20-08-2013, 03:35 PM
SINGLE PHASE STEP UP CYCLOCONVERTER
AIM :
To design and simulate a Single Phase Step up Bridge configuration Cycloconverter.
THEORY:
The circuit of a single-phase to single-phase cyclo-converter is shown in Fig Two full-wave fully controlled bridge converter circuits, using four thyristors for each bridge, are connected in opposite direction (back to back), with both bridges being fed from ac supply (50 Hz). Bridge 1 (P – positive) supplies load current in the positive half of the output cycle, while bridge 2 (N – negative) supplies load current in the negative half. The two bridges should not conduct together as this will produce short-circuit at the input. In this case, two thyristors come in series with each voltage source. When the load current is positive, the firing pulses to the thyristors of bridge 2 are inhibited, while the thyristor of bridge 1 are triggered by giving pulses at their gates at that time. Similarly, when the load current is negative, the thyristors of bridge 2 are triggered by giving pulses at their gates, while the firing pulses to the thyristors of bridge 1 are inhibited at that time. This is the circulating-current free mode of operation. Thus, the firing angle control scheme must be such that only one converter conduct at a time, and the changeover of firing pulses from one converter to the other, should be periodic according to the output frequency. However, the firing angles the thyristors in both converters should be the same to produce a symmetrical output.
When a cyclo-converter operates in the non-circulating current mode, the control scheme is complicated, if the load current is discontinuous. The control is somewhat simplified, if some amount of circulating current is allowed to flow between them. In this case, a circulating current limiting reactor is connected between the positive and negative converters, as is the case with dual converter, i.e. two fully controlled bridge converters connected back to back, in circulating-current mode.
The readers are requested to refer to any standard text book. This circulating current by itself keeps both converters in virtually continuous conduction over the whole control range. This type of operation is termed as the circulating-current mode of operation. The operation of the cyclo-converter circuit with both purely resistive ®, and inductive (R-L) loads is explained.
RESULT :
Thus a Single Phase Step up Bridge configuration Cyclo-converter for given value of output frequency was designed, simulated and the output waveforms were analyzed.