Analysis of the Magnetic Field in Rotating Armature Electronically Commutated DC Machines by Finite Elements

A method for analysis of magnetic fields in rotating armature electronically commutated dc machines is presented. The resulting finite element model is suited for analyzing such machines under any load condition, including no-load. The model is used in the analysis and determination of characteristic parameters of such rotating armature machines of the type designed for use in conjunction with modern brushless excitation systems which supply field currents to large turbine generators. The analysis reveals the effect of various load conditions on the values of machine leakage inductances, and emfs. A considerable influence of the load on leakage inductances is determined. The analysis shows considerable reduction in leakage inductance values at higher saturation. This means that such parameters, contrary to prevailing practices, cannot be treated as constant. Interesting similarities (and differences) between the method of analysis of this type of rotating armature electronically commutated dc machines and that of analyzing ordinary synchronous machines is demonstrated clearly in the model development and results. The model is useful in determination of machine equivalent circuit parameters suited for simulation of armature-diode bridge dynamic performances.