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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