active harmonic filter

second generation of high power active harmonicconditioner based on the current injection principle

MGE UPS SYSTEMS MGE0121UKI - 06/98 1

authors:n Serge BERNARDn Grard TROCHAIN

page

n abstract...............................................................................................2

1. introduction......................................................................................3

2. topologies of active harmonic conditioners....................................4n series conditioners................................................................................4

n pararrel conditioners..............................................................................4

n hybrid conditioners................................................................................5

3. second generation of parallel active harmonic conditioner:system description ..............................................................................6n operating principle.................................................................................6

n recording of real currents.......................................................................6

n detailed description...............................................................................7

n product range description.......................................................................8

4. points of connection and configuration ......................................... 10n point of connection of the active conditioner........................................... 10

n parallel configuration............................................................................ 11

n cascade configuration.................................................................... 11

5. application tests results ................................................................ 12n 60 A conditioner upstream a three phase UPS......................................... 12

n 30 A conditioner connected between the UPS output and computer loads

(case study).......................................................................................... 13

n 60 A conditioner upstream of computer loads.......................................... 14

n 60 A conditioner upstream of computer loads, compensating only 3rd

harmonic............................................................................................... 15

n 120 A conditioner upstream of a variable speed drive............................... 16

n 30 A conditioner upstream of a 40 kW variable speed drives (case study)...18

6. comparison between harmonic conditioner and tuned passive(LC) filter............................................................................................. 19

7. conclusion ..................................................................................... 20

appendice 1 ....................................................................................... 21n references......................................................................................... 21

second generation of high power active harmonicconditioner based on the current injection principle (cont.)


In little more than ten years, electricity power quality has grown from obscurityto a major issue.

Particularly, the increasing penetration of power electronics-based loads iscreating a growing concern for harmonic distortion in the AC supply system.Then, electricity power quality is a major issue for utilities and for theircustomers, and both are quickly adopting the philosophy and the limits proposedin the new International Standards (IEC, EN, BS, IEEE).

Consequently, power conditioning equipment is becoming more important forelectric utilities and their customers.

Up to now, various harmonic mitigation equipment or solutions have beenproposed. Most of them are of the passive type: transformers, tunedpassive filters, series reactors. Actually, these solutions experience somedisadvantages such as limited attenuation, high cost, risk of system resonanceand destruction of phase displacement capacitors.

Hopefully, recent advances in power electronic technology are now providing anunprecedented capability for conditioning and compensating harmonic distortiongenerated by the non-linear loads, thanks to the active harmonic conditioner oractive filters.

Among the various topologies of Active Harmonic Conditioner, MGE UPSSYSTEMS has selected the parallel or shunt topology.

After a review of the existing active conditioning technologies, the paperevaluates the second generation of a three phase Active Harmonic Conditionerdesigned by MGE UPS Systems. Its principle is based on the injection, at theconnection point, of the image of the harmonic current consumed by the load.The conditioner architecture is described, as well as the new innovativefeatures.

This second generation of active conditioners uses the most advancedtechnologies, such as IGBT's and DSP, resulting in an unmatched compactnessand low cost solution combined with unsurpassed harmonic reduction.

The paper describes the two methods of harmonic compensation, global or FFT , as well as the method of phase displacement compensation.

Harmonic currents from orders 2 to 25 are reduced with a minimum attenuation of10:1 of the total harmonic current distortion. The results of the tests, carried outboth in laboratory and in the field, are presented to demonstrate the here aboveexcellent performances, whatever is the type of load.

Also, this second generation is extremely compact. By using the most advancedtechnologies, and a high level of integration of the sub-assemblies, the size ofthe conditioner was drastically reduced.

Finally, this new innovative active conditioner offers ease of use, with highdegree of flexibility, and very low heat rejection. It is cost effective, withcapability to compensate up to 360 A rms of harmonic currents (excludingfundamental).

abstract

1. introduction


Today, the situation on low-voltage AC systems has become a serious concern.The quality of electrical power in commercial and industrial installations isundeniably degrading.

In addition to external disturbances, such as outages, sags and spikes due toswitching and atmospheric phenomenon, there are inherent, internal problemsspecific to each site, resulting from the combined use of linear and non-linearloads.

Untimely tripping of protection devices, harmonic overloads, high levels ofvoltage and current distortion, temperature rise in conductors, transformers andgenerators all contribute to reducing the quality and the reliability of a low-voltage AC systems.

The above disturbances are well understood and directly related to theproliferation of loads consuming non-sinusoidal current, referred to as non-linear loads . This type of load is used for the conversion, variation andregulation of electrical power in commercial, industrial and residentialinstallations.

The prospect of a rapid return to linear-load conditions will remain a dream.Recent studies show that the consumption of non-linear current will sharplyincrease in the years to come.

However, the remarkable progress acheived in the field of power electronicdevices in the recent years, fast IGBT's, makes it possible to design and offerself adaptable harmonic suppressors called Active Harmonic Conditioner,known also as Active Filters. Active Harmonic Conditioners are proving to beviable option for controlling harmonic distortion levels across a wide band ofharmonics.

2. topologies of active harmonic conditioners


The idea of Active Harmonic Conditioners, also named Active Filters, isrelatively old, however the lack of an effective technique at a competitive priceslowed its development for a number of years.

To-day, the wide-spread use of IGBT components, mastery of theirimplementation and the availability of new digital signal processing (DSP)techniques are pavingthe way to a much brighter future for the Active Harmonic Conditioner.

The Active Harmonic Conditioner concept uses power electronics to produceharmonic components which cancel the harmonic components of the non-linearloads. A number of different topology are being proposed, and some of them aredescribed here after. Within each topologies there are issues of requiredcomponents ratings and method of rating the overall conditioner for the loads tobe compensated.

This type of conditioner, connected in series in the distribution network,compensates both the harmonic currents generated by the load and the voltagedistortion already present on the AC system. This solution is technically similartoa line conditioners and must be sized for the total load rating.

NL

load

Active

Conditsource

Fig. 01 - NL = non-linear

Also called shunt conditioners, they are connected in parallel with the AC lineand need to be sized only for the harmonic power (harmonic current) drawn bythe non linear load(s). The parallel topology selected for SineWave is in no waydependent on the load or electrical AC system characteristics. It is described indetail in the section 3.

Active

Condit

sourceNL

load


series conditioners

parallel conditioners

2. topologies of active harmonic conditioners (cont.)


This solution, combining an active conditioner and a passive filter, may be eitherof the series or parallel type. In certain cases, it may be a cost-effectivesolution.

The passive filter carries out basic filtering (5th order, for example) and theactive conditioner, due to its precise and dynamic technique, covers the otherharmonic orders.

Active

Condit

sourceNL

load


hybrid conditioners

3. second generation of parallel active harmonicconditioner: system description


The Active Conditioner is connected in-parallel with the AC line, and constantlyinjects harmonic currents that precisely correspond to the harmonic componentsdrawn by the load. The result is that the current supplied by the power sourceremains sinusoidal.

ActiveHarmonic

Conditioner

Non-linear

loadPowersource

Ic

Is II

I load = I fundamental + I harmonicI conditioner = I harmonicI load = I source + I conditioner

Fig. 04 - Active harmonic compensation principle

Hence, the only source supplies the load with the fundamental component of thecurrent.

The normal power source provides the fundamental current, and the harmoniccurrents required by the load are supplied by the Active Harmonic Conditioner(AHC).

The entire low-frequency harmonic spectrum (H2 to H25) is supported.

If the harmonic currents drawn by the load are greater than the rating of theActive Conditioner, the Conditioner automatically limits its output current to itsmaximum rating,therefore avoiding overload situation.

Easy to implement, an active conditioner may be installed at any point on a low-voltage AC network to compensate the power drawn by one or several non-linearloads, thus avoiding the circulation of harmonic currents throughout the low-voltage AC distribution system.

s0,010 0,015 0,020 0,025 0,030 0,035 0,040 0,045

V

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0C:(0,0 s, -1,58181 V) Fichier 1

I load = load current (Graetz bridge)I rms = 82 A THDI = 41 %

Fig. 05

operating principle

recording of real currents

3. second generation of parallel active harmonicconditioner: system description (cont.)


s0,010 0,015 0,020 0,025 0,030 0,035 0,040 0,045

V

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

C:(0,0 s, 0,49542 V) Fichier 1

I conditioner, I rms = 30 A

Fig. 06

s0,005 0,010 0,015 0,020 0,025 0,030 0,035 0,040 0,045

V

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

C:(0,0 s, 0,77771 V) Fichier 1

I source = source currentI rms = 75 A THDI = 3.6 %

Fig. 07

FU1

R1

Cf

Lf L1CT2

K1

C2

C3

CT1EXTRACTION

OF HARMONICS

LOAD

SOURCE

REGULATION

GENERATION OF

CONTROL SIGNALS

INVERTER LEG

CONTROL ELECTRONICS

Ih

Im

Udc

AND MONITORING

Control Signals

Fig 2

Fig. 08 - Active conditioner single-line diagram

The Active harmonic Conditioner is made up of the following elements:n R1 and contactor K1: precharge system for electrolitic capacitors C2 & C3;n Lf & Cf: filter intended to attenuate the effects of chopping;n L1, DC/ac converter, C2 and C3: PWM inverter leg;n CT2: current transformers for inverter currents;n control electronics;n CT1: external current transformer for current drawn by the load.

detailed description



The converter comprises of a three phase IGBT current inverter leg that chopsat an average switching frequency of 16 kHz, electrolitic capacitor C2 and C3providing back up energy. The conditioner draws from the power source only theactive power required for its operation.

The control electronics comprise:n an harmonic-extraction module which generates a regulation set pointproportional to the harmonic components of the load current;n a module that regulates inverter currents and the DC voltage;n a monitoring module which ensures filter protection in the event of overload oran internal fault;n a control module which generates the control signals necessary for inverteroperation.

To enhance the compensation current capacity at a given point in theinstallation,it is possible to connect up to three active conditioners in parallel.

n power ratings and main characteristics:The first generation of Active conditioner was limited to one single power rating(30A).

This second generation is composed of six power ratings: 20, 30 45, 60, 90, and120 A rms of harmonic compensation at 400 V three phases, 3 or 4 wires, 50 or60 Hz.

Harmonic currents from 2nd order to 25th order are compensated, with aminimum attenuation ratio of 10:1 of the Total Harmonic Current Distortion(THDI).

Response time is lower than 40 ms.

sinewave

Fig. 09

n features:Thanks to multi-language graphic interface, users can access:o measurements such as % load, Irms, THDI, harmonic spectrum, line voltage;o status and alarms, diagnosis and help menu;o personnalisation: selection of language, compensation of phase displacement.

product range description



F1 F2 F3

7 8 9

4 5 6

1 2 3

0 RUN

ENT

ESC

STOP

Fig. 10



n methods of harmonic compensation:Two methods are proposed:o the global method allows for compensation of the harmonics andinterharmonics, and is really suited to the unstable and fluctuating loads;o the FFT method , allows for compensation of the harmonics andinterhamonics, and also for a given (user selectable) harmonic order. It is mainlysuited for stable loads, and offers a greater level of attenuation than the globalmethod.

In addition to the harmonic compensation, the Active Harmonic Conditioner canalso compensate the phase displacement. Therefore, power factor can be unity.

n size (in mm):

sinewavesinewave

sinewave

SW 20/30 SW 45/60 SW 90/120H x L x D:680 x 540 x 280 780 x 590 x 325 (2 x 780) x 590 x 325

Fig. 11

The second generation 30 A Conditioner is only 1/7th of its previous size.

The compactness of the unit allows for either wall mounted installation orintegration within LV distribution switchboard.

n cost:Thanks to the integration of advanced technologies (DSP, SMD, microcontroler),and to the use of variable speed drive converter bridges produced in highquantities, the cost was drastically reduced.

Expected price on the market is between US $ 200 and 300 per Amp rms ofcompensated harmonic, depending on the power rating.

This new generation of Active Conditioner is to very cost-competitive whencompared with the bulky tuned passive (LC) filter.

4. points of connection and configuration (cont.)


finalpanelboard

feeder S1 feeder S2 feeder S3

LOADS

AHC

AHC

AHC

C

B

A

secondary

switchboard

main low-voltage

switchboardMLVS

feeder MS1 feeder MS2 feeder MSn

MV

LV

M M M

Fig. 12 - Three level radial low voltage AC distribution system

The Active Conditioner may be installed at different points in AC distributionsystems:n centrally, at the CPC level, for global compensation of harmonic currents(position A);n partial compensation of harmonic currents (position B);n close to the loads generating high level of harmonic pollution to ensure localcompensation of harmonic currents (position C).

Ideally, compensation of harmonics should take place at their point of origin.A number of costing and technical criteria are used for optimum solution. Inorder to optimize the harmonic compensation, several conditioners may beconnected in various configurations.

These configurations can be used at any point in the AC distribution system,offering a total flexibility and a large choice of compensation strategies. Themost common configuration are described in the next two paragraphs.

point of connectionof the active conditioner

4. points of connection and configuration


This configuration meets two different requirements:n increased compensation capacity at a given point of the AC system byconnecting up to three conditioners of the same rating;n increased compensation capacity for any future load expansion;n improved reliability by using conditioner of the same rating in redundantoperation mode.

sinewave sinewave

Fig. 13

This configuration have the following benefits:n increase the overall compensation capacity using conditioner of the same ordifferent rating;n compensate partly and locally the harmonics or a specific harmonic order of agiven load, and compensate globally a group of non linear loads.

sinewavesinewave

Fig.14

parallel configuration

cascade configuration

5. application tests results (cont.)


This section describes the waveform and the characteristics of the currentsupplied by the power source to different types of loads, with and without ActiveHarmonic Conditioner of various ratings.

The data presented below is the result of in-depth study of several differenttypes of pollutant loads both in house and on site. The figures demonstrate thecompensation levels achieved with typical applications, in industry and incommercial buildings.

-1,5

-1

-0,5

0

0,5

1

1,5

Fig. 15 - Line (load = source) current waveform without Active Conditioner

-1,5

-1

-0,5

0

0,5

1

1,5

Fig. 16 - Line (source) current waveform with Active Conditioner

0102030

405060708090

100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21

Fig. 17 - Line (load=source) current spectrum (% of H1) without Active Conditioner

60 A conditioner upstreama three phase UPS

5. application tests results


010

2030405060

708090

100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21

Fig. 18 - Line (source) current spectrum (% of H1) with Active Conditioner

Conclusion:For three phase rectifiers as a load, the characteristics of the active harmonicconditioner at its full rating are per following:n attenuation ratio: 12:1 (from 30.4 % to 2.6 %);n improvement of the power factor from 0.84 (without conditioner) to 0.89 (with).

-2-1,5

-1-0,5

00,5

11,52

Fig. 19 - UPS output load current waveform without Active Conditioner

-1,5

-1

-0,5

0

0,5

1

1,5

Fig. 20 - UPS output load current waveform with Active Conditioner

30 A conditioner connectedbetween the UPS output andcomputer loads (case study)



-1

-0,5

0

0,5

1

Fig. 21 - UPS output voltage waveform without Active Conditioner

-1,5

-1

-0,5

0

0,5

1

1,5

Fig. 22 - UPS output voltage waveform with Active Conditioner

Conclusion:The characteristics of the 30 A active harmonic conditioner at 87 % its full ratedcapacity, with harmonics compensation limited to 13th order, are:n THDI attenuation ratio: 12:1 (from 82.6 % to 9 %);n reduction of 21 % in the UPS output current RMS value;n improvement of the power factor from 0.73 (without conditioner) to 0.98 (with).

Fig. 23 - Line (load=source) current waveform without Active Conditioner


60 A conditioner upstreamof computer loads



0

10

2030

4050

6070

80

90100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21


0102030405060708090

100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21

Fig. 26 - Line (source) current spectrum (% of H1 ) with Active Conditioner

Conclusion:For computer loads, the characteristics of the 60 A active harmonic conditionerat 100 % of its full rated capacity are:n THDI attenuation ratio: 32:1 (from 92.6 % to 2.9 %);n reduction of third-order harmonic and their multiples circulating in the neutralcurrent;n reduction of 21 % in the line current RMS value;n improvement of the power factor from 0.73 (without conditioner) to 1.0 (with).

-2

-1

0

1

2


60 A conditioner upstreamof computer loads,compensating only 3rdharmonic



-1,5

-1

-0,5

0

0,5

1

1,5


0102030405060708090

100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21


010203040

506070

8090

100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21



120 A conditioner upstreamof a variable speed drive




0102030405060708090

100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21


01020

30405060

708090

100

H1 H3 H5 H7 H9 H11 H13 H15 H17 H19 H21


Conclusion:For such loads as variable speed drives, the characteristics of the activeharmonic conditioner are:n attenuation ratio: 9.3:1 (from 124.3 % to 13.4 %);n reduction of 30 % in the line current RMS value.



-1,5

-1

-0,5

0

0,5

1

1,5


-1

-0,5

0

0,5

1

Fig. 36 - Line (source) current waveform active with Active Conditioner

0

10

20

30

40

5060

70

80

90

100

H1 H5 H7 H11 H13 H15


30 A conditioner upstreamof a 40 kW variable speeddrives (case study)



0

10

20

30

40

50

60

70

80

90

100

H1 H5 H7 H11 H13 H15

0

10

20

30

40

50

60

70

80

90

100

H1 H5 H7 H11 H13 H15


Conclusion:For this load, the characteristics of the active harmonic conditioner, withharmonics compensation limited to 13th order, are:n attenuation ratio: 9:1 (from 20.5 % to 2.3 %);n reduction of 5 % in the line current RMS value.

6. comparison between harmonic conditioner and tunedpassive (LC) filter


LC passive filter active harmonicconditioner

harmonic-current control requires a filter for eachfrequency (bulky)

simultaneously monitorsseveral frequencies

influence of a frequencyvariation

reduced effectiveness no effect

influence of a modification inthe impedance

risk of resonance no effect

influence of an increase incurrent

risk of overload and damage no risk of overload, but lesseffective

added equipment (load) in certain cases, requiresmodifications to the filter

no problem if I-conditioner > I-load-harmonics

harmonic control by order very difficult possible via personalisations

modification in the fundamentalfrequency

cannot be modified possible via repersonalisationof software

dimensions large small

weight high low

losses average average

7. conclusion


The second generation of shunt topology Active Harmonic Conditioners,ranging from 20 to 120 A rms, is successfully developed, and will be launchedduring early part of 1997.

The tests carried out, both in laboratory and in the field, demonstrate excellentperformances for a wide range of applications. The active harmonic conditionercan control and compensate harmonic currents for all types of non linear loads,including high neutral harmonic currents. Harmonic order from H2 to 23 arecovered with a high THDI attenuation ratio (minimum 10:1).

The unique features at competitive cost gives very good reasons to expect in avery short time the development of active harmonic conditioners market, fromlow to high compensation power ratings.

High rise intelligent buildings and industrial applications are the prefered fields ofapplications for this new generation of active conditioners.

appendice 1


G W Massey, Power Distribution System Design for Operation Under Nonsinusoidal Load Conditions , IEEE Trans. Ind.Applic., vol.31 n 3, may/june 95.

S Fukuda and T Endoh, Control Method for a Combined Active Filter SystemEmploying a Current source Converter , IEEE Trans. Ind. Applic., vol. 31 n3,may/june 95.

T Deflandre, C Courty, C Greiveldinger, EDF, Impact des Harmoniques sur lesRseaux Publics Franais , PPRD ,1995.

T Key and J S Lai, Costs and benefits of Harmonic Current reduction forSwitch-mode Power Supplies in a Commercial Building , sept 1995.

W Russell, Hardening data Lines to IEC 1000-4-2, Compliance EuropeanEdition , jan/fen 1996.

J Moravek, Benefits of Using a harmonic monitoring Program , EC&M, sept.1994.

L Lachaume and JM Vialars, Electric Energy Metering in Presence ofHarmonics , EDF study, nov. 1994.

R Waggoner, Beware of Single-phase Harmonic interactions , EC&M,jun.1994.

P N Enjeti, W Shiren, P Packebush, I Pitel, Analysis and Design of a newactive Power Filter to Cancel Neutral Current harmonics in Three-phase Four-wireElectric Distribution Systems , IEE Trans. Ind. Applic., vol. 30 n6, dec.1994.

S Bernard, G Trochain, A New High PerformanceActive HarmonicConditionerBased on the Current Injection Mode , Power Quality 95, nov. 1995 .

M Mc Granaghan, L Tang, S Beranrd, S Papoz, Evaluation of Active FilterDesign and performance Using a Detailed EMTP Model , PQA 95, may 1995.

H Akagi, New Trends in Active Filters , EPE 95, sept 1995.

T Key, JS Lai, Comparison of Standards and Power Supply Design Options forLimiting Harmonic Distortion in Power Systems , IEEE Trans. Ind. Applic. , vol29 n4, jul/aug 1993.

references

active harmonic filter

Documents

active conditioner

n references

n parallel configuration

n series conditioners

n cascade configuration

n point of connection

ups output

phase ups