Frequency changer | EPFL Graph Search

A frequency changer or frequency converter is an electronic or electromechanical device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose, since voltage conversion of alternating current is much easier to achieve than frequency conversion. Traditionally, these devices were electromechanical machines called a motor-generator set. Also devices with mercury arc rectifiers or vacuum tubes were in use. With the advent of solid state electronics, it has become possible to build completely electronic frequency changers. These devices usually consist of a rectifier stage (producing direct current) which is then inverted to produce AC of the desired frequency. The inverter may use thyristors, IGCTs or IGBTs. If voltage conversion is desired, a transformer will usually be included in either the AC input or output circuitry and this transformer

Contribution to the active generator principle for high power electric supply

Massimiliano Visintin

In recent years the use of solid state frequency converters is rapidly increasing in the industrial and power plants where electric machines are installed, since it allows variable speed operations for the electric system, thus becoming a key factor which is capable of increasing the overall efficiency, as well as the global plant flexibility. The benefits that can be reached when electric motors are under investigation can be so enticing, in particular from the perspective of the operating machine coupled to the motor, that drawbacks take a back seat and can be overcome. On the contrary, power electronic for variable speed is generally not used in power generation, since the gains brought out by the present technology are not sufficient to attract anyone's interest. There are some exceptions in the wind- and the hydro power plant businesses, where there are some cases of variable speed already introduced. However in the former applications the output power is limited to some MW, while in the latter the converter is sized only to a fraction of the whole generating power, since it feeds the machine's rotor.This dissertation investigates on a possible electronic converter for power generation in the 40 MW range and above, which is also attracting from both the cost's and the efficiency's point of view, as well as from the operation reliability perspective and thus may be proposed as a breakthrough in this field. Among the possible frequency converters, those ones have been selected which perform natural commutations only, i.e. those that employ thyristors as the semiconductor devices, since the efficiency, the robustness and the relatively high performances are actually the key success factors to be addressed from the beginning. Well known matrix converter topologies will be referred to, as well as new matrix converter arrangements will be brought out and analyzed: their behaviours will be targeted by the dissertation, in particular when different strategies are adopted for controlling the operations. Specifically comparisons will be carried out when the same converter topology is used, but driven by either the well-known cycloconverter strategy or the newly brought out "active generator" one. In addition several generator winding arrangements will be proposed and analyzed, with the aim of increasing the actual feasibility of the proposed solution. Finally some test results on a sized down experimental rig will be analyzed and compared to the simulation outcomes.

EPFL2006

A Rapid DC Component Elimination Strategy for Alternative Current in Frequency Converter

Aziza Benaboud, Alfred Rufer

The principle achievement of this contribution is to develop and to describe a rapid DC component elimination strategy for AC currents in the frequency converter, simply by selecting transient period. To avoid DC component on the line current, it’s known that the transition of active and/or reactive power should not be rapid. If the transition time is relatively long compared to the fundamental period, the current may be considered as symmetrical and the DC component can be neglected. In comparison to the usually slow transient that characterizes a DC component free current transient; in this paper much faster transient also without DC component is achieved, simply by choosing a well-defined transition period. The present method is verified for a simple linear circuit. It can also be used, for example, with a three or more level inverter including, but not limited to, a Neutral Point Clamped. Simulation and verification results for different operating points and transitions between them highlight the capabilities of the proposed control strategy. These include the ability to operate with unity power factor and better current quality without continuous component.

2015

A front-end ASIC for ionising radiation monitoring with femto-amp capabilities

François Krummenacher, Daniel Perrin, Evgenia Voulgari

An ultra-low leakage current Application Specific Integrated Circuit (ASIC) called Utopia (Ultralow Picoammeter) has been designed and fabricated in AMS 0.35 mu m CMOS, in order to be used as the front-end for ionising radiation monitoring at CERN. It is based on the topology of a Current to Frequency Converter (CFC) through charge balancing and demonstrates a wide dynamic range of 8.5 decades without range changing. Due to a design aimed at minimising input leakage currents, input currents as low as 10 fA can be measured.

Iop Publishing Ltd2016

Contribution to the active generator principle for high power electric supply

Massimiliano Visintin

EPFL2006