iTCM-Operated Three-Phase Three-Wire Voltage-Source Converter System Featuring Capacitor-Split Virtual Ground Connection

Journal article (2024)

Authors

Gang Zhang University of Twente
Y. Wu DC systems, Energy conversion & Storage - EEMCS
Junzhong Xu Shanghai Jiao Tong University, Ministry of Education, Shanghai
Thiago Batista Soeiro University of Twente
Research Group
DC systems, Energy conversion & Storage (EEMCS) (TU Delft)
Power Factor Correction Voltage Source Converter Bidirectional Rectifier Integrated Triangular Current Mode Zero Voltage Switching
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Published Date

2024

Language

English

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Faculty

Electrical Engineering, Mathematics and Computer Science

Department

Electrical Sustainable Energy

Research Group

DC systems, Energy conversion & Storage

Abstract

High efficiency can be achieved in grid-connected converters by implementing a zero-voltage switching mechanism, such as the integrated triangular current mode (iTCM) modulation, which reduces the switching losses in the semiconductors. The iTCM can be readily adapted to a three-phase three-wire voltage-source converter (VSC) with the help of virtual ground (VG), which decouples the operation of three-phase switching cells. However, conventional methods of VG have all the zero-sequence currents flowing through the dc-link capacitors, resulting in an increase in the rms current, hence, extra loss for those passive components. This article, thus, introduces a capacitor-split VG topology that can relieve this issue by excluding the dc-link capacitors from the circulating path of the main zero-sequence currents, helping to reduce current stress for the dc-link capacitors. This topology is characterized by its filter capacitors being split into two halves and connected to the top and the bottom dc rails, respectively. Herein, the working principles of the proposed iTCM-operated three-phase three-wire VSC are comprehensively explained, and a detailed design guideline for the LC branch and LCL filter is offered. Analytical models for component stresses and the reverse current waveform have been developed and corroborated through PLECS simulations. A 3-kW, heatsink-less VSC system was constructed and tested, confirming both the system's effective functionality and the enhanced power efficiency of the proposed capacitor-split VG connection. Therein, the studied system demonstrated a significant efficiency improvement, ranging from 0.51% to 2% across the entire operating power spectrum, as compared to the conventional VG connection in iTCM-operated VSCs.