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Energies 2015, 8(12), 13758-13777; doi:10.3390/en81212396

Transient Oscillations Analysis and Modified Control Strategy for Seamless Mode Transfer in Micro-Grids: A Wind-PV-ES Hybrid System Case Study

1
College of Automation, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
2
School of Computer Science, University College Dublin, Dublin 4, Ireland
3
Earth Institute, University College Dublin, Dublin 4, Ireland
*
Author to whom correspondence should be addressed.
Academic Editor: Neville Watson
Received: 20 August 2015 / Revised: 30 November 2015 / Accepted: 30 November 2015 / Published: 4 December 2015

Abstract

With the rapid development of the micro-grid associated with new and clean energies, the smooth switching between grid-connected and islanded operation modes of the micro-grid is a key issue that needs to be addressed urgently. In traditional solutions, V/f (Voltage/frequency) control is adopted for the master micro sources when the micro-grid works in islanded mode, while PQ (real and reactive power) control is adopted when in grid-connected mode. However, when the two controllers switch when mode transfer occurs, transient oscillations usually occur and thereafter the dynamic response will be degraded. This paper considers an archetypical micro-grid with Wind-PV-ES (Wind, Photovoltaic and Energy Storage) hybrid system, which forms the basis of our case study. The underlying reason for such transient oscillation is analyzed in this paper. Thereafter a modified control strategy for seamless mode transfer is designed and implemented. An improved PQ control method is designed by which the output of the PQ controller always synchronously tracks the output of the V/f controller for micro-grid switches from islanded mode to grid-connected; furthermore, a dq rotating coordinate synchronization based V/f control method is proposed for transition from grid-connected mode to islanded mode. Finally, experiments and analysis are undertaken on some basic and important operating cases; the results in our case study indicate that the modified control strategy is effective in dominating the micro-grid during mode transfer and thus yielding significantly better performances. View Full-Text
Keywords: distributed energy resources; micro-grid; grid-connected operation; islanded operation; mode transfer distributed energy resources; micro-grid; grid-connected operation; islanded operation; mode transfer
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Zhang, T.; Yue, D.; O’Grady, M.J.; O’Hare, G.M.P. Transient Oscillations Analysis and Modified Control Strategy for Seamless Mode Transfer in Micro-Grids: A Wind-PV-ES Hybrid System Case Study. Energies 2015, 8, 13758-13777.

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