load commutated chopper
Post on 06-Apr-2017
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Load commutated chopper
By Kaviyarasan.s
commutation
Commutation is the process of turning of a circuit.
Types Forced commutationLoad commutation
commutation
Forced commutation
Load commutation Voltage commutation
Current commutation
constructionThyristor t1Thyristor t2Thyristor t3Thyristor t4CapacitorFree wheeling
diodeLoad
load commutationAchieved by a) The IL = 0 due to the nature of
load circuit parameters b) IL is transferred to another device
from conducting SCR
Principle Working of this chopper starts
only if the Capacitor “C” is charged
Thyristor working:
If T1,T2 – Main Thyristors, then T3,T4 & C forms commutating elements
If T3,T4 – Main Thyristors , then T1,T2 & C forms commutating elements
Assumptions:
Load current is constantThyristor and Diodes are Ideal
Mode 1 (t=o)T1,T2 are triggeredT3,T4 are reverse biased
Mode 2(T=T1)Capacitor gets chargedFree wheeling diode is forward biased
Mode 3(t=t2) T3,T4 are triggered
T1,T2 are reversed biased and turned-off
wave form
merits Capable of commutating any
amount of load current
No commutating inductor is required
As it can work in high frequencies (KHz),Filtering requirements are minimal
demerits Peak load voltage is twice the supply
voltageFor high power applications – higher
switching losses at high operating frequencies –efficiency may low
FD is subjected to twice the supply voltage
Capacitor current which is alternating to be sensed to turn on one pair of SCRs when the other pair is commutated
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