Lamination core losses in motors with nonsinusoidal excitation with particular reference to PWM and SRM excitation waveforms

The effects of varying the modulation index and the switching frequency on steel lamination core losses when excited with pulse width modulated waveforms are first investigated. A switched reluctance motor flux model is also developed and flux waveforms for different parts of the machine are synthesized. Using these flux waveforms, the paper presents the loss trend inside a switched reluctance machine, showing the core loss variation of the machine. The rotor was found to incur higher losses than any other part inside the switched reluctance motor. The paper further identifies the flux density harmonics that contribute to higher core losses in the rotor. Using the Fourier series, an attempt to predict core losses under switched reluctance motor flux density waveforms is done and the predicted results are compared with measurements. An Epstein frame was used for direct core loss measurements on 0.0140 in. [0.36 mm] commercial electrical steel; the methods and test bench used, along with test results are detailed in the paper.