DEPARTMENT OF ELECTRICAL POWER ENGINEERING

COLLEGE OF ENGINEERING

POWER ELECTRONICS

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Topics Covered - DC To DC Converters - Introduction

TOPICS COVERED:

DC TO DC CONVERTER

•  Introduction

Buck (Step Down) Converter

•  Assumptions Made for Analysis of the Buck Converter

•  *Circuit Operation Switching Modes

•  Output Voltage Average

•  The Inductor Current Ripple

•  The Load and the Capacitor Current

•  Continuous Conduction Condition

•  The Capacitor Voltage Ripple

Boost (Step Up) Converter

•  Assumptions Made for Analysis of the Boost Converter

•  *Circuit Operation Switching Modes

•  Output Voltage Average

•  The Inductor Current Ripple

•  The Inductor Current

•  Continuous Conduction Condition

•  The Diode and Capacitor Currents

•  The Capacitor Voltage Ripple

Designing DC-DC Converters

•  Converter Design Consideration

PULSE WIDTH MODULATED INVERTERS

•  Introduction

•  Inverter Types

•  Basic Inverter

•  Performance Parameters

•  Fourier Series

•  Total Harmonic Distortion

Single Phase Inverter

•  Single Phase Half Bridge Inverter

•  Single Phase Full Bridge Inverter

•  Square-wave Inverter

•  Square-wave Inverter with RL Load

•  Pulse-Width Modulation (PWM) Control Strategy

•  Amplitude & Harmonics Control

•  Sinusoidal Pulse Width Modulation (SPWM)

•  PWM Definitions & Considerations

Bipolar Switching (Single Phase)

•  PWM Outputs

•  PWM Harmonics

Unipolar Switching (Single Phase)

•  PWM Outputs

•  PWM Harmonics

Three Phase Inverter

•  Introduction

•  Switch State for Six Step Inverter

•  Six Step Inverter (continue)

•  Three Phase SPWM

 

 

 

DC TO DC CONVERTER

Introduction

  • Convert the voltage level of a direct current (DC) source to a different dc voltage level.
  • Very useful for electronic devices with components that run on various levels of voltage requirement, such as cellular phones, portable cassette radios, etc.

 

In this course, we are going to learn about buck and boost converters.

Linear Regulator:

  • Transistor is operated in linear (active) mode.
  • Output voltage is the product of the current and resistance.
  • The transistor can be modelled by an equivalent variable resistor as shown in figure.
  • can only produce output at lower voltages from the input.
  • Inefficient when the voltage drop is large and the current is high as heat dissipated is equal to the product of the output current and the voltage drop

Switching Converter:

  • When switch is opened, no current flow in it.
  • When switch is closed, no voltage drop across it.
  • Power loss is zero for ideal switch.
  • convert one DC voltage level to another by storing the input energy temporarily and then releasing that energy to the output at a different voltage.
  • The storage is in magnetic field storage components (inductors) and electric field storage components (capacitors).

 

 

In general, DC-DC converters have the following properties when operating in the steady state:

1. The inductor current is perioodic (repeating).

  • i L (t + T ) = i L (t)

2. The average inductor voltage is zero.

  • V L = = 0

3. The average capacitor current is zero.

  • Ic =

4. The power supplied by the source is the same as the power delivered to load.

  • P in = P out

The figure below shows the current in different states:

Before going further, there are several important parameters with the symbol to be known:

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