SAFACTIVE FILTER - COMAR CONDENSATORI SpA

UNI EN ISO 9001:2000 

C 

E 

R 

T 

I 

F 

MANAGEMENT 

I 

E 

D 

SYSTEM 

ec 

UNI EN ISO 14001 

H&S 

OH SAS 18001 

SAF ACTIVE FILTER

Shunt active filters for 

active compensation of 

harmonic currents 

The COMAR factory, established in 1968, was built with the future in 

mind. By installing superior equipment the factory has remained 

technologically advanced even by to-day’s standards. Originally, the 

production was based on a wide range of “oil-paper” capacitors. The 

quality of the product was such that the COMAR brand was soon 

acknowledged both in Italy and world wide. A large investment in 

research and development during this early period made it possible 

to commence production of the innovative metallized polypropylene 

film capacitors. The capacitors became part of the standard range in 

the 1972 and are still produced by all the main manufactures in the 

capacitors market. In the following years, the range was enlarged by 

addition of electrolytic capacitors and capacitors specifically for power 

electronics. Power factor correction equipment and power factor 

regulators were also developed in this period. 

Within recent years, because of the diffusion of static power converters, 

COMAR has examined and resolved the intricate problems of reactive 

compensation presented by harmonics. Their study of this subject 

has been so successful that COMAR is on of the leaders in this very 

demanding field. At present, due to the complete automation of all 

production lines and advanced test equipment it has been possible 

to increase production and improve the level of quality. This is COMAR. 

UNI EN ISO 9001 quality management system 

UNI EN ISO 9001:2000 

ec 

UNI EN ISO 14001 

UNI EN ISO 14001 enviromental management system 

H&S 

OH SAS 18001 

OHSAS 18001 occupational health and safety 

management system 

Products listed in the present catalogue are in conformity with: 

73/23/EEC Low voltage Directive, 89/336 Electro-Magnetic 

Compatibility and 93/68EEC Directive.

Index 

• Introduction ........................................................................................................................ 4 

• Why filtering ....................................................................................................................... 4 

• Operatine mode ................................................................................................................. 6 

• The hysteresis control ........................................................................................................ 8 

• SAF interface ..................................................................................................................... 9 

• Led interface .................................................................................................................. 10 

• Active filter performances ............................................................................................... 10 

• Sizing SAF ..................................................................................................................... 11 

• Connection of SAF ......................................................................................................... 12 

• The SAF system............................................................................................................. 13 

• SAF features .................................................................................................................. 14 

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3

Introduction 

In the last twenty years the fast introduction on the market of electronic equipment has brought along with 

their advantages many problems due to the noise on the electrical distribution network. In particular the most 

dangerous phenomena that degrades the power quality is the presence of harmonic currents generated by 

these non linear loads that are continuously changing their impedance during their working cycle, the 

absorption of current from the mains is not perfectly sinusoidal at the fundamental frequency, but is a sum of 

current with a different frequency multiple of the fundamental. 

Why Filtering 

These loads can cause many problems to the network and to the other loads connected. Here below is a list 

of some types of load that can generate harmonic pollution in the installation during our normal working day: 

‣ personal computers 

‣ welders 

‣ UPS 

‣ lifts/elevators 

‣ printers 

‣ motor speed regulator (AC and DC) 

‣ rectifier 

‣ semiconductor system with angle regulator 

‣ fluorescent lamps with ballasts 

‣ SMPS 

‣ frequency regulator 

Some of this equipment if considered alone does not have a large impact on the installation, but the 

influence they have on the network and the other loads connected to it became very important and can 

cause serious problems to the integrity of the network. 

Then other particular loads that work in critical conditions such as medical equipment (X-ray machinery, 

magnetic resonance equipment, etc.) not only can generate harmonic distortion in large amounts, but also 

they introduce harmonic pollution in an intermittent manner whilst rapidly changing their working conditions 

during a cycle of operation. 

So the harmonic currents generated by this load causes great problems and it is important to eliminate them 

not only for the immediate effects but also for the problem that can arise in the machinery, other equipment 

and the installation. 

Many problems can be caused by harmonics, the most common are: 

‣ vibration of motors 

‣ overheating of the cables 

‣ tripping of protective devices 

4 http://www.comarcond.com

The presence of harmonic current in the installation can be a large problem because while the 

equipment works coupled with the impedance network, it creates also voltage distortion: this distortion 

can have a so high level to introduce problems with the other connected equipments in the installation as 

in example: 

‣ vibration and overheating on the electric motors 

‣ noise and loss in the transformers 

‣ shortened life of components and conductors in the installation 

‣ erratic working of the control circuits that synchronize to the zero-crossing point of the sine wave. 

In fact there could be errors in reading the synchronizing signal 

‣ voltage difference between the neutral conductor and the protective conductor ( Ground / Earth ) 

‣ voltage fluctuation of the supply system 

‣ erratic operation of voltage or phase loss monitoring equipment 

Typical absorption current by a non linear load 

Then we have to consider the penalties that the electrical distribution companies charge to their customers 

for bad power factor correction due to harmonics. 

In order to solve all these problems in accordance with international regulations, the usually adopted 

standard is IEEE519 “Recommended Practices and Requirements for Harmonic Control in Electric Power 

System” this attempts to establish reasonable harmonic goals for an electrical system that contains non 

linear loads to satisfy both customer and distribution company requirements. 

The objective is to propose steady-state harmonic limits that are considered reasonable both for electrical 

utilities and their customers. 

The underlying philosophy is that the customer should limit harmonic currents; electrical utilities should limit 

harmonic voltage and both parties share the responsibility for holding harmonic level in check avoiding faults 

in installations and loads. 

To eliminate harmonic current a passive filter can be used. They are efficient but are also not suitable for 

some applications where their characteristics don’t exactly match the requirements: 

‣ the filter is difficult to dimension 

‣ when a change occurs in the filtered installation (for example: it could be necessary to connect a 

new machinery or to substitute an old one with new electrical features) the filter has to be changed 

‣ it has partial filtering 

‣ it has a very slow dynamic response, so it is not responsive to fast load variation 

‣ it’s easy to overload 

‣ there’s risk of electrical oscillation with the network impedance 

‣ the efficiency depends from the voltage network quality (harmonic voltage distortion) 

To overcome these growing technical problems Comar Condensatori S.p.A. has developed SAF, a new 

innovative active filter designed to eliminate the harmonic distortion phenomena due to industrial non linear 

loads (by its filtering action) and at the same time compensate the reactive power demand of the load (power 

factor correction) bringing the installation emission within the recommended levels of IEEE519. 

SAF is designed to correct latest generation electronic load harmonic problems. 


5

So: 

‣ it recognizes and compensates all the current up to the 50 th harmonic order 

‣ it has excellent dynamic response to fast load variation 

‣ it compensates if network features change due to new machinery or equipment in the installation 

‣ it is impossible to overload 

‣ it’s easy to size 

‣ every module is easily connected 

‣ it fits every kind of load so it will not be obsolete 

These good performance of SAF, with the possibility to connect it to existing an installation and its 

modular design allows the filter to give the right solution for every problem with harmonic pollution, 

in every kind of condition. 

Current from a non linear load (top) 

and his relative filtered current (bottom) 

Operating mode 

The active filter is based on “compensation”, that means that in order to eliminate in a three phase 

system the harmonic current absorbed by the non linear load, the filter from the current of the load, 

calculates and injects the same harmonics (over the fundamental) shifted by 180 degrees. It results in a 

complete elimination from the installation of the dangerous component of the current. 

Figure 1 

LOAD 

Active Filter operation scheme 

At the same way it is possible to have a power factor correction of the load, producing three sinusoidal shaped 

current waveforms, with an amplitude in line with the load. 

In order to understand how SAF operates, look at the picture below there are three different blocks, each one 

showing different operating stages of the Active Filter: 


Active Filter block schematic 

• Input block, it has: 

- Main break switch; fuses; 

- EMC filter; 

- contactor; 

- pre-charge circuit for electrolytic capacitors ; 

- line filter; 

The main break switch with automatic turn-off and the pre-charge relay, allows the filter to turn-off 

and completely disconnect from the network when a internal fault occurs. So that an internal 

malfunction of the SAF (i.e. capacitor / microprocessor etc.) doesn’t damage the installation. 

To guarantee rapid protection of the input line, the filter is connected with ultra-fast fuses. This 

protects the line from every internal problem such as short-circuit, overload, etc. Then the input filter 

avoids the emission of harmonic current at the switching frequency of the inverter bridge. 

• Inverter block it has: 

- semiconductor; 

- induction coil; 

- electrolytic capacitors; 

- heatsink; 

- fan; 

- power board; 

It’s the heart of the power module of SAF. 

It can be see as the actuator of the regulator block; in fact it converts the current set point (analog 

signal with low power given by the regulation, calculated from the load current) in a current that is in 

real time the same as the load harmonic current but 180 degree shifted. 

It is established by a typical six-switch semiconductor structure, IGBT technology based, with three 

smoothing induction coils and an electrolytic capacitor bank for the DC bus voltage. 

• The regulation, it has: 

- Microprocessor board 

With the regulation based on the hysteresis control, the active filter designed by Comar Condensatori 

S.p.A. adapts in real time its dynamic response to the real harmonic and reactive load request. 

The response at the amplitude of the harmonic load current is in real time so the harmonic 

mitigation is good even for loads with very quick variation of the working condition. 

These performances are guaranteed in every field of application and the dynamic characteristic of the 

control gives to SAF features hard to find in the market. 


7

Only harmonic 

compensation 

HP 

Filter 

Load 

current 

Line 

current ref. 

Total 

compensation 

Vdc_ref 

+ 

Vdc 

feedback 

– 

PI 

Regulator 

+ 

– + 

– 

I_SAF 

feedback 

Hysteresis 

control 

SAF current 

transducer 

SAF 

DC voltage 

transducer 

Control filter chart 

The hysteresis control 

The typical current emitted by Active Filter with a PWM modulation and hysteresis control is shown in the 

figure below where the current has a triangular shape with a carrier frequency of 10 kHz: 

This current is then modulated with the next rule: it changes continuously between the upper band and the 

bottom band, where it is forced to change. These two bands are shaped from the regulation block based on 

the load harmonic current and the internal regulation PWM control rules. 

Then a DC internal bus composed by two electrolytic capacitor banks, one with a positive potential and the 

other with a negative potential is the current source for the filter (so when the inverter block of the filter 

injects on to the network the “correcting” current it takes it from this bus). 

When SAF works, it switch on the upper side of the semiconductor bridge, the current flows to the load with an 

amplitude up to the upper band of the control shaped waveform (see t1 time in figure). 

Then this upper semiconductor is switched off and the lower side IGBT is switched on: so the current 


flows to the load from the negative potential, reaching the lower side of the band control 

shaped (t2 time in figure) 

With this operations a current wave shape as the calculated one is flowing to the network, after that the 

waveform is filtering by the induction coil working in high frequency. 

In the same way (with the same method of control) the filter can generate current to correct the reactive power 

of the load, giving at the same time correcting the harmonics. 

In order to give a full power factor correction of the load, where it is necessary a reactive power greater than 

the one available in the active filter, it is possible to connect external capacitor banks to satisfy the full 

reactive power demand. The control of these banks can be performed by the filter with a command from a 

volt free contact of a relay. 

Other important feature of the filter is the possibility to adapt itself to the maximum possible current. So that 

when a current higher than the rated one is needed, SAF doesn’t stop the operations and continue to give 

the current to correct the harmonic absorption of the load, limiting it’s self to the maximum rating without 

cutting out (this could introduce distortion on the network) but modelling in the best way possible the 

emission of the current. The critical condition is displayed with an alarm. 

SAF interface 

In the base version SAF is equipped with an easy interface, based on led indication and can effectively 

monitor the active filter operation, all the internal conditions, to allow for a fast diagnosis of any fault. 

It is also possible to use a volt free contact on the relay to give a remote indication of the alarm, the state of 

the filter, the control of other values or the control to switch-on the filter. 

The values shown in the display are also a part of all the possible state that the active filter can monitoring 

as security value, control variable, value of current or voltage of the network. 

A microprocessor continuously monitoring all the parameters of the system and the filter is working under its 

control every time. Sophisticated algorithms allow the equipment to work in the best condition possible so the 

internal components are always without electrical stress and consequently this increases their life. 

This kind of control: 

‣ limits the maximum current flowing; 

‣ keeps under control the voltage of the system and of the active filter; 

‣ runs in a security way the inverter switch by the control of the “blanking time” and the “dead time” 

inside with a precision about a microsecond; 

‣ monitors the three phase supply voltage of the network; 

‣ controls the current flowing when the power is the maximum rated even if the load is absorbing a 

current greater than the rated (so the filter doesn’t turn off); 

‣ checks the maximum temperature 

In addition to this basic easy version of the interface, Comar Condensatori S.p.A. provides an 

advanced interface that can monitor the values of all the parameters run by SAF: an alphanumeric 

display updated continuously in real time the changing values of: 

‣ network rms voltage and THD v 

‣ cosϕ 

‣ bus voltage DC 

‣ load rms current THD i 

‣ filter rms current 

‣ power absorption by the filter and the load 

‣ current rms value before the load connection 

So it possible to see the efficiency of the filter, monitoring the current before the load and the current after it. 

It is also possible to check the fault history in order to analyze them for fast error diagnostics. 


9

Led interface 

The easy basic interface allows with leds to understand the system operation and the changing internal 

state. 

In particular the green led monitors the right function of the system during the compensation, and the startup 

procedure, lighting in two different way to show the “pre-charge” operation and the “contactor on” 

operation. 

The four red leds are monitoring the fault that occurs in the filter: 

‣ Power supply out of the rated range (“Supply voltage”) 

‣ Fault of the contactor or of the inverter section start-up (“Contactor”) 

‣ Fault of the internal temperature (“Temperature”) 

‣ Fault on the inverter section (“Inverter”) 

Active Filter performances 

Harmonic pollution: in the following figure there are two waveform of the absorbed current of a typical non 

linear load before and after the filtering. In the upper wave a 42 Arms current with THD i of 73% is filtering 

and it results the lower wave with 38 Arms and a residual THD i of 8%. 

Absorbed current of a non linear load before and after the filtering 


Power factor correction: It is possible to select on the regulator board the possibility of a partial 

power factor correction while filtering with a good final result. 

Voltage and current before the filtering (left waveforms) and with the filter with both the 

operation of harmonic pollution and power factor correction (right waveforms) 

In the two pictures it is possible to see the initial displacement between the voltage and the current 

of a non linear load before filtering that is with the current affected by harmonics. In the right figure 

it is possible to see that after the filtering the current is not affected by harmonics and it is shifted to 

the left nearer the voltage waveform, improving the power factor. 

Current limit: When the harmonic current to be compensated is higher than the rated current of the 

filter connected, the equipment doesn’t stop its operation, but gives to the network a well shaped 

compensated current up to the rated limit. This permits to have compensation of the harmonic 

current even if not in the optimum mode, but without cutting off the compensating current at the 

rated value thus avoiding additional harmonics. 

Sizing SAF 

To understand which is the right size of the filter Comar Condensatori S.p.A. it is necessary to take some 

measurements on the installation in order to select the right reactive power of the fundamental component 

and of the other harmonics. 

For this measurement it’s necessary an instrument that can measure the harmonic components (oscilloscope; 

data logger etc.). 

It is so possible to have a series of value of current of the fundamental component (I1 50Hz ) and of the other 

harmonics as in the next example: 

I1 50Hz =30A, I5 250Hz =10A, I7 350Hz =5A, I11 550Hz =3A, I13 650Hz =1A, ..... 

or, that is the same, the value of the parameter of the harmonic current distortion: 

THD (Total Harmonics Distortion =X % 

THD is a number that represents the harmonic pollution and it mathematically given by the next expression 

where I means the rms value of the fundamental current: 

THD := 

I 2 

2 

2 

+ I + 3 

I + 4 

I + 5 

...... 

I 


11

If SAF is working also as a power factor correction equipment, it is necessary to measure the parameter 

cosϕ 1 for the fundamental components, remembering the relation Q 1 =V·I 1·sinϕ 1. 

Now it’s easy to find the right current for the filter for the reactive power compensation that is: 

( ) 

2 

I FA 

:= I . 1 sinφ 1 

+ ( ITHD . ) 

2 

When used only for harmonic mitigation it’s possible easily find out the formula giving a zero value to the 

sinΦ term in the expression. 

Connection of SAF 

The C.T.’s transformer are one of the most important part of the filtering system, because is from 

them that we can read the current to compensate. So this reading must be accurate and in order to 

read all the harmonic in the network, the quality should be high. And the secondary must be in 

according with the input stage of the regulator board of the filter. 

All these features combine to allow the component selection with Comar Condensatori S.p.A. after an 

accurate analysis of the plant. 


The SAF system 

The active filter has an extreme flexibility of connections in the existing plant and in the new ampliable 

installation. The possibility to insert a new filter in the installation with the easy connection of a couple of 

C.T.’s with the right dimension gives to the equipment great modularity speech. 

In every plant it’s easy to find a point for the connection of the current sensor (C.T.’s): for example inside a 

distribution panel or directly on the non linear load 

The filter has the possibility to be connected in parallel to increase the current to be compensated or in 

cascade to permit a new filter to be connected where an other filter is working before. 

So we can say that, SAF is the optimal solution to solve all the problems of filtering in harmonic current 

distortion. 


13

Power supply 

SAF features 

Supply Voltage 400 V ac (+10% -20%) 

Frequency 50 Hz / 60 Hz ± 1% 

Number of phase 

3 phase , 3 wire or 4 wire 

Type of load 

everything 

Standard C.T.’s 

Technical speech 

200 / 1A 1,5 kHz Cl. 0,5 not included 

Harmonic compensation 

Up to 50 order 

Response time 

< 1 ms 

Over load capability 

1,2 Irms 

Short circuit current 

120 kA, with fuse 

PFC 

Partial (selectable on board)) 

Load with dynamic variation 

Yes 

Connection in parallel or cascade 

Yes 

Compatibility with passive filter 

Yes 

Net impedance 

Yes 

Limitation of the rated current 

Yes 

High modularity 

Yes 

Easy dimensioning 

Yes 

Auto tuning 

Yes 

THDi residual after filtering < 10% 

Class of protection IP 41 

Noise 

< 60 dB 

Ventilation 

forced 

Display 

Standard 

Option 

led 

LCD 

Operation condition 

Operating temperature 0 – 40 °C 

Operating altitude 

< 1000 m o.s.l. 

Relative humidity Up to 95% 

Electromagnetic compatibility 

Immunity 

Emission 

EN50081-2 

EN50082-2 


Grafica Junior - Tel. 051.733020 

COMAR CONDENSATORI S.p.A. 

Headquarter: 

Via del Lavoro, 80 - CRESPELLANO (Bologna) ITALIA 

Export Department: 

P.O. Box 150 - 40011 ANZOLA EMILIA (Bologna) ITALY 

Tel. +39 051 733.383 - FAX +39 051 733.620 

Technical Department: project@comarcond.com 

Sales Department: export@comarcond.com 


I dati e le dimensioni possono essere modificati senza alcun preavviso. 

ED.02.62.ING REV.1 - Cod. 383026202

SAFACTIVE FILTER - COMAR CONDENSATORI SpA

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