Frequency changer

A frequency changer or frequency converter is electronic or electromechanical equipment that converts alternating current (AC) of one frequency to alternating current of another frequency. The equipment 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 were electromechanical machines called a motor-generator set. There were also mercury arc rectifiers or vacuum tubes in use. With the advent of solid state electronics, it has become possible to build completely electronic frequency changers. These 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.

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