In the simplest sense, frequency changer or frequency converter is a device which can change the frequency of an alternating current. It could be changing the frequency of the mains supply to match another grid like changing from a 50 Hz to 60 Hz which is used in another region. Another application is changing the frequency for use in aircraft electrical system for which the standard frequency is 400 Hz. So airports, aircraft hangars and ships need 400 Hz frequency converters. Higher frequency would mean lighter cables and transformers in the aircrafts, compared to standard 50 Hz power supply. Reducing weight of components is an important consideration in the design of aircrafts, as expected. In radio communications, frequency conversion is an important part of superheterodyne receivers. Another situation in which frequency conversion is used is in satellite communications. Satellites typically receive signals in the uplink frequency band and convert them to signals in another band and transmit them down to Earth stations in the downlink frequency band. Still another important application is in the variable frequency drive used for controlling speed of alternating current motors and compressors of devices like air conditioner and refrigerators. Similar frequency conversion is also occurring in the commonly used switch mode power supplies as well. In them, usual 50 or 60 Hz alternating current mains supply is rectified into direct current and then run oscillators or switching circuits which generate high frequency alternating current.
