Investigation of power loss in wound toroidal cores under PWM excitation

The pulse width modulation (PWM) inverter is widely used when voltage-frequency regulation is required. When laminated cores are energised by PWM voltage supplies additional losses occur due to flux distortion. The iron loss of three types of grain-oriented 3.25% Si-Fe toroidal cores was measured by means of a computer aided system under PWM and sinusoidal voltage excitation at different flux densities. The loss increase under PWM excitation was found to be higher at high flux densities due to higher harmonic distortion. Another important difference between sinusoidal and PWM voltage excitation is a significant difference in the variation of instantaneous energy loss through the magnetising cycle which is also believed to contribute to the additional losses. The losses in the three different geometries were greater under PWM excitation than under sinusoidal voltage and flux