Analysis of Electromechanical Processes in Asynchronous Machines during Tests by the Loading-Back Method with Energy Recovery in the Network

Abstract

The article discusses the interrelated electromechanical processes in asynchronous machines when testing by the loading-back method with energy recovery in the network. We analyze a system of two asynchronous machines connected by a common shaft, in which one machine operates as an engine with the voltage supply of increased frequency from the frequency converter and the external machine operates as a network generator. Electromechanical processes in machines have an influence on each other. We have carried out the simulation of electromechanical processes in the motors with allowance for several factors—namely, different degrees of saturation of magnetic cores, torque equalization, and the change in parameters of the windings when changing the operating mode with a nonsinusoidal voltage supply to the asynchronous motor from the frequency converter. A modeling technique with mutual matching of the electromagnetic field models of machines through the relationship of torques on the shaft, based on system minimization of the electromagnetic energy functionals has been presented. The results of simultaneous numerical calculations of interrelated electromagnetic fields in machines and electromechanical processes have been presented. The calculations of electromechanical processes and the characteristics of an asynchronous motor–generator system with a common shaft, mutual load and energy recovery in the network have been performed. The results of experimental studies of a two-machine unit are presented, confirming the theoretical results. It is established that the application of the calculation technique with direct computing the interrelated electromagnetic fields in the engine and generator with allowance for the electromagnetic torque on the shaft provides an error of no more than 7% compared with the experiment.