AC VOLTAGE CONTROLLER (AC-AC CONVERTER)

Transcription

1 AC LAGE CRLLER (AC-AC CERER) AC volage corollers (ac lie volage corollers) are eployed o vary he RM value of he aleraig volage applied o a load circui by iroducig hyrisors bewee he load ad a cosa volage ac source. he RM value of aleraig volage applied o a load circui is corolled by corollig he riggerig agle of he hyrisors i he ac volage coroller circuis. brief, a ac volage coroller is a ype of hyrisor power coverer which is used o cover a fixed volage, fixed frequecy ac ipu supply o obai a variable volage ac oupu. he RM value of he ac oupu volage ad he ac power flow o he load is corolled by varyig (adjusig) he rigger agle α (RM) AC pu o la g e f s s f s AC o la g e Coroller a ria b le AC RM /P olage f here are wo differe ypes of hyrisor corol used i pracice o corol he ac power flow -ff corol Phase corol hese are he wo ac oupu volage corol echiques. -ff corol echique hyrisors are used as swiches o coec he load circui o he ac supply (source) for a few cycles of he ipu ac supply ad he o discoec i for few ipu cycles. he hyrisors hus ac as a high speed coacor (or high speed ac swich). PHAE CRL phase corol he hyrisors are used as swiches o coec he load circui o he ipu ac supply, for a par of every ipu cycle. ha is he ac supply volage is chopped usig hyrisors durig a par of each ipu cycle. he hyrisor swich is ured o for a par of every half cycle, so ha ipu supply volage appears across he load ad he ured off durig he reaiig par of ipu half cycle o discoec he ac supply fro he load. By corollig he phase agle or he rigger agle α (delay agle), he oupu RM volage across he load ca be corolled. he rigger delay agle α is defied as he phase agle (he value of ω) a which he hyrisor urs o ad he load curre begis o flow. hyrisor ac volage corollers use ac lie couaio or ac phase couaio. hyrisors i ac volage corollers are lie couaed (phase couaed) sice he ipu supply is ac. Whe he ipu ac volage reverses ad becoes egaive durig he egaive half cycle he curre flowig hrough he coducig hyrisor decreases ad

2 falls o zero. hus he hyrisor aurally urs off, whe he device curre falls o zero. Phase corol hyrisors which are relaively iexpesive, coverer grade hyrisors which are slower ha fas swichig iverer grade hyrisors are orally used. For applicaios upo 4Hz, if riacs are available o ee he volage ad curre raigs of a paricular applicaio, riacs are ore cooly used. Due o ac lie couaio or aural couaio, here is o eed of exra couaio circuiry or copoes ad he circuis for ac volage corollers are very siple. Due o he aure of he oupu wavefors, he aalysis, derivaios of expressios for perforace paraeers are o siple, especially for he phase corolled ac volage corollers wih RL load. Bu however os of he pracical loads are of he RL ype ad hece RL load should be cosidered i he aalysis ad desig of ac volage coroller circuis. YPE F AC LAGE CRLLER he ac volage corollers are classified io wo ypes based o he ype of ipu ac supply applied o he circui. igle Phase AC Corollers. hree Phase AC Corollers. igle phase ac corollers operae wih sigle phase ac supply volage of 3 RM a 5Hz i our coury. hree phase ac corollers operae wih 3 phase ac supply of 4 RM a 5Hz supply frequecy. Each ype of coroller ay be sub divided io Ui-direcioal or half wave ac coroller. Bi-direcioal or full wave ac coroller. brief differe ypes of ac volage corollers are igle phase half wave ac volage coroller (ui-direcioal coroller). igle phase full wave ac volage coroller (bi-direcioal coroller). hree phase half wave ac volage coroller (ui-direcioal coroller). hree phase full wave ac volage coroller (bi-direcioal coroller). APPLCA F AC LAGE CRLLER Lighig / lluiaio corol i ac power circuis. ducio heaig. dusrial heaig & Doesic heaig. rasforer ap chagig (o load rasforer ap chagig). peed corol of iducio oors (sigle phase ad poly phase ac iducio oor corol). AC age corols. PRNCPLE F -FF CRL ECHNQUE (NEGRAL CYCLE CRL) he basic priciple of o-off corol echique is explaied wih referece o a sigle phase full wave ac volage coroller circui show below. he hyrisor swiches ad are ured o by applyig appropriae gae rigger pulses o coec he ipu ac supply o he load for uber of ipu cycles durig he ie ierval. he

3 hyrisor swiches ad are ured off by blocig he gae rigger pulses for uber of ipu cycles durig he ie ierval FF usually cosiss of a iegral uber of ipu cycles.. he ac coroller ie R R L Load Resisace Fig.: igle phase full wave AC volage coroller circui s w o i o w i g Gae pulse of w i g Gae pulse of w Fig.: Wavefors Exaple Referrig o he wavefors of -FF corol echique i he above diagra, wo ipu cycles. hyrisors are ured durig for wo ipu cycles. 3

4 e ipu cycle. hyrisors are ured FF durig FF for oe ipu cycle Fig.: Power Facor hyrisors are ured precisely a he zero volage crossigs of he ipu supply. he hyrisor is ured o a he begiig of each posiive half cycle by applyig he gae rigger pulses o as show, durig he ie. he load curre flows i he posiive direcio, which is he dowward direcio as show i he circui diagra whe coducs. he hyrisor is ured o a he begiig of each egaive half cycle, by applyig gaig sigal o he gae of, durig. he load curre flows i he reverse direcio, which is he upward direcio whe coducs. hus we obai a bi-direcioal load curre flow (aleraig load curre flow) i a ac volage coroller circui, by riggerig he hyrisors aleraely. his ype of corol is used i applicaios which have high echaical ieria ad high heral ie cosa (dusrial heaig ad speed corol of ac oors). Due o zero volage ad zero curre swichig of hyrisors, he haroics geeraed by swichig acios are reduced. For a sie wave ipu supply volage, v siω siω s RM value of ipu ac supply RM phase supply volage. f he ipu ac supply is coeced o load for uber of ipu cycles ad discoeced for uber of ipu cycles, he, FF Where ipu cycle ie (ie period) ad f f ipu supply frequecy. coroller o ie. coroller off ie. FF upu ie period ( ) ( ) + +. FF 4

5 We ca show ha, upu RM volage ( RM ) i ( RM ) Where irm is he RM ipu supply volage. DERE AN EXPRE FR HE RM ALUE F UPU LAGE, FR -FF CRL MEHD. upu RM volage i ωd. ( ω) RM ω ω ω ω i d RM ω ω. ( ω ) ubsiuig for Cosθ i θ ω Cos ω d RM ω ( ω ) ω ω. RM d ω Cos ωd( ω) ω ω ω iω ( ω) RM ω si ω si ω ( ω ) RM Now A iegral uber of ipu cycles; Hece,,3, 4,5,... & ω, 4,6,8,,... Where is he ipu supply ie period ( ipu cycle ie period). hus we oe ha si ω RM ω ω 5

6 RM i( RM ) Where irm RM value of ipu supply volage; FF ( + ) RM duy cycle (d). PERFRMANCE PARAMEER F AC LAGE CRLLER RM upu (Load) olage si. RM ωd( ω) ( + ) RM i( RM ) ( + ) irm RM Where irm RM value of ipu supply volage. Duy Cycle + + FF Where, ( + ) duy cycle (d). RM Load Curre RM upu AC (Load) Power RM RM Z R ; for a resisive load Z R. L P RL RM L 6

7 pu Power Facor P oupu load power P PF A ipu supply vol aperes RM PF R L irm irm ; i( RM ) RM ipu supply curre. he ipu supply curre is sae as he load curre i L Hece, RM supply curre RM load curre; i RM ( RM ). RL RM RM irm PF i( RM ) i( RM ) i( RM ) i( RM ) PF + he Average Curre of hyrisor ( Avg) i Wavefor of hyrisor Curre 3 ω si ωd. + ( ) si ωd. + ( ) ( ω ) cosω + ( ) + ( ω ) [ cos + cos ] 7

8 ( ) + ( + ) + [ ]. ( + ) duy cycle ( + ) ( + ) FF. ( + ), Where axiu or pea hyrisor curre. RL RM Curre of hyrisor ( RM) si ω. ( ω ) d ( + ) si. ωd( ω) ( + ) ( cosω ) d( ω) ( + ) ( RM) d d 4 ( + ) 4 ( ) ( ω ) cos ω. ( ω ) si ω ( ω) + ( ) si si ( ) 4 + 8

9 { } ( + ) 4( + ) ( + ) PRBLEM. A sigle phase full wave ac volage coroller worig o -FF corol echique has supply volage of 3, RM 5Hz, load 5Ω. he coroller is for 3 cycles ad off for 4 cycles. Calculae & FF ie iervals. RM oupu volage. pu P.F. Average ad RM hyrisor curres. ELAMA BELAJAR 9