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International Journal of Electronics

ISSN: 0020-7217 (Print) 1362-3060 (Online) Journal homepage: http://www.tandfonline.com/loi/tetn20

Shunt Hybrid Active Power Filter under Non idealVoltage Based on Fuzzy Logic Controller

Papan Dey & Saad Mekhilef

To cite this article: Papan Dey & Saad Mekhilef (2016): Shunt Hybrid Active Power Filter underNon ideal Voltage Based on Fuzzy Logic Controller, International Journal of Electronics, DOI:10.1080/00207217.2016.1138515

To link to this article: http://dx.doi.org/10.1080/00207217.2016.1138515

Accepted author version posted online: 06Jan 2016.

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Publisher: Taylor & Francis

Journal: International Journal of Electronics

DOI: 10.1080/00207217.2016.1138515

Shunt Hybrid Active Power Filter under Non ideal Voltage Based on

Fuzzy Logic Controller

Corresponding Author:

Papan Dey

Power Electronics &Renewable Energy Research Laboratory (PEARL), Dept. of

Electrical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia;

E-mail: papan@siswa.um.edu.my

Contact no. 0060143247702

Co-author:

Saad Mekhilef

Senior member, IEEE, Power Electronics &Renewable Energy Research

Laboratory (PEARL), Dept. of Electrical Engineering, University of Malaya, Kuala

Lumpur 50603, Malaysia;

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Shunt Hybrid Active Power Filter under Non ideal Voltage Based on

Fuzzy Logic Controller

In this paper a synchronous reference frame (SRF) method based on a modified

phase lock loop (PLL) circuit is developed for a three phase four wire shunt

hybrid active power filter (APF). Its performance is analyzed under unbalanced

grid conditions. The dominant lower order harmonics as well as reactive power

can be compensated by the passive elements whereas the active part mitigates the

remaining distortions and improves the power quality. As different control

methods show contradictory performance, Fuzzy logic controller is considered

here for DC-link voltage regulation of the inverter. Extensive simulations of the

proposed technique are carried out in a MATLAB-SIMULINK environment. A

laboratory prototype has been built on dSPACE1104 platform to verify the

feasibility of the suggested SHAPF controller. The simulation and experimental

results validate the effectiveness of the proposed technique.

Keywords: Phase lock loop; Fuzzy logic controller; Harmonic compensation;

Synchronous Reference frame (SRF) method; Total harmonic distortion (THD)

1. Introduction

The presence of current harmonics, unbalanced loading, reactive power and excessive

neutral current play an important role in deciding power quality in a three-phase four-

wire distribution system. These harmonics interfere with sensitive electronic equipment

and cause undesired power losses in electrical equipment. In order to solve the power

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quality problem and to deliver clean power several methods have been proposed and

developed by the researchers (El-Habrouk, Darwish, & Mehta, 2000).

Passive filters that work as the least impedance path to tune harmonic frequencies, are

simple and less expensive but have several drawbacks including fixed compensation,

they are bulky devices and the resonance problem of the L-C filters; however, APF has

been developed for complete compensation of distortions (Das, 2004). Owing to the

rapid improvement in power semiconductor device technology, active Due to the

absence of any resonance problem in the system, APF has attracted favorable feedback

compared to tuned passive filters. The APFs use power electronic converters that insert

harmonic components into the electrical network that cancel out nonlinear load

harmonic currents. With the harmonic compensating ability, APFs are also capable of

reactive power reduction and balancing the unbalanced load (Patnaik & Panda, 2013).

Although different types of active filters have been proposed to increase the electric

system quality, pure APF is limited due to its high cost and rating constraints by power

devices. To make the active filter smaller, cheaper and more practicable in industrial

applications, a hybrid configuration of the APF appears very attractive in power

distribution networks. However, series hybrid APF is complex, unreliable and

expensive. Therefore, a shunt hybrid filter topology is characterized by a combination of

a parallel-connected passive filter and a small rated active filter. This has been

considered in this paper for its capability of attenuation and effective operation. Many

harmonic revealing control concepts and approaches for active filters such as fast

Fourier transform (FFT); recursive discrete Fourier transform (RDFT); instantaneous

active and reactive power (p–q); direct testing and calculating (DTC) method;

instantaneous active and reactive current component (id–iq); notch filter, sine

multiplication, generalized integral, synchronous detection algorithm; adaptive filter,

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flux based controller; artificial neural network (ANN); adaptive linear neuron

(ADALINE); wavelet transform; particle swarm optimization (PSO); and genetic

algorithm (GA) techniques have been proposed in have been suggested in the literature

(Corasaniti, Barbieri, Arnera, & Valla, 2009). Among these control schemes, SRF is one

of the most conventional and practically applicable method (Mikkili & Panda, 2012).

Although it performs an excellent job, it requires a PLL circuit for synchronization.

Different types of PLL have been introduced in the literature; however, the conventional

types of PLL have low performance in extremely unbalanced and distorted networks. So

this paper is aimed at the competency of the SRF method with the modified PLL. An

additional essential task in active filters development is to maintain a constant DC link

voltage across the capacitor which is attached to the inverter. The energy loss due to the

switching power and conduction losses associated with the IGBTs and diodes of the

inverter in APF must be compensated that reduce the DC capacitor voltage. Normally,

to control the DC link voltage a PI controller is used. However, precise linear

mathematical models are required for the tuning of the PI controller. It is difficult to

obtain and cannot give satisfactory performance under load disturbances and parameter

variations (Ponpandi & Durairaj, 2011).In addition, in this conventional method, the

shaping of source current is realized with a good amount of spikes. Recently, a great

deal of interest has focused on Fuzzy logic controllers regarding their application to

APFs. Fuzzy logic is considered more advantageous than conventional controllers as

there is no requirement of an accurate mathematical model, they are capable of working

with imprecise inputs, handling nonlinearity and are more robust (Suresh, Panda, &

Suresh, 2011).

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In this paper, a new technique has been developed on SRF using the PLL algorithm and

its performance is analyzed and demonstrated for unbalanced source conditions. Here, a

Hysteresis current regulator is used to generate switching signals of APF, and for

maintaining the DC link capacitor a voltage fuzzy logic controller is introduced for

robustness and superior performance compared to the conventional PI controller.

The structure of this paper is as followed: The hybrid APF is discussed in section 2.

Section 3 describes the control algorithm of APF. The simulation results and a brief

analysis are presented in section 4. In section 5 experimental results are shown. Finally,

conclusions are drawn in section 6.

2. Hybrid APF topology

The proposed hybrid filter structure shown in Figure1 comprises a shunt passive filter

and shunt active filter. A 3-leg inverter with split capacitor works as the APF. It is

designed to be associated in parallel with the single phase and three phase loads that are

considered as a non-linear and unbalanced load for a 3-phase 4-wire distribution system

while its complex control circuitry and massive DC link capacitors are necessary for

perfect operation. The inner point of every branch is attached to the power network

through an inductor, which is used to filter the ripples of inverter current. The

considered LC passive filter at the 5th harmonic tuned frequency is connected in shunt to

the power line before the load. This provides a low impedance trap for harmonics to

which the filter is tuned, and, correspondingly, aids in reduction of the active filter

power rating.

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Figure 1. Schematic diagram of 3-phase 4-wire SHAPF

3. Proposed Control algorithm

3.1 Modified PLL Operation

In order to extract the voltage peak and instantaneous phase information the best way is

to convert the three phase unbalanced voltage in a two 2-D stationary frame. If voltage

is perfectly balanced and this transformed voltage vector is drawn on a q-d frame, a

circular vector rotating at speed equal to the frequency is seen. However, for the case of

an unbalanced vector, there are two vectors, one corresponding to positive sequence

rotating in one direction and the other because of the negative vector rotating in the

opposite direction. Thus, if a transformed unbalanced voltage vector in the d-q frame is

drawn, an eclipse is formed as a resultant of both positive and negative sequence

components. Now, suppose the frequency and phase information are already known and

taking an arbitrary frame that is rotating in the same direction as that of a positive

sequence component and at a speed equal to the frequency, then a positive sequence

component appears as a stationary and negative sequence component that seems to be

rotating at a speed twice that of the frequency. For safe and consistent operation of an

APF in an unbalanced and distorted grid voltage situation, the frequency and phase

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extraction of the positive sequence component of the voltage should be obtained quickly

and accurately. Because of the dynamic behavior, conventional SRF-PLL performance

is unsatisfactory under non-ideal voltage mains (Kesler & Ozdemir, 2011). The

improved PLL developed in this study is shown in Figure 2, which is put forward for

the determination of positive sequence components with stability and rapidity. For non-

ideal mains voltage:

+

+

=

= −

−

+

+

+

0

0

0

_c

b

a

c

b

a

c

b

a

c

b

a

V

V

V

V

V

V

V

V

V

V

V

V

Vsabc

(1)

Vo

Sin

Sin

Sin

V

Sin

Sin

Sin

V +

−++

+−= −+

3/2(

)3/2(

)3/2(

)3/2(

πθπθ

θ

πθπθ

θ

(2)

Using transform, the voltage vectors are:

[ ] abcVT

V

VV αβ

β

ααβ =

=

(3)

Where,

−−

=

2

3

2

30

2

1

2

11

32][ αβT

So:

+−+

=

= −−++

−+++

θθθθ

β

ααβ

CosVCosV

SinVSinVV

VV

(4)

Performing d-q transform:

[ ] αβVT

V

VV dq

q

d

dq =

=

=

+−+

− −−++

−+++

θθθθ

θθθθ

CosVCosV

SinVSinV

CosSin

SinCos^^

^^

=

++−−++−−−++

−−++

)()(

)()(^^

^^

θθθθθθθθ

CosVCosV

SinVSinV

(5)

The estimated phase angle= ^θ ; assuming tωθ ≈^ . PLL successfully tracks the phase at

−+ == θθθ ^ .

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So,

+−≈

−+

−

)2(

)2(^

^

θθ

CosVV

SinVV

V

q

d

(6)

Here ^2θ is the double frequency to be eliminated. It is the basic concept of the

modified PLL structure. It can provide the positive sequence component by cancellation

of 2ω oscillations (Venkatachalam, Chandrasekaran, & Rama Rao, 2009).The modified

PLL circuit uses Clarke and Park transform for identifying the peak of positive

sequence voltage. The three phase unbalanced voltages are converted to the stationary

coordinate system. Through the measured phase angle, the voltages in stationary co-

ordination are transformed to the d-q frame. The PI controller forced the d-axis

component Vd to zero so as to align the mains voltage space vector with the q-axis. The

estimated phase angle θ, which is attained by integrating the proportion-integral (PI)

controller output, is, in turn, used for the coordinate transformation process (Sinha &

Sensarma, 2011). Here, a second order resonant filter is used instead of the conventional

low pass filter for suppressing the double fundamental frequency, which is created for

unbalancing and the gain adaptation block shows the convergence of any value of

system voltages and creates normalized templates of fundamental voltage (De &

Ramanarayanan, 2010).The rate limiter block works as an attenuator against the ripple.

The modified PLL can perform satisfactorily as long as the gains of the PI are adjusted

accordingly under highly inaccurate and disturbed system voltages.

Figure 2. PLL circuit block diagram

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The transfer function of the resonant filter is given in:

22

22

44

4)(

ωωω

+++=

−offcuts

ssH

(7)

and the open loop PLL gain is written as:

)().

11.(.

1.)( sH

sTk

sVSG p +=

(8)

Where T and Kp are the time constant and gain of the PI controller correspondingly.

Now a critically damped system is taken into consideration and the value of the cut-off

frequency is chosen as it is equal to double the fundamental frequency of the system

(Indu Rani, Aravind, Saravana Ilango, & Nagamani, 2012). For selection of the PI

controller gains, the resonant filter is approximated as a low pass filter and the

parameter design is obtained via the calculation through the optimum symmetrical

method:

τ4=T (9)

And:

τVk P 2

1=

(10)

Whereτ is the time constant of the low pass filter.

3.2. Reference Current Generation

The three phase load currents are measured using a hall-effect current sensor and

converted into d-q-0 by means of a rotational frame that is synchronous with the system

voltage positive sequence in equation 11.

+−

+−

=

C

B

A

sss

sss

q

d

i

i

i

ttt

ttt

i

i

i

2

1

2

1

2

1

)3

2cos()

3

2cos()cos(

)3

2sin()

3

2sin()sin(

3

2

0

πωπωω

πωπωω

(11)

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ωst ω is considered here as the transformation-angle of the positive sequence source

voltage and is delivered by the phase lock loop (Jianben, Qiaofu,Jun,2012).

Figure 3. SRF based control block diagram

The system under observation is a three phase-four wire in which the active component

id and oscillating part iq are reflected. After the load currents id and iq are found, they are

allowed to pass over a low pass filter to separate the AC and DC part through which the

active and reactive fundamental current components (id-DC, iq-AC) are obtained. Both

the currents (id-DC, iq-AC) AC parts are related with the responsibility for active and

non-active harmonic components. The filters used in the circuit are the 2nd order

Butterworth type and their cut off frequency is identical to one half of the fundamental

frequency (Mikkili & Panda, 2011). In consideration of the reactive current, the passive

filter provides its DC value while the VSI delivers an AC voltage to sink the harmonics.

The filtered active and non-active currents from equation 12 are used for generation of

the accurate references to the modulator:

−

=

qDC

dDC

q

d

qAC

dAC

i

i

i

i

i

i

(12)

As well as providing harmonic currents, the DC voltage of the PWM VSI should be

maintained for accurate operation (Saad , Tarek & Nasruddin, 2011). The voltage of the

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capacitor is controlled by regulating the reactive current (Salmeron & Litrán, 2010) as

shown in Figure 3. Then the a-b-c frame reference currents are:

++

−−=

*

*

)3

2cos()

3

2sin(

)3

2cos()

3

2sin(

)cos()sin(

q

d

ss

ss

ss

CC

CB

CA

i

i

tt

tt

tt

i

i

i

πωπω

πωπω

ωω

(13)

3.3. DC Link Capacitor Voltage Control

3.3.1. Fuzzy controller

Figure 4. DC voltage optimization with Fuzzy approach

A Fuzzy logic controller is used to regulate the DC link voltage and added to the active

part of the fundamental load current. The obtained voltage of the capacitor is matched

with a preset reference value (Mikkili & Panda, 2011). The loss component is then

handled by a Fuzzy logic controller, which contributes to the zero steady error in

tracking the reference current signal, as shown in Figure 4. A low pass filter and a rate

limiter block have been used here for optimum performance. The supply current peak

value is calculated using the output component of the fuzzy logic controller

(Park,Jeong,Kwon,2001),(Younus, Rahim& Mekhilef,2009).

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A linguistic control approach is converted into an automatic control strategy, and with a

knowledge database, Fuzzy rules are constructed by proficient experience. To begin

with, ‘µ(E)’, the input error, and ‘µ(∆E)’, the change in error, have been used as the

input variables of the fuzzy logic controller (Singh, Singh, & Mitra, 2007). Then the

control current ‘Imax’ represents the output variable. Seven Fuzzy sets are chosen here

to adapt these numerical variables into linguistic variables: PB (positive big), PM

(positive medium), PS (positive small), ZE (zero), NS (negative small), NM (negative

medium) and NB (negative big), as can be seen in Figure 5. The intransient state

requires coarse input/output variables for controlling based on large errors and fine

input/output variables are essential for controlling the small errors properly with the

development of Fuzzy logic rules in the steady state (Saad & Zellouma, 2009). With this

perception, the rule table elements and view of the surface is obtained, as shown in Fig.

6, where ‘µ (E)’ and ‘µ (∆E)’ are used as inputs.

Figure 5. Normalized membership functions for the input and output variables

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(a) (b)

Figure 6. (a) Fuzzy control rule (b) Surface Viewer (E vs ∆E)

3.4. Harmonic current generator

The active filter switching patterns are decided by the current controller. A hysteresis

comparator is used here for a quick response and appropriate sinusoidal current tracking

capability (W.u,2011). The desired current, Ia (t), and the injected inverter current,

Ia*(t) are compared with one another. The logic of switching is as follows:

If Ia< (Ia*-hb) upper switch S1 is OFF & lower switch S4 is ON in leg of ‘a’ of APF. If

Ia> (Ia*-hb) upper switch S1 is ON & lower switch S4 is OFF in leg of ‘a’ of APF.

Correspondingly, in the legs ‘b’ & ‘c’ the switches are initiated. Here ‘hb’ is the

hysteresis band and determines the variation of load current harmonics and switching

frequency of the devices.

4. Simulation results and analysis

The performance of a 3-legs 4-wire Hybrid APF for filtering current distortions,

compensation of neutral current, load current balancing and reactive power mitigation

has been examined under unbalanced source-balanced load. The goal of this case study

is to demonstrate the validity and evaluation of the proposed approach, where the source

is greatly unbalanced.

ΔE E

NB

NM

NS

Z

PS

PM

PB

NB NB NB NB NB NM NS Z

NM NB NB NB NM NS Z PS

NS NB NB NM NS Z PS PM

Z NB NM NS Z PS PM PB

PS NM NS Z PS PM PB PB

PM NS Z PS PM PB PB PB

PB Z PS PM PB PB PB PB

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The results are specified in the following simulation studies for before compensation,

compensation using only passive filter and after the operation of the hybrid filter. Three

and single phase diode rectifier nonlinear loads are coupled in the power system for

producing unbalanced, reactive current and harmonics in the load current as well as a

neutral current. The widespread simulation outcomes are discussed below.

4.1 Unbalanced source condition

Voltage unbalance occurs when the relative magnitudes and phase angle of the three

phases are not equal. The source voltage magnitude of phase-b is 20% smaller than the

source voltage of phase-a, and the phase-c voltage is 50% lower than phase-a. This is

done by using a three phase programmable voltage source block in Simulink.

The three phase unbalanced voltages are considered as: Vsa= 100 sin ωt, Vsb= 80 sin

(ωt-120) and Vsc= 50 sin (ωt+120). In unbalance source voltages, the fundamental

components are first derived using PLL to make the unit templates for the balanced and

sinusoidal voltages. Then the synchronizing phase angle is extracted and simulation is

performed through it. The source voltage is shown in Figure 7 (a). The load current and

its FFT graph without compensation are given in Figure 7 (b) and (c), which is highly

non-linear in nature. After the application of the passive filter lower order harmonics are

reduced but non-linearity and distortion still exists, which is presented in Figure 7 (d).

The THD of the source current is reduced from 21.07% to 1.33% in the case of the

fuzzy controller, which is below the IEEE standard as shown in Figure 7 (g). In Figure 7

(l) the extracted transformation angle from PLL is also shown. The values of source

current and THD levels are listed in table 1.Although, the source currents are not purely

balanced but the results are quite satisfactory.

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(a)

(b)

(c) (d)

(e) (f)

(g) (h)

(i) (j)

(k) (l)

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Figure 7. Simulation results for operational performance of SHAPF a) Source voltage b)

load current c) THD before compensation d) passive filtering source current e)THD

after passive filtering f) source current g) THD after SHAPF h) injecting current i) DC

link voltage J) Real power (p) k) Reactive power (Q) l)Transformation angle (wt)

Table 1.System performance for unbalanced source condition

Table 2.

Fuzzy logic controller performance evaluation

Table 3.Simulation parameters

Source current Before filter After Passive

filter

After Hybrid

active filter

THD (%)

A-phase 21.07 14.69 1.33

B-phase 48.59 27.11 1.52

C-phase 21.18 10.64 1.03

Neutral 52.5 -

RMS(A)

A-phase 1.58 2.32 5.84

B-phase 0.87 1.41 5.67

C-phase 1.54 2.23 5.39

Neutral 5.25 3.21 0.41

Condition DC voltage settling time with Fuzzy

Real & Reactive power without Active filter

Real & reactive power with Active filter

Unbalanced source

0.24s 910w, 370var 2.89kw,130var

Parameters Values Source impedance R = 0.01Ω, L = 2 mH Load impedance 3-phase diode rectifier R = 80 Ω, L = 60 mH

1-phase diode rectifier R= 0.1Ω, L=1 mH

Passive Filter 5th harmonic tuned, R=0.2Ω, L=5mH, C=60μF Shunt APF R=0.001Ω, L=2mH,

Two DC link capacitor = 2100μF,Vdc=220 V Source voltage 100 V (r.m.s), 50 HZ

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It has been observed that the shunt hybrid APF performance with fuzzy logic controller

shows outstanding characteristics compared to the conventional controller under

unbalance voltage condition. The calculation of real (p) and reactive (Q) power for

unbalance case are arranged in Table 2. It also shows the effectiveness of the fuzzy

logic controller. The parameters used in this study for SHAPF system are listed in Table

3.

Table 4. THD comparison between recommended topology and conventional controller

A comparative analysis between the proposed control method, conventional method

(Corasaniti et al., 2009), P-Q theory (Mikkili & Panda, 2012) and modified P-Q theory

(Patnaik & Panda, 2013) is shown in Table 4 in terms of THD % and reactive power.

The P-Q theory and modified P-Q theory are simulated with the used parameters. From

the table it is observed that they are capable of mitigating harmonics but fail to reduce

the THD % below 5% under a non-ideal voltage source. The proposed method allows

2% THD values of source current and compensates reactive power, which is satisfactory

when compared with the conventional control technique.

5. Experimental Results

The system parameters selected for the experimental verification: Vs=50V (peak),

f=50HZ, Ls=5mH, Lc=5mH, RL=100Ω, Ll=20mH, Cdc=2000μF, Vdc =70V. Parameters

System voltage conditio

-n

Source current

Before SHAPF After SHAPF

Phase THD (%)

Q (VAR)

P-Q theory (Mikkili)

Modified P-Q theory

(Patnaik)

PI controller with SRF-

PLL(corasanti)

Proposed controller

THD (%)

Q (VAR)

THD (%)

Q (VAR)

THD (%)

Q (VAR)

THD (%)

Q (VAR)

Unbala-nce

A 21.0 370

6.32 305

5.21 280

3.41 150

1.33 130 B 48.5 5.23 5.03 3.32 1.52

C 21.1 6.49 5.43 2.89 1.03

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of passive filter, Lf =3mH, Cf =60μH. A prototype model of three-phase- four wire APF

is developed in the laboratory for experimentation shown in Figure 8.

For the generation of unbalancing in the voltage, two different values of resistance are

connected in series with the two phases of supply, and, just after that, a constant 3-phase

load is fixed. Another phase is kept as usual. The flow of current through the series

impedance will cause a different voltage drop in each phase, so that unbalanced voltages

occur in the system. In this case, the equivalent supply will be after the series

impedance and constant 3-phase load.

There are two single-phase bridge inverters connected in series in each phase. Suitably

designed snubber circuit is connected across each device. DC link capacitor is

connected at DC side of the inverter. Three coupling inductors are connected in series

with the three lines on AC-side of the inverter. Three-phase diode rectifier with R-L

elements on DC side is used as a nonlinear load which draws nonlinear current. The

AC and DC voltages are sensed using the isolation amplifier (AD202JN). The AC

source currents are sensed using the PCB-mounted Hall-effect current sensors (LEM-

25-NP). The IGBT driver circuits are used for pulse amplification and isolation

purposes. The driver circuit has special features like the fault protection and protection

against the under-voltage lockout. The load current, the source voltage and injected

filter currents, ifabc, are measured. The sensed signals are used for processing in the

designed control algorithm. Because real-time simulation is an important aspect for

control engineering, the same is true for the automatic generation of real-time code,

which can be implemented on the hardware.

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Figure 8. Experimental setup for shunt hybrid APF

5.1 Unbalance source condition

For an unbalanced source, 14% amplitude unbalance is introduced in the ‘b’ and ‘c’

phases so that the phase voltages are 50V in phase ‘a’, 43 V in phase ‘b’, and 38 V in

phase ‘c’. The unbalance is also reflected in the load currents in the three phases.

However, the source currents are balanced with the proposed APF. Figure 9 shows the

total response of the system for this condition. From the results it is observed that the

proposed control method gives satisfactory results under unbalanced source. The load

current waveform of phase ‘a’ is distorted before filtering shown in Figure 9(b). FFT

result is also listed. After the operation of hybrid APF controlled by fuzzy controller

sinusoidal source current waveform is obtained instantaneously after the insertion of

active filter as illustrated in Figure 9 (f). In figure it is also shown that the experimental

results of the dc-side capacitor voltage which is nearly constant with small ripple. The

current THD is reduced from 28% to 4.8% as shown in the frequency current spectrum.

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(a)

(b) (c)

(d) (e)

(f) (g)

(h)

Figure 9. Experimental results for unbalance source a) Supply voltage (25v/div) b) Load

current before compensation (0.8A/div) c) %THD before compensation d) Source

current after passive filtering e) %THD after passive filter f) Source current after

compensation g) %THD after SHAPF compensation h) DC link voltage

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6. Conclusion

A modified PLL with SRF theory is developed for computation of the reference current

and employed effectively for grid voltage synchronization under unbalanced mains

conditions. It is seen from the simulated figures that the Fuzzy logic controller shows

better dynamic performance to mitigating current harmonics and compensating reactive

power. The figures illustrate that the feedback currents of the filter approximately agree

with the generated reference currents. The proposed method has been evaluated with

simulations under non-ideal mains voltage conditions where it is shown that percentage

of THD is reduced from 21.07% to 1.33% for unbalance source. Moreover, 53%

amount of reactive power has been compensated after using the shunt hybrid APF. The

impact of source current unbalance has also been minimized. A laboratory prototype is

developed and it has been found that value of THD has been reduced from 28% to 4.8%

for unbalance voltage which is in the mark of 5% specified in the IEEE-519 standard.

The value of power factor has been increased to 0.632 to 0.963. Therefore, with the

combination of fuzzy logic and modified SRF theory approach, SHAPF can be

considered as a reliable harmonic isolator for its quick response and good quality of

filtering.

Acknowledgement

The authors wish to acknowledge the financial support from university of Malaya HIR-

MOHE project UM.C/HIR/MOHE/ENG/24.

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