This article presents a dc-link capacitor lifetime improvement method for three-level photovoltaic hybrid active neutral-point clamped inverters in full modulation index range. The capacitors are one of the components with vulnerable reliability in a power conversion system. The dc-link capacitor current ripples lead to temperature rise and wear-out failure of the capacitors. The accumulated thermo-mechanical damages from the temperature rise reduce the capacitor lifetime and reliability of the system. The proposed modulation method suppresses effectively the dc-link capacitor current ripple to improve the capacitor lifetime. In this article, the proposed method is discussed via a comparison with conventional space-vector pulsewidth modulation in full modulation index range. The modulation index range is divided into two regions, namely medium-vector modulation and hybrid modulation region. The capacitor lifetime is evaluated by the capacitor lifetime model according to the modulation methods and modulation regions. The effectiveness of the proposed modulation method is verified through simulation and experimental results.
Manuscript received June 15, 2020; revised August 24, 2020; accepted September 24, 2020. Date of publication September 29, 2020; date of current version January 22, 2021. This work was supported in part by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and in part by the Ministry of Trade, Industry and Energy (MOTIE) of Republic of Korea under Grants 20182410105160 and 20206910100160. Recommended for publication by Associate Editor K. Wada. (Corresponding author: Kyo-Beum Lee.) The authors are with the Department of Electrical and Computer Engineering, Ajou University, Suwon 16499, South Korea (e-mail: yj11004@ajou.ac.kr; smkim@ajou.ac.kr; kyl@ajou.ac.kr).
