paralleling of four -leg shunt active power filters …

International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)

ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.

143

Abstract— This paper proposes the concept of Paralleling of

four leg Shunt Active Power Filter (SAPF) in order to

compensate the four wire electrical network without disturbing

the others Performance. A New Control Strategy of Space Vector

Pulse Width Modulation (SVPWM) is introduced for an effective

Operation of SAPF in Distribution Side. Fuzzy Logic Controller

(FLC) is used to maintain the same Amplitude and Frequency of

each inverter output. Both Fuzzy Logic Controller (FLC) and

Space Vector Modulation (SVM) together provides robustness,

Reactive Power Compensation, DC Voltage Stabilization and also

used to minimizing the Source Current Harmonics, reducing the

magnitude of Neutral Current, eliminating the Zero-Sequence

Current, reducing the Switching Losses. Analysis of mentioned

devices includes theoretical calculations and simulations

performed in MATLAB/Simulink software.

Index Terms—Shunt Active Power Filter (SAPF), Harmonic

Elimination, Paralleling of SAPF, Space Vector Modulation

(SVM), Fuzzy Logic Controller (FLC).

I. INTRODUCTION

Harmonic voltages and currents present in an electrical

power system are a result of non-linear electric loads.

Harmonic frequencies are the major cause of power quality

problems in the power grid [1]. Harmonics in power systems

results in increased heating effect in both an equipment and

conductors, misfiring in variable speed drives, and torque

pulsations in motors. When a non-linear load, for example

a rectifier, is connected to the system, it draws an unequal

current that is not necessarily sinusoidal. According to the

type of load and its interaction with other equipments of the

system, the current waveform will get distorted. Even though

it is very complex the current waveform becomes, as

described through Fourier series analysis, it is possible to split

it into a number of simple sinusoids, which start at the power

system fundamental frequency and occurs at integer multiples

of the fundamental frequency (50 Hz). With increasingly

higher density of loads basing on rectifiers and switched mode

power supplies, harmonic content in supply networks becomes

widely discussed and analyzed. This leads to current

harmonics mitigation devices application. Historical approach

to mitigate an harmonic current based on passive power filters.

Semiconductor switches development allowed researchers and

engineers to introduce more sophisticated devices offering

much higher accuracy active power filters as shown in Fig.1.

As the effectiveness of these devices is in most cases more

than sufficient, the problem with their application is related

with their significant costs, especially for compensation of

industrial loads harmonic currents. In this paper an approach

to reduce transistor current and voltage rating is based on

installing additional passive power filter. Proposed passive

power filter is tuned to mitigate 5th

and 7th

harmonic current

expected highest amplitude harmonic orders [2]. As highest

harmonic currents are compensated by the passive power

filter, required converter power rating is reduced.

The potential benefits of paralleled VSI systems have led to

the investment of considerable development effort. Many of

the early systems were passive in nature, relying entirely on

incidental load balancing actions in combination with standard

control methods, sometimes combined with output filter

impedances, to keep the circulating current within reasonable

limits. These systems are still widely employed due to their

simplicity and robust nature; however their poor performance

with respect to load sharing demands significant concessions

are made during the design process.

PARALLELING OF FOUR-LEG SHUNT

ACTIVE POWER FILTERS BASED ON SVPWM

USING FUZZY LOGIC CONTROL

1G.Shobana*,

2 Dr. R.Arivalahan

#

*PG Scholar,

#Associate Professor

Department of Electrical and Electronics Engineering

Valliammai Engineering College, Kattankulathur-603 203, Tamilnadu, India.

[email protected], [email protected]

Three

Phase

Source

Harmonic

Loads

Shunt

Active

Power Filter

IS IL

IF

Vpcc

https://en.wikipedia.org/wiki/Electric_power_system

https://en.wikipedia.org/wiki/Electric_power_system

https://en.wikipedia.org/wiki/Power_quality

https://en.wikipedia.org/wiki/Rectifier

https://en.wikipedia.org/wiki/Fourier_series

https://en.wikipedia.org/wiki/Fundamental_frequency

mailto:[email protected]

mailto:[email protected]



144

Fig. 1: SAPF Connection Diagram

An improvement in manufacturing methods has lead to a

reduction in variances between components of the same

model, which has important implications for passive

paralleling. However, as it has been proven, installation of

passive power filter in shunt connection with active power

filter is not an effective solution. Inverter power rating can

become the subject of further reduction by applying other

possible connections of filters. The implementation of the

control is almost the same in complexity for all the selected

topologies and obtained harmonic mitigation performance is

similar maintaining system current THD below 5 %.

II. THEORETICAL CONSIDERATIONS

A. SHUNT ACTIVE POWER FILTER

The APF is an effective means of Harmonic Suppression,

it utilizing the pulse width modulation (PWM) technique is

used to generate switching harmonic current, which is power

grid leakage at high frequency and it should be eliminated by

output filter [3]. Output filter connected between the inverter

and grid connection, as shown in Fig 2. As the complexity of

its working principle, must be synthetically considered the

compensation performance of APF and filtering performance

of output filter etc, and this is a multi-objective optimization

problems..

Fig. 2: General Topology for Shunt Active Filter

Active filters are designed using passive and active

components, and require an outside power source. Operational

amplifiers are used in design of active filter [4]. These can

have high reactive power and quality factor, and can achieve

resonance without using inductors. However, their higher limit

is limited by the bandwidth of the amplifiers used in that

system. Filters having multiple elements are usually

constructed as a sequence network. These can be designed as a

continuation of the L, T and π format of filters. More elements

are required when it is desired to improvise some parameters

of the filter like stop-band rejection, slope of transition from

pass band to stop band.

A three-phase system connected with an inverter load has

been considered to study the operation of the SAPF. It has

been concluded that due to the characteristics change of power

electronics loads the Total Harmonic Distortion of source

current and terminal voltage fall below the IEEE-519 standard

and in main APF system is used to inject a current with equal

magnitude but opposite in phase to harmonic current to get a

pure sinusoidal current waveform in phase with the supply

voltage [7]. Fig. 3 shows the control strategy for proposed

method. The main component of the Active Power Filter is the

IGBT based Voltage Source Inverter. A dc capacitor is used to

deliver power for the inverter circuit. For the desired operation

of APF, capacitor voltage should be minimum of 150 % of

maximum line to line supply voltage.

B. SPACE VECTOR PULSE WIDTH MODULATION

TECHNIQUE

The voltage space vector synthesization is critical in the

conventional SVPWM method. As it uses Clarke

transformation to transform the reference voltages to d-q

coordinates in order to generate reference vectors.

Fig. 3: Phase Voltage Space Vector

Subsequently, the reference vectors are synthesized by

some optimally selected basic vectors with specific time

duration. In that method, the sectors of reference vectors are

determined by their phase angles, and the time duration of

basic vectors are calculated through the computation of phase

angles and reference vectors as shown in Fig. 4.

a1Vr

0Vr

3Vr

2Vr

4Vr

5Vr

6Vr

bj

POO

PPOOPO

OPP

OOP POP

refVr

q

OOOPPP

SECTOR ISECTOR III

SECTOR IV SECTOR VI

SECTOR V

SECTORII

w



145

Fig. 4: Control Scheme model of SVPWM Technique

As these computations involve huge quantities of irrational

numbers and trigonometric functions, the computation burden

would be enormous. These operations may bring about major

calculation errors which would corrupt the performance of

shunt APF. To solve this problem, an effective time concept

based SVPWM is used to generate the switching signals. It is

possible to reconstruct the actual gating time without

separation and recombination effort. The switching state

diagram of the VSI is shown in Fig. 3. The six non-null states

are represented by space vectors mathematically represented

as follows

Reference Vector Voltage is calculated using

where,

Rotating in space at w =2πf

C. FUZZY LOGIC CONTROLLER TECHNIQUE

Your unclear controller will be characterized as follows:

1) Seven fuzzy sets for each input and output.

2) Fuzzification using continuous universe of discourse.

3) Implication using Mamdani’s “min” operator.

4) De-fuzzification using the “centroid” method.

The block diagram of Fuzzy logic controller is shown in

Fig. 5. It consists of following blocks

Fuzzification Interface.

Knowledge base.

Decision making logic.

Defuzzification.

Fig 5: Block Diagram Of Fuzzy Logic Controller

A new fuzzy controller switches some sort of linguistic control

approach straight into a computerized control approach[12], in

addition to fuzzy guidelines usually are created by simply

specialist practical knowledge or maybe knowledge data-base

[13].

Table 1: Rule Base for Fuzzy Logic Controller

(de/dt)/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

To start with, input mis-calculation E in addition to change

with mis-calculation are already placed with the angular

velocity to become the actual input parameters with the fuzzy

reason controller. Then your output changing [13] with the

fuzzy reason controller is usually offered through the control

Current Imax.

)()()( tvjtvtVba

r(1)

qj

refrefeVV

r (2)



146

The above graphs shows that the how the fuzzy Parameter

changes its ranges at each value. According to that the system

will perform its function.

To be able to change these numerical parameters straight into

linguistic parameters, these several fuzzy ranges or maybe sets

usually are decided on as: NB (negative big), NM (negative

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

PM (positive medium), in addition to PB (positive big) as

shown in Table 1.

III. WORKING PRINCIPLE OF SHUNT ACTIVE FILTER

Active filters are designed using passive and active

components, and require an outside power source. Operational

amplifiers are used in design of active filter [4]. These can

have high reactive power and quality factor, and can achieve

resonance without using inductors. However, their higher limit

is limited by the bandwidth of the amplifiers used in that

system. Filters having multiple elements are usually

constructed as a sequence network. These can be designed as a

continuation of the L, T and π format of filters. More elements

are required when it is desired to improvise some parameters

of the filter like stop-band rejection, slope of transition from

pass band to stop band.

Fig. 6: Block Diagram Representation for Proposed SAPF

Control Strategy

A three-phase system connected with an inverter load has

been considered to study the operation of the SAPF. It has

been concluded that due to the characteristics change of power

electronics loads the Total Harmonic Distortion of source

current and terminal voltage fall below the IEEE-519 standard

and in main APF system is used to inject a current with equal

magnitude but opposite in phase to harmonic current to get a

pure sinusoidal current waveform in phase with the supply

voltage [7]. Fig. 6 shows the control strategy for proposed

method. The main component of the Active Power Filter is the

IGBT based Voltage Source Inverter. A dc capacitor is used to

deliver power for the inverter circuit. For the desired operation

of APF, capacitor voltage should be minimum of 150 % of

maximum line to line supply voltage.

A. Harmonic Loop

To eliminate harmonic resonances, the HAFU is proposed to

operate as variable conductance at harmonic frequencies as

follows:

i∗h = G∗ ec (3)

where,

i∗h represents the harmonic current command. The

conductance command.

G∗ is a variable gain which has to be provide damping for

all harmonic frequencies.

using SRF transformation [9] Harmonic voltage component eh

is obtained where a phase-locked loop (PLL) is used to

determine the fundamental frequency of the power system. In

the SRF, the basic component becomes a dc value, and other

harmonic components are still ac values[10]. Therefore,

harmonic voltage component can be extracted from graph by

using high pass filters. After transferring back to a three-phase

system, the harmonic current command i∗h is obtained by

multiplying eh and the conductance command G∗.

415V

50Hz

Harmonic

Loads

Distribu

-tion

Transfor

-mer

Detection

Unit

Fuzzy Logic

Controller

and

Selectivity

DC Side

Voltage

Control

Strategy

4-leg

SVPWM

Inverter

IF Ig

Iref

Vc

Source Delta Star PCC



147

The conversion of three axes frame to two axes frame is done

by using Park’s and Clarke’s transformation as shown below

𝑖𝑐𝑎𝑖𝑐𝑏𝑖𝑐𝑐

= 2/3

1 0 1\√2

−1\2 √3\ 1\√2

−1\2 −√3\2 1\2√2

𝑖𝐿𝑎𝑖𝐿𝑏𝑖𝐿𝑐

𝑖𝐿𝑎𝑖𝐿𝛽

= 𝑐𝑜𝑠(𝜔𝑡) −𝑠𝑖𝑛(𝜔𝑡)𝑠𝑖𝑛(𝜔𝑡) 𝑐𝑜𝑠(𝜔𝑡)

𝑖𝐿𝑑𝑖𝐿𝑞

B. Current Regulator

The current command i∗ is consisted of i∗h and i∗f . Based on

the current command i∗ and the measured current i, the voltage

command v∗ can be derived by using a proportional controller

as follows:

v∗ = Kc (i∗ − i) (6)

where,

Kc is a proportional gain. According to the voltage

command v∗, space-vector pulse width modulation (PWM) is

employed to synthesize the required output voltage of the

inverter. The computational delay of digital signal processing

is equal to one sampling delay T, and PWM delay

approximates to half sampling delay T/2. Hence, the

proportional gain Kc can be simply evaluated from both open-

loop and closed-loop gains for suitable stability margin and

current tracking capability[11].

IV. RESULT ANALYSIS

A summary of the simulation values is presented in Table 2.

Since inverter power is the main factor in this comparison, the

following quantities were taken into account: harmonic

mitigation efficiency considered by measuring the current

THD after connection of harmonic compensation device, the

voltage value on the capacitor at the dc-side of the inverter,

the RMS current flowing through the inverter in steady state

operation of the device. These quantities allow determining

the inverter power.

Table 2: Test System Specifications

S. No. Parameters Values

1 Three Phase Source Voltage 415 V

2 Frequency 50 Hz

3 DC Capacitor 5000 µF

4 Diode Resistance 1 mΩ

5 DC Link Voltage 500 V

6 Rectifier Load 10 Ω, 60 mH

The results obtained in simulations show that the pure active

filter provides the best harmonic mitigation efficiency. It

decreased the THD of the system current from near 25% to

3%, which is considerably low regarding no switching

frequency filter installed, and thus the ripple also contributes

to the harmonic distortion [13].

Fig. 7: Non Linear Load (Rectifier) model for SAPF system

According to IEEE std. 519-1992 [31], voltage THD is limited

to 5%, and individual distortion should be below 4%. Thus,

THD∗ is set in the range of 3% and 5%. If Vs,h and Rs are

neglected, voltage THD at E, due to harmonic current load I,

can be expressed as follows:

𝑇𝐻𝐷1 = 1\𝐼1 𝐼2∞

ℎ−2

= 𝐼𝑟𝑚𝑠

𝐼1,𝑟𝑚𝑠

2

− 1

Nevertheless, ability to compensate current distortion is only

slightly worse and should be sufficient for most applications.

It is measured that all the presented topologies provide

satisfactory current harmonic compensation. The dc-voltage

value of both hybrid filters is 3.5 times lower then the dc-

voltage of an active power filter.

Fig. 8: Fuzzy control for Power Filter System

100......

100%

1

22

3

2

2

1

,

V

VVV

V

VTHD

NRMSh

V

(5)

(4)



148

This is because, in order to create any current flowing

through the line inductor, the dc-voltage needs to be higher

than the maximum voltage on the ac-side of the inverter [14].

The inverter currents vary considerably between the presented

topologies. Fig. 7 shows the fuzzy control scheme for

proposed system. Some fundamental component is also

necessary to feed the dc capacitor[15], in order to maintain the

inverter in operation, and thus a real current is used by the

APF.

A. SIMULATION OUTPUT

i) Output Waveform for Without SAPF System

Fig. 9: Load voltage without using Active Filter

Fig. 10: Load current without using Active Filter

Fig. 11: Harmonic spectrum for load current without SAPF

ii) Output Waveform for With SAPF System

Fig. 12: Output Graph for Phase Voltage at PCC

Fig. 13: Phase Voltage when breaker is in on Condition

Fig. 14: Phase Current when Breaker is in on Condition



149

Fig. 15: Inverter Output Voltage for Compensation

Fig. 16: Output Voltage across the DC Capacitor

Fig. 17: Output Graph for Voltage after Compensation

Fig. 18: Load Side Voltage Graph after Compensation

Fig. 19: Harmonic Spectrum Graph after Compensation

However it is reduced by the harmonic component (5th

harmonic), which flows through the active filter as shown in

Fig. 19.The overall inverter power, which roughly determines

the cost of the harmonic mitigation device, is an important

factor in cost-sensitive applications[17]. Low inverter power

rating rapidly improves the profitability of the investment in

harmonic compensation. In presented comparison the pure

active power filter requires the largest inverter, which apparent

power is 46% of the load apparent power[18].

V. CONCLUSION

In this paper an active power filter with SVPWM based on

fuzzy logic was analyzed and simulated. The main goal was to

find a solution, which has as profitable relationship between

the accuracy and cost, as possible. Current distortion was

mitigated sufficiently by the all proposed devices, meeting

IEEE-519 limits. However, as it was proved in this paper,

there is a great difference in inverter sizes between these

topologies. According to above presented simulations and

practical experiments, active device connected between the

elements of the shunt passive filter is the most advantageous

topology. It ensures proper harmonic mitigation with minimal

initial costs, which frequently is crucial factor in cost-sensitive

applications. In addition, in high power applications, this shunt

active power filter topology can be used as an upgrade to the

existing passive filter improving its performance and

cancelling its serious drawbacks.

ACKNOWLEDGEMENT

The Author are grateful for the valuable comments and

suggestions for the reviewers. The valuable comments and

suggestions will enhance the strength and significance of this

paper.



150

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