This paper describes the dynamic and stability properties of wind turbine generators connected to power systems. Both synchronous and induction generators are considered. A comparison is made between wind turbines, steam, and hydro units. The unusual phenomena associated with wind turbines are emphasized. The general control requirements are discussed, as well as various schemes for torsional damping such as speed sensitive stabilizer and blade pitch control. Interaction between adjacent wind turbines in a "wind farm" is also considered.

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Dynamics and Stability of Wind Turbine Generators

Methods which have been proposed for increasing the margin of stability in large generators generally act by controlling the generator electrical power output. A more direct control of the stability can be achieved by regulating the power input to the turbine. Simultaneous control of the field excitation and the turbine

Optimisation of Turbo-Generator Transient Performance by Differential Dynamic Programming

Stabilization of a synchronous machine through the control of its exciotation is discussed in this paper. The control laws are derived from the linearized equation of performance of the synchronous machine by the minimization of a scalar performance index. The manipulated variable is an increment to the exciter reference voltage having an amplitude constraint. Control laws are dependent on the selection of the weighting coefficients of the states and the input. Guidelines are given for the selection of these coefficients so that both the small signal dynamic performance and the large signal transient performance of the machine are improved. It is shown that suboptimal controls corresponding to the feedback of machine slip velocity and its derivatives produce substantial improvement of machine response. Different transient conditions are simulated on the nonlinear machine model and the extent of improvement of machine performance by using the proposed control laws is demonstrated.

Stabilization of a Synchronous Machine Through Ooutput Feedback Control

Automatic control in electric power systems

Damping of synchronous machines by means of rapid response excitation control is analyzed for a one-field and two-field machine connected through a line impedance to an infinite bus. Emphasis is placed on the influence of the control parameters upon the damping characteristics of a conventional one-field machine. Regions of instability which may occur due to improper controller design or adjustment are established. Optimization of controller parameters and the effect of controller compensation are considered. Also, the damping characteristics of a two-field machine are presented and compared with those of a one-field machine. The application of the two-field machine to damp frequency oscillations in power systems has the potential of being of practical importance. Damping by excitation control ("forced" damping) is compared to damping due to the action of damper windings. The advantages of forced damping are clearly established; particularly in systems where long line lengths exist between large generating units.

Synchronous Machine Damping by Excitation Control with Direct and Quadrature Axis Field Windings

A digital computer study of synchronous generators which aims to optimize transient stability is described. Mathematical modeling checked by site tests is used, and alternative excitation controls are investigated. It is shown that the appropriate excitation control can produce substantial positive damping of rotor angle excursion without prejudice to the automatic voltage control.

Anthony J. Morris

Papers

Optimized Transient Stability from Excitation Control of Synchronous Generators