Laboratory Tests, Modeling and the Study of a Small Doubly-Fed Induction Generator (DFIG) in Autonomous and Grid-Connected Scenarios

Doubly-Fed Induction Generators (DFIGs) are widely used in wind power production nowadays.Their key advantages are the low power rating of the converter used for connecting to the network, and the ability to produce and feed the network with reactive power.This paper investigates the capabilities of DFIGs in low-cost wind turbine systems.Namely, it examines the performance and constraints of using general-purpose motor drives instead of back-to-back connected inverters in such systems.A small laboratory DFIG machine is studied in this context, assuming both autonomous and grid-connected scenarios.The analytical model of the machine is initially calculated, and the system is simulated in MATLAB-Simulink, using a uni-directional power converter.Simulation results are presented, accompanied by an analysis of the control technique of the power converter.Experimental results from a laboratory setup based on a low-cost commercial inverter, normally used for controlling a 1kW 3-phase induction motor, are also presented.Finally, the system efficiency -optimal operation points and limitations on the turbine range of operation are discussed.