Fuzzy controller based current harmonics suppression using shunt active filter

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING
6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME
& TECHNOLOGY (IJEET)

ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
IJEET
Volume 4, Issue 1, January- February (2013), pp. 162-170
© IAEME: www.iaeme.com/ijeet.asp ©IAEME
Journal Impact Factor (2012): 3.2031 (Calculated by GISI)
www.jifactor.com

FUZZY CONTROLLER BASED CURRENT HARMONICS
SUPPRESSION USING SHUNT ACTIVE FILTER WITH PWM
TECHNIQUE

Dr. Leena G1, Bharti Thakur2, Vinod Kumar3, Aasha Chauhan4
1
(H.O.D, EEE Department, MRIU University, India)
2
(Electrical Department, MRIU University, India)
3
(EEE Department, Al-Falah School of Engineering & Technology, India)
4
(Electrical Department, YMCA University, India)

ABSTRACT

Harmonics present in the supply as well as at the load sides creates various
problems in the smooth operation of devices like variable frequency drives (VFDs),
electronic ballasts, battery chargers, and static Var compensators. Active Power Filter
(APF) gained much more attention due to good harmonic compensation. The performance
of the active power filter depends upon different control strategies. This paper presents
detailed analysis about mitigation of harmonics using APF in shunt active mode. The well
known control method, instantaneous real active and reactive power method (p-q) method
has been utilized in this paper. Extensive Simulations are carried out with fuzzy controller
for p-q method for different voltage conditions and adequate results were presented.
Simulation results validate the harmonics suppression capability of shunt active power
filter under active and reactive power control strategy (p-q) with fuzzy controller.

Keywords: Fuzzy Controller, Harmonic Compensation, p-q Control Strategy, Shunt
Active Power Filter.

162


I. INTRODUCTION

In recent years, power quality problems and compensation techniques have gained a
bulk amount of attention. Highly nonlinear electric equipments, in particular, cause severe
economic loss every year. These days single-phase electronic equipments like computers,
communication equipments, electronic lighting ballasts etc have been widely used in
domestic, educational and commercial appliances. These devices having different types of
rectifiers to convert AC electricity to DC supply. Hence these instruments utilize non-
sinusoidal currents which are a mixture of different harmonics. These current harmonics
pollute utility line and also results in many unwanted disturbances in the utility power supply
network [1]. Few of these problems can be named as: low power factor, low energy
efficiency, electromagnetic interference (EMI), distortion of line voltage etc. Owing to all
these problems, an appropriate harmonics compensator is necessary to avoid the
consequences due to harmonics [2]. One such compensator can be achieved by implementing
the active power filters for power conditioning. it provides functions such as reactive power
compensations, harmonic compensations, harmonic isolation, harmonic damping, harmonic
termination. Though for developing these compensators different control strategies have been
proposed by different researchers but still two control strategies, instantaneous active and
reactive currents (id-iq) method and instantaneous active and reactive power (p-q) methods
have been always preferred upon others. Present paper is mainly focused on how to reduce
the effect of harmonics while using shunt active filters. For extracting reference current of
shunt active filters, control strategy (p-q) has been utilized with fuzzy controller [3]. For the
validation purpose, extensive simulations are carried out with the above mentioned
configuration p-q method for sinusoidal voltage conditions and adequate results were
presented

II. CONTROL STRATEGY: INSTANTANEOUS REAL AND REACTIVE POWER
METHOD (P-Q)

In this section the Instantaneous Real and Reactive Power (p-q) control strategy,
which has been utilized in the present paper, is discussed in detail. Ideal analysis has done in
steady state conditions of the active power filter. The p-q theorem is basically a time domain
analysis tool and it has been proven to be especially adequate as one of the active filters
control strategies. The notations p and q represents active and reactive powers of the non-
linear load. The currents for active power filter are obtained from these active and reactive
powers. Fig. 1 shows the block diagram to attain reference currents from load. The main
objectives of active power filters [4] are compensations of the harmonics present in the input
currents. Present configuration represents three phase four wire and it is realized with
constant power controls strategy [6].Basically, the three phase instantaneous voltages, va, vb,
and vc and the load currents iLa, iLb, and iLc, are expressed as instantaneous space vectors these
parameters are transformed into orthogonal coordinates, α-β coordinates using the equations
(2.1-2.6). The instantaneous power calculation is given in detail form in equation (2.3). By
deriving from these equations, the compensating reactive power can be identified. The
compensating current of each phase can be derived by using the inverse orthogonal
transformations as given in the equation (2.5-2.6). It is Important to note that system used is
three phase four wire, so additional neutral currents has to be supplied by the shunt active
power filter.

163


Figure. 1. A basic architecture of three phase four wire shunt active filter

V 0  1 / 2 1 / 2 1 / 2  V a 
   
V α = 2 / 3 1 − 1 / 2 − 1 / 2  V b 
  ( 2 . 1)
V β  0 3 / 2 − 3 / 2  V c 
    

I 0  1 / 2 1 / 2 1 / 2   I La 
   
Iα = 2 / 3 1 − 1 / 2 − 1 / 2   I Lb


 ( 2 .2 )
I β  0 3 / 2 − 3 / 2   I Lc 
    

 p0  V 0 0 0  I 0 
p  = 0 V Vβ 
  
( 2 .3 )
   α Iα 
q  0 V − Vα  I β 
   β   

The three phase coordinates a-b-c is mutually orthogonal. As a result, the conventional power
for three phase circuits can be derived by using the above equations. The instantaneous active
power of the three phase circuit, p, can be calculated as shown in equation and the
instantaneous reactive power is defined as follows:-
~
q = ~× i
e
~ ~ ~ ~ ~
q = eα × iβ + eβ × iα = eα iβ − eβ iα (2.4)

From the instantaneous power can be rewritten as,
ICα*   Vα Vβ  − ~ +∆p
p
 *  =1/ Vα2 +Vβ2    (2.5)
ICβ 
  Vβ −Vα   −q 
 
As the compensator will only compensate the instantaneous reactive power, the real power is
always set to zero. The instantaneous reactive power is set into opposite vectors in order to
cancel the reactive component in the line current. From the equation (2.5), yields

164


 ic α *  1 / 2 1 0  − i0 
     
 ic β *  = 2/3 1 / 2 − 1/ 2 3 /2   ic α *  ( 2 .6 )
i *     ic β * 
 cc   1/ 2
 − 1/ 2 − 3 /2 
  

By deriving from the equation (2.1) to (2.6), the compensating reactive power can be
identified. The compensating current of each phase can be derived by using the inverse
orthogonal transformations. This p-q theorem performs instantaneously as the reactive power
is detected based on the instantaneous voltages and currents of the three phase circuits. This
will provide better harmonics compensations as the response of the harmonics detection
phase is in small delay.

Figure 2 Conventional Fuzzy Logic Controller

The actual capacitor voltage is compared with a set reference value. The error signal is then
processed through a Fuzzy controller, which provides zero steady error in tracking the
reference current signal. In fuzzy logic controller a linguistic control strategy has been
converted into an automatic control strategy with the use of different fuzzy rules. These fuzzy
rules are constructed by expert experience or knowledge data-base available with the system.
So the first step of working of fuzzy controller will be comparison of input voltage Vdc and
the input reference voltage Vdc-ref[14]. Then the output variable of the fuzzy logic controller
is followed by the limiter which generates control current Imax

.

Figure 3. FIS Editor

165


Figure 4 Membership function of input variable

Figure. 5 Membership function of output variable

Figure. 6 Rule Editor

166

January

III. SIMULINK MODEL AND SIMULATION RESULT

Figure 7. A Simulink model based on reduction of current harmonics using shunt active filter
with PWM technique and a PI controller in control unit.

Figure.8 Three phase source voltages i.e of phases( a,b,c)

Figure.9 3-phase source current with PI controller and THD=32.98% i.e before
phase
compensation

167


Figure 8 & 9 clearly shows the waveform of 3-phase source voltage and source current
with PI controller and it is clear from the waveform that source current has THD=32.98%(
i.e before compensation.

Figure.10 FFT analysis of input source currents with THD= 32.98% before compensation

Figure 11 & 12 clearly shows that the Total Harmnic Distortion in 3-phase source current has
been reduced from from 32.8% to 0.13% using PI Controller.

Figure.11. 3-phase source current with THD=0.13% with PI controller after compensation

Figure.12. FFT analysis of source current after compensation using SAF with PI controller.

168


Figure.13. 3-phase source current with THD=0.12% after compensation in fuzzy simulink

Figure.14 FFT analysis of source current after compensation using fuzzy controller

IV. CONCLUSION

The performance of the shunt active power filter is analyzed using PWM with PI
controller & fuzzy logic for minimizing harmonics, compensating reactive power and
improving the pf in the power system..The SAF theory is used to generate reference
current from the distorted load current and maintain the PWM VSI DC side capacitor
nearly constant.Also Fuzzy logic controller is used to extract the reference current and
maintain the PWM VSI DC side voltage nearly constant. The beauty of this controller is it
can applicable to any system where mathematical models are difficult to get.The performance
of the PWM with PI Controller and shunt active power filter are verified with the simulation
results. Form the results; it clearly indicates that, the current ripple is less in load current as
compared to source current.
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