I. Advantages of Nanocrystals

Nanocrystalline materials simultaneously possess the advantages of silicon steel, permalloy, and ferrite: high magnetic flux density—its saturation magnetic flux density Bs reaches 1.2 T, which is twice that of permalloy and 2.5 times that of ferrite. Moreover, these materials exhibit a high power density in the core, reaching 15 kW to 20 kW per kilogram.

High Permeability: The static initial permeability μ0 can reach as high as 120,000 to 140,000, comparable to that of permalloy. The permeability of this material, when used for power transformer cores, is more than ten times that of ferrite, significantly reducing the magnetizing power and improving the transformer's efficiency.

Low loss: Within the frequency range of 20 kHz to 50 kHz, the loss is 1/2 to 1/5 that of ferrite, thereby reducing the temperature rise of the core.

High Curie Temperature: The Curie temperature of nanocrystalline materials reaches 570℃, whereas the Curie temperature of ferrites is only between 180℃ and 200℃.

Due to the aforementioned advantages, transformers manufactured using nanocrystalline materials, when applied to inverter power supplies and voltage regulators, have played a significant role in enhancing power supply reliability.

With low losses and a low temperature rise, long-term practical use by numerous customers has demonstrated that the temperature rise of nanocrystalline transformers is significantly lower than that of IGBT modules.

The iron core has high magnetic permeability, which reduces the magnetizing power, minimizes copper losses, and improves the transformer’s efficiency. The transformer’s primary inductance is large, thereby reducing the current surge that impacts the IGBT during switching.

It features high magnetic flux density and high power density, reaching up to 15 kW/kg. This reduces the volume of the iron core. In particular, for high-power inverter power supplies, the reduced size creates more internal space within the enclosure, which facilitates better heat dissipation for the IGBT modules.

The transformer has strong overload capacity. Since the operating magnetic flux density is selected at around 40% of the saturation magnetic flux density, when an overload occurs, the heating is caused solely by the increase in magnetic flux density, and the IGBT transistor will not be damaged due to core saturation.

Nanocrystalline materials have a high Curie temperature. For instance, when the temperature reaches above 100℃, ferrite transformers can no longer function properly, whereas nanocrystalline transformers can continue to operate normally.

The advantages of nanocrystalline materials are increasingly recognized and adopted by power supply manufacturers. A number of domestic manufacturers have already begun using nanocrystalline cores and have been applying them for many years. More and more manufacturers are starting to adopt or pilot-test these materials. Currently, nanocrystalline cores are widely used in fields such as inverter welding machines, communication power supplies, electroplating and electrolysis power supplies, induction heating power supplies, and charging power supplies. In the coming years, their adoption is expected to increase even more significantly.

II. Several Issues of Concern to Everyone

In the process of applying nanocrystalline materials to inverter power supplies, several issues—such as noise problems, brittleness, and consistency issues—have emerged, which to some extent have hindered their wider adoption and drawn attention. Now, these issues have been gradually resolved.

(1) Noise Issues

Noise is caused by a variety of factors:

1. The reason lies in the magnetostriction coefficient of the material itself. Ferrite materials have a relatively high magnetostriction coefficient. Although ferrite cores are solid, they can still generate noise during operation in certain cases. The magnetostriction coefficients vary depending on the composition of nanocrystalline materials. In previous years, the commonly used composition was a general-purpose alloy, which led to particularly prominent noise issues in transformers. As applications and development have deepened, different alloy compositions have been tailored for specific purposes to meet the unique magnetic requirements of various devices. For instance, specialized compositions have been developed for power output transformers, current transformers, common-mode inductors, and other similar components. By adjusting the alloy composition according to the requirements of power transformers, the magnetostriction coefficient has been reduced. User feedback has confirmed that the noise issue has significantly improved.

2. The looseness or tightness of the iron core winding is closely related to the quality of the strip material used. Deviations in strip dimensions and uneven thickness can lead to an improper winding tightness, making the core prone to noise generation. After adjusting the composition, the molten steel exhibits good fluidity, which helps improve the forming quality of the strip and, to a certain extent, provides a favorable guarantee for reducing iron core noise.

3. Regarding issues with the inverter circuit, a large DC component in the circuit leads to an increased working magnetic flux density in the core, which in turn causes noise. Our experiments have confirmed that the noise level increases as the working magnetic flux density rises. Some manufacturers have adopted DC-blocking measures in their circuits, and by using nanocrystalline cores for many years, they have not encountered any noise problems.

Thanks to the improvements mentioned above, the noise issue has been basically resolved.

(2) Brittleness Issues

The brittleness of nanocrystalline iron cores primarily manifests itself in the chipping and flaking of core material, which has become a major concern reported by users. This issue not only poses significant challenges during installation and handling but also creates a potential risk of short circuits in the circuitry. After years of practical experience and research, the problem of brittleness has been greatly alleviated through adjustments to both composition and manufacturing processes. Following compositional adjustments, the flexibility of the strip material has improved. Additionally, reducing the thickness of the strip material has further decreased brittleness. Moreover, in the core manufacturing process, immersing the core in a stress-free adhesive helps prevent the core from breaking easily, thereby effectively addressing the brittleness-related issue of core material flaking. At the same time, since the stress-free adhesive fixes the gaps between the layers of the core’s strip material, it reduces the likelihood of resonance, thus minimizing noise generation.

(3) Consistency Issues

Consistency is related to production scale and the capacity of production equipment. From the perspective of strip quality, compared with a 50-kg-capacity device, a 500-kg-capacity device—when both produce 500 kg of strip—will clearly yield products with superior consistency in terms of composition and magnetic properties. The same holds true for heat treatment during the production process. Therefore, larger production scales and higher-capacity production equipment are conducive to achieving better consistency.

In terms of user application, the consistency of nanocrystalline materials is mainly reflected in significant variations in saturation voltage and inductance—sometimes differing by more than a factor of two. The primary reasons for this are the poor effectiveness of magnetic field heat treatment and the lack of categorized screening during production inspection. With adjustments made to the composition used in power transformers, not only has brittleness been improved, but also the residual magnetic induction intensity of the material has been reduced. Consequently, the effectiveness of magnetic field heat treatment has been enhanced, leading to an increase in the saturation voltage of the core and playing a crucial role in improving product consistency.

There has been a gradual process of gaining a deeper understanding of the magnetic performance requirements for inverter power supplies. In recent years, due to relatively small volumes of use, the primary focus was simply on meeting the specified loss requirements. Consequently, performance testing initially involved measuring only the loss parameter. For specific customers, the inspection criteria were later expanded to include the measurement of induced voltage values. As the scale of application has continued to grow, increasingly diverse requirements have emerged—among which the demand for consistent performance has become particularly prominent. Because there has been a learning curve regarding these requirements, progress has lagged somewhat in areas such as compositional improvements, production organization, and testing standards. As a result, this has had some impact on the wider adoption and application of these products. Today, however, this issue has received sufficient attention, and a variety of effective measures have been implemented, leading to a significant improvement in performance consistency.

(4) Price Issues

Price is a key concern for users, especially those who are about to start using or have just begun using these products. The price is directly related to production volume. In recent years, as the applications of nanocrystalline iron cores have expanded rapidly—no longer limited to inverter welders but now widely used in electroplating equipment, induction heating devices, charging equipment, communication power supplies, UPS systems, X-ray machine power supplies, laser power supplies, variable-frequency drive power supplies, and other fields—production volumes have steadily increased, leading to significant price reductions. Currently, prices have fallen by approximately 40% compared to their initial levels. As application volumes continue to grow, prices will keep declining further, and the price of nanocrystalline materials will gradually approach that of ferrites.

Currently, for power supplies with outputs exceeding 15 kilowatts, the price of nanocrystalline cores has actually fallen below that of ferrite cores. This is because ferrite cores have size limitations, making it difficult to obtain magnetic cores suitable for high-power transformers—often requiring several cores just to meet power demands. In contrast, a single nanocrystalline core can suffice. Although ferrite cores are significantly cheaper on a per-unit basis, the total cost of several ferrite cores ends up being higher than the price of a single nanocrystalline core.

III. Products of Nanocrystalline Transformers

Nearly all the nanocrystalline transformers used are wound by the OEMs themselves. Since different manufacturers have varying designs for their inverter circuits, differing levels of expertise in nanocrystalline materials, and varying degrees of mastery over transformer manufacturing processes, the quality of the transformers they produce also varies considerably. Thus, manufacturing high-frequency transformers has become a critical step in the production process. Consequently, some manufacturers have proposed whether it would be feasible to specialize in the production of high-frequency transformers, allowing OEMs to simply purchase these transformers directly.

Transformers operating in the frequency range of 20 kHz to 50 kHz typically use ferrite as the transformer core material. The core shapes are mostly U-shaped or EI-shaped, with a few using O-shaped cores. From a structural standpoint, it is difficult to reduce the leakage inductance of transformers with U-shaped or EI-shaped cores.

Thanks to the advantages of nanocrystalline materials, an ideal material has been provided for the miniaturization of high-frequency transformers. These new materials have also spurred the development of a novel structural design for high-frequency transformers.

This patented transformer, originally named “Beetle,” was later improved by others and renamed the “H”-type transformer, which also received a patent. Both types of transformers take full advantage of the nanocrystalline material’s magnetic properties—such as high permeability, high magnetic induction intensity, and low losses—as well as the ring-shaped core’s characteristic of minimal magnetic leakage. They introduce innovative designs in both the primary and secondary windings of the transformer. Specifically, the metal protective enclosure of the core is used as the secondary winding, making it ideal for high-current applications. The primary winding is uniformly wound around the secondary winding, resulting in very low leakage inductance. Furthermore, the transformer’s fixed support structure is integrated with the current-collecting output terminal, which facilitates effective heat dissipation.

The advantages of this type of transformer are:

1. High power: 10 kW to 20 kW, with a power density reaching 15 kW to 20 kW/kg.

2. Low leakage inductance—typically less than 5 μH, and often less than 2 μH.

3. High efficiency, reaching over 99%

4. Small in size and lightweight—the 15 kW transformer weighs 3 kg and measures 160×150×95 mm.

5. Beautiful appearance.

Due to factors such as the transformer’s structure and manufacturing processes, this type of transformer is relatively expensive and currently finds limited application—mainly in electroplating and electrolysis power supplies. It remains challenging to promote its use in industries characterized by intense price competition. To address this issue, a new “Ω”-shaped transformer has been introduced.

The “Ω”-shaped transformer has the same structure as a conventional toroidal transformer, but its winding method has been improved, thereby reducing leakage inductance and distributed capacitance. The leakage inductance can typically be less than 10 μH. The price of this type of transformer is about 40% lower than that of “beetle” or “H”-shaped transformers. Its excellent performance-to-price ratio has attracted many manufacturers.

The commercialization of nanocrystalline transformers leverages the superior properties of nanocrystalline soft magnetic materials in a rational manner. This approach facilitates the commercialization and standardization of high-frequency power transformers, helps improve transformer efficiency and performance levels, and enhances the productivity of equipment such as inverter welders, electroplating units, and electrolytic devices. Currently, several manufacturers are already capable of producing these transformers.

Currently, some complete-machine manufacturers have begun adopting “Ω”-shaped transformers to achieve integrated production—a move that is “multi-faceted, fast, high-quality, and cost-effective.”

IV. Concluding Remarks

Due to their outstanding properties, amorphous and nanocrystalline soft magnetic materials have addressed the shortcomings of silicon steel and ferrite materials in various applications, elevating a wide range of electronic products to a new level, enhancing efficiency, and achieving significant energy-saving effects. These new materials demonstrate vibrant and dynamic potential.

Today, an increasing number of people are becoming familiar with amorphous and nanocrystalline materials. Beyond transformers, these materials can also serve as core materials for devices such as current transformers, reactors, sensors, and filters. Their applications extend to everyday household appliances, smart meters, DC inverter air conditioners, residual-current circuit breakers, and other products. They are also used in power systems for transmission and transformation measurement, power distribution, remote sensing, and telemetry; in railway systems for locomotive air conditioning, inverter power supplies for electric locomotives, and railway signaling sensors. Moreover, these materials have been standardized and adopted in numerous military and national high-tech projects spanning aerospace, aviation, and marine industries.