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Publication Title | A Micro-turbine Model for System Studies Incorporating Validated Thermodynamic Data

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A Micro-turbine Model for System Studies

Incorporating Validated Thermodynamic Data G. J. Kish, Member, IEEE, and P. W. Lehn, Senior Member, IEEE

Abstract—There is an apparent lack of micro-turbine dynamic models available in literature that include valid experimental data. In an effort to help fill this gap a thermodynamic based micro-turbine model supplemented with experimental data & validated calculations is introduced. The data was extracted from a study on the 60 kW Capstone C60 MicroTurbineT M . Transfer functions describing the micro-turbine model valid for various types of studies are defined; namely EMTP studies, controller design, small signal and stability analyses. Simulations are performed in PSCAD/EMTDC to validate the derived transfer functions, and to investigate the micro-turbine transient response. Researchers can utilise this calibrated model within their power system studies to quantify the application of micro-turbines as distributed generating sources within the distribution network.

Index Terms—Distributed power generation, dynamics, micro- turbine, PSCAD, thermodynamics.

I. INTRODUCTION

DUE to numerous driving factors the penetration of dis- tributed generation (DG) within the distribution network has been steadily increasing in recent years. Depending on the application there are various DG technologies that util- ities and industry can select from for inclusion into their power generation projects. Some specific technologies include photo-voltaic, wind, biomass, micro-turbines and fuel cells. Of these, micro-turbines have garnered attention lately as a promising DG technology because of their [1] (i) ability to provide baseload generation, load-shedding and peak-shaving functionalities, (ii) ability to operate for extended periods with minimal maintenance, (iii) small size relative to other DG, (iv) flexibility in using various commercially available fuel types, (v) low NOX emissions, and (vi) increased energy efficiency when functioning as a combined heat and power (CHP) system. They are also well suited for remote electrification projects or micro-grid applications.

Because of its rising popularity as a DG candidate the simulation of micro-turbine based power generation systems is an active research area. Researchers are performing nu- merous studies to investigate the response characteristics of micro-turbines. Such studies include micro-turbines in grid- connected and stand-alone configurations, load-following ap- plications and transient stability analysis. To accommodate these system studies there is an obvious desire for dynamic models to closely reflect the actual micro-turbine operation; ideally the model should contain accurate data. However, a lack of simple dynamic models with experimental data valid for micro-turbines has been noted in the literature.

The authors are with the Department of Electrical and Computer Engineer- ing, University of Toronto, Toronto, ON M5S 3G4 Canada.

The majority of models presently being used for dynamic analyses of micro-turbines were originally developed for much larger capacity gas-turbines on the scale of megawatts (i.e, 18 MW to 106 MW [2]). In comparison, micro-turbines are designed for capacities in the range of 25 to 300 kW [1].

A significant number of publications utilise the two fol- lowing dynamic models: (i) the heavy-duty gas-turbine model developed by W. I. Rowen [2] at GE in 1983, which has been used by several authors [3]–[9] (commonly supplemented with the data from [10]), and (ii) the Western System Co- ordinating Council (WSCC) compliant GAST model, which has been employed by [11]–[14]. Although other models exist in literature [15]–[18] the Rowen and GAST models are the most prevalent. Both of these models were developed based on large capacity gas-turbines normally situated in central power generating plants.

The experimental data in the Rowen and GAST models consist of fuel system dynamics, compartment temperatures, speed-governor coefficients and rotor inertias. In many cases this data is being directly applied to the modelling of micro- turbines with little or no modification [7]. As such it is reasonable to infer any time constants would not accurately represent the response characteristics of modern micro-turbine designs. Moreover, it is unlikely that micro-turbine compart- ment temperatures or governor controls would remain identical to their gas-turbine counterparts, which in the case of the Rowen model are over 25 years old. To aid researchers in performing system studies of micro-turbines it would be highly beneficial to provide a dynamic model that could better characterise their performance.

In this paper a micro-turbine thermodynamic model is presented that incorporates experimental data & validated calculations based on a study of the 60 kW Capstone C60 MicroTurbineTM by [19]. This data is used to calibrate the micro-turbine model of [20], which was adapted from [21] formicro-turbineapplications.TheC60MicroTurbineTM [22] was chosen as it is an established model available from Cap- stone, a prominent commercial micro-turbine manufacturer. By merging the separate works of [19] and [20] a calibrated model is provided to researchers for adoption into their power system dynamic studies of micro-turbines, to be used for further evaluation.

The model provides a mechanical shaft power output for input to a high-speed permanent magnet synchronous gen- erator (PMSG). Because the focus of this work pertains to a thermodynamic micro-turbine model for inclusion into a micro-turbine based generation system, the PMSG and grid- interfacing power electronics are not represented. Transfer functions of varying complexity are derived from the model

978-1-4577-1002-5/11/$26.00 ©2011 IEEE

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