DESC:Field of the Invention

The present invention relates to harmonic filters, more particularly, the present invention relates to a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter for single-phase and three-phase electric supply feeding non-linear loads. The method and system thereafter allow realization of hardware based Zero Reactive Power Passive Current Harmonic Filter for a given single-phase or three-phase electric supply feeding non-linear loads.

Background of the Invention

Over a period of time the industrial requirements have undergone substantial change and have become extremely demanding/challenging. More than linear, the non-linear loads have proliferated. The power supply systems has to withstand fluctuating load demands causing dynamic variation in active power, reactive power, current harmonics, and unbalanced current operation particularly in star connected unbalanced loads such as welding loads, fabrication shops, distributed loads within factories, low voltage distribution transformers, arc furnaces and the like.

The non-linear load dynamics causes variation in dynamic Volt Amperes Reactive (VAr) and hence causing dynamics in the fundamental power factor. The fundamental power factor needs be maintained close to unity for reducing losses in a system and reduction in electricity bills.

The current harmonics and hence the supply current distortion needs to be maintained below certain limits as per international standards (like IEEE 519) to restrict supply voltage distortion for given short circuit capacity at the Point of Common Coupling (PCC).

Neutral currents caused by unbalanced load currents (linear or non-linear loads) can have fundamental frequency current component as well even and / or odd harmonic frequency components. They can also have sub-cycle harmonic frequency components depending on the type of non-linear load.

Unbalance in the load currents and hence the supply currents, can give rise to unacceptable magnitude of neutral current. It increases system losses and heating of the neutral cable or conductor. Further, it increases and even gives rise to changing neutral to earth potential/voltage. This in effect can lead to changing phase to neutral supply voltages causing disturbances to other loads connected on the same supply voltage bus. The unbalance in supply currents also leads to reduced life of the supply transformers. This is applicable to all (low to high) types of supply voltage systems.

Out of the three major issues related to non-linear loads as mentioned above, viz. dynamic reactive power, supply current harmonics, and unbalanced load currents resulting in unwanted neutral current, the issue related to the supply current harmonics is considered here for reduction / elimination.

Earlier, when diode rectifiers or thyristor converters were used by the industrial applications, the supply current contained characteristic harmonics, such as 3, 5, 7, 9, 11, 13….and so on. Passive (L-C) filters were employed to shunt these harmonics from entering the supply networks. Such applications many times involved use of these passive (L-C) filters along with switched compensation for reactive power drawn by such non-linear loads. The products such as Automatic Power Factor Controller (using contactors for switching ON or OFF the filters) or Thyristor Switched Capacitor (TSC) or even Thyristor Controlled Reactor (TCR) came into existence serving the need for dynamic reactive power as well as supply current harmonic compensation.

Following important points need to be noted when such passive (L-C) filters are designed for supply current harmonic reduction / elimination.

• Most of the non-linear loads used diode or thyristor rectifiers as the front end rectifiers and hence produced characteristic current harmonics. These loads hence employed tuned filters for current harmonic 3rd, 5th, 7th, 11th, 13th…. etc. and also at times detuned filters with detuned frequencies such as 138 Hz or 189 Hz for 3rd and 5th current harmonic and considering 50 Hz as the nominal supply frequency.

• Arc furnace is an exceptional load where filters have been used for 2nd and 4th current harmonics in addition to normal characteristic current harmonic filters.

• Lower order current harmonics (such as 3rd or 5th) are more difficult to filter, especially when the filers are also supposed to cater for the non-linear load reactive power compensation.

• Normally or in general the simplest approach followed for the filter designs (calculating the values of the filter components L and C) is to use required VAr / kVAr as one of the conditions and tuned or detuned frequency given by
1/[2*?*vLC] as the other condition.

• There has always been a fear of a possible resonance which can be caused by the filter L-C and the supply short circuit inductance Ls, more so when number of filters (5th, 7th, 11th …etc.) are used in parallel.

• It is also true that the passive filters become bulky or increase in size / volume as the tuning frequency goes down (from 13th to 11th to 5th to 3rd).

These are also the major reasons why research shifted to “Active Filters” which use self commutated devices like IGBTs (Insulated Gate Bi-polar Transistors) with different control strategies for reduction / elimination of supply current harmonics. Because of the higher switching frequencies and the self commutation characteristic, these active filters slowly got popular with industrial users. These filters also offer accurate reduction / elimination of current harmonics, specific harmonics if required, even zero reactive power compensation, and generally satisfy the IEEE 519 standard on “Recommended Practices and Requirements for Harmonic Control in Electric Power Systems”. Though not considered as an argument or a part of this document, Active Filters in general require a step down transformer for voltages beyond 690 V / 1 kV and have a much higher cost tag.

What is hence required as an industrial or an application user could be an effective and implementable hardware based solution (based on a properly developed mathematical method) for the supply current harmonic reduction / elimination which should overcome at least functional drawbacks of passive filters and meet performance requirements close to the active filters or within specified limits of IEEE 519 standard while satisfying the needed economics for the user.

Objects of the Invention

Object of the present invention is to provide a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter for current harmonic filtering for electric supply system.

Another object of the present invention is to provide a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter for current harmonic filtering in electric supply systems, which can be mathematically formulated, designed, simulated, and is then implementable for any given power system based on the supply Short Circuit Inductance / Capacity and non-linear load connected to the system.

Yet another object of the present invention is to provide a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter for current harmonic filtering in electric supply systems, which can be designed to achieve a given supply current harmonic distortion as per IEEE 519 standard or as per user specification with zero reactive power for given supply voltage.

Further object of the present invention is to provide a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter for current harmonic filtering in electric supply system, without use of any step down transformer for given system voltage and can be employed / designed for low to high voltage systems.

One more object of the present invention is to provide a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter for current harmonic filtering in electric supply system, ensuring “NO REONANCE” between the filter banks and the supply Short Circuit Inductance and the same is assured through its mathematical formulation and design and can be checked by using modeling and simulation with Matlab / Simulink software / platform (accepted simulation platform all over the world).

Another object of the present invention is to provide a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter for current harmonic filtering in electric supply system, which can also be used for filtering non-characteristic harmonics generated by load.

Further one object of the present invention to provide a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter, which can be used along with Neutral Current Compensator (NCC) for reducing the efforts of consideration of filters for the reduction of 3rd harmonic current, triplens that is multiples of 3rd harmonic, and unbalanced component of other current harmonics.
Summary of the invention:

According to the present invention there is provided a method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter (ZRPPCHF) for a non-linear load. The method and the system thereof having steps of identifying supply voltage and frequency. Thereafter, obtaining Short Circuit Capacity and hence a Short Circuit Inductance of an electric supply at the point of PCC (Point of Common Coupling), and details of non-linear load which includes VA/kVA, Watts/kW, VAr/kVAr and current harmonics produced by the non-linear load. Further, identifying Short Circuit Current to Rated Load Current Ratio (SCR) for the electric supply at PCC. Then identifying specified current harmonic and voltage harmonic distortion of the electric supply. Thereafter, deriving filter error impedance to achieve specified current harmonic distortion (based on IEEE 519 standard or as specified by the user). Further, configuring a filter system in parallel with the non-linear load for absorbing current harmonics from the non-linear load, wherein the difference between nth harmonic filter impedance error is 1/20th of that of Short Circuit Impedance for the nth harmonic. At last, configuring an additional very low frequency parallel filter (Li and Ci) to compensate fundamental capacitive reactive power absorbed by the filter system configured for absorbing non-linear load current harmonics.

The filter system realizable as a hardware based filter (for given LV to HV system voltage) in an actual single or three-phase system to mitigate characteristic as well as non-characteristic current harmonics generated by non-linear loads and to achieve total current harmonic distortion within IEEE 519 standard or user specification for the supply current.

The filter system ensures resonance free operation of the filter with Supply Short Circuit Inductance.

The filter system can be configured for a star connected unbalanced linear or non-linear load using Neutral Current Compensator (NCC) along with it to achieve reduction of 3rd harmonic current, triplens, and unbalanced component of other current harmonics, if present in the load neutral.

Brief Description of the Drawings

Figure 1 shows a flowchart of a method and a system thereof for providing close to Zero Reactive Power Passive Current Harmonic Filter (ZRPPCHF) for non-linear loads;

Figure 2 shows a test circuit diagram for establishing Short Circuit Capacity / Inductance of incoming power supply;

Figure 3a shows circuit diagram of a single-phase supply feeding a non-linear load with “nth” harmonic filter inductance;

Figure 3b shows an equivalent circuit for “nth” harmonic current;

Figure 4(a) shows a 1800 square wave theoretical waveform generated by single-phase rectifiers;

Figure 4(b) shows a 1800 square wave practical waveform generated by single-phase rectifiers;

Figure 5(a) shows a 1200 square wave theoretical waveform generated by three-phase rectifiers;

Figure 5(b) shows a 1200 square wave practical waveform generated by three-phase rectifiers;

Figure 6(a) shows Matlab / Simulink model developed / used for the system (supply, load, filter banks) etc.;

Figure 6(b) shows figure 6(a) represented block schematically;

Figure 7 shows Matlab / Simulink model developed / used for three-phase diode rectifier and unbalanced 3rd harmonic current injection (part of the figure 6);

Figure 8 shows Matlab / Simulink model developed / used for the Neutral Current Compensator (NCC) (part of figure 6);

Figure 9 shows Matlab / Simulink model developed / used for current harmonic filter banks (part of figure 6);

Figure 10 shows internal configuration of the filter banks shown in figure 9;

Figure 11 shows simulation results for supply currents and NCC input and output currents (scope 1 in figure 6 (a));

Figure 12 shows supply phase voltages after Short Circuit Inductance, supply phase “a” current, active power per phase, diode rectifier and 3rd harmonic current as the total per phase load current, distortion of the total per phase load current, supply phase current distortion, and distortion of supply phase voltage after the Short Circuit Inductance (scope 2 in figure 6(a));

Figure 13 shows fundamental current displacement for the load current along with its power factor and fundamental current displacement of supply current along with its power factor (scope 3 in figure 6(a));

Figure 14 shows practically observed three input currents of the three-phase diode rectifier captured on the experimental set up;
Figure 15 shows practically observed supply input current and rectifier input current captured on the experimental set up;
Figure 16 shows practically observed voltage and current waveforms for supply and rectifier captured on the experimental set up;
Figure 17 shows practically observed rectifier and supply input current distortion (24.5% and 4.9%) captured on the experimental set up;
Figure 18 shows the experimental set up;
Figure 19 shows the 12.24 mF capacitor specifically developed for the experimentation;
Figure A3.1 shows simulation results for the Matlab / Simulink model of NCC for unbalanced non-linear load;

Figure A4.1 shows NCC experimental results for 30 kVA unbalanced load (with three load currents and neutral current shown by Green) “with NCC installed, but non-operational”, at a Hospital in Sangli (South Maharashtra, India), and

Figure A4.2 shows NCC experimental results for the same 30 kVA unbalanced load (with three load currents and neutral current shown by Green) “with NCC installed and operational”, at the same Hospital in Sangli (South Maharashtra, India).

Detailed description of the invention

For a thorough understanding of the present invention, reference is to be made to the following detailed description, including the appended claims, in connection with the above-described drawings. Although the present invention is described in connection with exemplary embodiments, the present invention is not intended to be limited to the specific forms set forth herein. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

The present invention provides a method and a system thereof for providing close to Zero Reactive Power Passive Current Harmonic Filter (herein after referred as ZRPPCHF) for current harmonic filtering for electric supply systems. The method and the system for providing ZRPPCHF can be formulated, designed, simulated, and is then implementable (in terms of actual hardware based filters) for any power system based on its Short Circuit Inductance / Capacity and non-linear load served by the system. Further, the method and system for providing ZRPPCHF can achieve a given supply current harmonic distortion as per IEEE 519 standard or as per user specification with zero reactive power. Also, the ZRPPCHF does not require step down transformer for any given system voltage and can be designed for low to high voltage systems. The ZRPPCHF is free from resonance (filter banks resonating with supply short circuit inductance) and the same is assured through its mathematical formulation and design and can be checked by using modeling and simulation with Matlab / Simulink software / platform (accepted simulation platform all over the world). Further, the method and system for providing ZRPPCHF can also be used for filtering of non-characteristic harmonics injected in supply system by the non-linear load. The method and the system thereof, thereafter allow realization of hardware based ZRPPCHF for a given single-phase or three-phase electric supply feeding non-linear loads.

Furthermore, the method and the system thereof for providing ZRPPCHF can be used along with Neutral Current Compensator (NCC), for reducing the efforts of consideration for the reduction of 3rd harmonic current, triplens that is multiples of 3rd harmonic and unbalanced component of other harmonics.

The present invention thus covers mathematically formulating, designing, simulating, and then implementing actual hardware based passive current harmonic L-C shunt filters (more specifically R-L-C filters) for a given electric supply system. It covers the following cases and aspects.

Brief introduction about the method and the system thereof for providing ZRPPCHF of the present invention:

Electric supply systems using non-linear loads get polluted by the characteristic as well as non-characteristic current harmonics introduced by the non-linear loads into the supply system. These current harmonics develop unacceptable supply voltage distortion. The IEEE 519 standard defines how much amount of current harmonics or more specifically current harmonic distortion can be allowed (sometimes also specified by user) based on the voltage level and the Short Circuit Current to Rated Load Current Ratio (SCR) at the Point of Common Coupling (PCC)). In order to achieve acceptable current distortion, shunt passive current harmonic filters are required. These filters shunt or mitigate the current harmonics and reduce or eliminate them so that only acceptable level of current harmonics can be present in the incoming supply system.

The present invention makes use of the supply Short Circuit Capacity / Inductance to formulate a mathematical approach or method for design of the current harmonic filters to achieve proper reduction or elimination of these harmonics so that only acceptable level of current harmonics can be present in the incoming supply system or in other words achieve desired current harmonic distortion for the supply currents within specification of the IEEE 519 standard or as given by the user and also based on the actual values of the current harmonics produced by the non-linear load and the system voltage.

Based on the details of supply voltage, Supply Short Circuit Capacity / Inductance, actual values of the current harmonics produced by the non-linear load, and desired current harmonic distortion for the supply currents within specification of the IEEE 519 standard or as given by the user, the mathematical formulation is done for actually getting the filter values to achieve the desired performance of reduced current and voltage harmonic distortion at the supply. This is the “method” as termed above. The method then allows design of the actual ZRPPCHF and then allows the entire electric system (supply voltage, Supply Short Circuit Inductance, non-linear load, and current harmonic filters) to be modeled and simulated using the Matlab / Simulink software or platform. This is for validation of desired results before the actual filters can be employed on the given electric power supply system. The process of achieving the final results as detailed above and based on the “method” is the “system” as termed above.

Cases covered:

Case-1: Incoming supply three-phase star connected (with neutral available). The non-linear load is star connected with neutral available.

Case-2: Incoming supply three-phase star connected (with neutral available). The non-linear load is either star connected without neutral available or delta connected.

Case-3: Incoming supply three-phase star connected (without neutral available). The non-linear load is star connected with neutral available.

Case-4: Incoming supply three-phase star connected (without neutral available). The non-linear load is either star connected without neutral available or delta connected.

Case-5: Incoming supply three-phase delta connected. The non-linear load is star connected with neutral available.

Case-6: Incoming supply three-phase delta connected. The non-linear load is either star connected without neutral available or delta connected.

Case-7: Incoming supply single-phase powering a single-phase non-linear load. It is considered part of Case-1 without the use of NCC as explained subsequently.

Aspects covered

• Frequency range as nominal of 50 Hz ± 3%
• Though the write up covers details based on 50 Hz supply frequency, it can be extended to all other supply frequencies, such as 60 Hz or 16? Hz.
• Filter banks are assumed to be star connected (though they can be suitably converted to delta connection) with neutral connection available.
• Total reactive power drawn by all the shunt filters together is close to zero, causing no extra reactive power stress on supply system.
• No requirement of step down transformer for any voltages (LV to HV) and Short Circuit Current to Rated Load Current Ratio (SCR) as specified by IEEE 519 standard for the given supply system voltage or as measured for the supply system.
• Simple approach, based on use of supply Short Circuit Inductance / Capacity, ensuring “NO” resonance with Supply Short Circuit Inductance and required supply current distortion as specified by IEEE 519 standard or user (based on Short Circuit Current to Rated Load Current Ratio (SCR) as specified by IEEE 519 standard or as measured for the supply system).
• Simple approach, based on use of supply Short Circuit Inductance / Capacity, ensuring required supply current distortion as specified by IEEE 519 standard or user (based on Short Circuit Current to Rated Load Current Ratio (SCR) as specified by IEEE 519 standard or as measured for the supply system).
• Complete elimination of 3rd harmonic, triplens that is multiples of third harmonic, and unbalance components of other current harmonics in Cases-1, 3, and 5 discussed above. This is based on use of Neutral Current Compensator (NCC) whose details are given in Annexure-I or any other compensator which offers similar functions. There is a patent applied for NCC and its details are also given in Annexure-I. The use of NCC, hence, is considered as an integral part of the total filter design and implementation for these cases (Case-1, 3, 5). For Case-7 it is not applicable as NCC is meant for only three-phase systems.
• Largely covers many applications which otherwise (but not necessarily) could have called for use of “Active Filter”.

Figure 1 shows flowchart of a method 100 for configuring a system for providing Close to Zero Reactive Power Passive Current Harmonic Filter for non-linear loads in accordance with the present invention. The method 100 starts at step 10.

At step 12, electric supply voltage and frequency are identified.

At step 14 Short Circuit Capacity and hence Short Circuit Inductance of an electric supply at the point of PCC (Point of Common Coupling) is obtained. Also, other details of non-linear load which includes VA/kVA, Watts/kW, VAr/kVAr and current harmonics produced by the non-linear load are obtained.

Method for obtaining/establishing Short Circuit Capacity / Inductance of supply network

It is necessary to know the Short Circuit Capacity and hence the Short Circuit Inductance of the supply network before any shunt filter design can be attempted.

Figure 2 shows a single-phase source with nominal RMS voltage as “V” with Ls as its Short Circuit Inductance and disconnected form a serving non-linear load. It also shows a capacitor C with its small internal loss resistor R loss. The RMS voltage at terminals “a” and “b” is first measured. This is called as VT1. The capacitor is then switched on closing the switch “S1”. Once again the terminal RMS voltage (now across the capacitor) is measured as VT2 along with the established RMS current “I”. The Short Circuit Inductance Ls is now given by following equation (considering R loss is very small compared to the capacitive impedance 1/[C*?]).

Ls = [VT2 – VT1] / ? --- Eq. (1)
Where
? = 2*?*f ---- Eq. (2)
and
f = Supply frequency (nominal 50 Hz)

For arriving at better and practical value of Ls, the current “I” should be at least 20% of the rated capacity of the load and many readings in a similar way may have to be taken for calculating the average Ls.

The Short Circuit (SC) VA / MVA is then given by

SC VA = V*V/ [?*Ls] ---- Eq. (3)
SC MVA = V*V*10-6/ [?*Ls] ---- Eq. (4)

In a similar way, total SC VA / MVA of a three-phase supply can be established or also can be taken as 3*short circuit VA / MVA capacity of its single-phase part.

[For establishing Short Circuit Capacity / Inductance in high voltage systems, one can use a step down transformer with small but known VA / kVA and percentage / per unit impedance and carry out the given experiment on secondary / low voltage side of the transformer. Once the Sort Circuit Capacity is experimentally determined (as above) on secondary side of the transformer, the primary side Short circuit Capacity can be calculated based on following relation.

SCCs = SCCp * [TrMVA / TrpuImp] / (SCCp + [TrMVA / TrpuImp] )

Where,

SCCs indicates Short Circuit Capacity on secondary / low voltage side of the transformer in MVA;
SCCp indicates Short Circuit Capacity on primary / high voltage side of the transformer in MVA;
TrMVA indicates rating of the transformer in MVA;
TrpuImp indicates transformer impedance in per unit]

At step 16, Short Circuit Current to Rated Load Current Ratio (SCR) for the electric supply at PCC is obtained. The formula for obtaining SCR is given below:

SCR
= (SC VA or MVA of the supply) / (Rated load VA or MVA of the load) Eq. (5)

Further, supply current harmonic distortion allowed by the IEEE 519 standard for different system voltages and Short Circuit Current to Rated Load Current Ratios (SCR’s) is given Annexure –II.

Usually, the Short Circuit Current to Rated Load Current Ratio (SCR) in supply networks is lower than specified by the IEEE 519 standard and in case of Diesel Generator supplies it could be even further lower. This means the Ls value will go up (than what it could be based on specified SCR by the standard).

Thus, the actual harmonic current filter is expected to face Ls more than the one considered based on SCR given by the IEEE 519 standard for a specified voltage.

At step 18, specified current harmonic and voltage harmonic distortion are identified.

Method for providing ZRPPCHF

Figure 3a shows a single-phase, 50 Hz, supply with short circuit inductance Ls feeding a given non-linear load supposed to be generating characteristic harmonics (n=3,5,7,9,11,13…..or 3 & triplens and 5,7,11,13…etc.). A filter Rfn-Lfn-Cfn is connected in shunt which is supposed to absorb a given nth harmonic current generated by the non-linear load. The discharge resistor Rdn is quite large as compared to capacitive impedance 1/( n*?*Cfn) and does not play any role in harmonic filtering.

The equivalent circuit for this nth harmonic is given in figure 3b. The supply inductance Ls presents n*?*Ls as the impedance for the nth harmonic. Similarly the filter components Lfn and Cfn present n*?*Lfn and 1/[ n*?*Cfn] as their respective impedances for the nth harmonic. The current In indicates nth harmonic RMS current produced by the non-linear load.

Eliminating the harmonic current In flowing in the supply means theoretically the difference between the Lfn and Cfn impedances (n*?*Lfn - 1/[ n*?*Cfn]) should be zero. This is difficult to achieve due to manufacturing tolerances of the Lfn and Cfn components. On the other side, the difference can be controlled. This means part of the In flowing in the supply inductance Ls can be controlled. It is adequate for practical purposes that approximately 5% of In flows in the supply inductance Ls and 95% flows in the shunt Lfn-Cfn (in this particular case Rfn-Lfn-Cfn filter). The selection of Rfn and also its advantages are mentioned in subsequent section. However, for all practical purposes the filter impedance can considered as (n*?*Lfn - 1/[ n*?*Cfn]).

If the filter impedance (n*?*Lfn - 1/[ n*?*Cfn]) is (1/20)th or 5% as that of the short circuit impedance n*?*Ls, theoretically 95.25% of In will flow in the filter impedance.

If the difference, that means error impedance, (n*?*Lfn - 1/[ n*?*Cfn]) is positive, it means the error impedance is inductive for the nth harmonic. If the difference (n*?*Lfn - 1/[ n*?*Cfn]) is negative, it means the error impedance is capacitive for the nth harmonic.

At step 20 filter error impedance is derived to achieve specified current harmonic distortion.

It is always is preferred to have the error impedance as inductive for every connected filter so that the network sees all filter error impedances as inductive (for nth harmonic for which it is designed or any harmonic greater than “n”) and hence eliminates possibility of resonance between the supply short circuit inductance Ls and the error impedance.

It should be noted that the supply current harmonic distortion is given by

ITHD = [v? In2] / I1 --- Eq. (6)

where I1 is the fundamental RMS current.

Thus, if there are number of filters in parallel designed for n= 3,5,7…etc. and if each of them flows 95% of corresponding nth harmonic In current, the supply current distortion ITHD should be less than the one specified by IEEE 519 standard for given Short Circuit Current to Rated Load Current Ratio (SCR) and supply voltage (for example, = 5% for SCR of 20 and system voltage 120 V to 69 kV) .

Further, while designing the nth harmonic filter, the supply Short Circuit Inductance Ls to be considered should be based on the Short Circuit Current to Rated Load Current Ratio (SCR) specified by IEEE 519 standard (for example, SCR as 20 for system voltage 120 V to 69 kV). This gives the Short Circuit Inductance Ls based on maximum Short Circuit (SC) VA / MVA. Since in reality, the SCR is less than one given by the IEEE 519 standard, it offers more Short Circuit Inductance Ls in the system and better performance for the filters. This happens in most of the cases and especially when there is one dedicated single load served by the supply through a transformer.

In some cases, it can happen that for the load for which current harmonic filters are required is VA / kVA wise lesser than the supply rated capacity. This happens, especially when supply feeds many loads in parallel. For such a situation then, Short Circuit Current to Rated Load Current Ratio (SCR) for that particular load can be higher than the one specified by the IEEE 519 standard (for example, Short Circuit Current to Rated Load Current Ratio (SCR) as 20 for system voltage 120 V to 69 kV) and can allow > 5% total current harmonic distortion for that load. If such a situation arises, the filters can be designed for actual Short Circuit Current to Rated Load Current Ratio (SCR) ratio and for allowed total harmonic distortion by the user or >5% as the total current harmonic distortion.

Other practical considerations

It is clear that each individual filter (3,5,7….etc.) design is considered based on error impedance of 5% as that of the n*?*Ls, system voltage, Short Circuit Current to Rated Load Current Ratio (SCR) based on system voltage as per IEEE 519 standard, and corresponding current harmonic distortion allowed by the standard or as specified by the user.

In most of the practical single-phase or three-phase systems, the current harmonic amplitude decreases as the value of harmonic number “n” increases. Single-phase systems will have lowest current harmonic as n=3 (3rd harmonic) and three-phase systems will have lowest current harmonic as n=5 (5th harmonic). If the currents are unbalanced, three-phase systems may also have lowest current harmonic as n=3 (3rd harmonic).

Thus, based on and starting from the lowest harmonic, the filter systems are generally designed. With the suggested invention, the lowest harmonic for single-phase system remains same as n=3 (3rd harmonic). However, for three-phase systems the lowest harmonic to be considered is for n=5 (5th harmonic) since the NCC is considered as an integral part of the total design and implementation.

The loads which require current harmonic reduction usually have rectifiers producing 1800 square wave or 1200 square wave waveforms. Theoretical as well as practical waveforms are shown in figs. 4 and 5.

The 1800 square wave waveform gives the harmonics as under.

For the theoretical waveform based on figure 4(a)

RMS I1= 0.9 Id (where Id is the dc value of the current as in figure 4)

RMS “nth” harmonic = RMS I1/n

Thus, the 3rd harmonic will be 33.33% of the fundamental current I1, 5th harmonic will be 20% of the fundamental I1, 7th harmonic will be 14.2857% of the fundamental current I1 and so on.

The practical values based on figure 4(b) are always lesser than the theoretical values (based on IEEE 519 standard). Thus, the 3rd harmonic could be 27% of the fundamental current I1, 5th harmonic could be 17% of the fundamental I1, 7th harmonic could be 12% of the fundamental current I1 and so on.

The 1200 square wave waveform gives the harmonics as under.

For the theoretical waveform based on figure 5(a)

RMS I1= 0.78 Id (where Id is the dc value of the current as in figure 5)
RMS “nth” harmonic = RMS I1/n

Thus, 5th harmonic will be 20% of the fundamental I1, 7th harmonic will be 14.2857% of the fundamental current I1, the 11th harmonic will be 9.091% of the fundamental current I1 and so on. The third harmonic and triplens will be absent here.

The practical values based on figure 5(b) are always lesser than the theoretical values (based on IEEE 519 standard). Thus, 5th harmonic could be 17% of the fundamental I1, 7th harmonic could be 12% of the fundamental current I1, 11th harmonic could be 7.5% of the fundamental current I1 and so on.

These considerations can be used in case current harmonic data is not available for the application or also to assess the harmonic current data available for the application.

At step 22, a filter system configured and arranged in parallel with the non-linear load for absorbing current harmonics from the non-linear load, wherein the difference between nth harmonic filter impedance error is 1/20th of that of Short Circuit Impedance for the nth harmonic.

Design methodology for the ZRPPCHF

Having explained the basic approach for the “nth” harmonic current filter design and practical considerations for the current harmonics (does not matter even if harmonic current pattern is different), the actual design of the filter requires some amount of capacitive VAr / kVAr to be considered for the design in order to achieve 95% of nth harmonic current flowing in the filter as explained above. Based on the application data available, generally the lowest harmonic (such as 5th harmonic) current filter will require more capacitive VAr / kVAr for its design. As the harmonic number increases, the capacitive VAr / kVAr will decrease. The total number of filters to be put in parallel will depend upon number of current harmonics considered for reduction / elimination and to achieve the overall supply current distortion as = 5% as per IEEE 519 standard or as specified by the user.

As an example, for a three-phase, 433 V, 50 Hz, system supplying 50 kW load, the 5th, 7th, 11th, 13th current harmonic filters can have kVAr as 35 kVAr, 15 kVAr, 12 kVAr, and 10 kVAr.

Based on these VAr / kVAr first each filter components (Lfn and Cfn) are calculated considering the filter impedance (n*?*Lfn - 1/[ n*?*Cfn]) as (1/20)th or 5% as that of the short circuit impedance n*?*Ls.

Value of Rfn for each filter inductance Lfn should be such that it should be equal to greater than nmax*2*?*Lfn*30 where nmax is the maximum harmonic considered for reduction / elimination. This reduces the part of the nth harmonic current flowing in Rfn as compared to the nth harmonic current flowing in Lfn. Further, whenever the filters are disconnected from the system, the current flowing in Lfn circulates in the (Lfn – Rfn) loop and does not allow high Ldi/dt voltage developing across Lfn.

Further, exact fundamental (50 Hz) VAr / kVAr is calculated for each of the nth harmonic current filter. These VAr’s or kVAr’s are now added and total VAr / kVAr is calculated. Note this is capacitive.

To compensate this “capacitive total VAr / kVAr”, equal “inductive VAr / kVAr” is needed. Thus, even if the “capacitive total VAr / kVAr” exceeds the load kVA, it does not matter as it is cancelled by the equal “inductive VAr / kVAr” so that the total kVAr drawn from the supply is near zero. For the same total inductive VAr / kVAr, the inductance Li is to be calculated as below.

Li = (VL-L)2/(?*VAr) ----- Eq. (7)

where VL-L is the line to line (phase to phase) nominal system voltage.

The series capacitor Ci is now chosen in such a way that its fundamental impedance is approximately 5% as that of fundamental impedance of ?*Li. This yields the resonance frequency as 11.18 Hz which is quite low and acceptable. The relation between X% capacitive impedance and the resonance frequency is given by

Resonance frequency = f * v(X/100) --- Eq. (8)

where “f” is the supply fundamental frequency.

The discharge resistor Rdn or Rdi for the harmonic filter capacitors Cfn or capacitor Ci used for inductive VAr / kVAr filter can be calculated based on discharge time needed (60 seconds to 600 seconds) as below.

Discharge time (approximately 5*time constant)
= 5* ( Rdn or Rdi ) * (Cfn or Ci) ---- Eq. (9)

The current harmonic filters so designed establish required supply current distortion less than 5% (for Short Circuit Current to Rated Load Current Ratio (SCR) =20) or as desired by the application based on similar procedure for systems below 69 kV, with near zero reactive power drawn from the supply, with well calculated / known resonance frequencies not covered by the generated load harmonics, and without use of any step down transformer. The design procedure can be extended to higher voltages covering the relevant specifications as per the standard IEEE 519 standard.

In case of the situations as in Case-1, Case-3, and Case-5 as explained earlier, use of Neutral Current Compensator (NCC) improves the performance further or can reduce the filtering requirement further on the harmonic current filters by eliminating the 3rd harmonic, triplen (multiples of third harmonic) and unbalance components of other current harmonics.

The three-phase system will hence have supply, then filter banks, followed by NCC, and the finally the load when NCC is used or supply, then filter banks followed the load when NCC is not required / used.

The procedure allows systems to be modeled with “Matlab / Simulink platform” and assessed for the actual performance (including supply frequency variation and tolerances for filter components) before implemented on actual system using the hardware.

It should be noted that the supply voltage distortion depends upon the harmonic currents flowing in the supply and also the short circuit inductance of the supply. It is to be calculated / checked for rated load condition. The voltage distortion VTHD is given by

VTHD = [v? (n*Isn*?*Ls)2] / Vpn ------- Eq. (10)

where
n = Harmonic number for the concerned current harmonic
Isn = nth harmonic current flowing in supply network
Vpn = Line / Phase to neutral rated voltage in the system

Thus, as the value of Ls increases, the Short Circuit Ratio (SCR) falls down and the system becomes further weak. This means it can absorb less harmonic current distortion and vice versa.

Example of a three-phase system feeding a non-linear load

1. System details and specifications

An example is considered here to illustrate the design and validation of the invention with complete details and elaboration.

The system considered here is three-phase, 11 kV / 433 V (Delta / Star 200 kVA transformer), 50 Hz, supply feeding a three-phase diode rectifier drawing approximately 50 kVA. The Short Circuit Inductance measured / calculated for the supply (as per procedure explained earlier for establishing Short Circuit Capacity of supply network) is 240 µH on the secondary (433 V) side of the transformer. The rated current for the transformer on secondary side is 266.7 A. With 240 µH as the Short Circuit Inductance, the short circuit current works out as 3317.41 A. This gives the Short Circuit Current to Rated Load Current Ratio (SCR) as 12.439 (=3317.41/266.7), which is less than 20. Thus, as per IEEE 519 standard the supply can bear 5% total current harmonic distortion if 266.7 A rated current flows on the secondary side.

On the other side, the three-phase diode rectifier connected on secondary side of 50 kVA rating, draws a fundamental current of 66.67 A. If this is the only load on the secondary of the transformer, the Short Circuit Current to Rated Load Current Ratio (SCR) would have been 66.35 (=4423.21/ 66.67) and can allow even 12% total current harmonic distortion as per IEEE 519 standard. However, the total current harmonic distortion is considered to be limited to 5% maximum for the diode rectifier load (as explained in section the method 100 for providing ZRPPCHF”). Further, the diode rectifier theoretically has fundamental unity power factor and produces 5th, 7th, 11th, 13th, … and so on as the current harmonics which are drawn from the supply.

Thus, the filters are to be designed in such a way that supply total current harmonic distortion is = 5% and total VAr / kVAr to be drawn by the filters should be close to zero.

2. Design of filter banks

For the requirements given above under “System details and specifications” and based on the filter design approach explained in earlier sections, the harmonic filters are considered for 5th, 7th, and 11th, current harmonics for the rectifier. Values of the filter components are worked out are as given below.

5th harmonic filter:
Cf5 = 170 µF, 25A Lf5 = 2.4 mH, 25 A Rf5 = 250 O, 60W Rd5= 70 kO, 10W

7th harmonic filter:
Cf7 = 170 µF, 20A Lf7 = 1.23 mH, 20 A Rf7 = 127 O, 60W, Rd5 =70 kO, 10W

11th harmonic filter:
Cf11 = 170 µF, 18A, Lf11 = 0.5 mH, 18 A Rf11 = 51 O, 60W, Rd5 = 70 kO, 10W

At 170 µF, the capacitive kVAr is approximately 10 kVAr. The discharge resistors for capacitors are based on 60 seconds discharge time.

Further, a common value of 270 O is used for all filter inductances Lfn.

Compensating inductive filter bank:

Ci = 12.24 mF, 45A Li = 19.9 mH, 45 A Rfi = 2 kO, 60W Rdi = 1 kO, 10W
The diode rectifier requires a 3.5% inductive impedance in line as commutation impedance, which means it should give 0.035 V at full load current of 66.67A. For this consideration, it requires a three-phase 420 µH, 70A inductance as the input inductance.
For delivering approximately 50 kVA, the output dc side resistance required is 7 O, 80A and inductance required is 8 mH, 80 A.

3. Resonance check and results

3.1 Resonance check

For the 5th harmonic filter bank, the error impedance for 5th harmonic is -0.01413O indicating it is inductive as desired.

For the 7th harmonic filter bank, the error impedance for 7th harmonic is -0.019782O indicating it is inductive as desired.

For the 11th harmonic filter bank, the error impedance for 11th harmonic is -0.031086O indicating it is inductive as desired.

For 240 µH Short Circuit Inductance of the supply,, the inductive error impedance of 5% means -0.01884O for 5th harmonic, -0.026376O for 7th harmonic, and -0.041448 for 11th harmonic. The actual error impedances are 3.75% to allow for small variation in the available short circuit capacity of the supply network. The filter component values are chosen also based on availability of these components for the experimental check.

The low error impedances allow bulk of the respective harmonic currents to flow in those respective filter banks and negligible current in other harmonic filter banks. Further, for higher order harmonics, the impedances presented by each filter bank will be inductive eliminating the possibility of resonance with the supply short circuit inductance Ls. This will be further clear with the simulation results presented.

3.2 Simulation results

Figure 6(a) gives the Matlab / Simulink model for the system incorporating the three-phase diode rectifier and the filter banks as covered above. The same figure is shown block schematically as figure 6(b) for better clarity in understanding the system. Figure 7 gives the three-phase diode rectifier and third harmonic current injection. Further, figure 8 gives the Neutral Current Compensator, figure 9 gives the filter banks for 5th, 7th, 11th, and the inductive VAr compensation filter banks used, and figure 10 gives configuration for each of the filter bank.

Figure 11 shows simulation results for supply currents and NCC input and output currents (scope 1 in figure 6). The details are as under.

Ch1 to 3: Supply currents
Ch4: NCC input current showing unbalanced 3rd harmonic current
Ch5: NCC output current showing close to zero (<2 A peak) current as expected.

Figure 12 shows supply phase voltages after Short Circuit Inductance, supply phase “a” current, active power per phase, diode rectifier and 3rd harmonic current as the total per phase load current, distortion of the total per phase load current, supply phase current distortion, and distortion of supply phase voltage after the Short Circuit Inductance (scope 2 in figure 6). The details are as under.

Ch1, 3, 4: Supply phase voltages after the short circuit inductance
Ch2: Supply “a” phase current
Ch5: Active power per phase (approximately 18 kW)
Ch6: Diode rectifier and 3rd harmonic current as the total per phase load current
Ch7: Distortion of current in Ch6 (approximately 26.5%)
Ch8: Supply phase current distortion (approximately 4.175%)
Ch9: Distortion of supply phase voltage after the Short Circuit Inductance (approximately 2.2%)

Figure 13 shows fundamental current displacement for the load current along with its power factor and fundamental current displacement of supply current along with its power factor (scope 3 in figure 6). The details are as under.

Ch1: Fundamental current displacement for the load (approximately 120)
Ch2: Power factor of Ch1 current (approximately 0.978)
Ch3: Fundamental current displacement of supply current (approximately 14.30)
Ch4: Power factor of Ch3 current (approximately 0.969)

The Matlab / Simulink simulation results confirm the following.

• The supply current distortion <5% against load current distortion of approximately 26.5% (as required by IEEE 519 standard for the given three-phase voltage of 433 V and Short Circuit Current to Rated Load Current Ratio (SCR) of 12.439.
• Incoming distortion observed as 2.2% which is also < 8%, the allowed distortion as per IEEE 519 standard for voltages = 1 kV.
• The load and supply power factor is almost same (0.978 and 0.969 respectively) indicating that the filter banks work at close to Zero Reactive Power drawn from supply as desired.
• No 3rd harmonic current drawn from the supply indicating the NCC eliminating the unbalanced current generated by the injected 3rd harmonic current source.
• “NO” resonance with the supply Short Circuit Inductance, as desired.

3.3 Experimental set up and results

Experimental set up used is in line with figs. 6 (a) and (b) for verification purpose and does not make use of injected 3rd harmonic current (and hence does not use NCC), but uses only three-phase diode rectifier with output / dc side R-L impedance to generate required 1200 square wave waveform (as seen in figure 5(b). System details and specifications and design of filter banks remain same as explained earlier under the same headings. Resonance check carried out earlier based on the filter components also remains same as explained earlier under the same heading. Actual real power drawn by the rectifier is approximately 53 kW. Major experimental results for the same system as discussed above are given in figs. 14 to 17.

Figure 14 shows practically observed three input currents of the three-phase diode rectifier captured on oscilloscope for the experimental set up. Figure 15 shows practically observed supply input current and rectifier input current captured. Figure 16 shows practically observed voltage and current waveforms for supply and rectifier captured indicating that the power factor is nearly same (or filter banks drawing nearly zero reactive power as desired). Figure 17 shows practically observed rectifier and supply input current distortion captured. Rectifier current distortion observed is 24.5% and supply current observed distortion is 4.9%.
Figure 18 shows the experimental set up and figure 19 shows the 12.24 mF capacitor specifically developed for the experimentation.
The results show that the supply current harmonic distortion is less than 5%, no reactive power drawn from the supply, and there is no resonance with Supply Short Circuit Inductance as expected / desired. The experimental results, hence, by and large tally with the simulation results given in earlier part (part 3.2 Simulation Results) and confirm proper functioning of the Zero Reactive Power Passive Current Harmonic Filter (ZRPPCHF).

Conclusion

A Zero Reactive Power Passive Current Harmonic Filter (ZRPPCHF) can be a good, economical, and reliable alternative for filtering supply system current harmonics generated by non-linear loads. These passive filters do not require step down transformer and can be used effectively to constrain / obtain the supply current harmonic distortion within IEEE 519 standard limits or as specified by user for his system / application. This is made possible by suggested simple mathematical approach for the filter design(s) based on knowledge of the supply Short Circuit Capacity / Inductance and if not then by establishing the Short Circuit Capacity / Inductance.

At step 24, additionally a very low frequency parallel filter (Li and Ci) to compensate fundamental capacitive reactive power absorbed by the filter system configured for absorbing non-linear load current harmonics is configuring.

The harmonic filters may draw certain amount of fundamental capacitive reactive power which can be cancelled by a single inductive fundamental reactive power filter to achieve the close to Zero Reactive Power demand, a feature normally claimed by Active Filters.

The method and the system thereof for the design and Matlab / Simulink modeling allows the entire system (including supply with its Short Circuit Inductance, filters, and the non-linear load) to be simulated to check the supply current distortion within acceptable limits. The filter design can be iterated and simulated for final acceptance of supply current distortion figures even for variation of frequency (±3% or more) and finally the inductive filter can be chosen to achieve the Zero Reactive Power for all the filter banks connected in shunt.

The suggested method 100 and the system thereof for the design ensure and also allow checking for “NO Resonance Condition” with the Supply Short Circuit Inductance.

Further, the use of Neutral Current Compensator (NCC) allows reduction of 3rd harmonic current, triplens that is multiple of 3rd harmonic, and unbalanced component of other harmonics in the supply neutral.

The method 100 and the system thereof for providing ZRPPCHF can also be used for non-characteristic harmonics following the same procedure.

At step 26, the method ends.

Advantages of the present invention

The method 100 and the system thereof for providing ZRPPCHF current harmonic filtering in supply systems is mathematically formulated, designed, simulated and validated through experimental results.

The method 100 and the system thereof for providing ZRPPCHF for current harmonic filtering in supply systems can be mathematically formulated, designed, simulated, and is then implementable for any power system bases on the knowledge of its short circuit inductance / capacity and non-linear load.

The method 100 and the system thereof for providing ZRPPCHF filters the supply current harmonics and can be designed to achieve a given supply current harmonic distortion (as per IEEE 519 standard or as per user specification) at zero reactive power.

The method 100 and the system thereof for providing ZRPPCHF does not require step down transformer for any given system voltage and can be designed for low to high voltage systems.

The method 100 and the system thereof for providing ZRPPCHF also achieves / allows resonance free operation of the harmonic filter banks with respect to the Supply Short Circuit Inductance, assured through its mathematical formulation and design. The same also can be checked with modeling and simulation with Matlab / Simulink software (accepted simulation platform all over the world).

Even though the ZRPPCHF formulation considers characteristic harmonics (such as 3rd, 5th, 7th, 9th, 11th, 13th ….. and so on) it can also be designed for non-characteristic harmonics based on the suggested formulation / procedure.

The use of Neutral Current Compensator (NCC) allows reduction of 3rd harmonic current, triplens that is multiple of 3rd harmonic and unbalanced component of other harmonics in the supply neutral current. The ZRPPCHF when used along with NCC reduces the burden of consideration of filters for the reduction of 3rd harmonic current, triplens that is multiple of 3rd harmonic and unbalanced component of other harmonics.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.

Annexure -I

Neutral Current Compensator (NCC)
Simple and Reliable Solution Eliminates Neutral
Current Problems in LV to HV Systems

1.0 Neutral Current Causes, Effects, and Mitigation
1.1 Causes
• Unbalanced Fundamental active and or reactive currents
• Unbalanced current harmonics
(drawn by non-linear loads in three-phase systems)
1.2 Effects
• Heating of neutral busbar or burning/ insulation failure of neutral cables
• Shifting of supply neutral potential with respect to earth potential based on earth resistance and the neutral current
• Unacceptable unbalance or asymmetry in phase to neutral voltages damaging sensitive loads such as in medical applications
• Disconnection from supply neutral point or earth resulting in phase to phase voltages appearing across loads and subsequently causing damage to loads (example: Tube Lights, Bulbs, Fans, TVs, Refrigerators, and other household appliances)
• Disturbances in synchronization voltages for connected active power converter
• Large unbalanced loads causing voltage disturbances to other loads connected on same bus, sometimes resulting in visible flicker
• Reduction in life of incoming supply transformer
• Associated monitory / financial loss due to non-availability of load

2.0 Salient Features / Advantages of the NCC
• Can be used for star as well as delta connected supply feeding power to star connected balanced / unbalanced and linear / non-linear load
• Reduces neutral current flowing in the supply (directly or through earth) to near zero value, irrespective of the type of non-linear load
• Helps in retaining supply neutral voltage (star point) close to earth or zero potential even when earth resistance is high (earth pit goes dry) or supply neutral point gets disconnected from earth or load neutral gets disconnected from supply neutral point or load neutral gets disconnected from earth
• Eliminates “performance” dependency of load neutral connection to supply neutral point or earth
• Reduces unbalance current caused by triplens as well as by other unbalance in other harmonics present in the load currents
• Reduces asymmetry in phase to neutral voltages (deviation from average value) by almost 50%, which further helps in reducing the unbalanced load neutral current.
• Uses only magnetic components offering high reliability
• Robust (fit and forget)
• Easy to manufacture, erect, and commission
• Very economical
3.0 NCC Matlab Simulation Results
Figure A3.1 shows simulation results for unbalanced non-linear load
Ch1, Ch2, Ch3: Line currents ia, ib, ic (100+ to 200 A peak to peak)
Ch4: Uncompensated Neutral Current inL (200 A peak to peak) of the load
Ch5: Compensated Neutral Current inNCC (0 A) flowing out from the NCC
4.0 NCC Experimental Results for 30 kVA Unbalanced Load with NCC installed at a Hospital in Sangli
Figure A4.1: The three load currents and neutral current shown by Green (with peak approaching 35 A without NCC installation) entering the supply neutral point
Figure A4.2 shows the three load currents and neutral current shown by Green (almost close to zero with NCC installation) entering the supply neutral point

Annexure –II
IEEE 519 (2014) Standard: Supply Current and Voltage Distortion Limits

,CLAIMS:We Claim:

1. A method and a system thereof for providing Zero Reactive Power Passive Current Harmonic Filter (ZRPPCHF) for a non-linear load, the method comprising steps of:
identifying supply voltage and frequency;
obtaining Short Circuit Capacity and hence a Short Circuit Inductance of an electric supply at the point of PCC (Point of Common Coupling), and details of non-linear load which includes VA/kVA, Watts/kW, VAr/kVAr and current harmonics produced by the non-linear load;
identifying Short Circuit Current to Rated Load Current Ratio (SCR) for the electric supply at PCC;
identifying specified current harmonic and voltage harmonic distortion;
deriving filter error impedance to achieve specified current harmonic distortion (based on IEEE 519 standard or as specified by the user);
configuring a filter system in parallel with the non-linear load for absorbing current harmonics from the non-linear load, wherein the difference between nth harmonic filter impedance error is 1/20th of that of Short Circuit Impedance for the nth harmonic, and
additionally configuring a very low frequency parallel filter (Li and Ci) to compensate fundamental capacitive reactive power absorbed by the filter system configured for absorbing non-linear load current harmonics.

2. The method as claimed in claim 1, wherein the filter system realizable as a hardware based filter (for given LV to HV system voltage) in an actual single or three-phase system to mitigate characteristic as well as non-characteristic current harmonics generated by non-linear loads and to achieve total current harmonic distortion within IEEE 519 standard or user specification for the supply current.

3. The method as claimed in claim 1, wherein the filter system ensures resonance free operation of the filter with Supply Short Circuit Inductance.

4. The method as claimed in claim 1, wherein the filter system can be configured for a star connected unbalanced linear or non-linear load using Neutral Current Compensator (NCC) along with it to achieve reduction of 3rd harmonic current, triplens, and unbalanced component of other current harmonics, if present in the load neutral.