Development of a continuous input current buck boost AC-AC converter

Abstract

AC voltage controllers regulate ac power to load. Usually they are phase controlled single phase and three phase type. Phase controlled AC- AC voltage controllers are subclass of matrix converters which converts voltage down only. These solid state converters are mainly used in lighting, heating, ac motor starters and speed controllers and voltage restore etc. In phase control and integral cycle controlled voltage controllers, the load voltage is nonsinusoidal and the input current to the converters are also. As a result, at very low output voltages their power factor is small and input current total harmonic distortion are high. These phenomenons are detrimental to power quality of utility lines. Switch mode ac-ac converters similar to switch mode dc-dc converter are available which have the advantages of being higher, efficient and provide high power quality with small input/output filters. Certain switch mode ac-ac voltage controllers also can produce step down and step up voltages at the load as per requirements. In this research work a modified single phase AC-AC Buck Boost converter has been investigated. Performance parameters like voltage gain, input power factor, input current THD and efficiency have been evaluated for single phase conventional (1and 2 inductor) and modified (2 inductor) BuckBoost converter. It is observed that proposed converter posses better performance in regards to voltage gain, power factor and input current THD. However the efficiency in both the cases were not satisfactory. A similar modified circuit of ideal switch with some changes in parameter has also been investigated to improve upon the overall efficiency. It is observed that efficiency can be increased more than 50%. As such if we can select the parameters of the proposed circuit correctly it is expected that overall efficiency of the circuit will improve further. In future by properly selecting the parameters and implementing the circuit in the laboratory overall efficiency can be increased. Also, output voltage regulation by duty cycle control and input current shaping by average inductor current feedback method needs attention in future research on the subject. Successful investigation in two feed backs in future research may result in a practical single phase AC-AC converter that will have a constant voltage across load and near sinusoidal input current with almost unity input power factor for wide range of input voltage and output voltage /load change.