Steady state analysis of a doubly-fed induction generator under synchronous operation

Abstract

106 82 Athens , Greece Ab_strac_f, A detailed analysis of the performance o f the Doubly-Fed Induction Generator (DFG) under synchronous operating condition in the steady state is presented. The rotor is excited by a voltage phasor the magnitude and the frequency of which can vary independently. The frequency supplied has always such a value that, if superimposed on the rotor speed a synchronous rotating field results. This produces variable-speed constantfrequency characteristics of the DFG over a wide speed range. By varying the excitation voltage magnitude the stator and rotor power factor can be controlled so that maximum efficiency tan b e achieved. By varyinq the angle a between the stator and the rotor applied voltages, DFG active power delivered can be controlled. The wide range of variable-speed constant-frequency operation and the capability o f load variation and power factor control, makes the DFG attractive for wind power conversion systems a5 well a s variable speed hydroelectric generators, 0885-8%9/89/093%0495WI .OO 0 1989 IEEE 4% angle a between the stator applied voltage 0 1 and the rmztor excitation voltage VZ referred t o the stator.In the following each one of the performance characteristics ; f the DFG i.e. stator and rotor currents I 1 and I n , active power P a and P2, reactive power Q I and Q z , copper losses Pri and P,P, mechanical power P, and electromagnetic torque T are deduced as functions of the slip 5 , the magnitude Vz and the angle a. All magnitudes except P . and T are considered per phase. All electrical quantities entering the terminals of both stator and rotor are considered positive. This also holds f o r P,. The electromagnetic torque T is considered positive i f it is motoring. a. Stator Quantities

Doubly Fed Induction Generator Maximum Wind Power Extraction Study Through Integrated Steady-state and Close-loop Control Evaluation

“…Conventionally, DFIG electrical and aerodynamic characteristics associated with the peak power tracking control design are inspected in separate environments [7][8][9]. Differing from transient or steady-state studies conducted previously [7][8][9][10][11][12], the main features of this article are (1) a study of generator electrical characteristics using a DFIG d -q steady-state model, (2) an investigation of extracted wind power and peak power tracking characteristics of the turbine blades versus generator slip, (3) an integration of generator characteristics, extracted wind power characteristics, and peak power tracking characteristics in a joint environment, and (4) integrated steady-state and transient closeloop control studies that assist in better understanding of peak power tracking control designs in both feedback control and steady-state environments.…”

A control scheme for improving the efficiency of DFIG at low wind speeds with fractional rated converters

“…Studies [8][9][10] presented the steady state analysis of DFIG for wide speed operation. The rotor voltage is linearly proportional to the slip (0.49 p.u.…”

“…for a wind speed of 5 m/s at a slip of 0.47) while the aspect of efficiency is not examined [8]. The active power delivered is controlled by varying the angle between the stator and rotor voltages and magnitude of rotor voltage [9]. Increased rating of the power converter is implied at speeds below 70% of synchronous speed [10].…”

“…Among the variable speed wind turbines DFIGs are widely used due to the advantages such as four quadrant operation, decoupled power control, fractional rated converters and reduced mechanical stresses [4][5][6][7]. As the operating speed of DFIG is limited to 30% above and below synchronous speed, the rating of power converters used are typically 30% of the machine rating.Studies [8][9][10] presented the steady state analysis of DFIG for wide speed operation. The rotor voltage is linearly proportional to the slip (0.49 p.u.…”

A control strategy for stand-alone wound rotor induction machine

“…WRIM supplying isolated loads can be found in refs. [12][13][14][15], where the application feasibility of this machine on stand-alone systems is analyzed. In refs.…”