High-frequency inverter power supplies operate at a frequency range of 20 kHz to 50 kHz. The main transformer serves as the core component of a power supply. Although ferrite, the traditional magnetic core material, features relatively low high-frequency loss, it delivers unsatisfactory magnetic properties at frequencies below 100 kHz. In addition, its low saturation magnetic flux density (Bs) leads to larger size and heavier weight of magnetic cores. Furthermore, ferrite has a low Curie temperature and poor thermal stability. A slight temperature rise will reduce its Bs value, making the core susceptible to magnetic saturation and unstable operation, so it is not suitable for high-frequency and high-power operating conditions. With excellent comprehensive magnetic properties, nanocrystalline toroidal cores (ultra-microcrystalline cores) have become the premier choice as transformer cores for high-frequency inverter power supplies nanocrystalline core
I. Advantages of Nanocrystalline Materials
Nanocrystalline toroidal cores integrate the advantages of silicon steel, permalloy and ferrite, detailed as follows:
High Magnetic Flux Density Its saturation magnetic flux density Bs is 1.2 T, twice that of permalloy and 2.5 times that of ferrite. The core achieves high power density ranging from 15 kW/kg to 20 kW/kg.
High Magnetic Permeability Its static initial permeability μ₀ can reach 120,000 to 140,000, equivalent to that of permalloy. For power transformer applications, Nanocrystalline Cores for High-Power Transformers is more than ten times that of ferrite, which greatly cuts down excitation power and improves transformer efficiency.
Low Core Loss Within the frequency band of 20 kHz to 50 kHz, its core loss is 1/2 to 1/5 of ferrite, effectively suppressing temperature rise of the magnetic core.
High Curie Temperature The Curie temperature of nanocrystalline toroidal cores is up to 570 °C, while the Curie temperature of ferrite is only 180 °C to 200 °C.
Benefiting from the above merits, transformers made of nanocrystalline cores greatly improve the reliability of inverter power supplies:
Low loss brings low temperature rise of transformers. Long-term practical application by numerous users proves that the temperature rise of high-permeability nanocrystalline transformer cores is far lower than that of IGBT devices.
High core permeability reduces excitation power and copper loss, boosting transformer efficiency. The large primary inductance of the transformer alleviates current impact on IGBT devices during switching operations.
High operating magnetic flux density brings a high power density of 15 kW/kg, realizing miniaturization of magnetic cores. Especially for high-power inverter power supplies, the smaller core size leaves more internal space inside the cabinet, facilitating heat dissipation of IGBT devices.
Strong overload resistance of the transformer. Since the operating magnetic flux density is set at approximately 40% of the saturation magnetic flux density, overload conditions only generate extra heat caused by increased magnetic flux, instead of damaging IGBT devices due to magnetic core saturation.
Thanks to the high Curie temperature of nanocrystalline toroidal cores, ferrite transformers will fail to work normally when the temperature exceeds 100 °C, whereas nanocrystalline transformers can operate stably without abnormality.
These superior properties of nanocrystalline materials have been recognized and adopted by an increasing number of power supply manufacturers. Many domestic manufacturers have adopted nanocrystalline cores and put them into practical use for years, and more manufacturers are starting formal adoption or trial application. At present, nanocrystalline cores are widely applied in inverter welding machines, communication power supplies, electroplating and electrolysis power supplies, induction heating power supplies, charging power supplies and other fields, and their application scale will expand significantly in the next few years.
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