High-Frequency Litz Wires for Wide-Bandgap On-Board Chargers
Efficiency Increase in Electric Vehicles
Modern electric vehicles use wide-bandgap semiconductors (SiC, GaN) in on-board chargers to achieve higher power at higher switching frequencies. This technology enables more compact chargers; at the same time, the demands on winding technology and inductors increase, as skin and proximity-related losses become more dominant at high frequencies. PACK LitzWire developed a customized litz wire solution for an OBC manufacturer that meets power requirements while offering high efficiency and reliability.
The Technical Challenge
OBC transformers must transmit high currents at switching frequencies around 70–180 kHz. In solid copper conductors, significant AC resistance losses occur at these frequencies due to skin and proximity effects. At the same time, strict high-voltage insulation and EMC requirements apply in the automotive industry. Conventional windings reach their limits here: they become large, heavy, and easily overheat. Pack LitzWire worked with the customer to determine that the winding requires heat-resistant HF litz wires with fine individual wires and an optimized structure.
The toroidal core choke shows the implementation of the optimized litz wire solution in the real OBC component and illustrates the contribution of the winding to increased efficiency and thermal stability of modern AC/DC on-board chargers.
This detailed image illustrates the precise winding structure of the HF litz wire, specifically designed for use in on-board chargers with wide-bandgap semiconductors to reduce AC losses at high switching frequencies.
Our Solution Strategy
PACK LitzWire used a high-frequency litz wire (e.g., RUPALIT® Safety HF Litz Wire), consisting of several hundred thin (0.05 mm), individually enamel-insulated copper wires. This construction distributes current and heat much more evenly: "RUPALIT® HF Litz Wires" offer lower skin and proximity effects and higher efficiency through lower AC copper losses. The litz wires received special insulation layers for the required dielectric strength using a suitable film combination. Using its in-house LiWiCalc® tool, PackLitzWire optimized the litz wire geometry with regard to skin depth, fill factor, number of wires, and stranding steps. The improved winding achieved thermally optimized operation and a proven efficiency gain.
RUPALIT® Plus Profil
This solution combines precise outer insulation wrapping with a square or rectangular profile geometry for maximum space utilization. The reinforced insulation offers the highest dielectric strength and reliably protects against voltage breakdowns in the smallest installation spaces.
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