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.
