An Intelligent Control of Three-Phase Distributed Power ...tierarztliche.com/gallery/39.10.9.pdf · An Intelligent Control of Three-Phase Distributed Power Flow Controller for Power

An Intelligent Control of Three-Phase Distributed Power Flow

Controller for Power Quality Improvement

*Rajarathinam P1 and Vijayakumar G2 1(Research Scholar, Anna University), Principal, Dept. of EEE, Adhiyamaan

Polytechnic, Hosur, T.N., India, 2Associate Professor in the Department of Electrical Engineering at Muthayammal

Engineering College, Rasipuram, T.N., India, 1Email: [email protected]

2Eemail: [email protected]

Abstract: This paper illustrated the harmonics elimination in the line current using

intelligent control technique based Distributed Power Flow Controller (DPFC) for

injecting compensating current to the transmission lines. Voltage fluctuations is

caused in transmission lines by non-linear loads, abrupt load conditions, which

results in reducing the usage of distributed system. A simple shunt and series 3 arm

converters are used in making the Distributed Power Flow Controller. To control

and regulate the voltage through the DC link capacitors, Fuzzy Logic Controller

(FLC) is executed. Using the propounded method, line harmonics is terminated by

injecting compensational current reference which handles the reactive power

requirement for dynamic load conditions.

Keywords: Distributed Power Flow Controller, fuzzy logic controller, Active Power

Flow, Total Harmonic Distortion

1. Introduction:

The harmonic content in the consumer end of ac mains is increased by the

impact of abrupt loads in the power grid. Generally, AC electric loads are non –linear

loads. The poor power factor and poor efficiency in the utility side is maintained due

to the harmonics and excessive reactive power in the transmission line. A bulky

component size and occurrence of resonance is introduced by the passive filters are

widely used in the transmission line for harmonic reduction and improving power

factor. Some advantages like less response time and better performance than the

active power filter (APF) [1] – [3]. The main source for producing the harmonic

contents in the power network are power electronic device and non linear load which

damages the quality of power. The line harmonics due to non-linear load compensated

by shunt converter by injecting compensation current to the grid line which has the

merits of control ability and quick response and line voltage can be compensated by

shunt converter. An effective approach the suppress the harmonic pollution can be

done by inhibiting the flicker and compensating reactive power.

Line harmonics leads to poor distribution system utilization factor by the non-

linear load. Using series and shunt converters, the harmonics in transmission lines are

suppressed. The recommended levels of harmonics are not affecting the function of

electrical gadgets from high voltage. Low power factor and overheating is occurred

by large and a massive resonance effect. A reference current is generated by shunt

converter based on the types of load and load current. For neutral line compensation

Tierärztliche Praxis

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active power filter are used rarely. Hysteresis current control and adaptive control

methods are some of the conventional control methods which can only be used to

certain extend and then involve a complex theory. A highly structured control

particularly in terms of robustness is needed for using of non-linear loads and three

phase unbalanced loads. To decide the compensation current to be injected by shunt

converter in to line one of the harmonic detecting and eliminating method with rapid

reactive power compensation theory is considered to be useful.

Shut converter is more potent for medium and high voltage application rather

than large transformers and passive filters to diminish reactive power, to improve

power factor and to accomplish sinusoidal source current a series of reactive power

compensators are suggested. The compensation characteristics are influenced by the

selection of the control strategy for Distributed Power Flow Controller (DPFC) [4].

Total Harmonic Distortion (THD) of source current is increased by increase in power

factor under distorted supply of voltages. The unity of power factor is not provided by

the total compensation for current harmonics. The reference current generated by

control strategy of DPFC is injected to compensate harmonic content in the line

current and reactive power required by non linear load as shown in figure1. A

multilevel converter is used to design APF in recent years [5]-[7]. lower harmonic

distortion, lower switching frequency are some merits of multilevel inventor

topologies which has a drawback of high switching loss caused by implementing

more numbers of components compared to the Distributed Power Flow Controller

(DPFC). Increase in switching loss, high THD value in line current and extra

Electromagnetic induction are caused by more number of power switches and bulky

transformers which are required in case of using cascaded inverter.

Figure 1 Schematic diagram of Distributed Power Flow Controller

A separate DC link for each H bridge is required by cascaded converters [8], if

complexity of control strategy increases in order to regulate DC voltage, using various

methods, the models of voltage source converter is established and using advanced

control approaches [9], the behavior of reference signal tracking is improved. In

recent literature, many control techniques are propounded to minimize the harmonics

in wide range of variations in load current, power factor, harmonics in wide range of

variations in load current, power factor, harmonic compensation under the random

conditions.

To incorporate into fuzzy control system, sliding mode control is needed due

to the presence of model uncertainties and external disturbance. Sliding model control

Vs

Shunt

Converter 3Ø AC

Source

Fuzzy

Controller

Series Converter

ic δ

IS IL

δ

δ

Nonlinear

load


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[10] is a robust control technique with many attractive features like robustness to

parameter variations [1], [11] and the tracking capability of switching surface. But

systematic stability analysis and controller design of fuzzy logic control with

application to shunt and series converters [12] are not found in literature. Therefore, it

is necessary to adopt intelligent control technique such as Fuzzy Logic Control that

can be adjusts automatically to control system parameters for the harmonic

elimination of proposed converter.

2. Proposed Control Scheme

Reference power is generated; Compared with a reference set value, a

reference voltage is generated by the dc link capacitor voltage of DPFC. By the

resulted error value and with change of error value by fuzzy controller which

regulates the DPFC through the reference current generator. In figure 2, fuzzy logic

control structure of proposed DPFC is given.

1

Ploss

-K-

e

-K-

ce

z

1

Unit Delay

Fuzzy Logic

Controller850 Constant

1

Vdc

Figure 2.Fuzzy Logic Controller Simulink Model

A reference current is generated by sensing the load current and source

voltage to the current controller by rapid active and reactive power theory (P-Q

theory) [5] . The preset reference value is compared to the original filter current to

give the gate pulse to the voltage source inverter (VSI) by the hysteresis controller.

The VSI output flows through the active filter to the line which draws an unwanted

harmonics from the line. As a result, the line current harmonics can be eliminated,

compensate the reactive power and improvement of power factor can be achieved.

Fuzzy logic method uses input and output membership function whose values

are varies between 0 and 1. Problems having vagueness uncertainty or imprecision are

specially dealt by fuzzy logic methods rather than Boolean or crisp logic. Human

control logic is replicated by fuzzy, one of the best proved method for many system

applications. To estimate the power loss of active power filter the DC link voltage is

regulated .The original capacitor voltage is compared with a set of reference value.

Using fuzzy logic controller (FLC), the error signal generated from the comparator is

processed. In tracking the Iref fuzzy sets are chosen, based on the error in the DC link

voltage, in which FLC contributes to nearly zero steady error. A 7X7 membership

function is considered, {NE (negative extreme), NM (negative middle value), N

(negative), Z (zero), PS (positive), PM (positive Middle), PE (positive extreme)} are

used for the flexibility of program for input and output membership functions. In the

figure 3-6, input and output membership functions are used in fuzzy interference

system (FIS) and surface view are given.


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Figure 3 Input Membership Function _ Error (e)

Figure 4 Input Membership Function _ change in error (Δe)

Figure 5 Output Membership Function _ (u)

A rule base is constructed to manage the output variable, in fuzzy logic control

method. A simple IF-Then rule with a predetermined condition was constructed. The

rules that relate the input variables to the output variable are defined by the design of

fuzzy control rule. The input of FLC is an error (e) and change in error (Δe) value of

capacitor dc voltage and the output (u) of the fuzzy is power requirement (Ploss) for

the voltage regulation. The control rule shows input and output Table1.


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Table 1 Control Rule Structure

e

Δe NE NM N Z P PM PE

NE NE NE NE NE NM N Z

NM NE NE NE NM N Z P

N NE NE NM N Z P PM

Z NE NM N Z P PM PE

P NM N Z P PM PE PE

PM N Z P PM PE PE PE

PE Z P PM PE PE PE PE

-1-0.5

00.5

1

-1

0

1

-0.4

-0.2

0

0.2

0.4

ece

u

Figure 6 Surface view of applied Fuzzy rules

4. Hysteresis Current Generation

The main function of the hysteresis current generator was that; generate gate

pulse with the proper duty cycle for the DPFC controller. Output of the Fuzzy

controller Ploss was given to the MATLAB function block of the p-q theory and

compensation current (IComp*) was generated by consideration of load current (ILoad)

and source voltage (VS). In the hysteresis current generator block, there were upper

and lower band created based on the reference current and compensation current. The

upper hysteresis band limit was equal to the sum of the compensation current of

maximum limit and reference current. The lower hysteresis band can be setup the

subtraction of the compensation current of minimum limit and reference current. The

appropriate gate pulses were generated with the proper duty cycle for DPFC

controller when the upper and lower band was hit on its wall at every instance. The

instantaneous active and reactive power theory (p-q theory) was used. In figure 7,

MATLAB simulated schematic diagram of reference current generator is given.


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The 5 main steps for reference current generator are Clarke transformation,

selection of compensating power, reference α β axis current calculation, instantaneous

pq calculation, and Clarke transformation.

c

b

a

V

V

V

v

v

2

3

2

30

2

1

2

11

3

2

1

c

b

a

I

I

I

i

i

2

3

2

30

2

1

2

11

3

2

2

The instantaneous power for the 3ϕ

i

i

vv

vv

q

P 3

Where p & q are instantaneous real power and imaginary power

By observing the formulations of p and q, it is possible to put the following form:

*

*

qqq

PPP

4

Figure 7 MATLAB simulated schematic diagram of reference current generator.

Where:

P - DC component related to fundamental active current conventional.

Coupling Inductor

1 Icomp*

3 c

2 b

1 a

v + -

Voltage

g

A

B

C

+

-

Universal Bridge 3 arms

Iabc A

B

C

a b c

Three-Phase V-I Measurement

A B C

A B C

Vs Is

PQ meas.

Vabc

Iabc

Ploss

ICabc

ICabc1

PQ & I-compensation Calc

Vdc Ploss

Fuzzy Logic Controller

I_ref I_meas

g

Hysteresis controller

Iapf

Ploss Goto3

-T- Goto2

Vdc

Is Vs

Vs

Ploss

Iload

DC Cap1

DC Cap


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*P - AC component of P, mean value and associated with harmonic caused by

the AC component of instantaneous real power.

q - DC component related to the reactive power generated by the components

fundamental currents and voltages.

*q - AC component of q and related to harmonic currents caused by the

components of AC instantaneous reactive power.

q

P

vv

vv

vvi

i

22

1 5

22

Re

~

~101

0

1

vvwhere

q

P

vv

vv

qvv

vvP

vv

vv

i

i

CurrentHarmonicCurrentActiveCurrentactive

6

The (α – β) inverse transformation is used to calculate the 3ϕ distorted currents

representing reference current (Iref), is shown in the relation (6) presented below.

I

I

I

I

I

ref

ref

ref

2

3

2

1

2

3

2

1

01

3

2

3

2

1

7

To validate the method of the p-q theory the quality of the voltage must be

good. To charge the dc capacitor in the VSI, the corresponding power signal Ploss is

needed and is regulated with fuzzy controller. By applying the inverse Clark

transformation when all the parameters are calculated in α β reference, the

instantaneous reference current is obtained.

5. Hysteresis Current Controller

The significant aspect of the proposed method is tracking of the reference

current. The current controller provides the proper gate pulses with a Voltage Source

inverter. To control the power converters gate pulse, hysteresis current controller is

used. The original source currents are periodically compared to the reference currents

generated by the proposed algorithm. Quick response is provided by getting an

accurate control on Switching to IGBT device which is done when the error signal

always approaches to zero. The uniqueness of the hysteresis band current control are

unconditioned stability, very fast response and good accuracy.

The actual current is compared to the reference current of desired magnitude

and frequency the lower switch is turned on when the current exceeds the upper limit

of the hysteresis band, and upper switch of the inverter is turned off. The current starts

to decay as a result of it. If the current crosses the permissible limit of the hysteresis

band this process becomes contrariwise .The reference current is tracked by the force

of the actual current within the hysteresis band.


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6. Simulation Results and Analysis

To find out the working of the propounded shut active power filter under

different loading conditions like non-linear and unbalanced loadings MATLAB

simulation is carried out. In simulation results three different cases of loads are

considered. In case of non-linear load.

In figure 8(a) a 3-phase voltage of Vm of 325v, 50Hz is shown. Power quality

of the line is drastically reduced when the load draws a current from the source as

shown in figure 8(b) which is affected by the non-linear load conditions. To improve

the power quality of the line, a Distributed Power Flow Controller (DPFC) is

designed which intern avoid the source current being affected by the non-linear load.

As shown in figure 8(c) the Distributed Power Flow Controller (DPFC) is connected

with the line after 0.02 second.

Non–linear load affects the source currents from 0 to 0.2s. A sudden surge

current is produced in the line with a current range of 150A which is caused when the

DPFC is connected at 0.02s to the line and within 0.015s, it settles down to the rated

current. A constant current magnitude is maintained with sinusoidal shape from

0.015s. Even with the non-linear loads the angle between source voltage and current

remains zero.

0 0.01 0.02 0.03 0.04 0.05 0.06-400

-200

0

200

400

V load

0 0.01 0.02 0.03 0.04 0.05 0.06

-100

0

100

I lo

ad

0 0.01 0.02 0.03 0.04 0.05 0.06

-200

0

200

Time (sec)

Is


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Fig. 8 (a) Source voltage (b) 3phase load current (c) After filtering: 3phase source

current.

0 0.01 0.02 0.03 0.04 0.05 0.06-400

-200

0

200

400V

s

0 0.01 0.02 0.03 0.04 0.05 0.06

-50

0

50

Iapf

0 0.01 0.02 0.03 0.04 0.05 0.06

0

1000

2000

3000

Time (sec)

Vdc

Fig.9 (a) source voltage (b)IDPFC (c) Vdc Plots

As shown in figures 9(a) and (b), to improve the quality of the line current, the

output current of shunt controller is injected to the line. In figure 9(c) the simulated

results of the DC link capacitor voltage is shown, which adjust itself based on the load

condition.


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0 0.01 0.02 0.03 0.04 0.05 0.06

-50

0

50

Selected signal: 3.282 cycles. FFT window (in red): 2 cycles

Time (s)

0 5 10 15 200

2

4

6

8

10

12

14

Harmonic order

Fundamental (50Hz) = 57.58 , THD= 27.05%

Mag

Fig. 10 a. Source Current THD at Before Activating Shunt Active Filter

0 0.05 0.1 0.15 0.2 0.25 0.3

-100

0

100

200

Selected signal: 15 cycles. FFT window (in red): 2 cycles

Time (s)

0 2 4 6 8 10 12 14 16 18 200

0.5

1

1.5

2

2.5

Harmonic order

Fundamental (50Hz) = 147.4 , THD= 3.52%

Mag


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Fig. 10 b. Source Current THD at After Activating DPFC

For the fundamental frequency 27.05% is the THD of the source current which

is shown in figure 10(a).As shown in figure 10(b), the THD of the source current

becomes less them 3.52% when the current is injected through Distributed Power

Flow Controller (DPFC) and the comparison Table 2 as shown.

TABLE 2: THD value for Source Current

THD

Source current

Before DPFC

Source current

after DPFC

27.05% 3.52%

0 0.01 0.02 0.03 0.04 0.05 0.06

-50

0

50

100

Ia c

om

p

0 0.01 0.02 0.03 0.04 0.05 0.06-100

-50

0

50

Ib c

om

p

0 0.01 0.02 0.03 0.04 0.05 0.06

-50

0

50

Time (sec)

Ic c

om

p

Fig.11 Compensation current (IC) for source current

The source current Is, properly compensated and the harmonics are removed

which resulting THDs of 3.52% for the nonlinear load due to the compensated current

as shown in Fig. 11.


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7. Conclusion

The significant objective of this Simulation are improving the power factor, to

balance the current from an unbalanced load condition and to reduce the harmonics

produced in the non-linear loads to compensate reactive power from the distributive

line. The working of the active filter satisfies to compensate the harmonics reactive

power, unbalanced load and also to improve power land these shown as the result of

the analysis .To fulfill the objectives the DPFC works perfectly which is shown by the

simulations that are simulated in MATLAB/SIMULINK. Using unity power factor

and less harmonics, Sinusoidal source current is produced. The harmonics and

reactive power of the system is compensated by the DPFC which has a controller

based on p-q theory.

References

[1] Singh, R., Singh, A. K., & Arya, R. K. (2012). Approximated fuzzy logic controlled shunt active

power filter for improved power quality. Expert Systems, 30(2), 152–161.

[2] Joydeep Sutradhar, U. Venkat A Reddy and Akhilesh A. Nimje, (2015) ‘Distributed Power Flow Controller for Power Quality Enhancement’, International Journal of Electrical, Electronics and Data Communication,

Special issue: 43-47.

[3] Prakash S and Hameed Hussain J, (2018) ‘Power Quality Improvement using FACTS Controllers using

DPFC’, International Journal of Pure and Applied Mathematics; 118(18): 301-309

[4] Yuan, Z., Haan, S. W. H. de, Ferreira, J. B., and Cvoric, D. (2010) A FACTS Device: Distributed Power-Flow

Controller (DPFC). IEEE Transactions on Power Electronics; 25(10): 2564–2572.

[5] Akhib Khan Bahamani, G.V. Siva Krishna Rao, A.A. Powly Thomas and Dr V.C. Veera Reddy, (2013)

‘Modelling and Digital Simulation of DPFCSystem using Matlab Simulink’, ‘International Journal of Emerging

Trends in Electrical and Electronics (IJETEE – ISSN: 2320-9569); 6(1).

[6] Shanker N., B. Sampath Kumar, (2010) Voltages sag and swell mitigation using DPFC for

Multibus system, International Journal of Engineering Research & Technology (IJERT), Vol. 2 issue

10.

[7] P. Ramesh, M. Damodara Reddy, 2012 ‘Modeling and Analysis of Distributed Power- Flow

Controller (DPFC)’, International Journal of Engineering Research and Applications; 2(2): 609-615.

[8] Y.-H. Song and A. Johns, (1999) ‘Flexible ac Transmission Systems (FACTS) (IEE Power and

Energy Series)’, vol. 30. London, U.K.: Institution of Electrical Engineers.

[9] N. G. Hingorani and L. Gyugyi, (2000) ‘Understanding FACTS : Concepts and Technology of

Flexible AC Transmission Systems’, New York: IEEE Press, 2000.

[10] L.Gyugyi, C.D. Schauder, S. L.Williams, T. R. Rietman,D. R. Torgerson, and A. Edris, (1995)

“The unified power flowcontroller:Anewapproach to power transmission control,” IEEE Trans. Power

Del.; 10(2) : 1085– 1097.

[11] Khazaie, J., Mokhtari, M., Badkubi, S., Khalilian, M., & Nazarpour, D. (2012) ‘ Sub-synchronous

resonance mitigation via distributed power flow controller’, International Transactions on Electrical

Energy Systems; 23(6) : 751–766

[12] Kumar, R., & Bansal, H. O. (2019) ‘Real-time implementation of adaptive PV-integrated SAPF to

enhance power quality’, International Transactions on Electrical Energy Systems: 1-22.


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Prof.P.Rajarathinam is currently as a Principal at Adhiyamaan Polytechnic College,

Hosur, Tamilnadu, India. He has totally 16 years of experience in teaching (Till

September 2019) and 10 years of industrial experience. His research concentrated on the

behavior of power quality improvement using FACTS devices. His research interests

include Power quality, shunt/series active filter, and he has 16 years of experience in

teaching and research. He received post graduate degree M.E –Power electronics and

drives at Anna University, Chennai and He received his B.E Degree in EEE at Madurai Kamaraj

University, Madurai. He is persuing PhD in the area of power quality improvement.

Dr. G.Vijayakumar (ORCID Id: 0000-0003-1412-9879) is currently an Associate

Professor in the Department of Electrical Engineering at Muthayammal Engineering

college, Rasipuram, Tamilnadu, India. He has totally 13 years of experience in teaching

(Till May 2018). He received his doctorate in Electrical Engineering from Anna

University, Chennai, Tamilnadu, India in November 2014. He has been guiding 6 Ph.D.,

research scholar and has guided 04 post graduate projects and 11 undergraduate projects.

His research concentrated on the behaviour of Shunt active filter during harmonic compensation and

energy conservation. He has published over 19 articles in the peer-reviewed National & International

journals, and over 17 conference proceedings, and has delivered over 06 guest lecturers in the college

programmes. His h-index of 04 (Total citations 42, Source-Google Scholar) strongly endorses his

high research productivity. His research interests include Power quality, shunt/series active filter,

hybrid renewable energy sources, intelligent controllers. Currently, he is a reviewer for Journal of the

Institution of Engineers (India): series B- springer, Asian journal of control, journal of power

electronics and Journal of Circuits, Systems & Computers. He organized 05 Faculty Development

Programmes (Seminar/Workshop/Value added courses. He has acted as the chairperson on

international conference. He taught Electrical engineering students at under graduate and post graduate

level, over his experience, he produced 100 % results in many courses. He has the well known

professional experiences on board of studies, research and development activity, project coordination,

Exam coordination, Time table coordination, class advisor, NBA & NIRF activity and technical

training coordination to the students.


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