September 15th 2020

Summary Power Quality event

The first Global EV Charging Test Power Quality webinars were a great success! Twelve experts on Power Quality presented during two days in June 2020 their research, findings and advice to a total of more than 200 attendees.

The first day opened with a very insightful presentation by Alex McEachern, founder of PSL labs and one of the pioneers in Power Quality research, who also turned out to have great restaurant tips and who admitted to sometimes even makes PQ mistakes in his own designs. His core message: electric vehicle chargers are relatively new devices with no specific standards to ensure compatibility with the grid yet, while they can have high loads and coupling effects and, with that, create PQ issues in unexpected places. The good news: it is possible to make the chargers immune to PQ disturbances, we just need to justify the extra costs to management and customers.

The presentations later that day by Sjef Cobben, Karima Boukir, Kevin Lorenzo and Cédric Chauvenet followed that line. Sjef Cobben started by giving more insight in the grid as part of a “smart system”, where an electric vehicle can be used as a “Money Making Machine”. Also, an electric vehicle creates new Power Quality challenges, like more voltage variations and supraharmonic distortions. Kevin and Cedric on their part showed with real life examples how Supraharmonics can interact and influence devices and communication. Kevin Lorenzo “observed a strong interaction between a particular EV and PV inverter, with a HF current of 4 amps at 10 kHz between the equipment (not going to the grid). As well inducing some earth leakage current”.  And Cédric followed by clarifying that PLC communication uses a frequency between 35 and 95 kHz, which is exactly the frequency range in which you may have disturbances from EV charging.

During the other two presentations that day, by Erik de Jong of KEMA labs and Alexandre Lucas of the JRC Ispra, the attendees were taken on a virtual tour of their labs. The KEMA Flex Power Grid Lab focusing on Hardware in the Loop (HIL) testing, which enables testing of modern switching devices in real world situations, without truly bringing the real world in a lab. This to ensure we keep “the biggest man-made system ever built: the electric grid” stable while introducing all new kinds of loads. Erik also encourages everyone to consider the Erigrid European research program on smart grid infrastructure, where it is possible to use different European labs for free to perform power system research. Alexandre showed that the power quality and efficiency of DC chargers is not only influenced by external factors like the grid quality or grid impedance, but also by the State of Charge of the vehicle and the outside temperature. Alexandre: “when we decrease the temperature to minus 15 or minus 25 its (efficiency) could be as low as 60(%)”

The second day of the Power Quality event focused on the state-of-the-art research at the Lulea University of Technology (LTU), TU Dresden and TU Eindhoven on Power Quality and, especially, Supraharmonics.

That day kicked off with a presentation from Math Bollen of the LTU. Apart from giving an overview of the history of Power Quality (like the “Television peak” which emerged between 6 and 8 in the evening caused by the AC/DC converters in TVs) and the different research projects on Power Quality at the LTU, he also shed some light on the question who came up with the name Supraharmonic. Apparently, Alexandra von Meier deserves the credits for first mentioning the name. His presentation was followed up by Angela Espin Delgado, PhD student at the LTU, who gave insight in their research on Supraharmonics using hundreds of LED lights. A very economical and practical way to research the effects of large amounts of the same devices. One of her most important findings was that in some situations “the best fit for the grid impedance seemed to be a capacitive modelrather than a resistive or inductive one.

Next was Jan Meyer from the TU Dresden, who during his research was confronted with the fact that not only the standards concerning limits of Supraharmonics need to be defined, but also standards regarding tests and measurements. He made this clear by showing the discontinuity in the current standardization framework “the sudden jump at 9 kHz is only due to the different LISNs that are used according to the test standards” which is not always logical.

Also, he gave insight in certain customer complaints due to Supraharmonics, like a coffee machine only giving water. An example used more often: Math Bollen also mentioned a coffee machine only making tea, and at EDF they had the experience of a coffee machine blowing up the coffee pad. A totally different way to get energized by a cup of coffee.

The second day ended with two presentations from the TU/e: first by Vladimir Cuk, who gave an overview of the research at the TU/e. Vladimir showed that, just because of harmonics of EVs, the maximum penetration grade of electric vehicles in a given area could be lowered by 10 percent, because the maximum capacity of the transformer is reached earlier. Tim Slangen continued with his research at ElaadNL, concerning Electric Vehicles and their PQ impact. He pointed out that 8th out of the 9 measured EVs were a source of supraharmonic currents, and 6 of these EVs emitted at frequencies in the human hearing range. He showed that the behaviour of chargers, and with that the PQ impact, can change radically when charging at non-nominal levels, making a case for specialized standards for EV PQ testing. To end he also gave insight in how the distortions of multiple vehicles propagate and interact, which can create unexpected effects and can make it very hard to determine who is accountable. So, when doing measurements “always take into account the current as well!”

During both days, also some requests and invitations were made. Most importantly: measure! If you have the ability to take measurements in your device, or in the grid, do not hesitate to collect data and to share this with the grid operators and research organisation. This will help you to gather knowledge about intermittent issues with your device, helps to improve the overall insight in PQ in the grid and helps further research. As Math Bollen stated “(if) any of the viewers have reports on interference due to supraharmonics; document it, write a paper about it, and send it to CIRED”. And if you really want to dive into this, Supraharmonics is a new and very interesting research field where a lot of work still needs to be done.

You are all welcome to (re)watch the presentations on our YouTube channel, to contact us for more information or to come around for a cup of coffee (as long as the machine does not fail due to Supraharmonic distortions). We are happy to help. As Erik de Jong stated: “the better we do our job with the integration of EV, the more this becomes the reality sooner rather than later”.