Estimation of Critical Inductance for DC Separately Excited Motor Fed by Load-Dependent Chopper

ABSTRACT

This paper describes a method to estimate the value of a critical inductance for a dc separately excited motor fed by load dependent chopper to eliminate the discontinuous conduction of armature current. A trapezoid approximation has been used to estimate the value of the commutation time of the chopper. To verify the suitability of the method, the performance equations corresponding to different intervals of a chopping cycle are solved numerically on a digital computer. The value of critical inductance has also been obtained using the method developed for rectangular wave chopper. It is found that the proposed method predicts more accurate value of the critical inductance than that of a rectangular wave chopper. It is also seen that a much larger value of the inductance is needed to eliminate the discontinuous conduction in dc separately excited motor fed by load dependent chopper than using rectangular wave chopper.