Yehia S. Mohamed

Robust controller design for automatic generation control based on Q-parameterization

This paper presents a robust controller design based on Q-parameterization theory for the automatic generation control problem of a power system. This controller is used in order to achieve both robust stability and good dynamic performance against the variation of system parameters. In the Q-parameterization method, the set of all stabilizing controllers of the power system is characterized by a free parameter Q. This free parameter is chosen to satisfy robust stability and other design requirements. Simulation results have confirmed the effectiveness of the proposed controller.

Grid Synchronization Enhancement of a Wind Driven DFIG Using Adaptive Sliding Mode Control

Besides power decoupled control, soft and fast synchronization is an important issue because it enables the DFIG to be connected to the grid with minimum impact on the WECS and the grid [135].

Control of a Wind Driven DFIG Connected to the Grid Based on Field Orientation

Field orientation, with autonomous control of reactive power, using PI controller is the most widely used controlling method of doubly-fed induction generators (DFIG). This paper describes a method for separate control of active and reactive power of grid-connected DFIG using PI controller. Using MATLAB/SIMULINK software, the behavior of controller is evaluated during variation of wind speed. Simulation results represent the behavior of controller when facing the variations. This paper first explains the model of DFIG and the second part is explaining field oriented control of DFIG.

Novel Scheme for Improving the Performance of a Wind Driven Doubly Fed Induction Generator during Grid Fault

Enhancement of fault ride-through (FRT) capability and subsequent improvement of rotor speed stability of wind farms equipped with doubly fed induction generator (DFIG) is the objective of this paper. The objective is achieved by employing a novel FRT scheme with suitable control strategy. The proposed FRT scheme, which is connected between the rotor circuit and dc link capacitor in parallel with Rotor Side Converter, consists of an uncontrolled rectifier, two sets of IGBT switches, a diode and an inductor. In this scheme, the input mechanical energy of the wind turbine during grid fault is stored and utilized at the moment of fault clearance, instead of being dissipated in the resistors of the crowbar circuit as in the existing FRT schemes. Consequently, torque balance between the electrical and mechanical quantities is achieved and hence the rotor speed deviation and electromagnetic torque fluctuations are reduced. This results in reduced reactive power requirement and rapid reestablishment of terminal voltage on fault clearance. Furthermore, the stored electromagnetic energy in the inductor is transferred into the dc link capacitor on fault clearance and hence the grid side converter is relieved from charging the dc link capacitor, which is very crucial at this moment, and this converter can be utilized to its full capacity for rapid restoration of terminal voltage and normal operation of DFIG. Extensive simulation study carried out employing MATLAB/SIMULINK software vividly demonstrates the potential capabilities of the proposed scheme in enhancing the performance of DFIG based wind farms to fault ride-through.

Cascade Sliding Mode Torque Control of a Permenant Magnet Synchronous Motor

This paper presents the direct torque control (DTC) of an interior permanent magnet synchronous motor (IPMSM) based on sliding mode technique. Two adaptive sliding mode controllers are designed; one is used for regulating the motor speed and the other is dedicated for controlling the electromagnetic torque. Consequently, the demerits of classical DTC (large torque and current ripples due to sector changes, low speed problems, and sensitivity to uncertainties) could be avoided in the proposed scheme. The control law of each sliding controller has been designed in such a way that the chattering effects associated with the classical sliding mode are reduced to a great extent. Also, the reaching phase could be eliminated using the idea of total sliding mode control. Moreover, a simple adaptive algorithm is used to estimate the upper bound of lumped uncertainty. The stability analysis of the proposed control system is carried out using Lyapunov stability theorem. The feasibility and effectiveness of the proposed system have been demonstrated through computer simulations. A comparison between the proposed system and conventional techniques has been made in order to confirm the validity of the proposed approach. The superiority of the proposed system has been proved through comparative simulation results.

A Modified MRAS Observer for Sensorless Control of a Wind Driven DFIG Connected to Grid

The Doubly Fed induction generator (DFIG) is a popular wind turbine system due to its high energy efficiency, reduced mechanical stress on the wind turbine, and relatively low power rating of the connected power electronics converter of low costs [126].

Conclusions and Suggestions for Future Work

In view of the analysis and investigations presented, one can draw the following main conclusions: The phase angle between grid voltage and current waveforms is changed from leading to lagging within one cycle for step change in reactive component of grid current reference \( i_{\text{gq}}^{*} \). This confirms that, the capability of the GSC control to regulate the grid received reactive power for controlling the system power factor.

Adaptive Sliding Mode Control for Grid Synchronization of a Wind Driven DFIG Under Unbalanced Grid Voltage

However, wind energy conversion system (WECS) is usually located in rural areas with weak grid connection, in which grid voltage unbalance may arise even during normal operation. The unbalanced grid voltage may be caused by unbalanced transmission line impedance, three-phase unbalanced load, and single-phase high-power load. Hence, the strategies to improve the performance of DFIGs under unbalanced network conditions have obtained a worldwide concern.