Considerations on islanded microgrid frequency control capability within different generation configurations Yuri R. Rodrigues, M. F. Zambroni de Souza, A. C. Zambroni de Souza Institute of Electrical Systems and Energy - ISEE Federal University of Itajuba Itajubá, Brazil
The development and increase penetration of Dispatchable Distributed Generation and Renewable Power Generation are making self-sustainable operational areas a reality.
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Thus, a distribution system becomes a microgrid, and a microgrid may evolve into smart grid, if controls and communications are considered.
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This work addresses
◉ Islanded microgrid’s frequency control capability within different generation configurations; ◉ Proposes a frequency control method based on microgrid nodes demand.
Methodology
When a microgrid is no longer connected to a bulk system providing a frequency reference, the islanded region must regulate itself.
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Primary Control Droop Control
◉ Plays the primary level at the microgrid frequency and voltage control.
Figure. 1. Representation of the ‘droop’ method
Although, if the microgrid generation is substantially based on variable sources as renewable generation and significant load variations are faced.
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Self-regulation becomes a great challenge being necessary some sort of secondary control.
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Secondary Control Proposed Method ◉ This control allows pre-defined contributors to adjust their droop parameters in order to maintain the network frequency at reference level. Figure. 2. Droop with primary and secondary control
Methodology
Microgrid Demand Update (Predicted or Measured) Actualization of ‘m’ and ‘n’ parameters Demand Share between Dispatchable Generators
Load Flow
Droop Method
Voltage Regulation
Converged ?
No
Yes Loss Determination Figure. 3. Simplified flowchart of the methodology
Test System A modified IEEE 34-bus systems considering dispatchable, non-dispathacle and renewable source generators was employed. ◉ Three different generation scenarios were held. Figure. 4. Modified IEEE 34 bus system used for testing
Generation Scenarios first
Dispatchable DGs second
Plus nondispatchable DGs with fixed contribution
last
Plus nondispatchable variable renewable generation
Microgrid Load Profile
Figure. 5. Microgrid active and reactive system demand profile per phase for the base case
Results
Droop Control ◉ Only Dispachable DGs
Figure. 6. Microgrid frequency response considering only dispatchable DGs with Droop Control
◉ Dispatchable and fixed nondispatchable DGs
Figure. 7. Microgrid frequency response considering dispatchable and fixed non-dispatchable DGs with Droop Control
Droop Control ◉ Dispachable DGs and variable nondispatchable DGs
Figure. 8. Microgrid frequency response considering dispatchable and variable non-dispatchable DGs with Droop Control
Loading Factor (fc) 0
1
2
3
4
5
6
7
8
9
10
Only dispatchable DGs
Generation Scenario
1
Dispatchable and fixed non-dispatchable DGs 2
3
Dispatchable and variable non-dispatchable DGs
Renewable Sources
Scenario 3
Scenario 2
Scenario 1
Figure. 9. Maximum loading factor for each generation scenario
Proposed Secondary Control Method ◉ Scenario 1
Figure. 10. Microgrid frequency response considering only dispatchable DGs with Droop Control and Proposed Secondary Control
◉ Scenario 2
Figure. 11. Microgrid frequency response considering dispatchable and fixed non-dispatchable DGs with Droop Control and Proposed Secondary Control
◉ Scenario 3
Figure. 12. Microgrid frequency response considering dispatchable and variable non-dispatchable DGs with Droop Control and Proposed Secondary Control
Frequency Variation [Hz] -0,08
-0,06
-0,04
-0,02
0
0,02
0,04
0,06
1
Generation Scenario
-0,1
2
3
Scenario 3
Scenario 2
Renewable Sources
Scenario 1
Maximum Frequency Variation
Figure. 9. Maximum loading factor for each generation scenario
0,08
0,1
Conclusions ◉ Firstly, considerations on the influence exercised by the type of generation on the microgrid frequency control capability were performed. ◉ The results indicate that microgrids within significant dispatchable generation capability are able to perform satisfactory frequency control even for great demand variations with droop method.
Conclusions ◉ However, when the penetration of variable sources as renewable generations are considered, microgrid’s control level is diminished and some sort of secondary control may be adopted. ◉ In this perspective, the proposed frequency control method is presented as a viable candidate, given its great results regarding the distinct microgrid generation configurations performed.
Acknownlegments The authors thank for financial support to: ◉ Universidade Federal de Itajubá (UNIFEI); ◉ Fundação de Amparo à Pesquisa do estado de Minas Gerais (FAPEMIG); ◉ Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES);
◉ Conselho Nacional de Pesquisa e Desenvolvimento (CNPq); ◉ Instituto Nacional de Energia Elétrica (INERGE).
References [1] Ravichandran, A.; Malysz, P.; Sirouspour, S.; Emadi, A., "The critical role of microgrids in transition to a smarter grid: A technical review," in Transportation Electrification Conference and Expo (ITEC), 2013 IEEE , vol., no., pp.1-7, 16-19 June 2013. [2] Peças Lopes, J.A., Moreira, C.L., Madureira, A.G., ‘Defining control strategies for microgrids islanded operation’, IEEE Trans. on Power Systems, 21, (2), May 2006, pp. 916- 924. [3] Guerrero, J.M., García de Vicuña, L., Matas, J., Castilla, M. and Miret, J. , ‘A wireless controller to enhance dynamic performance of parallel inverters in distributed generation systems’, IEEE Trans. on Power Eelectron., 19, (5), September 2004, pp. 1205-1213 [4] A. C. Zambroni de Souza, M. Santos, M. Castilla, J. Miret, L. G. de Vicuña, D. Marujo, “Voltage security in AC microgrids: a power flow-based approach considering droop-controlled inverters”, IET Renewable Power Generation, DOI: 10.1049/iet-rpg.2014.0406, Available online: 25 June 2015. [5] Abdelaziz, M. M. A., Farag, H. E., El-Saadany, E. F., Mohamed, Y, A. I. ‘A Novel and Generalized Three-Phase Power Flow Algorithm for Islanded Microgrids Using a Newton Trust Region Method’, IEEE Trans. on Power Systems, 28 (1), 2013, pp. 190-201 [6] Rese, L., Simões Costa, A., Silva, A. S. ‘A Modified Load Flow Algorithm for Microgrids Operating in Islanded Mode’, IEEE PES Innovative Smart Grid Technologies Latin America (ISGT LA), 2013, April 15-17, São Paulo, Brazil. [7] Wenyu, Y., Xuying, Y., Jiandong, D., Xiaozhong, W., Yue, F., ‘Power Flow Calculation in Distribution Networks Containing Distributed Generation’, 2008 China International Conference on Electricity Distribution, 2008, December 10-13, Guangzhou, China. [8] Rodrigues, Y. R., Zambroni de Souza, M. F., Zambroni de Souza, A. C., Lima Lopes, B. I., Oliveira, D. Q., ‘Unbalanced Load Flow for Microgrids Considering Droop Methods’, IEEE General Meeting, 2016, July, Boston, USA. ◉
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