Step up Cycloconverter

 

Power Circuit of Step up Cycloconverter

• It is Cycloconverter in which the output frequency is greater than the input frequency of the supply. 
• It is only Cycloconverter in which commutation of SCRs is done by forced commutation. 
• The power circuit of the step up Cycloconverter is shown in the figure A.
• There are two group of SCRs in which one group ( SCR T1 and SCR T2 ) generates positive half cycle and other group ( SCR T3 and SCR T4 ) generates negative half cycle. 

Operation of Step up Cycloconverter

The operation of the Cycloconverter is explained as below.

Positive half cycle

• The SCR T1 is turned on during positive half cycle of the alternating supply during time 0 to t₁ therefore the load current flows through path A – SCR T1 – D – LOAD – C. 
• The output voltage becomes positive. The SCR T1 is turned off by forced commutation at time t₁ and SCR T4 is turned on. 
• The load current flows through path C – LOAD – D – SCR T4 – B. The output voltage becomes negative during this time.

Negative half cycle

• The SCR T2 is turned on during negative half cycle ( at π time ) of alternating cycle therefore the load current flows through path B – SCR T2 – D – LOAD – C . 
• The output voltage becomes positive. The SCR T4 is tuned off at time t₄ by forced commutation and SCR T2 is turned on. 
• The output voltage becomes negative during this time interval. 
• The SCR T3 is turned off at time t₅ by forced commutation and SCR T2 is again turned on. 
• This will result in output voltage becomes positive. The cycle completes in this way. The output frequency ( from figure B )

       f₀ = 1 / ( t₂ – t₁ ) Hz

• The output frequency of the Cycloconverter f₀  is always greater than the supply or input frequency.

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