Magnetic behaviour of GOES wound cores of transformers fed by square or sine voltages

An experimental approach compares core losses in a transformer fed by rectangular or sine voltages at several kHz. The proposed transformer technology is based on a wound core made of Grain Oriented Electrical Steel (GOES) thin strips. The proposed transformer design allows a core much hotter than coils. Experimental results show that core losses are lower for rectangular voltages than for sine ones at the same frequency and peak flux density. This counter-intuitive results are interpreted with Fourier series for low peak flux densities. This effect exists only for large pulse widths for a 3-level voltage or for a square one (2 levels). The minimum pulse width that produces this effect is determined. The experimental results also show a decrease of core losses with tem-perature. These measurements open a way toward the design of medium-frequency transformer with GOES wound cores at high temperatures for high power solid-State Transformers (SST).