power quality factor improvement using shunt active power line conditioner

7/25/2019 Power Quality Factor Improvement Using Shunt Active Power Line Conditioner

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2014 IEEE Inte ational Conference on Advanced Communication Control and Computing Tec nologies (ICACCCT)

transfer of a t ree-phase network. The PQF considers variousquality aspects (QA) notably the current and voltage harmoniclevels the phase displacements between corresponding phasevoltages and currents at the ndamental equency and thedegree of unbalance in the different phase voltages andcurrents [ ]. The various QAs are measured separately so thatif needed the particular quality aspect that requires correctioncan be recognized easily.

A high level of power quality is understood as a low levelof disturba ces; agreement on acceptable levels ofdisturbances is needed [6]. Under steady-state conditions t ree power-system parameters equency waveformdistortion and symmetry can serve as ames of reference toclassi the dist bances according to their impact on thequality of the available power[8]. The power factor has beenconsidered as another prominent quality aspect.A. Total Current and Voltage Harmonic Distortion:

The total voltage and current harmonic distortion and' respectively for single-phase and t ree-phase networks

have been expressed as

(1)

where V and I represents rms values and 1 and h denote thendamental and the harmonic order respectively.

The total voltage and current harmonic distortions and are considered as two quality aspects for a t ree phase unbala ced system and are given by

(2)where and represents the equivalent fundamental phasevoltage and current.

B. Unbalance Factor:Relevant quality aspects are the unbalance factors of the

voltage and current and respectively expressed as

=

c r, = xeC. De nition of the Power-quality Factor

The power quality factor (PQF) is chosen as a singlemeasurable indicator which integrally re ects the various power-qualit aspects de ned in the previous sections.

(4)

whereWiare judiciously selected weight factor that sum up toandQAiare the de ned quality aspects.

D. De nition of the Voltage-quality FactorThe voltage quality factor (VQF) is chosen as a single

measurable indicator which integrally re ects the variousvoltage quality aspectsQAi =1 ) fo ulated above. This isde ned as

(5)

wherewia e judiciously selected weight factor of the voltage

waveform that sum up to 1.

IV. NST NT NEOUS EACTIVE OWER HEORYIn 198 Akagi Kanazawa and Nabae introduced the

instantaneous reactive power theor the so-called p qtheor[4]. The main target was to realize an effective scheme tooptimize nonlinear loads using active power lters. Prima ilyit was implemented to t ree-phase t ree-wire balancedsystems and then it was diversi ed to four wire unbal cedsystems.

This theory represents the power terms in new axesWhere a d abc axes are coplanar and the 0 axis isorthogonal to both. In coordinates the power terms are theinstantaneous real and imaginary powers respectively. Theload current can be illustrated in the real and imaginarcomponents. The main purpose of p q control scheme is to geta constant source power a er the compensation with APFs.Also it is required to introduce the -axis to consider fourwire systems. The instantaneous zero-sequence real powerwill be the new power term. So an additional compensationaim is to nulli the neutral current. A necessary constraint of the static compensation is that the active power of theconditioner will be zero.

The abc system is transformed to coordinates as follows:

:;]JV V V:l 2 2 (6)0 , ,2 2So the instantaneous real power is:

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The p q theor de nes two instantaneous real powersPoandPa ' and one instantaneous imaginary powerqa

[Po

1[eo

Pa =

0qa 0The instantaneous currents in coordinates are:. 10 = ; Po

(8)

(9)

where:e = e eiois the instantaneous zero-sequence currentiapis the instantaneous active current of the -axisi p is the instantaneous active current of the -axisia is the instantaneous reactive current of the -axisi is the instantaneous reactive current of the -axis.

Now it is possible to formulate the instantaneous powercomponents of the t ree axes.

So the instantaneous real power is:

t ) = o t ) PaCt ) P ( t ) ( )= Po( t ) Pap( t ) P p( t ) Pa ( t ) P ( t )

e e -e"ef e"ef= eolo + e 2 + e 2 P a( + e 2 + e 2 P a( + e 2 + e 2 qa( + e 2 +e 2 qa( " f " f " f " f

The currents and powers in abc axes can be calculatedom the terms t rough the inverse transformation. If[T]is the transformation matrix om abc to axes it is possible to write:

(12)

where:

1

0.[Tr 1 = 1 1. 2 21 1. 2 2

All represented power terms o( t ),Pa ( t ) nd qa ( t ) can be indicated as the sum of a constant term equal to itsaverage value in a period and a variable term. The rst one isassigned with a capital letter and the second one with a "symbol over the proportional term.

o t ) = o o t )(1 )

To get a constant source power o a theequations are:

Pco( t ) = PLO( t ) - LO= LO( t )

(14)

where the subscript" with respect to the compensator and the subscript with respect to the load.These equations represent the power terms. So the

compensation currents can be formulated in coordinatesas:

where = e e .

Finally the compensation currents in abc coordinates

l$1; lI 1 1 i. 2 2

(15)

are:

(16)

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Sour

PiJs s

Hte sibardu c nt 1

Fig: 2. Schematic block diagram of three-phase shunt PF system

V. YSTERESIS B D CURRENT CONTROLLERThe hysteresis band control is shown in Fig: . A single

phase inverter and a sinusoidal reference are presented. When the obtained current crosses a band around the current reference the switching devices change (it turns N/ FF) and the current goes back to the band.

+_e o h

GBT ggf .

gnall c mpa a ir ui

il /eas y t r s P w-

Fig: 3. Control scheme of hysteresis-band method

The control performance is later: the currents are obtainedand compared with the reference signals; the inputs of a hysteresis comparator will be the error signals; their outputsare the IGBT trigger pulses. If the measured current is more (ay per cent of the band value) than the reference current it is

required to adjust the corresponding switching devices toobtain a negative inverter output voltage; this voltage in tudecreases the output current and it retu s to the referencecurrent band. n the other hand if the measured current islesser (a fty per cent of the band value) than the referencecurrent the switching devices adjusted to get a positiveinverter output voltage; this in turn increases the outputcurrent and it returns to the reference signal band. As a result the output current will be in a band following the referencecurrent.

VI. IMULATION RESULTSThe simulation results were obtained by using Matlab

Simulink Power System Toolbox so ware for a t ree phase power system with a shunt APLC. The proposed method has been simulated under two cases balanced non-linear load and unbalanced non-linear load conditions. For a t ree phase balanced sinusoidal supply system using shunt APLC both

cases a e investigated by detailed simulation study. Thesimulation results a e discussed below.Case 1: Balanced non -linear load

Fig:4 shows the simulation results of the proposedalgorit m under t ree phase mains voltages when balanced non-linear load is connected. The t ree-phase mains currentsa er compensation are balanced sinusoidal and in phase with t ree-phase mains voltages. The instantaneous reactive power theor is feasible. A er compensation the THD of sourcecu ent is reduced and is presented in Table 1.

Fig: 4. Three phase source voltage load current lter current and sourcecurrent when balanced non-linear load is connected.

Case 2: Unbalanced non-linear loadFig:5 shows the simulation results of the proposed

algorit m under t ree phase mains voltages when unbala ced non-linear load is co nected. The t ree-phase source currentsa er compensation are balanced sinusoidal and in phase with

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0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08-400

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0

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Time (sec)

S o u r c e

v o l t a g e ( V )

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20

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L o a d

c u r r e n t ( A )

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F i l t e r

c u r r e n t ( A )

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t ree-phase mains voltages. The instantaneous reactive power theory is feasible. A er compensation the THD and unbalancefactor of source current are reduced and a e presented inTable .

Fig: 5Three phase source voltage, load current, lter current and sourcecurrent when unbalanced non-linear load is connected.

T BLE 1: RESULTS WITH D WITHOUT ACTIVE POWER FILTER( PF) FOR CASES

IND 2

Balanced Non-linear Unbalanced Non-linear loadload

ITHDwithout apf 29.17% 21.04%ITHDwithapf .47% 4.64%I UNBwithout apf - 5. 9%IUNBwithapf - 0.76%PQFwithout apf 85.40% 86.70%PQFwithapf 98.20% 97. 0%

VI. ONCLUSIONIn this paper a control method is presented to compensate

unbalanced and harmonic cu ents. The shunt active powerlter has been simulated and investigated for two cases i.e. for

balanced and unbalanced non-linear loads. The results shows that the shunt active power lter compensated the harmonicand unbalanced components of the load current. The total harmonic distor ion and unbalance factors a e measured for the source cu ent and power quality factor is derivedconsidering the measured harmonics and unbalances of thesource currents under balanced and unbalanced non-linear

load conditions. The low level of harmonics and unbalancesmeans the high level of Power quality factor. For the twocases the power quality factor has been improved.

CKNOWLEDGMENT

This work was supported by Central Power ResearchInstitute ofBangalore (vide no. /5/R

&D/RS P/2011).

EFERENCES

[1] H kagi ' rends in active power line conditioners" IEEE Transactionson power Electronics vol 9 no 3 1994 pp263-268.

[ 2] Ledwich G Ghosh A. A Flexible DSTATCOM Operating in Voltageor Current Control Mode". IEEProc. Generation Transm. dDistribution Vol. 149 No. 2 2002 pp. 215 224.

[3] ntonio Moreno-Mu oz (Ed.) Power Quality MitigationTechnologies in a Distributed Environment" Springer-Verlag LondonLimited 2007.

[4] kagi H Kanazawa Y Nabae A. Generalized Theory of theInstant eous Reactive Power in Three-Phase Circuits". ProceedingsIPEC83 Tokio Japan 1983 pp.1375 1386.

[5] L. Gyugyi and E. C. Strycula Active AC power lters" IEEE ASnnu. Meeting 1976 p. 529.

[6] Singh B A -Haddad K ChandraA. A Review of Active Filters forPower Quality Improvement". IEEE Transactions on IndustrialElectronics Vol. 46 No. 5 1999 pp. 960 971.

[7] Oleg Vodyakho and Chris C. Mi Senior Three-Level Inverter- BasedShunt Active Power Filter in Three-Phase Three-Wire and Four-WireSystems" IEEE Transactions On Power Electronics Vo .24 No. 5 May 2009.

[8] Practical de nitions for powers in systems with non-sinusoidal waveforms and unbal ced loads: A discussion" IEEE Trans. PowerDel. vo no. pp. 79 101 J . 1996.

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power quality factor improvement using shunt active power line conditioner

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