Frequency Characteristics of Power Transformer for Isolated DC-DC Converter

Takayuki Nakamura,Toshiyuki Murakami

doi:10.1109/access.2022.3145200

Abstract

The operational frequency of a transformer is an important factor in the configuration of an isolated DC-DC converter. However, discussions of this frequency are inadequate. This study focuses on the frequency characteristics of the transformers. The frequency characteristics of the impedance and loss of the transformer were obtained to explain their fundamental attributes. When a transformer is employed in a power electronic transformer (PET), the waveform of the voltage is rectangular. The loss under this waveform was obtained in order to observe its characteristics. Furthermore, the problems with the isolated DC-DC converter are explained. The natural frequency, composed of leakage inductance and equivalent-parallel capacitance, determines the performance of the isolated DC-DC converter. When the operational frequency of the isolated DC-DC converter is below its natural frequency, the loss increases under the no-load or light-load conditions. This increase in the loss is caused by the current, which contains the natural frequency of the transformer owing to the ringing.

Highlights

Transformers are electrical machines used for voltage conversion and isolation
As the transformers have frequency characteristics, the performances of the isolated DC-DC converters are determined by the operational frequency
To clarify the fundamental characteristics of the frequency, this study acquires the frequency characteristics of the impedance and that of the loss

Summary

Introduction

The size and weight of a transformer depends on the frequency at which it operates. The transformer is lighter and smaller in size. PET is employed for AC-AC conversion system, and DC-DC conversion system [2][3] The study in this area is largely conducted in Europe for railway vehicles. The effort in increasing the frequency of the traction transformer has been conducted from 1980s. These efforts are summarized in [4]-[6]. Some “FLIRT (Fast Light Intercity and Regional Train)”, named and produced by STADLER, a Swiss railway manufacturer, employs isolated DC-DC converter with PET for commercial operation. The traction converters are manufactured by ABB, and the vehicles, by STADLER. The operational frequency of the transformer is 100 Hz [9]

Results

Discussion

Conclusion