Current Commutated Chopper:
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| Current commutated chopper |
- Capacitor is charged to Vs, main thyristor T1 is fired at t = 0. So that load voltage Vo = Vs.
- At t = t1, auxiliary thyristor is turned on to commutate main thyristor.
- With turning on of TA, an oscillatory current ic is set up in the circuit.
- At t2, Vc = - Vs and ic tends to reverse in the auxiliary thyristor TA, it gets naturally commutated.
- As TA is reverse biased and turned off at t2. Oscillatory current ic begins to flow through C, L, D2 and T1.
- At t3 ic rises to io so that iT1 = 0. As a result main SCR T1 is turned off at t3. Since oscillating current through T1 turns it off it is called current commutated chopper.
- After t3 ic supplies load current io and the excess current. iD1 = ic - Io is conducted through diode D1.
- Afetr t4, a constant current equal to Io flows through Vs, C, L, D2 and load.
- Capacitor c is charged linearly to source voltage Vs at t5, so during time ( t5 - t4 ) ic = Io.
- In this commutation an opposite current pulse will be injected through SCR. As a result currents decreases and finally comes to zero if both the currents would be equal and opposite.
- Anti parallel diode is useful to apply the reverse voltage after current through SCR becomes to zero. The value of reverse voltage is low. So
- Turn off time increases.
- Turn off power loss increases.
- Jones chopper employes the principle of voltage commutation.
- Morgan's chopper based on the principle of current commutation.
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| Current and Voltage waveforms for current commutated chopper |
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