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],
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
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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)
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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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
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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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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