Cycloconverter Operation with Inductive Load (Noncirculating Current Mode)

Cycloconverter Operation with Inductive Load (Noncirculating Current Mode)

• In practice the load is never purely resistive. In case of the inductive loads, due to the energy stored by the load inductance, the conducting pair of SCRs continues to conduct in the next half cycle as explained in the AC to DC converters . 
• Therefore as shown in the Figure a portion of negative half cycle will appear in the positive half cycle of the load voltage waveform and a portion of positive half cycle will appear in the negative half cycle of the load voltage waveform as shown in Figure. 
• For a divided by three output frequency the sequence of triggering the thyristors is as given in the Table.

Operation of Cycloconverter Operation with Inductive Load :

The sequence of operation is as follows :

• SCR₁ and SCR₂   are turned on at instant (ωt  = α), this will make the load voltage positive.
• These SCRs will conduct throughout the first positive half cycle and continues to conduct in the negative half cycle of the ac supply due to the stored energy by the load inductance.
• At instant (ωt = π + α), SCRs 3 and 4 are triggered. This will turn off the conducting SCRs 1 and 2 due to the line commutation.
• The load voltage becomes positive. SCRs 3 and 4 will conduct upto the instant (ωt = 2π + a) where it is turned off due to the line commutation when SCRs 1 and 2 is turned on.
• The load voltage will be positive in the third half cyder of the supply and SCRs 1 and 2 conducts from (2π + α) to (3π + α).
• But the previously conducting pair (S₁ S₂) will continue to conduct for some time. Thus S₁, S₂, S₅,
  S₆ conduct simultaneously for some time making the instantaneous load voltage zero. At (3π + β) S₁ S₂ stop conducting S₅, S₆  take over the conduction and load voltage becomes negative.
• At (ωt = 3π + α), the SCRs 5 and 6 is triggered, in order to develop a negative load voltage.