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THREE-PHASE TO SINGLE-PHASE CYCLOCONVERTER

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-A three-phase to single phasecycloconverter is a type of cycloconverterthat converts a three-phase voltage system(AC Supply) to a single-phase system (ACsupply).

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-Has a constant input frequency and a

variable output frequency.

- It is a step do n cycloconverter thereforethe output frequency is less than the inputfrequency voltage. (f o ! f i)

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2 Types of Three phase toSing e Phase

Cy! o!on"erter

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2 Types of Three phase to Sing e PhaseCy! o!on"erter

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- "hree-#hase to Single-#hase Cycloconverter can bea half ave or full- ave (bridge). $i%e the singlephase to single phase& a recti'ed voltage is alsoapplied to the load terminals by each group ofthyristors.

- uring positive half cycle of the input& conduction of

the positive group thyristors is controlled and duringnegative half-cycle& conduction of negative group ofthyristors is controlled in order to produce an outputvoltage at desired frequency.

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- "herefore& the cyclo-converter can operate in fourquadrants& i.e.& recti'cation modes of ( *& i) and (-*& -i) and inversion modes of ( *& -i) and (-*& i).

- In a bridge type of cyclo-converter& both positiveand negative converters can generate voltages at

either polarity& but negative converter only suppliesnegative current hile positive converter supplypositive current.

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"he above 'gure sho s the conversion of threephase supply at one frequency to single phasesupply of lo er frequency. In this& the 'ring angleto a positive group of thyristors is variedprogressively to produce single phase outputvoltage.

At point +& the 'ring angle is , degrees and it isreduced till point S here it is ero. Again from point " to

/& the delay angle is progressively increased.

"his varied triggering signals to the thyristors& varies itsconduction time periods and hence the frequency of theoutput voltage.

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"he polarity of the current determines if the positive ornegative converter should be supplying po er to the load.Conventionally& the 'ring angle for the positive converteris named a#& and that of the negative converter is nameda0.

- 1hen the polarity of the current changes& the converterpreviously supplying the current is disabled and theother one is enabled.

- "he load al ays requires the fundamental voltage to becontinuous. "herefore& during the current polarityreversal& the average voltage supplied by both of theconverters should be equal.

- 2ther ise& s itching from one converter to the otherone ould cause an undesirable voltage 3ump. "oprevent this problem& the converters are forced toproduce the same average voltage at all times.