Steady state evaluation of distributed secondary frequency control strategies for microgrids in the presence of clock drifts

Abstract

©2017 IEEE. This is an author produced version of a paper published in Proceedings of 25th Mediterranean Conference on Control and Automation. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works. Uploaded in accordance with the publisher's self-archiving policy.eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.Steady state evaluation of distributed secondary frequency control strategies for microgrids in the presence of clock drifts* Abstract-Secondary frequency control, i.e., the task of restoring the network frequency to its nominal value following a disturbance, is an important control objective in microgrids. In the present paper, we compare distributed secondary control strategies with regard to their behaviour under the explicit consideration of clock drifts. In particular we show that, if not considered in the tuning procedure, the presence of clock drifts may impair an accurate frequency restoration and power sharing. As a consequence, we derive tuning criteria such that zero steady state frequency deviation and power sharing is achieved even in the presence of clock drifts. Furthermore, the effects of clock drifts of the individual inverters on the different control strategies are discussed analytically and in a numerical case study.

Analysis of the Effect of Clock Drifts on Frequency Regulation and Power Sharing in Inverter-Based Islanded Microgrids

“…The analysis focuses on steady-state properties of the frequency control and active power sharing, as well as on stability properties considering clock drifts. It covers the results presented in [27]- [30], and extends them with additional policies, with steadystate expressions of the equilibrium points, with a robust stability characterization of the equilibrium points, and/or with experimental validation. In addition, it complements the analysis of local policies given in [32] because the focus of this paper is mainly on control schemes that exchange control data to accomplish the frequency control.…”

“…In [28] it is shown that local clock drifts in local integral controllers designed for frequency regulation make the MG unstable, results that are illustrated with simulations. The work by [30] provides an steady-state analysis of several distributed secondary frequency control strategies with consideration to clock drifts, illustrated with simulation results. In [31], and focusing in angle droop control, stabilizing controllers based in consensus are derived to remove the negative effects that drifts have on frequency control and power sharing.…”

A Consensus-Based Control Law for Accurate Frequency Restoration and Power Sharing in Microgrids in the Presence of Clock Drifts

“…A GFI is a voltage source inverter which is controlled using pre-defined voltage and frequency values [2], [3]. Inspired by conventional power systems, a hierarchical control strategy is advocated in case of MGs [4], out of which, in this paper, we are interested in distributed secondary frequency control [1], [5]- [9] which uses local information as well as neighboring information over a communication network to ensure frequency restoration and power sharing (PS).…”

“…In an inverter-dominated MG, each inverter typically has only a local understanding of time, which leads to clock inaccuracies [10]. In practice, clock drifts [11], [12] are non-negligible phenomena in distributed MG control [1]. A main reason for this is that in the presence of clock drifts, the internal frequency of an inverter differs from its actual electrical frequency [10], [13].…”

Risk-Averse Model Predictive Operation Control of Islanded Microgrids

“…The lower control layers, i.e., primary and secondary control, are designed such that the MG can run autonomously for several minutes, so providing power setpoints to the units on the same timescale is sufficient. These control layers ensure a desired power sharing (see, e.g., [46], [47]) among the grid-forming units.…”