Frequency changer

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The Sakuma frequency converter station is one of the stations that links Japan's two grids (see Electricity sector in Japan SS Transmission). 20040905 jpower sakuma 02.jpg
The Sakuma frequency converter station is one of the stations that links Japan's two grids (see Electricity sector in Japan § Transmission).

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.

Contents

Traditionally, these devices were electromechanical machines called a motor-generator set. [1] 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 may also provide galvanic isolation between the input and output AC circuits. A battery may also be added to the DC circuitry to improve the converter's ride-through of brief outages in the input power.

Frequency changers vary in power-handling capability from a few watts to megawatts.

Applications

Frequency changers are used for converting bulk AC power from one frequency to another, when two adjacent power grids operate at different utility frequency.

A variable-frequency drive (VFD) is a type of frequency changer used for speed control of AC motors such as used for pumps and fans. The speed of a Synchronous AC motor is dependent on the frequency of the AC power supply, so changing frequency allows the motor speed to be changed. This allows fan or pump output to be varied to match process conditions, which can provide energy savings.

A cycloconverter is also a type of frequency changer. Unlike a VFD, which is an indirect frequency changer since it uses an AC-DC stage and then a DC-AC stage, a cycloconverter is a direct frequency changer because it uses no intermediate stages.

Another application is in the aerospace and airline industries. Often airplanes use 400 Hz power so a 50 Hz or 60 Hz to 400 Hz frequency converter is needed for use in the ground power unit used to power the airplane while it is on the ground. Airlines might also utilize the converters to provide in-air wall current to passengers for use with laptops and the like. Radio and combat systems equipment on Navy warships is often also powered by 400 Hz to reduce noise on the DC signal after rectification.

In renewable energy systems, frequency converters are an essential component of doubly fed induction generators (DFIGs) as used in modern multi-megawatt class wind turbines. [2]

An HVDC-system can serve as frequency converter for large loads.

Alternate uses

Frequency converter may also refer to a much-lower-powered circuit that converts radio frequency signals at one frequency to another frequency, especially in a superheterodyne receiver. See srequency mixer. The circuit usually consists of a local oscillator and frequency mixer (analog multiplier) that generates sum and difference frequencies from the input and local oscillator, of which one (the Intermediate frequency) will be required for further amplification, while the others are filtered out. The same result was achieved historically by the pentagrid converter or a triode and hexode in a single tube, but can be implemented in transistor radios economically by a single transistor functioning as a self-oscillating mixer.

See also

Related Research Articles

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A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation is performed by an inverter.

<span class="mw-page-title-main">Power supply</span> Electronic device that converts or regulates electric energy and supplies it to a load

A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power. Examples of the latter include power supplies found in desktop computers and consumer electronics devices. Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault, power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction, and storing energy so it can continue to power the load in the event of a temporary interruption in the source power.

<span class="mw-page-title-main">Power inverter</span> Device that changes direct current (DC) to alternating current (AC)

A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of rectifiers which were originally large electromechanical devices converting AC to DC.

<span class="mw-page-title-main">Switched-mode power supply</span> Power supply with switching regulator

A switched-mode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently.

In all fields of electrical engineering, power conversion is the process of converting electric energy from one form to another. A power converter is an electrical or electro-mechanical device for converting electrical energy. A power converter can convert alternating current (AC) into direct current (DC) and vice versa; change the voltage or frequency of the current or do some combination of these. The power converter can be as simple as a transformer or it can be a far more complex system, such as resonant converter. The term can also refer to a class of electrical machinery that is used to convert one frequency of alternating current into another. Power conversion systems often incorporate redundancy and voltage regulation.

A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low to very high.

<span class="mw-page-title-main">Voltage regulator</span> System designed to maintain a constant voltage

A voltage regulator is a system designed to automatically maintain a constant voltage. A voltage regulator may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.

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<span class="mw-page-title-main">Motor–generator</span> Device for converting electrical power to another form

A motor–generator is a device for converting electrical power to another form. Motor–generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line. Large motor–generators were widely used to convert industrial amounts of power while smaller motor–generators were used to convert battery power to higher DC voltages.

<span class="mw-page-title-main">Variable-frequency drive</span> Type of adjustable-speed drive

A variable-frequency drive, variable-speed drives, AC drives, micro drives, inverter drives, or drives) is a type of AC motor drive that controls speed and torque by varying the frequency of the input electricity. Depending on its topology, it controls the associated voltage or current variation.

A H-bridge is an electronic circuit that switches the polarity of a voltage applied to a load. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backwards. The name is derived from its common schematic diagram representation, with four switching elements configured as the branches of a letter "H" and the load connected as the cross-bar.

<span class="mw-page-title-main">Rotary phase converter</span> Electrical machine

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<span class="mw-page-title-main">Phase converter</span>

A phase converter is a device that converts electric power provided as single phase to multiple phase or vice versa. The majority of phase converters are used to produce three-phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service. Phase converters are used where three-phase service is not available from the utility provider or is too costly to install. A utility provider will generally charge a higher fee for a three-phase service because of the extra equipment, including transformers, metering, and distribution wire required to complete a functional installation.

A voltage converter is an electric power converter which changes the voltage of an electrical power source. It may be combined with other components to create a power supply.

An induction heater is a key piece of equipment used in all forms of induction heating. Typically an induction heater operates at either medium frequency (MF) or radio frequency (RF) ranges.

Doubly-fed electric machines also slip-ring generators are electric motors or electric generators, where both the field magnet windings and armature windings are separately connected to equipment outside the machine.

A Royer oscillator is an electronic relaxation oscillator that employs a saturable-core transformer in the main power path. It was invented and patented in April 1954 by Richard L. Bright & George H. Royer, who are listed as co-inventors on the patent. It has the advantages of simplicity, low component count, rectangle waveforms, and transformer isolation. As well as being an inverter, it can be used as a galvanically-isolated DC-DC converter when the transformer output winding is connected to a suitable rectifying stage, in which case the resulting apparatus is usually called a "Royer Converter".

The Sparse Matrix Converter is an AC/AC converter which offers a reduced number of components, a low-complexity modulation scheme, and low realization effort. Invented in 2001 by Prof Johann W. Kolar , sparse matrix converters avoid the multi step commutation procedure of the conventional matrix converter, improving system reliability in industrial operations. Its principal application is in highly compact integrated AC drives.

A solid-state AC-to-AC converter converts an AC waveform to another AC waveform, where the output voltage and frequency can be set arbitrarily.

The following outline is provided as an overview of and topical guide to electronics:

References

  1. Blalock, Thomas J., " The Frequency Changer Era: Interconnecting Systems of Varying Cycles Archived 2007-06-07 at the Wayback Machine ". The history of various frequencies and interconversion schemes in the US at the beginning of the 20th century.
  2. Renewable Energy World (May 2008), " Excited About Power Quality "