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Energy Procedia 50 (2014) 528 - 535

The International Conference on Technologies and Materials for Renewable Energy, Environment

and Sustainability, TMREES14

Three-Phase For-Wire Shunt Active Filter With Unbalanced loads

T. MAHNIa, M.T Benchouiaa, k. Srairib,A.Ghamrib A.Goleaa ,

aBiskra University, Laboratory LGEB Department of Electrical Engineering bBiskra University Laboratory LMSE Department of Electrical Engineering BP. 145, 07000 Biskra, ALGERIA E-mail: ksrairi@yahoo.fr

Abstract

The electrical power quality at low voltage alternative networks became a serious concern because of the increased use of nonlinear loads and pollutants. This work is to improve the quality of electric current in such networks. Four-Wire Shunt Active Filter is studied; deferent loads (balanced and unbalanced) are discussed. We propose to identify harmonic and reactive currents at the base of Self-Tuning-Filters, which proved very good filtering performance, either in transient or steady state. The simulations demonstrate the importance of this work in harmonic filtering and reactive power compensation.

© 2014ElsevierLtd. Thisisanopenaccessarticle under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) Keywords — Shunt Active Filter (SAF), Total Harmonic Distortion(THD), Self-Tuning-Filter (STF), Unbalanced loads..

1. Introduction

Generally, harmonic currents are produced by power electronic equipment. These harmonic currents are the source of adverse effects for many types of equipment such as heating in distribution transformer and perturbation of sensitive control equipment.

Many solutions have been studied in the literature to mitigate the harmonic problems, such as the passive filters which cannot completely eliminate all of the harmonic currents, and the active filters which is developed and widely used to overcome to the drawbacks of the passive filters and improve power quality [1].

The identification approach is based on the Phase Locked Loop (PLL), which is not sensitive to the disturbances, specifically to the harmonic and unbalanced voltage [2], [3].

Corresponding author. Tel./ fax: +21333543158. E-mail: ksrairi@yahoo.fr

1876-6102 © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) doi:10.1016/j.egypro.2014.06.064

As known, the performances of the active filter system mostly depend on the accuracy of the harmonic isolation and DC voltage control. Many works recently dealt with Active Power Filters for three-wire power system [7], and using Self-Tuning Filter to isolate harmonic currents without reactive power [1-2], [4-5]. This STF is used instead of classical harmonics extraction based on High Pass Filters or Low Pass Filters, it proved excellent performances.

This paper presents a new control scheme of 3-phase 4-wire Power Active Filter, to compensate harmonic and reactive power simultaneously, using Self-Tuning-Filters. The effectiveness of the proposed method is verified by computer simulation, and presented in this paper.

Fig. 1. Filter configuration

2. System Configuration

2.1 Self-Tuning-Filter

In this paper, we propose to use Self-Tuning-Filter (STF) in the place of Low Pass Filter or High Pass Filter. The STF is introduced by Hong-sock Song in [6].

The STF principle is described in the Fig. 2 below.

Fig. 2 Self-Tuning-Filter

From Fig. 2, the following expressions can be obtained:

*a(s) = - -^Xp(s)),

xP(s) = (7h?(s) — *p(s)] +-;гxa(s)), Where:

(1) (2)

xa, Xp: input signals in Clark axes

xa, Xp: output signals in Clark axes (the fundamental of the input signals) K: Selectivity parameter Mf: Fundamental pulsation

2.2 Harmonics and reactive identification by the instantaneous power theory using STF

The load currentsiil,ti2 and iL3 of the three-phase four-wire system are transformed into thea — ft — oaxis as follows:

0 V3 -H

-Vf n n

As known, the currents in the stationary frames can be respectively decomposed into DC and AC components by:

ia + ia îp + ïp,

i ^n + ^

Then, the STF extracts the fundamental components at the pulsation Mf directly from the currents in the a — f> axis.

The a — P harmonic components of the load currentsare computed by subtracting the STF input signals fromthe corresponding outputs. The resulting signals are the AC components, la andt^, which correspond to the harmonic components of the load currents iL1, iL2 and iL3 in the stationary reference frame. If: t0 = 0, ( three identical loads)then the o harmonic component of the load is:

î0 = i0, (5)

which correspond to the harmonic component of the neutral current in in the stationary reference frame. For the source voltage, the three voltages vS1, vS2 and vS3are transformed to the a — preference frame as follows:

Then, we applied the STF to these a — P voltage components. This filter allows suppressing the harmonic components of the distorted mains voltages and consequently leads improves the harmonic isolator performances.

After the computation of the fundamental component p^and the computation of the harmonic currents iap0, we calculate the alternative instantaneous real power p(t) and the instantaneous imaginary power q(t)as follows [8-9]:

q(t) = ipva — iavp

lava + ïpVp,

And so we identify harmonics and reactive power at the same time. The references of current in the a — P reference frame are calculated by:

ifa = PT^T (?a X(p + pDC) —vpx q), irfe/ = fa X(p + Vdc) + va X ci):,

.ref _ . lfo ~ l0,

(10) (11)

Where:pDC is a small amount of active power absorbed from or realised to the DC capacitor so as to regulate the DC bus voltage. Then the filter reference current in the 1, 2, 3 coordinates are defined by:

r -refi

.ref Lf2 •ref L'/3 J

— V3 2

r.ref-\

■ ref

.ref Llf0 J

Fig. 3 below describes the identification scheme.

„ref vdc

PI controller

Instantaneous powers calculation

Pdc'X1

ififlnd ip

Calculation

Fig.3 Identification scheme

3. Simulation Results

Fig. 4 presents the system of loads studied. 3.1 Balanced loads

The simulation parameters are defined in Tab. II. For the loads we consider three identical loads powered by three non-controlled rectifiers. Fig. 5shows the simulation results for the system of load depicted in the Fig.5. Before inserting the APF (between 0 and 0.1 s), The Total Harmonic Distortion (THD) of the source (and the load) current is equal to 28.94 %. At 0.1 s the APF is inserted and the source current becomes perfectly sinusoidal.

Fig.4 The three loads configuration

With classic low pass filter the obtained THD of the supply currents is 1.99 % after compensation. Using STFs the THD is reduced to 0.97 %, (K = 50 for the STF). At 0.2 s the same system of load is inserted. And the supply currents remain quickly sinusoidal.

For the inverter of the active power filter we used two topologies; three-leg (with split DC capacitor) and for-leg inverter. The THDs that we mentioned (1.99 % and 0.97 %) are those of the three-leg configuration. The THDs obtained by the for-leg topology are 2.00 % with low pass filter and 1.07 % with STF.

When we compare between the three-leg and the for-leg topologies, we find the results shown in Tab. I. In this simulation the same balanced system of loads of the period between 0.1s and 0.2s is used:

Î *0|

Fund am nul * 4 J31 . T«)- 6 «TS

r. —

...............i...............;................

S 10 is «

htaf momç qrdtr

A ÏOD

FundlmtfilM I SCW| » 4 UJ , ThO- IIKS

_ l 1 i LJ. J. J

►♦rmûnii ùpdtr

Fig.5 Simulation results of STFs under three balanced loads: (a) Supply and loads currents, (b) 1st phase filter current, (c) Neutral currents, (d) Harmonic current spectre of 1st phase load, (e) Harmonic current spectre of 1st phase of supply

Table 1: Simulation results for the three and for-leg topologies

Between 0.1s and 0.15s Between 0.25s and 0.29s

3-leg 4-leg 3-leg 4-leg

THD (%) 3.27 4.07 0.64 0.62

The results of Tab. 1 show that for transient regime the three-leg topology gives the best THD and for steady regime for-leg topology gives the best THD. For-leg topology is the best because in this topology the neutral is piloted directly (by hysteresis command) so the THD is best. In three-leg topology the neutral is indirectly piloted so the THD is high. The simulation results verify the effectiveness and the performances of the proposed harmonic isolation under balanced load in harmonic elimination for different topologies of rectifier.

3.2 Unbalanced loads

To examine the effectiveness of the STF, simulations under unbalanced system of load are done. This new system is described below: Resistive load (Rd1 = 26 Q) powered by dimmer connected between phase 1 and neutral (a1 = 60°), Inductive load (Rj2 = 26 Q et Ld2 = 30 mH) powered by rectifier, Resistive load (R^ = 26 Q) powered by dimmer connected between phase 3 and neutral (a3 = 30°).

Fig. 6 shows the simulation results for this system. The THDs of loads are respectively: 32.41 %, 11.87 % and 13.01 %. While the THDs of supply currents are respectively: 3.83 %, 3.43 % and 2.34 %. Im-is the neutral load current; it contains the third order harmonic, and odd multiple of three harmonics. Ins is the neutral supply current, it is became zero after compensation.

— rmflnnitu (MMK "!.B.rHO»J¡.41!4

Flrn»--íful ¡iíKtj» i.lN ,T№ ".If*

Junälmlruf IKKJ ■ 1.411 .THDHÎ

li FiritpMte .............. imwiBii ......... ■ - -

- - -.-

M "i « \

FumutwmI [«WH ««II 1MÜ ---

i 1» i: Hrflin lc

Fu nsrrfiul IJCHIJ ■ ÍJJ3Í , I» JJJ ti

iTNrd pM i*

M .......li.«-—.« .............{...........

■ ■ . -

I 10 U

itrniitceijtr

Bjno.mtf.m |Jim) . iJU1, T ». Î.MS

■7---

Fl in pJiin

S 10 11

: in J*Jin'irJ i

Fig.6 Simulation results under three unbalanced loads:

*Mrd pra**:

......... —1™...........

¡ 11 11 Hlfmsflï «dir

(a)Source and loads currents, (b) Neutral currents, (c) Filter currents,(d) Harmonic current spectres of loads,(e) Harmonic current spectres of supply

3.3 Reactive power compensation

In this simulation STFs are used to compensate reactive and harmonics of source current. The same parameters of the balanced load case are used. Fig. 8.a demonstrates that there is a phase difference between source voltage and source current (before compensation). Fig.7.b demonstrates that there is no difference of phase between source voltage and current (phase 1), it means that power factor is became equal to 1 (after compensation).

(a) Before reactive power compensation

(b) After reactive power compensation

Fig.7 Supply voltage and current (phase 1)

4. Conclusion

In this paper we have presented a new tree-phase for-wire active power filter based on STF extraction, to identify harmonic current and reactive power. The objective was to improve the dynamic of identification method and also selectivity. The advantages of this filter are:

STFs don't introduce any displacement between input and output, at the fundamental pulsation. Good dynamic, and high selection of fundamental signal. Their selectivity is improved by reducing K. They can filtrate the voltages that are used to calculate instantaneous powers, to identify perturbation, and so PLL is not used. This method reduces the complexity of the control scheme and consequently facilitates the digital implementation of the control system. Those results demonstrate the good performances of the proposed control.

References

[1] M. Abdusalam, P. Poure,S. Saadate, "Hardware Implementation of a Three-PhaseActive Filter System with Harmonic IsolationBased on Self-Tuning-Filter", IEEE. Power Electronics Specialists Conference, Aug. 2008, pp. 2276-2278.

[2] M. Abdusalam, P. Poure, S. Saadate, "A New Control Method of Hybrid Active Filter to Eliminate the 5th and 7th Harmonic Frequency Using Self-Tuning-Filter in the Feedforward Loop". IREE, International Review of Electrical Engineering, Feb. 2008, pp. 65-72.

[3] A Ghamri, M.T Benchouia, A.Golea.,Sliding-mode Control Based Three-phase Shunt Active Power Filter: Simulation and Experimentation; Electric Power Components and Systems Journal, 2012, 40( 4): 383-398.

[4] M. Abdusalam, P. Poure, S. Saadate, "A New ControlScheme of Hybrid Active Filter Using Self-Tuning Filter", POWERENG, International Conference on Power Engineering, Energy and Electrical Drives, Setubal Portugal,April. 2007, pp. 12-14.

[5] M.C. Benhabib, S. Saadate, " New Control Approach for Four-Wire Active Power Filter Basedon the Use of Synchronous Reference Frame",.Elsevier B. V. Electric Power Systems Research 73,Nov. 2004, pp. 353-362. .

[6] Hong-Scok Song, "Control Scheme for PWM Converter and Phase Angle Estimation Algorithm Under Voltage Unbalance and/or Sag Condition",Ph.D. in electronic and electrical engineering. South Korea, 2000.

[7] R. Pregitzer, J. C. Costa, Julio S. Martins, L. Alfonso "Simulation and Implementation Results of a 3-Phase 4-Wire Shunt Active Power Filter", ICHQO '06- International Conference on Harmonics and Quality Power, Oct. 2006.

[8] J. L. Afonso, C. Couto, J. S. Martins, "Active Filters with Control Based on the p-q Theory", IEEE Industrial Electronics Society Newsletter, vol. 47, n° 3, Sept. 2000.

[9] H. Akagi, Y. Kanazawa, A. Xabae,"Generalized Theory of the Instantaneous Reactive Power in Three-phase Circuits"JPEC'83- Int. Power Electronics Conference, Tokyo, Japan, 1983.