dc to ac inverters
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-1
Chapter 8
Switch-Mode DC-AC Inverters
converters for ac motor drives and
uninterruptible power supplies
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-3
Switch-Mode DC-AC Inverter
Block diagram of a motor drive where the power
flow can be bi-directional
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-4
Switch-Mode DC-AC Inverter
Four quadrants of operation
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-5
One Leg of a Switch-Mode DC-AC Inverter
The mid-point shown is fictitious
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-6
Synthesis of a Sinusoidal Output by PWM
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-7
Details of a Switching Time Period
Control voltage can be assumed constant during
a switching time-period
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-8
Harmonics in the DC-AC Inverter Output
Voltage
Harmonics appear around the carrier frequency
and its multiples
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-9
Harmonics due to Over-modulation
These are harmonics of the fundamental
frequency
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-10
Output voltage Fundamental as a Function
of the Modulation Index
Shows the linear and the over-modulation
regions; square-wave operation in the limit
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-11
Square-Wave Mode of Operation
Harmonics are of the fundamental frequency
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-12
Half-Bridge Inverter
Capacitors provide the mid-point
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-13
Single-Phase Full-Bridge DC-AC Inverter
Consists of two inverter legs
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-14
PWM to Synthesize Sinusoidal Output
The dotted curve is the desired output; also the
fundamental frequency
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-15
Analysis assuming Fictitious Filters
Small fictitious filters eliminate the switching-
frequency related ripple
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-16
DC-Side Current
Bi-Polar Voltage switching
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-17
Output Waveforms:
Uni-polar Voltage
Switching
Harmonic
components around
the switchingfrequency are absent
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-18
DC-Side Current in a Single-Phase Inverter
Uni-polar voltage switching
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-19
Sinusoidal Synthesis by Voltage Shift
Phase shift allows voltage cancellation to
synthesize a 1-Phase sinusoidal output
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Copyright 2003by John Wiley & Sons, Inc.
Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters
8-20
Single-Phase Inverter
Analysis at the fundamental frequency
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-22
Push-Pull Inverter
Low Voltage to higher output using square-wave
operation
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-24
Three-
Phase
PWMWaveforms
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-25
Three-Phase Inverter Harmonics
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-26
Three-Phase Inverter Output
Linear and over-modulation ranges
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-27
Three-Phase Inverter: Square-Wave Mode
Harmonics are of the fundamental frequency
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-28
Three-Phase Inverter: Fundamental
Frequency
Analysis at the fundamental frequency can be
done using phasors
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-29
Square-Wave and PWM Operation
PWM results in much smaller ripple current
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-30
DC-Side Current in a Three-Phase Inverter
The current consists of a dc component and the
switching-frequency related harmonics
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters8-31
Square-Wave Operation
devices conducting are indicated
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-32
PWM Operation
devices conducting are indicated
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-33
Short-Circuit States in PWM Operation
top group or the bottom group results in short
circuiting three terminals
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-34
Effect of Blanking
Time
Results innonlinearity
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-35
Effect of Blanking Time
Voltage jump when the current reverses direction
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-36
Effect of Blanking Time
Effect on the output voltage
Programmed Harmonic Elimination
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-37
Programmed Harmonic Elimination
Angles based on the desired output
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-38
Tolerance-Band Current Control
Results in a variable frequency operation
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Copyright 2003by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DC-Sinusoidal AC Inverters 8-39
Fixed-Frequency Operation
Better control is possible using dq analysis
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C i ht 2003 Ch t 8 S it h M d DC 8 41
Summary of DC-AC Inverters
Functional representation in a block-diagram form
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