A Novel Topology for Solar PV Inverter Based on an LLC Resonant Converter With Optimal Frequency and Phase-Shift Control


ALTIN N., ÖZDEMİR Ş., Khayamy M., Nasiri A.

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, vol.58, no.4, pp.5042-5054, 2022 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 58 Issue: 4
  • Publication Date: 2022
  • Doi Number: 10.1109/tia.2022.3163372
  • Journal Name: IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Aerospace Database, Applied Science & Technology Source, Business Source Elite, Business Source Premier, Communication Abstracts, Compendex, Computer & Applied Sciences, INSPEC, Metadex, Civil Engineering Abstracts
  • Page Numbers: pp.5042-5054
  • Keywords: Combinedmodulation, Lagrange multiplier, LLC resonant converter, medium voltage (MV), solar inverter, DC-DC CONVERTER, DESIGN METHODOLOGY, BATTERY CHARGER, IMPLEMENTATION, OPTIMIZATION, TRANSFORMER
  • Gazi University Affiliated: Yes

Abstract

In this article, a new topology for a grid-connected solar photovoltaic inverter for the direct connection to the medium-voltage grid is proposed. This topology employs an LLC resonant converter with a high-frequency (HF) isolation transformer in the dc-dc stage. The output of the dc-dc stage is a rectified sine wave voltage and current at the line frequency. An unfolder inverter interfaces between this dc stage and the grid. A combined phase-shift and frequency control method is used to control the LLC resonant converter. The phase-shift angle and switching frequency values of the LLC resonant converter are regulated to track the reference current signal for the whole operation range. The Lagrange multiplier method is applied to find the optimal trajectory to calculate the optimal phase-shift angle and switching frequency pairs for any operation condition by considering power converter and HF transformer losses to achieve the highest efficiency at a varying current. The transformer leakage and magnetization inductances are properly designed to provide a zero-voltage switching (ZVS) for a wide operation area, and additional resonant inductor requirement is removed. The LLC converter operates in a ZVS region except in a narrow band around the zero-current crossings of the inverter output. Using an HF transformer in the LLC resonant converter, a bulky line frequency transformer requirement is eliminated, and thus, a more compact and efficient design is obtained. The proposed topology is validated by the simulation and experimental results.