1 April 2017

Class B Commutation or Self Commutation ( Type B Commutation )

  • The commutating components L and C are connected in parallel with SCR T1 in the class B commutation. 
  • When SCR T1 is turned off, the charging of capacitor is done through path(+)Vdc – (+)C –C(-) – L – RL –Vdc(-). 
  • When the SCR T1 is turned on, the load current flows through path (+)Vdc – SCR T1 –RL – Vdc(-). 
  • As soon as SCR T1 is turned on, the discharging of capacitor is done through path (+)C – SCR T1 – L–C(-).
  • Therefore the load current as well as capacitor discharging current flows through SCR T1. 
  • Once capacitor discharges, it will again charge with opposite polarity ( upper plate negative and lower plate positive ).
  • Therefore the commutating current IC flows in the opposite direction to that of load current IL
  • When the capacitor current IC is greater than the load current, the SCR T1 is turned off.
  • As the SCR T1 is turned off, the charging of capacitor again done through path (+)Vdc – (+)C – C(-) – L – RL – Vdc(-). 
  • When the voltage across capacitor becomes Vdc, the SCR T1 is again switched on. 
  • The SCR T1 turned on and turned off automatically in this way. 
  • The switching time of SCR T1 depends upon commutating components L and C.
class-b-commutation.png
  

Application
  • The application of class B chopper is in the DC chopper
  • The SCR T1 is turned on during TON time and turned off during TOFF time automatically.
  • The SCR automatically turned on and turned off in the class A and class B commutation therefore it is called as self commutation.

You may also like :

No comments:

Post a Comment