DEPARTMENT OF ELECTRICAL POWER ENGINEERING

COLLEGE OF ENGINEERING

POWER ELECTRONICS

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Topics Covered - DC To DC Converters - Buck (Step Down) Converter - Important Parameters

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

Output Voltage Average

  • Waveform of inductor voltage is considered to determine the load average voltage.
  • Area under the curve should be zero since inductor average voltage is zero for entire cycle.

The Inductor Current Ripple

  • Inductor current increases when switch is on (closed) and decreases when switch is off (opened).
  • Inductor current average = output current

The Load and the Capacitor Current

  • In steady state condition, average capacitor current is zero.
  • Output current can be determined by the output voltage and resistance.
  • Capacitor current has a triangle waveform due to ripple of inductor current.

Continuous Conduction Condition

The boundary or critical average inductor current (minimum inductor current) is zero for continuous conduction condition.

The minimum continuous current is:

Note: In practice, L is designed to be 125% greater or 10 times larger than the calculated minimum inductor value. (for allowing continuous current)

The Capacitor Voltage Ripple

  • When the capacitor current is positive, the capacitor is charging.
  • The voltage increases from minimum to maximum.
  • The change in charge is the area of the triangle above the time axis.

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