Characteristics of sub-synchronous oscillation in grid-connected wind farm system

With the rapid development of wind power, wind turbines are accompanied by a large quantity of power electronic converters connected to the grid, causing changes in the characteristics of the power system and leading to increasingly serious sub-synchronous oscillation (SSO) problems, which urgently require the generalized classification and characterization of the emerging oscillation problems. This paper classifies and characterizes the emerging types of SSO caused by grid-connected wind turbines to address these issues. Finally, the impact of the typical system parameters changes on the oscillation pattern is analyzed in depth to provide effective support for the subsequent suppression and prevention of SSO.

Optimal Robust Control for Unstable Delay System

Proportional-Integral-Derivative control system has been widely used in industrial applications.For uncertain and unstable systems,tuning controller parameters to satisfy the process requirements is very challenging.In general,the whole system’s performance strongly depends on the controller’s efficiency and hence the tuning process plays a key role in the system’s response.This paper presents a robust optimal Proportional-Integral-Derivative controller design methodology for the control of unstable delay system with parametric uncertainty using a combination of Kharitonov theorem and genetic algorithm optimization based approaches.In this study,the Generalized Kharitonov Theorem(GKT)for quasi-polynomials is employed for the purpose of designing a robust controller that can simultaneously stabilize a given unstable second-order interval plant family with time delay.Using a constructive procedure based on the Hermite-Biehler theorem,we obtain all the Proportional-Integral-Derivative gains that stabilize the uncertain and unstable second-order delay system.Genetic Algorithms(GAs)are utilized to optimize the three parameters of the PID controllers and the three parameters of the system which provide the best control that makes the system robust stable under uncertainties.Specifically,the method uses genetic algorithms to determine the optimum parameters by minimizing the integral of time-weighted absolute error ITAE,the Integral-Square-Error ISE,the integral of absolute error IAE and the integral of time-weighted Square-Error ITSE.The validity and relatively effortless application of presented theoretical concepts are demonstrated through a computation and simulation example.

TORQUE CAPACITY AND CONTACT EFFICIENCY OF A HALF TOROIDAL CONTINUOUSLY VARIABLE TRANSMISSIONS

The automotive industry is seeking new concepts for a continuously variabletransmission (CVT) in the driveline. One possible solution for a CVT design is half toroidaltraction drive, providing a high torque capacity with quick ratio change. An analytical study on thecontact points of the half toroidal CVT has been detailed. The shapes of the contact areas amongthe input disk, power roller and output disk are considered ellipses. Mathematical equations forestimating the torque capacity, power loss due to spin action, and contact efficiency of theelliptical contacts of the half toroidal CVT are formulated and expressed in the form of integralswhich can be readily evaluated by numerical scheme. The contact efficiency calculations of the halftoroidal CVT have been developed for the proper spin point locations under the effect of systemparameters. Numerical results are presented hi graphical forms for considered parameters, which canhelp the designer to select the proper system parameters to minimize the undesirable spin effects.