The study of power generation system based on double-fed induction generator running in parallel with power grid
Based on static modes’ calculations of power generating system based on double-fed induction generator (DFIG) running together with industrial power grid at rotation frequencies higher and lower the synchronous one, the article presents the information on the required properties of the static converter being connected to the generator rotor windings. It is shown that the static converter should have the properties of active power reversibility, capability of providing the rotor windings of induction motor with reactive power, capability to form at DFIG rotor windings AC voltage of an adjustable level with slip frequency with direct or reversed phase sequence. The list of the required properties and calculation results are the necessary information for the initial stage of engineering design of both generation system separate components (electric motor, static converter) and generation system at large, determining its composition, technical realization of its components and their interaction. The static modes calculations results are presented in the form of a table and vector diagrams. The individual questions of the simulation model realization, allowing study besides static the dynamic processes in generation system are also considered. As an example, the authors present the structure of a generation system simplified simulation model with the capability of active and reactive power control of double-fed induction generator. The results of generation system simulation for the pre calculated analytically static modes are demonstrated. The results are presented in the forms of a table and oscillograms of currents and voltages in induction generator stator and rotor windings for frequency values 30% higher and lower the synchronous frequency. The oscillograms show that regardless of the shaft rotation frequency the current in rotor windings remains inductive; at frequencies higher than the synchronous frequency, the rotor windings generate active power, while at rotation frequencies lower than the asynchronous frequency they consume active power. The numeric values of the simulation and static modes’ calculation results correlate each other with sufficient accuracy.