Hybrid Electronic-Embedded Transformer-Based DC Transformer (EET-DCX): A New Family of Soft-Switching DCXs

With an integrated full bridge, the concept of an electronic-embedded transformer (EET) offers a solution of high-frequency, high-power fixed-gain isolated dc–dc conversion, known as a dc transformer (DCX), through the parallel operation of EET units with natural current sharing [1]. Besides, the trapezoidal current modulation can further reduce the root-mean-square (rms) current through the transformer [2]. However, this modulation will increase the voltage stress on the integrated full bridge, especially when the leakage inductance is large and variable, such as in the wireless charging application. To address this tradeoff between rms current and voltage stress, this article proposed the concept of a hybrid resonant-type EET-DCX with series resonant capacitor. Following this concept, two specific topologies named hybrid EET-DCX and hybrid resonant commutation (RC) EET-DCX were proposed. The main difference between these two topologies is the former adopted a full bridge and the latter utilized only one bidirectional ac switch. In hybrid RC EET-DCX, a resonant current commutation scheme was developed. Among these two topologies, since the leakage inductance impedance can be mainly canceled by the passive capacitor, the full bridge or ac switch only needs to handle the remaining part of the impedance. And thus, the device voltage stress on active components can be dramatically decreased. In addition, these two proposed topologies can both retain all the advantages of previous EET-DCX designs, including natural current sharing, load-independent voltage gain, simple open-loop operation, and full-load range zero-voltage switching. Finally, two 12-kW prototypes were built to verify the analysis and performance.