The team worked with Power Research Electronics and Last Mile Solutions, funded by the Dutch Urban Energy Top Consortium (TKI Urban Energy).
Solar panels produce direct current (DC) and this normally has to be converted to alternating current (AC) before it can charge an electric car. The team developed a two-way 10kW direct charger using silicon carbide FETs and quasi-resonant technology which results in a high efficiency of over 96% for both full load and partial load and is a third the size of a conventional AC charger.
“Charging stations are currently using the 50Hz AC network to exchange power between the solar panels and the vehicle,” said Chandra Mouli at TU Delft. “However, this is not efficient or cost-effective, for two reasons. Firstly, converting to AC results in unnecessary steps and loss. And, secondly, it requires two separate DC-AC converters, one for the vehicle and one for the solar panels, resulting in increased costs and dimensions.”
“A more self-evident solution would be to use a single converter, which could charge the vehicle from the panels via a DC link while also being connected to the AC electricity grid. In this study, we designed a 10kW converter with an internal DC link and three terminals, which can charge the vehicle both from the solar panels and the electricity grid. The integrated DC charger has a higher efficiency and is about three times smaller than existing solutions based on AC power exchange.’
This means the electricity grid is no longer needed as an interim stage in charging. In addition, the charged car battery can be used to supply a house with electricity.
“The developed converter is used in a solar charging station, including smart charging algorithms. Charging the vehicle with solar energy resulted in zero CO2 emission, lower fuel costs, tax benefits and less dependence on the feed-in tariffs for renewable energy,” he said. The charger is compatible with the CHAdeMO and CCS/Combo charging standard and is designed for implementing smart charging algorithms that integrate several applications together: PV forecast, EV user preferences, multiplexing of EVs, vehicle-to-grid demand, energy prices, regulation prices and distribution network constraints. These algorithms reduced the net costs by up to 427% and 651% when compared to average rate charging.
In principle, the system can be expanded by connecting several chargers and solar panels together for power flows up to 150kW. This would enable business parks and residential districts to supply electricity in a new way, partly separate from the electricity grid. Power Research Electronics has now produced a number of high-speed chargers based on the design.