Charging Infrastructure for Electric Vehicles
Challenges to managing the transformation from passive end user to active grid user
The future energy supply grid in the low-voltage range (grid levels 6 and 7) will no longer operate according to the top-down principle that has been common up to now, in which the load flow was from the higher-level medium-voltage grid to the low-voltage grid and thus to its consumers. The electricity customers connected there, usually consisting of small or medium-sized industrial, commercial and agricultural enterprises and households are predominantly ohmic/inductive consumers (e.g. heating/drive motors). However, this principle is becoming replaced by a grid operation in which the originally passive consumers also become active electricity producers. Responsible for this development are new technologies, including decentralized renewable energy sources (RES) such as photovoltaics, but also decentralized power storage. Likewise, locally distributed, high-performance consumers such as charging stations for electric vehicles or air conditioners/heat pumps are penetrating all layers of electricity consumption right through to the single-family home. Due to the increasing number of such components, whose generation or consumption often fluctuates greatly, former pure consuming customers also become generators (prosumers) for a time. In addition, their output and consumption will increase in the future due to rising volatility on the electricity market. This poses new challenges for the low-voltage grid. Research topics in this environment are dealt with in a scientifically and practically oriented way at the Institute of Electrical Power Systems at Graz University of Technology in the form of research projects, cooperation projects with industry and commerce.
Due to IEAN's experience in these fields and its high motivation to advance new technologies, charging stations for electric vehicles have established themselves as one of the research priorities at the institute. Examples of research foci on this topic at the Institute are:
Charging electric vehicles
In general, a widespread charging infrastructure for electric vehicles is now part of the public image; charging stations can be found in charging parks in car parks, at service stations or in underground car parks, but also in front of public or semi-public buildings (e.g. administration and industry) and in the private sector. From the outside, it may seem that safe and reliable operation of these charging stations is a matter of course, but there is a great deal of know-how behind these electrical components and their interconnection. By way of illustration:
There are two approaches to charge electric vehicles by means of conductive charging devices from an electrical engineering point of view: Charging with direct current and charging with alternating current. Both variants are state of the art, a distinction is made between alternating current charging stations (AC-EVCS) and direct current charging stations (DC-EVCS). In the first case, the electric vehicle is charged using single- or three-phase alternating current in the range from 3.7 kW (slow) to 11/22 kW (accelerated). The conversion from alternating to direct current (which is required by the battery of the electric vehicle) is done by means of the vehicle's internal charger (en. on-board charger, OBC). The advantage of DC-EVCS is that they supply electric vehicles directly with direct current required by the accumulator, which leads to a higher possible charging power (50/150/350 kW) and thus the EV is charged faster. The transformation from alternating current to direct current takes place in the converter integrated in the charging station, which is fed from the low-voltage grid and, if necessary, buffered by a battery. The connection between the electric vehicle and the charging station is established either manually by means of a charging cable set or automatically with a robot arm or pantograph.
Alternatively, there are also developments regarding inductive (i.e. contactless) charging of electric vehicles, although this is of little practical importance today (May 2020).
Due to the widespread distribution and the challenges for the (low-voltage) grid, approaches to remote controlled charging are already popular. This would allow an individual regulation of the charging power depending on the infrastructure utilisation and these systems could then be used for load control in the low-voltage grid to optimise the use of renewable energy sources and to prevent overloading of the electric grid.
It can already be seen, that the different approaches for electric vehicle charging result in a broad research need. The IEAN is concerned with all these approaches and is already setting research priorities in these fields. The following topics are also dealt with in more detail:
Initial and periodic testing of charging infrastructure
Operators of charging infrastructure assume certain responsibilities towards their employees or towards their customers with regard to the maintenance of the necessary level of appropriate safety precautions, among other things with regard to ensuring personal protection and protective measures against electric shock, during construction or the subsequent commissioning and operation. Essentially, the aim is to ensure that protection is permanently guaranteed, thereby reducing the danger posed to people by electric current to an acceptable minimum. For regular and reproducible testing of the protection and protective measures, suitable methods including associated test equipment are required. In the case of AC-EVCS, this can be achieved without any problems in compliance with national regulations (including in Austria the Elektrotechnikverordnung ETV 2010, Elektroschutzverordnung ESV 2012, OVE E 8101, OVE Richtlinie R 30) using a conventional installation tester combined with appropriate adapter solutions - for example to type 2 connectors. The periodic testing of DC-EVCS, however, represents a correspondingly bigger challenge and cannot currently be carried out using simple adapters and commercially available testing devices. In cooperation with partners from industry (KS Engineers) and the Institute for Electrical Systems and Networks of Graz University of Technology, guidelines and regulations to this effect are currently (May 2020) being drawn up and a testing device for DC-EVCS is being developed. The following figure illustrates a corresponding verification setup to test a DC charging station with a test device prototype developed at IEAN together with the company KS Engineers as part of a research project.
Integration of charging infrastructure in low-voltage grids
The charging infrastructure for electric vehicles is mainly located at the low-voltage level (grid levels 6 and 7). High-performance charging stations with 11/22 kW AC and ≥ 50 kW DC can lead to a corresponding additional load on the assigned grid level. Of interest and therefore part of several research projects is the analysis of the integration of an appropriate number of charging stations into existing power grids, e.g. by means of penetration scenarios and load control options.
If the required charging power cannot be provided by the existing or appropriately adapted grid, it is essential to expand the grid. It is quite possible that the system components required for supply, such as cables, transformers and protective devices, will have to be re-dimensioned. In the case of newly constructed charging parks with a corresponding number of EVCS with charging powers in the range of 50/150/350 kW, this is common practice anyway.
The institute also deals with relevant topics concerning the controlled charging of electric vehicles, which primarily address the supply dependency of electric energy from renewable sources as well as the possible limits of the infrastructure (utilisation of the grid, etc.).
Herbst, D., Schürhuber, R., Schmautzer, E.
Methods for the verification of protective measures for safety of DC charging stations for electric vehicles
In: Renewable Energy & Power Quality Journal, 17, 390-393., https://doi.org/10.24084/repqj17.320, 01.07.2019 [Journal Paper]
Herbst, D., Schürhuber, R., Schmautzer, E.
A contribution to protective measures against electric shock at DC charging stations
In: IEEE Transportation Electrification Conference and Expo - ITEC 2019, Novi, USA / Vereinigte Staaten, 21.06.2019 [Paper und Vortrag]
Herbst, D., Schürhuber, R., Schmautzer, E., Fürnschuß, M., Auer, Ch.
Überprüfung der Schutzmaßnahmen zum Schutz gegen elektrischen Schlag von DC-Ladestationen für Elektrofahrzeuge
In: 11. Internationale Energiewirtschaftstagung - IEWT 2019, Freiheit, Gleichheit, Demokratie: Segen oder Chaos für die Energiemärkte?, 13.02.2019 [Paper und Vortrag]
Herbst, D., Schmautzer, E., Schürhuber, R., Jauk, B., Unterweger, M., Wolf, C.
Konzept und Prototyp zur Überprüfung der Schutzmaßnahmen gegen elektrischen Schlag von DC-Ladestationen für Elektrofahrzeuge
In: 15. Symposium Energieinnovation - EnInnov2018, Neue Energie für unser bewegtes Europa, 14.02.2018 [Paper und Vortrag]