DOI: https://doi.org/10.15407/techned2016.01.081

HIERARCHICAL CONTROL STRATEGY FOR UNBALANCED VOLTAGE IN AN ISLANDED MICROGRID

Authors
Tianyi Ma^1,2, Guangyao Cheng¹, Xinjun Liu^2
1 – Beijing Institute of Graphic Communication,
Room C318, Unit No.2, Xinghua Street, Daxing District, Beijing, 102600, China,
e-mail: Этот e-mail адрес защищен от спам-ботов, для его просмотра у Вас должен быть включен Javascript
² – Tsinghua University,
Room 1502, Building 9003, Shuangqing Street No.30, Haidian District, Beijing, 100084, China

Abstract

When the microgrid is running in an islanded mode, unbalanced loads result in microgrid voltage unbalance. The voltage unbalance factor at the Point of Common Coupling (PCC) is a key parameter in measurement of microgrid power quality. To improve microgrid power quality, many documents utilize micro-source voltage measurement results to help adjust the unbalance factor of microgrid voltage. However, due to line impedance presence, there are differences between micro-source output voltage and PCC voltage. Therefore, it is impossible for a micro-source to control the unbalance factor of PCC voltage with high precision by measuring its own output voltage. Based on equivalent circuit, the present paper analyzes the negative sequence component relationship among micro-source output voltage, line impedance voltage drop, and PCC voltage. It further proposes a hierarchical-control-based method to control the unbalance factor of PCC voltage with high accuracy, and analyzes the impact of secondary control delay on system stability by root locus calculating. Finally, the control strategy is validated in an islanded microgrid system with two micro-sources. The experimental results show the effectiveness and feasibility of the proposed control strategy. References 8, figures 7.

Key words: microgrid, hierarchical control, islanded mode, voltage unbalance, line impedance.

Received:    18.11.2015
Accepted:    04.01.2016
Published:   29.01.2016

References

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