As the types of loads have been diversified and demand has increased, conventional distribution transformers are difficult to maintain the constant voltage against voltage drop along with distance, grid voltage swell/sag, and various loads. Also, it is hard to control the power flow when connecting renewable energy sources. Active hybrid solid state transformer (AHSST) is application to keep the voltage and power quality. AHSST is a system that combines conventional distribution transformer and converter. Accordingly, it can be applied directly to distribution infrastructure and it has both the advantages of solid state transformer (SST) and conventional transformer. AHSST is capable of active voltage and current control and power factor control. It has a simpler structure than SST and it can perform the same performance with the lower rating converter. This paper presents two stage AHSST system based on multi-level converter. The converter is composed of the back-to-back converter using silicon carbide (SiC) metal-oxide semiconductor field effect transistor (MOSFET). Proposed system has a wider voltage and power flow control range, lower filter size, and simpler control sequence than existing AHSST systems. The performance of the proposed system was verified by prototype system experiments.
A Simplified Voltage Balancing Method Applied to Multi-level H-bridge Converter for Solid State Transformer
