Abstract:
AC to DC conversion is a very common need in many applications. The conversion is
usually accomplished by controlled or uncontrolled single phase or three phase rectifiers.
Rectifiers are popular in industrial and commercial applications due to their low ripple
contents in the voltage waveform and capability of high power handling capacity with
light weight small diode circuits. But their non sinusoidal input current, low power factor
and low efficiency create problems for utilities. In this respect, switch mode regulated
rectifier offer efficient, compact, high efficiency operation. The improvement of input
current is possible by the addition of Boost or C"uk regulator with single or three phase
rectifier. A high frequency pulse width modulation (PWM) technique is used to control
the switching device of Boost or C"uk regulator in such rectifiers. In this thesis, a three
phase rectifier is analyzed with Boost regulator and then with C"uk regulator. Same low
pass filter made the input current almost sinusoidal in both the cases. But high THD and
resonance problem remains. This thesis work shows, when a high frequency harmonics
filter is attached with passive filter, the improvement of input current is observed at the
highest level. Power factor is found almost unity and efficiency is improved in both
cases. It is seen that, the C"uk rectifier is more advantageous than Boost rectifier.
Because in C"uk rectifier the input current is smooth and continuous due to the capacitive
energy transfer. It provides the facility of control of output voltage lower or greater than
input voltage by the wide variation of duty cycle. Moreover, C"uk rectifier draws lower
input current than that of Boost rectifier for similar loads.
