Power line voltage regulation by PWM AC buck-boost voltage controller

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.