Modeling, Analysis, and Experimental Validation of Clock Drift Effects in Low-Inertia Power Systems

Abstract

Abstract-Clock drift in digital controllers is of great relevance in many applications. Since almost all real clocks exhibit drifts, this applies in particular to networks composed of several individual units, each of which being operated with its individual clock. In the present work, we demonstrate via extensive experiments on a microgrid in the megawatt-range that clock drifts may impair frequency synchronisation in low-inertia power systems. The experiments also show that-in the absence of a common clockthe standard model of an inverter as an ideal voltage source does not capture this phenomenon. As a consequence, we derive a suitably modified model of an inverter-interfaced unit that incorporates the phenomenon of clock drifts. By using the derived model, we investigate the effects of clock drifts on the performance of droop-controlled grid-forming inverters with regard to frequency synchronisation and active power sharing. The modelling and analysis is validated via extensive experiments on a microgrid in the megawattrange.Index Terms-Smart grid applications, low-inertia power systems, microgrids, grid-forming inverters, droop control, power sharing.

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

“…with F given in (14), completing the proof. Since the coefficients µ i are unknown, Lemma 2 reveals that unlike in the case of ideal clocks [9], [7], [10], when taking clock drifts explicitly into account, it is hard to derive necessary and sufficient conditions for the controller gains B, C, D and k to guarantee power sharing.…”

“…The term clock drifts describes the fact that all units, operated with different processors have a slightly different "understanding" of time, i.e., their clock rates are not synchronized [14]. Most of the distributed control approaches, as they make use of the internal frequencies that are calculated by the controls of the inverters, are influenced by clock drifts.…”

A Flexible Experimental Laboratory for Distributed Generation Networks Based on Power Inverters

“…This characteristic makes difficult to emulate the complex interactions of different DSPs working distributely with inherent transmission delays and also, and more important, with different physical clock generators. In this way, recent works deal with clock synchronization issues in digitally controlled distributed generation networks [38][39][40][41][42]. To the best of the authors' knowledge, most of these works provide only simulation results due to the inherent difficulty in obtaining experimental results.…”

Research on Control Parameters for Voltage Source Inverter Output Controllers of Micro-Grids Based on the Fruit Fly Optimization Algorithm

“…With the rapid development of micro-grid technologies in recent years, modern smart power grids, characterized by diversified energy types [1,2], an individualized energy supply [3,4], a multilayer control system [5,6], multi-type network structures [7,8], and flexible working modes [9,10] have gradually come into being. Since micro-grids have characteristics such as strong intermittency, low damping of output power, and high generation-demand sensitivity [11], the core goal of research on micro-grid control methods is to realize a stable, rapid, and reliable control system. As Figure 1 shows, in a modern micro-grid, primary control-level research has mainly focused on inverter output control, power sharing control [9], and coordinated control of inverters [12].…”