MET4EVCS PROJECT: DEVELOPING A REFERENCE INFRASTRUCTURE FOR ELECTRIC VEHICLE CHARGING STATIONS

MET4EVCS PROJECT: DEVELOPING A REFERENCE INFRASTRUCTURE FOR ELECTRIC VEHICLE CHARGING STATIONS Javier Díaz de Aguilar, Albert Pueyo Balsells, Centro Español de Metrología (CEM) David de la Vega, Igor Fernández, Universidad del País Vasco (UPV/EHU) Summary: The MET4EVCS project, which started on July 1, 2024 and will last for 3 years, aims to develop an integrated, reliable and balanced electric vehicle charging infrastructure for the traceable evaluation and metrological characterisation of electric vehicle charging systems under real operating conditions. It is composed of 22 participants, including national metrology institutes, universities and research centres, whose work is based on four main lines: regulation and standards, grids, measurement equipment and reference standards. This article aims to explain the objectives of the project, the current status with a description of the available equipment for the development of the reference laboratory for characterisation of charging stations, as well as the equipment for analysis in its interaction with the grid. Keywords: Charging stations, Electric vehicle, Power grid, Conducted emissions, Grid impedance, Electric power INTRODUCTION Electric vehicle charging infrastructure is in the process of expanding, being a key element to achieve the development and implementation goals of electric mobility, as defined by the Alternative Fuels Infrastructure Directive 2014/94/UE [1] and the European Green Deal. Currently, the assessment of electric vehicle charging systems lacks test procedures, methods and other influencing factors that may occur during its actual operation. This may pose challenges when ensuring accuracy of energy measurements and its reliability. The main objective of the European MET4EVCS project is to provide a comprehensive electric vehicle charging infrastructure to enable accurate and reliable energy metering and associated losses. In addition, the project will include the detailed characterisation of negative effects of electromagnetic interference and power quality as a result of the actual operation of the charging stations and on the charging stations. New reference standards will be developed for real-world conditions in the form of quantified grid distortions and for a wide variety of operating modes. The project started in July 2024 and is expected to last 3 years. It is funded by European Partnership on Metrology (EPM) [2], with a budget of 2M € and is composed of 22 participants from 15 countries across Europa and America, including national metrology institutes, universities and research centres. PROJECT The project focuses on developing metrological capabilities for the traceable measurement of electric vehicle charging stations under real operating conditions. To this end, work is being done in four areas:  The regulatory framework, where an analysis and review of the relevant standards is being carried out [3].  The study and evaluation of the grid distribution conditions and the impact on its quality in the surrounding of electric vehicle charging stations.  The measurement equipment necessary to assess electric vehicle charging systems.  The development of definition of reference standards for the calibration of the measuring systems for charging stations. Work plan The specific objectives are structured according to the work plan outlined below: 1. Evaluation of the impact of the electric vehicle charging process on the grid distribution Charging points in operation, like any other electronic device connected to the electricity grid, generate an impact in the form of modifications to grid impedance and conducted emissions through the distribution grid. The objective is to evaluate this dual impact through several measurement campaigns conducted in the countries of the project participants. The selection of the charging points to be evaluated will aim to cover different technologies (both AC and DC), charging stations with different power levels, as well as various electric vehicle models and different operating conditions (charging states). These measurements will be carried out both on the distribution network and in several laboratories, where available charging points can be operated under controlled conditions. In all these scenarios, the impact on the power grid will be measured on-site, in the form of conducted disturbances in the local grid and changes in its impedance. The frequency range covered in the project extends up to 150 kHz, as previous studies have shown that the charging process can generate highamplitude emissions, as well as variations in grid impedance, across this entire frequency range. To achieve this, measurement systems specifically designed for these tests have been developed. These measurement systems, in addition to providing high accuracy and good resolution in both the time and frequency domains, must be portable and independent of power supply, and must provide the robustness required for measurements in the power grid (protection against high-amplitude transients). Furthermore, the data processing must enable detailed analysis in both the time and frequency domains, detailed characterisation of the emissions and the evaluation of shortand longterm variations caused by the charging process. 2. Development of traceable methods and test benches for the characterisation of alternating current charging stations, under real and controllable operating conditions The objective is to develop a reference electric vehicle charging infrastructure through the design, integration, and verification of test benches to characterise and ensure the performance and accuracy of energy metering of charging stations, with target uncertainties of 0.1%. The characterisation involves introducing real and controllable operating conditions in the form of grid distortions, based on quantitative data obtained from the work described in the previous subsection. This must be done for a wide range of charging conditions, including different power and current levels as well as representative dynamic loads, in compliance with relevant international standards (IEC 61851-1). The operational range will cover voltage values of 230 V (+/- 15%), currents up to 64 A, and charging powers up to 44 kW. This infrastructure will support the performance of alternating current charging stations for electric vehicles, in terms of consistent, reliable, and traceable measurements. 3. Development of traceable methods and test benches for the characterisation of direct current charging stations in the laboratory and in-situ verifications The objective is to develop traceable methods and measurement standards for the characterisation of direct current charging stations under real operating conditions, for low, medium, and high power levels. This includes developing measurement methods and an infrastructure for in-situ verification of the energy measurement of charging stations. To achieve this, a test bench will be designed and integrated to apply different realistic operating conditions, such as: various types of distribution networks (rural, urban and industrial), aggregated emission scenarios, dynamic loading, bidirectional transfer of energy, and varying grid impedance. The operational range will cover voltages up to 1000 V, currents up to 500 A, charging powers up to 350 kW, and emissions generated at frequencies up to 150 kHz. 4. Dissemination of results The project will disseminate the results obtained and facilitate the adoption of the developed technology and measurement infrastructure by directly related stakeholders:  The measurement supply chain.  Standard and model regulation development organisations. Those directly involved with the results include: IEC TC 69, WELMEC WG 11, OIML TC 12/p3, EC WgMI E01349.  End users, who, in this case, are the companies involved in the electric vehicle charging process: grid distribution operators, charging point manufacturers, charging service providers, CPOs, etc. IMPACT OF ELECTRIC VEHICLE CHARGING SYSTEMS ON THE POWER DISTRIBUTION GRID Several studies have shown that charging systems generate unintended emissions and changes in grid impedance, which can pose electromagnetic compatibility issues and affect PLC (Power Line Communications) [4]. On one hand, emissions generated by the internal rectifiers of power electronics in chargers, with switching frequencies of up to several hundreds of kHz, can be significant in amplitude and propagate through the grid, creating and impact not only in the vicinity of the charger itself but also at various points in the low-voltage network [5]. However, there have also been instances where the emissions during charging are found to be colored noise decreasing with frequency [6]. Figure 1 illustrates the emissions generated by the electric charging process (in the figure, EVCP), in an isolated network compared to the situation without charging (“default” in the figure) [6]. The results show generated emissions at multiples of the inverter switching frequency (16 kHz), with amplitudes significantly exceeding the out-of-band emission limits defined for communication equipment [7] (emission limits for conducted disturbances generated by electric vehicles during charging have not been defined). Figure 1. Emissions generated during the electric vehicle charging process (EVCP2), at two states of charge (75% and 100%), compared to the situation without charging (default) [6] On the other hand, recent measurement campaigns have shown that charging processes cause changes in grid impedance [8]. Due to the lack of measurement aimed at characterising this phenomenon, the results of this project will be of great interest for assessing the effect of impedance changes on the propagation of conducted emissions. EQUIPMENT FOR THE CHARACTERISATION OF CONDUCTED EMISSIONS The research group TSR (Tratamiento de la Señal y Radiocomunicaciones) of UPV/EHU has designed and implemented a measurement system capable of accurately capturing and subsequently processing the conducted emissions generated by electric vehicle charging processes [6]. The system (see figure 2) is connected to the power grid via a voltage probe specifically designed for these types of measurements [9], which provides galvanic isolation and filters the strong 50 Hz component of the grid voltage. This way, the signal acquisition part, based on a digital oscilloscope, is protected from overvoltage and transient phenomena. The system is completed by a portable computer which runs software specifically designed to automate and process the measurements. The software enables realtime visualization of conducted emissions, up to a frequency of 500 kHz. Figure 2. Measuring system for the characterisation of conducted emissions up to 500 kHz. EQUIPMENT FOR THE CHARACTERISATION OF GRID IMPEDANCE A specific measurement system has also been designed and implemented to characterise the average grid impedance up to 500 kHz, as well as its rapid variations within a 20 ms period. The system allows for realtime visualization of the average impedance [10]. The system (see figure 3) consists, on one side, of electronic circuitry designed to provide grid coupling, in addition to protecting the other equipment in the complete system. An arbitrary signal generator is used to generate and inject a test signal covering the frequency band of interest, and a digital oscilloscope captures the current measured at two different points in the implemented circuit. Both the injection of the test signal and the measurement capture from the grid are performed using commercial current probes. Additionally, a commercial voltage probe is used to capture the grid voltage, providing a reference signal for measuring rapid impedance variations. The entire system is controlled by software specifically designed by the TSR group (UPV/EHU). Figure 3. Measurement system for the characterisation of grid impedance up to 500 kHz. EQUIPMENT AND DEVELOPMENT OF THE REFERENCE LABORATORY One of the reference laboratories will be established at Centro Español de Metrología (CEM), in Madrid. This centre (see figure 4) is equipped with a testing system and electric vehicle emulators, for both alternating current (30 kVA) and direct current (360 kW), including configuration connections, network installation, and the definition of communication protocols between the electric vehicle and the charging station. These emulators are capable of simulating the behaviour of all types of electric vehicles, with a wide range of loads and in a regenerative way, providing the necessary energy dissipation after each charging cycle. This method avoids energy waste during charging tests while allowing for a large number of measurements. Although some preliminary results have been obtained to verify the installation, in the coming months the development of testing procedures will begin to evaluate and characterise charging stations under a wide variety of conditions, including different power and current levels, as well as varying load conditions. The necessary equipment has also been defined for introducing some grid distortion (mainly conducted emissions covering a wide frequency range) to analyse its influence on charging in terms of voltage and frequency. In summary, the goal is to conduct a comprehensive analysis of the system, especially regarding its boundary conditions and the effects produced in its interaction with the grid. In particular, one of the tasks to be developed will be the evaluation of the distortions caused in the grid by the emulators and its impact on the measurement system. Figure 4. CEM Laboratory for testing of electric vehicle charging stations. ACKNOWLEDGEMENTS The project 23IND06 MET4EVCS has received funding from the European Partnership on Metrology, cofinanced from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States REFERENCES [1] European Union, “Directive 2014/94/EU of the European Parliament and of the Council of 22 October 2014 on the deployment of alternative fuels infrastructure”, Official Journal of the European Union, Octubre 2014. [2] EURAMET, European Partnership on Metrology. Available at: https://www.euramet.org/researchinnovation/metrology-partnership/ [3] Organisation Internationale de Métrologie Légale (OIML), “OIML G 22:2022, Electric Vehicle Supply Equipment (EVSE)”, 2022. [4] M. Wasowski et al., “Sources of Non-Intentional Supraharmonics in LV Network and Its Impact on OSGP PLC Communication – Experimental Study,” IEEE Transactions on Power Delivery, vol. 37, no. 6, pp. 5244–5254, 2022, doi: 10.1109/TPWRD.2022.3175090. [5] B. Grasel, J. Baptista, and M. 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