Advanced Control of a Resistance Spot Welding System

This paper deals with a middle-frequency resistance spot welding system. It consists of an input converter, welding transformer, and a full-wave rectifier mounted at the transformer secondary. The welding current at the full-wave rectifier output is normally controlled by the pulse width modulated primary voltage of the transformer supplied by the input converter. The unequal ohmic resistances of the two transformer's secondary circuits and the different characteristics of the diodes of output rectifier certainly lead to the magnetic saturation which, consequently, causes the unwanted spikes in the transformer's primary current and over-current protection switch-off. This disadvantage of classical spot welding systems is completely eliminated by the proposed advanced hysteresis controller (AHC), which keeps transformer iron core saturation within prescribed bounds regardless of how unequal the ohmic resistances and diodes' characteristics in the transformer's secondary circuits are. This is achieved by a combined closed-loop control of the welding current and closed-loop control of the iron core saturation level. The proposed AHC assures a very short rise time of the welding current and the best possible utilization of the transformer iron core.     

Sliding Transformer With Long Magnetic Circuit for Contactless Electrical Energy Delivery to Mobile Receivers

A new type of sliding transformer with long magnetic core and movable secondary winding is presented. The basic transformer configurations and wiring are described. The magnetic flux distribution along the magnetic circuit and its influence on transformer parameters are discussed and examined. Also, the leakage inductance of the transformer primary winding, as the main cause of voltage drop and energy losses, has been discussed. The main experimental results of transformer model investigation are presented in this paper     

环面点胶对电源磁性器件可加工性的影响

变压器、电感等磁性器件性能显著影响电源参数指标。针对E型变压器磁芯气隙制作一致性差、效率低的问题,建立了不同点胶方案的有限元分析模型,进行了高黏度环氧绝缘胶非牛顿流体的剪切力机理分析。结果表明,通过减小胶点尺寸、改变胶点形态及分布的方法,可以提高磁芯器件的一致性和加工效率。采用全自动点胶工艺精确控制胶点半径和中心距,制作出了满足电感量要求的变压器,提升了加工效率,验证了仿真和机理分析的正确性。获得了一种高精度、高效的环面点胶和磁性器件制作工艺方法。     

Resonance transformer power conditioners

One solution to the problem of high-power transformers is the concept of the resonance transformer, which uses a set of resonant circuits, made up of discrete inductors and capacitors, to achieve a transformerlike voltage gain. A brief overview of the general approach is presented. Because this approach does not require the magnetic core material associated with a conventional transformer, a significant savings in both size and weight can be realized, particularly at higher power levels. Technical issues associated with the conventional transformer, such as coupling of the primary and secondary windings at both high voltages and high frequencies and thermal management of heat generated in the transformer core, are also avoided. Several designs have been generated and tested, including a 20-kHz, 10- to 15-kW average power system. This power supply provides a voltage gain of 50 and weighs less than 45 kg. Additional designs for higher power levels above 1 MW are discussed along with information on expected sizes, weights, and general scaling tendencies     

A novel iron loss reduction technique for distribution transformersbased on a combined genetic algorithm - neural network approach

The paper presents an effective method to reduce the iron losses of wound core distribution transformers based on a combined neural network/genetic algorithm approach. The originality of the work presented is that it tackles the iron loss reduction problem during the transformer production phase, while previous works concentrated on the design phase. More specifically, neural networks effectively use measurements taken at the first stages of core construction in order to predict the iron losses of the assembled transformers, while genetic algorithms are used to improve the grouping process of the individual cores by reducing iron losses of assembled transformers. The proposed method has been tested on a transformer manufacturing industry. The results demonstrate the feasibility and practicality of this approach. Significant reduction of transformer iron losses is observed in comparison to the current practice leading to important economic savings for the transformer manufacturer     

行波管高压电源中变压器的优化设计

研究了行波管高压电源中变压器的铁芯损耗、绕组损耗(铜损)和工作频率,主要通过理论推导和仿真对磁性元件的设计进行了优化分析,并用PC95材质PQ40/40磁芯设计了一种输出电压10kV、输出功率450 W的行波管高压电源变压器。变压器设计结果满足电源要求,实验结果验证了理论分析。     

Finite-element analysis of copper loss in 1-10 MHz transformers

Issues related to the copper loss in the planar windings of 1-1 MHz power transformers are discussed. The relationship between current distribution, copper loss, and core geometry is investigated with the aid of finite-element analysis. Magnetizing current proximity effects are shown to cause excessive copper loss in a simple sandwich transformer, a structure formed by sandwiching the planar winding between two plates of magnetic material. Three alternative transformer structures that reduce this problem are compared. These alternative structures are: the cofired transformer, the slotted gapped transformer, and the slotted ungapped transformer. It is concluded that a slotted transformer design should be used if the magnetizing current is relatively large. Both a slotted gapped and a slotted ungapped design relies strongly on the exact permeability of the material and may suffer from higher core losses because all of the energy is stored in the magnetic material, rather than in an air gap. In either case, the depth of the slot should be About 40% of its width     

Analysis and design of electronic transformers for electric powerdistribution system

A transformer performs many functions such as voltage transformation, isolation and noise decoupling, and it is an indispensable component in electric power distribution systems. However, at low frequencies (60/50 Hz), it is a bulky and expensive component. In this paper, the concept of electronic transformers is further extended and explored for its suitability in power distribution systems. It should be noted that from the input/output behavior, the electronic transformer and the conventional transformer are identical. Possible topologies employing static converters connected on the primary and secondary sides are explored to realize high-frequency operation of the magnetic core. To assist the commutation process, a four-step switching has been developed which does not require the use of snubbers. Reduced size, losses, higher efficiency, and better voltage regulation are some of the advantages of this approach. A 10 kVA design example along with experiment results are discussed. It is shown that a transformer designed with a conventional grain-oriented silicon-steel core can process three times the power at 1 kHz operating frequency as compared to 60 Hz. The proposed method is scalable in voltage/current with the currently available insulated gate bipolar transistor (IGBT) devices connected in series without special snubbers     

High voltage breakdown of titania in vacuo

The electrical breakdown of titania in a vacuum using static electric fields is investigated experimentally, by examination of current and temperature variation at different applied voltages. Thermal instability is found to occur at voltages above a critical value. This leads to sufficiently high temperatures to cause the reduction of the titania into a lower-order semiconducting oxide, which carries the breakdown current. The breakdown of titania and a vacuum gap in series is also investigated. Evidence gathered from temperature and current readings suggests that, at high voltages, part of the voltage originally across the vacuum gap appears across the titania. Evidence to support this theory is obtained from measurements of the mechanical force appearing across the vacuum gap which enable the voltage redistribution to be calculated. The voltage redistribution is due to an excess charge appearing on the surface of the ceramic, due to pre-breakdown currents in the vacuum gap. When the voltage across the titania reaches a large enough value, thermal instability occurs leading to breakdown of the titania.     

Optimized transformer design: inclusive of high-frequency effects

Switching circuits, operating at high frequencies, have led to considerable reductions in the size of magnetic components and power supplies. Nonsinusoidal voltage and current waveforms and high-frequency skin and proximity effects contribute to power transformer losses. Traditionally, power transformer design has been based on sinusoidal voltage and current waveforms operating at low frequencies. The physical and electrical properties of the transformer form the basis of a new design methodology while taking full account of the current and voltage waveforms and high-frequency effects. Core selection is based on the optimum throughput of energy with minimum losses. The optimum core is found directly from the following transformer specifications: frequency; power output; and temperature rise. The design methodology is illustrated with a detailed design of a push-pull power converter     

一种低漏感平面变压器

变压器的漏感是电磁干扰的主要来源之一,这是因为开关管在高速关断时,在变压器的漏感上产生感应电动势,叠加在变压器绕组的关断电压上,形成关断电压尖峰,这些电压尖峰不但造成电磁干扰,还会使开关管的电压应力增大,重者可能击穿开关管,并增大开关损耗,降低开关电源的效率。本文提出一种分布磁路结构的低漏感平面变压器,其原边绕组的匝数降低为一匝,副边绕组的等效匝数降低为小于一匝,因而漏感显著减小,这种分布磁路结构可以用于低压大电流电源的变压器,其有效性通过Maxwell 3D得到验证。     

Formation of shallow photodiodes by implantation of boron into mercury cadmium telluride

Hall-effect measurements on p-type MCT implanted with 1 × 1014 B+/cm2 at 150 keV show that an abrupt junction is formed at a depth of 0.6 ± 0.12 ?m after annealing at 230° for 7 min with a ZnS cap. Prior to the anneal the carrier profile was graded and extended to a depth of 5.0 ± 1.0 ?m. Photodiodes have been formed by a dual implant of 5 × 1014 B+/cm2 at 100 keV and 50 keV, and after annealing a five-fold improvement in Ro A has been measured to give a value of 1.2 ?cm2.     

Josephson junctions with 1 ?m dimensions and with picosecond switching times

Josephson junctions with 1 × 3 ?m dimensions have no resonances. For a current density of about 1000 A/cm2, the risetime of the switching transient from zero to the gap voltage is below 38 ps.     

诺模图在反激变压器设计中的应用

针对开关电源变压器设计中存在公式繁多,磁心难以选择等问题,提出了利用磁心诺模图直观地选择最优磁心,并确定最优磁通密度摆幅等参数的方法。由给出的工作频率和输出功率选择磁心,并通过磁心确定原副边绕组和反馈绕组匝数等参数指标,进行了实例设计。实验结果显示,以此变压器制作的输出为24 V开关电源,空载时纹波电压为220 mV,低于输出电压的,满足一般行业要求,证实了磁心诺模图方法的可行性与实用性。     

A contact-less system using a series resonant converter and a rectangular type core

Since the contact-less power transmission system accomplishes power transfer using magnetic coupling of the transformer without a mechanical contact, it has the advantages of electric isolation, safety, reliability, low maintenance and a long-product life. However, a contact-less transformer with a large air gap has a low coupling coefficient and high leakage inductance. This, in turn, results in poor power conversion efficiency. In this article, a contact-less power transmission system based on a rectangular type core and a series resonant converter is proposed to improve system efficiency and performance. The proposed system is designed with an air gap of 1 mm and 50 kHz switching frequency, but it is assumed that in a practical application, the air gap varies. It is verified by experimental results that the proposed contact-less power transmission system based on the rectangular type core and a series resonant converter can substantially reduce the circulating current and improve the system efficiency. Also, it is verified that even with an increased air gap, the proposed system maintains soft switching and avoids switching devices' current spikes while suppressing the increase of the circulating current caused by an air gap increase.     

Transformer miniaturization for transcutaneous current/voltage pulse applications

A general procedure for the design of a miniaturized step up transformer to be used in the context of surface electrode based current/voltage pulse generation is presented. It has been shown that the optimum secondary current pulse width is 4.5 tau, where tau is the time constant associated with the pulse forming network associated with the transformer/electrode interaction. This criteria has been shown to produce the highest peak to average current ratio for the secondary current pulse. The design procedure allows for the calculation of the optimum turns ratio, primary turns, and secondary turns for a given electrode load/tissue and magnetic core parameters. Two design examples for transformer optimization are presented.     

Integrated magnetic full wave converter with flexible output inductor

A new integrated magnetic full wave DC/DC power converter that provides flexible transformer design by incorporating an independent output inductor winding is introduced. The transformer is implemented on a traditional three-leg magnetic core. The inductor winding can be separately designed to control the output current ripple. The cross-sectional area of the inductor core leg can be reduced dramatically. The operation and performance of the proposed circuit are verified on a 100 W prototype converter.     

Design of 48 V Voltage regulator modules with a novel integrated magnetics

The push-pull forward topology with the current-doubler and synchronous rectifier is a suitable approach for high-input voltage regulator modules (VRMs) used to supply high-performance microprocessors. In order to improve efficiency and reduce size, this paper proposes an improved push-pull forward converter with a novel integrated magnetics. All the magnetic components including input filter inductor, step-down transformer and output filter inductors are integrated into a single EI or EE core. This topology is essentially the modified push-pull converter with the built-in input filter and the coupled-inductor current doubler rectifier. The proposed integrated magnetic structure features a simple core structure, a small leakage inductance and low winding and core losses. A design is given for a 48-V VRM with a 1.2-V and 70-A output, and its experimental results show that the proposed approach can offer a great improvement in efficiency.     

低强度超声对鼻咽癌细胞生物学效应的研究

目的：研究不同剂量低强度超声对人低分化鼻咽癌细胞CNE-2的急,、慢性生物学效应。方法：人鼻咽癌细胞CNE-2受不同剂量、频率为1.7MHz的超声波辐照,利用台盼兰染色法确定三种未致细胞急性损伤的超声剂量,并观察受此三种剂量超声辐照后细胞的增殖能力以及克隆形成力的变化。结果：0.30W/cm^2×35s、0.65W/cm^2×10s和1.35W/cm^2×5s未致细胞急性死亡。受0.30W/cm^2×35s、0.65W/cm^2×10s、1.35W/cm^2×5s辐照及对照组细胞倍增时间分别为：15.8h、23.6h、31.6h和22.9h;克隆形成率分别为：（41.54±1.48）%、（25.41±1.70）%、（15.62±1.60）%和（28.03±1.2）%。受0.30W/m^2×35s辐照后细胞增殖和克隆形成较对照组均有所增加,受1.35W/cm^2×5s辐照后细胞增殖和克隆形成较对照组均受到抑制。（p〈0.05）结论：CNE-2细胞对超声敏感性高,其生物学效应取决于超声剂量。     

Study of the Thin Film Pulse Transformer

A great interest has been attracted in planar magnetic devices to miniature various electronic equipment including pulse transformers and inductors, especially for the IT electronics applications and ISND modem systems, such as switching converters and inverters in portable equipments[1~3]. In Internet system,the thin film pulse transformer, with the sandwich structure of core/coil/core and coil/core/coil, in general,will be fabricated directly on ceramics substrate by lithography and ion et…