In recent years, the prices of core materials and conductive materials used in electronic transformers in power supplies have continued to rise, and upstream raw materials have formed a seller’s market. As a power supply user of downstream electronic transformers, they can select and purchase globally to form a buyer's market. In the middle of the electronic transformer industry, only take the road of technological innovation to get rid of this dilemma. However, in the mature electronic transformer industry, technological innovation is more difficult. However, the improvement of every small link can bring new ideas and new products.
To take the road of technological innovation, we must always remember the purpose to be achieved. The electronic transformer in the power supply, like any product that is a commodity, carries out any technological innovation, and must complete specific functions under specific conditions of use. The pursuit of performance is the best price. Today's power supply products are generally characterized by "lightness, thinness, shortness, and smallness," and are becoming smaller and more portable. The electronic transformer must adapt to the volume and weight requirements of the user's power supply product. At the same time, the prices of raw materials (core materials and conductive materials) for electronic transformers have increased. Therefore, how to reduce the volume and weight and how to reduce the cost has become the main direction for the development of electronic transformers in recent years.
Silicon steel is an iron core material that is widely used in electronic transformers in industrial frequency power supplies. To reduce the amount of iron used in an electronic transformer, the working flux density (working magnetic density) of silicon steel must be increased. The working magnetic density of silicon steel is determined by both the saturation flux density and the loss. Because efficiency is an important performance indicator for electronic transformers, many power supply products now offer standby loss requirements in order to save energy. The core loss of the electronic transformer is the main component of the standby loss. Therefore, all of them require clear and strict requirements on the efficiency or loss of the electronic transformer.
In recent years, the prices of oriented and non-oriented cold-rolled silicon steels have risen. Compared with R-type, CD-type, and EI-type cores, roll-type annular cores can save more than 20% of the cost of core materials and expand electronics compared to R-type, CD-type, and EI-type cores. The scope of use in the transformer. The wound-type toroidal core can give full play to the performance of oriented cold-rolled silicon steel, which is much higher than that of non-oriented cold-rolled steel. At the same time, unlike the R, CD, and EI iron cores, silicon steel materials can be fully utilized with no corner waste, and material utilization can reach over 98%.
As a large class of power transformers for electronic transformers, cores with high magnetic core density can reduce the number of coil turns and reduce the amount of copper without reducing the core section and volume. In the present situation where the price of copper is much higher than that of iron core material, it may be a better design improvement plan.
Soft ferrite is a core material used in a large number of electronic transformers in high-frequency and high-frequency power supplies. Soft magnetic ferrites have a lower saturation magnetization, a lower magnetic permeability, and a lower Curie temperature than metal soft magnetic materials. Several major weaknesses. In particular, the Curie temperature is low, the saturated magnetic density Bs and the unit volume power loss Pcv will change with temperature. As the temperature rises, Bs drops, Pcv begins to fall, and rises after reaching the trough. Therefore, under high temperature conditions, as long as Bs maintains a high level, the working magnetic density Bm can be selected to be higher, thereby reducing the number of turns of the coil and reducing the amount of copper used and the cost. High-temperature, high-saturation, magnetically-encapsulated ferrite materials can also extend the upper limit of the temperature used by electronic transformers to 120 or even 150 angstroms. For example, in a high-frequency electronic transformer in an automotive electronic device, a high-temperature, high-saturation, magnetically-encapsulated soft ferrite must be used under high temperature conditions in which the outside temperature condition changes and the engine room heats up. Soft Magnetic Composite (SMC) is a new type of soft magnetic material developed in the 1990s. Its starting point is to extend the working frequency of metal soft magnetic materials to MHz and GHz levels, so the metal soft magnetic material and other high resistance Materials, such as quartz, ceramics, polymer materials, and so on, as long as the control of the volume percentage of metal soft magnetic material below the percolation limit, it is possible to maintain the soft magnetic properties, and reduce various high-frequency losses, becoming a new Soft magnetic material? ? Soft magnetic composite material, take the first letter of the English name, referred to as SMC material. The magnetic particles in the soft magnetic composite material may be pure iron, nickel, cobalt metal, iron-nickel alloy, iron-nickel-molybdenum alloy, iron-aluminum alloy, iron-based amorphous alloy, iron-based nanocrystalline alloy, and soft ferrite after being crushed Made of powder. The non-magnetic object may be an insulator such as silicon dioxide, and a polymer material such as silicone resin, polyethylene, epoxy resin may be used as a binder and stearic acid may be used as a lubricant. After the magnetic particles and the non-magnetic objects are mixed, they can be processed into a magnetic powder core through processes such as insulation treatment, press forming, and sintering, and can also be molded into magnetic cores of various complex shapes using current plastic engineering techniques. Soft magnetic composite materials have the advantages of low density, light weight, high production efficiency, low cost, and good product consistency. Disadvantages are due to the fact that the magnetic particles are separated by non-magnetic objects, magnetically blocked, and the magnetic permeability is now generally within 100. Recently, it has been reported that through nanotechnology and other measures, soft magnetic composites with magnetic permeability of over 1000 have been developed. Up to 6000.
Polymer soft magnetic composites have developed rapidly in recent years. They have been used in foreign countries to manufacture high frequency power transformers and inductors, and to establish corresponding analytical theory and design procedures. According to the author's knowledge, although domestic research and development of polymer soft magnetic materials have been conducted, there are no reports of electronic transformers used in power supplies.
At present, various aluminum conductors are being developed for use in electronic transformers in power supplies. Some companies have developed copper-clad aluminum conductors with copper wires in the outer layer, occupying an area of ​​15% and a total specific gravity of 3.63 g/cm3. Considering the watch-and-effect and proximity effects, the resistivity of such copper-clad aluminum wires will be higher than that of pure aluminum wires. A lot of small, but the cost increase is not much, is a kind of composite materials to fully play the role of copper and aluminum.
In recent years, another notable development trend is the selection of 180 polyesterimide QZY enameled wire and 220 polyimide QYZ enameled wire with high temperature index and high heat-resistant grade. The allowable current density of the wire increases and the diameter of the wire decreases. As the amount of copper is reduced, the area of ​​the core window is reduced, and the amount of iron used is also reduced, which can reduce the overall cost. Especially for small-frequency high-frequency low-power power transformers, the use of more heat-resistant enameled wire, can show more technical and economic benefits.
The AC voltage conversion technology included in power supply technology and power electronics technology is a "pure" electronic transformer, which can also convert low voltages to high voltages for boost conversion, or convert high voltages to low voltages for step-down conversion. It is the use of power electronics to increase the power conversion frequency, thereby reducing the size of the transformers and inductors in the circuit, and not eliminating the transformers and inductors therein. In the past, this method of combining power electronic circuits and electronic transformers has not received sufficient attention. In recent years, with the power system requirements to reduce the input and output harmonics, increase the power factor of the grid side, the call for "green transformation" is increasing, and research on "power electronic transformers" has been carried out at home and abroad, and an upsurge of research and development has only begun. Study how to use power electronics technology to transform and control the power and replace the traditional electromagnetic distribution transformer with a power electronic transformer. There are various circuit types such as single-phase conversion and three-phase conversion. This power electronic transformer can be used not only in the high-voltage and high-current power fields, but also in high-voltage or low-voltage low-current fields, such as some high-voltage power generators and small Power regulator power supply.
The number of units engaged in the research, development and production of electronic transformers in China has exceeded 2,000, including state-owned, private, and foreign-funded enterprises. The world’s largest manufacturer of electronic transformers, the United States Plex Corp., and the world’s largest manufacturer of soft ferrites, Japan’s TDK Corporation, all have production facilities in China. Many advanced electronic transformer technologies, production processes and products in the world are all brought together in China. Faced with such a variety of platforms, technological exchanges are promising.