As new energy vehicles develop towards high performance and high integration, the performance requirements for magnetic materials are getting higher and higher, and some materials are difficult to meet the requirements of terminal vehicle applications.
For example, in the low-voltage side power inductor of the DC-DC module, low-permeability nickel-zinc ferrite is generally used, but as the power of the DC-DC module continues to increase, the anti-saturation characteristics of nickel-zinc ferrite are no longer sufficient. Therefore, the magnetic material industry urgently needs to develop magnetic materials with high impedance and high anti-saturation capabilities in high-frequency environments, as well as stability in high and low temperatures and under stress.
Under the 800V high-voltage platform, EMC technology faces the following challenges:
1. Silicon carbide devices are prone to high-frequency common-mode noise due to their high switching speed and high voltage characteristics.
2. System coupling interference problems increase the difficulty of compatibility design.
3. The reuse of charging functions increases the challenges of EMC filtering.
4. The iteration cycle of filtering design is long and the cost is high.
In order to meet the above challenges, when applying 800V high-voltage platform technology, car companies need to redesign the EMC filtering systems of the core three-electric systems such as electric drive, OBC (on-board charger), and DC-DC module, which increases the high requirements for magnetic ring design and related material design. In high-power application scenarios, magnetic materials with better anti-saturation characteristics are required.
The anti-saturation characteristics of magnetic materials are related to their magnetic permeability. In theory, the higher the magnetic permeability, the less likely the material is to be magnetically saturated when working under a higher magnetic field. However, when the magnetic field intensity reaches a certain level, even high-permeability materials may be magnetically saturated, resulting in a decrease in magnetic permeability.
Under the action of DC bias current, the magnetic permeability of the magnetic core will decrease due to saturation. The lower the magnetic permeability of the material, the less decay it has under unbalanced current or DC.
Nanocrystalline materials have obvious advantages in miniaturization, lightweight, and high efficiency. Its advantages include compactness, efficiency, and stability. Compactness is reflected in the high saturation magnetic density of nanocrystalline materials, which is smaller than other soft magnetic materials with the same performance; high efficiency is reflected in high magnetic permeability and low loss, which effectively suppresses electromagnetic interference; stability is reflected in high Curie temperature, low temperature coefficient, and stronger reliability.
In vehicle applications, such as the three-phase common mode inductor in the high-power OBC module and the nanocrystalline filter magnetic ring used in the electric drive, there is an unbalanced current, which makes the high magnetic permeability nanocrystalline magnetic ring enter the saturation state, causing heat and even burning. Therefore, how to reduce the magnetic permeability characteristics of the nanocrystalline magnetic ring in high current applications to improve its anti-saturation characteristics has become a technical difficulty in the nanocrystalline industry.
Low permeability nanocrystalline cores in DC-DC modules
At present, the industry generally adopts two methods to produce low magnetic permeability nanocrystals: adjusting material formula and processing by constant tension. However, it is generally difficult to adjust the material formula to achieve a magnetic permeability below 2000, and the flexibility is relatively poor.
Therefore, Savart adopts a constant tension solution, through high-precision tension adjustment combined with temperature curve adjustment, to achieve rapid adjustment of magnetic permeability from μ150-10000, fully meeting the needs of downstream customers for rapid design adjustment. At present, the domestic constant tension method can generally achieve a minimum magnetic permeability of about 500, and it is difficult to mass produce lower. Through our self-developed high-precision, high-stability constant tension annealing equipment, we have been able to mass-produce μ=150 products, and have launched an impact on lower magnetic permeabilities in the laboratory.
Curve of low magnetic permeability nanocrystals
Traditional nanocrystals are generally designed for frequencies of 10kHz-100kHz, but now the high-order harmonic interference in motor controller modules is becoming more and more high-frequency, which means that nanocrystal filter magnetic rings must have better high-frequency impedance and a wider frequency range to meet EMC requirements.
Therefore, Savart’s main research goals in the future are the high impedance of nanocrystalline materials at high frequencies, better anti-saturation capabilities, and stability under high and low temperatures and stress conditions.
In terms of design structure, since nanocrystals are wound from strips, they are more sensitive to stress. In order to maintain stable performance, stress needs to be reduced as much as possible during the manufacturing process. The ring is the least stressed during the manufacturing process, followed by the runway shape, and finally the rectangle. Therefore, there are more rings in traditional applications.
Toroidal and racetrack nanocrystalline cores
However, despite the superior performance of the ring shape, it is not commonly used in the automotive industry due to its insufficient space utilization. The runway shape is more commonly used now because it performs better in a small space, followed by the rectangular shape. Some high-power scenarios also use C-cut magnetic rings. Since these shapes are formed by ring deformation, how to eliminate the stress influence of the magnetic ring while maintaining the shape and maintain the stability of the magnetic ring is the main problem.
Racetrack-shaped nanocrystalline core
Savart Amorphous has optimized the curing formula through several years of experiments and precipitation, and the performance attenuation is smaller than that of the traditional curing process; at the same time, the magnetic ring itself has stronger stress resistance through a more optimized strong magnetic field heat treatment process. At the same time, for special-shaped cores, we also use stacking and punching methods to process, which greatly increases the application scenarios of nanocrystalline materials.
In the future, Savart will continue to work in the following aspects:
First, optimize the performance of existing products: continue to invest in R&D resources to optimize the performance of existing nanocrystalline cores and other products. For example, further improve the high-frequency magnetic permeability of the core and reduce losses to enhance the electromagnetic compatibility and energy conversion efficiency of the electrical system of new energy vehicles, and improve the vehicle’s endurance and overall performance.
Second, expand product application areas: actively expand the application of nanocrystalline materials in more key components such as on-board chargers and inverters. Develop customized products that are suitable for different models and different power requirements to meet the diverse needs of the market.
Third, develop new product series: based on market trends and technological development, develop new product series of nanocrystalline materials with higher performance and added value. Such as developing composite products of nanocrystals and other materials, developing round cross-section iron cores, amorphous one-piece injection molding, etc.
Fourth, in terms of equipment, it is planned to introduce advanced production equipment and inspection equipment from home and abroad, and the equipment team will upgrade and transform it, hoping to achieve automation and intelligent control of the production process and improve product consistency and stability.
