High Frequency Solid State Transformer Design Considerations for Power Systems Applications

Abstract

The conventional power frequency (50 or 60 Hz) transformers are economical, highly reliable and quite efficient but they suffer with certain drawbacks like sensitive to harmonics, voltage drop under load, no protection from system disruptions and overloads, poor performance under dc offset load unbalances and no scope to improve power factor. These transformers with copper wound wires on iron cores are unable to respond to control signals as power generations become distributed and intermittent. So, the need of electronic based regulated power supply with software based remote intelligence has become essential. Also, to easily connect the new energy sources to the grid and to improve the power quality by harmonic filtering, voltage sag correction and highly dynamic control of the power flow, a new type of transformer based on power electronics, known as SST has been introduced. The SST realizes voltage transformation, galvanic isolation, power quality improvements such as instantaneous voltage regulation, voltage sag compensation and power factor correction. It is a collection of high-powered semiconductor components, high frequency power transformer and control circuitry which is used to provide a high level of flexible control to power distribution networks. The SST is a high frequency switched Power Electronic Devices (PEDs) based transformer with high controllability that enables flexible connectivity between existing medium voltage power distribution network, low voltage AC residential system and envisioned DC residential system. In this paper a systematic constructional detail of a SST with a power rating of 2 kVA, operating frequency of 20 kHz and voltage rating of 600/60 V as a scaled-down prototype used for power converter topologies is presented. The design is simple and it avoids the difficulty of choosing massive amounts of empirical parameters.