Novel self-excited alternating operation of coupled commutator machines

Abstract

Through the coupling of commutator machines, self-excited alternating power can be spontaneously generated with no external electrical excitations. Standard frequency- domain analysis is applied to the various equivalent circuits for each configuration. Conventional series and shunt self-excited generators are shown to have a single pole in the right-half s plane, indicating growing exponential solutions, whereas coupled generators are shown to have a pair of complex conjugate poles in the right-half s plane, indicating overstable modes, which oscillate as they grow, resulting in self-excited two-phase alternating power generation. Because of this interesting result, the analysis is extended to consider N -coupled generators which shows the existence of many overstable modes, resulting in multi-frequency, multi-phase power generation. The existence of electromechanical alternating self-excitation is demonstrated with the periodic speed reversals of a separately exited d.c. motor, which has its armature in series with the field and armature windings of a generator. Experimental results are presented which indicate that the linear circuit representation is appropriate for the onset and early time interval of these self-excited machines. The magnetic saturation characteristic limits the exponential growth so that a steady state results. These devices are of use in low-frequency, high-power applications, as well as serving as a model for other spontaneous mechanisms in nature.