Twin Inverter-Fed Induction Machines Artificial Loading Without Mechanical Coupling

This article presents an artificial loading method for induction machines using industrial static frequency converters variable frequency converters (VFCs), low-cost programmable logic controllers for command and control, and standardized communication protocols. Different approaches of artificial loading method are presented in this article. Induction machine full load testing is difficult, especially at high power and almost impossible for vertical axis machines. Mechanized IM start/stop procedure and closed-loop loading method, here presented, reduce overall testing time. The overall manpower cost is reduced thanks to the lack of IMs mechanical coupling. Moreover, thermal test at rated IM current and power losses equivalation are presented in this article. Bi-directional VFC utilization for a single motor cannot always be a solution for artificial loading because of high variations of grid power (voltage). Two identical IMs without mechanical coupling driven by two identical dc bus interconnected VFCs artificial loading method is presented in this article. The power circulation between the machines is performed via the common dc link. This opens the possibility to test machines with rated power larger than the lab power source rating. The rated current artificial loading conditions are achieved without mechanical coupling, without VFC oversizing, and using standard equipment.