THE APPLICATION OF PSO TO HYBRID ACTIVE POWER FILTER DESIGN FOR 3 PHASE 4-WIRE SYSTEM WITH BALANCED & UNBALANCED LOADS

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This paper presents a application of PSO to Hybrid active power filter used to compensate for total harmonic distortion in three-phase four-wire systems. The shunt active filter employs a simple method for the calculation of the reference compensation current based on Fast Fourier Transform. The presented Shunt Active Power filter is able to operate in balanced, unbalanced and Variable load conditions. Classic filters may not have satisfactory performance in fast varying conditions. But auto tuned active power filter gives better results for harmonic minimization, reactive power compensation and power factor improvement. The proposed auto tuned shunt active filter maintains the THD well within IEEE-519 standards. The proposed methodology is extensively tested for wide range of different Loads with Improved dynamic behavior of shunt active power filter using PSO to Hybrid active power filter. The results are found to be quite satisfactory to mitigate harmonic Distortions, reactive power compensation and power factor correction thereby increase in Power Quality improvement and reduction in %THD.
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  International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-196332 Vol. 2, Issue 1, pp. 32-42 T HE A PPLICATION OF PSO TO H YBRID A CTIVE P OWER F ILTER D ESIGN FOR 3   P HASE 4-W IRE S YSTEM WITH B ALANCED &   U NBALANCED L OADS   B. Suresh Kumar 1 ,K. Ramesh Reddy 2 & S. Archana 3   1&3 Department of Electrical andElectronicsEngineering, CBIT, Hyderabad, India 2 Department of Electrical andElectronicsEngineering, GNITS, Hyderabad, India  A  BSTRACT    This paper presents a application of PSO to Hybrid active power filter used to compensate for total harmonicdistortion in three-phase four-wire systems. The shunt active filter employs a simple method for the calculationof the reference compensation current based on Fast Fourier Transform. The presented Shunt Active Power  filter is able to operate in balanced, unbalanced and Variable load conditions. Classic filters may not havesatisfactory performance in fast varying conditions. But auto tuned active power filter gives better results for harmonic minimization, reactive power compensation and power factor improvement. The proposed auto tuned shunt active filter maintains the THD well within IEEE-519 standards. The proposed methodology is extensivelytested for wide range of different Loads with Improved dynamic behavior of shunt active power filter using PSOto Hybrid active power filter. The results are found to be quite satisfactory to mitigate harmonic Distortions,reactive power compensation and power factor correction thereby increase in Power Quality improvement and reduction in %THD.  K   EYWORDS :    Hybrid active power filter (HAPF), Multiobjective optimization, particle swarm optimization(PSO), Total Harmonic distortion (THD), Power factor, Reactive power  I.   I NTRODUCTION   Power Systems have to cope with a variety of nonlinear Loads which introduce significant amounts of harmonics. IEEE Standard 519-1992 provides a guideline for the limitation and mitigation of harmonics. Passive power filters (PPFs), Active power filters (APFs), and hybrid active power filters(HAPFs) can all be used to eliminate harmonics. For Medium- and high-voltage systems, PPFs andHAPFs appear to be better choices considering cost where the ratings are of several tens of megavolt–amperes. The design of such PPFs and HAPFs is a complicated nonlinear programming problem.Conventional trial-and-error Methods based on engineering experience are commonly used, but theresults are not optimal in most cases.In recent years, many studies have appeared involving optimal PPF design. A Method based on thesequential unconstrained minimization Technique has been used for PPF design because of itssimplicity and versatility, but numerical instability can limit the application of this method. PPFdesign using simulated Annealing has been reported, but the major drawback is the repeatedannealing.Genetic algorithms (gas) have been widely used in PPF design, but the computing burden andconvergence problems are disadvantages of this approach. A design method for PPFs using a hybrid  International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-196333 Vol. 2, Issue 1, pp. 32-42 Differential evolution Algorithm has also been proposed, but the algorithm is Complex, involvingmutation, crossover, migrant, and acceleratedOperations For the optimal design of HAPFs, a method based on gas has been proposed in order tominimize the rating of APF, but no other optimal design methods appear to have been suggested.Many methods treated the optimal design of PPFs and HAPFs as a single objective problem. In fact,filter Design should determine the optimal solution where there are multiple objectives. As theseobjectives generally conflict with One another, they must be cautiously coordinated to derive a Goodcompromise solution.In this paper, optimal multi objective designs for both PPFs and HAPFs using an advanced particleswarm optimization (PSO) algorithm are reported. The objectives and constraints were developedfrom the viewpoint of practicality and the Filtering characteristics.For the optimal design of PPFs, the capacity of reactive Power compensation, the srcinal investmentcost, and the total Harmonic distortion (THD) were taken as the three objectives. The constraintsincluded individual harmonic distortion, fundamental Reactive power compensation, THD, andparallel and Series resonance with the system. For the optimal design of HAPFs, the capacity of theAPF, The reactive power compensation, and the THD were taken as the three objectives; theconstraints were as for the PPFs.The Uncertainties of the filter and system parameters, which will Cause detuning, were alsoconsidered as constraints during the optimal design process. A PSO-based algorithm was developed tosearch for the optimal solution. The numerical results of case Studies comparing the PSO method andthe conventional trial and- Error method are reported. From which, the superiority and Availability of the PSO method and the designed filters are certified. II.   S YSTEM U NDER S TUDY   A typical 10-kV 50-Hz system with nonlinear loads, as shown in Fig. 1, was studied to determine theoptimal design for both PPFs and HAPFs. The nonlinear loads are the medium frequency furnacescommonly found in steel plants with abundant harmonic currents, particularly the fifth and seventhorders, as shown in Table I. The utility harmonic tolerances given in IEEE Standard 519-1992 and theChinese National Standard GB/T14549-93 are listed in Table I as percentages of the fundamentalcurrent.   Fig 1 . Single diagram of system for case studies.  International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-196334 Vol. 2, Issue 1, pp. 32-42 Table I : Harmonic Current distributions in phase A and utility tolerancesHarmonicOrderMeasuredValue(%)NationalStandard(%)IEEEstandard519-1992(%) 5 6.14 2.61 47 2.77 1.96 411 1.54 1.21 213 0.8 1.03 217 0.6 0.78 1.519 0.46 0.7 1.523 0.95 0.59 0.625 0.93 0.53 0.6THD 7.12 5 5 Table I shows that current THD, and the 5th, 23rd, and 25th order harmonic currents exceed thetolerances based on both standards. In addition, the 7th and 11 th order harmonics exceed the tolerancebased on the National standard.Filters must therefore be installed to mitigate the harmonics sufficiently to satisfy both standards.Both PPF and HAPF are suitable and economical for harmonic mitigation in such systems. For thissystem with nonlinear loads as medium frequency furnaces, the even and triple harmonics are verysmall and far below the standard values, so these harmonics are not considered. In addition, theharmonic voltages are in fact very small, so the voltages are assumed to be ideal.The fundamental current and reactive power demands are 1012 A and 3–4 MVar, respectively. Theshort circuit capacity is 132 MVA, and the equivalent source inductance of the system is 2.4 mH III.   HAPF   D ESIGN B ASED ON PSO   A. HAPF Structure and Performance: In order to demonstrate the optimal design method of HAPFs based on PSO, an HAPF was designedand is shown in Fig. 2; it is supposed to be used in the same situation as that shown in Fig. 1. In thisHAPF, PPFs are mainly used to compensate for harmonics and reactive power, and an APF is used toimprove the filtering performance .The PPF consists of the fifth and seventh single-tuned filters and ahigh-pass damped filter. The APF is implemented with a three-phase voltage-source inverter. Fig. 3(a)shows the single-phase equivalent circuits of the HAPF, assuming that the APF is an idealcontrollable voltage V  AF and that the load is an ideal current source  IL .  ZS is the source impedance,  ZF  is the total impedance of the PPF, V  pcc is the voltage of the injected point, and K  is the controllinggain of the APF.   Fig.2. Shunt HAPF.    International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-196335 Vol. 2, Issue 1, pp. 32-42 Fig 3 .Single-phase equivalent circuits of the HAPF (a) Equivalent circuit.(b) Equivalent harmonic circuit. The equivalent harmonic circuit is redrawn as in Fig. 3(b). The harmonic current  Ish into the systemsource and the harmonic attenuation factor γ   are given in the following equations: ||(1)||(2) F shLhFSShF  LhFS  Z  II KZZ  IZ  IKZZ  γ   = →+ += = →+ +  Assuming that the fundamental component of the supply voltage is fully dropped across the PPF, thevoltage and current of APF can be derived as follows [24]: 1 ..(3)(4)  AFAFhFhAFhFhLhhhh AFAFAFhh VVZIZI  III  ′ ′ ′ ′= = − = →′ ′ ′= + → ∑ ∑ ∑∑  The rms value of ˙ V  AF is defined as 25,7,11,13,17,19,23,25 (5)  AFAFhh VV  = = → ∑  The capacity of the APF is determined by the current  I  ˙AF and the voltage ˙ V  AF. It is obvious that thelow VA rating of APF can be achieved by decreasing ˙  I  AF and ˙ V  AF. In this shunt hybrid topology,the current  I  ˙AF is almost constant, so the only way to reduce the VA rating of APF is to decrease thevoltage V  AF.  B. Multi objective Optimal Design Model for HAPF: As mentioned earlier, when designing an HAPF, it is very important to minimize the capacity of theAPF component, and there are some other objectives and constraints to be considered when the APFof the HAPF is cut off due to faults, the PPF part keeps work in to mitigate harmonics until the APF isrestored. It follows that some additional constraints should be included in respect of such occasions.The constructions of objective functions and constraints are described next. Three important objective functions are defined as follows . 1) Minimize the capacity of the APF, which is mainly determined by the harmonic voltage across it 25,7,11,13,17,19,23,25 min(6)  AFAFhh VV  = = → ∑  2) Minimize the current THD with HAPF 221 min(7)  N sh HAPF h  I THDI  I  =   = →    ∑  where THDI  HAPF is the current THD with the HAPF in place; and the definitions of   Ish ,  I  1, and  N  are the same as those in (7).3) Maximize the reactive power compensation 5,7, max(8) iiH  Q = → ∑  Where Qi is same with that in (9)
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