20-08-2013, 03:36 PM
SINGLE PHASE STEP DOWN CYCLOCONVERTER
AIM :
To design and simulate a Single Phase Step down Midpoint Cycloconverter.
THEORY:
A single-phase input to single-phase output cycloconverter is shown in Figure, the simplest Cycloconverter circuit. The secondary transformer of the power supply for the cycloconverter Consists of two separate windings, which can provide 180° displaced input voltages to each of the two thyristor half bridges. As there are two controlled timing pulses for each thyristor half bridge, this topology is referred as a 2-pulse (or 4-pulse in circulating current mode) cycloconverter.
The cycloconverter is connected as shown in Figure , which is operating without circulating current; the non-conducting thyristor should always be kept off otherwise the input power supply could be shorted via the positive and negative thyristor half bridges. When the load current is positive, the output voltage is only controlled by phase control of thyristor T1 and T3 whilst the other two negative thyristor T2 and T4 are kept off and vice versa when the load current is negative. When the load current changes direction whilst ensuring that the two thyristor half bridges do not conduct at the same time.
If the cycloconverter is operating in circulating current mode, both thyristor half bridges are continuously conducting, eliminating the output voltage distortion during load current zero crossing but additional coupled reactors are required between the two thyristor half bridges to limit the circulating current Although the output voltage of the cycloconverter can be improved in circulating current mode, the circulating current reactor tends to be bulky and more expensive and the presence of the circulating current will degrade the input power factor.
RESULT :
Thus a Single Phase Midpoint Step down Cycloconverter for given value of output frequency was designed, simulated and the output waveforms were analyzed.