Synthesis of transistor and thyristor switching 2-ports

Contents Realizability conditions of periodic waveforms presented in previous works are extended for multiport circuits. Formulae for an identification of state matrices and a complete synthesis method are given for RL, RC, and RLC 2-ports switching two times within a period. The synthesis presented in the paper is based on multiport transformer structures with switched windings. The reactance extraction method and state variable approach are used. Six general switching structures of 2-ports have been obtained as a result of the synthesis. The structures and the synthesis method can be applied to create new transistor and thyristor arrangements, e.g. D.C.-A.C. converters, frequency changers and compensators.

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Synthese der Transistor- und Thyristorschaltzweiklemmenpaare

Übersicht In dem Aufsatz wurden neue Realisierungsbedingungen der passiven Schaltkreise mit periodischen Zeitverläufen dargestellt. Die Identifizierungsformeln der Zustandsmatrixen für RL-, RC- und RLC-Zweiklemmenpaare wurden dargelegt. Die volle Synthesemethode der Schaltkreise, die zweimal in einer Periode umgeschaltet werden, wurde bestimmt, wobei die Extraktionsreaktanzelementenmethode verwendet wurde. Aufgrund der Synthesemethode wurden sechs allgemeine N-Klemmenpaartransformatorstrukturen bestimmt. Diese Strukturen ermöglichen die Beschreibung neuer Transistor- und Thyristorschaltungen.

     

1-ports with orthonormal properties

The paper deals with the problem of finding the immittance functions of a 1-port for which, in the case of periodic signals of Ω frequency, the voltage and current are orthogonal to one another, and in which the voltage and current have the same norms, i.e. they are related as a pair of Hilbert transforms. The need for the construction of such 1-ports arises, for example, in connection with the problem of the measurement of the reactive power of nonsinusoidal waves. Three sets of network functions have been found for the networks in which input and output signals are pairs of Hilbert transforms, and it has been proved that one of them is a set of positive-real and reactance functions, and that one is a set of transfer functions of all-pass networks composed of orthonormal 1-ports.     

Sufficient conditions for the unique solvability of linear networks containing memoryless 2-ports

Combinatorial necessary and sufficient conditions for the unique solvability of linear networks containing n-ports are well known for the ‘general’ case. They are only necessary if relations among n-port parameters are also taken into consideration. In the present paper combinatorial sufficient conditions are presented for linear networks containing RLC elements and memoryless 2-ports. The somewhat surprising result is proved that whether a 2-port can cause certain types of singularities can be predicted before the interconnection. A concept, similar to the normal tree (which intersects ideal transformers by one, gyrators by two or no edges) is introduced for arbitrary 2-ports. Its existence implies unique solvability. Relations to previous results and algorithmical aspects are also discussed.     

Optimization of cable terminations

This paper describes a study of various termination constructions for medium voltage cross-linked polyethylene (XLPE) power cables. A special device was used for electrical field measurements around the cable termination which made it possible to monitor how stress relief materials with different permittivity and placement of isolated or grounded embedded electrodes (EE) affected electrical stress grading. The results of measurements for each configuration were examined by mathematical modeling based on the finite element method (FEM). Finally, the selected constructions of cable termination have passed severe test conditions with load cycling     

Transformerless synthesis of transistor and thyristor switching RLC 1-ports

As an extension of the synthesis method developed in a previous paper, the transformerless synthesis of reciprocal switched 1-ports is presented in this paper. the transformerless structures of resistance switching n-ports described by impedance, admittance or hybrid matrices have been proposed. These structures enable the synthesis of dynamical switching RC, RL and RLC 1-ports. Using the state variables method, the realizability conditions and identification formulae for constant and sinusoidal input functions have been derived. Three numerical examples illustrate the developed methods. the present theory can be applied to create new thyristor and transistor arrangements, particularly compensators and auxiliary switching LC circuits facilitating the commutation of thyristors and transistors.     

Ground terminations of lightning protective systems

In a lightning protective system, the ground terminations must be designed to keep within fixed values the step voltage both inside and outside the protected structure and the maximum total voltage. Design criteria shall take into account that the behavior of ground systems is affected by their length, by soil resistivity, by amplitude and wave shapes of lightning currents. In this paper, investigations carried out on ground terminations when subjected to impulse currents are presented and typical phenomena which characterize their behavior are summarized. Theoretical analysis of the transient phenomenon and new experimental results on each electrode are presented. On the basis of maximum step voltage and of the statistical variation of lightning currents, the design of ground terminations is analyzed and curves for their practical sizing are given. Provisions to avoid discharges into the soil between ground conductors and buried cables or pipes are given, together with computation methods to evaluate overvoltage amplitudes between live conductors and ground in shielded cables     

Contamination performance of silicone rubber cable terminations

The authors describe the results of a systematic study of the performance of silicone rubber terminations under contaminated conditions. The terminations evaluated were of the 15 kV class cold shrink type for concentric neutral cables. They were evaluated in a fog chamber where the electric stress, water conductivity, water flow rate, and the deenergization time between subsequent fog chamber exposures were varied in order to alter the test severity. Changes in the surface hydrophobicity were monitored periodically by analyzing the samples using ESCA (electron spectroscopy for chemical analysis), SEM (scanning electron microscopy), and contact angle measuring techniques. The results indicate that the experimental conditions play a significant role in the outcome of the tests. It was demonstrated that the recovery of hydrophobicity can be studied by using several techniques     

一种新颖的PFC无损吸收方法

提出了一种新颖的无损吸收方法。利用Boost PFC输入电感的辅助绕组回路。将续流二极管反向恢复能量进行有效转移。从而使Boost PFC电路的效率明显提高。详细分析了提出电路的6种工作状态和工作时序。分别给出了各个状态的等效电路。实验结果证明,在相同开关频率下效率明显高于传统的PFC电路。功耗降低使电路体积显减小。     

一种新颖的磁耦合式无源无损吸收电路

文中利用磁耦合原理,将变换电路中的电感改为耦合电感,在耦合电感的二次绕组上获得一个受开关管控制的电压源,为开关管创造准谐振软开关条件。为此,提出了一种新颖的磁耦合式无源无损吸收电路,将其应用于Boost电路中,并详细分析了该电路的工作原理。计算机仿真和实验结果表明,采用这种吸收电路后,开关管能够实现零电流开通和零电压关断,减小了关断损耗,提高了电路的总体效率,尤其是在重载情况下,增加吸收电路可以使变换器效率提高8%左右。     

Comparative testing of simple terminations of high-voltage cables

In HV systems, cable terminations are one of the weakest links. The majority of failures occur on the ground shield side. This side is especially stressed by the electric field in free space connections. Field control and rigorous technological processes are key to reliable functioning. The first was realized for a century by stress relief cones in conjunction with solid dielectric fillings. Later, stress-grading nonlinear materials in the form of paint, tapes, and tubes were used with much success (see, e.g., [1]-[3] and their bibliography). In dc applications, which are the main interest of this paper, the falling resistivity-field characteristic effectively pushes the electric field off the shield terminus, where it is strongest.     

Dealing with interface problems in polymer cable terminations

Polymer technology has shown good performance and has certain advantages over ceramic technology in insulators. However, it often comes with a potentially weak point, i.e., the interface between two solid insulators. In The Netherlands, a cascade of 150 kV termination breakdowns occurred several years ago. The present paper gives the results of the research and precautions that were undertaken after those events. The problems started at the interfaces of these components, as will be explained. The investigation and monitoring of terminations is also described     

One numerical method to determine improved cable terminations

In HV and MV systems, cable terminations (CT) are one of the weakest links. The majority of cable failures on distribution system are caused by defects in cable terminations and cable joints. There is a number of CT developed in last few years, but cable failures still happen, causing great economic losses, mainly because of a CT breakdown. For that reason any improvement in the cable termination construction is of interest. Two different approaches have been proposed to evaluate a field distribution. Geometrical control of the electric field, applying multilayer dielectric deflectors with different permittivities, as well as application of the grounded embedded electrodes for strong electric field reduction at the cable ends, is presented in this paper.One numerical method, the equivalent electrodes method (EEM), has been applied for electric field calculation at the modelled cable terminations. The accuracy of results of the EEM depends on the number of used equivalent electrodes (EE). The method is very simple and exact and in limit process with the number of EE gives exact results. Improvement proposed in this paper enables accurate calculation using small number of EE. Some results obtained by the application of the EEM have been compared with values obtained using the finite elements method and a very good matches have been identified.     

Ultra-wide-band PD diagnostics of power cable terminations in service

During the past decade the PD probing in the ultra-high frequency (UHF) range has successfully been proven for on-site PD diagnostics of GIS cable terminations in service. Therefore it was decided to apply this non-conventional method also for condition assessment of the insulation integrity of outdoor cable terminations. In order to evaluate the minimum detectable PD level the paper deals with comparative PD studies using the IEC and the UHF method. Moreover, experimental studies on the attenuation of PD pulses traveling through power cables were performed in order to assess the spatial selectivity of the UHF method applied.     

非最小电压应力无源无损缓冲电路的研究

研究了适用于PWM变换器的非最小电压应力(Non Minimum Voltage Stress,简称NMVS)无源无损缓冲电路.它与有源软开关相比具有结构简单,控制方便的优点.与最小电压应力(Minimum Voltage Stress,简称MVS)的无源无损缓冲电路相比,NMVS无源无损缓冲电路更具有电流应力小,软开关范围更广,效率高等突出优点.     

一种无源无损缓冲电路的工程设计方法

介绍了一种具有较强工程实用价值的无源无损缓冲电路的工作过程,它利用辅助电感和辅助电容在主功率管开关过程中进行谐振,为开关管提供零电流开通(ZCON)和零电压关断(ZVOFF)条件,实现了软开关。详细讨论了这种缓冲电路的工程设计问题,提出一种基于缓冲电路损耗最小的优化设计方法。搭建了一台400V输入、110V/10A输出、开关频率为100kHz的带有该无源无损缓冲电路的Buck变流器样机,以验证无源无损缓冲电路的设计,并给出了实验波形和效率曲线。实验结果表明,缓冲电路有效地降低了开关管的电流和电压应力,抑制了主二极管反向恢复过程,变流器效率提高了约2%。实验中测得变流器的最高效率为95.2%。     

一种适用Boost变换器的无源无损缓冲电路

介绍一种适用于Boost变换器的无源无损缓冲电路,对电路的结构及工作原理进行了分析,并对相关问题进行了讨论。     

无损升压APFC电路研究与设计

有源功率因数校正(APFC)电路作为提高功率因数的有效措施,已成为电力电子装置应用与研究热点。实际应用中大多数APFC电路采用Boost变换电路。此电路结构简单,但开关管在高频工作状态下开关损耗较大。为解决这一问题,给出一种改进型无损软开关电路,该电路无需额外增加开关与控制器件,应用于升压式APFC电路能有效减小高频开关管损耗,提高变换器转换效率。通过2 kW实验样机,验证了该电路的有效性。     

Stress grading materials for cable terminations under fast-rise time pulses

The paper discusses the material properties and designs of stress grading coatings for cable terminations that can help to reduce the adverse effects of stepped voltages present in voltage source converters. Simulations using transient and quasistatic finite element method, as well as experimental measurements of stress grading materials are presented in this study. The use of two stress grading layers in cable terminations is suggested as an alternative design to reduce the hot spot temperature in conductive stress grading coatings.     

基于双次级无损箝位的大功率DC/DC变换器

研究了一种适用于高压大功率场合的新型双次级箝位全桥变换器拓扑,该拓扑通过移相控制实现H桥超前桥臂的零电压开关(ZVS),并通过新型低漏感高频变压器尽量减小滞后臂的损耗及对次级的影响;采用双变压器结合次级无源无损箝位吸收电路的拓扑结构,可以有效限制次级整流电压过冲、降低应力、减少损耗、提高效率并增强可靠性.理论分析和实验结果验证了该拓扑在高压大功率应用场合的优越性.