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Energies 2017, 10(7), 1067; doi:10.3390/en10071067

Control Strategy for a Grid-Connected Inverter under Unbalanced Network Conditions—A Disturbance Observer-Based Decoupled Current Approach

1
Department of Electrical and Electronics Engineering, University of Johannesburg, Auckland Park 2006, South Africa
2
Faculty of Engineering, Østfold University College, Kobberslagerstredet 5, 1671 Krakeroy-Fredrikstad, Norway
3
Department of Electrical Engineering & Mechatronics, Technical University of Kosice, Rampová 1731/7, 040 01 Košice, Džung’a-Džung’a, Slovakia
4
Mechatronics Engineering, Faculty of Engineering and Natural Sciences, Sabancı University, Istanbul 34956, Turkey
*
Author to whom correspondence should be addressed.
Received: 17 June 2017 / Revised: 3 July 2017 / Accepted: 10 July 2017 / Published: 22 July 2017
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Abstract

This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration of total utility power. However, restrictive grid codes require that renewable sources connected to the grid must support stability of the grid under grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a proportional current controller with a first-order low-pass filter disturbance observer (DOb). The proposed controller establishes independent control on positive, as well as negative, sequence current components under asymmetrical grid voltage conditions. The approach is independent of parametric component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb. A numerical simulation model of the overall power system was implemented in a MATLAB/Simulink (2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover, a set of simulation results provided in the article matches the developed theoretical background for its feasibility. View Full-Text
Keywords: power control; power electronics; pulse width modulation inverters; disturbance observer; grid connected system; grid stability; distorted voltage power control; power electronics; pulse width modulation inverters; disturbance observer; grid connected system; grid stability; distorted voltage
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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

Ozsoy, E.; Padmanaban, S.; Mihet-Popa, L.; Fedák, V.; Ahmad, F.; Akhtar, R.; Sabanovic, A. Control Strategy for a Grid-Connected Inverter under Unbalanced Network Conditions—A Disturbance Observer-Based Decoupled Current Approach. Energies 2017, 10, 1067.

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