Electric Vehicle Charging Stations in Magdeburg

Electric Vehicle Charging Stations in Magdeburg Thoralf Winkler, Przemyslaw Komarnicki Gerhard Mueller

Guenter Heideck, Maik Heuer Zbigniew A. Styczynski

Fraunhofer Institute for Factory Operation and Automation Magdeburg, Germany [email protected], [email protected] [email protected]

Otto von Guericke University Magdeburg Chair of Electric Power Networks and Renewable Energy Sources Magdeburg, Germany [email protected], [email protected] [email protected]

Abstract—Electrically powered vehicles represent an option to replace fossil fuel. Distributed charging stations are essential to ensure mobility. Charging stations not only charge electric vehicles’ traction batteries, they also function as an interface between vehicles and the grid. Two different types of charging stations have been developed for research projects and academic programs and will be presented in the paper. Keywords – electric drive vehicle, charging station, vehicle-togrid, communication interface

I.

INTRODUCTION

Integral to public and private transportation and mobility in general, motor vehicles are predominantly propelled by combustion engines that burn fossil fuels. The finiteness of fuel resources and the emissions from conventional vehicles have spurred a search for low CO2 alternatives. Combustion engines powered by fossil fuels have inadequate efficiencies and high pollutant and noise emissions. Efforts are underway to replace such vehicles, particularly in large cities and metropolitan areas. Research on batteries for laptops and cellular phones has led to significant improvements in energy storage capabilities. The findings are also advancing electric mobility through significant improvements in energy density and battery stability. These advances have made electric vehicles a viable alternative. Vehicle electrification entails numerous challenges. One is providing drivers the same mobility and comfort as in conventional vehicles. The ranges and charging times of electric cars continue to be factors that limit mobility. Energy storage systems usually need more than one hour of charging time. At present, a storage system cannot be “filled up” like the tank of a vehicle powered by a combustion engine. One option for battery charging is a widespread network of connection points, so-called charging stations. Motor vehicles in Germany are driven an average of 37 km a day. Electric vehicles can be connected with the grid while parked, typically 70-80% of a day. This makes it possible to utilize a vehicle’s storage capacity to store excess energy from the grid or to supply energy to the grid for so-called network services [1], [2]. Since this necessitates appropriate communications support, interfaces for communication between the grid, connection points and electric vehicle shall have to be defined, researched and implemented [3].

II. OTTO VON GUERICKE UNIVERSITY AND THE FRAUNHOFER IFF’S CONCEPTS FOR CHARGING STATIONS A. Objectives Two collaborating research organizations in Magdeburg, Otto von Guericke University and the Fraunhofer Institute for Factory Operation and Automation IFF have devised complementary charging station concepts that are presently undergoing testing. The two charging stations have been designed for both research and teaching purposes. They may be used to run tests, analyze different modes of operation and teach students about the technology. Since cost effective operation was not a priority of charging station development, they have not been optimized for everyday use (e.g. suitability for mass production, protection against vandalism). Nor were aspects of data security necessary for future use addressed. Naturally, current standards [5], [6], [7], [8] for connections and electrical safety were observed. Above all, the concepts devised are intended to furnish universal options to easily intervene in the structure and to research software and hardware for electricity connection and communication. The initial objective is to research energy storage system charging, communication between the grid and vehicles and billing concepts. The charging stations are upgradable for future requirements, e.g. vehicle-to-grid. B. General Requirements Different scenarios exist to charge electric vehicle batteries. Basically, batteries may either be charged by an external charging device or connected to the standard ac system. The former is frequently done when only vehicles of the same type or with identical batteries are being charged, e.g. one company’s transport vehicles (e.g. forklifts, warehouse vehicles). Electric vehicles and batteries utilized in public transportation vary widely and their charging electronics are specified for the particular type of battery. Therefore, just like other battery powered equipment, the actual charging electronics are mounted on the vehicle itself and integrated in the vehicle electronics. A charging station is not only the connection point to an electricity supply network but also a communications interface through which vehicle electronics communicate with a supply network and exchange information and data [9]. Commands for controlled charging and billing data on electricity received (or supplied to the grid in vehicle-to-grid concepts) are transmitted.

C.

Otto von Guericke University’s Charging Station

The charging station at Otto von Guericke University is primarily intended to demonstrate the practical implementation of theoretical approaches to electric mobility and to serve as a teaching tool for academic programs. The Chair of Electric Power Networks and Renewable Energy Sources’ charging station is a system for connecting electric vehicles to the grid and charging electric vehicles’ batteries. The hardware and software concept covers user management, administration and authentication. The charging station is connected to the network by Ethernet and thus supports bidirectional data exchange and external system control. This may be used for monitoring of the system state and electric parameters of the grid and consumers or for online billing through the interface. The system’s measuring electronics were selected to bidirectionally measure electric power and other relevant electrical parameters. Thus, consumers can be characterized and network condition analyzed. Cursor keys and a display have been integrated as an input/output interface for users and facilitate intuitive operation of the charging station.

grid to compensate for load peaks or fluctuating energy supply, e.g. from wind energy converters, requires such additional grid data in order to effectively utilize the vehicles’ energy storage systems. The multifunction meter provides such data. The user uses the rotary switch to select a desired socket (5) and the cursor keys to activate the charging station’s output (4). A control lamp illuminates to signal voltage at the selected port. The login function ensures the quantity of energy withdrawn is only allocated to the specific user. This is important for billing purposes. The system is either deactivated by cursor keys or automatically when the user logs out. Much like at a typical gas station, the user may view the price of the energy, the amount of energy stored in the batteries and the total price of the charged energy. Figure 2 presents the charging station’s task structure. Communication and information are provided by an 8-bit microcomputer. The multifunction instrument delivers various network parameters for later analysis. This block contains every structural element, e.g. electronic power converters, necessary for the charging station to connect both to the grid and electric vehicles. It also includes a user display that visualizes menu functions and a keypad for input. Communication with the service computer takes place through the microcomputer’s LAN adapter. The station requires a four-quadrant measurement to evaluate electric vehicles that feed energy back into the grid. Measurements of each of the phases’ currents and their symmetry deliver information on operational performance and power quality.

Fig. 2.

Fig. 1. The university’s charging station. 1 – universal measuring device; 2 – display; 3 – control lamps for sockets; 4 – cursor keys; 5 – selective switch for sockets; 6 – 3P 400V/16A socket; 7 – 1P 230V/16A socket; 8 – 3P 400V/32A socket

The charging station’s front panel (Fig. 1) has sockets at the bottom with variously configured plugs (230 V / 16 A, 400 V / 16 A and / 32 A) for electric vehicles. A class 1 energy meter with current and voltage classes 0.5, the multifunction meter (1) displays important network parameters. In addition to detecting bidirectional energy, it is also able to measure power harmonics and voltages, the power factor, THD, cos(phi) and network frequency. This supports analysis of the grid condition at the connection point and the connected consumer. The integration of electric vehicles in the

Block diagram of Otto von Guericke University’s charging station

The universal measuring device measures active and reactive power. For billing purposes, charging station parameters, e.g. power, must be measured with at least an accuracy class 2. Conventional instruments have at least an accuracy class 1 and thus easily meet charging station requirements. The microcontroller reads the measured values and transmits them by Ethernet (IEEE 802.3). The system may also be controlled by Ethernet. This option establishes the conditions for further research on vehicles as power providers to the grid (V2G). The interface for communication between the charging station and a smart meter in private households makes intelligent charging possible. Flexible tariffs enable owners to control the amount their vehicles charge or discharge. This opens the possibility of using electric vehicles to store energy to supply power system services.

D.

The Fraunhofer IFF’s Charging Station The Fraunhofer IFF’s charging station is an extension of a conventional power system connection point. Furthermore, it includes options for visualization and facilitates vehicle-system interaction. The charging station consists of a hardware block with switching elements that control an electric vehicle’s connection to the grid. The hardware block contains units for communication between a vehicle and the charging station and the charging station and the grid as well as metering units that measure electricity data (voltage, current, power factor, active and reactive power, transmitted electricity). The central element is a panel PC with a touchscreen that receives user input, coordinates communication with the grid and vehicles and records and visualizes system entries, operating states and energy consumption. The charging station includes two individual switched socket-outlets of 16A@1~230 V and 16A@3~400 V (Fig. 2) and thus covers a broad power range.

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standard charging, battery monitoring). Moreover, only onboard charging controllers guarantee safe and reliable battery operation, particularly when lithium batteries are used. European carmakers intend to connect their electric vehicles to the grid at 230 V or 400 V levels and a standard for plugs is being developed. Data transfer and protocols also require standardization.

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Fig. 3.

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III.

6

CHARGING STATION OPERATION

A. 7

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Schematic of the 3~400 V section; the 1~230 V section is designed analogously

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Fig. 3. The Fraunhofer IFF’s Charging station. 1 – mains fuse; 2 – RCD; 3 – Fuses; 4 – switch; 5 – USB relay card; 6 – single phase and three phase metering device; 7 – network router; 8 – panel PC; 9 – single phase AC socket; 10 – three phase AC socket

The charging station (Fig. 3) is connected to a three phase 400 V AC grid. An RCD protects users should a vehicle or the charging cable’s electric insulation malfunction. The industrial panel PC controls the charging through a USB relay card that activates the switch for the preselected socket (single or three phase). A metering device measures each of the sockets’ energy consumption. The current values of voltage, current, cos (phi) and active and reactive power are transmitted by RS232 to the panel PC and the measured values are stored in an external database. Moreover, the communication interface to the vehicle allows exchanging data between a superimposed control station and a vehicle. This is the prerequisite for other concepts such as command-controlled charging or the provision of power system services. Neither charging station influences the charging process or battery management. The function of the charging station is to provide vehicles access to the electric grid, to meter and bill energy consumption and to facilitate communication between cars and data control and data storage subsystems. Signals to start or stop charging may also transmitted to vehicles. Onboard electronics control the actual charging (including rapid or

Otto von Guericke University’s Charging Station Electrical consumers with different characteristics (heat gun at phase L1, PC at phase L2, soldering station at phase 3) were connected to verify the functionality of the charging station and the universal measuring device. The electrical network’s performance was tested and the measurement results were analyzed. An analysis of the total harmonic distortion (THD) for the phases revealed variances between the different singlephase consumers (Fig. 4). Equipment with nonlinear characteristics produce harmonic oscillations and interharmonics. The distorted currents cause a voltage drop across the grid impedance and thus system perturbation and distortion of the current’s fundamental sinusoidal oscillation. The monitor and PC power supply units, which may be considered switch devices, cause the high percentage of harmonics (Fig. 3). The heat gun and the soldering station on the other hand constitute resistive loads that only have a very low percentage of harmonics.

Fig. 3. Harmonics of the mains

The voltages and the frequency of the university’s threephase system were recorded over twenty-four hours and compared with a phasor measurement unit or PMU (Fig. 4).

consumed and the price of the energy appear on the display. The energy tariff is displayed too. Finally, a charging bill may be sent by email. “Conventional” current is presently used for charging. The use of renewable energy, e.g. generated directly by an integrated solar power system, is conceivable in the future.

Fig. 4. UMG96S and PMU measurement of mains voltage and frequency at university over 24 hours, on March 26, 2009.

The recorded frequency of the multimeter (UMD) and the reference device are almost identical. The measurements at the two different measuring points in the university’s supply network display a constant variance. During the measurements, the UMD’s voltage was 8V higher than the voltage measured at the charging station. The use of two different measuring instruments in two different measuring points (nearer to and farther from the transformer station) accounts for this. Tapchangers are activated to compensate load changes. Therefore, the voltage is stepped. The measurements demonstrate that the charging station correctly measures the power system parameters. This information may be accessed by the Internet connection. This type of data access and exchange will enable power system and charging station operators to activate different control and protective measures remotely in the future.

Fig. 6. Electric vehicle charging.

The user positions the switch to select the appropriate outlet and charging begins at a maximum loading power of 1.2 kW (Figure 6). Within two hours, the lead-acid batteries are charged up to 40%. The price for a full charge equaling 3.5 kWh sufficient for a range of 50 km is about ninety cents. B.

The Fraunhofer IFF’s Charging Station The Fraunhofer IFF’s charging station has been in operation since 2006. It supplies connected electric vehicles with electrical energy in time-controlled operation. At present, research is being done on the connection of electric vehicles to the grid, communication between electric vehicles and the charging station and communication between the charging station and superordinate control systems. The capture and billing of consumption data is being researched are also being investigated. To this end, the university’s electric vehicle is brought in to test the interoperability of the different billing systems and operating concepts.

Fig. 5. The university’s charging station with the electric car SAM.

Otto von Guericke University’ charging station at is located outdoors (Fig. 5). The user must enter a personal identification number to initiate charging. User name, the amount of energy

Fig. 7. Charging the university’s electric vehicle at the Fraunhofer IFF’s charging station.

Unlike the university’s charging station, the Fraunhofer IFF’s charging station is not publicly accessible. The charging station is fully controllable from a touchscreen input panel with soft keys (Fig. 7). Serving as the visual interface, the touchscreen may also display advertisements or other promotional information The operational concept is simple. When the screen is touched, an input window appears and the user enters the proper user name and password for identification. Then, the input screen for charging parameters opens (Fig. 8) and instructs the user to select the appropriate socket. In its current design, the charging station is unable to identify which socket a vehicle requires. Such a function is planned for the future. Fig. 9. Online data visualization of charging station power data

The electric power consumption of the entire Fraunhofer IFF building may be viewed and visualized online, e.g. the three phase mains current measured by a PMU at the Fraunhofer IFF’s transformer station (Fig. 10). Power consumption data is stored in the online data base.

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Fig. 8. Charging parameter screen input. 1 –voltage (socket for 230 V/ 16 A single phase or 400 V/ 32 A three-phase), 2 –charging time, 3 –odometer reading (optional)

The data captured by internal charging station sensors is stored in a database and archived. Depending on the application den, it is provided to vehicle users or vehicle control systems, e.g. battery management. The number of users or cars is unlimited. Ongoing research is focusing on the integration of the charging station control unit in a superordinate data control center and the transmission of data to and its evaluation in a database. Use of the integrated panel PC to store data is also being studied.

Fig.10. Typical variation of the Fraunhofer IFF building’s mains current over one day.

Its energy consumption is characterized by a remarkably high base load, even at night (servers, blowers, compressors), which increases during working hours. The measured charging current of an electric vehicle (Fig. 11) is relatively small compared to the mains current of the entire building.

The influence of charging stations on the local energy system is another focus of research. The high currents when simultaneously charging, and especially when rapidly charging, a large number of electric vehicles must be factored into the overall load of the grid. The online data visualization tool (Fig. 10) is able to access the connected charging stations’ combined database as well as the phasor measurement units (PMU), which analyze grid status and stability [11]. Power and energy parameter data may be accessed from any PC once a user name and password have been authenticated.

Fig.11. Charging current of an electric vehicle, connected to the single phase socket of the Fraunhofer IFF’s charging station.

The vehicle’s internal controller, which limits the current, controls charging. At the end of charging, the load current decreases according to the vehicle battery’s charging characteristic. When electric vehicles are charged with higher currents, the influence of loading becomes visible in the power consumption data. Moreover, it may be advisable to control the start time of charging when a large number of electric vehicles is charged at the same time. Adapting the time of charging to the grid’s load profile can prevent overload and/or load peaks. IV.

CONCLUSION

The use of electric vehicles promises to bring many advantages. By storing excess energy, e.g. generated by renewable energy sources, electrically powered vehicles would be environmentally compatible and simultaneously contribute to network stability e.g. by feeding power back into the network. Electric vehicles have substantially lower operating costs than conventional motor vehicles. Unlimited mobility, network stability and environmental compatibility will however necessitate organizing and establishing the appropriate charging station infrastructure. The nexus between electric vehicles and electric power systems, charging stations shall have to be able to transmit different technical as well as human parameters, e.g. login and billing parameters. The two types of charging stations presented here provide different options to upgrade them and to use them to test different measurement and communication technologies. Data transmission, access and user-friendly visualization concepts, e.g. Web based external or internal charging station applications, have already been developed. The potential influence their operation has on superordinate elements such as buildings deserves consideration. Both technical connections, including plugs, and IT aspects, e.g. data transmission protocols and billing mechanisms, shall have to be standardized for future use and thus constitute further field of research.

ACKNOWLEDGEMENTS The authors would like to thank Christoph Wenge for his input in this paper and for the practical calculations, which were part of his Diplom thesis completed at Otto von Guericke University Magdeburg. REFERENCES [1]

S.D. Jenkins, J.R. Rossmaier, and M. Ferdowsi, "Utilization and effect of plug-in hybrid electric vehicles in the United States power grid", in Proceedings of the Vehicle Power and Propulsion Conference VPPC'08: Harbin, China, 3-5 Sept. 2008. [2] S. Blumsack, C. Samaras, and P. Hines, "Long-Term Electric System Investments to Support Plug-in Hybrid Electric Vehicles", in Proceedings of the 2008 IEEE Power & Energy Society general meeting: Pittsburgh, PA, 20 - 24 July 2008. [3] T. Engel, Plug-in Hybrids. 1st ed. Munich: Hut, 2007. [4] M. Ferdowsi, "Plug-in Electric Drive Vehicles: Experiences in Research and Education", in Proceedings of the 2008 IEEE Power & Energy Society general meeting: Pittsburgh, PA, 20 - 24 July 2008, Piscataway, NJ: IEEE, 2008. [5] EN 61851-1: Electric vehicle conductive charging system - Part 1: General requirements [6] EN 62196-1: Plugs, socket-outlets, vehicle couplers and vehicle inlets Conductive charging of electric vehicles - Charging of electric vehicles up to 250 A a.c. and 400 A d.c. [7] EN 61851-21: Electric vehicle conductive charging system - Electric vehicle requirements for conductive connection to an a.c./d.c – supply. [8] EN 61851-22: Electric vehicle conductive charging system - A.C. electric vehicle charging station. [9] D.U. Sauer, "Energy Storage Systems: The Latest Trends", in International Summer CRIS Workshop on Distributed and Renewable Power Generation, Magdeburg, 16-19 September 2008. [10] T. Winkler, J. Kroitzsch: Intelligentes Batteriemanagementsystem für Elektrofahrzeuge. In: 6. IFF-Kolloquium, Magdeburg, November 2008., [11] P. Komarnicki; C. Dzienis; Z. A. Styczynski; J. Blumschein; V. Ce nteno: “Practical experience with PMU system testing and calibration requirements”, in Proceedings of the 2008 IEEE Power & Energy Society general meeting: Pittsburgh, PA, 20 - 24 July 2008, Piscataway, NJ: IEEE, 2008.