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Digital Active Power Conditioner (DAPC)
Written and Compiled by
Shivaji Waghmare
Addl. Gen. Manager - (R & D)
DB Power Electronics (P) Ltd. Pune
© 2006 DB Power Electronics (P) Ltd. All rights reserved. No part of this publication may be used, reproduced, photocopied, transmitted or stored in anyretrieval system of any nature, without the written permission of the copyright owner. www.dbups.com Rev. 2006-1.0 1
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Table of Contents
INTRODUCTION............................................................................................................................ 3
HARMONIC DISTORTION SOURCES AND EFFECTS ............................................................................. 3HARMONIC FILTERING AND REACTIVE POWER COMPENSATION ....................................................... 3
PASSIVE FILTER........................................................................................................................... 3
(A) 3-PHASE LINE R EACTORS ......................................................................................................... 3
(B) TUNED SINGLE ARM PASSIVE FILTER ......................................................................................... 4
(C) PHASE MULTIPLICATION METHOD ............................................................................................ 4
ACTIVE FILTER ............................................................................................................................ 5
SHUNT ACTIVE FILTER .................................................................................................................... 5
COMPARATIVE STUDY OF DIFFERENT FILTERS.............................................................. 6
DIGITAL ACTIVE POWER CONDITIONER (DAPC) FROM DB......................................... 7
I NTRODUCTION ............................................................................................................................... 7
OPERATING PRINCIPLE .................................................................................................................... 7
POWER CIRCUIT .............................................................................................................................. 7
PROTECTIONS.................................................................................................................................. 7
ALARMS AND PARAMETER DISPLAY .................................................................................................. 8
LOCAL ALARMS .............................................................................................................................. 8
I NDICATIONS .................................................................................................................................... 8
FEATURES AND SPECIFICATIONS.......................................................................................... 8
FEATURES ....................................................................................................................................... 8
SPECIFICATIONS .............................................................................................................................. 8
TEST RESULT ................................................................................................................................ 9
120 K VA UPS TESTED WITH AF-150 A......................................................................................... 9
C. PF + HARMONIC CORRECTION ..................................................................................................... 9
APPLICATION AREAS............................................................................................................... 10
ACTIVE FILTER SIZING CALCULATOR.............................................................................. 10
© 2006 DB Power Electronics (P) Ltd. All rights reserved. No part of this publication may be used, reproduced, photocopied, transmitted or stored in anyretrieval system of any nature, without the written permission of the copyright owner. www.dbups.com Rev. 2006-1.0 2
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INTRODUCTION
Harmonic distortion sources and effects
Events over the last several years have focused attention on
certain types of loads on the electrical system that results in
power quality problems for the user and utility alike. Equipmentwhich has become common place in most facilities including
Computer Power supplies
Solid state Lighting ballast
Adjustable Speed Drives (ASDs),
Uninterruptible Power Supplies (UPSs)
are the examples of non-linear loads.
Non-linear loads generate voltage and current harmonics which
can have adverse effects on equipments, designed for operation
as linear loads (i.e. Loads designed to operate on a sinusoidal
waveform of 50 or 60 Hz.).Effects of Non-linear load
Higher heating losses in the Transformers.
Harmonics can have a detrimental effect on emergency
generators, telephones and other sensitive electrical equipments.
When reactive power compensation (in the form of passive
power factor improving capacitors) is used with non-linear loads,
resonance conditions can occur that may result in even higher
levels of harmonic voltage and current distortion, thereby
causing equipment failure, disruption of power service, and fire
hazards in extreme conditions.
The electrical environment has absorbed most of these problems
in the past. However, the problem has now reached a magnitude
where Europe, the US, and other countries have proposed
standards to responsibly engineer systems considering the
electrical environment. IEEE 519-1992 and IEC 555 have
evolved to become a common requirement cited when specifying
equipment on newly engineered projects. The broad band
harmonic filter was designed in part, to meet these
specifications. The present IEEE 519-1992 document establishes
acceptable levels of harmonics (voltage and current) that can be
introduced into the incoming feeders by commercial and
industrial users. Where there may have been little cooperation
previously from manufacturers to meet such specifications, the
adoption of IEEE 519-1992 and other similar world standards
now attract the attention of everyone.
Harmonic filtering and reactive power compensation
Various techniques of improving the input current waveform are
discussed below. The intent of all techniques is to make the input
current more continuous so as to reduce the overall current
harmonic distortion. The different techniques can be classified
into four broad categories;
(a) Introduction of Line reactors and / or DC link chokes
(b) Passive Filters (Series, Shunt, and Low Pass broad band
filters)
(c) Phase Multiplication (12-pulse, 18-pulse rectifier systems)
(d) Active Harmonic Compensation.
The following paragraphs will briefly discuss the available
technologies, their relative advantages and disadvantages. The
term 3-phase Line Reactor or just Reactor is used in the
following paragraphs to denote 3-phase line inductors.
PASSIVE FILTER
(a) 3-Phase Line Reactors
Line reactors offer significant magnitudes of inductance, which
can alter the way that current is drawn by a non-linear load such
as an input rectifier bridge. The reactor makes the current
waveform less discontinuous resulting in lower current
harmonics. Since the reactor impedance increases with fre-
quency, it offers larger impedance to the flow of higher order
harmonic currents. It is thus instrumental in impeding higher
frequency current components while allowing the fundamental
frequency component to pass through with relative ease.
On knowing the input reactance value, one can estimate the
expected current harmonic distortion. A table illustrating the
expected input current harmonics for various amounts of input
reactance is shown in table below.
Input reactance is determined by the accumulated impedance of
the AC reactor, DC link choke (if used), input transformer and
cable impedance. To maximize the input reactance while
minimizing AC voltage drop, one can combine the use of both
AC input reactors and DC link chokes. One can approximate the
total effective reactance and view the expected harmonic current
distortion from the above chart. The effective impedance value
in % is based on the actual loading as derived below;
Percent Harmonics vs. Total Line Impedance
Harmonic 3% 4% 5% 6% 7% 8% 9% 10%
5th 40 34 32 30 28 26 24 23
7th 16 13 12 11 10 9 8.3 7.5
11th 7.3 6.3 5.8 5.2 5 4.3 4.2 4
13th 4.9 4.2 3.9 3.6 3.3 3.15 3 2.8
17th 3 2.4 2.2 2.1 0.9 0.7 0.5 0.4
19th 2.2 2 0.8 0.7 0.4 0.3 0.25 0.2%THID 44.13 37.31 34.96 32.65 30.35 28.04 25.92 24.68
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(b) Tuned single arm passive filter (c) Phase Multiplication Method
The principle of a tuned arm passive filter is shown in Figure 1.
A tuned arm passive filter should be applied at the single lowest
harmonic component where there is significant harmonic
generation in the system. For systems that mostly supply an
industrial load this would probably be the fifth harmonic. Above
the tuned frequency the harmonics are absorbed but below that
frequency they may be amplified.
By increasing pulse, numbers of harmonics in the line current
can be reduced.
6-pulse rectifier without inductor
Manufacturing cost 100%
Typical harmonic current components.
Fundamental 5th 7th 11th 13th 17th 19th
100% 63% 54% 10% 6,1% 6,7% 4,8%
6-pulse rectifier with inductor
Figure 1 - Tuned single arm passive filter . Manufacturing cost 120%. AC or DC choke added.
Typical harmonic current components.Detuned - Single tuning frequency
Above tuned frequency harmonics absorbedFundamental 5th 7th 11th 13th 17th 19th
100% 30% 12% 8.9% 5.6% 4.4% 4.1%
Below tuned frequency harmonics may be amplified
Harmonic reduction limited by possible over compensation at
the supply frequency and network itself
This kind of filter consists of an inductor in series with a
capacitor bank and the best location for the passive filter is close
to the harmonic generating loads. This solution is not normally
used for new installations.
Tuned multiple arm passive filter
The principle of this filter is shown in Figure 2 This filter hasseveral arms tuned to two or more of the harmonic components,
which should be the lowest significant harmonic frequencies in
the system. The multiple filter has better harmonic absorption
than the one arm system.
Figure 3
12-pulse with double wound transformer
Typical harmonic current components.
Figure 2 - Tuned multiple arm passive filter.
Fundamental 5th 7th 11th 13th 17th 19th
100% 3.6% 2.6% 7.5% 5.2% 1.2% 1.3%Capacitive below tuned frequency/Inductive above
Better harmonic absorption
Design consideration to amplification harmonics by filter
Limited by KVAr and network
The multiple arm passive filters are often used for large DC
drive installations where a dedicated transformer is supplying the
whole installation.
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Shunt Active filter
Fundamental only
Supply
Active
Filter
icompensation
idistortion
Load
Figure 5 - External active filter principle diagram.
The active filter compensates the harmonics generated by
nonlinear loads by generating the same harmonic components in
opposite phase as shown in Figure 6. External active filters are
most suited to multiple small drives. They are relatively
expensive compared to other methods.
Figure 4 24-pulse rectifier
Typical harmonic current components.
ACTIVE FILTER
Clean
Feeder
current
H a r m o n i c s
W a v e f o r m s
Load
current
Active filter
current+
A passive tuned filter introduces new resonances that can cause
additional harmonic problems. New power electronics
technologies are resulting in products that can control harmonic
distortion with active control. These active filters, see Figure 5,
provide compensation for harmonic components on the utility
system based on existing harmonic generation at any given
moment in time. Figure 6
There are different types of active filter configurations.
• Series active filter
• Shunt active filter
• Hybrid active filter.
• Active front end IGBT based PWM rectifier
• Most popular is Shunt Active filter.
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Comparative Study of Different Filters
Parameters Capacitor filter Tuned filter Active filter
Type Passive Passive
IGBT based digitally
controlled
CompensationOnly compensates power factor
Compensates Harmonic Multipletuned filters are required, one for each harmonic
Compensates PF and
Harmonics. One filter cancompensate multiple
harmonics simultaneously
Suitability
Not suitable in case of
more voltage distortion andcurrent distortion
Performance varies over
frequency variation and variationin voltage distortion.
Performance is dependent on loadlevel
Performance remains
constant over frequencyand voltage variation.
Suitable in any type of environment
ResonancePossibility of resonance.This results in premature
failure of capacitor.
Possibility of resonance if tunedat higher frequency. Performance
depends on source impedance
No possibility of resonance. Stable
operation
Size and weight Bulky in sizeBulky in size when multiple
harmonics are to be compensated
Light weight. Size doesnot change even if required to compensatemore harmonics
LifeLimited life in case of morevoltage and current
harmonics
More life as compared to
capacitor filter
Longer life, since
performance remainsconstant and resonance is
avoided
Cost CheapCostlier as compared to capacitor
filter
Initial cost is more as
compared to both thefilters
No load condition
Imposes capacitive PFwhen load is reduced.
Contactors are required tocompensate for leading pf.
Imposes leading PF atfundamental frequency. So notsuitable for generator source.Compensated filter is required for
generator. Performance is tunedat full load
No capacitive PF at noload. Smooth PF
compensation. No problemto Generator source.
Performance remainsconstant over load
variation
3rd harmonic
compensation Not possible Becomes very bulky
Same filter can be used to
compensate 3rd harmonicwithout increasing the size
Selectivity Andharmonic
Compensation No selectivity
Physical components are requiredto be changed
Stability through software.Cost vs. performance is
easily possible. Thismakes it more cost
effective and flexible
Capacity increasePossible by adding morecapacitor
Redesigning is required for change of load.
More units can be addedlater on for increasing
capacity
Safety
To take of resonance problem, lot of fuses must be used. Also resonance
causes failure of other sensitive circuits
Breakers and fuses must be added per tuned filter. Also transientvoltage absorbers must be used to
avoid of other circuitry in case of resonance
Only one set of Breakersand fuses are required for
all harmonics
Power loss Low loss More loss Moderate losses
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SelectivityDigital Active Power Conditioner (DAPC)from DB User can select whether to compensate both harmonics and PF or
to compensate either harmonics or power factor (Displacement
factor).Introduction
This filter works in shunt with the load. Due to this it is easier to
add it in the existing setup, even without taking load shutdown.Also it facilitates to use it at the source end with higher currents
and lower harmonics.
Power Circuit
It is based on High speed IGBT working at higher switching
frequencies. Due to which the required inductor value is reduced.
This helps in making corrections even at higher input voltages
without increasing DC operating voltages. Also it helps to
reduce losses in IGBT.
It is based on 32 bit DSP with full digital control. Digital control
makes it more stable, easy upgradeable, more flexible and no
variation or degradation of performance over a long period of
operation. Total operational technology can be changed without
changing any hardware component.
Optimized switching performance of IGBT inverter helps to
reduce EMI noise as well as improve efficiency of the inverter.
Figure 8 - Single Line Diagram for DAPC
Figure 7 Protections
DAPC is protected against
• Slow protection andOperating principle
• Fast ProtectionIt is based on source current harmonic sensing. Source current is
fed to high speed AD converter of DSP. Source current
harmonics are extracted by the DSP. These harmonics are
injected to the load by the filter. This in turn takes only
fundamental harmonic current from the mains.
Slow protection
It is for slow variations in input voltages and load. This is done
by sensing RMS values of load currents and input voltages. Each
input phase voltage is sensed independently and if, any phase
voltage is out of limit, DAPC is automatically isolated from
input.Harmonic compensation
Selective harmonic elimination method helps it to use it cost
effectively. Compromise in cost and performance can be easily
achieved. These can be set on field easily either by the traineduser or DB service engineer with the help of switches on the
control board. 5th, 7th, 11th, 13th, 17th and 19th harmonics can be
easily selected for their compensation. Also Programmable
harmonic reduction is possible.
Overload and over temperature
Filter RMS load current and Heat sink temperature of IGBT is
continuously monitored. At any instant the filter load or IGBT
temperature is exceeded than its preset level, current limit is
automatically reduced. This prevents tripping of the filter due to
overload or over temperature. It keeps filter running at reduced
capacity level (10% capacity reduction). This can happen in the
event of elevated ambient temperature. Reactive compensation
Along with harmonic compensation DAPC can compensate for
lagging or leading power factor. This compensation is also
programmable. User can have precise required PF correction set
as per his requirement. This also helps in compromising cost vs
performance. User can have PF compensation up to 0.95 or more
to reduce required capacity of Active filter. PF up to unity is possible from 0.6 lag to 0.6 lead.
Fast acting protections
These are achieved by using;
1. High speed semiconductor fuses
2. High speed protection to IGBTs.
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High speed mains abnormal sensing, which includes phase
reversal and negative sequence component sensing in the input
voltage. Filter will immediately isolate form mains and again
reconnect automatically after sensing confirming mains
healthiness. This requires no manual intervention.
1. Mains abnormal
2. Over temperature
3. Over load
4. Phase reversal
Dual levels with different delays DC Over voltage protection
with hardware and software. 5. DC over voltage
6. Filter trip300% over current protection for IGBT. (Redundant protections)
External Inhibit. (Includes filter off due to hardware protections
and ON/OFF switch operation).It is ensured that IGBT is protected against all severe operating
conditions.
FMECA statistical techniques are used for these protections. Indications
Appropriate alarm is provided for all Faults and Alarms
conditions.
Following LED indications are provided on the display.
1. Filter ON
2. Filter OFFAlarms and Parameter Display
3. OV/OC
4. Sync OK.
Remote alarms
Voltage free contacts are provided for
1. Filter running
2. Filter trip
Figure 9 - Front Panel LCD Display on DAPC
Monitoring of filter through PC is possible by
1. MODBUS connectivityRemote as well as local alarms are provided for getting the status
of DAPC. 2. Monitoring through SNMP and web browser
(optional features)Following parameters are displayed locally as well as remotely;
1. Input 3 phase voltage
2. Input frequency
Features and specifications3. DC bus voltage
4. Filter currents for all three phases
Features5. Heat sink temperature
1. Closed loop active filter with source current sensing
Local Alarms 2. High attenuation upto 96% of individual harmonics
A user friendly LCD display, along with Keypad is used locally
to indicate parameters, alarms and faults. Following alarms are
provided on LCD;
3. Programmable selective harmonic elimination
4. PF compensation, leading as well as lagging
5. Selection between PF and harmonic compensation
6. Remote monitoring and diagnosis
7. IGBT based inverter design
Specifications
3 phase / 3 wire non-zero sequence compensation
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Parameter DAPC 60 DAPC 100 DAPC 150
Input Voltage
range Frequency
400V, 3 Ph +10%, -15%, 50 Hz.
45 to 55 Hz
Capacity 60 A 100 A 150 A
HarmonicFiltering
5th to 19th harmonic compensation.Attenuation ratio up to 96%
Power loss infilter < 1700 w < 2800 w < 3500 w
IP ProtectionIP 32
IP42 optionalDimensions (mm)
(WxDxH)800 x 600 x
1000+100 P
800 x 600 x
1600 + 100 P
800 x 600 x
1600+ 100 P
Weight in kg. 150 275 275
Colour Havells Gray
InstallationFloor mounting. Lifting lugs provided
Cable Entry from bottom(From top Optional)
Ambient -5 to 40 0C
Humidity Up to 90 0 Rh, non condensing
OptionRemote monitoring through MODBUS,
SNMP, Web browser
Standards
• Meets IEEE 519 for compensatedharmonics.
• IEC 62040 Part II for conductedemission. Class A, for restricted use.
Potential free
contactsFilter Trip and Filter ON
B. Only Harmonic Correction
Input Current 146 A
VTHD 3.7 %
PF 0.92
DAPC Current 48 A
Voltage 221 V
ITHD 4.0 %
Power 93 kW
Figure 11
C. PF + Harmonic Correction
TEST RESULTInput Current 135 A
VTHD 2.2 %
PF 1.00
AF Bridge 95 A
Voltage 223V
ITHD 3.9 %
Power 93 kW
120 kVA UPS Tested with AF-150 A
A. Without Active Filter
Input Current 164 A
VTHD 4.8 %
PF 0.87
Voltage 217 V
ITHD 27.4 %
Power 93 kW
Figure 12
Figure 10
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Application areas Active Filter Sizing Calculator
1. At the Input side of Rectifier, AC Drive, UPS
Harmonic & PF compensation
Figure 13 Figure 16
Active Filter Sizing is a tool developed to find the required size
of the DAPC.2. PF Compensation
The data gathered at the site, where the DAPC is required to be
installed, need to be inserted in to appropriate fields of Active
Filter Sizing calculator. It will then size the DAPC and its output
characteristic will also be displayed.
Figure 14
Following are the details for the Active Filter Sizing Calculator :
Load Current - Here enter the per phase current in Amp of the
Load.
ITHD % - Enter the Current Total Harmonic Distortion
measured on the load side.
KW – Calculate the total power in KW, consumed by the load.
PF – The Load power factor.
Nom Volt Ph to Ph – Enter the Phase-to-Phase voltage.
After entering all this data, please check what type of Power
Factor compensation is required at the site. Though Unity is
always better, the cost implication for achieving it need to be
considered. Click the radio button for the percentage required.
(in the above example it is clicked at 50%)
3. At the source input
Figure 15
Now press calculate button to get the following results;
Output Effective Power factor
Output Filter Current
The “filter current” field is the required size of the DAPC.
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