PERFORMANCE INVESTIGATION OF SHUNT ACTIVE POWER FILTER ... · A. Shunt active power filter Shunt active power filter is voltage source inverter which can inject harmonics current

PERFORMANCE INVESTIGATION OF SHUNT ACTIVE POWER FILTER

UNDER VARIOUS CONTROL STRATEGIES IN DISTRIBUTION

GENERATION SOURCE (DGS) ENVIRONMENT

S.Ravikumar1, M.Muhaidheen2, S.Muralidharan3

PG Scholar1, Assistant professor 2, Professor3

Department of Electrical and Electronics Engineering,

Mepco Schlenk Engineering College,Sivakasi [email protected],

[email protected],

[email protected]

Abstract— Extreme use of non linear load by customer will

increase power quality problem in distribution line. In order to

mitigate power quality problem, shunt Active power filters

(SAPF) are extensively used to compensate the load current

harmonics and load unbalance at distribution level. This result in

an additional hardware cost and it consume the power from the

distribution line. Moreover, renewable energy resources

especially Solar PV and Wind mill are being increasingly

connected into distribution system. Because of environmental

pollution, fast depletion of fossil fuels and inability to meet out

ever increasing consumer demand for shorter duration by

conventional power generation system. But due to its intermittent

nature these are underutilized in real time. In this project, solar

PV are being incorporated in the conventional inverter as a DC

source to act as a shunt active power filter (SAPF) with a view to

reduce additional hardware cost. The Proposed system can

effectively be utilized to perform following important functions:

1) transfer of active power harvested from the Solar PV 2) load

reactive power demand support; 3) current harmonics

compensation at PCC; and compensation in case of 3-phase 3-

wire system. Moreover, the comparative study of SAPF

implementing two different current compensation techniques of

p-q theory and active and reactive current ( id-iq ) component

method is done.

Keywords— Shunt active power filters (SAPF), Solar PV, Point of

common coupling(PCC), p-q theory, id-iq method

I. INTRODUCTION

Due to extreme use of power converters and other non-

linear loads in industrial, commercial and domestic

applications which draws a non sinusoidal current and reactive

power from the source.[1] Mainly voltage harmonics and power distribution problems arise due to current harmonics [2]

produced by nonlinear loads. It is noted that non-sinusoidal

current results in many problems for the utility power supply

company, such as low power factor, low energy efficiency,

electromagnetic interference (EMI), voltage distortion and

sometimes result in operation failure of electronic equipments

etc.[2] Passive filters have been used as a solution to solve

harmonic current problems, because of the several

disadvantage of passive filter like it can mitigate only few harmonics and gives rise to resonance problem. Additionally,

passive filters have drawback of bulk size [1]. To cope with

these disadvantages, recent efforts have been concentrated in

the development of active power filters (APF) are extensively

used to compensate the load current harmonics and load

unbalance at distribution level [4]. But shunt active power

filter consumes power from distribution line. So it makes loss

to utility. Due to growing demand on electricity, the limited

stock, rising prices and environment pollution of conventional

sources, photovoltaic (PV) energy becomes a promising

alternative as it is omnipresent, freely available, environment friendly, and has less operational and maintenance costs [3].

Therefore, the demand of PV generation systems seems to be

increased for both standalone and grid-connected modes of

PV systems [5]. Due to nature of PV most of the time, it

underutilized and it requires additional hardware cost to

interface to distribution line. In proposed system, shunt active

power filter compensate power quality problem as well as it

transfer active power from solar PV.

This paper has been organized as follows: System

description, shunt active power filter and reference current

generating technique and solar PV are shown in Section II.

Simulation of shunt active power filter, two reference current generating technique and analysis based on the power factor,

THD of source current and source reactive power requirement

are shown in Section III. Finally, Section IV provides

conclusion.

II. SYSTEM DESCRIPSION

The proposed system consist of renewable energy source of

solar PV connect to dc link of shunt active power filter shown

in Fig 1. PV is used to generate electric power from solar

radiation. This power is used for shunt active power filter

(SAPF) to mitigate the power quality problem otherwise

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 9 (2015)© Research India Publications ::: http://www.ripublication.com

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mailto:[email protected]

Fig.1 Schematic of proposed renewable energy based shunt active power filter

SAPF consume power from distribution line. The dc

capacitor decouples the solar PV from distribution line and

also allows independent control of convert on either side of dc

link. [4] PI controller is used to maintain a capacitor voltage.

Reference current can be generated based on source voltage

and load current. Band less hysteresis current controller

generate gating signal to six leg inverter based on the

reference current and actual compensation current.

A. Shunt active power filter

Shunt active power filter is voltage source inverter which

can inject harmonics current equal and opposite (phase shifted

by 180o) to that of load current harmonics. So source is retrieve

as harmonics free [6]. It has voltage source at dc bus usually a

capacitor as energy storage device, whose power gets from distribution line. The more usual configuration of SAPF is

injecting current harmonics into the point of common

coupling (PCC)[4]. Fig. 2 is describes SAPF as current source

to generate current harmonic to cancel out the load current

harmonics.

Fig. 2 Generated filter current to compensate load-current harmonics.

The three main aspects of shunt active power filter are:

The configuration of power converter (the scheme

and the topology of converter and the electronics

device used)

The control strategy (the calculation of APF control

reference signals)

The control method used (how the power inverter follows the control reference).

In proposed system is three phase three wire system. So

inverter design as three legs, six switch inverter. Here two

control strategies (instantaneous p-q and id-iq methods) are

used for generating reference current control the shunt APF.

B. Instantaneous active and reactive power theory.

This theory, also known as "pq theory" was proposed in

1983 by Akagi et al. to control active filters. The p-q theory

consists of an algebraic transformation (Clarke transformation)

of the three-phase voltages and currents in the a-b-c

coordinates to - coordinates, followed by the calculation of the p-q theory instantaneous power components.

= (1)

= (2)

The power components p and q are related to the same - voltages and currents, and can be written together as,

= (3)

where,

p - instantaneous real power

q - instantaneous reactive power

(4)

(5)

where,

= mean value of the instantaneous real power

= alternated value of the instantaneous real power.

= mean value of the instantaneous imaginary power.

= alternated value of the instantaneous imaginary power.

To calculate the reference compensation currents in the α-

β coordinates from the powers to be compensated ( and q)

and - voltages the conversion shown in (6) must be applied.


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To regulate capacitor across voltage, PI controller output is

added with the active component reference current.

= (6)

In order to obtain the reference compensation currents in the a-b-c coordinates the inverse of the

transformation given in (7) is applied as,

= (7)

The p-q theory also permits a control strategy for the shunt

active filter to be used when voltages are distorted and/or unbalanced and sinusoidal supply currents are desired. [7, 8]

C. Instantaneous active and reactive current theory

In this method the active filter currents Ic can be obtained

from the instantaneous active and reactive current components

of the nonlinear load. By using Park transformation on two

phase α-β (by Clarke transformation) we will get (d-q)

components. In Park transformation two phase α-β are fed to

vector rotation block where it will be rotated over an angle θ

to follow the frame d-q .The calculation to obtain these components ( Id , Iq ) follows the same method to the

instantaneous active and reactive power(p-q) theory. In a same

manner the mains voltages Vs and the polluted currents Ii in α-

β components will be calculated as same way calculated in (2).

However, the d-q load currents components are derived from a

synchronous frame based on the Park transformation.

= (8)

Where θ is a transformation angle

Under balanced and sinusoidal mains voltage

condition θ is a uniformly increasing function of a time[8].

The transformation angle 'θ' is sensible to all voltage

harmonics and unbalanced voltages therefore, dθ/dt may not

be constant over a mains period. θ is calculated by using PLL.

Instantaneous active and reactive load currents Id and Iq

can be decomposed into oscillatory and average terms as

follows

and

The average current term will be eliminated by high pass

filters (HPF).The currents which will be compensated can be

obtained as Icd = and Icq = . Icd and Icq current

component are converted into reference frame by using (6) equation.

Finally the compensation currents can be calculated as:

= (9)

Fig. 3 SAPF control system based on the active and reactive current

component method.

D. Dc voltage regulation of capacitor

The DC side capacitor serves two main purposes: (i) it

maintains a DC voltage with small ripple in steady state, and

(ii) serves as an energy storage element to supply real power

difference between load and source during the transient period.

The design of the DC side capacitor is based on the principle of instantaneous power flow. The selection of Cdc can be

governed by reducing the voltage ripple. As per the

specification of the peak to peak voltage ripple and rated filter

current, the DC side capacitor Cdc can be found from equation.

= (10)

The voltage regulation on the Voltage Source Inverter (VSI)

dc side will be performed by a proportional-integral (PI)

controller. The input to the PI controller is the capacitor

voltage error(C*dc-Cdc). On regulation of first harmonic

active current of positive sequence id1h+ which is possible to

control the active power flows in the VSI and thus the capacitor voltage Cdc. The reactive power flow may be

controlled by the regulation of first harmonic quadrature

current of positive sequence iq1h+. On the contrary the

primary end of the active power filters is just the exclusion of

the harmonics caused by non-linear loads hence the current

iq1h+ is always set to zero. [8]

E. Solar PV:

Solar photovoltaic modules generate electricity from

sunlight, which can be fed into the mains electricity supply of building or sold to the public electricity grid. Although most

of time it is underutilized due intermittent of renewable

energy. Usually shunt active power filter consume a power

from distribution line. It makes addition loss to utility. In

proposed system solar PV panel provide real power to shunt

active power filter. PV panel is designed based on equation

[3].

Id=IL-I0[exp{ (V+IRs)/VT}-1] – (V +IRs)/Rsh (11)


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III. SIMULATION:

A. Photovoltaic module

In proposed system solar PV connect to dc link of ASPF to

provide real power

Fig . 4 Photovoltaic module

Fig. 4 shows the simulated photovoltaic module with solar power of 1000 w/m2 and the temperature as 25 º C respectively.

The irradiance or solar power is the input for photovoltaic

module. Basically PV module is a non linear device and its

electric power fluctuates depending on the solar irradiance

value and temperature. This module designed by 36 series

connected solar cell.

B. Three phase system with a non linear load

The three phase three wire system with a nonlinear load is

simulated to have a brief study on the nonlinear characteristics

of the load current and the effect of such nonlinear

characteristics in load current.The nonlinear load coupled with

the three phase three wire system represents the model of a

power system with a nonlinear load. the source parameters are

given in the Table.The nonlinear loads considered here is a

three phase uncontrolled bridge rectifier with RL load. Figure

shows voltages and current waveform of source and load

respectively.

Fig. 5 Voltage and current wave of source and load under uncompensated

condition.

The following observations are made from the figures Fig.5

The load current and system current remains the same

The load current pollutes the source current by

introducing harmonics phenomenon

This polluted source current is undesirable and it has

to be purified.

C. ASPF implementation of p-q – theory

The ASF is introduced in a system of nonlinear load for the

elimination of harmonics in source current just by supplying

only the harmonic component required by the load. The

extraction of harmonic current from the three phase load current is done by several methods. Here in the proposed system pq-

theory and instantaneous active and reactive current method is

used.

The simulation model of SAPF with pq-theory for current

extraction implementing PI voltage controller Fig. 6

Fig. 6 SAPF involving p-q theory of harmonic current extraction

The value of coupling inductor and ASF capacitor as well as

the reference voltage to the capacitor is given in the table. The

various steps involved in p-q-theory calculation that are

simulated as given in Fig.7

Fig. 7 Implementation of p-q theory calculations and gating signal

generation.

The aim of ASPF is to obtain the reduced harmonics in the

source current in order to have a pure supply current for the

other loads connected to the system and to avoid the ill effects

of source impurity on other sensitive loads. After simulating the


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ASPF implementing pq-theory the different system currents are

obtained and studied as shown in Fig. 8

Fig. 8 Waveform of current components in the system after ASF filtering

D. SAPF implementation of active and reactive current method

Instantaneous active and reactive current method is another

compensation current generation method. Here the Id-Iq

method compensation current generation adopted ASF,

implementing PI voltage controller is simulated as shown in

Fig.9

Fig. 9 Implementation of active and reactive current calculations and gating signal.

Simulating the ASF implementing Id-Iq the different system currents are obtained and studied as shown in Fig 10.

Fig.10 Waveform of current components in the system after ASF filtering.

E. Dc voltage regulation

The purpose of the voltage controller is to achieve a

regulated voltage profile across the capacitor and is achieved.

The PI controller gain Kp =0.07 and Ki =0.01 values are used

for p-q theory and Id-Iq method to generate reference current.

The response of voltage regulation is shown Fig 11.

Fig.11 Capacitor voltage controlled using PI controller

Fig.12 FFT analysis of source current

From the Fig. 12 we infer that before implementation of

filter, source current has THD of 25.39%, it requires reactive

power 18.28 var and power factor of 0.9501. After

implementing different current compensation methods along

with PI controllers in ASF, THD of source current is reduced to

1.48% in both compensation methods. The obtained THD of

Source current lies within the IEEE-519 recommendation and

reactive power required by source is reduced to 9.605 and 9.026

respectively and power factor is improved by 0.9874 and

0.9887 respectively to p-q method and Id-Iq method. Source,

load and filter parameter shown in below

Table System parameters

S.NO PARAMETERS VALUES

1. Source RMS voltage,

Vs,rms 30 V ( 50 Hz )

2. Source Resistance, Rs 0.001 Ω

3. Source Inductance, Ls 1 H

4. Load Resistance, Rl 26.66 Ω

5. Load Inductance, Ll 10mH

6. Reference voltage, Vdc ,ref 72 V

7. Filter capacitance, Cdc 600mF

8. Interfacing Inductance ,

Lc

12.5 mH

( 1 Ω )

IV. CONCLUSIONS

In this paper, two different control techniques have been implemented and compared in SAPF to perform following


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important functions i) transfer of active power from PV to grid.

ii) Shunt Active Power Filter at PCC; the comparative study

of ASPF implementing two different current compensation

techniques p-q-theory and instantaneous active and reactive

current method is done. it is inferred that p-q-theory based

control scheme performs well by having high transient

response than in the instantaneous active and reactive current

method based control scheme. The obtained THD of Source

current lies within the IEEE-519 Recommendation. The

capacitor voltage profile of ASPF has less ripples which will

again proves that the ASPF injects Real power into the distribution line. Among all configurations it is inferred that

the THD and reactive power compensation obtained in

instantaneous active and reactive current method current

extraction method is relatively good when compared to

instantaneous active and reactive power method of

compensation. REFERENCES

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[3]. Bidyadhar Subudhi, Raseswari Pradhan ―A Comparative Study on Maximum Power Point Tracking Techniques for Photovoltaic Power Systems‖ IEEE transactions on sustainable energy, vol. 4, no. 1, (2013):pp 89-97

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K. Varma,―Grid Interconnection of Renewable Energy Sources at the Distribution Level With Power-Quality Improvement Features‖ IEEE transactions on power delivery, vol. 26, no. 1, (2011) :pp 307-316

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[7]. Mostafa I. Marei, Ehab F. El-Saadany, “A Flexible DG Interface Based on a New RLS Algorithm for Power Quality Improvement” IEEE systems journal, vol. 6, no. 1, (2012) pp:68-76

[8]. Karuppanan P,Kamala Kanta Mahaptra, ― PI and fuzzy logic controllers for shunt active power filter‖ Elsevier ISA Transactions 51 (2012) pp163-169

[9]. C. Nagarajan, M.Madheswaran and D.Ramasubramanian- ‗Development of DSP based Robust Control Method for General Resonant Converter Topologies using Transfer Function Model‘- Acta Electrotechnica et Informatica Journal , Vol.13 (2), pp.18-31,April-June.2013

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PERFORMANCE INVESTIGATION OF SHUNT ACTIVE POWER FILTER ... · A. Shunt active power filter Shunt active power filter is voltage source inverter which can inject harmonics current