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Three-phase primary control for unbalance sharing between distributed generation units in a microgrid

Tine Vandoorn (UGent) , Jeroen De Kooning (UGent) , Jan Van de Vyver (UGent) and Lieven Vandevelde (UGent)
(2013) ENERGIES. 6(12). p.6586-6607
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Abstract
For islanded microgrids, droop-based control concepts have been developed both in single and three-phase variants. The three-phase controllers often assume a balanced network, hence, unbalance sharing and/or mitigation remains a challenging issue. Therefore, in this paper, unbalance is considered in a three-phase islanded microgrid where the distributed generation (DG) units are operated by the voltage-based droop (VBD) control. For this purpose, the VBD control, which has been developed for single-phase systems, is extended for three phase application and an additional control loop is added for unbalance mitigation and sharing. The method is based on an unbalance mitigation scheme by DG units in grid-connected systems, which is altered for usage in grid-forming DG units with droop control. The reaction of the DG units to unbalance is determined by the main parameter of the additional control loop, viz, the distortion damping resistance Rd. The effect of Rd on the unbalance mitigation is studied in this paper, i.e., dependent on Rd, the DG units can be resistive for unbalance (RU) or they can contribute in the weakest phase (CW). The paper shows that the RU method decreases the line losses in the system and achieves better power equalization between the DG unit's phases. However, it leads to a larger voltage unbalance near the loads. The CW method leads to a more uneven power between the DG unit's phases and larger line losses, but a better voltage quality near the load. However, it can negatively affect the stability of the system. In microgrids with multiple DG units, the distortion damping resistance is set such that the unbalanced load can be shared between multiple DG units in an actively controlled manner rather than being determined by the microgrid configuration solely. The unit with the lowest distortion resistance provides relatively more of the unbalanced currents.
Keywords
INVERTERS, COMPENSATION, DROOP CONTROL, DESIGN, CONVERTERS, IMPEDANCE, distributed generation, droop controllers, microgrid, unbalance sharing

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Citation

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Chicago
Vandoorn, Tine, Jeroen De Kooning, Jan Van de Vyver, and Lieven Vandevelde. 2013. “Three-phase Primary Control for Unbalance Sharing Between Distributed Generation Units in a Microgrid.” Energies 6 (12): 6586–6607.
APA
Vandoorn, T., De Kooning, J., Van de Vyver, J., & Vandevelde, L. (2013). Three-phase primary control for unbalance sharing between distributed generation units in a microgrid. ENERGIES, 6(12), 6586–6607.
Vancouver
1.
Vandoorn T, De Kooning J, Van de Vyver J, Vandevelde L. Three-phase primary control for unbalance sharing between distributed generation units in a microgrid. ENERGIES. 2013;6(12):6586–607.
MLA
Vandoorn, Tine, Jeroen De Kooning, Jan Van de Vyver, et al. “Three-phase Primary Control for Unbalance Sharing Between Distributed Generation Units in a Microgrid.” ENERGIES 6.12 (2013): 6586–6607. Print.
@article{4207111,
  abstract     = {For islanded microgrids, droop-based control concepts have been developed both in single and three-phase variants. The three-phase controllers often assume a balanced network, hence,  unbalance sharing and/or mitigation remains a challenging issue. Therefore, in this paper, unbalance is considered in a three-phase islanded microgrid where the distributed generation (DG) units are operated by the voltage-based droop (VBD) control.  For this purpose, the VBD control, which has been developed for single-phase systems, is extended for three phase application and an additional control loop is added for unbalance mitigation and sharing.  The method is based on an unbalance mitigation scheme by DG units in grid-connected systems, which is altered for usage in grid-forming DG units with droop control.  The reaction of the DG units to unbalance is determined by the main parameter of the additional control loop, viz, the distortion damping resistance Rd. The effect of Rd on the unbalance mitigation is studied in this paper, i.e., dependent on Rd, the DG units can be  resistive for unbalance (RU) or they can contribute in the weakest phase (CW). The paper shows that the RU method decreases the line losses in the system and achieves better power equalization between the DG unit's  phases. However, it leads to a larger voltage unbalance near the loads.  The CW method leads to a more uneven power between the DG unit's phases and larger line losses, but a better voltage quality near the load. However, it can negatively affect the stability of the system. In microgrids with multiple DG units, the distortion damping resistance is set such that the unbalanced load can be shared  between multiple DG units in an actively  controlled manner rather than being determined by the microgrid configuration solely. The unit with the lowest distortion resistance provides relatively  more of the unbalanced currents.},
  author       = {Vandoorn, Tine and De Kooning, Jeroen and Van de Vyver, Jan and Vandevelde, Lieven},
  issn         = {1996-1073},
  journal      = {ENERGIES},
  keyword      = {INVERTERS,COMPENSATION,DROOP CONTROL,DESIGN,CONVERTERS,IMPEDANCE,distributed generation,droop controllers,microgrid,unbalance sharing},
  language     = {eng},
  number       = {12},
  pages        = {6586--6607},
  title        = {Three-phase primary control for unbalance sharing between distributed generation units in a microgrid},
  url          = {http://dx.doi.org/10.3390/en6126586},
  volume       = {6},
  year         = {2013},
}

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