Optimal Design of Solid State Transformer-Based Interlink Converter for Hybrid AC/DC Micro-Grid Applications

Abstract

The conventional low-frequency transformer (LFT) in conjunction with power electronic converters is used as the conscientious device to provide galvanic isolation and voltage regulation for the hybrid micro-grid (HMG) applications. However, it may not be suitable for HMG applications where the high power density and active power flow control over a wide operating range are major concerns. This article presents the solid state transformer (SST)-based interlink converter (IC) used to provide high frequency (HF) galvanic isolation between the ac/dc micro-grid (MG) networks. The proposed structure of SST intends to meet out most of the aspects of HMG networks such as active control over the bidirectional power flow, high efficiency, high power density, and better voltage regulation. In SST, nonoptimal parasitic components of HF transformer (HFT) are used as a part of power transfer elements and are unable to assist soft-switching operation over the wide range of load variations that degrade its overall performance. In view of these concerns, the comprehensive design and analysis are carried out at different stages to decide the design constraints for the optimization of nonoptimal magnetizing components and their significant effect on the system performance. Furthermore, the influence of the system parameters is analyzed with analytical expression and graphical analysis. The proposed SST configuration is designed for minimum kVA rating and better voltage regulation at different buses by using the proposed dual degree control (DDC) scheme over the wide range of load variations. The 4-kW hardware prototype is built up in the laboratory which provides isolated dc dual-port output terminals. The design and testing are carried out under different loading conditions to validate the significant performance of the proposed SST structure.