Frequency changer
Encyclopedia
A frequency changer or frequency converter is an electronic
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.
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 thyristor
s, 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 watt
s to megawatts.
to another, frequency changers are also used to control the speed and the torque of AC motors
. 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). Semiconductor
switching devices and anti-parallel connected freewheeling diode
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 frequency and filters out the effects of harmonic frequencies.
Another application is in the aerospace
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. Airlines might also utilize the converters to provide in-air wall current to passengers for use with laptops and the like.
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 .
Frequency changers are typically used to control the speed of motors, primarily 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. This is particularly true in the nuclear power and weapons industry, where these devices regulate the operation of refinement centrifuges. The recently disclosed STUXNET worm targets specific Siemens brand frequency converters, causing erratic operation of Iran's centrifuge plant.
An HVDC-system can serve as frequency converter for large loads.
signals at one frequency
to another frequency
. The circuit usually consists of a local oscillator
and frequency mixer
. The same result was achieved historically by the pentagrid converter
.
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
device that converts alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
(AC
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
) of one frequency
Frequency
Frequency 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 current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
of another frequency. The device may also change the voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
, but if it does, that is incidental to its principal purpose.
Traditionally, these devices were electromechanical machines called a motor-generator
Motor-generator
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...
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
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
stage (producing direct current
Direct current
Direct current is the unidirectional 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 flow through...
) which is then inverted to produce AC of the desired frequency. The inverter
Inverter (electrical)
An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
may use thyristor
Thyristor
A 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 trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...
s, IGCTs or IGBTs. If voltage conversion is desired, a transformer
Transformer
A 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 battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
may also be added to the dc circuitry to improve the converter's ride-through
Low voltage ride through
In electricity supply and generation,low voltage ride through , or fault ride through , 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-handling
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
capability from a few watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s to megawatts.
Applications
Aside from the obvious application of converting bulk amounts of power from one distribution standardUtility frequency
The utility frequency, 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 motors
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
. 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). Semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
switching devices and anti-parallel connected freewheeling diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
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 frequency and filters out the effects of harmonic frequencies.
Another application is in the aerospace
Aerospace
Aerospace 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. Airlines might also utilize the converters to provide in-air wall current to passengers for use with laptops and the like.
In renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...
systems, frequency converters are an essential component of doubly fed induction generators (DFIGs
Doubly-fed electric machine
Doubly fed electric machines are electric motors or electric generators that have windings on both stationary and rotating parts, where both windings transfer significant power between shaft and electrical system...
) as used in modern multi-megawatt class wind turbines .
Frequency changers are typically used to control the speed of motors, primarily 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. This is particularly true in the nuclear power and weapons industry, where these devices regulate the operation of refinement centrifuges. The recently disclosed STUXNET worm targets specific Siemens brand frequency converters, causing erratic operation of Iran's centrifuge plant.
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
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
signals at one frequency
Frequency
Frequency 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 frequency
Frequency
Frequency 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 oscillator
Superheterodyne receiver
In electronics, a superheterodyne receiver uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency...
and frequency mixer
Frequency mixer
In electronics a mixer or frequency mixer is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. In its most common application, two signals at frequencies f1 and f2 are applied to a mixer, and it produces new signals at the sum f1 + f2 and difference f1 -...
. The same result was achieved historically by the pentagrid converter
Pentagrid converter
The pentagrid converter is a radio receiving valve with five grids used as the frequency mixer stage of a superheterodyne radio receiver....
.
See also
- Cascade converterCascade converterA 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-generatorMotor-generatorA 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...
- Static inverter plantStatic inverter plantA static inverter station, also known as an HVDC Converter 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