Harmonics and core losses of permanent magnet DC motors controlled by chopper circuits

The impact of chopper control on armature current harmonics and core losses of permanent-magnet DC motors is analyzed. A computer-aided two-dimensional finite-element method is used to analyze the magnetic field and obtain the nonlinear parameters of the machine. The armature current waveforms are predicted from the machine system network analysis at different chopping frequencies and decomposed into their AC and DC components. These currents with their ripple contents are further used in the field analysis to compute the core losses of a 1.2 hp permanent-magnet DC motor at different operating conditions. In addition to the numerical analysis, supporting experimental work was carried out for verification of some of the results. It is found that armature current harmonics can lead to significant increases in core losses