Digital pulse skipping modulation strategies for dc dc converters to improve the power conversion efficiency at partially loaded conditions and incorporation of pfc

Abstract

In Power electronics, control circuits play a vital role in the operation and performance of power converters. Main control methods used in switching converters include Pulse Width Modulation (PWM), Pulse Frequency Modulation (PFM), and Pulse Skipping Modulation (PSM). The Buck and Boost converters has two modes of operation. These converters are used for heavy load conditions, when they are in continuous conduction mode(CCM), and used for light load conditions, when they are in discontinuous conduction mode(DCM).In portable battery-powered applications, such as cell phones, digital cameras, Personal digital assistant, and laptops, efficiency of the DCDC converter is vital in determining the battery lifetime. Losses in DC-DC converters are divided into switching losses and conduction losses. Switching losses are energy loss due to turning on and off the switching devices; whereas conduction losses are losses due to the energy flow through the on-resistance, junction capacitance of the switching devices, and inductor in the circuit. In order to improve the light load efficiency, it is necessary to reduce the switching losses with reasonable conduction losses. Hence the capacitor and inductor components in the converter circuit and switching devices should be selected to get better efficiency. PSM has got higher efficiency at light load conditions compared to other controllers with reduced switching loss due to the constant frequency, constant width pulses applied to the switch are blocked(skipped) or released over a fixed duration of time equal to duty cycle. PSM lowers the switching frequency, once the circuit senses its light load condition, capacitor charges during specific time slots to send the pulses to the converter. The PSM mode permits higher conversion efficiency especially in light load conditions compared to other control methods under the same operating conditions. But PSM has higher ripple and large device peak currents. The conventional PSM also suffers from large overshoot during transient condition; and an abrupt change in the output regulation for very small change in either the load resistance or input voltage. The main goal of this research is aimed at improving the light load efficiency with PSM controller during the discontinuous mode of operation. In this research work, the design calculations of buck and boost converters are considered with varying load resistance and fixed switching frequency. newline