Some New Developments in Electronic Transformers in Power Supplies

Introduction 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 user of downstream electronic transformers, they can choose and purchase on a global scale to form a buyer's market. In the middle position of the electronic transformer industry, only by taking the road of technological innovation, can we get rid of this dilemma of anger at both ends. However, in the mature electronic transformer industry, technological innovation is more difficult. But every small link improvement can bring new ideas and new products. Therefore, this article introduces some new developments in electronic transformers in power supplies in recent years from four aspects: new materials, new structures, new principles, and new products, for readers' reference. Please correct me if there is any impropriety. Taking the road of technological innovation, we must always remember the purpose to be achieved. The electronic transformer in the power supply, like all products as a commodity, carries out any technological innovation, and must perform specific functions under specific conditions of use, pursuing the best performance-to-price ratio. The current power products are generally characterized by being "light, thin, short, and small" toward miniaturization and portability. Electronic transformers must adapt to the volume and weight requirements of power products as users. At the same time, the prices of raw materials (core materials and conductive materials) for electronic transformers have risen. Therefore, how to reduce the volume and weight, and how to reduce the cost, has become the main direction of the development of electronic transformers in recent years. 1. New materials 1.1 Silicon steel Silicon steel is a core material widely used in electronic transformers in industrial frequency power supplies. To reduce the amount of core in electronic transformers, the working magnetic flux density (working magnetic density) of silicon steel must be increased. The working magnetic density of silicon steel is determined by both the saturation magnetic flux density and the loss. Because efficiency is an important performance index of electronic transformers, many power products now require standby loss in order to save energy. The core loss of the electronic transformer is the main component of the standby loss, therefore, clear and strict requirements are put forward on the efficiency or loss of the electronic transformer. In recent years, the price of oriented and non-oriented cold-rolled silicon steel has risen. Compared with R-type, CD-type and EI-type cores, coiled toroidal cores can save more than 20% of the core material cost due to less consumption of materials. The scope of use in the transformer. The wound toroidal core can give full play to the performance of oriented cold-rolled silicon steel. Compared with non-oriented cold-rolled steel, the working magnetic density is much higher. At the same time, unlike R-type, CD-type and EI-type iron cores, silicon steel materials can be fully utilized, there will be no corner waste, and the material utilization rate can reach more than 98%. In recent years, there has been considerable improvement in cold-rolled oriented silicon steel. The domestically produced 0.23mm oriented cold-rolled silicon steel of 23Q110 has a working magnetic flux density of 1.7 T and 50 Hz, and the unit weight loss is 1.10 Wkg. The 0.23 mm thickness oriented cold-rolled silicon steel P1.750 produced in Japan is 0.88Wkg. After the surface treatment of silicon steel strip is coated with tension coating, P1.750 drops to 0.7Wkg. Changing the annealing process to refine the magnetic domains, P1.750 drops to 0.55～0.45Wkg, which is much lower than the 0.35mm thick non-oriented cold-rolled silicon steel at a working magnetic density of 1.5T and 50Hz (P1.550) of 2Wkg. Under the condition of ensuring the same loss, the working magnetic density of 0.23mm thickness oriented cold-rolled silicon steel can reach 1.85T. If it is selected to process the toroidal core, it is 1.23 times higher than the working magnetic density of non-oriented cold-rolled silicon steel 1.5 T. The core section and volume It can be reduced by more than 23%. Nowadays, EI type iron core power frequency power transformers are widely used in the power adapters of mobile phone chargers and household appliances, and sometimes overheating occurs. The EI core is made up of EI-shaped punched sheets. One-fifth of the length of the E-shaped punched sheet is orthogonal to the longitudinal direction (orientation direction). To withstand the transverse magnetic field, non-oriented cold-rolled silicon steel is generally used. In recent years, Japan’s Kawasaki Company has developed RGE series oriented cold rolled silicon steel that can be used for EI cores. The thickness is 0.35 mm, the longitudinal saturation magnetic density is 1.80～1.90 T, the lateral saturation magnetic density is 1.825T, and the loss P1.750 is 1.10～ 1.25Wkg. At the same time, the insulating film is relatively thin, and the stamping performance is good. Using it to make the iron core, the working magnetic density can be more than 1.7T, which is 15% higher than that of non-oriented cold-rolled silicon steel. The core section and volume can be reduced by more than 15%, and the loss is greatly reduced. , There will be no more overheating. Japan’s Kawasaki Company has also developed a non-oriented cold rolled steel with high saturation magnetic density. The thickness is 0.5mm, the silicon content is less than 1%, 0.6%, and the aluminum content is 0.3%. After adding 0.52% nickel, the saturation magnetic density is 1.96T. , The loss P1.550 is 3Wkg. Using it as an EI core material, the working magnetic density can also be 1.7T, but the loss is relatively large. It is worth noting that: as a large class of electronic transformers, the use of core materials with high working magnetic density can reduce the number of coil turns and reduce the amount of copper, instead of reducing the core section and volume. Under the situation that the price of copper material is much higher than that of core material, it may be a better design improvement plan. 1.2 Soft ferrites Soft ferrites are core materials that are widely used in electronic transformers in medium and high-frequency power supplies. Compared with metallic soft magnetic materials, soft ferrites have low saturation magnetic density, low permeability, and Curie temperature. Low is its major weakness. Especially when the Curie temperature is low, the saturation magnetic density Bs and the power loss per unit volume Pcv will change with temperature. The temperature rises, Bs drops, Pcv begins to drop, and then rises after reaching the valley point. Therefore, under high temperature conditions, as long as Bs maintains a high level, the working magnetic density Bm can be selected higher, thereby reducing the number of coil turns, reducing the amount of copper used and the cost. The high temperature and high saturation magnetic density soft ferrite material can also expand the upper temperature limit of electronic transformers to 120 or even 150 benefits. For example, high-frequency electronic transformers in automotive electronic equipment must use high-temperature, high-saturation magnetic-density soft ferrite to work under high-temperature conditions with large changes in external temperature conditions and heat in the engine room. As a MnZn soft ferrite for medium and high frequency electronic transformers, represented by Japan's TDK company, it has roughly experienced the development process of PC30→PC40→PC44→PC50→PC47→PC95→PC90. Under the test conditions of 100℃, 100kHz, and 200mT, the power loss per unit volume keeps decreasing. According to the data released by the company in April 2006, PC30 is 600mW/cm3; PC40 is 420 mW/cm3; PC44 is 340 mW/cm3; PC47 is 270 mW/cm3. However, the saturation flux density Bs under 100 benefits, PC30, PC40, and PC44 are basically 390 mT, PC47 is 410 mT, which is far from the theoretical value of 600 mT, and cannot be regarded as a high temperature and high saturation flux density material. In recent years, in order to compete with metal soft magnetic materials in the application of electronic transformers, there has been a wave of development of high temperature and high saturation magnetic density MnZn ferrite materials. Japan's FDK company developed the 4H series of high temperature and high saturation magnetic density materials in March 2003. Among them, the Bs of 4H45 and 4H47 are 520 mT and 530mT at 25℃, 450mT and 470mT at 100℃, but at 100℃, the power loss Pcv is relatively high, respectively 450mW/cm3 and 650mW/cm3. According to reports, FDK has developed a 4H50 material under laboratory conditions. The Bs at 100°C is 490 mT, but the Pcv is quite large at 800 mW/cm3. Japan TDK company developed PC90 material in September 2004. At 25℃, Bs is 540mT and Pcv is 680 mW/cm3; at 100℃, Bs is 450 mT and Pcv is 320mW/cm3, which is higher than 4H45 material level . TOKIN company developed the BH3 material. At 25°C, its Bs is 540 mT and Pcv is 600 mW/cm3; at 100°C, Bs is 440 mT and Pcv is 370 mW/cm3. NICERA has developed the BM30 material, with Bs of 540 mT and Pcv of 720 mW/cm3 at 25°C; at 100°C, Bs of 450mT and Pcv of 320mW/cm3. The high-iron and low-zinc ferrite material developed by Hitachi Metals, Bs is 563 mT at 25 ℃; 560 mT at 100 ℃, basically unchanged, 150 ℃ is 490 mT, but at 100 ℃, 100 kHz, Under the test condition of 200 mT, the Pcv is 1700mW/cm3, which is too high and needs improvement. Many power supply equipment not only require that the electronic transformer is in working condition, that is, the loss should be small at high temperature, but also in the standby state, that is, the loss should be small at normal temperature. These electronic transformers can use soft ferrite with wide temperature and low power consumption. PC95 developed by Japan's TDK is a high-level, wide-temperature ferrite material that has emerged in recent years. The power consumption Pcv is 350mW/cm3 at 25°C, 280mW/cm3 at 80°C, 290mW/cm3 at 100°C, 350mW/cm3 at 120°C, and saturation magnetic density of 410mT at 100°C. In recent years, a series of high permeability μ soft ferrite materials have been developed. They are used as pulse transformers in electronic power equipment. The permeability μ is required to be relatively high. There is H5C3 from TDK, which has a μ of 15 000±30. %, H5C5, μ is 30 000±30%. For EPCOS's T56, μ is 20000±30%. For electromagnetic interference filtering, good permeability frequency characteristics are required. TDK HS52, μ is 5 500 ± 25%; HS72, μ is 7 500 ± 25%; HS10, μ is 10000 ± 25%. HITACHI’s MP15T has a μ of 15000±25% and can work below 500kHz. For DC filtering, good DC superposition characteristics are required. TDK's DN45, μ is 4500±25%, operating temperature is 0～70℃, and improved DNW45, μ is 4 200±25%, operating temperature is -40 ℃～+85℃, Kawasaki’s SK-202G, operating temperature -40℃～+85℃, μ is 4300±25%, and high saturation magnetic density and high permeability materials, such as TDK’s DN50, μ is 5 200±20%, Bs is 550 mT at 25℃, 380 mT at 100℃, Curie temperature Tc≥210℃. 1.3 Amorphous and nanocrystalline alloys Since the beginning of 2005, due to the imbalance in domestic supply and demand of oriented cold-rolled silicon steel strips, the price of oriented cold-rolled silicon steel strips has risen rapidly, and has now exceeded the price of iron-based amorphous alloy strips. Under the current market price conditions, the replacement of oriented cold-rolled silicon steel by iron-based amorphous alloys in the field of power frequency power transformers is no longer just a possible thing, it has become a reality. In the power transformer industry, distribution transformer manufacturers have shifted core materials from oriented cold-rolled silicon steel to iron-based amorphous alloys. At the same time, from July 1, 2006, the mandatory national standard "Limited Values of Energy Efficiency and Energy Conservation Evaluation Values for Distribution Transformers" was formally implemented, which further promoted the use of iron-based amorphous alloys instead of oriented cold-rolled silicon steel in distribution transformers. upsurge. Like distribution transformers, the replacement of oriented cold-rolled silicon steel with iron-based amorphous alloys in power frequency power transformers will become a major new development in electronic transformers in power supplies. why? The reason can be seen from the comparison of technical and economic indicators of oriented cold-rolled silicon steel and iron-based amorphous alloy in Table 1. The medium-oriented cold-rolled silicon steel in Table 1 takes the high magnetic induction 23R100 and magnetic domain treatment 23R085 produced in Japan as examples, and the iron-based amorphous alloy takes the domestically produced 1K101 and the Metglas 2605SA1 produced by Hitachi as examples, as can be seen in Table 1. The following features are presented. [align=center] Table 1 Comparison of technical and economic indicators between oriented cold-rolled silicon steel and iron-based amorphous alloys[/align] (1) The saturation magnetic density Bs of iron-based amorphous alloys is lower than that of silicon steel, but at the same working magnetic density Bm (For example, 1.4T) lower loss is lower than silicon steel. The working magnetic density Bm of iron-based amorphous alloy is 1.40～1.45T for single-phase transformer and 1.35～1.40T for three-phase transformer. The working magnetic density Bm of silicon steel is 1.70T for single-phase transformer and 1.65～1.70T for three-phase transformer. The weight of iron-based amorphous alloy for power frequency transformer of the same capacity is about 120% of silicon steel. (2) The filling factor of iron-based amorphous alloys is 0.85 for domestically produced 1K101 and 0.86-0.90 for Metglas 2605SA1 produced by Hitachi, and some have reached 0.93. If 0.86 is compared with 0.945 of silicon steel, the volume of the iron-based amorphous alloy core of the same weight is about 110% of that of silicon steel. (3) The unit weight loss of iron-based amorphous alloy under 1.4T and 50Hz conditions is P1.450, which is only 26.4% to 43% of silicon steel, which can significantly reduce core heating. Under the same loss and same heat dissipation conditions, iron-based amorphous alloy power frequency transformers can reduce copper loss and reduce copper materials than silicon steel power frequency transformers. Under the condition that the price of copper materials is higher than that of iron materials, adopting this scheme is one An effective measure to reduce costs. It is worth noting that the loss per unit weight P1.450 is tested under a sine wave voltage with a distortion less than 2%. The actual power frequency grid is distorted to 5%. The unit weight loss under this distortion is P1.450, silicon steel is 123% P1.450, and iron-based amorphous alloy is 106% P1.450. At this time, P1.450 of iron-based amorphous alloy is only silicon steel. 22.7%～37% of the total. (4) The current price of silicon steel was taken from the market price of steel in a certain place in Guangdong in mid-August 2006, and the current price of imported iron-based amorphous alloys was taken from Japan’s Hitachi in July 2006, quoting US$2.85 per kilogram. The RMB exchange rate is 22.8 yuan kg, plus tariffs and value-added tax is 28 yuan kg. The current price of domestic iron-based amorphous alloys is an estimate, which is somewhat different from the quoted price of the production unit. (5) The annealing temperature of iron-based amorphous alloys is lower than that of silicon steel, with less time and less energy consumption. The additional processing cost for manufacturing iron cores should be lower than that of silicon steel. Iron-based amorphous alloy strips can be processed into winding toroidal cores, overlapping rectangular cores and open C-shaped cores. In the 1990s, Japan used several layers of bonded iron-based amorphous alloy strips to process EI cores, but the additional processing costs were high and core losses increased. Later, there was no relevant report. Now, the thickness of the bulk amorphous alloy under study can reach the millimeter and centimeter level. If it is put into production, it may be processed into an EI core like silicon steel. Combining the above factors, in the ring and C