Input current shaping and power factor improvement of a three phase rectifier by buck - boost regulator

Abstract

Three phase rectifiers are commonly used in high power applications due to their low cost and ease of control. Rectifiers are non-linear in nature and draw non sinusoidal input current from the ac power sources. This causes a number of problems in sensitive electronic equipments and in the power distribution networks. Moreover, increase in reactive power, low input power factor, large input voltage distortion etc. raises the degree of the problems. In this respect, switch mode regulated rectifiers offer efficient, compact and high efficiency operation. The improvement of input current is possible by addition of Buck, Boost, Buck-Boost and Ĉuk regulator with single or three phase rectifier. A high frequency pulse width modulation (PWM) technique is used to control the switching devices of these regulators. In this thesis, a three phase full wave diode rectifier is analyzed with Buck-Boost regulator. A three phase rectifier with buck-boost regulator has been analyzed first with constant switching frequency for different duty cycles. It has been found that though the THD remains low, the overall efficiency was not over 80% at all duty cycle. This thesis works shows, when a variable carrier frequency is applied for different duty cycle, the THD of the input current is low and the overall efficiency is more than 80% for lowest and highest output voltage as well. It provides the facility of control of output voltage to lower and greater than the input voltage efficiently by the wide variation of duty cycle.