacitors is analyzed at the component level first under different applied angles of DPWM. The reliability of DC-link capacitors is then evaluated at the system level by considering all capacitors of the NPC inverter. In addition, the current of the DC-link capacitor is analyzed through the experiment to validate the negative effect of the DPWM on the reliability of the DC-link capacitor.