Unified Virtual Oscillator Control for Grid-Forming and Grid-Following Converters

A unified virtual oscillator controller (uVOC) is proposed, which enables a unified analysis, design, and implementation framework for both grid-forming (GFM) and grid-following (GFL) voltage-source converters (VSCs). Oscillator-based GFM controllers, such as dispatchable virtual oscillator control...

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Bibliographic Details
Published in:IEEE journal of emerging and selected topics in power electronics 2021-08, Vol.9 (4), p.4573-4586
Main Authors: Awal, M. A., Husain, Iqbal
Format: Article
Language:English
Subjects:
Control systems design
Controllers
Converters
Data buses
Design parameters
Distributed generation
Electric potential
Fault ride-through
Flow control
grid-following (GFL) converter
grid-forming (GFM) converter
oscillator-based control
Oscillators
Overcurrent
Phase locked loops
Power flow
Switches
Synchronism
Synchronization
unified virtual oscillator control
unified virtual oscillator controller (uVOC)
Voltage
Voltage control
weak grid
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Description
Summary:A unified virtual oscillator controller (uVOC) is proposed, which enables a unified analysis, design, and implementation framework for both grid-forming (GFM) and grid-following (GFL) voltage-source converters (VSCs). Oscillator-based GFM controllers, such as dispatchable virtual oscillator control (dVOC), offer a rigorous analytical framework with enhanced synchronization but lack effective fault handling capability, which severely limits practical application. The proposed uVOC facilitates synchronization with an arbitrarily low grid voltage and fast overcurrent limiting; this enables effective fault ride-through unlike existing GFM controllers which typically switch to a back-up controller during the fault. GFM operation with uVOC is achieved in both grid-connected and islanded modes with seamless transitions between the two. In GFL converters, bidirectional power flow control and dc bus voltage regulation are achieved with uVOC. No phase-locked loop (PLL) is required for either GFL or GFM operation circumventing the synchronization issues associated with PLLs in weak grid applications. Detail small-signal models for GFM and GFL operation have been developed, and the systematic design guidelines for controller parameters are provided. The proposed controller is validated through hardware experiments in a hybrid ac-dc microgrid.
ISSN:2168-6777
2168-6785
DOI:10.1109/JESTPE.2020.3025748