Design methodology and optimization of a medium frequency transformer for high power DC-DC applications

Abstract

The high power medium frequency transformer (HPMFT) is one of the key elements of an isolated, bi-directional DC-DC converters in applications such as future all-DC offshore wind farms, traction and solid state transformers. This paper describes a design methodology taking into account the loss calculation, isolation requirements and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a design example to find the highest power density while the efficiency, isolation, thermal and leakage inductance requirements are all met.

Optimization and experimental validation of medium-frequency high power transformers in solid-state transformer applications

“…where k 1 to k 3 can be calculated according to the expressions presented in [6] for the foil and round conductors. However, in case of the rectangular litz wire used in this article, those coefficients should be adapted as follows…”

“…In order to evaluate the core losses, the modified expression of the improved generalized Steinmetz equation (IGSE) adapted for the square-wave excitation with arbitrary duty cycles and rise times presented in [6] has been used as…”

“…1. Utilizing this design methodology, an optimization process with a wide range of parameter variations is performed to get the highest power density while the efficiency, isolation, thermal and leakage inductance requirements are all met [6]. Using the proposed design and optimization approach, two optimized 50 kW, 1 / 3 kV, 5 kHz medium frequency transformers have been designed and manufactured.…”

Accurate Evaluation of Leakage Inductance in High-Frequency Transformers Using an Improved Frequency-Dependent Expression

“…h w is the winding height, n is the transformer turn ration, I 1 and I 2 are the peak current values of primary and secondary portions, respectively [14], [29].…”

“…This inductance, as shown in Fig. 1, can be seen as an integrated leakage inductance, L σ , in the high frequency transformer, so that the number and size of components can be reduced, hence achieving higher power densities [14]. It would thus be of great importance to accurately evaluate the leakage inductance of such a transformer in the design stage since an insufficient leakage inductance leads to a shift in soft switching which can adversely affect the converter efficiency.…”