CAREER POINT UNIVERSITYKOTA RAJASTHAN

MAJOR ASSIGNMENT

SUBMITTED BY SUBMITTED TO ASHUTOSH YADAV MR. SOMESH SIR U.I.D.-K10995 ASST. PROFESSOR OF EE.

BRANCH-MECHANICAL ENGG. DEPT. C.P.U. KOTA

Introduction

Definition

Theory

Application

Efficiency Factor

General And simulink diagram Conclusion

TABLE OF CONTENT

In this paper, a mathematical model of a Buck Converter for simulation using Simulink without any Sim Power System Elements is illustrated. We also explain how to use Matlab’s Tuning tools to obtain better rise time settling time and peak overshoot.

With this direct power transfer feature and sharing capacitor voltages, the converter is able to achieve efficient power conversion, high power factor, low voltage stress on intermediate bus (less than 130 V) and low output voltage without a high step-down transformer. The absence of transformer reduces the component counts and cost of the converter. Unlike most of the boost-type PFC cell, the main switch of the proposed converter only handles the peak inductor current of dc/dc .

INTRODUCTION

A buck converter (step-down converter) is a DC-to-DC power converter which steps down voltage (while stepping up current) from its input (supply) to its output (load). It is a class of switched-mode power supply (SMPS) typically containing at least two semiconductors (a diode and a transistor, although modern buck converters frequently replace the diode with a second transistor used for synchronous rectification) and at least one energy storage element, a capacitor, inductor, or the two in combination. To reduce voltage ripple, filters made of capacitors (sometimes in combination with inductors) are normally added to such a converter's output (load-side filter) and input (supply-side filter).

DC-to-DC converters provide much greater power efficiency than linear regulators (such as the LM7805), which are simpler circuits that lower voltages by dissipating power as heat, which does not step up output current.

DEFINITION

The basic operation of the buck converter has the current in an inductor controlled by two switches (usually a transistor and a diode). In the idealised converter, all the components are considered to be perfect. Specifically, the switch and the diode have zero voltage drop when on and zero current flow when off and the inductor has zero series resistance. Further, it is assumed that the input and output voltages do not change over the course of a cycle (this would imply the output capacitance as being infinite).

Theory of operation

Conduction losses that depend on load: Resistance when the transistor or MOSFET switch is conducting. Diode forward voltage drop (usually 0.7 V or 0.4 V for schottky diode) Inductor winding resistance Capacitor equivalent series resistance Switching losses: Voltage-Ampere overlap loss Frequencyswitch*CV2 loss Reverse latence loss Losses due driving MOSFET gate and controller consumption. Transistor leakage current losses, and controller standby consumption

Efficiency factors

• Switched-mode power supply (SMPS), • DC motor control,• battery chargers

APPLICATION

LOAD

Vcontrol(derived from

feedback circuit)

DC supply(from rectifier-filter, battery,fuel cell etc.)

DC output

General block diagram

SIMULINK DIAGRAM OF BUCK CONVERTOR

The mathematical model is derived from the system equations and provides an accurate representation of the Buck Converter. The Transfer Function of the system is also discussed in order to permit the use of the controller tuning tools provided by Matlab. One is free to replace the default PID block with their own 

CONCLUSION

THANK YOU