Digitalization of Excitation Control Circuit for Self-Starting Salient-Pole Synchronous Motor

Self-starting salient-pole synchronous motors are in great demand for use in large compressors and pumps because of their ability to reduce the initial and running cost of equipment. In recent years, compressor moment of inertia and torque requirements have become more stringent, requiring high starting torque despite the low starting current requirement. With the conventional excitation control circuit, the timing of the excitation input is delayed from the optimum phase angle, and the torque at pulling into synchronism cannot be maximized. Therefore, in this paper, we have attempted to digitize the excitation control circuit to improve the torque at pulling into synchronism.