Input current improvement of a three phase rectifier by C^uk regulator

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.