DESIGN AND EVALUATION OF DISTRIBUTED CONTROLLERS FOR OPTIMAL DISPATCH AND CONGESTION MANAGEMENT OF MICROGRIDS

Abstract

The microgrid is an alternative for the integration of distributed generation (DG), including renewable energy sources. Therefore, the control should ensure higher reliability, security and minimum operating cost in isolated or grid-connected mode of operation of the microgrid. In this context, the microgrid control tasks can be divided into 3 distinct levels:

1) Primary Control; which includes output current, voltage, and frequency control of DG units, 2) Secondary Control, at which level the frequency and voltage are restored to nominal values, and 3) Tertiary Control, at which level the optimal dispatch of the microgrid and coordination of the microgrid with the main grid are achieved. Each control level traditionally operates on a different time scale.

The primary control is performed within a shorter time scale (milliseconds), the secondary control in seconds, while the optimal dispatch requires several minutes or hours depending on the complexity of the optimization problem to be solved. Regarding the secondary and tertiary controllers, the centralized approach is the traditional control architecture used. However, the centralized approach is less practical because the DG units present a plug-and-play mode operation, which makes the electrical topology microgrid time-varying. Thus, the central controller needs to be modified.

Also, in microgrids line overloading or congestion can occur. The congestion can significantly affect the lifetime of the distribution lines and transformers in the microgrid. Furthermore, the activation of thermal protections can lead to unsupplied demand. Another challenge of microgrid control is related to the topologies of the communication network, which implies loss of data or delays. In order to solve the issues previously described, in this thesis a novel distributed control strategy is proposed, which is based on a consensus algorithm for frequency restoration, congestion management, and optimal operation of the microgrid.

The strategy improves the performance of the microgrid regarding robustness and reliability in the event of communication failure and during plug-and-play operation. The strategy also provides the capacity to cope with rapid changes in demand. The proposed control strategy solves Karush-Kuhn-Tucker (KKT) conditions of a linear optimal power flow formulation based on real system measurements, without requiring a mathematical power flow model. The distributed controller enables the optimal operation of the microgrid in the time-scale of the frequency restoration control.

The congestion problem is solved based on re-dispatch of the generating units using distributed control strategies that do not require adding new and/or expensive technology or solving complex optimization problems. Experimental and simulation results validate the implementation of the proposals.

Publicaciones de Jacqueline del Rosario Llanos Proano:

1.- J. Llanos, D. E. Olivares, J. W. Simpson-Porco, M. Kazerani, and D. Saez. “A Novel Distributed Control Strategy for Optimal Dispatch of Isolated Microgrids Considering Congestion”, IEEE Transactions on Smart Grid, vol. 10, no. 6, pp. 6595 – 6606, 28 March 2019.

2.- J. Llanos, R. Morales, A. Núñez, D. Sáez, M. Lacalle, R. Hernández, and F. Lanas. Load estimation for microgrid planning based on a self-organizing map methodology. Applied Soft Computing, vol. 53, no. 53, pp. 323-335, Jan. 2017.

3.- C. Burgos-Mellado, J. Llanos, R. Cárdenas, D. Sáez, D. Olivares, M. Sumner, A. Costabeber,”Distributed Control Strategy Based on a Consensus Algorithm and on the Conservative Power Theory for Imbalances and Harmonics Sharing in 4-Wire Microgrids”, IEEE Transactions on Smart Grid, vol. 11, no. 2, pp. 1604-1619, March 2020.

4.- E. Espina, J. Llanos, C. Burgos-Mellado, M. Martínez-Gómez, R. Cárdenas-Dobson, and D. Sáez, “Distributed Control Strategies for Microgrids: An Overview”, Accepted to IEEE Access.

5.- C. Burgos-Mellado, J. LLanos, R. Cárdenas, D. Sáez, D. Olivares, M. Sumner, A. Costabeber,”Distributed Control Based on a Consensus Algorithm and a Modified Single Phase Q-E Droop Controller for the Sharing of Imbalance and Voltage Regulation in 3-Wire Isolated Microgrids”, Accepted to IEEE Access.

6.- Espina, E.; Burgos, C. Gómez, J. S.; Llanos, J; Rute, E.; Navas, A.;  Martinez, M.; Sáez, D., and Cárdenas, R. (2020). “Experimental Hybrid ac/dc-Microgrid  Prototype for Laboratory Research”. In:2020 22st European Conference on Power Electronics and Applications (EPE’20 ECCE Europe).

7.- J. Llanos, J. Gomez, D. Saez, D. Olivares and John Simpson-Porco, “Economic Dispatch by Secondary Distributed Control in Microgrids”, 21st European Conference on Power Electronics and Applications, Italy, September 2019.

8.- V. Caquilpan, D. Sáez, R. Hernandez, J. Llanos, T. Roje and A. Nunez, “Load Estimation Based on Self-organizing Maps and Bayesian Networks for Microgrids Design in Rural Zones”, IEEE PES Innovative Smart Grid Technologies, Quito, September 2017.

9.- J. Llanos, D Ortiz Villalba, D. Saez, D. Olivares, “Economic Dispatch for Optimal 4 Management of Isolated Microgrids”, IEEE CONCAPAN XXXVI, Costa Rica, June 2016.