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Under the trend of high-frequencyization, how to solve the heat problem caused by core losses (iron losses)?
2026-08-18
As new energy power electronic equipment continuously progresses towards high-frequency, small size, and high power density, from vehicle DC-DC converters, charging station power modules, industrial high-frequency inverter equipment, to energy storage converters and smart home switch power supplies, the operating frequency has increased from the traditional dozens of kHz to 200 kHz to 1 MHz. Some wide bandgap GaN and SiC circuits even exceed the MHz level. High-frequency design can effectively reduce the volume of magnetic components, improve equipment integration, and reduce the overall weight. It is the core trend of current power electronic technology upgrade.
However, the most prominent engineering challenge brought by the increase in frequency is the sharp increase in core iron losses and the uncontrolled temperature rise of components. Unlike winding copper losses, core iron losses increase exponentially with frequency. In high-frequency conditions, it is very likely to encounter core overheating, magnetic performance degradation, thermal saturation, efficiency plummeting, and equipment power reduction protection issues, which are the core bottlenecks restricting the stability and service life of high-frequency power supplies. A large number of engineering measurements have proved that most problems such as aging failure, full-load overheating, and low efficiency of high-frequency power supplies, the root cause is not the circuit topology defect, but the inadequate control of iron losses.
- Composition and heat mechanism of core iron losses under high-frequency conditions
Core iron losses are the inherent losses of magnetic components in the alternating magnetic field and are also one of the main heat sources of high-frequency equipment. They are mainly composed of three parts: hysteresis loss, eddy current loss, and residual loss. Different loss types are affected by frequency to varying degrees. In low-frequency conditions, the iron loss value is small and the temperature rise is not obvious, which is often ignored in research and development. However, when entering the high-frequency working range, these three types of losses will simultaneously increase, causing the core to continuously accumulate heat.
Hysteresis loss is the loss generated by the repeated flipping of magnetic domains in the core. It is proportional to the working frequency and the amplitude of the magnetic flux. In high-frequency conditions, the number of magnetization and demagnetization per second of the core increases exponentially, the friction between magnetic domains intensifies, and a large amount of heat energy is generated, which is the core loss source in the middle and low-frequency high-frequency conditions. Eddy current loss results from the induced closed eddy currents in the core by the alternating magnetic field. The size of the eddy current is proportional to the square of the frequency, and the higher the frequency, the faster the doubling speed of the eddy current, and the more severe the heat accumulation, which is the core loss exceeding standard values in ultra-high-frequency conditions. Residual loss mainly comes from the material defects of the core and high-frequency resonant losses. At the MHz-level high-frequency scenario, it will quickly become prominent, further exacerbating the core temperature rise.
More importantly, core heating has a vicious cycle effect: an increase in temperature will lead to a decrease in magnetic permeability, an increase in coercivity, and further deterioration of magnetic performance, which further increases core iron losses. The increase in iron losses will continuously push up the temperature, ultimately causing magnetic core thermal saturation, device failure, and power supply oscillation protection. This is also the core reason why high-frequency equipment is prone to failure during long-term full-load operation.
- Core heating exacerbated by high-frequencyization's key influencing factors
In addition to frequency itself, multiple factors will compound and amplify the iron loss heating problem, which is also a key control point in high-frequency magnetic component design. The first is unreasonable selection of magnetic flux density. Many engineers follow the logic of low-frequency design and select the magnetic flux working point based on steady-state current. In high-frequency conditions, the magnetic flux density is too high, directly causing the hysteresis loss to double. The second is poor compatibility of magnetic materials. Ordinary general ferrite and low-end silicon steel have high loss coefficients for high-frequency operation and cannot adapt to high-frequency switching conditions, easily causing overheating and aging.
At the same time, circuit waveform distortion and harmonic superposition will exacerbate core losses. Modern high-frequency power supplies generally have problems such as PWM modulation distortion, switch spikes, and excessive current ripple. Non-sinusoidal alternating magnetic fields will cause core losses much higher than standard sinusoidal conditions. In addition, defects in magnetic core structure design, lack of heat dissipation paths, and unreasonable air gap layout will cause local magnetic flux concentration and local overheating, forming hot spot accumulation, accelerating core aging and failure.
- Comprehensive Solution for High-Frequency Core Iron Loss Heating
To address the problem of high-frequency core heating, it is not sufficient to rely solely on heat dissipation improvements. A systematic approach that combines source reduction of losses, structural optimization, circuit matching, and thermal management reinforcement must be adopted. This approach aims to fundamentally suppress iron loss generation and prevent the occurrence of thermal malcirculation.
1. Selecting specialized high-frequency magnetic materials to reduce basic iron loss from the source
The material of magnetic components is the core factor determining high-frequency iron loss. The difference in high-frequency loss performance among different magnetic materials can be several times. For high-frequency operating conditions above 200 kHz, ordinary high-loss magnetic materials must be eliminated, and high-frequency low-loss magnetic core materials must be precisely matched. For conventional high-frequency switching power supplies, materials such as PC95 and 3C95 with high-grade low-loss manganese-zinc ferrite can be selected. This type of material has been optimized in formulation, with extremely low high-frequency eddy current loss and magnetic hysteresis loss. Its loss performance is optimal in the 100 kHz to 500 kHz range, and its magnetic properties remain stable under high-temperature conditions, reducing the risk of loss drift.
For ultra-high-frequency circuits above 500 kHz and wide bandgap circuits, nano-crystalline and amorphous alloy magnetic cores should be prioritized. Their high-frequency hysteresis coefficient is extremely small, and the high-frequency loss is only 1/3 to 1/5 of that of ordinary ferrite. This can effectively solve the problem of high-frequency iron loss heating. For high-power high-frequency inverter scenarios, high-conductivity and low-loss silicon steel sheets and iron-silicon-aluminum magnetic powder cores can be selected, balancing saturation resistance and low-loss characteristics, and adapting to high-load and complex high-frequency operating conditions.
2. Reasonably reducing the flux working point to reduce magnetization loss
Flux density is a key parameter affecting magnetic hysteresis loss. In high-frequency design, the working margin of flux must be actively reduced, discarding the logic of high flux in low-frequency. By appropriately increasing the effective cross-sectional area of the magnetic core and optimizing the ratio of turns, the unit area flux density can be reduced, significantly cutting down magnetic hysteresis loss. Engineering measurements show that a 20% reduction in flux density can lead to a 40%+ reduction in the overall iron loss of the magnetic core, with a remarkable cooling effect. At the same time, it is necessary to avoid the problem of overly reduced flux density causing bulky components, balancing miniaturization and low-loss requirements, and adapting to the trend of high-density integration in high-frequency power supplies.
3. Optimizing the magnetic circuit and structural design to eliminate local hotspots
In an unreasonable magnetic circuit structure, flux distribution will be uneven, and local flux saturation will occur, leading to local high-temperature overheating. High-frequency magnetic components need to optimize the air gap design, replacing the traditional concentrated air gap with distributed micro-air gaps to balance the overall flux distribution and avoid local flux concentration at the air gap edge causing local loss heating. At the same time, the magnetic core structure should be optimized to eliminate defects such as magnetic core gaps, asymmetric magnetic paths, and excessive gap between magnetic core laminations, reducing leakage loss and stray loss.
For high-frequency transformers and resonant inductors, symmetrical winding and layered winding techniques can be adopted to reduce the high-frequency oscillation caused by parasitic parameters of the winding, reducing additional magnetic core excitation loss, and assisting in reducing iron loss heating from the structural level.
4. Optimizing circuit topology and control strategies to suppress dynamic losses
The operating state of the circuit directly determines the size of the magnetic core loss. Optimizing control strategies can effectively reduce dynamic iron loss. Prioritize soft-switching technology, using topologies such as LLC resonant soft switching, ZVS zero-voltage switching, and ZCS zero-current switching to eliminate voltage and current spikes and waveform distortions caused by hard switching, reducing high-frequency magnetic excitation disturbances, and significantly reducing dynamic hysteresis loss and eddy current loss.
At the same time, optimize PWM modulation logic to reduce current ripple amplitude, avoiding additional magnetic core losses caused by harmonic superposition; reasonably match the switching frequency to avoid the critical frequency point where magnetic core loss increases, and combine load dynamic frequency adjustment to appropriately optimize the frequency range in light-load conditions, reducing ineffective iron loss consumption.
5. Systematic thermal management reinforcement to break the thermal vicious cycle
On the basis of loss reduction, a complete thermal management solution should be provided to quickly discharge residual heat and prevent heat accumulation and aging. High-frequency magnetic core components use vacuum impregnation, full encapsulation, and sealing processes, combined with high-conductivity encapsulation glue, to enhance the overall thermal conductivity of the magnetic core. The device is combined with the heat dissipation pad, metal housing, and heat sink, shortening the heat dissipation path and reducing the contact thermal resistance.
The air duct layout of the entire machine is optimized, placing the high-frequency magnetic components in the main air channel to avoid heat accumulation; high-power high-frequency equipment is paired with intelligent temperature-controlled fans, actively improving the heat dissipation efficiency in high-temperature and heavy-load conditions, stabilizing the working temperature of the magnetic core, and breaking the vicious cycle of "heat generation → increased loss → further heat generation".
- Common Misunderstandings and Avoidance Points for Optimizing High-Frequency Magnetic Core Iron Loss
Many engineering rectification efforts have poor results, with the core issue stemming from design misunderstandings. Some R&D personnel blindly pursue miniaturization, reducing the cross-sectional area of the magnetic core, resulting in excessive high-frequency flux density and a sharp increase in iron loss; some teams mix low-frequency magnetic materials to adapt to high-frequency conditions, causing long-term high-temperature aging; some schemes only optimize heat dissipation without reducing loss, treating the symptoms but not the root cause, and the equipment still experiences performance degradation after long-term operation. In addition, ignoring the dynamic iron loss caused by waveform distortion and harmonic interference is also an important reason for the repeated failure of high-frequency magnetic component heating rectification. High-frequency magnetic core optimization must adhere to the core principles of "prioritizing loss reduction, auxiliary with heat dissipation, circuit matching, and structural synergy" to completely solve the heating problem.
- Summary
The high-frequencyization of power electronic equipment is an irreversible development trend in the industry, and magnetic core iron loss heating is the core technical barrier in high-frequency design. The magnetic core hysteresis loss and eddy current loss increase exponentially with frequency, combined with unreasonable flux design, poor magnetic material compatibility, circuit distortion, and insufficient heat dissipation, can easily cause component overheating, efficiency degradation, and equipment failure. Solving the problem of high-frequency magnetic core heating is not a single heat dissipation rectification, but a comprehensive technical upgrade including high-frequency low-loss magnetic material selection, flux working point optimization, magnetic circuit structure improvement, soft-switching circuit matching, and systematic thermal management, to suppress iron loss generation at the source and break the thermal vicious cycle.
In the industry background of continuous power density improvement and continuous breakthroughs in switching frequency, accurately controlling magnetic core iron loss and solving the problem of high-frequency heating is the core key to improving high-frequency power conversion efficiency, extending equipment service life, and ensuring the long-term stable operation of power electronic systems, and is also a necessary core technology for high-frequency magnetic components design and power supply research and development.
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