Abstract:
High frequency switching power supplies have become a part of electronic
equipments to provide regulated dc of desired voltages at a low cost and high
etliciency. These power supplies have several advantages over their counterpart the
linear power supplies. Main advantages are smaller compact size due to elimination of
step down transformer and small filters due to high frequency operation. These power
supplies have high efficiency because the regulating device(s) in them works as
switches ensuring low device loss. Their output voltage can be controlled for a wide
range of input voltage fluctuation by ON/OFF ratio (duty cycle) control.
Four common types of switch mode converters are used in dc to dc conversion. They
are BUCK (step down), BOOST (step up), BUCK-BOOST (step up/down) and Cuk
converters. At present these converters use high frequency multiple pulse switching to
generate the controlling signal(s) of power devices.
Utility AC voltage fluctuation both momentary and prolonged, affects adversely the
domestic, industrial and commercial customers. In this research, an electronic AC
Buck -Boost regulator has been proposed for maintaining constant voltage across the
output of the load during any change in load or input voltage variation. AC Buck-
Boost regulator made of ideal switches and practical IGBT switches have been
investigated. Control circuit is proposed for generating pulses (PWM) for maintaining
constant output voltage. The PWM controls the ON/OFF time (Duty cycle) of
switching devices (IGBTs) of the proposed regulator. By regulating duty cycle of the
control signal, output voltage can be maintained almost constant for wide range of
input voltage and load variation. Freewheeling path and surge voltage across switches
create problem in the proposed regulator. Snubbers are used for suppressing surge
voltage across switches. Input current of the proposed regulator is excessively high
and needs to be reduced by further research to make the regulator technically viable.
In this thesis input filter requirement is also calculated to determine the proper LC
values so that the current ripple of input/output currents are within prescribed limit.
