Spectral Analysis of Rotor Currents in Frequency-controlled Electric Drives

Abstract

The results of researches of asynchronous electric drives with the frequency control which are carried out for the purpose of establishment of causes and effect relationships between a control method, the implementable standard frequency converter of the Schneider Electric company (ATV-71, ATV-32) and its efficiency are given in article. The tests with asynchronous motors with a wound rotor were for the first time carried out. It allowed registering the instantaneous values of not only the stator currents, but also of rotor currents during the experiments. The authors for the first time applied a spectrum analysis of stator and rotor currents which showed that a «sensorless vector» control leads to the origin of high-frequency harmonicas with the considerable amplitude resulting in the nonsinusoidal form of the created moment and inefficiency of the electric drive. The accelerations that are carried out during the research to 94, 157 and 251 Rad/s confirmed this feature of vector control that appears incapable to linearize the asynchronous electric drive as it was supposed by the authors of the method. These results do not contradict theoretical provisions if not to neglect the assumptions which usually arise in case of an output of the equations of vector control. Unfortunately, the modern researchers do not subject these assumptions to doubts. The comparative tests conducted according to the proposed method are presented. The possibility of linearizing the scalar and vector controls with the introduction of a positive dynamic coupling with respect to the stator current was investigated in these tests. The continuous studies make it possible to create effective frequency management for asynchronous electric drives required for a current technology.