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A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54
www.ijera.com 48 | P a g e
A Technique for Shunt Active Filter meld micro grid System
A. Lumani*, G. Srikanth**
*(PG Scholar, GIT)
** (PG Scholar, GIT)
ABSTRACT
The proposed system presents a control technique for a micro grid connected hybrid generation system ith case
study interfaced with a three phase shunt active filter to suppress the current harmonics and reactive power
present in the load using PQ Theory with ANN controller. This Hybrid Micro Grid is developed using freely
renewable energy resources like Solar Photovoltaic (SPV) and Wind Energy (WE). To extract the maximum
available power from PV panels and wind turbines, Maximum power point Tracker (MPPT) has been included.
This MPPT uses the “Standard Perturbs and Observe” technique. By using PQ Theory with ANN Controller, the
Reference currents are generated which are to be injected by Shunt active power filter (SAPF)to compensate the
current harmonics in the non linear load. Simulation studies shows that the proposed control technique performs
non-linear load current harmonic compensation maintaining the load current in phase with the source voltage.
Keywords - Active filter, ANN controller, Distributed Energy resources, Harmonic distortion, Micro grid,
Maximum power point tracker, Photovoltaic, PQ Theory, Wind Energy
I. INTRODUCTION
Due to an extensive increase in energy demand,
and the distinct advantages offered by the micro grid
to customers as well as to the utilities such as lower
environmental impact, greater reliability, reduced
cost and higher efficiency keeping them as
fundamental requirements, the present power
scenario is sweeping towards the development of a
hybrid micro grid as an alternative for the flexible
extension of the actual energy distribution network
[1]. The basis of the Micro grid conception is to
congregate the loads and micro-sources operating as
a single controllable system adjoined at a single point
of common coupling (PCC) to furnish the power and
heat for its local area [2]. Renewable energy sources
like solar, wind, Biomass, hydro and Geo thermal
power are equipped in a micro grid. Micro sources
such as wind turbines and photovoltaic cells are well
known for their discontinuity in power generation,
the hybrid system which is proposed allows using an
adaptive MPPT algorithm along with the method of
standard perturbs and observes is to utilize ultimate
accessible energy from the renewable energy
resources [3].
Micro grid basically incorporates inverter-
interfaced distributed energy resources (DER) such
as PV arrays, wind turbines, fuel cells, micro turbines
which are hooked to the distribution system making
the power network weak and drawing non-sinusoidal
current from the load yielding to harmonics and
circulation of reactive power [4].
Basically the harmonics are materialized into
two categories.
• Short Term
• Long Term
Short-term harmonics are mainly associated with
enormous voltage distortion and easily noticeable. On
the flip side, long-term harmonics yield increased
voltage stresses. This harmonic current can
collaborate unfavorably with power system
equipment like motors and transformers causing over
loading, overheating and additional losses and can
also create interference with the telecommunication
system and may lead to erroneous operation in
metering devices. Due to these detrimental effects
Standards like IEEE 519-1992, IEC had developed to
define a clear-cut framework to control the
harmonics. These harmonic distortions of power
distribution systems can be compensated using two
fashions namely, passive and active filtering [5]-[7].
The passive filtering approach is the least expensive
and provides an elementary ordinary solution to
suppress the harmonic deformity. But it inherits of
several shortcomings such as the components are
Bulky in size, dependence on the source impedance,
the creation of the resonance problem and there by
perturbing the stability of the power distribution
system [8]. Therefore, the active power filter appears
to be a feasible solution for the compensation of
reactive power besides wiping out the harmonic
currents.
The main focus in designing and controlling of
APF is the estimation of compensation current and
generation of reference signal. Various schemes such
as Fast Fourier Transform (FFT), Kalman filter and
artificial neural networks (ANN) which are
developed by so many authors are studied for the
control of active filters [9]. However, Kalman filter
approach is unfit for on-line applications such as
active power filtering Even the Fast Fourier
RESEARCH ARTICLE OPEN ACCESS
A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54
www.ijera.com 49 | P a g e
Transform (FFT) technique gives inaccurate results,
if the signal has any DC component of decaying type
[10]. The ANNs are trained to compute the required
harmonic currents depending upon the back
propagation rule. This technique leads to imprecise
results in the existence of random noise and it
requires huge data for training of ANNs [11]. Most of
the above-said control techniques are troublesome
and complex to employ under non-ideal conditions.
In this paper, Maximum Power point tracking
(MPPT) controller using standard Perturbs and
observe approach [12] is used for both the
Photovoltaic (PV) array and the permanent magnet
synchronous generator (PMSG) wind turbine
generation system. The instantaneous active and
reactive power theory (PQ theory) strategy has been
implemented for the estimation of reference currents.
The stationary reference frame (abc) variables are
transformed into the Synchronous orthogonal
reference frame (αβ0) in the prospective approach.
This analysis was primitively particularized for three-
phase systems by Akagi in 1983 [13], and later it was
extended by various researchers [14]-[17]. In this
contemplated theory, the three phase system can be
represented as a single phase system by altering the
load current and grid voltage by 90°, thus facilitating
the single phase system to be represented as a
fictitious two-phase system. The proposed PQ theory
with the ANN controller yields a ripple free DC
voltage across the capacitor compared with the shunt
active filter with PI controller .When compared to the
other frequency-domain techniques, this approach
has an outstanding compelling response and it
requires lesser computational strain
II. Over view of the Proposed System
In the proposed system, a Hybrid micro grid
equipped by Solar and wind energy is interfaced with
a Shunt active filter using the PQ theory for the
generation of reference currents with ANN controller
is developed. Maximum power point tracker (MPPT)
controller using standard Perturbs and observe
approach is used to get hold of the maximum
accessible power from the distributed energy
resources (DER‟S) like Photovoltaic (PV) array and
permanent magnet synchronous generator (PMSG)
wind turbine generation system.
By Considering all attributes for power
generation from DES are considered and Concluded
Solar PV, Wind Energy and Fuel Cell have good
potential So among them Solar and Wind are
considered.
Fig.1 Overview of the proposed system
A. PV ARRAY
The PV cell can be epitomized by an electrical
equivalent circuit in which the current source is
placed in parallel with the diode as depicted in the
figure 2. The solar cell acts like a diode during the
darkness and therefore it neither produces a current
nor a voltage. Thus, the diode evaluates the I-V
characteristics of the cell [18]. The internal resistance
to the current flow is indicated by the series
resistance 𝑅 𝑆, and it counts on the impurities, PN
junction depth and contact resistance. The shunt
resistance 𝑅 𝑆ℎ and the leakage current to ground
inversely associated to each other. A slight increase
in 𝑅 𝑆 can diminish the PV output greatly. The PV
conversion efficiency is most receptive to the small
variations in 𝑅 𝑠, but it is impassive to the variations
in 𝑅 𝑆ℎ .
Fig.2.Equivalent circuit of PV Cell
The output current I and the output voltage
V of a solar cell [19] are provided by (1), (2) as
follows
I = 𝐼𝑝ℎ - 𝐼0(exp (
𝑞
𝑛.𝑘.𝑇
𝑉)-1 (1)
V=𝑉𝑑0-𝑅 𝑠I (2)
Here, 𝐼𝑝ℎ is the photocurrent, 𝐼0 is the reverse
saturation current, 𝐼𝑑𝑜 is the average current through
the diode, n indicates the diode factor, q is the
electron charge (q = 1.6∗
10−19
), k is the Boltzmann‟s
constant (k = 1.38∗
10−23
), and T is the solar array
panel temperature. Rs indicate the intrinsic series
resistance of the solar cell. Rsh is the equivalent
A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54
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shunt resistance of the solar cell, and its value is very
large. If the circuit is opened, then the current I=0,
and the open circuit voltage 𝑉𝑜𝑐 is symbolized by (3)
as follows
𝑉𝑂𝐶= (
𝑛.𝑘.𝑡
𝑞
) In (
𝐼 𝑝ℎ
𝐼 𝑜
+1) ≈ (
𝑛.𝑘.𝑡
𝑞
) In (
𝐼 𝑝ℎ
𝐼 𝑂
) (3)
If the circuit is short circuited, the output voltage
V=0, the average current through the diode is
generally ignored, and the short circuit current 𝐼𝑠𝑐 is
expressed by (4)
𝐼𝑠𝑐 = I =
𝐼 𝑝ℎ
1+
𝑅 𝑠
𝑅 𝑠ℎ
(4)
Lastly, the PV output power P, is asserted by
P = VI = (𝐼𝑝ℎ -𝐼𝑑𝑜 -
𝑉 𝑑0
𝑅 𝑠ℎ
) (5)
1) Perturb and Observe (P&O)
Perturb and observe algorithm has been used to
elicit the ultimate accessible power from the solar
panel. To achieve this, a slight perturbation is
introduced in the system. The perturbation is
preceded in the incremental direction, if the power
increases because of the introduced perturbation
[20]. And if the power is reached to the peak value
then at the next off the power decreases and the
perturbation direction will be reversed. After
reaching the steady state, the algorithm pivots around
the peak point. The perturbation size is stored up to a
small value to keep the power variation in a small
range. The module reference voltage is set by
referring to the peak voltage of the PV module with
the help of controller and thus it acts by sliding the
point of the module to that particular voltage level.
B. Wind Turbine
In this paper the modeling of the wind turbine
driven by PMSG is described. The three bladed rotor
is the most important and visible part of the wind
turbine. The working principle of the wind turbine
can be described in two processes that are
accomplished by its vital components: the rotor
extracts the kinetic energy from the wind passing
over the blades and it converts into mechanical
torque. The job of the generating system is to convert
the mechanical torque into electricity.
1) Mathematical model of Wind Turbine
Under constant acceleration, the kinetic energy of
an object of mass ‘m’ and velocity ‘v’ is equal to the
work done W in displacing the object from the rest to
a distance „s‟ under force F, i.e.,
E=W=Fs (6)
Therefore the kinetic energy of an object of mass
‘m’ with velocity „v‟ is
E =
1
2
𝑚𝑣2
(7)
The power from the wind is given by the rate of
change of energy
P=
𝑑𝐸
𝑑𝑡
=
1
2
𝑣2 𝑑𝑚
𝑑𝑡
(8)
As mass flow rate is given by
𝑑𝑚
𝑑𝑡
= 𝜌𝐴
𝑑𝑋
𝑑𝑡
And the rate of change of distance is given by
𝑑𝑋
𝑑𝑡
= 𝑣
We get
𝑑𝑚
𝑑𝑡
= 𝜌𝐴𝑣
Hence from the equation (4), the power can be
defined as
P =
1
2
𝜌𝐴𝑣3
(9)
The swept area of the turbine can be estimated
from the length of the turbine blades using the
equation for the area of a circle.
𝐴 = 𝜋𝑟2
(10)
Where „r‟ is the radius and is identical to the
blade length. The mechanical power available from
the wind turbine is expressed as
𝑃𝑇𝑢𝑟𝑏𝑖𝑛𝑒 =
1
2
𝜌𝐴𝐶𝑝(𝝀, 𝛽)𝑣3
(11)
Where 𝜌 is the air density (typically 1.225
kg/𝑚3
), A is the area swept by the rotor blades, 𝐶𝑝 is
the coefficient of power conversion and 𝑣 is the
wind speed(in m/s). The tip speed ratio λ is given by
λ =
𝝎 𝒎 𝑹
𝑣
(12)
Where 𝜔 𝑚 and R are the rotor angular velocity
(in rad/sec) and rotor radius (in m) respectively. The
wind turbine mechanical output torque is given by
𝑇 𝑚 =
1
2
𝜌𝐴𝐶𝑝(𝝀, 𝛽)𝑣3 1
𝜔 𝑚
(13)
If the swept area of the blade and air density are
constant, the value of 𝐶𝑝 is a function of λ and it is
maximum at the particular𝜆 𝑜𝑝𝑡 . Then
𝑃𝑇𝑢𝑟𝑏𝑖𝑛𝑒 =
1
2
𝜌𝐴𝐶𝑝𝑚𝑎𝑥 𝑣3
(14)
The mechanical torque obtained from the wind
turbine is fed to the permanent synchronous
generator, the AC power is converted to DC and it
acts as auxiliary supply voltage to the shunt active
filter [20]
C. Shunt Active Filter
The Shunt Active Filter comprises of Voltage
source inverter (VSI) fed through a DC capacitor to
mitigate the harmonics. The chore of the shunt active
filter is to compensate the load current harmonics by
injecting the equal and opposite compensating
current which are phase-shifted by 1800
.The shunt
active power filter with ANN controller is
contemplated to act as a current source by injecting
the equal and opposite harmonic components that are
generated by the load.
1) Extraction of Reference Compensation
Currents
The shunt active filter need to estimate the
reference current for each phase of the non linear
load, and the voltage of the DC bus must be
maintained constant and relevant gating signals has to
be generated by the control circuit in accordance
with the error signal that is being generated. The
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ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54
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suppression of the harmonics can be implemented in
time domain or frequency domain. In the present
proposed scheme, P-Q theory has been implemented.
The three-phase voltages and currents in abc co-
ordinates are altered to αβo co-ordinates (15) & (16),
followed by the computation of instantaneous power
components.
𝑉𝑜
𝑉𝛼
𝑉𝛽
= √
2
3
1
√2
1
√2
1
√2
1 −1
2
−1
2
0 √3
2
−√3
2
𝑉𝑎
𝑉𝑏
𝑉𝑐
(15)
𝑖 𝑜
𝑖 𝛼
𝑖 𝛽
= √
2
3
1
√2
1
√2
1
√2
1 −1
2
−1
2
0 √3
2
−√3
2
𝑖 𝑎
𝑖 𝑏
𝑖𝑐
(16)
𝑝
𝑞 = _
𝑉𝛼 𝑉𝛽
𝑉𝛽 𝑉𝛼
𝑖 𝛼
𝑖 𝛽
(17)
p= 𝑉𝛼 𝑖 𝛼 + 𝑉𝛽 𝑖 𝛽 Instantaneous Real power
q=𝑉𝛼 𝑖 𝛽 − 𝑉𝛽 𝑖 𝛼 Instantaneous Imaginary power
To grab the reference compensation current in
𝛼 − 𝛽 co-ordinates, invert the expression (17),
𝑖 𝑐𝛼
∗
𝑖 𝑐𝛽
∗ =
1
𝑉𝛼
2 + 𝑉𝛽
2
𝑉𝛼 −𝑉𝛽
𝑉𝛽 𝑉𝛼
𝑝𝑥
𝑞 𝑥
(18)
The reference compensation current in 𝑜 co-
ordinate is considered to be 𝑖0 itself, as the zero
sequence current must be compensated and is given
by (19)
𝑖 𝑐𝑜
∗
= 𝑖 𝑜 (19)
An inverse transformation has been applied to the
equation (16) to procure the reference compensation
currents in abc co-ordinates
𝑖 𝑐𝑎
∗
𝑖 𝑐𝑏
∗
𝑖 𝑐𝑐
∗
= √
2
3
1
√2
1 0
1
√2
−1
2
√3
2
1
√2
−1
2
√3
2
𝑖 𝑐𝑜
∗
𝑖 𝑐𝛼
∗
𝑖 𝑐𝛽
∗
(20)
The reference neutral current is delineated by
𝑖 𝑐𝑛
∗
= - (𝑖 𝑐𝑎
∗
+ 𝑖 𝑐𝑏
∗
+𝑖 𝑐𝑐
∗
) (21)
A fictitious two-phase system is elaborated using
a single phase system resulting in π/2 lag or π/2 lead
and the resultant two phase system can be
asseverated in 𝛼 − 𝛽 co-ordinates. The 𝛼 axis and 𝛽
axis quantities are considered to be the original load
voltages and load currents respectively. Whereas the
π/2 lead load or π/2 lag voltages are treated as 𝛼 axis
quantities and π/2 lead or π/2 lag load currents are
treated as 𝛽 axis quantities. The π/2 lead is
considered in the proffered work to achieve a two
phase system for each phase and it is expressed in
(22), (23).
The load voltage and current in α-β coordinates
for the phase „a‟, can be represented by π/2 lead as,
𝑣 𝐿𝑎_𝛼
𝑣 𝐿𝑎_𝛽
=
𝑣 𝐿𝑎
∗
(𝜔𝑡)
𝑣 𝐿𝑎
∗
(𝜔𝑡 +
𝜋
2
)
=
𝑣 𝐿𝑚 sin(𝜔𝑡)
𝑣 𝐿𝑚 cos(𝜔𝑡)
(22)
𝑖 𝐿𝑎_𝛼
𝑖 𝐿𝑎_𝛽
=
𝑖 𝐿𝑎 (𝜔𝑡 + 𝜑𝐿)
𝑖 𝐿𝑎 [ 𝜔𝑡 + 𝜑𝐿 +
𝜋
2
(23)
Where,
𝑣 𝐿𝑎
∗
= the reference load voltage
𝑣 𝐿𝑚 =magnitude of the desired load voltage.
Likewise for phase „b‟ and „c‟, the load voltage
and current in 𝛼 − 𝛽 coordinates are represented
respectively by π
2 lead as,
𝑣 𝐿𝑏_𝛼
𝑣 𝐿𝑏_𝛽
=
𝑣 𝐿𝑏
∗
(𝜔𝑡)
𝑣 𝐿𝑏
∗
(𝜔𝑡 +
𝜋
2
)
=
𝑣 𝐿𝑚 sin(𝜔𝑡 − 120°)
𝑣 𝐿𝑚 cos(𝜔𝑡 − 120°)
𝑖 𝐿𝑏_𝛼
𝑖 𝐿𝑏_𝛽
=
𝑖 𝐿𝑏 (𝜔𝑡 + 𝜑𝐿)
𝑖 𝐿𝑏 [ 𝜔𝑡 + 𝜑𝐿 +
𝜋
2
(25)
𝑣 𝐿𝑐_𝛼
𝑣 𝐿𝑐_𝛽
=
𝑣 𝐿𝑐
∗
(𝜔𝑡)
𝑣 𝐿𝑐
∗
(𝜔𝑡 +
𝜋
2
)
=
𝑣 𝐿𝑚 sin(𝜔𝑡 + 120°)
𝑣 𝐿𝑚 cos(𝜔𝑡 + 120°)
𝑖 𝐿𝑐_𝛼
𝑖 𝐿𝑐_𝛽
=
𝑖 𝐿𝑐 (𝜔𝑡 + 𝜑𝐿)
𝑖 𝐿𝑐 [ 𝜔𝑡 + 𝜑𝐿 +
𝜋
2
(27)
Instantaneous active power and reactive power can
be characterized by equation (28) and (29),
𝑝𝐿,𝑎𝑏𝑐 =𝑣 𝐿,𝑎𝑏𝑐 _𝛼 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛼 + 𝑣 𝐿,𝑎𝑏𝑐 _𝛽 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛽 (28)
𝑞 𝐿,𝑎𝑏𝑐 =𝑣 𝐿,𝑎𝑏𝑐 _𝛼 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛽 − 𝑣 𝐿,𝑎𝑏𝑐 _𝛽 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛼 (29)
In consideration of the phase „a‟, the instantaneous
load active and instantaneous load reactive powers
can be represented by,
𝑝𝐿𝑎
𝑞 𝐿𝑎
= _
𝑉𝐿𝑎_𝛼 𝑉𝐿𝑏_𝛽
𝑉𝐿𝑏_𝛽 𝑉𝐿𝑎_𝛼
𝑖 𝐿𝑎_𝛼
𝑖 𝐿𝑎_𝛽
(30)
Where,
𝑃𝐿𝑎 =𝑃𝐿𝑎 +𝑃𝐿𝑎 (31)
𝑞 𝐿𝑎 =𝑞 𝐿𝑎 +𝑞 𝐿𝑎 (32)
In (31) and (32), 𝑃𝐿𝑎 and 𝑞 𝐿𝑎 delineate the dc
components. Whereas 𝑃𝐿𝑎 and 𝑞 𝐿𝑎 delineate the ac
components. The phase fundamental instantaneous
load active and reactive power components are
derived from 𝑝𝐿𝑎 and 𝑞 𝐿𝑎 respectively by employing
a low pass filter.
In consequence, the instantaneous fundamental
load active and reactive power for phase-a are
portrayed by the equation (33), (34)
𝑃𝐿𝑎,1=𝑃𝐿𝑎 (33)
𝑞 𝐿𝑎,1=𝑞 𝐿𝑎 (34)
In the same way, the fundamental instantaneous
load active power and reactive powers for phases-b
and c can be enumerated as in the equations (35)-(38)
𝑃𝐿𝑏,1=𝑃𝐿𝑏 (35)
𝑞 𝐿𝑏,1=𝑞 𝐿𝑏 (36)
𝑃𝐿𝑐,1=𝑃𝐿𝑐 (37)
𝑞 𝐿𝑐,1=𝑞 𝐿𝑐 (38)
Total power is given by equation (39) as follows
𝑃𝐿,𝑇𝑜𝑡𝑎𝑙 =𝑃𝐿𝑎,1+𝑃𝐿𝑏,1 +𝑃𝐿𝑐,1 (39)
𝑃𝑠
𝑝ℎ
∗
= (𝑃𝐿,𝑇𝑜𝑡𝑎𝑙 )/3 (40)
Equation (40) signifies the distributed per phase
fundamental active power demand. In order to
achieve a perfectly balanced source currents, each
phase of utility should supply that much amount of
distributed per phase fundamental active power
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ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54
www.ijera.com 52 | P a g e
demand. The reference compensating currents can be
represented in a perfectly balanced three-phase
system by taking the inverse of equation (30).
𝑖∗
𝑆𝑎_𝛼
𝑖∗
𝑆𝑎_𝛽
= _
𝑉𝐿𝑎_𝛼 𝑉𝐿𝑎_𝛽
𝑉𝐿𝑎_𝛽 𝑉𝐿𝑎_𝛼
−1
.
𝑃𝑠
𝑝ℎ
∗
+ 𝑃𝑑𝑐/𝑝ℎ
0
(41)
In equation (41), 𝑃𝑑𝑐 /𝑝ℎ implies the explicit
amount of per-phase active power need to be taken
from the source so as to maintain a constant level of
dc-link voltage and also to overcome the losses
linked with SAF.
Therefore, Equation (42), (43) & (44) represent the
reference source currents for phase a, phase b and
phase c, respectively.
𝑖 𝑆𝑎
∗
(t)={𝑣 𝐿𝑎_𝛼(t)/(𝑣 𝐿𝑎_𝛼
2
𝑣 𝐿𝑎_𝛽
2
)}.{𝑃𝑠 𝑝ℎ
∗
(t)+ 𝑃𝑑𝑐 𝑝ℎ
∗
(t)}
(42)
𝑖 𝑆𝑏
∗
(t)={𝑣 𝐿𝑏_𝛼 (t)/(𝑣 𝐿𝑏_𝛼
2
+
𝑣 𝐿𝑏_𝛽
2
)}.{𝑃𝑠 𝑝ℎ
∗
(t)+ 𝑃𝑑𝑐 𝑝ℎ
∗
(t)} (43)
𝑖 𝑆𝑐
∗
(t)={𝑣 𝐿𝑐_𝛼(t)/(𝑣 𝐿𝑐_𝛼
2
+
𝑣 𝐿𝑐_𝛽
2
)}.{𝑃𝑠 𝑝ℎ
∗
(t)+ 𝑃𝑑𝑐 𝑝ℎ
∗
(t)} (44)
By simply adding the entire sensed load currents as
in (45), the reference neutral current signal can be
extracted.
𝑖 𝐿_𝑛 (t) = 𝑖 𝐿𝑎 (t) + 𝑖 𝐿𝑏 (t) + 𝑖 𝐿𝑐(t) (45)
The proffered model computes the balanced
per phase fundamental active power ,the dc link
voltage control Stationed on Fast acting DC link
voltage controller and the reference neutral current
extraction as shown in the below Figure(2)
respectively.
Fig .3 (a) Calculation of Per phase Fundamental
Active Power (b) DC link voltage control loop (c)
The Generation of Reference source current (d)
Neutral Current Compensation.
III. SIMULINK RESULTS
The Performance of shunt active filter interfaced
with a hybrid micro grid system is simulated and
modeled using MATLAB/SIMULINK and
SimPower System Block set is crafted. Figure 4(a)
and 4(b) represents the phase to neutral voltage and
grid current of the phase „a‟, grid current
compensated with integrated DG units respectively.
Fig.4 (a) The Phase to neutral voltage and grid
current for the phase ‘a’
Fig.4 (b) Grid Current Compensated with
integrated DG units
The Steady state operation of the contemplated
micro grid link for the injection of the maximum
available power to the grid continuously is traced
graphically in the figure 4(c).
The Grid voltage and current compensated
with DG system and the grid voltage after interfacing
with shunt active filter are delineated pictorially in
the figure 4(d) i & ii, figure 4(e) respectively.
Fig.4(c) Steady-state operation of the proposed
micro grid system link
Fig.4(d) i Grid Voltage compensated with DG
system
Fig.4(d) ii Grid current compensated with DG
System
A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54
www.ijera.com 53 | P a g e
Fig.4(e) Grid Voltage with SAF
The load current waveform with for different loads
and the Injection Current waveform of by Shunt
active filter are shown in the figure 4(f) and figure
4(g) respectively.
Fig.4(f) Load current variations with changed
load
Fig.4(g) Injection Current of SAF
The difference in the load voltage before doing the
compensation and after doing the compensation and
the compensated voltage and distorted current are
portrayed graphically in the figure 4(h) and figure
4(i) respectively.
The output power obtained from the PV panel and
the wind turbine generating system are shown in the
figure 4(j) and the figure 4(k) respectively.
Fig.4(h) Load Voltage with and without
Compensation
Fig.4 (i) Compensated voltage and distorted
current
Fig.4 (j) PV Power
Fig.4(k) Wind power
The voltage and current variations of the wind
turbine generating system are presented in the figure
4(l) and the figure 4(m) correspondingly.
Fig.4(l) Wind Voltage Variations
Fig.4(m) Wind Current Variations
IV. CONCLUSION
A multi objective control algorithm has been
proposed and presented in this Paper for the grid-
connected converter-based DG interface.
Adaptability of the proposed hybrid micro grid in
both transient state and steady state operations has
been verified through simulation results. Another
benefit from the proffered control method is that the
control loops are considered to be independent of
active and reactive power and it portrays fast
dynamic response in tracking reactive power
variations. In this, the models are developed for all
the converters to maintain stable system under
various loads, resource conditions and also the
control mechanism are studied. The Micro Grid can
provide a reliable, high quality and more efficient
power to the consumer. After simulating the
developed model in the SIMULINK, the results
unfold that in all the conditions, the load voltage and
source current are in phase and therefore the
integrated DG systems can act as power factor
corrector devices by improving the power factor at
A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54
www.ijera.com 54 | P a g e
PCC. The results revealed that the proposed hybrid
micro grid system can provide required harmonic
load currents in all situations. The proposed control
approach can be applied for numerous types of DG
resources as power quality enhancement devices in a
customer power Distribution network.
REFERENCES
[1.] M. F. Akorede, H. Hizam, and E.
Pouresmaeil, “Distributed energy resources
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[2.] Dr. H.P. Tiwari , Pradeep Anjana , Dr. Vikas
Gupta “Power Quality Improvement of
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(ICRAIE-2014), May 09-11,2014, Jaipur,
India.
[3.] BHATTACHARYA, S. CHENG, P., and
DIVAN, M.D.: 'Hybrid solutions for
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[4.] BHATTACHARYA, S., and DIVAN, D.:
'Design and implementation of a hybrid
series active filter system', ZEEE, June
1997,pp.189-195
[5.] Jinwei He and Yun Wei Li, Xiongfei Wang
and Frede Blaabjerg “An Improved Current
Control Scheme for Grid-Connected DG
Unit Based Distribution System Harmonic
Compensation” 978-1-4673-4355-
8/13/$31.00 ©2013 IEEE.
[6.] Ersoy KELEBEKLER, Ali Bekir YILDIZ
“Analysis of Passive and Active Filters
Using Modified Nodal Approach” 1-4244-
1055-X/07/$25.00 ©2007 IEEE.
[7.] G. Casaravilla, A. Salvia, C. Briozzo and E.
Watanabe, “Control strategies of selective
harmonic current shunt active filter” IEE
Proc.-Gener. Trunsm. Distrib., Vol. 149, No.
2, December 2002.
[8.] Sushil Karvekar, Aditi Kumbhojkar,
“Comparison of Different Methods of
Reference Current Generation for Shunt
Active Power Filter Under Balanced And
Unbalanced Load Conditions” 2013
International Conference on Circuits, Power
and Computing Technologies
[9.] Nitin Gupta, Student Member, IEEE, S. P.
Singh, Member, IEEE, and S. P. Dubey
“Neural Network Based Shunt Active Filter
for Harmonic and Reactive Power
Compensation under Non-ideal Mains
Voltage” 978-1-4244-5046-6/10/$26.00_c
2010 IEEE.
[10.] Riad Kadri, Jean-Paul Gaubert, and Gerard
Champenois, “An Improved Maximum
Power Point Tracking for Photovoltaic Grid-
Connected Inverter Based on Voltage-
Oriented Control”, IEEE transactions on
industrial electronics, vol. 58, no. 1, January
2011.
[11.] AKAGI, H.: 'Control strategy and site
selection of a shunt active filter for damping
of harmonic propagation in power
distribution systems', IEEE Truns. P o ~
Drel iu., 1997, 12, (l), ,pp. 354-362
[12.] Katiraei, F.; Iravani, M.R., “Power
Management Strategies for a Microgrid
With Multiple Distributed Generation
Units”, IEEE Transactions on Power
Systems, Vol. 21, Issue 4, Nov. 2006, pp.
1821– 1831.
[13.] H. Abaali, M. T. Lamchich, M. Raoufi, ”The
Three phase Shunt Active Filters for the
Harmonics Compensation Under Distorted
and Unbalanced Mains Voltages
Conditions”, IEEE International Conference
on Industrial Technology (ICIT), 2004.
[14.] M. Cirrincione, M. Pucci, G. Vitale, and A.
Miraoui, “Current harmonic compensation
by a single-phase shunt active power filter
controlled by adaptive neural filtering,”
IEEE Trans. Ind. Electron.,vol. 56, no. 8, pp.
3128-3143, Aug. 2009.
[15.] L. P. Kunjumuhammed and M. K. Mishra,
“Comparison of single phase shunt active
power filter algorithms,” in Proc. IEEE
Power India Conf., 2006, pp. 8–15.
[16.] B. Yang, W. Li, Y. Zhao, and X. He,
“Design and analysis of a gridconnected
photovoltaic power system,” IEEE Trans.
Power Electron.,vol. 25, no. 4, pp. 992–
1000, Apr. 2010.
[17.] B. Sahan, A. N. Vergara, N. Henze, A.
Engler, and P. Zacharias, “A singlestage PV
module integrated converter based on a low-
power currentsource inverter,” IEEE Trans.
Ind. Electron., vol. 55, no. 7, pp. 2602–
2609,Jul. 2008.
[18.] N. Femia, G. Petrone, G. Spagnuolo, and M.
Vitelli, “Perturb and observe MPPT
technique robustness improved,” in Proc.
IEEE Int. Symp. Ind.Electron., 2004, vol. 2,
pp. 845–850.
[19.] Shota Yamakura , Katsumi Kesamaru,
“Dynamic Simulation of PMSG Small Wind
Turbine Generation Systemwith HCS-MPPT
Control.
[20.] CHEDID R, MRAD F, BASMAM.
Intelligent control for wind energy
conversion systems.WindEng, 1998.

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A Technique for Shunt Active Filter meld micro grid System

  • 1. A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54 www.ijera.com 48 | P a g e A Technique for Shunt Active Filter meld micro grid System A. Lumani*, G. Srikanth** *(PG Scholar, GIT) ** (PG Scholar, GIT) ABSTRACT The proposed system presents a control technique for a micro grid connected hybrid generation system ith case study interfaced with a three phase shunt active filter to suppress the current harmonics and reactive power present in the load using PQ Theory with ANN controller. This Hybrid Micro Grid is developed using freely renewable energy resources like Solar Photovoltaic (SPV) and Wind Energy (WE). To extract the maximum available power from PV panels and wind turbines, Maximum power point Tracker (MPPT) has been included. This MPPT uses the “Standard Perturbs and Observe” technique. By using PQ Theory with ANN Controller, the Reference currents are generated which are to be injected by Shunt active power filter (SAPF)to compensate the current harmonics in the non linear load. Simulation studies shows that the proposed control technique performs non-linear load current harmonic compensation maintaining the load current in phase with the source voltage. Keywords - Active filter, ANN controller, Distributed Energy resources, Harmonic distortion, Micro grid, Maximum power point tracker, Photovoltaic, PQ Theory, Wind Energy I. INTRODUCTION Due to an extensive increase in energy demand, and the distinct advantages offered by the micro grid to customers as well as to the utilities such as lower environmental impact, greater reliability, reduced cost and higher efficiency keeping them as fundamental requirements, the present power scenario is sweeping towards the development of a hybrid micro grid as an alternative for the flexible extension of the actual energy distribution network [1]. The basis of the Micro grid conception is to congregate the loads and micro-sources operating as a single controllable system adjoined at a single point of common coupling (PCC) to furnish the power and heat for its local area [2]. Renewable energy sources like solar, wind, Biomass, hydro and Geo thermal power are equipped in a micro grid. Micro sources such as wind turbines and photovoltaic cells are well known for their discontinuity in power generation, the hybrid system which is proposed allows using an adaptive MPPT algorithm along with the method of standard perturbs and observes is to utilize ultimate accessible energy from the renewable energy resources [3]. Micro grid basically incorporates inverter- interfaced distributed energy resources (DER) such as PV arrays, wind turbines, fuel cells, micro turbines which are hooked to the distribution system making the power network weak and drawing non-sinusoidal current from the load yielding to harmonics and circulation of reactive power [4]. Basically the harmonics are materialized into two categories. • Short Term • Long Term Short-term harmonics are mainly associated with enormous voltage distortion and easily noticeable. On the flip side, long-term harmonics yield increased voltage stresses. This harmonic current can collaborate unfavorably with power system equipment like motors and transformers causing over loading, overheating and additional losses and can also create interference with the telecommunication system and may lead to erroneous operation in metering devices. Due to these detrimental effects Standards like IEEE 519-1992, IEC had developed to define a clear-cut framework to control the harmonics. These harmonic distortions of power distribution systems can be compensated using two fashions namely, passive and active filtering [5]-[7]. The passive filtering approach is the least expensive and provides an elementary ordinary solution to suppress the harmonic deformity. But it inherits of several shortcomings such as the components are Bulky in size, dependence on the source impedance, the creation of the resonance problem and there by perturbing the stability of the power distribution system [8]. Therefore, the active power filter appears to be a feasible solution for the compensation of reactive power besides wiping out the harmonic currents. The main focus in designing and controlling of APF is the estimation of compensation current and generation of reference signal. Various schemes such as Fast Fourier Transform (FFT), Kalman filter and artificial neural networks (ANN) which are developed by so many authors are studied for the control of active filters [9]. However, Kalman filter approach is unfit for on-line applications such as active power filtering Even the Fast Fourier RESEARCH ARTICLE OPEN ACCESS
  • 2. A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54 www.ijera.com 49 | P a g e Transform (FFT) technique gives inaccurate results, if the signal has any DC component of decaying type [10]. The ANNs are trained to compute the required harmonic currents depending upon the back propagation rule. This technique leads to imprecise results in the existence of random noise and it requires huge data for training of ANNs [11]. Most of the above-said control techniques are troublesome and complex to employ under non-ideal conditions. In this paper, Maximum Power point tracking (MPPT) controller using standard Perturbs and observe approach [12] is used for both the Photovoltaic (PV) array and the permanent magnet synchronous generator (PMSG) wind turbine generation system. The instantaneous active and reactive power theory (PQ theory) strategy has been implemented for the estimation of reference currents. The stationary reference frame (abc) variables are transformed into the Synchronous orthogonal reference frame (αβ0) in the prospective approach. This analysis was primitively particularized for three- phase systems by Akagi in 1983 [13], and later it was extended by various researchers [14]-[17]. In this contemplated theory, the three phase system can be represented as a single phase system by altering the load current and grid voltage by 90°, thus facilitating the single phase system to be represented as a fictitious two-phase system. The proposed PQ theory with the ANN controller yields a ripple free DC voltage across the capacitor compared with the shunt active filter with PI controller .When compared to the other frequency-domain techniques, this approach has an outstanding compelling response and it requires lesser computational strain II. Over view of the Proposed System In the proposed system, a Hybrid micro grid equipped by Solar and wind energy is interfaced with a Shunt active filter using the PQ theory for the generation of reference currents with ANN controller is developed. Maximum power point tracker (MPPT) controller using standard Perturbs and observe approach is used to get hold of the maximum accessible power from the distributed energy resources (DER‟S) like Photovoltaic (PV) array and permanent magnet synchronous generator (PMSG) wind turbine generation system. By Considering all attributes for power generation from DES are considered and Concluded Solar PV, Wind Energy and Fuel Cell have good potential So among them Solar and Wind are considered. Fig.1 Overview of the proposed system A. PV ARRAY The PV cell can be epitomized by an electrical equivalent circuit in which the current source is placed in parallel with the diode as depicted in the figure 2. The solar cell acts like a diode during the darkness and therefore it neither produces a current nor a voltage. Thus, the diode evaluates the I-V characteristics of the cell [18]. The internal resistance to the current flow is indicated by the series resistance 𝑅 𝑆, and it counts on the impurities, PN junction depth and contact resistance. The shunt resistance 𝑅 𝑆ℎ and the leakage current to ground inversely associated to each other. A slight increase in 𝑅 𝑆 can diminish the PV output greatly. The PV conversion efficiency is most receptive to the small variations in 𝑅 𝑠, but it is impassive to the variations in 𝑅 𝑆ℎ . Fig.2.Equivalent circuit of PV Cell The output current I and the output voltage V of a solar cell [19] are provided by (1), (2) as follows I = 𝐼𝑝ℎ - 𝐼0(exp ( 𝑞 𝑛.𝑘.𝑇 𝑉)-1 (1) V=𝑉𝑑0-𝑅 𝑠I (2) Here, 𝐼𝑝ℎ is the photocurrent, 𝐼0 is the reverse saturation current, 𝐼𝑑𝑜 is the average current through the diode, n indicates the diode factor, q is the electron charge (q = 1.6∗ 10−19 ), k is the Boltzmann‟s constant (k = 1.38∗ 10−23 ), and T is the solar array panel temperature. Rs indicate the intrinsic series resistance of the solar cell. Rsh is the equivalent
  • 3. A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54 www.ijera.com 50 | P a g e shunt resistance of the solar cell, and its value is very large. If the circuit is opened, then the current I=0, and the open circuit voltage 𝑉𝑜𝑐 is symbolized by (3) as follows 𝑉𝑂𝐶= ( 𝑛.𝑘.𝑡 𝑞 ) In ( 𝐼 𝑝ℎ 𝐼 𝑜 +1) ≈ ( 𝑛.𝑘.𝑡 𝑞 ) In ( 𝐼 𝑝ℎ 𝐼 𝑂 ) (3) If the circuit is short circuited, the output voltage V=0, the average current through the diode is generally ignored, and the short circuit current 𝐼𝑠𝑐 is expressed by (4) 𝐼𝑠𝑐 = I = 𝐼 𝑝ℎ 1+ 𝑅 𝑠 𝑅 𝑠ℎ (4) Lastly, the PV output power P, is asserted by P = VI = (𝐼𝑝ℎ -𝐼𝑑𝑜 - 𝑉 𝑑0 𝑅 𝑠ℎ ) (5) 1) Perturb and Observe (P&O) Perturb and observe algorithm has been used to elicit the ultimate accessible power from the solar panel. To achieve this, a slight perturbation is introduced in the system. The perturbation is preceded in the incremental direction, if the power increases because of the introduced perturbation [20]. And if the power is reached to the peak value then at the next off the power decreases and the perturbation direction will be reversed. After reaching the steady state, the algorithm pivots around the peak point. The perturbation size is stored up to a small value to keep the power variation in a small range. The module reference voltage is set by referring to the peak voltage of the PV module with the help of controller and thus it acts by sliding the point of the module to that particular voltage level. B. Wind Turbine In this paper the modeling of the wind turbine driven by PMSG is described. The three bladed rotor is the most important and visible part of the wind turbine. The working principle of the wind turbine can be described in two processes that are accomplished by its vital components: the rotor extracts the kinetic energy from the wind passing over the blades and it converts into mechanical torque. The job of the generating system is to convert the mechanical torque into electricity. 1) Mathematical model of Wind Turbine Under constant acceleration, the kinetic energy of an object of mass ‘m’ and velocity ‘v’ is equal to the work done W in displacing the object from the rest to a distance „s‟ under force F, i.e., E=W=Fs (6) Therefore the kinetic energy of an object of mass ‘m’ with velocity „v‟ is E = 1 2 𝑚𝑣2 (7) The power from the wind is given by the rate of change of energy P= 𝑑𝐸 𝑑𝑡 = 1 2 𝑣2 𝑑𝑚 𝑑𝑡 (8) As mass flow rate is given by 𝑑𝑚 𝑑𝑡 = 𝜌𝐴 𝑑𝑋 𝑑𝑡 And the rate of change of distance is given by 𝑑𝑋 𝑑𝑡 = 𝑣 We get 𝑑𝑚 𝑑𝑡 = 𝜌𝐴𝑣 Hence from the equation (4), the power can be defined as P = 1 2 𝜌𝐴𝑣3 (9) The swept area of the turbine can be estimated from the length of the turbine blades using the equation for the area of a circle. 𝐴 = 𝜋𝑟2 (10) Where „r‟ is the radius and is identical to the blade length. The mechanical power available from the wind turbine is expressed as 𝑃𝑇𝑢𝑟𝑏𝑖𝑛𝑒 = 1 2 𝜌𝐴𝐶𝑝(𝝀, 𝛽)𝑣3 (11) Where 𝜌 is the air density (typically 1.225 kg/𝑚3 ), A is the area swept by the rotor blades, 𝐶𝑝 is the coefficient of power conversion and 𝑣 is the wind speed(in m/s). The tip speed ratio λ is given by λ = 𝝎 𝒎 𝑹 𝑣 (12) Where 𝜔 𝑚 and R are the rotor angular velocity (in rad/sec) and rotor radius (in m) respectively. The wind turbine mechanical output torque is given by 𝑇 𝑚 = 1 2 𝜌𝐴𝐶𝑝(𝝀, 𝛽)𝑣3 1 𝜔 𝑚 (13) If the swept area of the blade and air density are constant, the value of 𝐶𝑝 is a function of λ and it is maximum at the particular𝜆 𝑜𝑝𝑡 . Then 𝑃𝑇𝑢𝑟𝑏𝑖𝑛𝑒 = 1 2 𝜌𝐴𝐶𝑝𝑚𝑎𝑥 𝑣3 (14) The mechanical torque obtained from the wind turbine is fed to the permanent synchronous generator, the AC power is converted to DC and it acts as auxiliary supply voltage to the shunt active filter [20] C. Shunt Active Filter The Shunt Active Filter comprises of Voltage source inverter (VSI) fed through a DC capacitor to mitigate the harmonics. The chore of the shunt active filter is to compensate the load current harmonics by injecting the equal and opposite compensating current which are phase-shifted by 1800 .The shunt active power filter with ANN controller is contemplated to act as a current source by injecting the equal and opposite harmonic components that are generated by the load. 1) Extraction of Reference Compensation Currents The shunt active filter need to estimate the reference current for each phase of the non linear load, and the voltage of the DC bus must be maintained constant and relevant gating signals has to be generated by the control circuit in accordance with the error signal that is being generated. The
  • 4. A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54 www.ijera.com 51 | P a g e suppression of the harmonics can be implemented in time domain or frequency domain. In the present proposed scheme, P-Q theory has been implemented. The three-phase voltages and currents in abc co- ordinates are altered to αβo co-ordinates (15) & (16), followed by the computation of instantaneous power components. 𝑉𝑜 𝑉𝛼 𝑉𝛽 = √ 2 3 1 √2 1 √2 1 √2 1 −1 2 −1 2 0 √3 2 −√3 2 𝑉𝑎 𝑉𝑏 𝑉𝑐 (15) 𝑖 𝑜 𝑖 𝛼 𝑖 𝛽 = √ 2 3 1 √2 1 √2 1 √2 1 −1 2 −1 2 0 √3 2 −√3 2 𝑖 𝑎 𝑖 𝑏 𝑖𝑐 (16) 𝑝 𝑞 = _ 𝑉𝛼 𝑉𝛽 𝑉𝛽 𝑉𝛼 𝑖 𝛼 𝑖 𝛽 (17) p= 𝑉𝛼 𝑖 𝛼 + 𝑉𝛽 𝑖 𝛽 Instantaneous Real power q=𝑉𝛼 𝑖 𝛽 − 𝑉𝛽 𝑖 𝛼 Instantaneous Imaginary power To grab the reference compensation current in 𝛼 − 𝛽 co-ordinates, invert the expression (17), 𝑖 𝑐𝛼 ∗ 𝑖 𝑐𝛽 ∗ = 1 𝑉𝛼 2 + 𝑉𝛽 2 𝑉𝛼 −𝑉𝛽 𝑉𝛽 𝑉𝛼 𝑝𝑥 𝑞 𝑥 (18) The reference compensation current in 𝑜 co- ordinate is considered to be 𝑖0 itself, as the zero sequence current must be compensated and is given by (19) 𝑖 𝑐𝑜 ∗ = 𝑖 𝑜 (19) An inverse transformation has been applied to the equation (16) to procure the reference compensation currents in abc co-ordinates 𝑖 𝑐𝑎 ∗ 𝑖 𝑐𝑏 ∗ 𝑖 𝑐𝑐 ∗ = √ 2 3 1 √2 1 0 1 √2 −1 2 √3 2 1 √2 −1 2 √3 2 𝑖 𝑐𝑜 ∗ 𝑖 𝑐𝛼 ∗ 𝑖 𝑐𝛽 ∗ (20) The reference neutral current is delineated by 𝑖 𝑐𝑛 ∗ = - (𝑖 𝑐𝑎 ∗ + 𝑖 𝑐𝑏 ∗ +𝑖 𝑐𝑐 ∗ ) (21) A fictitious two-phase system is elaborated using a single phase system resulting in π/2 lag or π/2 lead and the resultant two phase system can be asseverated in 𝛼 − 𝛽 co-ordinates. The 𝛼 axis and 𝛽 axis quantities are considered to be the original load voltages and load currents respectively. Whereas the π/2 lead load or π/2 lag voltages are treated as 𝛼 axis quantities and π/2 lead or π/2 lag load currents are treated as 𝛽 axis quantities. The π/2 lead is considered in the proffered work to achieve a two phase system for each phase and it is expressed in (22), (23). The load voltage and current in α-β coordinates for the phase „a‟, can be represented by π/2 lead as, 𝑣 𝐿𝑎_𝛼 𝑣 𝐿𝑎_𝛽 = 𝑣 𝐿𝑎 ∗ (𝜔𝑡) 𝑣 𝐿𝑎 ∗ (𝜔𝑡 + 𝜋 2 ) = 𝑣 𝐿𝑚 sin(𝜔𝑡) 𝑣 𝐿𝑚 cos(𝜔𝑡) (22) 𝑖 𝐿𝑎_𝛼 𝑖 𝐿𝑎_𝛽 = 𝑖 𝐿𝑎 (𝜔𝑡 + 𝜑𝐿) 𝑖 𝐿𝑎 [ 𝜔𝑡 + 𝜑𝐿 + 𝜋 2 (23) Where, 𝑣 𝐿𝑎 ∗ = the reference load voltage 𝑣 𝐿𝑚 =magnitude of the desired load voltage. Likewise for phase „b‟ and „c‟, the load voltage and current in 𝛼 − 𝛽 coordinates are represented respectively by π 2 lead as, 𝑣 𝐿𝑏_𝛼 𝑣 𝐿𝑏_𝛽 = 𝑣 𝐿𝑏 ∗ (𝜔𝑡) 𝑣 𝐿𝑏 ∗ (𝜔𝑡 + 𝜋 2 ) = 𝑣 𝐿𝑚 sin(𝜔𝑡 − 120°) 𝑣 𝐿𝑚 cos(𝜔𝑡 − 120°) 𝑖 𝐿𝑏_𝛼 𝑖 𝐿𝑏_𝛽 = 𝑖 𝐿𝑏 (𝜔𝑡 + 𝜑𝐿) 𝑖 𝐿𝑏 [ 𝜔𝑡 + 𝜑𝐿 + 𝜋 2 (25) 𝑣 𝐿𝑐_𝛼 𝑣 𝐿𝑐_𝛽 = 𝑣 𝐿𝑐 ∗ (𝜔𝑡) 𝑣 𝐿𝑐 ∗ (𝜔𝑡 + 𝜋 2 ) = 𝑣 𝐿𝑚 sin(𝜔𝑡 + 120°) 𝑣 𝐿𝑚 cos(𝜔𝑡 + 120°) 𝑖 𝐿𝑐_𝛼 𝑖 𝐿𝑐_𝛽 = 𝑖 𝐿𝑐 (𝜔𝑡 + 𝜑𝐿) 𝑖 𝐿𝑐 [ 𝜔𝑡 + 𝜑𝐿 + 𝜋 2 (27) Instantaneous active power and reactive power can be characterized by equation (28) and (29), 𝑝𝐿,𝑎𝑏𝑐 =𝑣 𝐿,𝑎𝑏𝑐 _𝛼 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛼 + 𝑣 𝐿,𝑎𝑏𝑐 _𝛽 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛽 (28) 𝑞 𝐿,𝑎𝑏𝑐 =𝑣 𝐿,𝑎𝑏𝑐 _𝛼 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛽 − 𝑣 𝐿,𝑎𝑏𝑐 _𝛽 . 𝑖 𝐿,𝑎𝑏𝑐 _𝛼 (29) In consideration of the phase „a‟, the instantaneous load active and instantaneous load reactive powers can be represented by, 𝑝𝐿𝑎 𝑞 𝐿𝑎 = _ 𝑉𝐿𝑎_𝛼 𝑉𝐿𝑏_𝛽 𝑉𝐿𝑏_𝛽 𝑉𝐿𝑎_𝛼 𝑖 𝐿𝑎_𝛼 𝑖 𝐿𝑎_𝛽 (30) Where, 𝑃𝐿𝑎 =𝑃𝐿𝑎 +𝑃𝐿𝑎 (31) 𝑞 𝐿𝑎 =𝑞 𝐿𝑎 +𝑞 𝐿𝑎 (32) In (31) and (32), 𝑃𝐿𝑎 and 𝑞 𝐿𝑎 delineate the dc components. Whereas 𝑃𝐿𝑎 and 𝑞 𝐿𝑎 delineate the ac components. The phase fundamental instantaneous load active and reactive power components are derived from 𝑝𝐿𝑎 and 𝑞 𝐿𝑎 respectively by employing a low pass filter. In consequence, the instantaneous fundamental load active and reactive power for phase-a are portrayed by the equation (33), (34) 𝑃𝐿𝑎,1=𝑃𝐿𝑎 (33) 𝑞 𝐿𝑎,1=𝑞 𝐿𝑎 (34) In the same way, the fundamental instantaneous load active power and reactive powers for phases-b and c can be enumerated as in the equations (35)-(38) 𝑃𝐿𝑏,1=𝑃𝐿𝑏 (35) 𝑞 𝐿𝑏,1=𝑞 𝐿𝑏 (36) 𝑃𝐿𝑐,1=𝑃𝐿𝑐 (37) 𝑞 𝐿𝑐,1=𝑞 𝐿𝑐 (38) Total power is given by equation (39) as follows 𝑃𝐿,𝑇𝑜𝑡𝑎𝑙 =𝑃𝐿𝑎,1+𝑃𝐿𝑏,1 +𝑃𝐿𝑐,1 (39) 𝑃𝑠 𝑝ℎ ∗ = (𝑃𝐿,𝑇𝑜𝑡𝑎𝑙 )/3 (40) Equation (40) signifies the distributed per phase fundamental active power demand. In order to achieve a perfectly balanced source currents, each phase of utility should supply that much amount of distributed per phase fundamental active power
  • 5. A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54 www.ijera.com 52 | P a g e demand. The reference compensating currents can be represented in a perfectly balanced three-phase system by taking the inverse of equation (30). 𝑖∗ 𝑆𝑎_𝛼 𝑖∗ 𝑆𝑎_𝛽 = _ 𝑉𝐿𝑎_𝛼 𝑉𝐿𝑎_𝛽 𝑉𝐿𝑎_𝛽 𝑉𝐿𝑎_𝛼 −1 . 𝑃𝑠 𝑝ℎ ∗ + 𝑃𝑑𝑐/𝑝ℎ 0 (41) In equation (41), 𝑃𝑑𝑐 /𝑝ℎ implies the explicit amount of per-phase active power need to be taken from the source so as to maintain a constant level of dc-link voltage and also to overcome the losses linked with SAF. Therefore, Equation (42), (43) & (44) represent the reference source currents for phase a, phase b and phase c, respectively. 𝑖 𝑆𝑎 ∗ (t)={𝑣 𝐿𝑎_𝛼(t)/(𝑣 𝐿𝑎_𝛼 2 𝑣 𝐿𝑎_𝛽 2 )}.{𝑃𝑠 𝑝ℎ ∗ (t)+ 𝑃𝑑𝑐 𝑝ℎ ∗ (t)} (42) 𝑖 𝑆𝑏 ∗ (t)={𝑣 𝐿𝑏_𝛼 (t)/(𝑣 𝐿𝑏_𝛼 2 + 𝑣 𝐿𝑏_𝛽 2 )}.{𝑃𝑠 𝑝ℎ ∗ (t)+ 𝑃𝑑𝑐 𝑝ℎ ∗ (t)} (43) 𝑖 𝑆𝑐 ∗ (t)={𝑣 𝐿𝑐_𝛼(t)/(𝑣 𝐿𝑐_𝛼 2 + 𝑣 𝐿𝑐_𝛽 2 )}.{𝑃𝑠 𝑝ℎ ∗ (t)+ 𝑃𝑑𝑐 𝑝ℎ ∗ (t)} (44) By simply adding the entire sensed load currents as in (45), the reference neutral current signal can be extracted. 𝑖 𝐿_𝑛 (t) = 𝑖 𝐿𝑎 (t) + 𝑖 𝐿𝑏 (t) + 𝑖 𝐿𝑐(t) (45) The proffered model computes the balanced per phase fundamental active power ,the dc link voltage control Stationed on Fast acting DC link voltage controller and the reference neutral current extraction as shown in the below Figure(2) respectively. Fig .3 (a) Calculation of Per phase Fundamental Active Power (b) DC link voltage control loop (c) The Generation of Reference source current (d) Neutral Current Compensation. III. SIMULINK RESULTS The Performance of shunt active filter interfaced with a hybrid micro grid system is simulated and modeled using MATLAB/SIMULINK and SimPower System Block set is crafted. Figure 4(a) and 4(b) represents the phase to neutral voltage and grid current of the phase „a‟, grid current compensated with integrated DG units respectively. Fig.4 (a) The Phase to neutral voltage and grid current for the phase ‘a’ Fig.4 (b) Grid Current Compensated with integrated DG units The Steady state operation of the contemplated micro grid link for the injection of the maximum available power to the grid continuously is traced graphically in the figure 4(c). The Grid voltage and current compensated with DG system and the grid voltage after interfacing with shunt active filter are delineated pictorially in the figure 4(d) i & ii, figure 4(e) respectively. Fig.4(c) Steady-state operation of the proposed micro grid system link Fig.4(d) i Grid Voltage compensated with DG system Fig.4(d) ii Grid current compensated with DG System
  • 6. A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54 www.ijera.com 53 | P a g e Fig.4(e) Grid Voltage with SAF The load current waveform with for different loads and the Injection Current waveform of by Shunt active filter are shown in the figure 4(f) and figure 4(g) respectively. Fig.4(f) Load current variations with changed load Fig.4(g) Injection Current of SAF The difference in the load voltage before doing the compensation and after doing the compensation and the compensated voltage and distorted current are portrayed graphically in the figure 4(h) and figure 4(i) respectively. The output power obtained from the PV panel and the wind turbine generating system are shown in the figure 4(j) and the figure 4(k) respectively. Fig.4(h) Load Voltage with and without Compensation Fig.4 (i) Compensated voltage and distorted current Fig.4 (j) PV Power Fig.4(k) Wind power The voltage and current variations of the wind turbine generating system are presented in the figure 4(l) and the figure 4(m) correspondingly. Fig.4(l) Wind Voltage Variations Fig.4(m) Wind Current Variations IV. CONCLUSION A multi objective control algorithm has been proposed and presented in this Paper for the grid- connected converter-based DG interface. Adaptability of the proposed hybrid micro grid in both transient state and steady state operations has been verified through simulation results. Another benefit from the proffered control method is that the control loops are considered to be independent of active and reactive power and it portrays fast dynamic response in tracking reactive power variations. In this, the models are developed for all the converters to maintain stable system under various loads, resource conditions and also the control mechanism are studied. The Micro Grid can provide a reliable, high quality and more efficient power to the consumer. After simulating the developed model in the SIMULINK, the results unfold that in all the conditions, the load voltage and source current are in phase and therefore the integrated DG systems can act as power factor corrector devices by improving the power factor at
  • 7. A. Lumani Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 5, Issue 8, (Part - 3) August 2015, pp.48-54 www.ijera.com 54 | P a g e PCC. The results revealed that the proposed hybrid micro grid system can provide required harmonic load currents in all situations. The proposed control approach can be applied for numerous types of DG resources as power quality enhancement devices in a customer power Distribution network. REFERENCES [1.] M. F. Akorede, H. Hizam, and E. Pouresmaeil, “Distributed energy resources and benefits to the environment,” Renewable Sustainable Energy Rev., vol. 14, no. 2, pp. 724–734, Feb. 2010. [2.] Dr. H.P. Tiwari , Pradeep Anjana , Dr. Vikas Gupta “Power Quality Improvement of Micro-Grid Using APF's With APC Theory” IEEE International Conference on Recent Advances and Innovations in Engineering (ICRAIE-2014), May 09-11,2014, Jaipur, India. [3.] BHATTACHARYA, S. CHENG, P., and DIVAN, M.D.: 'Hybrid solutions for improving passive filter performance in high power applications', IEEE Truns. Ina! Appl., 1997, 33, (3), pp. 732-747. [4.] BHATTACHARYA, S., and DIVAN, D.: 'Design and implementation of a hybrid series active filter system', ZEEE, June 1997,pp.189-195 [5.] Jinwei He and Yun Wei Li, Xiongfei Wang and Frede Blaabjerg “An Improved Current Control Scheme for Grid-Connected DG Unit Based Distribution System Harmonic Compensation” 978-1-4673-4355- 8/13/$31.00 ©2013 IEEE. [6.] Ersoy KELEBEKLER, Ali Bekir YILDIZ “Analysis of Passive and Active Filters Using Modified Nodal Approach” 1-4244- 1055-X/07/$25.00 ©2007 IEEE. [7.] G. Casaravilla, A. Salvia, C. Briozzo and E. Watanabe, “Control strategies of selective harmonic current shunt active filter” IEE Proc.-Gener. Trunsm. Distrib., Vol. 149, No. 2, December 2002. [8.] Sushil Karvekar, Aditi Kumbhojkar, “Comparison of Different Methods of Reference Current Generation for Shunt Active Power Filter Under Balanced And Unbalanced Load Conditions” 2013 International Conference on Circuits, Power and Computing Technologies [9.] Nitin Gupta, Student Member, IEEE, S. P. Singh, Member, IEEE, and S. P. Dubey “Neural Network Based Shunt Active Filter for Harmonic and Reactive Power Compensation under Non-ideal Mains Voltage” 978-1-4244-5046-6/10/$26.00_c 2010 IEEE. [10.] Riad Kadri, Jean-Paul Gaubert, and Gerard Champenois, “An Improved Maximum Power Point Tracking for Photovoltaic Grid- Connected Inverter Based on Voltage- Oriented Control”, IEEE transactions on industrial electronics, vol. 58, no. 1, January 2011. [11.] AKAGI, H.: 'Control strategy and site selection of a shunt active filter for damping of harmonic propagation in power distribution systems', IEEE Truns. P o ~ Drel iu., 1997, 12, (l), ,pp. 354-362 [12.] Katiraei, F.; Iravani, M.R., “Power Management Strategies for a Microgrid With Multiple Distributed Generation Units”, IEEE Transactions on Power Systems, Vol. 21, Issue 4, Nov. 2006, pp. 1821– 1831. [13.] H. Abaali, M. T. Lamchich, M. Raoufi, ”The Three phase Shunt Active Filters for the Harmonics Compensation Under Distorted and Unbalanced Mains Voltages Conditions”, IEEE International Conference on Industrial Technology (ICIT), 2004. [14.] M. Cirrincione, M. Pucci, G. Vitale, and A. Miraoui, “Current harmonic compensation by a single-phase shunt active power filter controlled by adaptive neural filtering,” IEEE Trans. Ind. Electron.,vol. 56, no. 8, pp. 3128-3143, Aug. 2009. [15.] L. P. Kunjumuhammed and M. K. Mishra, “Comparison of single phase shunt active power filter algorithms,” in Proc. IEEE Power India Conf., 2006, pp. 8–15. [16.] B. Yang, W. Li, Y. Zhao, and X. He, “Design and analysis of a gridconnected photovoltaic power system,” IEEE Trans. Power Electron.,vol. 25, no. 4, pp. 992– 1000, Apr. 2010. [17.] B. Sahan, A. N. Vergara, N. Henze, A. Engler, and P. Zacharias, “A singlestage PV module integrated converter based on a low- power currentsource inverter,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2602– 2609,Jul. 2008. [18.] N. Femia, G. Petrone, G. Spagnuolo, and M. Vitelli, “Perturb and observe MPPT technique robustness improved,” in Proc. IEEE Int. Symp. Ind.Electron., 2004, vol. 2, pp. 845–850. [19.] Shota Yamakura , Katsumi Kesamaru, “Dynamic Simulation of PMSG Small Wind Turbine Generation Systemwith HCS-MPPT Control. [20.] CHEDID R, MRAD F, BASMAM. Intelligent control for wind energy conversion systems.WindEng, 1998.