Dc Ac Converter

In: Computers and Technology

Submitted By pedrofamoreira
Words 1586
Pages 7
Switch-Mode DC-AC Inverters

1.
2.
3.
4.
5.

Introduction
Basic Concepts of Switch-Mode
Single-Phase Inverters
Three-Phase Inverters
Effects of Blanking Time on Output
Voltage in PWM
6. Rectifier Mode of Operation

• Main applications:
– ac motor drives;
– uninterruptible power supplies;
– grid connection of renewable energy sources
1

1

Switch-Mode DC-AC Inverter

• Block diagram of a motor drive where the power flow is unidirectional FEUP-MIEEC. Industrial Electronics

2

2

Switch-Mode DC-AC Inverter

• Block diagram of a motor drive where the power flow can be bi-directional
FEUP-MIEEC. Industrial Electronics

3

3

Switch-Mode DC-AC Inverter
• Four quadrants of operation FEUP-MIEEC. Industrial Electronics

4

One Leg of a Switch-Mode DC-AC Inverter

• The mid-point shown is fictitious
• Similar to the topology dc - dc for two-quadrants operation

FEUP-MIEEC. Industrial Electronics

5

Synthesis of a Sinusoidal Output by PWM
Carrier wave (triangle)
Modulating wave (sine)
Amplitude modulation index: ma =

ˆ
Vm
ˆ
Vtri

Frequency modulation index: mf =

fs f1 • Typical harmonic spectrum shows voltage components around multiples of the switching frequency
FEUP-MIEEC. Industrial Electronics

6

Details of a Switching Time Period

• Control voltage can be assumed constant during a switching time-period FEUP-MIEEC. Industrial Electronics

7

Analysis of output voltage
• In the inverter the switches TA+ and TA- are controlled based on the comparasition of vcontrol and vtri, where the output voltage is: vcontrol > vtri

Vd
2

TA+ is on,

v Ao =

TA− is on,

v Ao = −

or vcontrol < vtri

Vd
2

• This result are independent of the direction of output current.
• The Fundamental Component (very important!):
VA =

vcontrol Vd
, vcontrol ≤ Vtri
Vtri 2…...

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