Core Losses in Motor Laminations Exposed to High-Frequency or Nonsinusoidal Excitation

This paper first reviews three internationally standardized core loss measurement methods: the Epstein frame, toroids, and single sheet testers. A comparison of the Epstein frame and toroid test results is presented for annealed and unannealed steel. Two methods are used to predict core losses under nonsinusoidal supplies. The first method uses the Fourier series and an improved loss separation algorithm to predict no-load core losses under brushless DC motor flux waveform excitation with a flux density known spectrum. The second method uses the form factor concept and an improved loss separation algorithm to predict core loss. The combination of the improved loss separation algorithm and the form factor concept was found to yield results close to the measured losses under high-frequency supplies, such as pulsewidth-modulated waveforms. An Epstein frame with commercial 0.0140-in (0.356 mm) electrical steel was used for direct core loss measurements; the methods and test bench used are detailed in the paper, along with test results.