Active power sharing and frequency regulation in inverter-based islanded microgrids subject to clock drifts, damage in power links and loss of communications (original) (raw)

Abstract

Microgrids (MGs) are small-scale power systems containing storage elements, loads and distributed generators that are interfaced with the electric network via power electronic inverters. When an MG is in islanded mode, its dynamics are no longer dominated by the main grid. Then, the inverters, driven by digital processors that may exchange data over digital communication, must act as voltage source inverters (VSIs) to take coordinated actions to ensure power quality and supply. The scope of this thesis is bounded to control strategies for active power sharing and frequency regulation in islanded MGs. The focus is on the analysis of prototype control policies when operating conditions are no longer ideal. In particular, the thesis covers the effect that a) clock drifts of digital processors, b) damage in power transmission lines, and c) failures in digital communications have in control performance. The work is submitted as a compendium of publications, including journal and international conference papers, where two main areas of research can be distinguished. The first area refers to the analysis of the effect that clock drifts have on frequency regulation and active power sharing. VSI digital processors are equipped with oscillators which run at not necessarily identical frequencies. As consequence, the local clocks in the physically distributed inverters may differ. This part, reported in two conference papers and one journal paper, investigates state-of-the-art control policies when clocks of the computational devices drift. The contributions related to this part are a) the reformulation of existing control policies in terms of clock drifts, b) the steady-state analysis of these policies that offers analytical expressions to quantify the impact that drifts have on frequency and active power equilibrium points, c) the closed-loop model capable of accommodating all the policies, d) the stability analysis of the equilibrium points, and e) the experimental results. The second area copes with the analysis of the effect that electrical and communication failures have on frequency regulation and active power sharing. This investigation focuses on distributed/cooperative control policies where each inverter control action is computed using both local measures and data received from other inverters within the MG. This part, reported in one conference paper and two journal papers, investigates two control policies when the considered failures in terms of damage in power links and/or loss of communications between inverters provoke partitions within the MG. The contributions related to this part are a) the formulation of the MG as two connected graphs corresponding to the electrical and communication networks where both type of failures lead to disconnected electrical/communication sub-graphs, named partitions, that co-exist within the MG, b) the closed-loop Miguel Castilla, Jaume Miret and Antonio Camacho, for the scientific collaboration, resource management, and lab facilities, useful to successfully overcome this work.

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References (185)

  1. Paper I: Consensus for Active Power Sharing and Frequency Restoration in Islanded Microgrids Subject to Drifting Clocks C. X. Rosero, P. Martí, M. Velasco, M. Castilla, J. Miret and A. Camacho, "Consensus for active power sharing and frequency restoration in islanded micro- grids subject to drifting clocks," in 2017 IEEE 26th International Symposium on Industrial Electronics (ISIE), pp. 70-75, Edinburgh, June 2017. ATTENTION¡¡ Pages 38 to 44 of the thesis are available at the editor's web https://ieeexplore.ieee.org/document/8001225
  2. Summary 2.1 Introduction ................................................................ 39 2.2 Frequency regulation and power sharing .................... 40 2.3 Theoretical analysis of the impact of drifts ................. 40
  3. 4 Simulation results ....................................................... 42 2.5 Conclusions and future work .........................................44 2.6 Acknowledgment .............................................................44
  4. 7 References ................................................................... 44 Paper II: Impact of Clock Drifts on Active Power Sharing and Frequency Regulation in Distributed-Averaging Secondary Control for Islanded Microgrids C. X. Rosero, H. Carrasco, M. Velasco and P. Martí, "Impact of clock drifts on active power sharing and frequency regulation in distributed-averaging secondary control for islanded microgrids," in 2017 IEEE International Autumn Meeting on Power, Electronics and Computing (ROPEC), pp. 1-6, Mexico, November 2017. ATTENTION¡¡ Pages 46 to 52 of the thesis are available at the editor's web https://ieeexplore.ieee.org/document/8261675
  5. Summary 3.1 Introduction ................................................................ 47 3.2 Microgrid control ........................................................ 48 3.3 Impact of clock drifts on MG control .......................... 48 3.4 Simulation results ....................................................... 49
  6. 5 Conclusions and future work ......................................... 52
  7. 6 Acknowledgment ............................................................. 52
  8. 7 References ................................................................... 52
  9. Paper III: Analysis of the Effect of Clock Drifts on Frequency Regulation and Power Sharing in Inverter-Based Islanded Microgrids P. Martí, J. Torres-Martínez, C. X. Rosero, M. Velasco, J. Miret and M. Castilla, "Analysis of the Effect of Clock Drifts on Frequency Regulation and Power Sharing in Inverter-Based Islanded Microgrids," in IEEE Transactions on Power Electronics, vol. 33, no. 12, pp. 10363-10379, December 2018. ATTENTION¡¡ Pages 54 to 70 of the thesis are available at the editor's web https://ieeexplore.ieee.org/document/8290685
  10. Summary 4.1 Introduction ................................................................ 55
  11. 2 Problem formulation ................................................... 56 4.3 Frequency control and power sharing ......................... 57
  12. 4 Impact of clock drifts: steady-state analysis ................. 60 4.5 Impact of clock drifts: stability analysis ....................... 62
  13. 6 Experimental results ................................................... 64
  14. 7 Conclusion ................................................................... 68
  15. 8 Appendix ..................................................................... 68
  16. 9 References ................................................................... 69 Paper IV: Analysis of consensus-based active power sharing with respect to network topology in islanded microgrids
  17. C. X. Rosero, M. Velasco and P. Martí, "Analysis of consensus-based active power sharing with respect to network topology in islanded microgrids," in IECON 2017 -43rd Annual Conference of the IEEE Industrial Electronics Society, pp. 115-120, China, November 2017. ATTENTION¡¡ Pages 72 to 78 of the thesis are available at the editor's web https://ieeexplore.ieee.org/document/8216024
  18. Summary 5.1 Introduction ................................................................ 73 5.2 Background on MG control ......................................... 74 5.3 Theoretical analysis ..................................................... 74 5.4 Numerical example ...................................................... 76 5.5 Simulations ................................................................... 77 5.6 Conclusions and future work ......................................... 77 5.7 Acknowledgment ............................................................ 77 5.8 References ................................................................... 78
  19. Paper V: Analysis of Consensus-Based Islanded Microgrids Subject to Unexpected Electrical and Communication Partitions C. X. Rosero, M. Velasco, P. Martí, A. Camacho, J. Miret and M. Castilla, "Analysis of Consensus-Based Islanded Microgrids Subject to Unexpected Electrical and Communication Partitions," in IEEE Transactions on Smart Grid, vol. 10, no. 5, pp. 5125-5135, September 2019. ATTENTION¡¡ Pages 80 to 92 of the thesis are available at the editor's web https://ieeexplore.ieee.org/document/8501583
  20. Summary 6.1 Introduction ................................................................. 81 6.2 Modeling approach ...................................................... 82 6.3 Partition analysis ......................................................... 84
  21. 4 Results ......................................................................... 85
  22. 5 Conclusion ................................................................... 89
  23. 6 Appendix ..................................................................... 89
  24. 7 References ................................................................... 90 Paper VI: Active Power Sharing and Frequency Regulation in Droop-Free Control for Islanded Microgrids Under Electrical and Communication Failures
  25. C. X. Rosero, M. Velasco, P. Martí, A. Camacho, J. Miret and M. Castilla, "Active Power Sharing and Frequency Regulation in Droop-Free Control for Islanded Microgrids Under Electrical and Communication Failures," in IEEE Transactions on Industrial Electronics, in press, 2019. ATTENTION¡¡ Pages 94 to 104 of the thesis are available at the editor's web https://ieeexplore.ieee.org/document/8835156
  26. Summary 7.1 Introduction ................................................................ 95 7.2 Modeling approach ...................................................... 96 7.3 Partition analysis ......................................................... 97 7.4 Proposed control strategy ............................................ 99 7.5 Experimental results .................................................. 101
  27. 6 Conclusions ............................................................... 104
  28. 7 References ................................................................. 104 Analysis and conclusions Bibliography
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