Design and development of the middle-frequency isolation transformer for the high-voltage DC/DC converter

Document Type : Original Article

Authors

1 Tallinn University of Technology, Tallinn, Estonia.

2 Gdynia Maritime Academy, Gdynia, Poland.

3 Riga Technical University, Riga, Latvia.

Abstract

Abstract:
Among the performance requirements of railway equipment applied to the 3.0 kV DC
catenary-fed auxiliary power supplies (APS), the most significant one is compliance
with electric safety requirements. It provides the specific feature for the power circuit
topology of APS converter, requiring an isolation transformer to decouple input and
output sides (with the isolation voltage at least 12 kV). Since the isolation transformer in
switching-mode power supplies contributes about 25…30 % of the overall volume and
more than 30 % of the overall weight, the design of a compact and lightweight system
will be a great challenge for the designer [1]. This paper is mainly addressed to some
specific design issues that are encountered during the development of isolation
transformers for the rolling stock APS. For the middle-frequency (500...3000 Hz) highpower
transformers, the optimal transformer design rule of the copper and core loss
equalization will not work. Main attention here must be paid to select proper material
for the magnetic core and to define an optimal operating flux density to minimize the
dimensions and to improve operability and efficiency of the transformer, respectively.
For the isolation transformers designed for the APS converters with high input voltage
and load variations, threat related to magnetic core saturation caused by transient
conditions should be considered. These and some other specific design issues
(minimization of leakage inductance and parasitic capacitances, high-voltage isolation,
etc.) make the design of such devices very challenging.

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