Virtual Synchronous Generator: A Control Strategy to Improve Dynamic Frequency Control in Autonomous Power Systems


Ideally, diesel hybrid autonomous power systems would operate with high penetration of renewable energy sources such as wind and photovoltaic to minimize fuel consumption. However, since these are inherently intermittent and fluctuating, the grid-forming diesel engine generator sets are usually required to operate with larger amounts of spinning reserve, often at low loading conditions what tends to increases operating and maintenance costs. Frequency stability is of great concern in “small” systems, such as mini-grids, where any individual generator in-feed represents a substantial portion of the total demand. There, the initial rate of change of frequency is typically larger and a lower value of frequency can be reached in a shorter time than in conventional systems with all generation supplied by rotating machines, possibly resulting in under-frequency load shedding and tripping of renewable energy generators. The first part of this paper, discusses some general concepts regarding frequency stability in a diesel hybrid mini-grid and how energy storage systems can be used to enhance system performance. Then, a particular technique based on a virtual synchronous generator is presented and its effectiveness is demonstrated with simulation results.

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M. Torres and L. Lopes, "Virtual Synchronous Generator: A Control Strategy to Improve Dynamic Frequency Control in Autonomous Power Systems," Energy and Power Engineering, Vol. 5 No. 2A, 2013, pp. 32-38. doi: 10.4236/epe.2013.52A005.

1. Introduction

Historically, renewable energy sources (RESs) are integrated into autonomous power systems (mini-grids) already supplied by a diesel power plant with multiple diesel engine generator sets (gen-sets). With the addition of RES, it is more likely that the gen-sets will operate under low load conditions resulting in lower efficiency and potential of carbon build up and premature ageing of the diesel engines. Re-sizing of the gen-sets and implementation of appropriate cycling strategies, according to daily and seasonal variations of the mini-grid load and power output of the RESs to maintain optimum loading under various conditions, can help improve the RES contribution and displacement of diesel fuel [1]. Besides, one can also include shortor long-term energy storage systems (ESSs) and controllable (secondary) loads that can be used for improving stability and economic performance of the mini-grid. This can be done by a supervisory controller which should, at one level, (primary control) maintain grid stability and, at the other level, (secondary control) optimize the operation of the power sources, energy storage units and controllable loads, if applicable.

Figure 1 shows a schematic diagram of a supervisory controller of a diesel power plant. Each gen-set presents a primary controller, implemented in the governor, whose main function is to adjust the speed of the gen-set. Since most gen-sets employ a synchronous generator, the governor indirectly controls the frequency of the generated voltage. If the frequency is to be kept constant, an isochronous governor can be used. However, if multiple gen-sets are to operate in parallel, it is more convenient to use a droop based governor where the speed and frequency of a gen-set decrease as its output power increases. This behavior can be represented in steady-state by

Conflicts of Interest

The authors declare no conflicts of interest.


[1] F. Katiraei and C. Abbey, “Diesel Plant Sizing and Performance Analysis of a Remote Wind-Diesel Microgrid,” IEEE Power Engineering Society General Meeting, Tam pa, 24-27 June 2007, pp. 1-8.
[2] European Committee for Electrotechnical Standardization, “EN50160 European Standard on Voltage Characteristics of Electricity Supplied by Public Distribution Systems,” European Committee for Electrotechnical Standardization, Brussels, 2010.
[3] R. Tonkoski and L. A. C. Lopes, “Enhanced Part Load Operation of Hybrid Mini-Grids with High Penetration of Photovoltaics,” 3rd Brazilian Conference on Solar Energy, Belém, 21-24 September 2010.
[4] K. Elamari and L. A. C. Lopes, “Frequency Based Control of Electric Water Heaters in Small PV-Diesel Hybrid Mini-Grids,” 25th Canadian Conference on Electrical and Computer Engineering, Montréal, 29 April-2 May 2012.
[5] L. A. C. Lopes and M. Dalal-Bachi, “Economic Dispatch and Demand Side Management via Frequency Control in PV-Diesel Hybrid Mini-Grids,” 6th European Conference on PV-Hybrid and Mini-Grids, Chambéry, 24-26 April 2012.
[6] F. Katiraei, R. Iravani, N. Hatziargyriou and A. Dimeas, “Microgrids Management,” IEEE Power and Energy Magazine, Vol. 6, No. 3, 2008, pp. 54-65. doi:10.1109/MPE.2008.918702
[7] S. Lukic, S. Wirasingha, F. Rodriguez, J. Cao and A. Emadi, “Power Management of an Ultracapacitor/Battery Hybrid Energy Storage System in an HEV,” IEEE Vehicle Power and Propulsion Conference (VPPC’06), Windsor, 6-8 September 2006.
[8] N. Hamsic, A. Schmelter, A. Mohd, E. Ortjohann, E. Schultze, A. Tuckey and J. Zimmermann, “Increasing Renewable Energy Penetration in Isolated Grids Using a Flywheel Energy Storage System,” International Conference on Power Engineering, Energy and Electrical Drives, 12-14 April 2007, pp. 195-200.
[9] P. C. Loh and F. Blaabjerg, “Autonomous Control of Dis tributed Storages in Microgrids,” 2011 IEEE 8th International Conference on Power Electronics and ECCE Asia (ICPE ECCE), Jeju, 30 May 3 June 2011, pp. 536-542.
[10] W. Li, G. Joós and C. Abbey, “Wind Power Impact on System Frequency Deviation and an ESS Based Power Filtering Algorithm Solution,” 2006 IEEE Power Systems Conference and Exposition (PSCE’06), Atlanta, 29 October-1 November 2006, pp. 2077–2084.
[11] Y. Z. Sun, Z. S. Zhang, G. J. Li and J. Lin, “Review on Frequency Control of Power Systems with Wind Power Penetration,” 2010 International Conference on Power System Technology (POWERCON), Hangzhou, 24-28 Oc tober 2010.
[12] Q. C. Zhong and G. Weiss, “Synchronverters: Inverters That Mimic Synchronous Generators,” IEEE Transactions on Industrial Electronics, Vol. 58, No. 4, 2011, pp. 1259-1267. doi:10.1109/TIE.2010.2048839
[13] H. Brevani, “Robust Power System Frequency Control,” Springer Science+Business Media, New York, 2009.
[14] “Renewable Energy Cheaper than Coal,” Wind Data Files.

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