Engr. Affifa Adeeb

The Islamia University of BahawalpurUniversity College of Engineering &

Technology

EEN-324EEN-324Power ElectronicsPower Electronics

InvertersInvertersChp#10Chp#10

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INTRODUCTION Conversion of available DC source into AC of variable

frequency is accomplished by force commutated inverters.

The frequency of AC at output can be varied by controlling the conduction period of thyristors.

Output voltage of inverter has periodic waveform that is not sinusoidal but can be made to closely approximate this desired waveform.

Inverters are used in industrial applications, including speed control of induction and synchronous motor, aircraft power supplies, uninterruptible power supplies (UPS), and high-voltage DC transmision. 2

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Half-Bridge Inverter

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Square-wave output

Step-wave output

VOLTAGE SOURCE INVERTER

(VSI)

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Half-Bridge VSI

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Example 10.1

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Full-Bridge VSI

State S1 S2 S3 S4 Output Voltage

1 On Off Off On +E

2 Off On On Off -E

3 On Off Off On +E

4 Off On On Off -E

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With Inductive RL loadSquare-Wave output

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Step-Wave output

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Inverter Voltage Control Techniques

1- Control of DC input voltage supplied to the inverter

2- Control of AC output voltage of the inverter

3- Control of the voltage within the inverter

PULSE-WIDTH MODULATION

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(A) SINGLE PULSE-WIDTH MODULATION

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(B) MULTIPLE PULSE-WIDTH MODULATION

(a) m= 2(b) m= 3

Variable duty cycle withm= 5

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(C) SINUSOIDAL PULSE-WIDTH MODULATION

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PWM INVERTERS

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Single-phase Full-Bridge Inverters