Pole-wrapped Negative Equivalent Magnetic Reluctance Structure-based Transformer for Line-frequency Isolation-dependent Applications

Isolation-dependent applications require a transformer with high efficiency, low magnetizing current, and anti-DC bias capability. The kilohertz planar negative magnetic reluctance structure is used to achieve this target with its magnetic-frequency variation property, which reduces the magnetic reluctance of the fundamental component. However, this design cannot be applied to low-frequency transformers owing to the high loss caused by its limited self-inductance and quality factor. To solve this problem, a pole-wrapped negative equivalent magnetic reluctance (PNEMR) structure is presented. The proposed design employed a copper-based PNEMR structure wrapped around the magnetic poles to enhance the fundamental flux and suppress the DC component of flux. Accordingly, the magnetizing current is reduced, and the isolation transformer is less susceptible to the DC bias. The proposed design can simultaneously improve the anti-DC magnetic bias capability, efficiency, and power factor of the transformers. To verify the effectiveness of the proposed design, a 10 kW C-core PNEMR structure-based transformer for isolation-dependent applications was constructed and compared to the generalized structures and transformers with planar negative magnetic reluctance structures. Results indicate that the PNEMR-based transformer can enhance the efficiency and power factor from 96.1% and 0.87 to 96.6% and 0.93, respectively, under full load conditions.