Operation of a dc/1ϕ/3ϕ Power Converter Combining Single-delta Bridge-cells Converter and Single-phase Medium-frequency Transformer

Abstract

A modular multilevel cascade converter based on single-delta bridge cells, hereinafter referred to as an SDBC converter, is a prospective power converter for a STATCOM (STATic synchronous COMpensator) intended for voltage regulation and stability improvement. However, the SDBC converter cannot exchange a non-zero active power with a three-phase ac mains unless energy-storage elements such as batteries are connected to the dc side of each bridge cell. This paper presents a dc/1ϕ/3ϕ power converter combining the SDBC converter and a medium-frequency single-phase transformer with an operating frequency of 150Hz. It is characterized by controlling a non-zero active power between the dc side and the three-phase ac mains via the transformer, contributing to the enhancement of voltage regulation and stability improvement. The operating principles and the control method are discussed in this paper, followed by computer simulations using the “PSCAD/EMTDC” software package and experiments using a 110-V, 10-kVA downscaled model.