The digital grid interoperability under test

Background and context

Energy digitalisation is bringing an urgent need for testing the interoperability of smart grid components, applications and solutions. 

The next-generation electricity grid is expected to integrate interoperable technologies – particularly in the energy, transport, information and communication fields – with the aim to increase reliability, affordability and sustainability of grid and market operations. 

As an example, fast charging emerges as the user's preferred choice for e-mobility services. The rated power of fast chargers, their expected operation during peak hours, their clustering and interoperability raise significant concerns. On one hand standards are required for power quality, especially harmonic distortion due to the use of power electronics connecting to high loads. On the other hand, infrastructure dimensioning and design limitations for those investing in such facilities need to be considered. 

A unified approach towards a European framework for developing interoperability testing specifications is still missing. To this end, in our laboratories we systematically test and quantify the digital grid interoperability through real world implementationsThe establishment of an integrated distributed laboratory will facilitate the modelling, testing and assessment of power systems beyond the capacities of each single entity, enabling remote access to software and equipment anywhere in the EU.

Role

Against this background,

  • We established a Smart Grid Interoperability Laboratory within a European Interoperability Centre for Electric Vehicles and Smart Grids. The Smart Grid Interoperability Laboratory, deployed in the JRC Ispra (IT) and Petten (NL) sites, supports the development of EU policies by testing of the interoperability of devices and systems according to the applicable standards and with reference to relevant architecture and use cases.
  • We look into interoperability issues between the electric vehicles and the charging infrastructure, covering hardware and information exchange protocols. In particular, we assess EV fast charging devices' performances in different conditions and scenarios. Exposing electric vehicles to extreme temperatures limits their driving and charging performances. For the foreseen adoption of EVs not only it is important to study the technology behind it, but also the environment it will be inserted in. In Europe, temperatures ranging from -30 °C to +40 °C are frequently observed and the impacts on batteries are well known. However, the impact on the grid due to the performance of fast chargers under such conditions also requires analysis, as it affects both on the infrastructure’s dimensioning and design. 
  • We compiled best practices in a unified smart grid interoperability testing methodology, comprising of activities, inputs and outputs, and considering a wide range of smart grid implementations. We propose a detailed test set up, by designing an extensive template for the Basic Application Interoperability profile to be used as an interoperability testing protocol. The test specifications are created to guide the stakeholder through a step by step process by setting the Equipment under Test (EUT), the System under Test (SUT) and the control/measuring equipment. The whole process will be automated through a database, which will be made open source to be used as a common reference.
  • We realised the first test case addressing interoperability in the context of Demand Side Management. The two steps indicated in the Interoperability Testing Methodology have been followed: First, the Demand Side Management test bed was built and tested from scratch. We have realized and tested an end-to-end small scale system in the lab from the customer to the energy provider and the DSM concept has been followed by achieving communication between consumer-energy provider. Remote load control has been accomplished. Afterwards, the first interoperability test was carried out by embedding a new smart meter. Three interoperability layers have been tested. The importance of a DSM program has been highlighted and its feasibility has been proved emphasizing on the customers' involvement and active participation in reducing consumptions. 

2018 - NB-PLC channel: Estimation of periodic impulsive noise parameters and mitigation techniques

This paper proposes a method to estimate the occurrence and duration of the dominant category of noise, the periodic impulsive noise, which greatly degrades the signal quality. Narrowband Power Line Communication (NB-PLC) plays a key role in the deployment of smart grid, since it is a widely spread technology for smart grid applications and systems, like the Advanced Metering Infrastructure (AMI) system. In this paper, we study the characteristics of the NB-PLC channel and noise. A technique is proposed to mitigate the noise effect, with the use of Luby Transform (LT) codes. The proposed scheme exploits the features of the dominant noise on the NB-PLC channel and mitigates its effect especially in highly noisy environments. An estimation algorithm of the burst time occurrence and its duration is introduced. The system can estimate these parameters with an accuracy in the range of 10−4 and it can work even without channel state information. The proposed scheme is compared to two popular NB-PLC technologies, namely the PRIME and G3-PLC, whereas the results show that it can be very effective under severe noise conditions.

2018 - Smart Meter Traffic in a Real LV Distribution Network

This paper examines the smart meter traffic that needs to be accommodated by a real distribution system. Parameters such as the message size and the message transmission frequency are examined and their effect on traffic is showed. Limitations of the system are presented, such as the buffer capacity needs and the maximum message size that can be communicated. For this scope, we have used the parameters of a real distribution network, based on a survey at which the European Distribution System Operators (DSOs) have participated. For the smart meter traffic, we have used two popular specifications, namely the G3-PLC–“G3 Power Line communication” and PRIME–acronym for “PoweRline Intelligent Metering Evolution”, to simulate the characteristics of a system that is widely used in practice. The results can be an insight for further development of the Information and Communication Technology (ICT) systems that control and monitor the Low Voltage (LV) distribution grid. The paper presents an analysis towards identifying the needs of distribution networks with respect to telecommunication data as well as the main parameters that can affect the Inverse Fast Fourier Transform (IFFT) system performance. Identifying such parameters is consequently beneficial to designing more efficient ICT systems for Advanced Metering Infrastructure.

2018 - A DSM test case applied on an end-to-end system, from consumer to energy provider

This paper describes a small scale system, built and tested in our lab, which represents a real end-to-end system from the consumer to the energy provider. Real-time informed consumers can offer the needed flexibility through modifying their behaviour or by engaging with Demand Side Management (DSM) programs. The latter requires the intervention of several actors and levels of communication management which makes this task difficult from an implementation perspective. We programmed the system according to the Object Identification System (OBIS) specification to obtain consumers’ consumption through smart meters with high frequency (one minute). This allows remote control of their appliances in order to reduce the total neighbourhood consumption during critical time periods of the day (peak time). These results and the realisation of a realistic end-to-end system open the way to more complex tests and particularly to the possibility of benchmarking them with other lab tests.

 

2017 - Fast charging performances in different conditions and scenarios

This paper analyses the performances of seven different fast chargers  while charging a full battery EV under four temperature levels (-25 °C, -15 °C, +20 °C and +40 °C). The current total harmonic distortion, power factor and standby power were registered. Results show that the current total harmonic distortion THDI tends to increase with lower temperatures. The standby consumption shows no trend, but results range from 210 VA to 1800 VA. Four out of seven chargers lost interoperability at -25 °C. Such non-linear loads, present high current harmonic distortion as well as high reactive power, hence low power factor. The temperature at which the vehicle’s battery charged is crucial to the current it can take in, hence influencing the charger’s performance. This is a very practical situation where we can advise on the dimensioning/design and distribution of the charging infrastructure in Member States.

2017 - Fast charging diversity impact on total harmonic distortion due to phase cancellation effect

This report analyses performances and impact on power quality of different fast chargers for electric vehicles.

Full charging cycles were performed in the studied chargers and THDV and THDI were observed. From the measurements it can be observed that the phase angles vary within a preferential range, i.e. remain within a range which is actually <90˚of amplitude.

Two of the Chargers, working individually, failed to comply with the standards. Charger A barely makes it in terms of TDD and Charger C is out of the limit. In terms of individual harmonics also Charger A and Charger C are out of the limit of 4.5% for the 11th and 13th harmonics.

The next step of the research will be to obtain the statistical distribution of each of the phase angles for all Chargers and perform simulations with different scenarios. Results so far suggest that stand alone Chargers with low short circuit values are recommended to have filters <13% THD.

2017 - Multi-site European framework for real-time co-simulation of power systems

This paper describes a framework for virtual integration of laboratories enables co-simulation and joint experiments that include hardware and software resources hosted at geographically distributed laboratories. The underlying concept of such framework is geographically distributed real-time (RT) co-simulation. To this end, digital RT simulators are interfaced over long distances via shared communication network such as the Internet. This study proposes an architecture for a modular framework supporting virtual integration of laboratories that enable flexible integration of digital RT simulators across Europe. In addition, the framework includes an interface that enables access for third parties via a web browser. A co-simulation interface algorithm adopted in this study is based on representation of interface quantities in form of dynamic phasors. Time delay between RT digital simulators is compensated by means of phase shift that enables simulation fidelity for slow transients. The proposed architecture is realised for the integration of laboratories across Europe that are located at RWTH Aachen University in Germany, Politecnico di Torino in Italy and at European Commission Joint Research Centres in Petten, Netherland and in Ispra, Italy. The framework for virtual integration of laboratories presented in this study is applied for co-simulation of transmission and distribution systems.

2016 - A European Platform for Distributed Real Time Modelling & Simulation

This report presents the proposal for the constitution of a European platform consisting of the federation of real-time modelling and simulation facilities applied to the analysis of emerging electricity systems. Such a platform can be understood as a pan-European distributed laboratory aiming at making use of the best available relevant resources and knowledge for the sake of supporting industry and policy makers and conducting advanced scientific research.

The report describes the need for such a platform, with reference to the current status of power systems; the state of the art of the relevant technologies; and the character and format that the platform might take. This integrated distributed laboratory will facilitate the modelling, testing and assessment of power systems beyond the capacities of each single entity, enabling remote access to software and equipment anywhere in the EU, by establishing a real-time interconnection to the available facilities and capabilities within the Member States.

2016 - Smart Grid Interoperability lab at the JRC

This paper presents the scope of the Smart Grid Interoperability lab of the JRC. The lab is a testing facility on the interoperability of smart grid systems and its aim is to assess technological implementations according to proposed standards, use cases and processes in conjunction with applicable reference architectures. The goal is to contribute to policy making and industrial innovation regarding the modernization of the electricity grid.

The lab will work on the verification of the interplay among grid components, benchmarking of different solutions, and identification of gaps and challenges. The work is performed in collaboration with industry and research institutions.

The paper presents the latest research activities of the lab, focusing on interoperability and assessing new technologies as well as on the integration of its simulation facilities with other European smart grid labs with the aim to develop a pan-European platform for testing and simulation for power systems analysis. Emphasis is given to the European political context.

2015 - Grid harmonic impact of multiple electric vehicle fast charging

This paper reports results from four sets of measurements performed during the complete charging cycle of an EV, and analyses individual harmonic’s amplitude and phase angles behaviour. In addition, the voltage and current Total Harmonic Distortion (THD) and Total Demand Distortion (TDD) are calculated and the results compared with the IEEE519, IEC 61000/EN50160 standards. Additionally, two vehicles being fast charged while connected to the same feeder are simulated and an analysis is carried out on how the harmonic phase angles would relate. The study concludes that TDD is a better indicator than THD, since the former uses the maximum current (IL) and the latter uses the fundamental current, sometimes misleading conclusions, hence it is suggested it should be included in IEC/EN standard updates. Voltage THD and TDD for the charger analysed, were within the standard’s limits of 1.2% and 12% respectively, however individual harmonics (11th and 13th) failed to comply with the 5.5% limit in IEEE 519 (5% and 3% respectively in IEC61000). Phase angles tended to have preferential range differences from the fundamental wave. It was found that the average difference between the same harmonic order phase angles was lower than 90°, meaning that when more than one vehicle is connected to the same feeder the amplitudes will add. Since the limits depend on the upstream short circuit current (ISC), if the number of vehicles increases (i.e. IL), the standard limits will decrease and eventually be exceeded. The harmonic limitation is hence the primary binding condition, certainly before the power limitation. The most binding limit to the number of chargers is not the power capacity of the upstream power circuit but the harmonic limits for electricity pollution.

 

 

You may also be interested in:

Smart grid costs, benefits and impacts

Electricity security in the EU: features and prospects

Scanning the smart electricity ecosystem

Smart Metering deployment in the European Union