A cycloconverter (CCV) or a cycloinverter converts a constant amplitude, constant frequency AC

waveform In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electronic ...

to another AC waveform of a lower

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

by synthesizing the output waveform from segments of the AC supply without an intermediate DC link ( and ). There are two main types of CCVs, circulating current type or blocking mode type, most commercial high power products being of the blocking mode type.

Characteristics

Whereas phase-controlled SCR switching devices can be used throughout the range of CCVs, low cost, low-power

TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...

-based CCVs are inherently reserved for resistive load applications. The amplitude and frequency of converters' output voltage are both variable. The output to input frequency ratio of a three-phase CCV must be less than about one-third for circulating current mode CCVs or one-half for blocking mode CCVs.Bose (2006), p. 153 Output waveform quality improves as the ''pulse number'' of switching-device bridges in phase-shifted configuration increases in CCV's input. In general, CCVs can be with 1-phase/1-phase, 3-phase/1-phase and 3-phase/3-phase input/output configurations, most applications however being 3-phase/3-phase.

Applications

The competitive power rating span of standardized CCVs ranges from few megawatts up to many tens of megawatts. CCVs are used for driving

mine hoist In underground mining a hoist or winder is used to raise and lower conveyances within the mine shaft. Modern hoists are normally powered using electric motors, historically with direct current drives utilizing Ward Leonard control machines and l ...

s, rolling mill main motors,

ball mill A ball mill is a type of grinder used to grind or blend materials for use in mineral dressing processes, paints, pyrotechnics, ceramics, and selective laser sintering. It works on the principle of impact and attrition: size reduction is done ...

s for ore processing,

cement kiln Cement kilns are used for the pyroprocessing stage of manufacture of portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of ...

ship propulsion Marine propulsion is the mechanism or system used to generate thrust to move a watercraft through water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electr ...

systems, slip power recovery wound-rotor induction motors (i.e., Scherbius drives) and aircraft 400 Hz power generation.Bose (2006), p. 119 The variable-frequency output of a cycloconverter can be reduced essentially to zero. This means that very large motors can be started on full load at very slow revolutions, and brought gradually up to full speed. This is invaluable with, for example,

s, allowing starting with a full load rather than the alternative of having to start the mill with an empty barrel then progressively load it to full capacity. A fully loaded "hard start" for such equipment would essentially be applying full power to a stalled motor. Variable speed and reversing are essential to processes such as hot-rolling steel mills. Previously, SCR-controlled DC motors were used, needing regular brush/commutator servicing and delivering lower efficiency. Cycloconverter-driven synchronous motors need less maintenance and give greater reliability and efficiency. Single-phase bridge CCVs have also been used extensively in

electric traction A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. Electric railways use either electric locomotives (hauling passengers or freight in separate cars), ele ...

applications to for example produce 25 Hz power in the U.S. and 16 2/3 Hz power in Europe. Whereas phase-controlled converters including CCVs are gradually being replaced by faster PWM self-controlled converters based on IGBT, GTO, IGCT and other switching devices, these older classical converters are still used at the higher end of the power rating range of these applications.

Harmonics

CCV operation creates current and voltage ''

harmonics A harmonic is a wave with a frequency that is a positive integer multiple of the '' fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', ...

'' on the CCV's input and output. AC line harmonics are created on CCV's input accordance to the equation, * , where :* = harmonic frequency imposed on the AC line :* and = integers :* = pulse number (6, 12 . . .) :* = output frequency of the CCV :* Equation's 1st term represents the ''pulse number'' converter harmonic components starting with six-pulse configuration :* Equation's 2nd term denotes the converter's sideband characteristic frequencies including associated interharmonics and subharmonics.

References

; In-line references ; General references * * {{Electric motor Electronic circuits AC-to-AC converters Electric motor control Electric power systems components