Development of single-phase, single-switch AC-AC boost converter

Abstract

AC voltage controllers regulate ac power to load. Conventionally they are phase controlled single phase and three phase types. Phase control ac- ac voltage controllers are subclass of matrix converters which converts voltage down. These are mainly used in lighting, heating, ac motor starters and speed controllers and voltage restorers etc. In phase control and integral cycle controllers the load voltage and the input current to the converter are nonsinusoidal. At low output voltages power factor are small and input current total harmonic distortion are high. Low power factor and high THD are detrimental to power lines and apparatus. Switch mode ac-ac converters similar to switch mode dc-dc converters are available which have the advantages of being light weight and efficient. Switch mode ac-ac voltage controllers can produce step down and step up voltages at the load as needed. Single phase ac-ac boost converters with two and one bi-directional switch topologies are investigated in this thesis. The converters work as boost ac-ac converters on the instantaneous voltage basis. Their voltage gain conversion has buck-boost nature on rms voltage basis. The current gain of the proposed ac-ac boost converters is inverse to their voltage gains. Two topologies investigated show good input current THD and input power factor for a wide range of voltage control by duty cycle change. However, their efficiencies were found to be between 60-85%. Present study did not consider feedback control for voltage regulation and performance enhancement. It is necessary that in future feedback control scheme be incorporated with proper input-current/output-voltage filters in the proposed converters to enhance performance. The proposed circuits work in multiquadrants (particularly bi-directional two quadrant operation) with R-L and R-L with emf as load.