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© 2009 DB Power Electronics (P) Ltd. All rights reserved. No part of this publication may be used, reproduced, photocopied, transmitted or stored in any retrieval system of any nature, without the written permission of the copyright owner. www.dbups.com MK-IND-WP-AHF-R2-0909 1

Active Harmonic Filter

(AHF)

Written and Compiled by

Shivaji Waghmare

General Manager - (R & D)

DB POWER ELECTRONICS (P) LTD. Pune


Table of Contents

INTRODUCTION............................................................................................................................ 3

HARMONIC DISTORTION SOURCES AND EFFECTS ............................................................................. 3

HARMONIC FILTERING AND REACTIVE POWER COMPENSATION ....................................................... 3

PASSIVE FILTER ........................................................................................................................... 3

(A) 3-PHASE LINE REACTORS .......................................................................................................... 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

ACTIVE HARMONIC FILTER (AHF) FROM DB .................................................................... 7

INTRODUCTION ............................................................................................................................... 7

OPERATING PRINCIPLE .................................................................................................................... 7

POWER CIRCUIT .............................................................................................................................. 7

PROTECTIONS .................................................................................................................................. 7

ALARMS AND PARAMETER DISPLAY .................................................................................................. 8

LOCAL ALARMS .............................................................................................................................. 8

INDICATIONS .................................................................................................................................... 8

FEATURES AND SPECIFICATIONS ......................................................................................... 8

FEATURES ....................................................................................................................................... 8

SPECIFICATIONS .............................................................................................................................. 9

TEST RESULT ................................................................................................................................ 9

120 KVA UPS TESTED WITH AHF-150 A ....................................................................................... 9

APPLICATION AREAS ............................................................................................................... 10

ACTIVE FILTER SIZING CALCULATOR .............................................................................. 10


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. Equipment

which 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


(b) Tuned single arm passive filter

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.

Figure 1 - Tuned single arm passive filter.

Detuned - Single tuning frequency

Above tuned frequency harmonics absorbed

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 has

several 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 2 - Tuned multiple arm passive filter.

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.

(c) Phase Multiplication Method

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

Manufacturing cost 120%. AC or DC choke added.



100% 30% 12% 8.9% 5.6% 4.4% 4.1%

Figure 3

12-pulse with double wound transformer



100% 3.6% 2.6% 7.5% 5.2% 1.2% 1.3%


Figure 4

24-pulse rectifier


ACTIVE FILTER

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.

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.

Shunt Active filter

Fundamental only

Supply

ActiveFilter

i compensation

i distortion

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.

Clean Feedercurrent

Harm

onic

sW

avefo

rms

Loadcurrent

Active filtercurrent+

Figure 6


Comparative Study of Different Filters

Parameters Capacitor filter Tuned filter Active filter

Type Passive Passive IGBT based digitally

controlled

Compensation Only compensates power

factor

Compensates Harmonic Multiple

tuned filters are required, one for

each harmonic

Compensates PF and

Harmonics. One filter can

compensate multiple

harmonics simultaneously

Suitability

Not suitable in case of

more voltage distortion and

current distortion

Performance varies over

frequency variation and variation

in voltage distortion.

Performance is dependent on load

level

Performance remains

constant over frequency

and voltage variation.

Suitable in any type of

environment

Resonance

Possibility of resonance.

This results in premature

failure of capacitor.

Possibility of resonance if tuned

at higher frequency. Performance

depends on source impedance

No possibility of

resonance. Stable

operation

Size and weight Bulky in size Bulky in size when multiple

harmonics are to be compensated

Light weight. Size does

not change even if

required to compensate

more harmonics

Life

Limited life in case of more

voltage and current

harmonics

More life as compared to

capacitor filter

Longer life, since

performance remains

constant and resonance is

avoided

Cost Cheap Costlier as compared to capacitor

filter

Initial cost is more as

compared to both the

filters

No load condition

Imposes capacitive PF

when load is reduced.

Contactors are required to

compensate for leading pf.

Imposes leading PF at

fundamental frequency. So not

suitable for generator source.

Compensated filter is required for

generator. Performance is tuned

at full load

No capacitive PF at no

load. Smooth PF

compensation. No problem

to Generator source.

Performance remains

constant over load

variation

3rd harmonic

compensation Not possible Becomes very bulky

Same filter can be used to

compensate 3rd harmonic

without increasing the size

Selectivity And

harmonic

Compensation

No selectivity Physical components are required

to be changed

Stability through software.

Cost vs. performance is

easily possible. This

makes it more cost

effective and flexible

Capacity increase Possible by adding more

capacitor

Redesigning is required for

change of load.

More units can be added

later 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 transient

voltage absorbers must be used to

avoid of other circuitry in case of

resonance

Only one set of Breakers

and fuses are required for

all harmonics

Power loss Low loss More loss Moderate losses


Active Harmonic Filter (AHF ) from DB 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.

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.

Figure 7

Operating principle

It 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.

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 trained

user or DB service engineer with the help of configuration

software working on PC. Non-zero sequence 3rd to 31st

Harmonics (i.e. 5th ,7th, 11th, 13th, 17th, 19th, 23rd, 25th, 29th

& 31st) can be easily selected for their compensation. Also

Programmable harmonic reduction is possible.

Reactive compensation

Along with harmonic compensation AHF 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.

Load balancing

Active filter can be used to balance loads between three phases

in case of unbalance load.

Selectivity

User can select whether to compensate both harmonics and PF or

to compensate either harmonics or power factor (Displacement

factor).

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.

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 AHF

Protections

AHF is protected against

Slow protection and

Fast Protection

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, AHF is automatically isolated from input.

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.


Fast acting protections

These are achieved by using;

1. High speed semiconductor fuses

2. High speed protection to IGBTs.

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.

Dual levels with different delays DC Over voltage protection

with hardware and software.

300% over current protection for IGBT. (Redundant protections)

It is ensured that IGBT is protected against all severe operating

conditions.

FMECA statistical techniques are used for these protections.

Appropriate alarm is provided for all Faults and Alarms

conditions.

Alarms and Parameter Display

Figure 9 - Front Panel LCD Display on AHF

Remote as well as local alarms are provided for getting the status

of AHF

Following parameters are displayed locally as well as remotely;

1. Status 11. No.of failures

2. ID 12. Total Filter ON Time

3. Input Voltage 13. Alarm log

4. Input Voltage Waveform 14. Power Factor

5. Input Voltage FFT 15. DC Bus Voltage

6. Input Current 16. Filter Load %

7. Input current Waveform 17. Mains Frequency

8. Input current FFT 18. Heat Sink Temperature

9. Input Power (KW) 19. Date & Time

10. Input Power (KVA)

Local Alarms

A user friendly LCD display, along with Keypad is used locally

to indicate parameters, alarms and faults. Following alarms are

provided on LCD;

1. Wrong Phase sequence 8. Over load

2. External Inhibit 9. Over Temperature

3. Fast DCOV 10. Over Current

4. Rph CTFB Wrong 11. No Sync

5. Yph CTFB Wrong 12. Mains Abnormal

6. Bph CTFB Wrong 13. DC Under Voltage

7. DC Overvoltage 14. Filter Trip

External Inhibit. (Includes filter off due to hardware protections

and ON/OFF switch operation).

Indications

Following LED indications are provided on the display.

1. Ok (Filter running)

2. Alarm

3. Warning

Remote alarms

Voltage free contacts are provided for

1. Filter running

2. Fault

Monitoring of filter through PC is possible by

1. MODBUS & EDAPC-MON connectivity

2. Monitoring through SNMP and web browser LIFENET

(optional features)

Features and Specifications Features Synchronous Rotating Reference Frame principle

32 bit, DSP control

Employees high speed IGBTs in power circuit

Internal CAN Communication

Closed loop active filter with source current sensing

High attenuation up to 96 % of individual harmonics

Programmable selective harmonic elimination

PF compensation, leading as well as lagging

Load Balancing

Required PF can be set from 0.7 to unity

Selection between PF and harmonic compensation

Remote monitoring and diagnosis

Self current limiting, under overloading condition

Automatic current limit modification with respect to

ambient temperature

Alarm log with date and time stamp for fault diagnosis


Specifications

3 phase / 3 wire non-zero sequence compensation

Parameter Swan+ 60 Swan+ 100 Swan+150 Swan+ 300

Input Voltage

range

400 V, 3 Ph +10%, -15%, 50 Hz

(60 Hz optional)

Input

Frequency

range

45 to 55 Hz (for 50 Hz)

Capacity 60 A 100 A 150 A 300 A

Harmonic

Filtering

Non-zero sequence 3 rd to 31st harmonic

compensation.

Attenuation ratio up to 96%

Power loss in

filter < 2200 w < 3600 w < 5100 w < 7200 w

IP Protection IP 40

(IP41 optional)

Dimensions

(mm) (WxDxH)

800 x 600

x 1000

+150 P

800 x 600 x

1600

+150 P

800 x 600 x

1600

+150 P

1200 x 900

x 1600

+ 150 P

Weight in kg. 150 285 285 600

Colour Hawells Gray (RAL 7035)

Installation Floor mounting. Cable Entry from bottom

(Top Entry - Optional)

Ambient Temp. 0 to 40 °C

Humidity Up to 90 % RH (non condensing)

Optional Remote monitoring through EDAPC-MON,

MODBUS, SNMP, Web browser & LIFENET

Standards

Meets IEEE 519 for compensated harmonics

IEC / EN 62040-2 : Category C3

EN 50178

Potential free

contacts Filter running and Fault

TEST RESULT

120 kVA UPS Tested with AHF 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 10

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

Input Current 135 A

VTHD 2.2 %

PF 1.00

AF Bridge 95 A

Voltage 223V

ITHD 3.9 %

Power 93 kW

Figure 12


Application areas 1. At the Input side of Rectifier, AC Drive, UPS

Harmonic & PF compensation

Figure 13

2. PF Compensation

Figure 14

3. At the source input

Figure 15

Active Filter Sizing Calculator

Figure 16

Active Filter Sizing is a tool developed to find the required size

of the AHF.

The data gathered at the site, where the AHF is required to be

installed, need to be inserted in to appropriate fields of Active

Filter Sizing calculator. It will then size the AHF and its output

characteristic will also be displayed.

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 needs to be

considered. Click the radio button for the percentage required.

(in the above example it is clicked at 50%)

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 AHF.

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