A MODIFIED DC POWER ELECTRONIC TRANSFORMER BASED ON SERIES CONNECTION OF FULL-BRIDGE CONVERTERS

Abstract

This project proposes a novel DC power electronic transformer (DCPET) topology for locomotive, AC/DC hybrid grid, DC distribution grid and other isolated medium-voltage and high-power applications. Compared with conventional PET topology, the proposed DCPET has fewer power semiconductor devices and high-frequency isolation transformers, which can improve the power density and reliability. Fault handling or redundancy design can be achieved to further improve the reliability when some DC-DC modules break down. Also, input voltage sharing (IVS) control can be omitted to simplify the control system and improve the stability. Meanwhile, soft switching is guaranteed for all the switches, which is beneficial to increase switching frequency and improve power density. In this project, the principle, evolution, and control of the proposed DCPET are respectively presented and studied in detail. Finally, a prototype of the proposed DCPET is built and the experimental results verify the validity and superiority of the proposed topology.

Existing System

In the existing system, DCPET (DC power electronic transformer) with ISOP (input-series output-parallel) structure is used.

Proposed System

A novel DCPET topology is proposed in this project. Compared with previous work, the number of transformers and switches can be efficiently reduced at the same voltage level, which can increase power density and improve reliability. Also, the performance of fault handling and tolerance is improved, which can make DCPET more reliable even the sub-modules are numerous. In addition, by using this topology, IVS control strategy is not required because of the voltage self-balancing characteristic and thus the control loop will be further simplified.

Architecture

A typical structure diagram of the DC distribution grid based on DCPET

The basic structure of the proposed DCPET topology