Stringent power supply quality standards have been introduced which limit harmonic distortion in power systems. It is general practice to eliminate the harmonics and to design switch mode power converters in such a way as to draw a pure sinewave current from the supply installation with power factor close to one. The most typical way to meet this requirement is to design a converter with two conversion stages for wave shaping of the input current and generation of a smooth DC voltage. An AC/DC power converter where both functions are performed by means of a single switching power transistor and a single magnetic component, reducing the complexity of the circuit and saving the cost of components and space, is presented. A simpler circuit also enhances the reliability of the device. Voltage and current relationships in the converter connection are analyzed. The advantages and disadvantages of the connection are given. >

AC/DC converter with sinusoidal input current and a single conversion stage

Technical advances are of no real relevance to a user, if they cannot offer benefits which can be measured in terms of money. The countable measures are such as improvements in equipment and system reliability, in efficiency resulting in lower internal temperature, in weight and need of space as well as in lower price. However, quite often the benefits are just marginal from the users' viewpoint. The reason is the overutilization of the obtained benefits and this can, for instance, be realized in lower reliability performance, higher price, etc. The main source of uncertainty is always public power i.e. the energy flow is not perfectly continuous. It is normally the level of voltage in public power lines which determines whether the energy is available (i.e. usable) or not. The number of outages and brownouts can be substantially reduced by means of a rectifier system which has a proper amount of filtering capacity and an adaptive (i.e. load power depending) undervoltage shut down feature. There are also other topics mainly related to system reliability from the rectifier viewpoint such as output overvoltage shut down, testing of batteries by discharging, rectifier failure detection, etc. which are discussed and solutions proposed. >

Novel ways to improve rectifier performance from power systems' reliability viewpoint

Low-pass passive filters used in power converters attenuate low frequency ripple in a very inefficient way. The purpose of this paper is to show how small power active filters can effectively suppress low frequency ripple levels in large power systems. Switchmode power converters with high switching frequency and high gain voltage feedback control have been used as active filters. Three different devices are described - a dc/dc, ac/dc and dc/ac converter. In all three cases an impressive reduction of low frequency ripple level has been achieved.

Active Filter Technique for the Attenuation of AC Ripple in DC Power Plants and Distribution

Optimal uncertainty management schemes are defined and an implementation is described. These facilities have been in trial use for a year in three power supply systems. The optimal schemes stipulate that the onsite supervision facilities take care of brute uncertainty management work. The dynamic intelligence of power system expert(s) is used to verify the most probable explanations sent by the onsite facilities. The process is most effective if the upper level or service terminal software supports the human way of reasoning. >

http://ieeexplore.ieee.org/iel2/678/6696/00268432.pdf

Maintenance management by utilizing dynamic intelligence-implementations and experiences

Today's trends of development in the telecommunication industry and consequently in energy systems applications show a decreased technical lifetime of products. Not long ago, 20 years useful/market lifetime was a realistic approach. Nowadays, this is being reduced drastically due to the rapid development of new, better and more cost-effective components and technologies. These improvements imply much more frequent product changes which in normal cases lead to more maintenance costs from a customer perspective. In order to introduce a new generation of products which take advantage of newer technologies, components and result in less maintenance costs for the customer, it is absolutely necessary to take into consideration the backwards compatibility issues.

Backwards compatibility, for safe future [telecom. energy systems]

A switch-mode rectifier designed with a built-in microprocessor has been developed. This rectifier is custom-made to fit into a power plant that is controlled and supervised by a computer system. It operates with high efficiency, no audible noise, high power factor, sinusoidal input current, and low electrical noise. The microprocessor can also be used to facilitate production testing of the rectifier as well as power plant testing and operation. The rectifier ratings are an input of 208-204 V single-phase, a power factor of 0.99 at full load, and an output of 48 V (adjustable 40-57 V), 28 A. >

http://ieeexplore.ieee.org/iel2/769/892/00022387.pdf

A rectifier with an internal microprocessor, that is an essential part of a very flexible, computer controlled power system

Booster DC to DC converters operating with 20 kHz conversion frequency perform rapid regulation that make them very well suited to use as active filters for attenuation of low frequency noise. Booster converters with such filtering qualities are beeing used in a new series of 48 V DC power plants. The noise on the output is kept well below the limits that are specified in the CCITT-recommendations.

F. Ekelund

Papers

A rectifier with an internal microprocessor, that is an essential part of a very flexible, computer controlled power system

Attenuation of Noise using Booster Converters as Active Filters

Backwards compatibility, for safe future [telecom. energy systems]