![ROCOF analysis results ROCOF [Hz/s]](https://www.researchgate.net/profile/Ninoslav-Holjevac-2/publication/346037803/figure/tbl2/AS:960095479406616@1605916008357/ROCOF-analysis-results-ROCOF-Hz-s_Q320.jpg)
Content uploaded by Ninoslav Holjevac
Author content
All content in this area was uploaded by Ninoslav Holjevac on Nov 20, 2020
Content may be subject to copyright.
A preview of the PDF is not available
ROCOF importance in electric power systems with high renewables share: A simulation case for Croatia
Abstract and Figures
By integrating the new production technologies into the electric power system (EPS) which are mainly inverter-based, the characteristics of the conventional bulk EPS are significantly changed leading to a reduction of synchronous inertia which causes faster frequency dynamics. Synchronous inertia directly affects the maximum value of the rate of change of frequency (ROCOF). The importance of ROCOF is vital: ROCOF is the main parameter for Loss of Mains relay, it is used as an input parameter for Fast Frequency Response and Synthetic Inertial Response control algorithms and can be used as a metric parameter for under-frequency load shedding. In this paper, the importance of ROCOF in the inverter rich EPS will be described in detail, different grid code versions concerning ROCOF will be presented and the results of ROCOF analysis in Croatian EPS with respect to the future renewable energy source (RES) share scenarios will be shown.
Figures - uploaded by Ninoslav Holjevac
Author content
All figure content in this area was uploaded by Ninoslav Holjevac
Content may be subject to copyright.
... With the concept of frequency of CoI, we can deduce the "center" RoCoF that can present the frequency security feature of the power system as the time derivative of the frequency of CoI. The threshold to trigger the RoCoF protection of the power system in some countries, such as Britain [49] and Denmark [49], has been set as a maximal value of the system RoCoF. ...
... With the concept of frequency of CoI, we can deduce the "center" RoCoF that can present the frequency security feature of the power system as the time derivative of the frequency of CoI. The threshold to trigger the RoCoF protection of the power system in some countries, such as Britain [49] and Denmark [49], has been set as a maximal value of the system RoCoF. ...
... Relevant solutions are provided in this section, mainly using the method of slope estimation. The magnitude of the maximal RoCoF highly depends on the contingency and the inertia level of the system, which is an important index to present the frequency security of the power system [49][50][51]. This section discusses the estimation of the maximal RoCoF following an already-occurred event and the prediction of the maximal RoCoF following a potential contingency of the system; the specific classification is shown in Figure 3. Table 2 lists the nomenclature of parameters in Section 3. using the method of slope estimation. ...
As the traditional generation is gradually replaced by inverter-based resources, a lack of rotational inertia is now a common issue of modern power systems, which leads to an increasingly larger rate of change of frequency (RoCoF) following contingencies and may result in frequency collapse. As a crucial index of the frequency security and stability of power systems, the accurate estimation of the RoCoF can be a foundation for the development of advanced operations and control techniques of the future power system. This paper firstly analyzes the role of the RoCoF in typical blackouts occurring in recent years and discusses the physical and numerical nature of the RoCoF; then, by introducing the frequency spatial distribution of the power system, the paper discusses the concept of the “center” RoCoF that can present the frequency security and stability of the entire system. The estimation and prediction techniques of the maximal power system RoCoF following a contingency and the existing real-time tracking techniques of the power system RoCoF are comprehensively reviewed. Finally, the open questions and related research topics of the RoCoF estimation are discussed.
... The rate of change of frequency (RoCoF) is the most important parameter that is used in the loss of mains protection relays, as an oscillation between 1.5 to 2 Hz/s may lead to relay tripping and may result in cascaded failures of the generating units and hence a blackout [3]. Studies show that the RoCoF and the frequency nadir are indicators of the system's inertia [4]. In the traditional power systems, this issue was not significant as the synchronous machines' inertia limited the RoCoF and prevented tripping; however, on increasing the penetration level of renewable energy sources into the grid, the overall system inertia is decreased and the RoCoF needs to be monitored [5,6]. ...
In a world where the energy crisis is becoming overwhelming, demand for integrating renewable energy sources is increasing and forming microgrids is becoming an essential solution. The new microgrid systems, which depend mainly on renewable energy sources instead of conventional synchronous generators, come with a low inertia concern. This paper proposes a virtual inertia controller based on a high-pass filter (HPF) to support the frequency of the AC microgrid while maintaining the DC voltage of the DC microgrid within the nominal ranges in cases of contingencies. The proposed system encounters an AC-DC microgrid with a renewable energy source on the DC microgrid alongside constant power load and resistive loads, while on the AC microgrid side, a synchronous generator is used to present the low inertia of the grid with dynamic loads and static loads. The state-space linearized model of the system is developed and verified using Matlab Simulink. The dynamic response of the proposed controller is compared to the low-pas filter (LPF)-based controller. Moreover, the effect of changing the system’s parameters on eigenvalues is investigated.
The article describes the new application of a well-known protection criterion - Vector Shift (VS). In the paper, technical problems related to the utilization of this criterion have been described. Additionally, the authors conducted laboratory tests of a digital protection relay. The impact of different disturbances occurring in the power systems on the operation of the Vector Shift criterion has been examined. The obtained results have proved the validity of banning the Vector Shift criterion in some countries. Furthermore, a novel application of the Vector Shift criterion has been presented. This criterion could be utilized to determine the degree of balance of a separated island. This information may be helpful in novel power system protection devices used in Smart Grids or microgrids.
The paper presents the importance of the grid inertia constant for the frequency stability of the future high-res low-inertia power systems. Since more and more renewable energy sources (RES) are being connected to the power system via frequency converters, the grid inertia constant is reduced. This issue can be mitigated by applying appropriate control mechanisms through which RES can provide virtual inertia and provide rotating reserves for primary frequency control. The concept of a virtual synchronous generator for providing virtual inertia is elaborated, as a solution to the presented problems. By applying virtual synchronous generators, RES can provide support for frequency control during disturbances almost like conventional synchronous generators. The influence of virtual inertia on the stability of the Croatian power system was analyzed using a battery energy storage systems (BESS) with a control mechanism that enables its participation in frequency control.
Increased wind energy penetration influences the power system dynamic response to transient disturbances. Replacement of conventional production units with converter-connected wind turbines reduces natural power system inertia contained in rotational masses of synchronously connected turbine-generator units, therefore creating low-inertia power systems. Such a transition has an adverse effect on system resilience to disturbances and on the capability to maintain stable operation. This research examines the impact of high regional wind power production on system transient stability in the case of island operation of the Croatian power system. The system is divided into four geographical areas modeled as four centers of inertia with aggregated parameters. The study investigated initial transient RoCoF values in different areas for current and future wind capacity share scenarios, loading data, and primary frequency regulation settings. The modeling and scenario analysis have been performed on a detailed phasor power system model in the MATLAB/Simulink environment.
This presentation summarizes the current requirements for the grid connection of PV systems in Europe as well as the implementation of the European grid code "grid connection regulations for electricity generators" at the national level and describes recommendations for the future-oriented definition of requirements.
This paper investigates the impact of synchrophasor estimation algorithms in Under-Frequency Load-Shedding (UFLS) and Load-Restoration (LR) schemes, relying on frequency and Rate-of-Change-of-Frequency (ROCOF) measurements produced by Phasor Measurement Units (PMUs). We compare two consolidated window-based synchrophasor estimation algorithms, as representative approaches based on static and dynamic signal models, with a focus on the appropriateness of utilizing PMU-based ROCOF measurements. The performance of the proposed relaying scheme is assessed by means of a Real-Time Digital Simulator implementing the time-domain full-replica dynamic model of the IEEE 39-Bus power system.
Decrease of rotational mass in modern power systems is a common experience of system operators around the world. The increasing penetration of variable renewable energy production and thus the use of power converters are fundamentally changing the dynamic behaviour of the power system. The aim of the present paper is to provide an overview on the latest advancements of system operators regarding the analysis and mitigation of the reducing inertia. The theoretical background of power system stability and the calculation of the rate of frequency change are introduced to highlight the importance and the weaknesses of certain metrics used by system operators. Specific operational experiences are compared based on peak load and the nature of the systems. Possible responses by system operators which are discussed in the paper include synchronous and synthetic (emulated) inertia, other technical alternatives (virtual synchronous machines, adaptive load‐shedding schemes), and market‐based solutions. Besides summarising the advantages and disadvantages of those, grey areas of regulation and market structure are highlighted to facilitate forward‐thinking.
Over the last decade, many power systems have significantly changed with the proliferation of renewable generation sources such as wind and solar photovoltaic (PV). Due to their variability and non-synchronous nature, new challenges and complexities have emerged regarding operational security of modern power systems. The 2016 South Australia (SA) blackout exactly occurred under such a high renewable situation. An official report has been recently published to review the causes and provide the corresponding recommendations for improvement of network operation, control and security. However, there are still a number of critical issues and debates which remain unsolved, such as network bottleneck identification, over-voltage explanation, pole slip concern, frequency dip mystery, and frequency/voltage instability debate. In this paper, based on the reconstruction of the event, these unsettled issues are prudently analyzed to unveil their root causes. In addition, an innovative scheme is proposed to prevent the blackout by identifying the network separation at an early stage. This research will not only further advance the understanding of the 2016 SA blackout but also will provide valuable guidelines for the management of future renewable-rich networks.
Rate of Change of Frequency (RoCoF) withstand capability" ENTSO-E guidance document for national implementation for network codes on grid connection
- Entso-E
ENTSO-E "Rate of Change of Frequency (RoCoF)
withstand capability" ENTSO-E guidance document for
national implementation for network codes on grid
connection,", 2017.
Evaluation report on the problem of ROCOF measurement in the context of actual use cases and the 'wish list' of accuracy and latency from an end-user point of view
- G Rietveld
- D Colangelo
- A Roscoe
- K Johnstone
G. Rietveld, D. Colangelo, A. Roscoe, and K. Johnstone,
"Evaluation report on the problem of ROCOF measurement
in the context of actual use cases and the 'wish list' of
accuracy and latency from an end-user point of view."
project report, 2018.
Application on ROCOF protection function in distribution network
- M Lukač
- Z Matišić
M. Lukač, Z. Matišić, "Application on ROCOF protection
function in distribution network" HO CIRED session, 2018.
Frequency Measurement Requirements and Usage
- Entso-E
ENTSO-E, "Frequency Measurement Requirements and
Usage", -Final Version 7 published 29 Jan. 2018, Available
on-line at:https://docstore.entsoe.eu,