In the electrical DC system, due to widespread use of high-frequency module, the module is designed for high-frequency power is growing, while the volume is smaller, which its design raised a key question, and that is how solve problems and fever loss magnetic components.

Extensive use of high-frequency switching power supply a variety of magnetic components, such as input / output common mode inductors, power transformers, inductors, and various saturation differential mode inductance. Various magnetic components of the magnetic material requirements vary, such as differential mode inductance hope moderate μ value, but linearity, and not saturated; common mode inductors is desirable μ value to be high, frequency band; power transformer hopes μ value to moderate, temperature stability, small remanence, low loss. Before the emergence of amorphous materials, common mode inductance mainly high μ value (6K ~ 10K) Mn-Zn alloy, differential mode inductance to use more iron core or gapped ferrite materials, transformer ferrite material is used . These materials application technology is mature, species are very rich, and there are a variety of product shapes available. With the emergence of amorphous materials and technology continues to mature, the switching power supply design, amorphous materials exhibit many advantages over other materials can not match. Basic performance comparison of several commonly used magnetic material as shown in Table l.

1. Design of a main transformer

For the main heating element of high-frequency switching power supply design of the main transformer is particularly important, the size and select the size of the material is important.

1) The core of the main transformer must have the following characteristics

(1) low loss;

(2) a high saturation magnetic flux density and the temperature coefficient is small;

(3) Wide operating temperature range;

(4) μ value with the B value is small change;

(5) and the selected power device switching speed corresponding frequency response.

Earlier generally used in high-frequency transformer ferrite core, following on VITROPERM500F iron-based nanocrystalline core and the German Siemens company's N67 series ferrite core performance compared with Figure l.

Both can be seen from the above chart with the following differences:

(1) The same operating frequency (200kHz or less), the amorphous material loss was significantly lower than the ferrite, the lower the frequency, the higher the job B value, the more obvious advantages of amorphous material. But in the bands above 250kHz, ferrites loss is significantly lower than the amorphous material.

(2) The amount of amorphous material loss variation with temperature is much lower than ferrite, reducing the difficulty of transformer thermal design.

(3) amorphous material permeability greater variation with temperature is much lower than ferrite, reducing the difficulty of transformer design and improve the stability and reliability of power supply operation.

(4) an amorphous material Bs · μ value is 10 to 15 times the ferrite, which means that the volume of the transformer weight can be greatly reduced.

Transformer design process, the most difficult is the thermal design, heat transformers and a wide range of factors, such as core loss, copper loss and so on. The switching frequency is increased, the heating of the transformer increases exponentially. The use of ferrite core, due to lower ferrite Curie point, the need for transformer cores for heat treatment, the production process is more complicated. If improper heat treatment under high temperature volatile magnetic ferrite magnetic material, resulting in abnormal circuit. If you do use amorphous transformer that will work ΔB increase from 4,000 gauss to 100007 Garth, switching device operates at a frequency can be reduced to below 100kHz. Amorphous material in the 16 ~ 100kHz frequency range, loss / Bs lowest value, the corresponding transformer turns and smallest heat is also small, to improve the overall efficiency, reducing the volume of power modules has a huge help. In using the premise of soft switch control technologies, it can give full play to the low voltage drop, high current, high voltage IGBT of the advantages, greatly improve reliability of power supply.

2. core selection

Because the full bridge converter transformer working at both ends of the Br requirements are not very strict, it needs is 2Bm. However, if the selection of high-Br core, when a large power is power, prone to saturation. To this end, for the medium and high-power switching power supply, the choice of the main transformer high saturation magnetic flux density Bs, residual magnetic flux density B, low core. Although the saturation magnetic flux density Bs Fe-based amorphous material is high, but due to a low iron-based amorphous material operating frequency (<15kHz), high frequency loss increases. Taking into account the subject of the switching frequency of 20kHz, it was decided to use an iron-based nanocrystalline core low residual magnetism.

Selection of an iron-based Nanocrystalline toroidal: ONL-1308040, the core saturation flux density Bs = 1.25T, the residual magnetic flux density Br<0.2t, 5="" the="" curie="" temperature="" lo="" initial="" permeability="" i="">30000 , the maximum magnetic permeability μm> 50000, loss P (0.5T, 20kHz)<30W / kg. Dimensions: Diameter l30mm, an inner diameter of 80mm, a thickness of 40mm, core effective cross-sectional area Ac = 7.5cm2.

(1) take the set work, the maximum flux density Bm = 0.5T, so when the full bridge ΔB = 1T

(2) secondary turns calculation

(3) primary and secondary turns ratio select

The minimum input voltage transformer U1 = 500V, after secondary rectifier maximum output voltage U. = 300V, set the maximum duty cycle D = 0.8, U2 = U0 / D,

Have N1 = 13

(4) Calculation window utilization

Transformer input current I1 = 30A, the output current I2 = 50A, in accordance with the current density KJ of 2.5A / mm2 design; the primary winding cross-sectional area Ar1 = 12mm2, cross-sectional area of the secondary winding Ar2 = 20mm2 window area Aw = 50cm2.

Window Utilization:

Since the switching frequency is not too high, transformer winding and multi-strand wire wound, high outsourcing dielectric strength, low dielectric loss of the composite fiber insulating paper way, ensure that the insulation levels.

3. of the output inductor design

1) the output filter inductor core main requirements are the following:

(1) The temperature coefficient is small, the filter inductance is to be kept to a minimum rate of change over time;

(2) good linearity in different operating current small change in inductance;

(3)Electric loss and magnetic loss filter inductor low.

Selection of an iron-based nanocrystalline core CD-notch: JFQ-078025015040, the core saturation flux density Bs = 1.25T, the residual magnetic flux density Br

2) core selection

(1) turns, an air gap calculation

When setting work, the maximum flux density Bm = 0.8T, and the maximum peak current I = 60A, the inductance L = 0.15mH

Inductance defined formula

In the above formula, Ac is the effective cross-sectional area of the core.

Magnetic Ohm's Law

In the above formula, l0, l'c is the length of the air gap and the core, μ0, μ. It is the permeability of air and core.

From (5) can be obtained

From (9) can be obtained gap length

Computing (1) window utilization

The maximum average current through the filter inductor is 50A, in accordance with the current density KJ of 2.5A / mm2 design, winding cross-sectional area A, = 20mm2; window area AW = 19.5cm2.

Window Utilization

4. Saturated inductor design

1) core selection

Selection of cobalt-based amorphous toroidal, saturation magnetic flux density of the magnetic core of Bs = 0.53T, the residual magnetic flux density Br = 0.5T, the Curie temperature of 210 ℃, the magnetic permeability μ = 90000. Dimensions: diameter 42mm, inner diameter of 29mm, thick l8mm. Effective core cross-sectional area Ac = 0.82cm2.

2) Select the opening delay time in accordance with the requirements of ZCS select 0.5μs

3) The calculation of the number of turns

According to

Where N is the number of turns, tp to delay opening time, Bs for the core saturation flux density, Ac is the core of the effective cross-sectional area, ULS is applied to the inductor saturation voltage, approximately equal to Udc. Considered N = 3

4) Calculate the window utilization

The maximum average current through the inductor saturation is 50A, in accordance with the current density KJ of 2.5A / mm2 design, winding cross-sectional area Ar = 20mm2; window area AW = 6.6cm2.

Window Utilization

5. Conclusion

By optimizing the design of the main magnetic components of high-frequency power modules, and application of high-frequency power production, a good solution to heat loss and magnetic components of the problem, the high frequency