Fuzzy Logic Controlled Three phaseShunt Active Power Filter.hamid

8/7/2019 Fuzzy Logic Controlled Three phaseShunt Active Power Filter.hamid

1/12

Fuzzy Logic Controlled Three Phase Active Power

Filter for mitigation of harmonic and volt ampere

compensator

H.R.Imanijajarmi, AzahMohamad

Department of Electrical, Electronic & Systems Engineering

National University of Malaysia, Malaysia

ABSTRACT

Harmonic pollution is a serious and a damaging problem in electric power systems.

Active power filtering represents one of the most effective proposed solutions.The active power filter is operated to compensate harmonics and reactive power

generated by the non-linear load and power factor correction simultaneously.A fuzzy logic based control is developed to regulate the voltage of the DC capacitor.The system with control scheme is implemented in Matlab/Simulink.The simulation

results showquite satisfactory to mitigate harmonic distortions, reactive power

compensation and power factor improvement.

Keywords -Active Power Filter, Fuzzy logic controller,reference source current,nonlinear Load.

.1 INTRODUCTION

Nowadays, the applications of power electronics have grown rapidly. These powerelectronic systems provide highly nonlinear characteristics. These loads draw non-

sinusoidal currents that cause harmonic voltage drops across the network impedance,resulting in distorted voltages ]1[ . The shunt active powerfilter (APF) shows a mighty

strength in eliminatingreactive power andharmonics which has receivedwide concernin power electronic filed [2,3].

The shunt active power filters (APF), generally based on a voltage source inverter

structure, and seems to be an attractive solution to harmonic current pollution problems.In agreement with PWM control laws,By keeping the DC-link voltage of

inverter constant ,APF can compensate harmonics and reactive power effectively , fordo thissome actions must be taken because APF itself cannot produce powertomaintain the DC-link voltage[4]. Mostlyconventional PI controller by adding an

active component to the source current reference isused to control DC-link voltage[5,6]. Nevertheless,The PI controller based approach requires precise linearmathematical model which is difficult to obtain. Also, it fails to perform satisfactorilyunder parameter variations, non-linearity, and load disturbances, etc.


2/12

As a result ,when APF is plunged into the system ,It willcreate, DCvoltage overshootand inrush source current willlead to protection or even equipment damage. The

voltage overshoot andinrush current have been the constriction which limitsthedevelopment of APF.Recently, fuzzy logic controllers (FLCs) have generated a good deal of interest in

certain applications [7]-[9]. The main advantages of fuzzy controlover conventionalcontrollers are its linguistic description, independence of mathematical model,

robustness, and its universal approximation [10]. This paper proposes a fuzzy logic

controller for D.C bus voltage control [11]. Simulations results present theeffectiveness of the proposed approach in suppressing the harmonics andreactive

power.

.2 Shunt Active Power Filter

.2.1 Basic compensation principals

Fig 1 shows a current controlled voltage source inverter with necessary passivecomponents is used as an APF.It is controlled to draw/supply a compensated current

iffrom/to the utility, so that it cancels current harmonics on the ac side and makes the

source current in phase with the source voltage. In other words, removes reactive andharmonic currents of the non-linear load. Thus, the resulting total current drawn from

the ac mains is sinusoidal. Ideally, the APF requires to generate just the enoughreactive and harmonic current to satisfy the non-linear loads in the line. [12]-[14].

Fig.1.Connection of shunt active filter with non-linear load

.2.2 reference source currents

Source voltage is given by

vSt=Vm sin t (1)the instantaneous currents can be written as:iSt=iLt-iC(t) (2)

If a nonlinear load is applied, then the load current will have a fundamental

component and harmonic components, which can be represented as

iLt= In sin (nt+n=1 n) (3)=I1 sint+1+ In sin (nt+n=2 n)


3/12

The instantaneous load power canbe given as

pLt=vS(t)*iL(t) (4)

=VmI1sin2t *cos 1+VmI1 sint* cos t*sin 1+

Vm sin t* sin (nt+n)

n=2

=pf(t)+p

r(t)+p(t)

From (4), the real (fundamental) power drawn by the load is

pf(t) =vS(t)*iS(t) (5)

From (5), the sourcc current supplied by the source, after compensation.is

iS )t( =pf(t)/vS(t)=I1 cos 1sin t =Ismsin t

Where IsmI1 cos 1The utility must supply a small extra amount of current for the capacitor leakage andConverter switching losses in addition to the real power of the load. The total peak

current supplied by the source, is

Isp=Ism+Isl (6)

Where Isl is the peak value of loss current. If the active filter provides the total

reactive and harmonic power, then iS )t( will be purely sinusoidal and in phase with the

utility voltage. At this time, the active filter must provide the following compensationcurrent

ift=iLt-is(t) (7)The desired source currents, after compen sation, can be given

isa*

=Isp sint (8)

isb* =Isp sin (t-120)isb*

=Isp sin (t+120)

Where Isp=Ism+Isl is the amplitude of the desiredsource current, while the phase

angle can be obtained from the source voltages [3]. This peak value of the reference

current has been estimated by regulating the DC side capacitor voltage of the PWMconverter.

3. REVIEW OF FUZZY LOGIC CONTROL

Fuzzy logic control is a control algorithm established upon a linguistic controlscheme, which is derived from expert knowledge into an automatic control strategy.

Fuzzy logic control doesn't need any difficult mathematical calculation like the otherscontrol system. It only uses simple mathematical calculation to simulate the expert

knowledge,whereas the others control system use difficult mathematical calculation

to provide a model of the controlled plant . Although it doesn't need any difficult


4/12

mathematical calculation, but it can provide good performance in a control system.Therefore, it can be one of the best accessible answers today for a broad class of hard

controls problems. A fuzzy logic control usually contains of the following:

Fig.2.Block diagram of FLC

Fuzzification Inference Defuzzification

The above items are given below:

A. Fuzzification

The fuzzy logic controller requires that each input/outputvariable which define thecontrol surface be expressed in fuzzy set notations using linguistic levels. The

linguistic values of each input and output variables divide its universe of discourseinto adjacent intervals to form the membership functions. The member value means

the amount to which a variable belong to a particular level. The process of convertinginput/output variable to linguistic levels is termed as fuzzification.

B. InferenceThe behavior of the control surface which relates the input and output variables of the

system is stated by a set of rules. A standard rule would beIf x is A Then y is B

When a set of input variables are read each of the rule that has any degree of truth in

its premise is fired and contributes to the forming of the control surface byapproximately modifying it. When all the rules are fired, the resulting control surface

is stated as a fuzzy set to represent the constraints output. This process is named asinference.

C. Defuzzification


5/12

The process of conversion of fuzzy quantity into crisp quantity isDefuzzification.There are several procedures available for defuzzification. The essentiallywidespread

one is centroid method, which uses the following formula:

xxdx xdx

where is the membership degree of output x.Figure 2 show block diagram of a fuzzy logic controller (FLC) .

.4 FUZZY LOGIC CONTROL SCHEME

Fuzzy logic control is derived from fuzzy set theory introduced by Zadeh in 1965. In

fuzzy set theory, the transition between membership and non-membership can begradual. Therefore, boundaries of fuzzy sets can be unclear and indeterminate andmaking it useful for approximate systems. FLCs are an interesting choice when

precise mathematical formulations are not possible.In order to implement the control

algorithm of a shunt active power filter in closed loop, the DC side capacitor voltageis sensed and then compared with a reference value. The obtained error

and that are used as inputs for thefuzzy processing.

Where is reference dc side capacitor voltage and ce(n) is Change of error signalat the sampling instant. Figure3 shows the control strategy.The output of the fuzzy controller after a limit is considered as the amplitude of the

reference current Imax.(figure 4 )


6/12

Fig.3.Closed Loop Fuzzy Logic Controlled Shunt

Fig 4. Internal Structure of Fuzzy controller

This current Imaxlook afterthe active power demand of load and the losses in the

system.The switching signal for the PWM converter are obtained from comparing the

actual source currents ( ) with the reference current templates( ina hysteresis current controller. The output pulses are applied to the switching devices

of the PWM converter.

.4.1 Basic Fuzzy Algorithm

The error e and change of error ce are used numerical variables from the real system.To convert these numerical variables into linguistic variables, the following seven

fuzzy levels or sets are chosen as : NB (negative big), NM (negative medium), NS (negative small), ZE (zero), PS

(positive small), PM (positive medium), and PB (positive big) as shown infigures

5(a), 5(b).


7/12

The fuzzy cont olleri descri ed as follows:

Seven fuzzy sets for each input and output

Fuzzification using continuous universe of discourse.

Implication using Mamdani s 'min' operator.

Defuzzification using the 'centroid' method.

.Fig. 5(a).Input Normalized Membership Function

Fig. 5(b). Output Normalized Membership Function

4.2 Rul B :

As shown in Table 1,the elements of this rule base table are adjusted based on the

theory that in the transient state, large errors need coarse control, which requires

coarse input/output variables and in the steady state, small errors need fine control,

which requires fine input/output variab

les. Consequently, withe&ceasinputs theelements ofthe rule table are obtained.

T bl -Control rule base

5. HYSTERSIS B CURRE T TROL


8/12

The hysteresis current control with fixed band can be implemented to generate the

switching pattern in order to get precise and quick response. The hysteresis bandcurrent control technique has proven to be most suitable for all applications of currentcontrolled voltage source inverters in APF[15].

A hysteresis current controller is implemented with a closed loop control system. Anerror signal, e(t), is used to control the switches in an inverter.

This error is the difference between the desired current,iref(t) and the current being

injected by the inverter, iactual(t). When the error reaches an upper limit, the

transistors are switched to force the current down. When the error reaches a lower

limit the current is forced to increase. The range of the error signal, emax-emin, directly

controls the amount of ripple in the output current from the PWM-voltage sourceinverter.

.6 SIMULATION AND RESULTS

Simulation is done basedon the test system used to perform the analysis (figure 6)and system parametersgiven in table 2 to demonstrate the effectiveness of the

proposed control strategy for the SAF to reduce the harmonics. The test systemconsists of a three phase voltage source, and an uncontrolled rectifier with RL load.The active filter is connected to the test system through an inductor Lfand Capacitor

Cfand resistance Rf.The Matlab/Simulink is used to simulate the test power systemwith and without the proposed SAF.

Lf

Rf

Cf

if

iL

C

Fig.6.Test Power System

Ta le 2.Circuit parameters used for the SAF


9/12

Fig .7.Source Voltages

Fig .8(a).Source Currents withoutSAP

Fig.8(b).Harmonic spectrum of phase a source current withoutSAF

Fig.9(a).Source Currents with SAP


10/12

Fig.9(b).FilterCurrents with SAP

Fig.9(c).Load Currents with SAP

Fig.9(d).PowerFactor with SAP

Fig.9(e). DC capacitorvoltage

Fig.9(f).Harmonic spectrum of phase a source current with SAF


11/12

Ta

le 3. Total harmonic distortion Analysis of Test Power System & power factor

PARAMETERSSource Current

(phase a)

THD%

Power FactorReactive

Power(var)

Without SAF 16.83 0.8836 1756

With SAF 1.27 0.9998 98.9

7. CONCLUSIONS

Harmonic distortion is a kind of electrical noise. It is a superposition of signals, which are

of multiples of fundamental frequency. Growth of large power electronic systems results in

increased harmonic distortion. Harmonic distortion results in reduction of power quality and system

stability.This paper presents fuzzy control proper for active power filter for three-phase systems,

which are consisted of nonlinear loads. The SAF was simulated and its performance was analyzed

in a sample power system. The result(figures 7-9 and table3)of the simulation prove that the

injected harmonics are importantly reduced, system efficiency and power factor are improved.

REFERENCES

[1] S. Saad, L. Zellouma Fuzzy logic controller for three-level shunt active filter compensating harmonics and reactive

power Electric Power Systems Research, Elsevier, page no 13371341 May-2009

[2] A. Hamadi, K. Al -Haddad, S. Rahmani and H. Kanaan Comparison of Fuzzy logic and Proportional Integral

ControlIer of Voltage Source Active Filter Compensating Current Harmonics and Power Factor- IEEE

Conference(ICIT)PageNo 645-650-2004

[3] GuJianjun, XuDianguo, Liu Hankui, etal, "Active Power FilterTechnology and its Development". Electric Machines

and Conrol,vol.7, 2003, pp. 126-132.

[4] Ding Kai, Chen Yunping, Wang Xiaofeng, etal, "Investigation onRelevant Problems for DC side Voltage of Parallel

Active PowerFilter". Electric Engineering, vol.10, 2002, pp. 27-29..

[5] You Xiaojie, Li Yongdong, Victor Valouch, etal. "SAPF ControlStrategy under the Condition of Non-ideal Source

Voltages".Proceedings of the CSEE, vol.24, 2004, pp. 55-60.

[6] S.K. Jain, P. Agrawal and H.O. Gupta Fuzzy logic controlled shunt active power filter for power qualityimprovement-IEE proc.electr.power.appl,Vol 149, No.5, Sept -2002

[7] A. DellAquila, A. Lecci, and V. G. Monopoli, Fuzzy controlled active filter driven by an innovative current

reference for cost reduction,proc. IEEE Int. symp. Ind. Electron ., vol. 3, 2002, pp. 948-952.

[8] Y. H. Mansoor, G. Yao, L. Zhou, C. Chen, Harmonic mitigation of residential distribution system using a novel

hybrid active power filter, WSEAS Transactions on Power Systems, Vol. 2, No, 12, pp. 255-260.

[9] V. S. C. Raviraj and P. C. Sen, Comparative study of proportional -integral, sliding mode, and fuzzy logic controllers

for power converters,IEEE Trans. Ind. Appl. , Vol.33, No.2, 1997, pp. 518-524.

[10] L. R. Limongi, R. Bojoi, G. Griva and A. Tenconi, New Control Scheme for Single -Phase ActivePower

Filters978-1-4244-1668-4/08-2008 IEEE[11]S.K.Jain, P.Agrawal and H.O.Gupta, Fuzzy Logic controlledshunt active power filter for power quality improvement,IEEproceedings in Electrical Power Applications, Vol 149, No.5,September 2002.

[12]G.K. Singh, A.K. Singh, R. Mitra, A simple fuzzy logic based robust active power filter for harmonics

minimization under random load variation,Electr. Power Syst, 2006.

[13]Y. H. Mansoor, G. Yao, L. Zhou, C. Chen, Design and experimental investigation of a three-phase APFbased on feed-forward plus feedback control, WSEASTransactionsonPowerSystems, Vol. 3, No, 2, pp. 15-

20.[14]M. Rafiei, Verification of global optimality of the OFC active power filters by means of geneticalgorithms,Proc.WSEASInt. Conf.onSystems, Vouliagmeni, Athens, Greece, Jul. 10-12, 2006, pp. 559-564.

[15] Brod D.M, Novotny D.M Current control of VSI-PWM Inverter-IEEE Trans on Industry Appl,Vol.21, pp.562570-July/Aug.1985


12/12

Documents

Fuzzy Logic Controlled Three phaseShunt Active Power Filter.hamid