Silicon Conrolled Recifiers UNIT-1
Silicon Conrolled Recifier A Silicon Conrolled Recifier (or Semiconducor Conrolled Recifier) is a four layer solid sae device ha conrols curren flow The name silicon conrolled recifier is a rade name for he ype of hyrisor commercialized a General Elecric in 1957
Silicon Conrolled Recifier An SCR can be seen as a convenional recifier conrolled by a gae signal I is a 4-layered 3-erminal device When he gae o cahode volage exceeds a cerain hreshold, he device urns 'on' and conducs curren
Silicon Conrolled Recifier The operaion of a SCR can be undersood in erms of a pair of ighly coupled Bipolar Juncion Transisors SCR has hree saes: Reverse blocking mode, forward blocking mode, and forward conducing mode
V-I Characerisic Curve
Silicon Conrolled Recifier Indusrially SCRs are applied o produce DC volages for moors from AC line volage Recifier Half-wave recifier, full-wave recifier
Half-wave recifier
Half-wave recifier
Half-wave recifier
題目 : 已知 SCR 的 IGT 為 20mA, 請問直流電壓由 0V 向上調整, 要調到多少伏特,SCR 才導通? 解答 : 由基本原理說明可知 V=20m 150+0.7=3.7V
Reviews A SCR is essenially a diode wih an exra erminal added This exra erminal is called he gae, and i is used o rigger he device ino conducion by he applicaion of a small volage
Applicaion: DC Moor Driver DC moor speed generally depends on a combinaion of he volage and curren flowing in he moor coils and he moor loads or braking orque The speed of he moor is proporional o he volage, and he orque is proporional o he curren
DC Moors Curren Driver A recifier is one or more diodes arranged for convering AC o DC The curren used o drive he DC moor ypically comes from : Fixed volage: Baery Volage regulaor Adjusable volage: PWM curren source Silicon conrolled recifier modulaed AC source
Volage regulaor DC Moors Curren Drives
DC Moors Curren Drives Linear power ransisor & OP amp
DC Moors Curren Drives Pulse Widh Modulaion
DC Moors Curren Drives
DC Moors Curren Drives
DC Choppers 20
Inroducion Chopper is a saic device. A variable dc volage is obained from a consan dc volage source. Also known as dc-o-dc converer. Widely used for moor conrol. Also used in regeneraive braking. Thyrisor converer offers greaer efficiency, faser response, lower mainenance, smaller size and smooh conrol. 21
Choppers are of Two Types Sep-down choppers. Sep-up choppers. In sep down chopper oupu volage is less han inpu volage. In sep up chopper oupu volage is more han inpu volage. 22
Principle Of Sep-down Chopper Chopper i 0 + V R V 0 23
A sep-down chopper wih resisive load. The hyrisor in he circui acs as a swich. When hyrisor is ON, supply volage appears across he load When hyrisor is OFF, he volage across he load will be zero. 24
v 0 V V dc ON OFF i 0 V/R T I dc 25
V I dc dc ON OFF Average value of oupu or load volage. Average value of oupu or load curren. Time inerval for which SCR conducs. Time inerval for which SCR is OFF. T Period of swiching or chopping period. ON OFF 1 f Freq. of chopper swiching or chopping freq. T 26
Average Oupu Volage V V ON dc ON OFF V V ON V. d dc T bu ON d duy cycle 27
Average Oupu Curren I I dc dc V dc R V ON V R T R RMS value of oupu volage d V O 1 ON T 0 2 o v d 28
Bu during, v V ON Therefore RMS oupu volage o V O 1 T ON 0 2 V d 2 V V ON. V O ON T T V O d. V 29
Oupu power Bu P I Oupu power O O O O V I V O R P P O O V 2 O R dv R 2 30
Effecive inpu resisance of chopper R R i i V I R d dc The oupu volage can be varied by varying he duy cycle. 31
Mehods Of Conrol The oupu dc volage can be varied by he following mehods. Pulse widh modulaion conrol or consan frequency operaion. Variable frequency conrol. 32
Pulse Widh Modulaion ON is varied keeping chopping frequency f & chopping period T consan. Oupu volage is varied by varying he ON ime ON 33
V 0 V ON OFF T V 0 V ON OFF 34
Variable Frequency Conrol Chopping frequency f is varied keeping eiher ON or OFF consan. To obain full oupu volage range, frequency has o be varied over a wide range. This mehod produces harmonics in he oupu and for large OFF load curren may become disconinuous 35
v 0 V ON T OFF v 0 V ON OFF T 36
Sep-down Chopper Wih R-L Load Chopper i 0 + R V FWD L V 0 E 37
When chopper is ON, supply is conneced across load. Curren flows from supply o load. When chopper is OFF, load curren coninues o flow in he same direcion hrough FWD due o energy sored in inducor L. 38
Load curren can be coninuous or disconinuous depending on he values of L and duy cycle d For a coninuous curren operaion, load curren varies beween wo limis I max and I min When curren becomes equal o I max he chopper is urned-off and i is urned-on when curren reduces o I min. 39
v 0 V Oupu volage i 0 I max ON T OFF Oupu curren I min i 0 Coninuous curren Oupu curren Disconinuous curren 40
Principle Of Sep-up Chopper I + L D + V Chopper C L O A D V O 41
Sep-up chopper is used o obain a load volage higher han he inpu volage V. The values of L and C are chosen depending upon he requiremen of oupu volage and curren. When he chopper is ON, he inducor L is conneced across he supply. The inducor curren I rises and he inducor sores energy during he ON ime of he chopper, ON. 42
When he chopper is off, he inducor curren I is forced o flow hrough he diode D and load for a period, OFF. The curren ends o decrease resuling in reversing he polariy of induced EMF in L. Therefore volage across load is given by di V V L i. e., V V O O d 43
A large capacior C conneced across he load, will provide a coninuous oupu volage. Diode D prevens any curren flow from capacior o he source. Sep up choppers are used for regeneraive braking of dc moors. 44
Expression For Oupu Volage Assume he average inducor curren o be I during ON and OFF ime of Chopper. When Chopper is ON Volage across inducor L V Therefore energy sored in inducor Where = V. I. ON ON ON period of chopper. 45
When Chopper is OFF (energy is supplied by inducor o load) Volage across Energy supplied by inducor where OFF L V V O L V V I OFF period of Chopper. Neglecing losses, energy sored in inducor L = energy supplied by inducor L O OFF 46
VI V V I V O ON O OFF V ON OFF VO V T ON OFF Where T = Chopping period or period of swiching. T 47
T ON OFF V V O O V 1 V 1 1 T 1 d ON ON Where d duy cyle T 48
For variaion of duy cycle ' d ' in he range of 0 d 1 he oupu volage will vary in he range V V O V O 49
Performance Parameers The hyrisor requires a cerain minimum ime o urn ON and urn OFF. Duy cycle d can be varied only beween a min. & max. value, limiing he min. and max. value of he oupu volage. Ripple in he load curren depends inversely on he chopping frequency, f. To reduce he load ripple curren, frequency should be as high as possible. 50
Classificaion Of Choppers Choppers are classified as Class A Chopper Class B Chopper Class C Chopper Class D Chopper Class E Chopper 51
Class A Chopper i 0 + v 0 V Chopper FWD L O A D v 0 V i 0 52
When chopper is ON, supply volage V is conneced across he load. When chopper is OFF, v O = 0 and he load curren coninues o flow in he same direcion hrough he FWD. The average values of oupu volage and curren are always posiive. Class A Chopper is a firs quadran chopper. 53
Class A Chopper is a sep-down chopper in which power always flows form source o load. I is used o conrol he speed of dc moor. The oupu curren equaions obained in sep down chopper wih R-L load can be used o sudy he performance of Class A Chopper. 54
i g Thyrisor gae pulse i 0 Oupu curren v 0 CH ON FWD Conducs Oupu volage ONT 55
Class B Chopper D i 0 + v 0 V R L v 0 Chopper E i 0 56
When chopper is ON, E drives a curren hrough L and R in a direcion opposie o ha shown in figure. During he ON period of he chopper, he inducance L sores energy. When Chopper is OFF, diode D conducs, and par of he energy sored in inducor L is reurned o he supply. 57
Average oupu volage is posiive. Average oupu curren is negaive. Therefore Class B Chopper operaes in second quadran. In his chopper, power flows from load o source. Class B Chopper is used for regeneraive braking of dc moor. Class B Chopper is a sep-up chopper. 58
i g Thyrisor gae pulse i 0 OFF ON I max I min v 0 T D conducs Chopper conducs Oupu curren Oupu volage 59
Expression for Oupu Curren 60
During he inerval diode 'D' conducs volage equaion is given by LdiO V RiO E d For he iniial condiion i.e., i I a 0 O min The soluion of he above equaion is obained along similar lines as in sep-down chopper wih R-L load 61
A R R V E L L io 1 e Imine 0 R i I OFF O max OFF R V E OFF L Imax 1 e Imine R During he inerval chopper is ON volage equaion is given by 0 Ldi d O Ri O E R L OFF 62
Redefining he ime origin, a 0 i I The soluion for he saed iniial condiion is R R E L L io Imaxe 1 e 0 R A i I ON R ON E L Imin Imaxe 1 e R O R L min ON O max ON 63
Class C Chopper CH 1 D 1 i 0 + v0 V R CH 2 D 2 L v 0 Chopper E i 0 64
Class C Chopper is a combinaion of Class A and Class B Choppers. For firs quadran operaion, CH 1 is ON or D 2 conducs. For second quadran operaion, CH 2 is ON or D 1 conducs. When CH 1 is ON, he load curren is posiive. The oupu volage is equal o V & he load receives power from he source. When CH 1 is urned OFF, energy sored in inducance L forces curren o flow hrough he diode D 2 and he oupu 65
Curren coninues o flow in posiive direcion. When CH 2 is riggered, he volage E forces curren o flow in opposie direcion hrough L and CH 2. The oupu volage is zero. On urning OFF CH 2, he energy sored in he inducance drives curren hrough diode D 1 and he supply Oupu volage is V, he inpu curren becomes negaive and power flows from 66
Average oupu volage is posiive Average oupu curren can ake boh posiive and negaive values. Choppers CH 1 & CH 2 should no be urned ON simulaneously as i would resul in shor circuiing he supply. Class C Chopper can be used boh for dc moor conrol and regeneraive braking of dc moor. Class C Chopper can be used as a sep-up or sep-down chopper. 67
i g1 i g2 i 0 Gae pulse of CH 1 Gae pulse of CH 2 Oupu curren V 0 D 1 CH 1 D 2 CH 2 D 1 CH 1 D 2 CH 2 ON ON ON ON Oupu volage 68
Class D Chopper CH 1 v 0 D 2 V R i 0 + v 0 L E i 0 D 1 CH 2 69
Class D is a wo quadran chopper. When boh CH 1 and CH 2 are riggered simulaneously, he oupu volage v O = V and oupu curren flows hrough he load. When CH 1 and CH 2 are urned OFF, he load curren coninues o flow in he same direcion hrough load, D 1 and D 2, due o he energy sored in he inducor L. Oupu volage v O = - V. 70
Average load volage is posiive if chopper ON ime is more han he OFF ime Average oupu volage becomes negaive if ON < OFF. Hence he direcion of load curren is always posiive bu load volage can be posiive or negaive. 71
i g1 Gae pulse of CH 1 i g2 Gae pulse of CH 2 i 0 Oupu curren v 0 V CH,CH ON 1 2 D1,D2 Conducing Oupu volage Average v 0 72
i g1 Gae pulse of CH 1 i g2 Gae pulse of CH 2 i 0 Oupu curren v 0 V CH CH 1 2 D, D 1 2 Oupu volage Average v 0 73
Class E Chopper CH 1 D CH 3 1 D 3 V + i L E 0 R CH 2 D CH 4 2 D 4 v 0 74
Four Quadran Operaion v 0 CH 2- D 4Conducs D - D Conducs 1 4 CH 1- CH 4ON CH - D Conducs 4 2 i 0 CH 3- CH 2ON CH - D Conducs 2 4 D 2 - D3 Conducs CH 4- D 2Conducs 75