Enhanced Reactive Power Transfer Capability and ZVS Range Analysis for a Single-Stage DAB based Electronic Transformer Using Bidirectional Switches

A single-stage single-phase dual active bridge (DAB) based solid-state transformer (SST) offers various advantages over its multi-stage counterparts, including higher efficiency and reliability due to fewer components and the absence of bulky electrolytic capacitors. However, the lack of a DC link limits its reactive power transfer capability from the supply to the load, a capability even conventional transformers possess. To address this, external compensation elements are required across the load terminals to meet the desired reactive power, diminishing its primary advantage. This paper introduces a technique for a single phase AC-AC DAB-based SST to enhance the transformer's reactive power transfer capacity. It also presents a detailed analysis of the zero voltage switching range of the converter bridges under various operating conditions while supplying reactive power. The proposed schemes and analysis are further validated by experimental results on a 120/164 Vrms and 450 VA hardware prototype, demonstrating a correlation with the experimental results and highlighting the practical benefits of the proposed scheme.

I. Introduction

Traditional transformers have been known for their cost-effectiveness, high efficiency (ranging from 98% to 99%, depending on power rating), robustness, and reliability, as highlighted in [1]. However, operating at low frequencies of 50 Hz/60 Hz results in the need for a large amount of iron and copper, leading to low power densities. Furthermore, conventional transformers lack direct controllability such as power flow control, voltage and current regulation and fault current limitation [2], [3].