Tag Archives: Active Filter

Active Harmonic Filter- Mitigation Of Harmonics in a Poor Power Quality Environment-Case Study

Doctor_Character-04-1 Hello Everybody today’s article is a case study from our beloved Advanced Power Quality Solutions team. They have very neatly narrated how they helped a Steel Rolling mill with a unique power quality problem to extract more business benefit by cutting down their power quality problems. Interesting read don’t miss it.

InPhase has come across many customers dealing with various Power Quality problems. Our strength lies in providing customized and unique solutions, keeping in mind the problems that the customer confronts. In this article we share our experience with one of our customer, their problems, losses, and solutions. This customer is one of the largest steel manufacturers in India. Their annual production is in Billions of Rupees, but their production began to fall and penalties from Electricity Board increased because of presence of harmonics in their plant. So they decided to install Active Harmonic Filter to mitigate harmonics in their plant.  Initially the company had gone with a well known brand of Active Harmonic Filter but the filters had miserably failed owing to the unique situation of the customer. Luckily the customer came to know about InPhase and  Our Active Filter  through a channel partner, and approached us. InPhase conducted a Power Quality Analysis and suggested a cost effective solution accordingly (which cost lesser than the initial solution that failed) despite the challenging problem. The problem faced by the customer is outlined here,

  • Harmonic currents were high, the THDi was between 17-20% which is higher than the IEEE 519-2014 norms.
  • High Voltage Notches were also present in the plant.
  • Presence of even order harmonics which is normally zero in other plants.
  • Hot rolling mill loads were highly fluctuating and load patterns were abnormal.
  • The voltage varied up to 470V which is an abnormal behaviour.

Here, the main challenge faced while giving solution was to suppress current harmonics or THDi to less than 8% in an environment with high voltage spikes and indefinitely fluctuating plant load condition.

SOLUTION PROVIDED BY INPHASE:  InPhase proposed 2 x 450 Amps, 415V Active Harmonic Filter (Model:IPC150-AHF-450-V415) with CAN-bus communication that acts as a single 900A system. Specially designed RC tank circuits were incorporated  to handle notches and rigorous algorithm for high fluctuating loads. This was the  most cost effective, as well as the technically correct method to handle the situation. The 2 number of AHFs were connected in BUS A & BUS B, as the load distributes in those buses. The whole system has been pictorially described in the diagram below.


The major loads used by the customer are electric pre-heating furnace and rolling mill that generates the maximum harmonic current leading to increased losses in transformer, overheating of cables and thus polluting the electric network. The LT loads distributed among the Bus A & B are connected by an ACB Bus Coupler (Normally Closed). AHF calculates harmonic current, reactive current and unbalance current present in the entire plant from the current signal received from the CTs of respective transformers through the summation CT. Based on the on the dominance of power quality issue (harmonic, power factor or unbalance current) at any instant the AHF system injects the respective compensation current. InPhase AHF can achieve high level of modularity of up to 32 Equipments in parallel. CAN bus communication is used to communicate between two Active Harmonic Filters and operate in parallel to inject up 900A of compensation current.


The graph indicates the harmonic currents of various orders (3rd to 13th) before and after installation of Active Harmonic Filter. The successful installation of 2 x 450A Active Harmonic Filter has reduced the THDi from 17% to 4-5%, well below than the limits mentioned in IEEE 514-2014. This solution has helped the customer not only to cut down penalties but also to reduce failure of sensitive equipments which are vulnerable to harmonics. Also, various production losses were averted. Overall, InPhase was able to solve a problem of harmonics in very poor power quality environment. This was another feather in InPhase‘s cap. We would be extremely happy to help customers who face such outrageous Power Quality problems because at InPhase we are happy to tackle power quality challenges for our customers.

Get in touch today.

Meet you again with a interesting article, until then bye from Dr.InPhase

Thank you!


Thanks for reading…if you have questions don’t forget to ask me. You could write to me to info@inphase.in or call +919632421402

IInphaseLogo(300dpi) (1)nPhase Power is a Power Electronic Product company manufacturing products for Power Quality and Power Conversion. InPhase is manufacturer of Active Filter, Active Harmonic Filter, Solar Inverter. InPhase majors in power system design for power quality and conversion. Driven by a management that has a combined experience of over 60 years in power system and power electronics InPhase nurtures innovation and passion in this field.

Active Harmonic Filter Technology History, Evolution and Future


Doctor_Character-04-1Hello Readers, this article discusses the evolution of active filters as a harmonic mitigation solution and where it is getting to in the future. 


With the increasing number of power electronic equipment’s in the power system, the need to maintain sinusoidal line voltages and currents have become the need of the hour.

Harmonics in power system is caused by both domestic and industrial loads. Traditionally, harmonic distortion has been dealt with the use of passive LC filters. However, their application may result in parallel resonances with the network impedance, over compensation of reactive power at fundamental frequency, and poor flexibility for dynamic compensation of different frequency harmonic components.

Therefore, to overcome these problems and to provide adaptability to load variations in network and instantaneous adjustable solutions, Active Harmonic Filters were implemented. They regulate terminal voltage to improve voltage balance, compensate harmonics and reactive power and suppress flicker in electrical systems. The controller is the most indispensable part of the Active harmonic filter. The performance and reliability of the system greatly relies on it.


Starting from 1971, a number of configurations, such as the active series filter, active shunt filter, and combination of these filters have been developed and materialized for UPS applications. From 1976, a significant number of publications have reported on three phase three wire Active Harmonic Filter’s. Active shunt, active series, and combinations of both, named as active power quality conditioners, as well as passive filters combined with active shunt and active series Harmonic Filter’s are some typical configurations used. These configurations are used to resolve the problems of excessive neutral current, unbalanced load currents, heating issues and the previously mentioned problems which mainly occur due to nonlinear unbalanced loads and other power quality issues.


Passive Harmonic Filter


One of the major factors in advancing the Active Harmonic Filter technology was the invention of fast self-commutating solid-state devices. With the introduction of IGBT’s, the evolution of Active Harmonic Filter technology got a real boost and, at present, they are considered as ideal solid-state devices for Active Harmonic Filter’s. The improved sensor technology has also contributed to the enhanced performance of the Active Harmonic Filter. The next breakthrough in the evolution of Active Harmonic Filter development has resulted from the microelectronics revolution. Now, it is feasible to implement complex algorithms online for the control of the Active Harmonic Filter at a reasonable cost.

igbt                  18722-3172117


Selection of the Active Harmonic Filter for a particular application is an important task for end users and application engineers. There are widely varying application requirements, such as single-phase or three-phase, three-wire and four wire systems, requiring current-or voltage-based compensation. Moreover, there is a number of Active Harmonic Filter configurations which may cater to the needs of individual users. The proper rating of a passive harmonic filter must be concluded from the rating of a non-linear load without a harmonic filter and that of an active harmonic filter based on rectifier parameters without a filter. Selecting an Active Harmonic Filter of the correct size is the key to achieve optimum cost/benefit ratio, i.e. desired current harmonic reduction with minimum filtering effort.

Some of the leading Active Harmonic Filter manufacturers of today’s market are COMSYS, MERUS POWER, INPHASE POWER, SCHAFFNER and ABB. The InPhase Power Active Harmonic Filter stands out in the crowd in a number of ways. InPhase Power which is an Indian company provides 100% indigenous technology with up to 1000A in a single equipment. It has emerged as the only one in the market to provide Direct High Voltage Compensation with advanced DSP control and INPHASE CLOUD Computational system for online monitoring of faults in electrical systems with SMS alert facility. Application of LCL filters and rigorous algorithm for better compensation makes it the right choice power quality issues. InPhase Power also offers direct 690v Active Harmonic Filters  typically used in Furnace kind of applications. To top it all InPhase Power won the Ministry of MSME Award for Innovation in Renewable Energy & Power Quality Solutions which shows the reliability and dependability of InPhase Power products.

       ahf                                                    Active Harmonic Filter                                              


Today, Active Harmonic Filter technology is well matured, and a number of manufacturers are producing Active Harmonic Filter’s with large and varied capacities. The utilities in the long run will induce the consumers with nonlinear loads to use the Active Harmonic Filter’s for maintaining the power quality at acceptable levels. Many Active Harmonic Filter configurations are available to compensate harmonic current, reactive power, neutral current, unbalance current and harmonics these days.

With the advent of new and improved technology implementing faster devices the filter size and its performance can greatly improve, increasing the reliability and adaptability to perturbations in our power system network. The future looks promising as the IGBT technology  which is the key system component in Active Filters are evolving very faster and with robust capability.  The futuristic Active Filters might be compact, modular with ability to compensate higher orders and respond much quicker. Not leaving the reliability of these Active Filters will also be high in comparison to the current generation filters with more rugged capability for Industrial environments. InPhase as a pioneer in power quality and as a manufacturer of Active Harmonic Filter is working towards bringing these latest generation products to your door steps.

Meet you again with a interesting article, until then  bye from Dr.InPhase

Thank you!


Thanks for reading…if you have questions don’t forget to ask me. You could write to me to info@inphase.in or call +919632421402

IInphaseLogo(300dpi) (1)nPhase Power is a Power Electronic Product company manufacturing products for Power Quality and Power Conversion. InPhase is manufacturer of Active Filter, Active Harmonic Filter, Solar Inverter. InPhase majors in power system design for power quality and conversion. Driven by a management that has a combined experience of over 60 years in power system and power electronics InPhase nurtures innovation and passion in this field.


IEEMA the industrial association for Electrical Industries is very proactive in educating and creating awareness in the market. Today IEEMA has announced a very insightful workshop on  Power Quality and Reactive Power Compensation. Take a look at the agenda and get in touch today to be part of this excellent program. We will meet you there.


Reactive Power Management has become very important now-a-days because of introduction of power factor based tariff. Power Factor (PF) is crucial in all Electrical Power utilizing environments. A good understanding of Power Factor is essential for practicing Electrical Engineers and middle level managers as a good control of PF could lead to many advantages – energy saving, reduction of current loading, higher output from motor and generators, longer life for cables and equipment  – to mention a few. However, the equipment that is used to improve power factor interacts with network harmonics and brings down overall reliability. This workshop addresses such issues and gives solution to mitigate these problems.





14th October 2016, Friday

10:00 am to 5:00 pm

The Fern Citadel Hotel
No. 41, Seshadri Road,
Ananda Rao Circle, Bangalore – 560 009
Tel : +91 080 4240 2222

Key Benefits

  • Gives basic knowledge of fundamentals of Reactive Power Management
  • Can be applied directly to any installation and hence a boon for Engineers and others
  • Gives knowledge about Power Quality in general and Harmonic pollution in particular along with practical solution to mitigate them


  • Benefits of Power Factor Improvement
  • Evaluating PF from Electricity Bill
  • Methods of improving Power Factor
  • Automatic Power Factor Correction (APFC)
  • Issues in Power Quality
  • Power Factor Improvement of DG Sets
  • Harmonics – Causes, Measurement and Mitigation
  • Harmonics and effect of adding Capacitors in the System
  • Harmonic Filters and Active Compensation

Target Audience

Transmission and Distribution Operating Personnel, Engineers involved in Planning, Designing and Testing of Power Control Equipment and Engineers in charge of Electrical Maintenance, Engineers from Public / Private Sector Power Utilities.

However, anyone with enthusiasm and interest for Power Systems are most welcome to attend.



k-subramanianA  Masters Degree in Electrical Engineering and having an overall experience exceeding over 30 years in various fields such as Design, R&D, Production, Erection & Commissioning. Presently working as a freelancer in Bangalore. His current activities include promoting Electrical Power Quality awareness in the fields of Harmonics and Reactive Power Management. A regular faculty in PSTI (Min of Power), Bangalore, Larsen & Toubro Switchgear Training Centres, and conducted program on DRUM (Distribution Reforms, Upgradation and Modernization) organized by (Min of Power) Govt. of India and aided by Govt. of USA. Visiting faculty in various Engineering Colleges.

WorkShop Fees:
Members : 3000
Non Members: 3500

For Registration Contact:  k.seetharaman@ieema.org
Mobile : +91 99800 04982 (Seetharaman K)

Visit www.ieema.org for more details!


Team InPhase will be hoping to meet you there! Cheers!

InPhase Power Active Harmonic Filter and Load Unbalance Compensation – A Case Study

Doctor_Character-04-1Well Good day readers, Today I bring to you a very interesting case study of how InPhase helped one of our customers to achieve Unbalance compensation. I was very impressed with our team on the effort that they have given on this as they made the customers extremely delighted. I hope you all enjoy reading it as well.

The brief story

InPhase Active Harmonic Filters are an all-in-one package, capable of compensating for reactive currents, harmonic currents and unbalance currents, we claim. However, in most sites InPhase was tasked to compensate for reactive and harmonic currents alone. Then, came along a company. We will call it ‘ABC’. ABC approached us saying they had a problem of current unbalance, and that they were being threatened penalisation and disconnection of the supply by the Utility, for the same.

ABC had approached various other well-known names in the PQ industry, but none were prepared to propose a solution. And so, InPhase conducted a PQ Analysis at their site. The study results were appalling. Currents in the 3 phases read: 175A, 352A and 174A respectively.

InPhase proposed to install our beloved Active Harmonic Filter to mitigate this problem. ABC said “Go ahead, do anything. Just fix this problem for us.” And so, the InPhase Active Harmonic Filter was installed at the site.

Everybody, including us, held their breaths. “Will it work?” was the question in everyone’s minds. Then came the time, to find the answer. Annnnd Lo! The phase currents read: 52A, 50A and 51A.

Everyone’s apprehension about the InPhase Active Harmonic Filter had turned into awe. The Managing Director of ABC going to the extent of saying “Dr. InPhase has come down to save us like Lord Vishnu (Hindu god; Preserver of everything and everyone in the Universe).” Not only did the Active Harmonic Filter go on to mitigate the unbalance, it was also compensating for reactive and harmonic currents, all at the same time.

If ever there was a happy ending, this was it. 🙂

The technical explanation

Moving on to the technical side of the problem. The cause for current unbalance of such magnitude was the nature of load being 2-phase. The currents before compensation in R, Y and B phases were 175A, 352A and 174A respectively. You might notice how the current in Y-phase was double that of R and B phases. Excellent observation, that! Now, here is the explanation:


The above diagram shows a delta-star step-down transformer. The outer windings represent the primary of the transformer. The windings on the inner side represent the secondary. Notice that the load is connected to the secondary across two phases only i.e. R and B.

The load forces the current direction in the secondary windings as indicated by Ir and Ib. Since the phase r and b are connected in series, Ir= Ib.

Ir and Ib are secondary currents induced from primary currents IRY and IRB. Subsequently,
IRY = IRB = I. Note also, how the direction of secondary currents differ from their corresponding primary currents.

From Kirchoff’s current law, incoming current at node R must be I+I = 2I.

The outgoing currents from node Y and B are ‘I’ each. What is observed here is that one phase carries twice the amount of current than the other two individual phases. This explains the observed readings of 175A, 352A and 174A.

It is a known fact that current has three components viz. positive sequence, negative sequence and zero sequence. Since our incoming current is through a 3-ph 3-wire system, we can ignore the zero sequence component.

Also, let us recall that both positive and negative sequence components are “balanced”, individually. It is only when they combine, unbalance occurs in the load current.  Just to be on the same page, let us understand what a “balanced current” means. In a 3-ph system, is the current flowing in each phase is equal, the system is said to be balanced in simple terms.

The magnitude of unbalance is calculated in percentage.


The calculation for this case would go as follows:

IR=352A ; IY=175A ; IB=174A

The average current,


Maximum deviation from Iavg = 352-233.67 = 118.33A



As a consequence of NEMA Standard MG-1, acceptable limit on current unbalance is 10%. Clearly, the unbalance in this industry was far from acceptable.

Now that the cause and magnitude of the problem were known, the next step was to mitigate it. And, to meet this objective, InPhase Active Harmonic Filter was installed.

It should be noted that the initial current readings IR=352A, IY=175A, IB=174A are a combination of reactive currents, harmonic currents and unbalance currents. And because we are concentrating exclusively on unbalance, let us take an arbitrary example to understand the same.


In the above example, the incoming currents are 100A, 100A and 40A. The underlying assumption here is that these currents are purely unbalance currents and they have no reactive or harmonic component.

InPhase Active Harmonic Filter takes feedback from 3-ph CTs. This allows the Active Harmonic Filter to measure current flowing in each line. Subsequently, this input is processed by the main controller in the equipment. The Active Harmonic Filter being an AC-DC-AC converter, can absorb and pump current from the line to the load such that the incoming current from the metering point is balanced.

The controller is capable of calculating the positive sequence component and negative sequence component from this input. Once this is calculated, it is a simple case of pumping the counteractive current to the negative sequence component, so that all that remains is the positive sequence. Recollect that positive sequence current is balanced and thus consequently, the line current is also balanced.


The above diagram is a representation of the aforementioned compensation process. Note how the line currents are balanced (80A each) whereas the load currents (100A, 100A and 40A) remain unchanged.

This way, the customer is happy that his electrical system is healthy, and the Utility is happy that the consumer’s loads are balanced and the grid is stable. Lastly, Dr. InPhase is also happy that he made it all possible. 🙂

It is time now, for you to experience the InPhase Active Harmonic Filter. Get in touch with us, we’ll help you to get your Power Quality problems resolved.

Thank you!



Thanks for reading…if you have questions don’t forget to ask me. You could write to me to info@inphase.in or call +919632421402

IInphaseLogo(300dpi) (1)nPhase Power is a Power Electronic Product company manufacturing products for Power Quality and Power Conversion. InPhase is manufacturer of Active Filter, Active Harmonic Filter, Solar Inverter. InPhase majors in power system design for power quality and conversion. Driven by a management that has a combined experience of over 60 years in power system and power electronics InPhase nurtures innovation and passion in this field.

Dr.InPhase Edu Series – Active Harmonic Filter Vs Detuned Filters

Hello Readers,

As part of my educational series today we are going to try to understand the different kinds of Harmonic filters namely the Active Harmonic Filter Vs Detuned Filters.

Educational Series Dr.InPhase

The objectives of Active Harmonic Filter and Detuned Filters are not the same and also not so different. It all depends on requirement specific.

When to use Active Harmonic Filter or Detuned Filter?

Industries operating with huge non-linear loads, ex:  manufacturing plants like steel, automobiles, cement, textile, refineries, Data Centers, Multi Specialty Hospitals, Shopping Malls and all other processing industries.


Why do we need AHF or DF?

Industries operating with more inductive loads and drive based loads have tendency to generate more  Harmonics and consume more Reactive Power . This increase in harmonics and reactive power would result in;


What are Harmonics and why it has to be mitigated ?

Harmonics are sinusoidal voltage or current waveforms oscillating at a frequency which are integer multiple of fundamental operating frequency (50Hz or 60Hz).

When an ideal sinusoidal voltage is applied to the linear loads, they absorb power as the way it is supplied, but in case of non-linear loads which are connected through converters will draw the current inexplicably with voltage, as the current is drawn w.r.t switching frequency (frequency = 1 / Time ) of the converter. This change in current w.r.t time leads to current harmonics and also due to momentous impedance between the power supply and the load, current harmonics will also raise the harmonics in voltage waveform. Increase in harmonics would cause neutral overheating, failures with electronic components, overloading of capacitors, heating of transformers and etc.

What is Reactive Power and why it has to be minimized?

Apparent Power (KVA) = Real Power (KW) + Reactive Power (KVAR)

Reactive power is the magnetizing power for motors to operate, but however it is not a useful power. i.e. work done by reactive power always equals zero.  So, higher the reactive power equals higher electric billing under KVAh scheme. Reducing reactive power implies increase in power factor and reduced electric billing.

How to minimize reactive power and mitigate  harmonics ?

Active Harmonic Filter are preferred when the requirement is for both power factor improvement and harmonic mitigation. Whereas Detuned filters can only achieve in improving power factor i.e. minimizing reactive power.

detuned filter


Comparison Chart on non-linear loads without filters / with Detuned Filter / with Active Harmonic Filter


How Active Harmonic Filter mitigates harmonics and minimize reactive power ?

Dr.Inphase Interesting

Interesting right that is what will be discussed in detail in our next Edu series. See you until then


At InPhase Power we are very serious about improving the power quality of the nation. Our products provide unmatched improvement in Power Quality by effectively curbing harmonics and maintaining steady power factor. Explore our Products Active Harmonic Filter(IPC150-AHF) and STATCOM (IPC150-SCOM) to find how they can improve your power quality.