A Small-AC-Signal Injection-Based Decentralized Secondary Frequency Control for Droop-Controlled Islanded Microgrids

In an islanded microgrid composed of droop-controlled parallel inverters, the system frequency endures deviations as the load changes. To compensate for frequency deviation without involving communication infrastructures among distributed generators (DGs), the proportional-integral regulator based s...

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Bibliographic Details
Published in:IEEE transactions on power electronics 2020-11, Vol.35 (11), p.11634-11651
Main Authors: Liu, Baojin, Wu, Teng, Liu, Zeng, Liu, Jinjun
Format: Article
Language:English
Subjects:
Compensation
Computer simulation
Decentralized secondary control
Distributed generation
droop control
Dynamic models
Frequency control
Frequency deviation
frequency restoration
Inverters
microgrid
Microgrids
Proportional integral
real power sharing
Regulators
Restoration
Signal injection
Switches
Voltage control
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Summary:In an islanded microgrid composed of droop-controlled parallel inverters, the system frequency endures deviations as the load changes. To compensate for frequency deviation without involving communication infrastructures among distributed generators (DGs), the proportional-integral regulator based secondary frequency control (PI-SFC) method has been proposed in the literature. However, PI-SFC may incur real power-sharing errors because the integrator accumulates disturbances and noise in each DG, leading to different compensation values of nominal real power. To achieve frequency restoration while maintaining equal real power sharing among DGs, this article proposes a small-ac-signal injection-based secondary frequency control (SACS-SFC) method, which is implemented by injecting an additional ac signal into the output voltage of each DG. Furthermore, a droop relation between the frequency of the injected SACS and the compensation value of nominal real power is innovatively established to trim the output real power of each DG to be equal. Frequency deviations caused by primary droop control are thus eliminated, and even real power sharing can be maintained among DGs. Moreover, the control parameters of the proposed SACS-SFC are comprehensively designed via steady state and dynamic model of the system. Simulation and experimental results demonstrate the effectiveness of the proposed method.
ISSN:0885-8993
1941-0107
DOI:10.1109/TPEL.2020.2983878