Solid-State Transformers of Smart High-Power Battery Charger for Electric Vehicles

Abstract

There is no doubt that society will not turn back: most thermal vehicles will switch to electric ones, not only for cars but also for bigger vehicles. Fast chargers will become more and more essential parts of the global system, they will provide a charge control of batteries and galvanic insulation from the grid. At the present times, compact realizations are based on Solid-State Transformers (SSTs) operating at high frequencies with their well-known advantages and disadvantages, including power limits and reasonably high costs. The authors propose a medium-frequency transformer (MFT) structure using Grain Oriented Electrical Steel (GOES) wound cores and aluminum foil windings. Thanks to this solution, the cost of the device can be reduced. GOES has losses that increase with frequency but decrease with temperature; therefore, the authors propose a transformer structure allowing a hot core inside coils at usual temperatures. This idea is applied to a 400-kW compact battery charger connected to a DC smart grid.