Influence of Material Properties and Geometric Shape of Magnetic Cores on Acoustic Noise Emission of Medium-Frequency Transformers

Medium-voltage, medium-frequency transformers (MFTs) are much smaller in size and weight compared to conventional line frequency transformers. MFTs are very attractive for applications where full control of the power flow and high power density are required, such as power electronic interfaces in smart grids and traction converter systems. Because of the switching loss of high-voltage semiconductor switches and the limitation of volume reduction at high frequency due to isolation requirement, MFTs are usually operated in the kHz range, which results in acoustic noise emission. In this paper, the origins of acoustic noise associated with MFTs are investigated based on vibration and acoustic measurements. The work focuses on the influence of material properties and geometric shape of the magnetic core. Based on the measurement results, nanocrystalline uncut cores with oval shape is the best solution for MFT design regarding high efficiency, high power density, and low acoustic noise emission. Finally, the low acoustic noise emission of a prototype transformer built with nanocrystalline uncut cores is verified by measurement. The winding is found to have major contribution to transformer acoustic noise if the low-magnetostrictive uncut core is used.