Effects of chopper control circuits on core losses of permanent magnet DC motors

A two-dimensional finite-element method was used to compute the armature core losses of a permanent magnet DC motor when it was operated by a chopper control circuit. A comparison is made with the losses of the same machine when it was supplied from a pure DC source under the same operating conditions. For both cases, minor hysteresis loop and eddy current correction factors due to the restored waveforms of flux densities were considered. The numerical work was carried out in conjunction with experimental work on a 1.2-hp permanent magnet DC machine, and the effects of excitation current and electronic forces revealed by the test were compared with those computed from the numerical model in order to validate the parameters used in obtaining the numerical data. According to the analysis of the example presented here, an increase in the motor core losses of 63% took place as a result of chopper operation. This indicates that the effect of chopper operation on the overall losses and the efficiency of such a motor can be significant