Trends in Active Power Filters

Trends in Active Power Filters
Dr. Mohamed Darwish
Brunel University
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Normal Operating Conditions
Supply
Impedance
Supply Current
Supply
Voltage
PCC
+
VPCC
Linear
Load
-
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Non-linear Operating Conditions
Supply
Impedance
PCC
+
Supply Current
Supply
Voltage
VPCC
Linear
Load
-
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Source of Power System
Harmonics
• Large Sources
– Arc-furnaces
– Megawatts sized adjustable-speed-drive
(ASD) systems
– Static converters
– Transformer magnetisation non-linearities
• Small sources
– TV sets
– Computer equipments
– Fluorescent and other discharge lightingabcdefgh
A Typical Computer Load Current
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A Typical Computer Load Current in
Sleep Mode
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Voltage Harmonics in Residential Areas
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Example of total harmonic distortion
caused by a typical residential home
Washer
Dryer
Fridge/
Freezer
Microwave
T.V.
Personal
Computer
26%
14%
27%
121%
140%
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A Typical Harmonic
Problem
Phase A
(50Amps)
Phase B
(50Amps)
Phase C
(50Amps)
Neutral
(80Amps)
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Effect of Harmonics
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Effect of Harmonics
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How to Eliminate Harmonics
•Preventing harmonic generation for
newer systems
–High input power factor regulators
–Switching regulators
–High pulse number AC/DC converters
•For existing sources of harmonics
– Installing filters on DC side of rectifier
– Installing filters on AC side
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Need for Filters
• Eliminate / Reduce harmonics
in voltage & current
waveforms.
• Improve power factor.
• Reduce harmonic power
losses.
• Combinations of the above.
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Available Filter Configurations
Shunt
configuration
Series
configuration
• Provides a low
impedance path
to ground
• Provides a high
series impedance
path
• Does not
necessitate a
series filter
• Must work in
conjunction with
a shunt filter
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Passive Filters
• Use L - C tuned components
• Tuned for the undesired
harmonics
L
L
C
C
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Passive Filters
AC System
Converter
Filters
8 Uncharacteristic Harmonics
8 Higher Cost
8 Bulky
8 Depend on System
impedance
9 Reliable
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Advantages of Passive Filters
• Reliable operation
• Easy design procedure
• Act as reactive power compensators
• Cheap configurations per harmonic
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Disadvantages of Passive Filters
• Large number of components
• Bulky
• Depend on system impedance
• Tuned for a certain loading condition
• Parallel and series resonance may occur for
certain harmonics
• Affected by capacitor ageing
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Active Filters
• Use
active
switching
components
• Only one filter needed to
eliminate all the unwanted
harmonics
• Used for power factor correction
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Classification of Active Filters
•Active Filters attached to Large
Single-Source Offenders
•Active Filters for ‘Retrofit’
Applications
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Analogy Between Harmonic Pollution
and Air Pollution Sources
SOURCES
UNIDENTIFIED
IDENTIFIED
HARMONIC
POLLUTION
AIR POLLUTION
• TV sets and PCs
• Gasoline-fuelled
vehicles
• Small electronic
loads
• Diesel powered
vehicles
• Bulk rectifiers
• Cycloconverters
• arc-furnaces
• Chemical Plants
• Coal/oil steam
power stations
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Triple-frequency
current generator
Interphase
transformer
3rd Current Harmonic Injection Method
by Bird, Marsh, and Mclellan (1969)
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Active Filters for Retrofit
Applications
•Active Filters based on voltage-fed inverters
•Active Filters based on current-fed inverter
•Variable Characteristics Filters
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Basic Idea of Active Filters
1 3 5 7 9
1 3 5 7 9
C. T.
Nonlinear
Load
3 5 7 9
+
Switching Power
Amplifier
1 3 5 7 9
-
Low Pass
Filter
3 5 7 9
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Typical Active Filter Circuit
~
Non-linear
Load
Actual Current
Feedback
Power Circuit
PWM
Switching Strategy
Overall System
Controller
Reference Current
Generator
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Active filters on Commercial Basis
Objective
Rating
Harmonic
compensation
with or without
reactive power
compensation
below
100KVA
Flicker
compensation
100VA ~
10 MVA
Voltage
regulation
above
10MVA
Switching Devices
IGBT
MOSFETS
IGCT
GTO
IGBT
GTO
Applications
Diode or thyristor
rectifiers and
cycloconverters for
industry
Arc furnaces
Sinkansen (the
Japanese “bullet”
trains)
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Inverter Configurations
~
Nonlinear
Load
Current-Fed Inverter Filter
~
Nonlinear
Load
Voltage-Fed Inverter Filter
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Disadvantages of Inverter
Filters
•High tracking switching frequency
particularly at zero crossing.
•Large reservoir capacitor (in voltage
source inverters).
•Difficulties in keeping voltages constant on
dc-link capacitor.
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New Configurations
•Reactive Power Compensation.
•Switched-Capacitor SC side Filters.
•Variable Characteristics DC Filters
•Lattice Structure Filters
•Voltage Regulator Configuration
•Active/Passive Filter combinations.
•& Others . . .
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Switched-Capacitor Techniques
Nonlinear
Load
Nonlinear
Load
L
L
C
C
C
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Lattice Structures
Nonlinear
Load
L
C
Nonlinear
Load
L
L
L
C
Nonlinear
Load
L
C
L
C
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Voltage Regulator Filters
Non-linear
Load
~
Lf
Cf
SA1
SA
Cdc1
Closed-loop
SB1
Lch
SB
OR
Cdc2
Open-loop
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Passive / Active Filter
Combination
VSI
iDC
S2
Linv
S1
LComp
iinv
iF
vinv
LS
iS
iComp
vld
RF
VDC
PCC
ild
vF
vS
LF
CDC
S3
S4
CF
AC-Passive Filter Non-linear
Load
T-Network
Supply
Voltage
System Controller
(Actual current, Reference current, Switch conditions, PWM
and Hysterisis controller, Supply voltage, Load current)
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Active Filter with R-L Load
~
Source
Active
Filter
Highly Inductive
Load
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Active Filter with R-L Load
Supply
Voltage
Supply
Voltage
Filter
Current
Load
Current
Supply
Current
Reference
Supply
Current
Supply
Voltage
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Active Filter with R-C Load
~
Source
Active
Filter
Highly Capacitive
Load
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Active Filter with R-C Load
Supply
Voltage
Supply
Voltage
Filter
Current
Load
Current
Supply
Current
Reference
Supply
Current
Supply
Voltage
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Typical Active Filter Circuit
~
Non-linear
Load
Actual Current
Feedback
Power Circuit
PWM
Switching Strategy
Overall System
Controller
Reference Current
Generator
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Control of Active Filters
using Wavelet Transform
Active filtering of the variable harmonic
contents of an arc furnace current
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Active filtering of several disturbances
such as: spikes, notches, transient
responses, harmonics of several orders etc.
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New Ideas for Control
•DSPs
•Genetic Algorithms
•Adaptive Controllers
•Fuzzy Logic Controllers
•Neural Networks
•& Many others
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Advantages of Active Filters
•Lower switching frequency
•Smaller sizes of components
•Cheaper solutions
•Basis for future improvements
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Future Control Strategies for
Active Filters Using ANN
Harmonic
Generating
Load
~
Active
Filter
&
Reactive Power Controller
Sensory
Units
Association
Units
Response
Units
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Conclusions
• Passive Filters
• Active Filters & Reactive Power Controllers
– Large Offenders
– Retrofit Applications
– AI ? (NeuraLogix’s NLX420 Neural Processor Slice)
• Devices ?
• Control ?
• Availability & Cost ?
• Regulations & Standards ?
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