Buck-Boost Converter Design and Analysis

Running head: BUCK-BOOST CONVERTER
BUCK-BOOST CONVERTER
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1BUCK-BOOST CONVERTER
Introduction:
The buck boost converter is a DC to DC converter which are also known as choppers. The
Buck-boost converter operates either as a step down converter or as step up converter based
on its duty cycle D. The schematic diagram of the buck-boost converter is shown below.
The input source voltage is mainly connected to a particular solid state device. A diode is
used as a second switch to the system. In between inductor and the capacitor a diode is
connected in reverse of the direction of current flow from source to the capacitor. A resistive
load is connected to the capacitor in which output voltage is needed to be monitored. The
switching frequency of the switch can be controlled by pulse width modulation system. The
PWM modulation is either time based or frequency based. As the frequency based has the
main disadvantage of operation over a wide frequency range to output the desired output
voltage hence the time based modulation is used for designing the buck-boost converter
circuit. The design is very simple and easy to use and the switching frequency is constant in
this particular type of PWM modulation.

2BUCK-BOOST CONVERTER
The operation of a buck-boost converter is subdivided in two stages.
Mode 1: Diode is OFF and the switch is ON:
The equivalent circuit is shown below.
In ideal case when the switch is ON then zero resistance is offered to the current flow and the
current will circulate in the path of switch and inductor. The charge is stored by the inductor
during switch ON time and when the switch is off the inductor polarity reverses and the
current flows through load and the diode and then fed back to the inductor. Hence, the current
direction remains the same.
Let, the on time of the switch is TON and the off time for the switch is TOFF. Hence, the
switching frequency is f = 1/T.
The duty cycle is given by, D= T ON
T
Circuit design, analysis and modelling:
The circuit of the buck-boost converter as designed in Simulink as shown below.