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DEPARTMENT OF ELECTRICAL POWER ENGINEERING

COLLEGE OF ENGINEERING

POWER ELECTRONICS

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Topics Covered - Pulse Width Modulated Inverters - Three Phase Inverters

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

 

 

Three Phase Inverter

  • The circuit below (three phase inverter) produces a three phase ac output from a dc input.

  • Application: speed control of induction motors, where the output frequency is varied.

  • Three arms are delayed by 120 degrees to each other to generate three phase supply.

  • The three phase load connected to this output voltage may be connected in delta or undergrounded neutral wye.

  • We are going to learn on wye connected load, which is more common load connection.

Mouse over the image below (three phase inverter) to see the label of voltage and current

Click on it to see the switch state for three phase inverter

 

  • The switches are closed and opened in the sequence shown in figure below.

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  • Each switch has a duty ratio of 50 % (not allowing for blanking time) and a switching action takes place every T/6 time interval (60 degrees angle interval).
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  • Switches S1 and S4 should be complement to each other ( S1 on, S4 off and vice versa), so do switch pairs ( S2, S5 ) and (S3, S6).
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  • Switch pairs must coordinate so that they do not close or open at the same time which would result in a short circuit across the source.

  • With this scheme, the instantaneous voltages VA0, VB0 and VC0 are + Vdc or zero. The figure below shows line to neutral output voltages.

  • Line to line output voltages VAB, VBC and VCA are + Vdc, 0 or - Vdc.

  • For a wye connected load of inverter, it is also called as six step inverter due to six steps in the output waveforms for the line to neutral voltage resulting from the six switching transitions per period.

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