DEPARTMENT OF ELECTRICAL POWER ENGINEERING

COLLEGE OF ENGINEERING

POWER ELECTRONICS

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Topics Covered - DC To DC Converters - Buck (Step Down) Converter - Assumptions Made for Analysis of the Buck Converter

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

 

 

 

Buck (Step Down) Converter

  • Step down DC input voltage to lower DC output voltage.
  • Fully controlled switches such as IGBT, MOSFET are used.

Assumptions Made for Analysis of the Buck Converter

  • The circuit is operating in steady state.
  • The inductor current is continuous (always positive).
  • The capacitor is very large, the output voltage is held at constant at voltage Vo. (ripple AC component goes to capacitance, DC component goes to load )
  • The switching period is T: the switch is ON at DT and OFF at (1 - D ) T
  • The components are ideal (P loss = 0).

Circuit Diagram of Buck Converter

 

Note:

  • Capacitor current is the ripple (AC component) of the inductor current while output current is the DC component of inductor current.
  • LC low pass filter is used to produce pure DC output.
  • Diode provides path for inductor current during off mode.

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