Calculation of the leakage inductance of medium frequency transformers having rectangular-shaped windings using an accurate analytical method

Direct current (DC) can be used advantageously in transmission of power from offshore wind farms. A dual active bridge (DAB) converter is among those popular topologies which can be used for this high-power application. A DAB can benefit from the MFT’s leakage inductance (Ls) to transfer the power between the input and output bridges and this will result in higher power density. By controlling the switching on the two sides, the square wave voltage from the primary and the secondary converters will be adjusted to have a defined phase shift relative to each other. Such a transformer serves as an inductance, in addition to its natural duty of voltage adoption between the primary and secondary bridges. In other words, the design of the transformer should fulfil the criteria of having a determined leakage inductance. The voltage wave forms applied to the MFT in a DAB converter are not sinusoidal as in a conventional low frequency transformer.To achieve the lowest loss by the Zero-Voltage Switching of a Dual Active Bridge converter, it is crucial to precisely calculate the embedded Leakage Inductance of the used Medium Frequency Transformer (MFT). An effective analytical method is proposed for calculation of the leakage inductance of the MFT with rectangular-shaped windings