The detailed test plan to be followed by WP6a for POC testing was developed during the second year of the project based on several workshops hosted by WP6a, where selected work packages or the whole consortium were involved as needed. During this process the requirements and recommendations from other work packages were collected based on the their technologies “in the making” and prioritized with respect to technical focus areas as well as the degree of flexibility in the scope of the plan to allow necessary adjustment naturally related to new technologies. The test plan was finalised in December 2010 and specifies 5 key focus areas:
· Batteries, BMS and battery models; driving pattern simulation and charging controls; battery life test and prediction
· Communication technologies and standardized interfaces to enable open network communication and interoperability
· Grid impact of EV charging; the interaction between the charging inverter and the SYSLAB power grid
· Fast charging capabilities and control algorithm; fast charging station design
· System integration between the EV/battery, the charging point and the SYSLAB micro grid.
The detailed scope of each test categories is documented in the working version of the test plan and has been adjusted during the 3rd project year based on the new knowledge gained in the project and the actual capability of the test lab.
III Key Findings from POC (Proof Of Concept) Testing
The different types of EV batteries have different characteristics regarding cost, energy density, safety, energy efficiency, degradation etc., making them suitable for different EV applications. On the EDISON POC test platform, we have tested two types of batteries: A 50 Ah / 16 kWh LFP battery for PHEV applications, and a 75 Ah / 26 kWh NMC battery, suitable for pure EV applications. The test results we have obtained from the performance characterisation of the batteries in general confirm the performance characteristics specified by the suppliers and reported generally in the literature.
Today, batteries are still a critical component in the EV industrialization due to their high price, technical complexity, limited records of long term operational data, etc. BMS functionalities are very important for the optimal use and handling of batteries; lack of knowhow towards these new types of batteries among EV academic and industrial professionals is an issue with respect to safe and optimal operation and correct handling of EV batteries. To validate battery aging models, one needs to understand the correlation between stress patterns and battery degradation mechanism; the lifetime prediction of the batteries can only be made generically and semi-quantitatively based on the battery type, charging and driving patterns, quality of the battery product and diagnostic measurements of SOH (State of Health).
EV fast charging (or alternatively battery swapping) infrastructure is expected to be requested for specific EV applications in the urban areas, like EVs in regular services (public transport, delivery vans etc.), and along the highways to compensate for the limited driving range provided by a fully charged battery (typically 150-200 km). Fast charging and battery swapping are expected to be provided from central stations with multiple charging posts or swapping stands.
In principle, fast charging in itself is not necessarily harmful for EV battery’s lifetime, but it does require sufficient understanding of the battery system and charging technology. The functionality of the BMS could play a critical role to make an EV battery robust or vulnerable towards fast charging. Temperature seems to be the critical factor, and cooling system is important to secure controlled fast charging without compromising the service life of the battery.
Power system impact
The bottom line is, the charging hardware connected to the grid has to live up to the existing grid code requirements for such devices and it is the responsibility of the device suppliers to secure this. The design of the charger will determine the grid impact of EV charging depending on the active/reactive power characteristics of the charging inverter.
One of the major conclusions of EDISON is that smart charging can turn electric vehicles from grid congestion threats to flexibility resources. The smart charging tests performed have demonstrated that even with a very simple control algorithm (without any forecasting) it is possible to provide the required charging and at the same time provide power system services in terms of regulation of the aggregated local power, reducing the peak power (reducing the power capacity of the power connection) and the total energy exchange (reducing the energy losses in the power connection line) of the power exchange with the national grid. This shows the potential to use EV batteries to successfully deliver power balancing services to the grid when the communication interfaces between the battery BMS, charging inverter and the control room of the grid are standardized for interoperability.
Standardization and compatibility
It is very important to implement standardized and compatible communication and control interfaces ICT platforms for charging infrastructure to support intelligent and controllable charging in an open network for optimal socioeconomic impact. Such technologies have been successfully developed and demonstrated in EDISON. At the “fast charging and batteries” demonstration stand on the Bornholm EDISON day in September 2011, we demonstrated in lab scale that EV charging can be intelligently and remotely controlled. Furthermore, the EDISON EV batteries have been used to stabilize the SYSLAB power grid with the 10 kW wind turbine, 8 kW PV panel and the 10 kW flexible load in both charging and V2G modes based on the control strategy selected for the SYSLAB grid. This demonstration provides the proof of concept for using EVs as flexible distributed energy resources (DER) to maximise the use of wind power and avoid unnecessary grid upgrade due to congestion in the distribution grid caused by uncontrolled EV charging in peak load time windows.
Please find more details about WP6a lab testing of the interplay between the EV batteries and the DTU Risø SYSLAB micro grid in these reports: