Theoretical Comparison in Energy-Balancing Capability Between Star- and Delta-Configured Modular Multilevel Cascade Inverters for Utility-Scale Photovoltaic Systems

• Published in: IEEE transactions on power electronics Vol. 31; no. 3; pp. 1980 - 1992
• Main Authors: Sochor, Paul, Akagi, Hirofumi
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-03-2016; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Arrays; Asymmetry; Bridge circuits; Bridges (structures); Cascades; Comparative analysis; DC-DC power converters; delta; Electric currents; Electricity generation; energy balancing; Inductors; Inverters; Modular; Multilevel; Multilevel inverter; Photovoltaic cells; Power generation; Power supply; Solar cells; star; utility-scale grid-tied photovoltaics; Voltage control; multilevel inverter; star; Delta; energy balancing; utility-scale grid-tied photovoltaics
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2015.2442261

This paper provides a theoretical discussion and comparison in energy balancing between a modular multilevel cascade inverter based on single-star bridge cells (SSBC) and that on single-delta bridge cells (SDBC). Attention is paid to applications involving asymmetric active-power generation in utility-scale grid-tied photovoltaic systems. Both qualitative and quantitative evaluation metrics to assess the energy-balancing capability are introduced and applied to both SSBC and SDBC inverters. As for the SSBC inverter, six zero-sequence voltage waveforms with different harmonic content enabling enhanced energy-balancing capability are analyzed and compared regarding their effectiveness. This paper also emphasizes on the SDBC as an alternative to the SSBC and highlights its superior operating characteristics under asymmetric active-power generation.