Power generated from wind is a fast growing renewable source of the world energy consumption. A test bench for comprehensive research on the doubly fed induction generator (DFIG) used as wind turbine is implemented. The wind energy is emulated with a synchronous machine according to the wind profile specified in the computer. Two inverters in a back to back configuration between the rotor and the grid are used to control the DFIG. The space vector pulse width modulation (SVPWM) technique is used in both inverters. Special attention has been placed in the offset adjustment of the encoder and the stator synchronization and connection to the grid. Finally, the regulation of the DFIG is performed controlling the active and reactive power to their reference values.
This paper presents an effective Proportional Derivative (PD) position controller of induction motor drives. A new procedure for controller design in frequency domain and the d-q synchronous rotating reference frame is presented, where the indirect vector control has been used. This position controller is validated experimentally using an industrial induction motor of 7.5 kW and an incremental encoder of 4096 impulses per revolution. The position regulator includes an effective Feed-Forward (FF) term instead of the Integral action (I), reducing drastically the undesirable effect of the unknown load disturbance on the position tracking. The presented algorithm has been tested using several simulation and real experiments, in suitable conditions and also in adverse conditions employing the unknown load disturbance, parameter uncertainties and measurement noise in the position and stator current loops signals, where its functional robustness is clearly demonstated. The obtained results are very satisfactory, suggesting its use in industry and in the research area to be used as a reference with other advanced position regulators. The stability of the controlled system is demonstrated in frequency domain and also by discretization of poles.
In this paper, the multiple period speed measurement is compared with the classical frequency and/or period methods used. The proposed speed method is used to examine the quality of the three implemented speed estimators. These estimators get the information from measured stator currents and from motor stator voltage. Open loop estimators or observers are used to estimate rotor or stator flux and rotor speed to use as feedback signals. An improved open loop estimator, an MRAS, and an EKF observer are tested utilizing a 7.5 kW induction motor. They have different accuracy, robustness and sensitivity against parameter variations and all of them have the same problem when the rotor speed is around zero.
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