Pseudo-Hermitian Coreless Transformer for Current Source Converter

This article proposes a pseudo-Hermitian coreless transformer (PH-CLT) based on the pseudo-Hermitian theory. Based on the motion equations, the corresponding Lagrangian and Hamiltonian functions are constructed, and the bifurcated frequencies are derived. Benefiting from the pseudo-Hermiticity, the operating frequency can be fixed, which significantly simplifies the system design. Input impedance angle, secondary current, stresses on resonant components, and efficiency are analyzed in detail. The analysis reveals that the proposed CLT has a current-source output characteristic, and the output current can be adjusted by changing the primary voltage. Therefore, a current source converter with adjustable output current based on the PH-CLT is designed. The proposed coreless design converter requires no superconducting technology and the operating frequency is similar to conventional converters, while it can still maintain high output power and efficiency. Finally, the feasibility and performance are experimentally evaluated by a prototype with an operating frequency of 216 kHz and a rated power of 2.4 kW. The experimental results demonstrate that the efficiencies of the PH-CLT and the converter at full load are 95.6% and 92.8%, respectively. The gravimetric power density of the PH-CLT prototype is as high as 12.96 W/g, which is several times that of the magnetic core transformer.