On Magnetic Shielding for Axial Winding Segmented Coreless Transformers in Self-sustained Converters

In this paper, the magnetic field characteristics and shielding design for the axial winding segmented coreless transformer (CLT) in self-sustained converters are studied. The axial winding segmented design can reduce the volume of CLTs, and its magnetic field is constrained in a smaller space, effectively decreasing the dimensions and cost of the electromagnetic shielding enclosure. The shielding is equivalent to a passive RL circuit coupled with CLTs, and then the virtual magnetic permeability is introduced to derive the expressions for self- and mutual impedance, transformation ratio, power loss, operating frequency, and the current phase angle. The analysis results show that the self-sustained converter with CLTs can adapt to the parameter variations caused by the shielding insertion, i.e., the electrical, thermal, and structural parameter design of CLTs be separated from its shielding design. Meanwhile, in order to solve the contradiction among power density, magnetic shielding, and heat dissipation, a closed-form design method of conductive shielding with aperture array is proposed, which integrates the heat sink with the shielding to satisfy the magnetic shielding and improve the heat dissipation capability of the system. A 1.5kW prototype is fabricated to verify the theoretical analysis. Compared with the unshielded design, the peak efficiency of the shielding design is almost the same, reaching 95.65%, but a lower hot spot of only 58.1°C and magnetic field radiation (9.28μT) below the standard limit (27μT) can be achieved.