A
frequency changer or
frequency converter is an
electronicElectronics is a branch of science and technology that deals with the controlled flow of electrons. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation,...
device that converts
alternating currentIn alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
(
ACIn alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
) of one
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
to
alternating currentIn alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
of another frequency. The device may also change the
voltageVoltage is commonly used as a short name for electrical potential difference. Its corresponding SI unit is the volt...
, but if it does, that is incidental to its principal purpose.
Traditionally, these devices were electromechanical machines called a
motor-generatorA motor-generator is a device for converting electrical power to another form. In some contexts, the other form is mechanical energy; in other contexts, it is a different form of electricity. The two senses refer to different types of equipment.The Motor-generator set is used to convert...
set. Also devices with mercury arc rectifiers or vacuum tubes were in use.
A
frequency changer or
frequency converter is an
electronicElectronics is a branch of science and technology that deals with the controlled flow of electrons. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation,...
device that converts
alternating currentIn alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
(
ACIn alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
) of one
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
to
alternating currentIn alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again...
of another frequency. The device may also change the
voltageVoltage is commonly used as a short name for electrical potential difference. Its corresponding SI unit is the volt...
, but if it does, that is incidental to its principal purpose.
Traditionally, these devices were electromechanical machines called a
motor-generatorA motor-generator is a device for converting electrical power to another form. In some contexts, the other form is mechanical energy; in other contexts, it is a different form of electricity. The two senses refer to different types of equipment.The Motor-generator set is used to convert...
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 economically. These devices usually consist of a
rectifierA rectifier is an electrical device that converts alternating current to direct current , a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals...
stage (producing
direct currentDirect current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
) which is then inverted to produce AC of the desired frequency. The
inverterAn inverter is an electrical device that converts direct current to alternating current ; the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
may use
thyristorThe thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased .Some sources define silicon controlled...
s, IGCTs or IGBTs. If voltage conversion is desired, a
transformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field...
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
batteryAn electrical battery is a combination of one or more electrochemical cells, used to convert stored chemical energy into electrical energy. Since the invention of the first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial...
may also be added to the dc circuitry to improve the converter's
ride-throughIn electricity supply and generation,low voltage ride through , or ride through faults, is what an electric device, especially wind generator, may be required to be capable of when the voltage in the grid is temporarily reduced due to a fault or load change in the grid. The voltage may be reduced...
of brief outages in the input power.
Frequency changers vary in
power-handlingIn physics, power is the rate at which work is performed or energy is converted. It is an energy per unit of time. As a rate of change of work done or the energy of a subsystem, power iswhere P is power, W is work and t is time....
capability from a few
wattThe watt is a derived unit of power in the International System of Units . It measures rate of energy conversion. One watt is equivalent to 1 joule of energy per second....
s to megawatts.
Applications
Aside from the obvious application of converting bulk amounts of power from one
distribution standardThe line frequency or mains frequency is the frequency at which alternating current is transmitted from a power plant to the end user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz...
to another, frequency changers are also used to control the speed and the torque of AC
motorsAn electric motor uses electrical energy to produce mechanical energy, usually through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. Traction motors used on...
. In this application, the most typical frequency converter topology is the three-phase two-level voltage source inverter. The phase voltages are controlled using the power semiconductor switches and pulse width modulation (PWM).
SemiconductorA semiconductor is a material that has an electrical resistivity between that of a conductor and an insulator, that is, generally in the range 10
3 Siemens/cm to 10
−8 S/cm. Devices made from semiconductor materials are the foundation of modern electronics, including radio,...
switching devices and anti-parallel connected freewheeling
diodeIn electronics a diode is a two-terminal electronic component which conducts electric current asymmetrically or unidirectionally; that is, it conducts current more easily in one direction than in the opposite direction. The term usually refers to a semiconductor diode, the most common type today,...
s form a bridge, which can connect each motor phase to the positive or negative dc-link potential. The PWM changes the connections of the phases between the positive and the negative dc-link potentials so that the fundamental wave voltage has the desired frequency and amplitude. The motor reacts primarily to the fundamental voltage and filters out the effects of the harmonic voltages.
Another application is in the
aerospaceAerospace comprises the atmosphere of Earth and surrounding space. Typically the term is used to refer to the industry that researches, designs, manufactures, operates, and maintains vehicles moving through air and space...
and airline industries. Often airplanes use 400 Hz power so 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.
In
Renewable EnergyRenewable energy is energy generated from natural resources—such as sunlight, wind, rain, tides, and geothermal heat—which are renewable . In 2006, about 18% of global final energy consumption came from renewables, with 13% coming from traditional biomass, such as wood-burning...
, frequency converters are an essential component of doubly fed induction generators (
DFIGsDoubly-fed electric machines belong to a category of electric machines that incorporate two multiphase winding sets of similar power rating that have independent means of excitation...
) as used in modern multi-megawatt class wind turbines .
Frequency changers are typically used to control the speed of pumps and fans. In many applications significant energy savings are achieved. The most demanding application areas are found on the industrial processing lines, where the control accuracy requirements can be very high.
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 frequencyRadio frequency is a frequency, or rate of oscillation, of electromagnetic radiation within the range of about 3 Hz to 300 GHz. This range corresponds to the frequency of alternating current electrical signals used to produce and detect radio waves...
signals at one
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
to another
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
. The circuit usually consists of a
local oscillatorIn electronics, the superheterodyne receiver is a receiver which uses the principle of frequency mixing or heterodyning to convert the received signal to a lower "intermediate" frequency, that can be more conveniently processed than the original radio carrier frequency...
and
frequency mixerIn telecommunications, a mixer is a nonlinear or time-varying circuit or device that accepts as its input two different frequencies and presents at its output a mixture of signals at several frequencies:# the sum of the frequencies of the input signals...
. The same result was achieved historically by the
pentagrid converterThe pentagrid converter was a radio receiving valve with five grids used as the frequency mixer stage of a superheterodyne radio receiver....
.
See also
- Cascade converter
A Cascade Converter is a type of motor-generator which was patented in 1902 by J. L. la Cour and O. S. Bragstad.It consists of an induction motor driving a dynamo through a shaft...
- Motor-generator
A motor-generator is a device for converting electrical power to another form. In some contexts, the other form is mechanical energy; in other contexts, it is a different form of electricity. The two senses refer to different types of equipment.The Motor-generator set is used to convert...
- Static inverter plant
A static inverter station is the terminal equipment for a high voltage direct current transmission line, in which direct current is converted to three-phase alternating current, and, usually, the reverse...
- Variable-frequency drive
- HVDC