Growing prizes of fossil fuels, environmental issues and bigger capacity accumulators transform the way of transportation.
International Electrotechnical Commission (IEC) has developed a standard IEC61851, which classifies charging stations into 3 categories. Level three charging stations are publicly used fast charging stations with maximum charging power 50 to 240 kW, witch can charge the electric vehicle batteries to 80 % level within 15 minutes and to a 100 % level within 30 minutes. Due to high energy demand and needed high input currents a fast charging stations are placed near to the substation that contains low frequency transformer. Inside the fast charging station intermediate DC-bus connects energy storages, supply grid rectifier and charging converters. Low voltage (570 V) causes high currents and results in high losses at busbars, magnetic components and semiconductor devices. Due to electric safety regulations galvanic isolation transformers are used in charging converters thus the component count is increased along with equipment cost and power losses in additional transformers and energy conversion stages.
The problems in state of-the art electric vehicle fast charging stations are:
- low frequency sub-station transformer;
- additional energy losses due to many energy conversion states;
- separate isolation transformers in each charging converter;
- low intermediate DC-bus voltage (high conduction losses).
To overcome those problems, found in state of the art electric vehicle fast charging stations, a novel integrated multiport converter technology will be proposed.
During the project it is planned to study state of the art of electric vehicle fast charger technology, design a new electric vehicle fast charger prototype, develop new control algorithms, develop mathematical models and computer simulation models, analyze simulation results, analyze of the energy storage control, energy flow control and energy storage optimization methods, develop and test new power circuit topologies for fast charging stations. It is also planned to construct and test a scaled down prototype of electric vehicle fast charging station and integrate it with TUT microgrid.
In fast charging station an integrated converter topology with common high frequency transformer is used instead of separate converters, that are connected by DC-link.
6 kV substation with low frequency transformer is replaced with the high voltage AC/AC front end converter and intermediate DC-bus is replaced by the common high frequency transformer that lowers voltage and also ensures the needed galvanic isolation. Charging converters can be built without DC/AC stage and additional isolation transformers.
Benefits of the proposed multiport converter topology are: 1. smaller weight and volume (due to less energy conversion stages); 2. smaller cost; 3. lower losses (higher voltage, less transformers, instead of low frequency sub station transformer by AC/AC converter and high frequency transformer, less energy conversion stages); 4. simpler construction and power circuit topology.