An Integrated Solid-State Transformer With High-Frequency Isolation for EV Fast-Charging Applications

Abstract

In this article, an integrated solid-state transformer (I-SST) with high-frequency (HF) isolation for electric vehicle (EV) fast-charging applications is proposed. In the approach proposed in this article, a three-phase I-SST is used as HF galvanic isolation for the system with respect to the medium-voltage grid. A direct multipulse ac–dc rectifier is shown to eliminate low-order harmonics in the input current over a wide range of output dc voltage variation. The proposed approach has the following advantages: no dc link, hence no bulky electrolytic capacitors, galvanic isolation is via a three-phase HF transformer, high-power density, and simple control scheme for regulating output voltage. The approach is easily scalable to several hundreds of kilowatts and is ideal for high-power level-3 EV fast-charging stations. A simplified output voltage regulation scheme for the proposed topology is discussed. Regulating the output voltage enables the circuit to be used as a direct topology for level-3 charge stations with ac bus architecture. Experimental results on a scale down laboratory prototype at 208 V, 1.5 kW are discussed. 1