State of the art in the research area

In the last ten years, renewable energy sources in Europe began to represent an important factor in achieving the goal of reduction in emission of harmful greenhouse gasses. Simultaneously, they assure the provision of electrical energy. For example, in Europe in 2017 for the first time, the yearly amount of electrical energy generated from renewable energy sources has exceeded the amount of electrical energy generated from conventional fossil fuels.

Parliament and the EU Council have agreed that the ratio of the energy from renewable sources become at least 32% of the gross total consumption of the EU until 2030. Also, energy efficiency should increase by 32,5% by 2030 and ease the households to autonomously generate, store and spend green energy.
On the other hand, supply from renewable energy sources (e.g. solar panels, wind generators) is unstable considering the source of the energy they convert (e.g. sun, wind). Furthermore, if those sources are left unsupervised and unchecked, the increase of their use will result in deterioration of power quality (PQ), instability of electric power system (EPS) with the possibility of situational system failure and disruption of the electrical energy distribution system.
For a long time, scientists and expert public in the field regard intelligent (i.e. smart) electrical grid (figure 1.) as the only possible response to reliably manage energy provided from large scale renewable sources, which is also issued through EU directives and local legislature (e.g. [1] and [2]).
In Europe, and especially in the Republic of Croatia, complete metrological infrastructure that provides measuring equipment and verified protocols is missing in order to:
1. monitor and manage the stability of future intelligent power grid and quality of electrical energy,
2. develop, test and recalibrate necessary equipment needed to achieve this complicated task.

Electrical grid system operators (EGSO’s) need tools for monitoring grid stability and energy quality under especially difficult dynamic conditions that occur in power grids where significant amount of power comes from renewable sources (as this is expected to happen in Croatia in the near future). Among those tools is so-called WAMS or WAMPAC (system for surveillance, management and protection of EPS in real time) whose core function is based on processing data obtained from phasor measurement units (PMU) and phasor data concentrators (PDC) nearly in real time [3]. Furthermore, data acquisition and signal adaptation merging units (MU) are used.
Inside of these measuring devices, signals obtained from voltage and current transformers are sampled. Then, computer determines the phasors (complex numbers that represent a transformation of current values of three-phase voltage into a first complex number, and the current value into the other) according to the internationally standardized algorithm. After determining amplitude and angle for all voltage phases and current phases, they are timestamped with a precise international (UTC) time value. By doing that, phasors became synchrophasors, whose phase angles are mutually comparable since their time of sampling is known. Standard C37.118.1 prescribes important requirements for measuring and computing of synchrophasors. Measurement accuracy is defined as the vector difference of measured and referent value (total vector value). Apart from the synchronous measurement of phasors, PMU communicates with its master system in real time. Formats and communication protocols for data transmission are prescribed in standard C37.118.2. The instructions for synchronizing, calibrating and installing the PMU device are defined in the C37.242 standard, though they are still subject to a series of researches and enhancements.

Euramet projects ENG04 and ENG52 (from 2010 to 2017) [7] and [8] made significant progress in this area, but Croatia did not participate in the same because of lack of energy and energy measurement infrastructure and research related to smart grids. At the same time, these projects highlighted the important lack of the existence of measuring traceability and lack of standards for power and energy measurement.
The home research project "Smart grid metrology infrastructure - SMAGRIMET" (for the period 2015-2019) has launched the first serious research in this area, not just in the Republic of Croatia, but also wider. Significant project results are reflected in highly developed precision voltage and current metering transducers and completely new algorithms for accurate analysis of obtained data, which has been recognized through published scientific papers at conferences and journals.

This project also identified a number of metrological challenges and needs (creating algorithms for faster and more accurate determination of actual situation in the electrical grid, providing stationary and portable calibration systems for PMU and MU units and providing a development model/prototype of PMU unit for research of algorithms in this project, but also in future research activities) that provide the necessary support in assuring the security of electrical energy supply and grid stability.
It is important to emphasize the fact that the topic of "intelligent energy grids", especially in the area of PMU modelling and associated algorithms, is a highly propulsive research area in which many things are still not completely defined. Additionally, intense research is also being carried out in the field of "intelligent grid” analysis. The goal of these international research activities is to create a new type of supplies and consumers that independently analyse and adapt to events on the grid.

The main objective of this new project is to develop, examine and validate new measuring tools and equipment, which will support the management of increasingly complex intelligent grid paradigms and ensure the stability and quality of the delivered electrical energy.
This project will also ensure the continuity of existing domestic successful research in this area and open up the possibility of a better linkage with foreign research institutes.