Kayo Amorphous mass production of 150 ultra-low permeability nanocrystalline magnetic rings

Nanocrystalline materials, due to their superior performance, are widely used in applications such as on-board chargers, inverters, motor bearing protection, and charging stations for electric vehicles. They are often made into components such as inductors, chokes, CTs, and magnetic rings.

However, as new energy vehicles develop towards higher performance and higher integration, the performance requirements for magnetic materials are becoming increasingly stringent, and some materials struggle to meet the requirements of end-use automotive applications.

For example, low-permeability nickel-zinc ferrite is commonly used in low-voltage power inductors in DC-DC modules. However, as DC-DC module power continues to increase, the saturation resistance of nickel-zinc ferrite is no longer sufficient. Therefore, the magnetic materials industry urgently needs to develop magnetic materials that exhibit high impedance and high saturation resistance in high-frequency environments, as well as stability at high and low temperatures and under stress.

This article, based on an interview with Guo Zhenwei, Sales Manager of Anyang Jiayou Amorphous Technology Co., Ltd. (hereinafter referred to as "Jiayou"), explains the technical requirements and trends for nanocrystalline materials in 800V electric drive systems, as well as Jiayou's industry-leading nanocrystalline material technology.

The 800V high-voltage platform places higher demands on magnetic materials.

EMC technology faces the following challenges in the 800V high-voltage platform:

1. Silicon carbide devices, due to their high switching speed and high voltage characteristics, are prone to generating high-frequency common-mode noise.

2. System coupling interference increases the difficulty of compatibility design.

3. The reuse of charging functions increases EMC filtering challenges.

4. Filter design iteration cycles are long and costly.

To address these challenges, automakers applying 800V high-voltage platform technology need to redesign the EMC filtering systems for core electric drive systems, including the electric drive, on-board charger (OBC), and DC-DC module. This places higher demands on the design of magnetic rings and related materials. In high-power applications, magnetic materials with improved saturation resistance are required.

The saturation resistance of a magnetic material is related to its magnetic permeability. In theory, the higher the magnetic permeability, the less likely the material is to saturate when operating in higher magnetic fields. However, when the magnetic field intensity reaches a certain level, even high-permeability materials may saturate, resulting in a decrease in magnetic permeability.

Under the influence of a DC bias current, the magnetic permeability of a magnetic core decreases due to saturation. The lower the permeability of a material, the less it degrades under unbalanced current or DC.

Nanocrystalline materials offer significant advantages in miniaturization, lightweighting, and high performance. These advantages include compactness, efficiency, and stability. Compactness is reflected in the high saturation flux density of nanocrystalline materials, which allows for smaller size compared to other soft magnetic materials with comparable performance. Efficiency is reflected in high permeability and low loss, effectively suppressing electromagnetic interference. Stability is reflected in high Curie temperature and low temperature coefficient, resulting in enhanced reliability.

In automotive applications, such as three-phase common-mode inductors in high-power OBC modules and nanocrystalline filter rings used in electric drives, unbalanced currents can cause high-permeability nanocrystalline rings to enter saturation, leading to overheating and even burn-in. Therefore, reducing the permeability of nanocrystalline rings in high-current applications to improve their saturation resistance has become a technical challenge in the nanocrystalline industry.

Currently, the industry generally uses two methods to produce low-permeability nanocrystalline materials: adjusting the material formulation and using constant-tension processing. However, adjusting the material formula to achieve a permeability below 2000 is generally difficult, and flexibility is limited.

Therefore, Jiayou adopted a constant tension solution. Through high-precision tension adjustment combined with temperature curve adjustment, the permeability can be quickly adjusted from μ150 to 10,000, fully meeting the needs of downstream customers for rapid design adjustments. Currently, the domestic constant tension method can generally achieve a minimum permeability of around 500, and lower permeabilities are difficult to mass produce. Jiayou has developed its own high-precision, high-stability constant tension annealing equipment, enabling mass production of products with μ=150 and even challenging even lower permeabilities in the laboratory.

To meet the demand for automotive nanocrystal materials, Jiayou has adopted a novel design structure.

Traditional nanocrystals are generally designed for frequencies between 10kHz and 100kHz. However, the increasing frequency of high-order harmonic interference in motor controller modules means that nanocrystal filter rings must have better high-frequency impedance and a wider frequency range to meet EMC requirements.

Therefore, Jiayou's future research focuses on improving nanocrystalline materials' high impedance at high frequencies, improved saturation resistance, and stability under high and low temperatures and stress.

In terms of design structure, nanocrystalline materials are relatively sensitive to stress because they are wound from a ribbon. To maintain stable performance, stress must be minimized during the manufacturing process. The ring shape is subject to the least stress during manufacturing, followed by the racetrack shape, and finally the rectangle. Therefore, the ring shape is more common in traditional applications.

However, despite its superior performance, the ring shape is currently not widely used in the automotive industry due to its limited space utilization. The racetrack shape is currently more common due to its better performance in confined spaces, followed by the rectangle. C-shaped cut magnetic rings are also used in some high-power applications. Since these shapes are formed by deforming the ring shape, the key challenge is how to eliminate stress effects on the magnetic ring while maintaining the shape and maintaining magnetic stability.

Through years of experimentation and research, Jiayou Amorphous has optimized the curing formula, resulting in less performance degradation than traditional curing processes. Furthermore, through a more optimized high-magnetic field heat treatment process, the magnetic ring itself has enhanced its stress resistance. Jiayou also uses stacking and punching methods to process irregularly shaped cores, significantly expanding the application scenarios of nanocrystalline materials.

Going forward, Jiayou will continue to focus on the following areas:

First, optimize the performance of existing products: Continuously invest in R&D resources to optimize the performance of existing nanocrystalline cores and other products. For example, efforts will be made to further improve the high-frequency magnetic permeability and reduce losses in the cores to enhance the electromagnetic compatibility and energy conversion efficiency of new energy vehicle electrical systems, improving vehicle range and overall performance.

Second, expand product applications: Actively expand the application of nanocrystalline materials in more key components such as on-board chargers and inverters. Develop customized products for different vehicle models and power requirements to meet diverse market demands.

Third, develop new product lines: Based on market trends and technological developments, develop new product lines of nanocrystalline materials with higher performance and added value. Examples include developing composite products of nanocrystalline materials with other materials, developing circular cross-section cores, and using amorphous one-piece injection molding.

Fourthly, in terms of equipment, we plan to introduce advanced production equipment and inspection equipment from home and abroad, which will be upgraded and renovated by the equipment team, in the hope of achieving automated and intelligent control of the production process and improving product consistency and stability.