Accurate power sharing for parallel DGs in microgrid with various-type loads

Document Type : Research Paper


1 Department of Electrical Engineering, University of Kashan, Kashan, Iran

2 Illinois Institute of Technology, Chicago, USA


Microgrids are nowadays used to produce electric energy with more efficiency and advantage. However, the use of microgrids presents some challenges. One of the main problems of the microgrids widely used in electrical power systems is the control of voltage, frequency and load sharing balance among inverter- based distributed generators (DGs) in islanded mode. Droop method performance degrades when the feeder impedances of two DGs are different and thereby, further modification is required. In this article, a new method based on virtual impedance and compensating voltage is proposed and simulation results show that this method combined with droop control results in balanced power sharing with negligible voltage and frequency drop. Simulation results have been extracted from the Simulink, MATLAB and showed that the proposed method has a good performance in equal load sharing between two DGs with different feeder impedances; both in equal and different droop gains, and with different loads such as nonlinear or unbalanced ones.


[1] Majumder R., Modeling Stability Analysis and Control of Microgrid, Ph. D. Thesis, Queensland University of Technology (2010).
[2] Vilathgamuwa D. M., Loh P. C., Li Y., Protection of  Microgrids During Utility Voltage Sags, IEEE Transactions on Industrial Electronics (2006) 53: 1427-1436.
[3] Marwali  M.  N.,  Dai  M.,  Keyhani  A., Robust   Stability   Analysis   of   Voltage   and Current Control for Distributed Generation Systems, IEEE Transactions on Energy Conversion (2006) 21(2): 516-526.
[4] Marwali M. N., Dai M., Keyhani A., Stability Analysis of Load Sharing Control for Distributed Generation Systems, IEEE Transactions on Energy Conversion (2007) 22(3):737-745.
[5] Chandorkar M., Divan D., Decentralized Operation of Distributed ups Systems International Conference on Power Electronics, Drives and Energy Systems for Industrial Growth (1995) 1: 565–571.
[6] Guerrero J., Berbel N., Vicuna L. de, Matas J., Miret J., Castilla M., Droop Control Method for the Parallel Operation of Online Uninterruptible Power Systems using Resistive Output Impedance, IEEE Applied Power Electronics Conference and Exposition (APEC)(2005)1716–1722.
[7] Guerrero J., Vicuna L. de, Matas J., Castilla M., Miret J., Output Impedance Design of Parallel-Connected ups Inverters with Wireless Load-Sharing control, IEEE Transactions  on Industrial Electronics (2005)52(4): 1126–1135.
[8] Katiraei F., Iravani M. R., Power Management Strategies for a Microgrid with Multiple Distributed Generation Units, IEEE Transactions on Power Systems (2006)21: 1821-1831.
[9] Azim M. I., Hossain M. A., Hossain M. J., Pota H. R., Effective Power Sharing Approach for Islanded Microgrids, Smart Grid Technologies - Asia (ISGT ASIA), IEEE Innovative, Bangkok(2015)1-4.
[10]Reza M., Sudarmadi D., Viawan F. A., Kling W. L., Van Der Suis L., Dynamic Stability of Power Systems with Power Electronic Interfaced DG, In Power Systems Conference  and Exposition, PSCE06, IEEE PES (2006) 1423-1428.
[11]Zhong Q. C., Robust Droop Controller for Accurate Proportional Load Sharing Among Inverters Operated in Parallel, IEEE Transactions on Industrial Electronics (2013) 60(4):1281-1290.
[12]Guerrero J., Vicuna L. de, Castilla J. M., Miret J., A Wireless Controller to Enhance Dynamic Performance of Parallel Inverter in Distributed Generation Systems, IEEE Transactions on Power Electronics (2004) 19:1205-1213,.
[13] Paquette A. D., Divan D. M., Virtual Impedance Current Limiting for Inverters in Microgrids with Synchronous Generators, IEEE Transactions,Industry Applications (2015) 51(2):1630-1638.
[14]Kim J., Guerrero J. M., Rodriguez P., Teodorescu R., Nam K., Mode Adaptive Droop Control with Virtual Output Impedances for an Inverter-Based Flexible AC Microgrid, IEEE Transactions on Power Electronics (2011) 26(3): 689–701.
[15] Katiraei F., Iravani R., Hatziargyriou N., Dimeas A., Microgrids Management, IEEE Transactions on Power (2008) 6:54–65.
[16] Diaz G., Gonzalez-Moran C., Gomez-Aleixandre J., Diez A., Scheduling of Droop Coefficients for Frequency and Voltage Regulation in Isolated Microgrids, IEEE Transactions on Power Systems (2010)25:489–496.
[17] Lee C. T., Chu C.-C., Cheng P.-T., A New Droop Control Method for the Autonomous Operation of Distributed Energy Resources Interface Converters, IEEE Transactions on Power Electronics (2013) 28(4):1980–1993.
[18]Sao C. K., Lehn W., Autonomous Load Sharing of Voltage Source Converters, IEEE Transactions on Power Del (2005)20:1009–1016.
[19]Sao C. K., Lehn W., Control and Power Management of Converter Fed Microgrids, IEEE Transactions on Power Systems (2008) 23: 1088–1098.
[20]Marwali M. N., Jung J. W., Keyhani A., Control of Distributed Generation Systems–Part II: Load Sharing Control, IEEE Transactions on Power Electronics (2004) 19: 1551–1561.
[21] Lee T. L., Cheng P. T., Design of a New Cooperative Harmonic Filtering Strategy for Distributed Generation Interface Converters in an Islanding Network, IEEE Transactions on Power Electronics (2007) 22: 1919–1927.
[22] Vasquez J. C., Guerrero J. M., Luna A., Rodriguez P., R. Teodorescu, Adaptive Droop Control Applied to Voltage-Source Inverters Operating in Grid-Connected and Islanded Modes, IEEE Transactions on Industrial  Electronics, (2009) 56: 4088–4096.
[23] He J., Li Y. W., Guerrero J. M., An Islanding Microgrid Power Sharing Approach Using Enhanced Virtual Impedance Control Scheme, IEEE Transactions on Power Electronics, (2013) 28(11):5272-5282.
[24] Li Y., Li Y. W., Power Management of Inverter Interfaced Autonomous Microgrid Based on Virtual Frequency-Voltage Frame, IEEE Transactions Smart Grid (2011) 2: 30–40.
[25]Wu T., Liu Z., Liu J., Wang S., You Z., A Unified Virtual Power Decoupling Method for Droop-Controlled Parallel Inverters in Microgrids, In IEEE Transactions on Power Electronics (2016) 31(8): 5587-5603.
[26]Yao W., Chen M., Matas J., Guerrero J. M., Qian Z., Design and Analysis of the Droop Control Method for Parallel Inverters Considering the Impact of the Complex Impedance on the Power Sharing, IEEE Transactions on Industrial Electronics (2011) 58: 576–588.
[27]Yazdani D., Bakhshai A., Joos G., Mojiri M., A Nonlinear Adaptive Synchronization Technique for Grid-Connected Distributed Energy Sources, IEEE Transactions on Power Electronics (2008) 23: 2181–2186.
[28]McGrath B. P., Holmes D. G., Galloway J. J. H., Power Converter Line Synchronization using a Discrete Fourier Transform (DFT) Based on a Variable Sample Rate, IEEE Transactions on Power Electronics(2005) 20: 877–884.
[29]Lee S. J., Kim H., Sul S. K., Blaabjerg F., A Novel Control Algorithm for Static Series Compensators by use of PQR Instantaneous Power Theory, IEEE Transactions on Power Electronics (2004) 19: 814–827.
[30]Yazdani A., Iravani R., A Unified Dynamic Model and Control for the Voltage Source Converter under Unbalancedd Grid Conditions, IEEE Transactions on Power Del (2006) 21: 1620–1629.
[31] Savaghebi M., Jalilian A., Vasquez J. C., Guerrero J. M., Secondary Control Scheme for Voltage Unbalanced Compensation in an Islanded droop-Controlled Microgrid, IEEE Transactions  Smart Grid (2012) 3(2): 797-807.
[32]Vanthournout K., Brabandere K. D., Haesen E., Driesen J., Deconinck G., R. Belmans, Agora, Distributed Tertiary Control of Distributed Resources, In Proceedings 15th Power Systems Computation Conference (2005) 1–7.
[33] Setiabudy R., Bs H., Budiyanto, Development Energy Management Strategy to Optimize Battery Operation in Islanding Microgrid using Zero One integer programming," Quality in Research (QiR), 2015 International Conference on, Lombok (2015) 125-128.
[34]Guerrero J. M., Vasquez J. C., Matas J., Hierarchical Control of Droop-Controlled AC and DC Microgrids—A General Approach Toward Standardization, IEEE Transactions on Industrial Electronics, (2011) 58(1):158-172.
[35]Guerrero J. M., Loh P., Chandorkar M., Advanced Control Architectures for Intelligent MicroGrids−Part I, Decentralized and Hierarchical Control, IEEE Transactions on Industrial Electronics (2013) 60(4):1254-1262.
[36]Zhang Y., Xie L., Ding Q., Interactive Control of Coupled Microgrids for Guaranteed System-Wide Small Signal Stability," in IEEE Transactions on Smart Grid (2016) 7(2):1088-1096.
[37]Khodayar M., Shahidehpour M., Cutting Campus Energy Costs with Hierarchical Control: The Economical and Reliable Operation of a Microgrid,” IEEE Electrification Magazine (2013) 1(1):40-56.
[38]Che L., Shahidehpour M., DC Microgrids, Economic Operation and Enhancement of Resilience by Hierarchical Control, IEEE Transactions on Smart Grid (2014) 5(5): 2517-2526.
[39] Nasirian V., Shafiee Q., Guerrero J. M., Lewis F. L., Davoudi A., Droop-Free Distributed Control for AC Microgrids," in IEEE Transactions on Power Electronics (2016) 31(2):1600-1617.
[40]Falahati S., Taher S., M Shahidehpour, Smart Deregulated Grid Frequency Control in Presence of Renewable Energy Resources by EVs Charging Control, IEEE Transaction on Smart Grid (2016).
[41]Chandorkar M. C., Divan D. M., Adapa R., Control of Parallel Connected Inverters in Standalone ac Supply Systems, IEEE Transactions Industry Applications (1993) 29(1).
[42]Rocabert J., Luna A., Blaabjerg F., Rodriguez P., Control of Power Converters in AC Microgrids, IEEE Transactions on Power Electronics (2012) 27:4734-4749,.
[43] Brabandere K. De, Voltage and Frequency Droop Control in Low Voltage Grids by Distributed Generators with Inverter Front-End, Ph.D. Dissertation, Faculteit Ingenieurswetenschappen, K.U. Leuven, Belgium (2006).
[44]Mahmood H., Michaelson D., Jiang J., Accurate Reactive Power Sharing in an Islanded Microgrid Using Adaptive Virtual Impedances, IEEE Transactions Power Electronics (2015) 30 (3):1605-1617.
[45]Li Y. W., Kao C. N., An Accurate Power Control Strategy for Power Electronics-Interfaced Distributed Generation Units Operating in a Low Voltage Multibus Microgrid, IEEE Transactions on Power Electronics (2009)24 (12): 2977–2988.
[46]He J., Li Y. W., An Enhanced Microgrid Load Demand Sharing Strategy, IEEE Transactions on Power Electronics (2012) 27(9):3984–3995.