Research and application of microcrystalline materials for electronic ballast transformers

Research and application of microcrystalline materials for electronic ballast transformers

Lighting is an indispensable energy-consuming equipment in today's daily life and industrial and commercial activities. It accounts for a considerable proportion of the electricity consumption in various countries. Therefore, how to improve the efficiency and energy saving of lighting fixtures is an important issue in today's industry. Improving the efficiency and energy saving of lighting fixtures mainly starts from the light source, ballast, lampshade, etc., and the efficiency of the ballast has the greatest impact. The total energy consumption of the current traditional iron core type 40W ultra-high power fluorescent lamp ballast is 47W, the instantaneous energy consumption is about 52W, and the energy-saving type consumes about 43W. In the early 1980s, Philips of the Netherlands launched a high-frequency electronic ballast, which has the functions of inductive ballast and starter. Because electronic ballasts have the characteristics of energy saving, no flicker, no noise, high power factor, and low starting voltage, they have gradually replaced inductive ballasts. However, since ferrite is mostly used as a transformer in current electronic ballasts, its rapid development is hindered by the low magnetic induction and poor temperature stability of ferrite, so a new type of magnetic material is urgently needed to replace it.

2. Working principle of electronic ballast circuit

Before explaining the material research work, it is necessary to explain the working principle of the electronic ballast.

The working principle structure diagram of most current electronic ballasts can be represented by the block diagram shown in FIG1 .

Figure 1. Block diagram of the working principle of electronic ballast

As can be seen from the block diagram, it converts 50Hz AC mains into a high-frequency voltage of more than 20Kc, and its core part is essentially an inverter. We know that at high frequencies, transformers or inductors can use high-frequency magnetic cores to greatly reduce the number of turns of the coil, thereby greatly reducing the size, weight and price of the transformer or inductor.

The working current delivered to the load through high frequency rectification is about 20Kc~30Kc, which is approximately a sine wave.

3. Material development

Since the operating frequency of electronic ballast is 20Kc~30Kc, the material is required to have good high-frequency characteristics.

As can be seen from Table 1, in terms of comprehensive performance indicators, iron-based microcrystals are ideal. They not only have high Bs, but also low losses. Since the working environment temperature of electronic ballasts varies greatly, trace elements are added to improve thermal stability while maintaining high Bs.

Iron-based microcrystalline materials have more comprehensive magnetic properties than Co-based amorphous materials. Since the material was announced by Hitachi Yoshizawa in 1998, it has quickly attracted widespread interest in the field of magnetic materials and physics in various countries. In addition to fully reaching and exceeding Co-based amorphous alloys in terms of high-frequency loss characteristics and high-frequency magnetic permeability, Fe-based microcrystalline materials have a saturation magnetic induction Bs≈12000Gs, which is almost twice that of Co-based amorphous materials. The magnetic permeability is as high as more than 100,000, which is much higher than that of ordinary Co-based amorphous materials. The Curie temperature of iron-based microcrystalline materials is 540℃~570℃, which is much higher than that of Co-based amorphous materials. Since it is a microcrystalline state, from the perspective of thermodynamics, its stability should theoretically be better than that of amorphous materials. In fact, from the data reported in foreign or domestic research in this regard, the △μ/μ or △L/L of iron-based microcrystalline materials are very small (≤5%), and the time stability is also very excellent.

The general composition of iron-based microcrystalline materials is:

N=Co, Ni N=Nb, W, Ti, Zr, Hf, Ti, Mo 等。

Judging from the composition of iron-based microcrystalline materials, the adjustable range is relatively wide, which brings great convenience to research and development.

1. Alloy Preparation

Industrial pure Fe, intermediate alloy Fe-B, crystalline Si, metal Mo, Nb, V-Fe, Cr, Mn, Cu, graphite C are used. According to the formula, they are smelted in a vacuum induction furnace to become master alloy bars, which are polished and sanded. Amorphous strips of various specifications and widths are produced on amorphous strip making equipment. The entire strip making process must strictly control the steel tapping temperature, rotation speed, air pressure, etc. The strip thickness is preferably controlled at 25 mm. The strip surface is flat and smooth, and voids and thickness tolerances are eliminated as much as possible. These are prerequisites for obtaining high performance.

2. Physical characteristics of alloy testing

The CL-6 DC circuit tester was used to measure the hysteresis loop of the iron core; the SY8218 magnetic characteristic tester was used to measure the AC loss characteristics of the iron core; and the 4274A and muti-Frequencg LCR Meter were used to measure the high permeability and permeability characteristic curve of the iron core.

The crystallization temperature Tx and Curie temperature Tc of the microcrystalline material were determined by differential thermal analyzer; the crystallization phase and degree of crystallization of the material were determined by D-5X-ray diffractometer.

4. Material development results

1. Relationship between composition and material properties

The addition of Cu in Fe-based amorphous is mainly to utilize its insolubility in iron, and first precipitate during heat treatment to form the nucleus of microcrystals. Adding elements such as Nb, Mo, and V is beneficial to increase the crystallization temperature of amorphous. Once α-Fe(Si) crystals are precipitated, an amorphous phase with high crystallization temperature rich in Nb, Mo, and other elements is formed around it, thereby inhibiting the growth of -Fe(Si) microcrystalline phase. For this reason, we prepared six different addition amounts of Mo, Nb, and V, and their crystallization characteristics are shown in Table 2.

The thermal differential analysis measured by six alloy compositions reflects some characteristics of Fe-based microcrystalline materials during their crystallization process:

(1) A high Nb content is beneficial to increasing the crystallization temperature of the amorphous state, followed by Mo and V.

(2) Adding Nb and Mo to the alloy is beneficial to widening the distance between the Fe peak and the FeB peak during the crystallization process, while adding V is less effective. Widening the distance between these two peaks is the key to forming microcrystalline materials with excellent magnetic properties.

(3) It is easier to make strips by adding Nb or Mo, but it is more difficult to make strips by adding V alloy. Mo or Nb must be added at the same time to make strips.

The five alloys mentioned above all have good soft magnetic properties. The first three alloys have better properties, lower coercivity, and easier to control heat treatment. Based on comprehensive considerations such as the strip production rate, magnetic properties, heat treatment performance consistency, and material price factors, the LH-M-2 alloy was selected.

2. Properties of alloys used

From the conventional magnetic property parameters in Table 3, Figure 2, Figure 3, Figure 4, and Figure 5, it can be seen that the alloy has excellent high-frequency characteristics. Some performance indicators have not been seen in current domestic and foreign data reports, such as

=27.13W/kg，

=63W/kg。

Figure 2: The alloy is annealed and then circulated

Figure 3. The alloy was treated with a transverse magnetic field.

Fig.4 p~f curve of this alloy

Figure 5 ~f curve of this alloy

5. Material application

This material is used in DBN-1 neon lamp electronic ballast.

Circuit diagram of DBN-1 electronic ballast.

Figure 6 DBN-1 electronic ballast circuit diagram

1. Production of iron core

Due to the limitation of the high voltage wire package of the main transformer, our core can only be similar to it. The core size is CD38×38×11, c=10m/m, and the oscillation inductance is Φ6×8×5 m/m.

(1) Winding

The iron-based microcrystalline material is wound into rectangular cores and ring cores according to practical sizes using semi-automatic constant tension core winding equipment.

(2) Heat treatment

The iron core is microcrystallized at 520°C to 570°C in an Ar atmosphere furnace and in a vacuum, and then cooled at a suitable cooling rate before being taken out of the furnace.

(3) Bonding

The operating frequency of the electronic ballast transformer core is about 30Kc. In order to reduce the transformer

The bonding of the core is very important due to the noise and the need to cut the core.

Table 4 lists the three types of binders used in this study. Since the choice of binder has a great influence on the magnetic properties, we have selected the self-adjusting binder based on the above three situations, which has better overall performance.

(4) Cutting

Use wire cutting machine to cut the core

Figure 7 shows the hysteresis loops produced by different air gaps. It can be seen from the figure that the core is a constant value in a wide magnetic field range, that is, the magnetic permeability μ is constant when the resonant capacitance is constant and the inductance in the resonant charging state is:

because

so

Figure 7 Loops with different air gap widths

2. Static performance changes

This experiment conducted a temperature test on the iron-based microcrystalline core used and the original ferrite.

From the above data, we can get the following result: the inductance of the iron-based microcrystalline core remains basically unchanged in the temperature range of 20~130℃, while the change rate of iron oxide δ≈24%.

To obtain a stable voltage source, LC must be kept as a constant:

。

It can be seen from the formula that when the resonant capacitance is constant, the inductance L must also be a constant value, and it must also have good temperature characteristics. At this time, because it works at a high frequency, it is very easy to generate heat and affect the performance of the alloy. In other words, within the operating temperature range of the original electronic ballast, its magnetic parameters are always a variable, which means that the corresponding components are always working at an unfixed frequency, resulting in a series of vicious cycles. In this regard, iron-based amorphous has shown great advantages and can increase the service life of each component.

3. Dynamic testing

The core was directly installed on the DBN-1 electronic ballast for testing and compared with its original ferrite. The results are as follows:

a. Temperature changes of transformers at room temperature

b. Temperature change of transformer under high temperature conditions

Judging from the above temperature changes, it will meet the requirements for use of electronic ballasts.

c. Output power

Under the same load condition, the output power of ferrite is measured to be 130W, while that of iron-based microcrystalline core is 150W, 15% more than that of iron-based microcrystalline core. That is to say, under the same condition, the length of the lamp tube can be extended to achieve the purpose of saving.

d. Output waveform of each transformer

The period of the output waveform of ferrite changes due to the change of its inductance, but this does not happen in iron-based microcrystalline cores.

VI. Conclusion

1. Through research this year, we have successfully developed an iron-based microcrystalline material with superior magnetic properties, good amorphous forming ability and stable heat treatment process.

2. Initial magnetic permeability of the new material △

=130,000, Hc=0.005Oe, =63w/kg，

△m/m ≤5%.

3. The iron-based microcrystalline material developed can meet the use requirements of electronic ballasts, and its performance is superior and has reached the domestic advanced level.

4. Its application in electronic ballast has good performance stability and large output power, which improves the utilization rate of electronic ballast.