3002 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 28, NO. 3, AUGUST 2013 Distributed Automatic Generation Control Using Flatness-Based Approach for High Penetration of Wind Generation Maryam Hassani Variani, Student Member, IEEE, and Kevin Tomsovic, Fellow, IEEE Abstract—To allow for high penetration of distributed genera- tion and alternative energy units, it is critical to minimize the com- plexity of generator controls and the need for close coordination across regions. We propose that existing controls be replaced by a two-tier structure of local control operating within a global context of situational awareness. Flatness as an extension of controllability for nonlinear systems is a key to enable planning and optimiza- tion at various levels of the grid in this structure. In this study, flatness-based control for automatic generation control (AGC) of a multi-machine system with high penetration of wind energy is investigated. The local control tracks the reference phase which is obtained through economic dispatch at the global control level. As a result of applying the flatness-based method, the machine system is decoupled into linear controllable systems in canon- ical form. Therefore, the control strategy results in a distributed AGC formulation which is significantly easier to design and imple- ment compared to conventional AGC. Practical constraints such as generator ramping rates can be considered in designing the local controllers. The proposed strategy demonstrates promising perfor- mance in mitigating frequency deviations and the overall structure could facilitate operation of other nontraditional generators. Index Terms—Automatic generation control (AGC), flatness, frequency regulation, trajectory generation, trajectory tracking, wind power. NOMENCLATURE Rotor electrical angle, in rad (subscript denotes the th generator). Rotational speed of rotor, in rad/s. Machine electrical synchronous speed, in rad/s. Governor power, in p.u. Mechanical power, in p.u. Speed changer position. Voltage behind reactance, in p.u. Manuscript received June 28, 2012; revised November 23, 2012 and January 31, 2013; accepted March 10, 2013. Date of publication April 26, 2013; date of current version July 18, 2013. This work was supported in part by GCEP at Stanford University and in part by the Engineering Research Center Program of the National Science Foundation and the Department of Energy under NSF Award Number EEC-1041877 and the CURENT Industry Partnership Program. Paper no. TPWRS-00738-2012. The authors are with the Min H. Kao Department of Electrical Engineering and Computer Science, The University of Tennessee, Knoxville, TN 37996 USA (e-mail: mhassani@utk.edu; tomsovic@eecs.utk.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPWRS.2013.2257882 Machine terminal voltage, in p.u. and rad. Direct axis transient reactance, in p.u. Inertia constant, in seconds. Damping constant, in p.u. Slope of the machine speed-droop characteristic, in p.u. , Governor and turbine time constants in seconds. Frequency bias setting, in MW/0.1 Hz. I. INTRODUCTION T HE rapid introduction of wind power has begun to impact overall power system control, and particularly frequency control. As a fundamental characteristic of electric power oper- ations, frequency of the system deviates from its nominal value due to generation-demand imbalance. Conventional generators, in which the turbine rotational speed is nearly constant, provide inertia and governor response against frequency deviations; however, the speed of a wind turbine is not synchronous with the grid and is usually controlled to maximize active power production. Therefore, wind plant power production is not inherently coupled to the system frequency, and historically, wind plants have not been required to participate in frequency regulation. Still, modern wind plants offer limited ability to contribute in frequency regulation within few seconds after loss of generation [1]. With increased penetration of wind energy, system operators have begun to study the performance of the primary frequency response. The California ISO frequency response study shows that the reduced system inertia due to penetration of wind units has an impact on the initial rate of change of frequency but it has little impact on the severity of the frequency excursion and settling frequency. Inertia controls from wind generation can significantly improve the frequency nadir but they do relatively little to correct a shortage in the amount of available response. Unlike inertial response, wind plant governor like control will significantly improve frequency nadir and settling frequency. This control requires the wind plants to work below available power [2]. According to the investigation of wind generation penetration in the ERCOT market, the percentage increase in regulation requirements has been found to be equal to the percentage wind penetration on a capacity basis. The regulation needs increase much more for certain times of the year [3]. Another assessment of frequency 0885-8950/$31.00 © 2013 IEEE