Analysis and Design Considerations of a Contactless Magnetic Plug for Charging Electric Vehicles Directly From the Medium-Voltage DC Grid With Arc Flash Mitigation
Authors: Richard B. Beddingfield, Suvendu Samanta, Mark S. Nations, Isaac Wong, Paul R. Ohodnicki Jr., and Subhashish Bhattacharya
High power electric interconnects are challenging to create safely. Furthermore, disconnecting them while a load is energized can often lead to a localized arc within the plug as the electrical contact is broken. Communication failures can lead to unsafe plug operation in ‘smart’ plugs. Similarly, exposed electrical contacts make medium voltage plugs inherently unsafe. This paper re-envisioned the plug into a gapped magnetic coupling for applications where safety is paramount or MV training is not requisite for general users (e.g. data centers, electric vehicle charging, and harsh environments). This novel magnetic plug guarantees safe operation and connection through galvanic and physical separation from the MV side. It achieves this with a gap and barrier in the transformer core in between the MV and LV windings. We introduce a unique asymmetry in the core to localize parasitic capacitance, fully separating the medium and low voltage regions. This approach eliminates arcing risk and allows high power, MV interconnect capabilities to be delivered to the general public. Detailed results from finite element analysis are presented in the reference along with experimental data to verify operation in an EV charging application.
A 20kW, 1kV to 50V scaled hardware prototype, representative of the 300kW, 8kV to 800V (150kW at 400V output) paper design, is demonstrated. The power and voltage are scaled with the winding turns to provide accurate representations of the magnetic and electric fields with respect to the magnetic core. Thus, the scaled magnetic core is the same as the rated magnetic core. This design is also likely to have similar costs to conductive plug options when manufactured at scale with the reduction of MV interlock equipment and cooling.
The authors would like to thank the ARPE-E CIRCUITS for sponsoring the efforts that originated this concept.
Continued advanced magnetics are being designed in the newly founded university / industry consortium: Advanced Magnetics for Energy Development (AMPED). www.go.ncsu.edu/amped