Single-Delta Bridge-Cell Converter With Single Single-Phase Medium-Frequency Transformer Capable of Active Power Control

Abstract

A modular multilevel cascade converter based on single-delta bridge cells, hereinafter referred to as the single-delta bridge-cell (SDBC) converter, is a prospective power converter for a static synchronous compensator intended for voltage regulation and stability improvement of electric power systems. However, the SDBC converter cannot exchange nonzero active power with the three-phase ac mains unless energy storage elements such as batteries are connected to the dc side of each bridge cell. This article presents a dc/1φ/3φ power converter that combines the SDBC converter with a single-phase converter via a single-phase medium-frequency transformer with an operating frequency of 150 Hz. It can control the active power of 37% of the rated reactive power between the dc source and three-phase ac mains, thus enhancing voltage regulation and stability improvement. The operating principles and control method are first discussed, followed by a description of experiments using a downscaled 110-V, 5-kVA model.