DEPARTMENT OF ELECTRICAL POWER ENGINEERING

COLLEGE OF ENGINEERING

POWER ELECTRONICS

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Topics Covered - DC To DC Converters - Boost (Step Up) 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

 

 

Boost(Step Up) 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

  • It can be determined through on mode and off mode. Here on mode is used:

For more information, you may also visit this website: http://www.ipes.ethz.ch/ipes/PWMsimpel/e_pwmcurrent.html

[This website, Interactive Power Electronics Seminar (iPES) provides Java applets as aid for teaching by Prof. Kolar at the ETH Zurich.]

The Inductor Current

  • According to analysis made on two switching modes in the circuit, inductor current is equal to input current.

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 Diode and Capacitor Currents

  • Diode current is equal to zero during on mode and equal to inductor current during off mode.
  • Capacitor current is the negative of output current when the switch is off and it is the ripple of diode current (also inductor current) when switch is on.
  • Refer to graphs of example for further understading.

The Capacitor Voltage Ripple

  • The del Vc can be determined from on state interval
  • The change in charge is the area of the triangle above the time axis.

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