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DEPARTMENT OF ELECTRICAL POWER ENGINEERING

COLLEGE OF ENGINEERING

POWER ELECTRONICS

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Topics Covered - Pulse Width Modulated Inverters - Single Phase Inverter - Unipolar Switching - PWM Output

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

 

 

 

Single Phase Inverter

Unipolar Switching

MOSFET is used as switch, the gate signal is ON for + Vdc and OFF for 0V.

PWM Output

  • The output is switched either from high to zero or from low to zero.

    Vo = +Vdc, 0, - Vdc

  • Switch pairs (S1, S4) and (S2, S3) are complementary (when one switch in a pair is closed, the other is opened)

    S1 is on when Vsine > Vtri

    S2 is on when -Vsine < Vtri

    S3 is on when -Vsine > Vtri

    S4 is on when Vsine < Vtri

  • The voltages Va and Vb alternate between + Vdc and zero.

  • The output voltage, Vo = Vab = Va - Vb

  • Another unipolar switching scheme has only one pair of switches operating at the carrier frequency while the other pair operates at the reference frequency. ( Thus, there are two high frequency switches and two low frequency switches)

    S1 is on when Vsine > Vtri (high frequency)

    S4 is on when Vsine < Vtri (high frequency)

    S2 is on when Vsine > 0 (low frequency)

    S3 is on when Vsine < 0 (low frequency)

    Here, S1 and S4 are high frequency switches while S2 and S3 are low frequency switches. Alternatively, it could be vice versa.

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