IMPROVED THREE PHASE AC-DC CUK CONVERTER

Abstract

Conventional off-line dc power supply usually uses input a full-bridge rectifier with capacitive output filter. The diode bridge rectifies the ac input voltage and the capacitor smoothens out the resulting voltage to make it pure do waveform. However in such an arrangement the current drawn from the ac utility source is highly non-sinusoidal (peaky current) and it results in poor power factor and current THD violating international standards. In this scenario an active power factor correction method (PFC) can be used. One of the active power factor correction method is to use a do-dc converter as an interface between the full-bridge rectifier and the load. The basic idea of such an active PFC method is to control the switching action of dc-dc converter so that the current drawn from the supply is sinusoidal and also in phase with the supply voltage so that near unity power factor can be achieved. The most commonly used Boost do-dc converter has got some limitations eventhough it is very simple in implementation. This is the reason for increased use of Cuk converter in the recent years. So the aim is to develop a three phase isolated AC-DC Cuk rectifier with a suitable control strategy such that input current is sinusoidal and gives almost unity power factor and current THD close to international standards. Improvements that are implemented compared to the ordinary AC-DC Cuk rectifier system; are use of coupled inductors and a peak current control strategy. Design equations for the whole system is discussed. Both simulation and hardware results are also presented.