An analytic and simulation study of a wound-rotor asynchronous machine at positive slides

Abstract

The characteristics of a wound-rotor asynchronous machine (a double-fed machine) upon positive slides are studied in the present article. The double-fed machine (DFM) allows one to adjust the internal and external flows of the active and reactive power at any rotor speed. This feature of the DFM enables one to build various electromechanical systems, such as power-efficient electric drives for transport systems, power generators with variable shaft speed, power-efficient load stands for electric machines and combustion engines, and power-efficient stands for testing an asynchronous machine with the wound rotor without the additional load. The main modes of DFM operation, which are motor and generator modes of operation at a speed below a synchronous one, are studied. The analysis that has been carried out allows one to determine the main properties of the DFM: the direction of the rotor and stator active power flows proves that the positive power feedback appears at positive sliding; the motor mode of DFM operation occurs at the negative modulation phase, while the generator mode takes place at the positive one; the active power transformed in the machine is proportional to the modulation phase; and the sign of reactive power in the stator circuit depends on the relationship between the rotor voltage and the slide. A virtual model of the DFM is constructed in the SimPower System of Matlab-Simulink. It is used for studying the static and dynamic characteristics of the DFM. These characteristics confirm the theoretical results of the analysis.