SlideShare a Scribd company logo
38 International Journal for Modern Trends in Science and Technology
Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST
Adaptive Control Scheme for PV Based
Induction Machine
M. Siva Kumar1
| D. Ramesh2
1PG Scholar, Department of Electrical & Electronics Engineering, Malla Reddy Engineering College,
Maisammaguda, Medchal (M), Rangareddy (Dt), Telangana, India.
2AssistantProfessor, Department of Electrical & Electronics Engineering, Malla Reddy Engineering
College, Maisammaguda, Medchal (M), Rangareddy (Dt), Telangana, India.
An adaptive control scheme for maximum power point tracking of a single-phase grid-connected
photovoltaic system is presented. The difficulty on design a controller that may operate a photovoltaic system
on its maximum power point (MPP) is that, this MPP depends on temperature and solar irradiance, ambient
conditions that are time-varying and difficult to measure. A solution using an on-line sliding mode estimator
is presented. It estimates three different parameters that depend on solar irradiance and temperature,
eliminating the necessity of having any sensor for these environmental variables. It is capable of estimate
time-varying parameters. A complete analysis was done taking into account the non-linearity’s showed by
the closed-loop system. An adaptive law was found to substitute a perturbation bound and also to eliminate
possible chattering due to the discontinuous controller term. Computer simulations are presented to show the
good performance of the controller. The controller detects the deviation of the actual trajectory from the
reference trajectory and corresponding changes the switching strategy to restore the tracking. Prominent
characteristics such as invariance, robustness, order reduction, and control chattering are discussed in
detail. Methods for coping with chattering are presented. Both linear and nonlinear systems are considered
The proposed concept can be implemented to adaptive control scheme for induction machine using
Matlab/Simulink software.
KEYWORDS: Grid-connected photovoltaic (PV) system, matching conditions, nonlinear controller, partial
feedback linearzing scheme, structured uncertainty.
Copyright © 2016 International Journal for Modern Trends in Science and Technology
All rights reserved.
I. INTRODUCTION
The utilization of grid-connected photovoltaic
(PV) systems is increasingly being pursued as a
supplement and an alternative to the conventional
fossil fuel generation in order to meet increasing
energy demands and to limit the pollution of the
environment caused by fuel emissions. The major
concerns of integrating PV into the grid are
stochastic behaviors of solar irradiations and
interfacing of inverters with the grid. Because of
the high initial investment, variations in solar
irradiation, and reduced life-time of PV systems, as
compared with the traditional energy sources, it is
essential to extract maximum power from PV
systems [1].
Maximum power point tracking (MPPT)
techniques are widely used to extract maximum
power from the PV system that is delivered to the
grid through the inverter [2]–[4]. Recent
improvements on MPPT can be seen in [5] and [6].
Interconnections among PV modules within a
shaded PV field can affect the extraction of
maximum power [7]. A study of all possible shading
scenarios and interconnection schemes for a given
PV field, to maximize the output power of PV array,
is proposed in [7]. Inverters interfacing PV modules
with the grid perform two major tasks—one is to
ensure that PV modules are operated at maximum
power point (MPP), and the other is to inject a
sinusoidal current into the grid. In order to perform
these tasks effectively, efficient stabilization or
control schemes are essential. In a grid-connected
ABSTRACT
39 International Journal for Modern Trends in Science and Technology
Adaptive Control Scheme for PV Based Induction Machine
PV system, control objectives are met by a strategy
using a pulse width modulation (PWM) scheme
based on two cascaded control loops [8].
The two cascaded control loops consist of an
outer voltage control loop to settle the PV array at
the MPP, and an inner current control loop to
establish the duty ratio for the generation of a
sinusoidal output current, which is in phase with
the grid voltage [8]. The current loop is also
responsible for power quality issues and current
protection for which harmonic compensations and
dynamics are the important properties of the
current controller.
Linear controllers such as proportional-integral
(PI), hysteresis, and model predictive controllers
are presented in [9]–[14], which provide
satisfactory operation over a fixed set of operating
points as the system is linearized at an equilibrium
point. Since the PV source exhibits a strongly
nonlinear electrical behavior due to the variation of
solar irradiance and nonlinear switching functions
of inverters. As linear controllers for nonlinear PV
systems affects all the variables in the system and
the electrical characteristics of the PV source are
time varying, the system is not linearizable around
a unique operating point or trajectory to achieve a
good performance over a wide variation in
atmospheric conditions. The restrictions of
operating points can be solved by implementing
nonlinear controllers for nonlinear PV systems.
A sliding-mode current controller for a
grid-connected PV system is proposed in [15],
along with a new MPPT technique to provide robust
tracking performances. In [15], the controller is
designed based on a time-varying sliding surface.
However, the selection of a time-varying surface is
a difficult task, and the system stays confined to
the sliding surface. Feedback linearization has
been increasingly used for nonlinear controller
design. It transforms the nonlinear system into a
fully or partly linear equivalent by canceling
nonlinearities. A feedback linearizing technique
was first proposed in [16] for PV applications where
a superfluous complex model of the inverter is
considered to design the controller. To overcome
the complexity, a simple and consistent inverter
model is used in [17], and a feedback linearization
technique is employed to operate the PV system at
MPP. In [16] and [17], a feedback linearizing
controller is designed by considering the dc-link
voltage and quadrature-axis grid current as output
functions. Power-balance relationships are
considered to express the dynamics of the voltage
across the dc-link capacitor. However, this
relationship cannot capture nonlinear switching
functions between inverter input and output; to
accurately represent a grid-connected PV system
but it is essential to consider these switching
actions. The current relationship between the
input and output of the inverter can be written in
terms of switching functions rather than the power
balance equation. Therefore, the voltage dynamics
of the dc-link capacitor include nonlinearities due
to the switching actions of the inverter.
The inclusion of these nonlinearities in the model
will improve the accuracy; however, the
grid-connected PV system will be partially, rather
than exactly, linearized, as presented in [18].
Although the approaches presented in [16]–[18]
ensure MPP operation of the PV system, they do not
account for inherent uncertainties in the system.
In the design of both linear and nonlinear
controllers for grid-connected PV systems, most of
the difficulties stem from the analytical complexity
of the dynamic model of a PV system,
which, on one hand, exhibits a nonlinear
parametric dependence on the PV array
current–voltage characteristics varying with the
irradiation and temperature levels and, on the
other, a sinusoidal time dependence due to the grid
connection of PV systems. These difficulties may
lead to some barriers in developing a meaningful
and realistic mathematical model. The mismatch
between the mathematical model and true system
may lead to serious stability problems for the
system. Therefore, the designs of robust control
strategies that consider the model uncertainties
are of great importance to design nonlinear
controllers. Variable structure control with sliding
mode, or sliding-mode control is one of the effective
nonlinear robust control approaches since it
provides system dynamics with an invariance
property to uncertainties once the system
dynamics are controlled in the sliding mode.
A sliding-mode controller for grid connected PV
system is presented in [19] and [20] to achieve
robust MPPT under uncertainties within the
system model. With this control approach, the
insensitivity of the controlled system to
uncertainties exists in the sliding mode but not
during the reaching phase, i.e., the system
dynamic in the reaching phase is still influenced by
uncertainties. A mini-max LQG technique is
proposed in [21] to design a robust controller for
the integration of PV generation into the grid where
the higher order terms during the linearization is
considered as the uncertainty. A feed forward
mechanism is proposed in [22] to control the
40 International Journal for Modern Trends in Science and Technology
Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST
current and dc-link voltage and the robustness of
this mechanism is analyzed through modal
analysis. A robust fuzzy controlled PV inverter is
presented in [23] for the stabilization of a grid
connected PV system where the robustness is
adopted by using the Taguchi-tuning algorithm.
However, the main difficulties of the robustness
algorithm, as presented in [21] [23], are the
consideration of linearized PV system models that
are unable to maintain the stability of the PV
system over a wide changes in atmospheric
conditions. Although there are some advances in
the robust control of grid-connected PV systems,
research into the robustness
Fig. 1. Three-phase grid-connected PV system.
analysis and the controller design of nonlinear
uncertain PV systems remains an important and
challenging area. Since the feedback linearization
technique is widely used in the design of nonlinear
controllers for power systems, this paper proposed
the extension of the partial feedback linearizing
scheme, as presented in [18], by considering
uncertainties within the PV system model. In this
paper, matching conditions are used to model the
uncertainties in PV systems for given upper
bounds on the modeling error, which include
parametric and state-dependent uncertainties.
These uncertainties are bounded in such a way
that the proposed controller can guarantee the
stability and enhance the performance for all
possible perturbations within the given upper
bounds of the modeling errors of nonlinear PV
systems. The effectiveness of the proposed
controller is tested and compared with that of a
partial feedback linearizing controller without
uncertainties, following changes in atmospheric
conditions.
II. PHOTOVOLTAIC SYSTEM MODEL
The schematic diagram of a three-phase
grid-connected PV system, which is the main focus
of this paper, is shown in Fig. 1. The considered PV
system consists of a PV array, a dc-link capacitor
C, a three-phase inverter, a filter inductor L, and
grid voltages ea, eb, ec. In this paper, the main aim
is to control the voltage vdc (which is also the
output voltage of PV array vpv) across the capacitor
C and to make the input current in phase with grid
voltage for unity power factor by means of
appropriate control signals through the switches of
the inverter.
A. Photovoltaic Cell and Array Model: A PV cell
is a simple p-n junction diode that converts the
irradiation into electricity. Fig. 2 shows an
equivalent circuit diagram of a PV cell that consists
of a light generated current source IL, a parallel
diode, a shunt resistance Rsh, and a series
resistance Rs. In Fig. 2, ION is the diode current
that can be written as
(1)
where α = qAkTC , k = 1.3807 × 10−23 JK−1 is the
Boltzmann’s constant, q = 1.6022 × 10−19 C is the
charge of electron, TC is the cell’s absolute working
temperature in Kelvin, A is the p-n junction ideality
factor whose value is between 1 and 5, Is is the
saturation current, and vpv is the output voltage of
the PV array which is also the voltage across C, i.e.,
vdc. Now,
Fig. 2. Equivalent circuit diagram of the PV cell.
Fig. 3. Equivalent circuit diagram of the PV array.
41 International Journal for Modern Trends in Science and Technology
Adaptive Control Scheme for PV Based Induction Machine
by applying Kirchhoff’s current law (KCL) in Fig. 2,
the output current (ipv) generated by a PV cell can
be written as
(2)
The light generated current IL depends on the solar
irradiation that can be related by the following
equation:
(3)
where Isc is the short-circuit current, s is the solar
irradiation, ki is the cell’s short-circuit current
coefficient, and Tref is the reference temperature of
the cell. The cell’s saturation current Is varies with
the temperature according to the following
equation [17]:
(4)
Where Eg is the band gap energy of the
semiconductor used in the reference temperature
and solar irradiation.
Since the output voltage of a PV cell is very low, a
number of PV cells are connected together in series
in order to obtain higher voltages. Then, they are
encapsulated with glass, plastic, and other
transparent materials to protect them from harsh
environments and are called a PV module. To
obtain the required voltage and power, a number of
modules are connected in parallel to form a PV
array. Fig. 3 shows an electrical equivalent circuit
diagram of a PV array, where Ns is the number of
cells in series, and Np is the number of modules in
parallel. In this case, the array ipv can be written
as
(5)
B. Three-Phase Grid-Connected Photovoltaic
System ModelIn the state-space form, Fig. 1 can
be represented through the following equations
[17], [18]:
(6)
where Ka, Kb, and Kc are the input switching
signals. Now, by applying KCL at the node where
the dc link is connected, we obtain
(7)
However, the input current of the inverter idc can
be written as [19]
(8)
which yields
(9)
The complete model of a three-phase
grid-connected PV system can be presented by (6)
and (9), which are nonlinear and time variant and
can be converted into a time invariant model by
applying dq transformation using the angular
frequency (ω) of the grid, rotating the reference
frame synchronized with grid where the d
component of the grid voltage Ed is zero [17]. By
using dq transformation, (6) and (9) can be written
as
(10)
where Idq = Tabc dq iabc, edq = Tabc dq eabc, Kdq =
Tabc dq Kabc. Equation (10) represents the
complete mathematical model of a three-phase
grid-connected PV system and this model is a
nonlinear model due to the nonlinear behavior of
the switching signals and the output current (ipv)
of the PV array. The transformation matrix T dqabc
42 International Journal for Modern Trends in Science and Technology
Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST
can be written as
(11)
At this point of mathematical modeling, the key
issue the selection of the current component that
can be obtained from the power delivered into the
grid. Since Ed = 0, the real power delivered to the
grid can be written as
(12)
From (12), it can be seen that the maximum power
delivery into the grid can be maintained by
controlling the q component of the grid current,
i.e., Iq . Based on this mathematical model, the
overview of the partial feedback linearizing
stabilization scheme is shown in the following
section.
III. OVERVIEW OF PARTIAL FEEDBACK LINEARIZING
STABILIZATION SCHEME
As the three-phase grid-connected PV system as
represented by (10) has two control inputs (Kd and
Kq) and two control outputs (Iq and vpv), the
mathematical model can be represented by the
following form of a nonlinear multi-input
multi-output (MIMO) system
(13)
The partial feedback linearizing scheme transforms
the nonlinear grid-connected PV system into a
partially linearized PV system, and any linear
controller design technique can be employed to
obtain the linear control law for the partially
linearized system. However, before obtaining a
control law through partial feedback linearizing
scheme, it is essential to ensure the partial
feedback linearizability and internal dynamics
stability of the PV system. The details of partial
feedback linearizability and internal dynamics
stability of the considered PV system are presented
in [18] from where it can be seen that the PV
system is partially linearized and that the internal
dynamic of the PV systems is stable. The partially
linearized PV system can be written
(14)
where z͂ represents the transformed states, and v
represents the linear control inputs that are
obtained through the PI design approach [18]. The
nonlinear control law can be written as
(15)
Equation (15) is the final control law that is
obtained through a partial feedback linearizing
scheme, and the controller ensures the stability of
the PV system for the considered nominal model
and exact parameters of the system need to be
known. However, in practice, it is very difficult to
determine the exact parameters of the system.
Thus, the considered partial feedback linearizing
scheme is unable to maintain the stability of the PV
system with changes in system conditions and the
consideration of uncertainties within the PV
system is necessary, which is shown in the
following section.
IV. UNCERTAINTY MODELING
In a practical PV system, atmospheric conditions
change continuously for which there exists a
variation in cell working temperature, as well as in
solar irradiance. Because of changes in
atmospheric conditions, the output voltage,
current, and power of the PV unit changes
significantly. For example, if a single module of a
series string is partially shaded, and then its
output current will be reduced, which will change
the operating point of the whole string. Since the
amount of the PV generation depends on solar
irradiation that is uncertain, there are
uncertainties in ipv which in turn causes
uncertainties in the current (in the dq-frame, Id
and Iq ) injected into the grid. Moreover, as the
values of the parameters used in the PV model are
not exactly known, there are also parametric
uncertainties. The PV system model as shown by
(10) cannot capture these uncertainties. Therefore,
it is essential to consider these uncertainties within
the PV system model. In the presence of
uncertainties, the nonlinear mathematical model of
the three-phase grid-connected PV system, as
43 International Journal for Modern Trends in Science and Technology
Adaptive Control Scheme for PV Based Induction Machine
shown in (13), can be represented by the following
equation:
(16)
The uncertainties need to be modeled in such a
way that the controller will robustly stabilize the
original system despite the uncertainties Δf(x) and
Δg(x), i.e., the robust controller will attenuate the
influence of system uncertainties. In order to
achieve the control objective of robust stabilization,
the structure of uncertainties and the locations of
unknown parameters should satisfy the following
conditions:
(17)
which is known as the matching condition [24]. If
this matching condition holds, the following
condition is true:
(18)
where r is the total relative degree of the nominal
system, which is 2 [18], w is the relative degree of
uncertainty Δg(x), and ρ is the relative degree of
uncertainty Δf(x). In order to match the
uncertainties with the PV system model, the
relative degree of the uncertainty Δf should be 2 as
it needs to equal to the relative degree of the
nominal system in (10), which is 2. The relative
degree of the uncertainty Δf can be calculated from
the following equation:
(19)
If the relative degree of Δf corresponding to the
outputs h1 and h2 is 1, then the total relative
degree of Δf will be 2, which will happen if Δf1 and
Δf3 are not equal to zero. To match the uncertainty
Δg, the relative degree of Δg should be equal to or
greater than the relative degree of the nominal
system and will be 2 if the following conditions
hold:
(20)
Where Δg11 must not be zero and either Δg31 or
Δg32 can be zero, to match the uncertainty with
the structure of the PV system. Since the proposed
uncertainty modeling scheme considers the upper
bound of the uncertainties, it is important to set
these bounds, and the controller needs to be
designed based on these
bounds. If the maximum allowable changes in the
system parameters is 30% and the variations in
solar irradiation and environmental temperature
are considered up to 80% of their nominal values.
The partial feedback linearizing scheme as
presented in [18] cannot stabilize the PV system
appropriate if the aforementioned uncertainties are
considered within the PV system model as the
controller is designed to stabilize only the nominal
system. However, in the robust partial feedback
linearizing scheme, the aforementioned
uncertainties need to be included to achieve the
robust stabilization of the grid-connected PV
system. The robust controller design by
considering the aforementioned uncertainties
within the grid-connected PV system model is
shown in the following section.
V. ROBUST CONTROLLER DESIGN
This section aims the derivation of the robust
control law that robustly stabilizes a
grid-connected PV system with uncertainties
whose structures are already discussed in the
previous section. The following steps are followed
to design the robust controller for a three-phase
grid-connected PV system.
1) Step 1 (Partial feedback linearization of grid
connected PV systems): In this case, the partial
feedback linearization for the system with
uncertainties, as shown by (16), can be obtained as
For the PV system, the partially linearized system
can written as
44 International Journal for Modern Trends in Science and Technology
Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST
(21)
If v1 and v2 are linear control inputs for the
aforementioned partially feedback linearized
system, (21) can be written as
(22)
Which can be obtained using any linear control
technique, and in this paper, two PI controllers are
used. However,
Fig. 4. Implementation block diagram.
before designing and implementing the controller
based on partial feedback linearizing scheme, it is
essential to check the stability of the internal
dynamics that is similar to that described in [18].
2) Step 2 (Derivation of robust control law): From
(22), the robust control law can be obtained as
follows:
(23)
Equation (23) is the final robust control law for a
three grid connected PV system, and the control
law contains the modeled uncertainties. The main
difference between the designed robust control law
(23) and the control law (15) is the inclusion of
uncertainties within the PV system model. The
performance of the designed robust stabilization
scheme is evaluated and compared in the following
section with our previously published partial
feedback linearizing scheme with no uncertainties
[18]. The performance of the controller is evaluated
in the following section.
VI. INDUCTION MOTOR
An induction motor is an example of
asynchronous AC machine, which consists of a
stator and a rotor. This motor is widely used
because of its strong features and reasonable cost.
A sinusoidal voltage is applied to the stator, in the
induction motor, which results in an induced
electromagnetic field. A current in the rotor is
induced due to this field, which creates another
field that tries to align with the stator field, causing
the rotor to spin. A slip is created between these
fields, when a load is applied to the motor.
Compared to the synchronous speed, the rotor
speed decreases, at higher slip values. The
frequency of the stator voltage controls the
synchronous speed. The frequency of the voltage is
applied to the stator through power electronic
devices, which allows the control of the speed of the
motor. The research is using techniques, which
implement a constant voltage to frequency ratio.
Finally, the torque begins to fall when the motor
reaches the synchronous speed. Thus, induction
motor synchronous speed is defined by following
equation,
(24)
Where f is the frequency of AC supply, n, is the
speed of rotor; p is the number of poles per phase of
the motor. By varying the frequency of control
circuit through AC supply, the rotor speed will
change.
A. Control Strategy of Induction Motor
Power electronics interface such as three-phase
SPWM inverter using constant closed loop Volts l
45 International Journal for Modern Trends in Science and Technology
Adaptive Control Scheme for PV Based Induction Machine
Hertz control scheme is used to control the motor.
According to the desired output speed, the
amplitude and frequency of the reference
(sinusoidal) signals will change. In order to
maintain constant magnetic flux in the motor, the
ratio of the voltage amplitude to voltage frequency
will be kept constant. Hence a closed loop
Proportional Integral (PI) controller is implemented
to regulate the motor speed to the desired set point.
The closed loop speed control is characterized by
the measurement of the actual motor speed, which
is compared to the reference speed while the error
signal is generated. The magnitude and polarity of
the error signal correspond to the difference
between the actual and required speed. The PI
controller generates the corrected motor stator
frequency to compensate for the error, based on the
speed error.
VII. SIMULATION RESULTS
Fig 5 Matlab/simulation circuit of Adaptive Control Scheme
for Pv Based system
Fig 6 Performance under standard atmospheric conditions
(Blue line—grid voltage, red line—grid current with the
RPFBLSS, and green line—grid current with the PFBLS)
Fig 7 Performance under changing atmospheric conditions
(Blue line—grid voltage, red line-grid current with the
RPFBLSS, and green line—grid current with the PFBLS).
Fig 8 Performance under a three-phase short-circuit fault
(Red line—grid current with the RPFBLSS, and green
line—grid current with the PFBLS).
Fig 9 Matlab/simulation circuit of Adaptive Control Scheme
for Pv Based system with Induction Motor
Fig 10 simulation wave form of line output voltage with IM
Fig 11 simulation wave form of line output current with IM
Fig 12 simulation wave form of phase voltage with IM
46 International Journal for Modern Trends in Science and Technology
Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST
Fig 13 simulation wave form of stator current, speed and
torque
VIII. CONCLUSION
In this paper, a robust stabilization scheme is
considered by modeling the uncertainties of a three
phase grid-connected PV system based on the
satisfaction of matching conditions to ensure the
operation of the system at unity power factor. In
order to design the robust scheme, the partial
feedback linearization approach is used, and with
the designed scheme, only the upper bounds of the
PV systems’ parameters and states need to be
known rather than network parameters, system
operating points, or nature of the faults. The
resulting robust scheme enhances the overall
stability of a three-phase grid connected PV
system, considering admissible network
uncertainties. Thus, this stabilization scheme has
good robustness against the PV system parameter
variations, irrespective of the network parameters
and configuration. Future work will include the
implementation of the proposed scheme on a
Induction machine system to study the
characteristics of speed, torque.
REFERENCES
[1] S. Jain and V. Agarwal, ―A single-stage grid
connected inverter topology for solar PV systems
with maximum power point tracking,‖ IEEE Trans.
Power Electron., vol. 22, no. 5, pp. 1928–1940, Sep.
2007.
[2] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, ―A
review of single-phase grid-connected inverters for
photovoltaic modules,‖ IEEE Trans. Ind. Appl., vol.
41, no. 5, pp. 1292–1306, Sep./Oct. 2005.
[3] T. Esram and P. L. Chapman, ―Comparison of
photovoltaic array maximum power point tracking
techniques,‖ IEEE Trans. Energy Convers., vol. 22,
no. 2, pp. 439–449, Jun. 2007.
[4] I. Houssamo, F. Locment, and M. Sechilariu,
―Maximum power point tracking for photovoltaic
power system: Development and experimental
comparison of two algorithms,‖ Renewable Energy,
vol. 35, no. 10, pp. 2381–2387, Oct. 2010.
[5] U. Zimmermann and M. Edoff, ―A maximum power
point tracker for long-term logging of PV module
performance,‖ IEEE J. Photovoltaics, vol. 2, no. 1, pp.
47–55, Jan. 2012.
[6] E. Koutroulis and F. Blaabjerg, ―A new technique for
tracking the global maximum power point of PV
arrays operating under partial-shading conditions,‖
IEEE J. Photovoltaics, vol. 2, no. 2, pp. 184 190, Apr.
2012.
[7] L. F. L. Villa, D. Picault, B. Raison, S. Bacha, and A.
Labonne, ―Maximizing the power output of partially
shaded photovoltaic plants through optimization of
the interconnections among its modules,‖ IEEE J.
Photovoltaics, vol. 2, no. 2, pp. 154–163, Apr. 2012.
[8] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V.
Timbus, ―Overview of control and grid
synchronization for distributed power generation
systems,‖ IEEE Trans. Ind. Electron., vol. 53, no. 5,
pp. 1398–1409, Oct. 2006.
[9] A. Kotsopoulos, J. L. Darte, and M. A. M. Hendrix,
―Predictive DC voltage control of single-phase PV
inverters with small dc link capacitance,‖ in Proc.
IEEE Int. Symp. Ind. Electron., Jun. 2003, pp.
793–797.
[10]C. Meza, J. J. Negroni, D. Biel, and F. Guinjoan,
―Energy balance modeling and discrete control for
single-phase grid connected PV central inverters,‖
IEEE Trans. Ind. Electron., vol. 55, no. 7, pp.
2734–2743, Jul. 2008.
[11]R. Kadri, J. P. Gaubert, and G. Champenois, ―An
improved maximum power point tracking for
photovoltaic grid-connected inverter based on
voltage-oriented control,‖ IEEE Trans. Ind. Electron.,
vol. 58, no. 1, pp. 66–75, Jan. 2011.
[12]J. Selvaraj and N. A. Rahim, ―Multilevel inverter for
grid-connected PV system employing digital PI
controller,‖ IEEE Trans. Ind. Electron., vol. 56, no. 1,
pp. 149–158, Jan. 2009.
[13]N. A. Rahim, J. Selvaraj, and C. C. Krismadinata,
―Hysteresis current control and sensorless MPPT for
grid-connected photovoltaic systems,‖ in Proc. IEEE
Int. Symp. Ind. Electron., 2007, pp. 572–577.
[14]A. Kotsopoulos, J. L. Duarte, and M. A. M. Hendrix,
―A predictive control scheme for DC voltage and AC
current in grid-connected photovoltaic inverters with
minimum DC link capacitance,‖ in Proc. IEEE Ind.
27th Annu. Conf. Electron. Soc., 2001, pp.
1994–1999.
[15]I. Kim, ―Sliding mode controller for the single-phase
grid connected photovoltaic system,‖ Appl. Energy,
vol. 83, pp. 1101 1115, 2006.
[16]A. O. Zue and A. Chandra, ―State feedback
linearization control of a grid connected photovoltaic
interface with MPPT,‖ in Proc. IEEE Electr. Power
Energy Conf., Oct. 2009.
[17]D. Lalili, A. Mellit, N. Lourci, B. Medjahed, and E. M.
Berkouk, ―Input output feedback linearization
control and variable step size MPPT algorithm of a
grid-connected photovoltaic inverter,‖ Renewable
Energy, vol. 36, no. 12, pp. 3282–3291, Dec. 2011.
[18]M. A. Mahmud, H. R. Pota, and M. J. Hossain,
―Dynamic stability of three-phase grid-connected
photovoltaic system using zero dynamic design
47 International Journal for Modern Trends in Science and Technology
Adaptive Control Scheme for PV Based Induction Machine
approach,‖ IEEE J. Photovoltaics, vol. 2, no. 4, pp.
564–571, Oct. 2012.
[19]I.-S. Kim, ―Robust maximum power point tracker
using sliding mode controller for the three–phase
grid–connected photovoltaic system,‖ Sol. Energy,
vol. 81, no. 3, pp. 405–414, Mar. 2007.
[20]C.-C. Chu and C.-L. Chen, ―Robust maximum power
point tracking method for photovoltaic cells: A
sliding mode control approach,‖ Sol. Energy, vol. 83,
no. 8, pp. 1370–1378, Aug. 2009.
[21]M. J. Hossain, T. K. Saha, N. Mithulananthan, and
H. R. Pota, ―Robust control strategy for PV system
integration in distribution systems,‖ Appl. Energy,
vol. 99, pp. 355–362, Nov. 2012.
[22]A. Yazdani and P. P. Dash, ―A control methodology
and characterization of dynamics for a photovoltaic
(PV) system interfaced with a distribution network,‖
IEEE Trans. Power Del., vol. 24, no. 3, pp.
1538–1551, Jul. 2009.
[23]Y.-K. Chen, C.-H. Yang, and Y.-C. Wu, ―Robust fuzzy
controlled photovoltaic power inverter with Taguchi
method,‖ IEEE Trans. Aerosp. Electron. Syst., vol. 38,
no. 3, pp. 940–954, Jul. 2002. [24] S. Behtash,
―Robust output tracking for nonlinear systems,‖ Int.
J. Control, vol. 51, no. 6, pp. 1381–1407, 1990.

More Related Content

PDF
Nonlinear Current Controller for a Single Phase Grid Connected Photovoltaic S...
PDF
DESIGN A TWO STAGE GRID CONNECTED PV SYSTEMS WITH CONSTANT POWER GENERATION A...
PDF
IRJET- Energy Management and Control for Grid Connected Hybrid Energy Storage...
PDF
IRJET- High Accurate Sensorless Dual Axis Solar Tracking System Controlle...
PDF
IRJET- Microgrid Control Techniques
PDF
IRJET- Application of Model Predictive Control in PV-STATCOM for Achieving Fa...
PDF
Analysis of Double Moving Average Power Smoothing Methods for Photovoltaic Sy...
Nonlinear Current Controller for a Single Phase Grid Connected Photovoltaic S...
DESIGN A TWO STAGE GRID CONNECTED PV SYSTEMS WITH CONSTANT POWER GENERATION A...
IRJET- Energy Management and Control for Grid Connected Hybrid Energy Storage...
IRJET- High Accurate Sensorless Dual Axis Solar Tracking System Controlle...
IRJET- Microgrid Control Techniques
IRJET- Application of Model Predictive Control in PV-STATCOM for Achieving Fa...
Analysis of Double Moving Average Power Smoothing Methods for Photovoltaic Sy...

What's hot (20)

PDF
Iisrt hariharan ravichandran(31 36)
PDF
IRJET - Maximum Power Extraction by Introducing P&O Technique in PV Grid
PDF
Banc d'essai expérimental de panneau photovoltaïque
PDF
IRJET- STATCOM based Control Scheme for Power Quality Improvement in Grid-Con...
PDF
Kw3419541958
PDF
Design and Analysis of Three Phase Inverter with Two Buck/Boost MPPTs for DC ...
PDF
STATCOM Based Wind Energy System by using Hybrid Fuzzy Logic Controller
PDF
A Novel Implementation of Demand Response on Smart Grid using Renewable Energ...
PPTX
Pvsolarcell
PDF
Current control of grid-connected inverter using integral sliding mode contro...
PDF
Defining Control Strategies for Micro Grids Islanded Operation with Maximum P...
PDF
COORDINATED CONTROL AND ENERGY MANAGEMENT OF DISTRIBUTED GENERATION INVERTERS...
PDF
An integrated framework_for_smart_microgrids_modeling_monitoring_control_comm...
PDF
A Hybrid Control Scheme for Fault Ride-Through Capability using Line-Side Con...
PDF
Aee 67-3-2018-10.09 art-1
PDF
Navigation of Mobile Inverted Pendulum via Wireless control using LQR Technique
PDF
hybrid
PDF
Stability Improvement in Grid Connected Multi Area System using ANFIS Based S...
PDF
IRJET - Power Quality Improvement using Statcom in PV Grid Connected System
PDF
IMPROVED SWARM INTELLIGENCE APPROACH TO MULTI OBJECTIVE ED PROBLEMS
Iisrt hariharan ravichandran(31 36)
IRJET - Maximum Power Extraction by Introducing P&O Technique in PV Grid
Banc d'essai expérimental de panneau photovoltaïque
IRJET- STATCOM based Control Scheme for Power Quality Improvement in Grid-Con...
Kw3419541958
Design and Analysis of Three Phase Inverter with Two Buck/Boost MPPTs for DC ...
STATCOM Based Wind Energy System by using Hybrid Fuzzy Logic Controller
A Novel Implementation of Demand Response on Smart Grid using Renewable Energ...
Pvsolarcell
Current control of grid-connected inverter using integral sliding mode contro...
Defining Control Strategies for Micro Grids Islanded Operation with Maximum P...
COORDINATED CONTROL AND ENERGY MANAGEMENT OF DISTRIBUTED GENERATION INVERTERS...
An integrated framework_for_smart_microgrids_modeling_monitoring_control_comm...
A Hybrid Control Scheme for Fault Ride-Through Capability using Line-Side Con...
Aee 67-3-2018-10.09 art-1
Navigation of Mobile Inverted Pendulum via Wireless control using LQR Technique
hybrid
Stability Improvement in Grid Connected Multi Area System using ANFIS Based S...
IRJET - Power Quality Improvement using Statcom in PV Grid Connected System
IMPROVED SWARM INTELLIGENCE APPROACH TO MULTI OBJECTIVE ED PROBLEMS
Ad

Viewers also liked (20)

PDF
Grid fault Control Scheme for Peak Current Reduction in Photovoltaic Inverte...
PDF
Improving Code Compression Efficiency of MIPS32 Processor using Modified ISA
PDF
Control Scheme for an IPM Synchronous Generator Based-Variable Speed Wind Tur...
PDF
Smart Millennials and their Changing Shopping Trends: A Case of Millennial St...
PDF
A Cryptographic Key Generation Using 2D Graphics pixel Shuffling
PDF
L-Z Source Based 11 Level Diode-Clamped Multi Level Inverter
PDF
Design and implementation of Closed Loop Control of Three Phase Interleaved P...
PDF
Modeling and Simulation of Cascaded Multilevel Inverter fed PMSM Drive with P...
PDF
Hybrid Power Quality Compensator for Traction Power System with Photovoltaic ...
PDF
An Improved UPQC Controller to Provide Grid-Voltage Regulation
PDF
Adaptive Variable Speed Control Scheme for Wind Based on PFC of BLDC Drive Ap...
PDF
Modelling Determinants of Software Development Outsourcing for Nigeria
PDF
Serial Peripheral Interface Design for Advanced Microcontroller Bus Architect...
PDF
Analysis of 7-Level Cascaded & MLDCLI with Sinusoidal PWM & Modified Referenc...
PDF
Multilevel Inverter for Grid-Connected PV System Employing Digital PI Contro...
PDF
Study of grid connected pv system based on current source inverter
PPTX
Design Aspect of Standalone PV system
PDF
PV solar Design and Installtion
PDF
Experimental Study on use of Crushed Rock Powder as Partial Replacement for F...
PDF
Graph Tea: Simulating Tool for Graph Theory & Algorithms
Grid fault Control Scheme for Peak Current Reduction in Photovoltaic Inverte...
Improving Code Compression Efficiency of MIPS32 Processor using Modified ISA
Control Scheme for an IPM Synchronous Generator Based-Variable Speed Wind Tur...
Smart Millennials and their Changing Shopping Trends: A Case of Millennial St...
A Cryptographic Key Generation Using 2D Graphics pixel Shuffling
L-Z Source Based 11 Level Diode-Clamped Multi Level Inverter
Design and implementation of Closed Loop Control of Three Phase Interleaved P...
Modeling and Simulation of Cascaded Multilevel Inverter fed PMSM Drive with P...
Hybrid Power Quality Compensator for Traction Power System with Photovoltaic ...
An Improved UPQC Controller to Provide Grid-Voltage Regulation
Adaptive Variable Speed Control Scheme for Wind Based on PFC of BLDC Drive Ap...
Modelling Determinants of Software Development Outsourcing for Nigeria
Serial Peripheral Interface Design for Advanced Microcontroller Bus Architect...
Analysis of 7-Level Cascaded & MLDCLI with Sinusoidal PWM & Modified Referenc...
Multilevel Inverter for Grid-Connected PV System Employing Digital PI Contro...
Study of grid connected pv system based on current source inverter
Design Aspect of Standalone PV system
PV solar Design and Installtion
Experimental Study on use of Crushed Rock Powder as Partial Replacement for F...
Graph Tea: Simulating Tool for Graph Theory & Algorithms
Ad

Similar to Adaptive Control Scheme for PV Based Induction Machine (20)

PDF
Modeling and Simulation of Solar System with MPPT Based Inverter and Grid Syn...
PDF
IRJET-Robot Control by using Human Hand Gestures
PDF
Design_of_Adaptive_Sliding_Mode_Controller_for_Single-Phase_Grid-Tied_PV_Syst...
PDF
DC MICROGRID USING PHOTOVOLTAIC IMPROVED INCREMENTAL CONDUCTANCE ALGORITHM FO...
PDF
Low-voltage Ride-through Methods for Grid-connected Photovoltaic Systems in M...
PDF
Control strategies for seamless transfer between the grid-connected and isla...
PDF
Integrated energy management converter based on maximum power point tracking...
PDF
Power quality optimization using a novel backstepping control of a three-phas...
PDF
IRJET- Different Control Strategies for Power Control of Voltage Source Conve...
PDF
IRJET- Level of Service & Throughput Maximization at Operational Toll Plazas
PDF
A New Simulation Modeling for Nonlinear Current Control in Single Phase Grid ...
PDF
Power-Sharing of Parallel Inverters in Micro-Grids via Droop control and Virt...
PDF
IRJET- A Review on Solar based Multilevel Inverter with Three Phase Grid Supply
PDF
Control technique for single phase inverter photovoltaic system connected to ...
PDF
A hybrid maximum power point tracking for partially shaded photovoltaic syste...
PDF
A Review paper on Power Quality Improvement Techniques in a Grid Integrated S...
PDF
IRJET - Implementation of Simulink and Hardware System of MPPT by using F...
PDF
Modeling of Solar System with MPPT Based Inverter Synchronization with Grid i...
PDF
s43067-022-00050-5.pdf
PDF
s43067-022-00050-5.pdf
Modeling and Simulation of Solar System with MPPT Based Inverter and Grid Syn...
IRJET-Robot Control by using Human Hand Gestures
Design_of_Adaptive_Sliding_Mode_Controller_for_Single-Phase_Grid-Tied_PV_Syst...
DC MICROGRID USING PHOTOVOLTAIC IMPROVED INCREMENTAL CONDUCTANCE ALGORITHM FO...
Low-voltage Ride-through Methods for Grid-connected Photovoltaic Systems in M...
Control strategies for seamless transfer between the grid-connected and isla...
Integrated energy management converter based on maximum power point tracking...
Power quality optimization using a novel backstepping control of a three-phas...
IRJET- Different Control Strategies for Power Control of Voltage Source Conve...
IRJET- Level of Service & Throughput Maximization at Operational Toll Plazas
A New Simulation Modeling for Nonlinear Current Control in Single Phase Grid ...
Power-Sharing of Parallel Inverters in Micro-Grids via Droop control and Virt...
IRJET- A Review on Solar based Multilevel Inverter with Three Phase Grid Supply
Control technique for single phase inverter photovoltaic system connected to ...
A hybrid maximum power point tracking for partially shaded photovoltaic syste...
A Review paper on Power Quality Improvement Techniques in a Grid Integrated S...
IRJET - Implementation of Simulink and Hardware System of MPPT by using F...
Modeling of Solar System with MPPT Based Inverter Synchronization with Grid i...
s43067-022-00050-5.pdf
s43067-022-00050-5.pdf

Recently uploaded (20)

PPTX
2025-08-10 Joseph 02 (shared slides).pptx
PPTX
Hydrogel Based delivery Cancer Treatment
PPTX
Role and Responsibilities of Bangladesh Coast Guard Base, Mongla Challenges
PDF
Nykaa-Strategy-Case-Fixing-Retention-UX-and-D2C-Engagement (1).pdf
PPTX
Primary and secondary sources, and history
PPTX
Relationship Management Presentation In Banking.pptx
PPTX
Intro to ISO 9001 2015.pptx wareness raising
PDF
Why Top Brands Trust Enuncia Global for Language Solutions.pdf
PPTX
Learning-Plan-5-Policies-and-Practices.pptx
PPTX
The spiral of silence is a theory in communication and political science that...
PPTX
Effective_Handling_Information_Presentation.pptx
PPTX
Self management and self evaluation presentation
PPTX
worship songs, in any order, compilation
PPTX
Human Mind & its character Characteristics
PPTX
_ISO_Presentation_ISO 9001 and 45001.pptx
DOCX
ENGLISH PROJECT FOR BINOD BIHARI MAHTO KOYLANCHAL UNIVERSITY
PDF
Instagram's Product Secrets Unveiled with this PPT
PPTX
Project and change Managment: short video sequences for IBA
PPTX
Introduction to Effective Communication.pptx
PPTX
fundraisepro pitch deck elegant and modern
2025-08-10 Joseph 02 (shared slides).pptx
Hydrogel Based delivery Cancer Treatment
Role and Responsibilities of Bangladesh Coast Guard Base, Mongla Challenges
Nykaa-Strategy-Case-Fixing-Retention-UX-and-D2C-Engagement (1).pdf
Primary and secondary sources, and history
Relationship Management Presentation In Banking.pptx
Intro to ISO 9001 2015.pptx wareness raising
Why Top Brands Trust Enuncia Global for Language Solutions.pdf
Learning-Plan-5-Policies-and-Practices.pptx
The spiral of silence is a theory in communication and political science that...
Effective_Handling_Information_Presentation.pptx
Self management and self evaluation presentation
worship songs, in any order, compilation
Human Mind & its character Characteristics
_ISO_Presentation_ISO 9001 and 45001.pptx
ENGLISH PROJECT FOR BINOD BIHARI MAHTO KOYLANCHAL UNIVERSITY
Instagram's Product Secrets Unveiled with this PPT
Project and change Managment: short video sequences for IBA
Introduction to Effective Communication.pptx
fundraisepro pitch deck elegant and modern

Adaptive Control Scheme for PV Based Induction Machine

  • 1. 38 International Journal for Modern Trends in Science and Technology Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST Adaptive Control Scheme for PV Based Induction Machine M. Siva Kumar1 | D. Ramesh2 1PG Scholar, Department of Electrical & Electronics Engineering, Malla Reddy Engineering College, Maisammaguda, Medchal (M), Rangareddy (Dt), Telangana, India. 2AssistantProfessor, Department of Electrical & Electronics Engineering, Malla Reddy Engineering College, Maisammaguda, Medchal (M), Rangareddy (Dt), Telangana, India. An adaptive control scheme for maximum power point tracking of a single-phase grid-connected photovoltaic system is presented. The difficulty on design a controller that may operate a photovoltaic system on its maximum power point (MPP) is that, this MPP depends on temperature and solar irradiance, ambient conditions that are time-varying and difficult to measure. A solution using an on-line sliding mode estimator is presented. It estimates three different parameters that depend on solar irradiance and temperature, eliminating the necessity of having any sensor for these environmental variables. It is capable of estimate time-varying parameters. A complete analysis was done taking into account the non-linearity’s showed by the closed-loop system. An adaptive law was found to substitute a perturbation bound and also to eliminate possible chattering due to the discontinuous controller term. Computer simulations are presented to show the good performance of the controller. The controller detects the deviation of the actual trajectory from the reference trajectory and corresponding changes the switching strategy to restore the tracking. Prominent characteristics such as invariance, robustness, order reduction, and control chattering are discussed in detail. Methods for coping with chattering are presented. Both linear and nonlinear systems are considered The proposed concept can be implemented to adaptive control scheme for induction machine using Matlab/Simulink software. KEYWORDS: Grid-connected photovoltaic (PV) system, matching conditions, nonlinear controller, partial feedback linearzing scheme, structured uncertainty. Copyright © 2016 International Journal for Modern Trends in Science and Technology All rights reserved. I. INTRODUCTION The utilization of grid-connected photovoltaic (PV) systems is increasingly being pursued as a supplement and an alternative to the conventional fossil fuel generation in order to meet increasing energy demands and to limit the pollution of the environment caused by fuel emissions. The major concerns of integrating PV into the grid are stochastic behaviors of solar irradiations and interfacing of inverters with the grid. Because of the high initial investment, variations in solar irradiation, and reduced life-time of PV systems, as compared with the traditional energy sources, it is essential to extract maximum power from PV systems [1]. Maximum power point tracking (MPPT) techniques are widely used to extract maximum power from the PV system that is delivered to the grid through the inverter [2]–[4]. Recent improvements on MPPT can be seen in [5] and [6]. Interconnections among PV modules within a shaded PV field can affect the extraction of maximum power [7]. A study of all possible shading scenarios and interconnection schemes for a given PV field, to maximize the output power of PV array, is proposed in [7]. Inverters interfacing PV modules with the grid perform two major tasks—one is to ensure that PV modules are operated at maximum power point (MPP), and the other is to inject a sinusoidal current into the grid. In order to perform these tasks effectively, efficient stabilization or control schemes are essential. In a grid-connected ABSTRACT
  • 2. 39 International Journal for Modern Trends in Science and Technology Adaptive Control Scheme for PV Based Induction Machine PV system, control objectives are met by a strategy using a pulse width modulation (PWM) scheme based on two cascaded control loops [8]. The two cascaded control loops consist of an outer voltage control loop to settle the PV array at the MPP, and an inner current control loop to establish the duty ratio for the generation of a sinusoidal output current, which is in phase with the grid voltage [8]. The current loop is also responsible for power quality issues and current protection for which harmonic compensations and dynamics are the important properties of the current controller. Linear controllers such as proportional-integral (PI), hysteresis, and model predictive controllers are presented in [9]–[14], which provide satisfactory operation over a fixed set of operating points as the system is linearized at an equilibrium point. Since the PV source exhibits a strongly nonlinear electrical behavior due to the variation of solar irradiance and nonlinear switching functions of inverters. As linear controllers for nonlinear PV systems affects all the variables in the system and the electrical characteristics of the PV source are time varying, the system is not linearizable around a unique operating point or trajectory to achieve a good performance over a wide variation in atmospheric conditions. The restrictions of operating points can be solved by implementing nonlinear controllers for nonlinear PV systems. A sliding-mode current controller for a grid-connected PV system is proposed in [15], along with a new MPPT technique to provide robust tracking performances. In [15], the controller is designed based on a time-varying sliding surface. However, the selection of a time-varying surface is a difficult task, and the system stays confined to the sliding surface. Feedback linearization has been increasingly used for nonlinear controller design. It transforms the nonlinear system into a fully or partly linear equivalent by canceling nonlinearities. A feedback linearizing technique was first proposed in [16] for PV applications where a superfluous complex model of the inverter is considered to design the controller. To overcome the complexity, a simple and consistent inverter model is used in [17], and a feedback linearization technique is employed to operate the PV system at MPP. In [16] and [17], a feedback linearizing controller is designed by considering the dc-link voltage and quadrature-axis grid current as output functions. Power-balance relationships are considered to express the dynamics of the voltage across the dc-link capacitor. However, this relationship cannot capture nonlinear switching functions between inverter input and output; to accurately represent a grid-connected PV system but it is essential to consider these switching actions. The current relationship between the input and output of the inverter can be written in terms of switching functions rather than the power balance equation. Therefore, the voltage dynamics of the dc-link capacitor include nonlinearities due to the switching actions of the inverter. The inclusion of these nonlinearities in the model will improve the accuracy; however, the grid-connected PV system will be partially, rather than exactly, linearized, as presented in [18]. Although the approaches presented in [16]–[18] ensure MPP operation of the PV system, they do not account for inherent uncertainties in the system. In the design of both linear and nonlinear controllers for grid-connected PV systems, most of the difficulties stem from the analytical complexity of the dynamic model of a PV system, which, on one hand, exhibits a nonlinear parametric dependence on the PV array current–voltage characteristics varying with the irradiation and temperature levels and, on the other, a sinusoidal time dependence due to the grid connection of PV systems. These difficulties may lead to some barriers in developing a meaningful and realistic mathematical model. The mismatch between the mathematical model and true system may lead to serious stability problems for the system. Therefore, the designs of robust control strategies that consider the model uncertainties are of great importance to design nonlinear controllers. Variable structure control with sliding mode, or sliding-mode control is one of the effective nonlinear robust control approaches since it provides system dynamics with an invariance property to uncertainties once the system dynamics are controlled in the sliding mode. A sliding-mode controller for grid connected PV system is presented in [19] and [20] to achieve robust MPPT under uncertainties within the system model. With this control approach, the insensitivity of the controlled system to uncertainties exists in the sliding mode but not during the reaching phase, i.e., the system dynamic in the reaching phase is still influenced by uncertainties. A mini-max LQG technique is proposed in [21] to design a robust controller for the integration of PV generation into the grid where the higher order terms during the linearization is considered as the uncertainty. A feed forward mechanism is proposed in [22] to control the
  • 3. 40 International Journal for Modern Trends in Science and Technology Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST current and dc-link voltage and the robustness of this mechanism is analyzed through modal analysis. A robust fuzzy controlled PV inverter is presented in [23] for the stabilization of a grid connected PV system where the robustness is adopted by using the Taguchi-tuning algorithm. However, the main difficulties of the robustness algorithm, as presented in [21] [23], are the consideration of linearized PV system models that are unable to maintain the stability of the PV system over a wide changes in atmospheric conditions. Although there are some advances in the robust control of grid-connected PV systems, research into the robustness Fig. 1. Three-phase grid-connected PV system. analysis and the controller design of nonlinear uncertain PV systems remains an important and challenging area. Since the feedback linearization technique is widely used in the design of nonlinear controllers for power systems, this paper proposed the extension of the partial feedback linearizing scheme, as presented in [18], by considering uncertainties within the PV system model. In this paper, matching conditions are used to model the uncertainties in PV systems for given upper bounds on the modeling error, which include parametric and state-dependent uncertainties. These uncertainties are bounded in such a way that the proposed controller can guarantee the stability and enhance the performance for all possible perturbations within the given upper bounds of the modeling errors of nonlinear PV systems. The effectiveness of the proposed controller is tested and compared with that of a partial feedback linearizing controller without uncertainties, following changes in atmospheric conditions. II. PHOTOVOLTAIC SYSTEM MODEL The schematic diagram of a three-phase grid-connected PV system, which is the main focus of this paper, is shown in Fig. 1. The considered PV system consists of a PV array, a dc-link capacitor C, a three-phase inverter, a filter inductor L, and grid voltages ea, eb, ec. In this paper, the main aim is to control the voltage vdc (which is also the output voltage of PV array vpv) across the capacitor C and to make the input current in phase with grid voltage for unity power factor by means of appropriate control signals through the switches of the inverter. A. Photovoltaic Cell and Array Model: A PV cell is a simple p-n junction diode that converts the irradiation into electricity. Fig. 2 shows an equivalent circuit diagram of a PV cell that consists of a light generated current source IL, a parallel diode, a shunt resistance Rsh, and a series resistance Rs. In Fig. 2, ION is the diode current that can be written as (1) where α = qAkTC , k = 1.3807 × 10−23 JK−1 is the Boltzmann’s constant, q = 1.6022 × 10−19 C is the charge of electron, TC is the cell’s absolute working temperature in Kelvin, A is the p-n junction ideality factor whose value is between 1 and 5, Is is the saturation current, and vpv is the output voltage of the PV array which is also the voltage across C, i.e., vdc. Now, Fig. 2. Equivalent circuit diagram of the PV cell. Fig. 3. Equivalent circuit diagram of the PV array.
  • 4. 41 International Journal for Modern Trends in Science and Technology Adaptive Control Scheme for PV Based Induction Machine by applying Kirchhoff’s current law (KCL) in Fig. 2, the output current (ipv) generated by a PV cell can be written as (2) The light generated current IL depends on the solar irradiation that can be related by the following equation: (3) where Isc is the short-circuit current, s is the solar irradiation, ki is the cell’s short-circuit current coefficient, and Tref is the reference temperature of the cell. The cell’s saturation current Is varies with the temperature according to the following equation [17]: (4) Where Eg is the band gap energy of the semiconductor used in the reference temperature and solar irradiation. Since the output voltage of a PV cell is very low, a number of PV cells are connected together in series in order to obtain higher voltages. Then, they are encapsulated with glass, plastic, and other transparent materials to protect them from harsh environments and are called a PV module. To obtain the required voltage and power, a number of modules are connected in parallel to form a PV array. Fig. 3 shows an electrical equivalent circuit diagram of a PV array, where Ns is the number of cells in series, and Np is the number of modules in parallel. In this case, the array ipv can be written as (5) B. Three-Phase Grid-Connected Photovoltaic System ModelIn the state-space form, Fig. 1 can be represented through the following equations [17], [18]: (6) where Ka, Kb, and Kc are the input switching signals. Now, by applying KCL at the node where the dc link is connected, we obtain (7) However, the input current of the inverter idc can be written as [19] (8) which yields (9) The complete model of a three-phase grid-connected PV system can be presented by (6) and (9), which are nonlinear and time variant and can be converted into a time invariant model by applying dq transformation using the angular frequency (ω) of the grid, rotating the reference frame synchronized with grid where the d component of the grid voltage Ed is zero [17]. By using dq transformation, (6) and (9) can be written as (10) where Idq = Tabc dq iabc, edq = Tabc dq eabc, Kdq = Tabc dq Kabc. Equation (10) represents the complete mathematical model of a three-phase grid-connected PV system and this model is a nonlinear model due to the nonlinear behavior of the switching signals and the output current (ipv) of the PV array. The transformation matrix T dqabc
  • 5. 42 International Journal for Modern Trends in Science and Technology Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST can be written as (11) At this point of mathematical modeling, the key issue the selection of the current component that can be obtained from the power delivered into the grid. Since Ed = 0, the real power delivered to the grid can be written as (12) From (12), it can be seen that the maximum power delivery into the grid can be maintained by controlling the q component of the grid current, i.e., Iq . Based on this mathematical model, the overview of the partial feedback linearizing stabilization scheme is shown in the following section. III. OVERVIEW OF PARTIAL FEEDBACK LINEARIZING STABILIZATION SCHEME As the three-phase grid-connected PV system as represented by (10) has two control inputs (Kd and Kq) and two control outputs (Iq and vpv), the mathematical model can be represented by the following form of a nonlinear multi-input multi-output (MIMO) system (13) The partial feedback linearizing scheme transforms the nonlinear grid-connected PV system into a partially linearized PV system, and any linear controller design technique can be employed to obtain the linear control law for the partially linearized system. However, before obtaining a control law through partial feedback linearizing scheme, it is essential to ensure the partial feedback linearizability and internal dynamics stability of the PV system. The details of partial feedback linearizability and internal dynamics stability of the considered PV system are presented in [18] from where it can be seen that the PV system is partially linearized and that the internal dynamic of the PV systems is stable. The partially linearized PV system can be written (14) where z͂ represents the transformed states, and v represents the linear control inputs that are obtained through the PI design approach [18]. The nonlinear control law can be written as (15) Equation (15) is the final control law that is obtained through a partial feedback linearizing scheme, and the controller ensures the stability of the PV system for the considered nominal model and exact parameters of the system need to be known. However, in practice, it is very difficult to determine the exact parameters of the system. Thus, the considered partial feedback linearizing scheme is unable to maintain the stability of the PV system with changes in system conditions and the consideration of uncertainties within the PV system is necessary, which is shown in the following section. IV. UNCERTAINTY MODELING In a practical PV system, atmospheric conditions change continuously for which there exists a variation in cell working temperature, as well as in solar irradiance. Because of changes in atmospheric conditions, the output voltage, current, and power of the PV unit changes significantly. For example, if a single module of a series string is partially shaded, and then its output current will be reduced, which will change the operating point of the whole string. Since the amount of the PV generation depends on solar irradiation that is uncertain, there are uncertainties in ipv which in turn causes uncertainties in the current (in the dq-frame, Id and Iq ) injected into the grid. Moreover, as the values of the parameters used in the PV model are not exactly known, there are also parametric uncertainties. The PV system model as shown by (10) cannot capture these uncertainties. Therefore, it is essential to consider these uncertainties within the PV system model. In the presence of uncertainties, the nonlinear mathematical model of the three-phase grid-connected PV system, as
  • 6. 43 International Journal for Modern Trends in Science and Technology Adaptive Control Scheme for PV Based Induction Machine shown in (13), can be represented by the following equation: (16) The uncertainties need to be modeled in such a way that the controller will robustly stabilize the original system despite the uncertainties Δf(x) and Δg(x), i.e., the robust controller will attenuate the influence of system uncertainties. In order to achieve the control objective of robust stabilization, the structure of uncertainties and the locations of unknown parameters should satisfy the following conditions: (17) which is known as the matching condition [24]. If this matching condition holds, the following condition is true: (18) where r is the total relative degree of the nominal system, which is 2 [18], w is the relative degree of uncertainty Δg(x), and ρ is the relative degree of uncertainty Δf(x). In order to match the uncertainties with the PV system model, the relative degree of the uncertainty Δf should be 2 as it needs to equal to the relative degree of the nominal system in (10), which is 2. The relative degree of the uncertainty Δf can be calculated from the following equation: (19) If the relative degree of Δf corresponding to the outputs h1 and h2 is 1, then the total relative degree of Δf will be 2, which will happen if Δf1 and Δf3 are not equal to zero. To match the uncertainty Δg, the relative degree of Δg should be equal to or greater than the relative degree of the nominal system and will be 2 if the following conditions hold: (20) Where Δg11 must not be zero and either Δg31 or Δg32 can be zero, to match the uncertainty with the structure of the PV system. Since the proposed uncertainty modeling scheme considers the upper bound of the uncertainties, it is important to set these bounds, and the controller needs to be designed based on these bounds. If the maximum allowable changes in the system parameters is 30% and the variations in solar irradiation and environmental temperature are considered up to 80% of their nominal values. The partial feedback linearizing scheme as presented in [18] cannot stabilize the PV system appropriate if the aforementioned uncertainties are considered within the PV system model as the controller is designed to stabilize only the nominal system. However, in the robust partial feedback linearizing scheme, the aforementioned uncertainties need to be included to achieve the robust stabilization of the grid-connected PV system. The robust controller design by considering the aforementioned uncertainties within the grid-connected PV system model is shown in the following section. V. ROBUST CONTROLLER DESIGN This section aims the derivation of the robust control law that robustly stabilizes a grid-connected PV system with uncertainties whose structures are already discussed in the previous section. The following steps are followed to design the robust controller for a three-phase grid-connected PV system. 1) Step 1 (Partial feedback linearization of grid connected PV systems): In this case, the partial feedback linearization for the system with uncertainties, as shown by (16), can be obtained as For the PV system, the partially linearized system can written as
  • 7. 44 International Journal for Modern Trends in Science and Technology Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST (21) If v1 and v2 are linear control inputs for the aforementioned partially feedback linearized system, (21) can be written as (22) Which can be obtained using any linear control technique, and in this paper, two PI controllers are used. However, Fig. 4. Implementation block diagram. before designing and implementing the controller based on partial feedback linearizing scheme, it is essential to check the stability of the internal dynamics that is similar to that described in [18]. 2) Step 2 (Derivation of robust control law): From (22), the robust control law can be obtained as follows: (23) Equation (23) is the final robust control law for a three grid connected PV system, and the control law contains the modeled uncertainties. The main difference between the designed robust control law (23) and the control law (15) is the inclusion of uncertainties within the PV system model. The performance of the designed robust stabilization scheme is evaluated and compared in the following section with our previously published partial feedback linearizing scheme with no uncertainties [18]. The performance of the controller is evaluated in the following section. VI. INDUCTION MOTOR An induction motor is an example of asynchronous AC machine, which consists of a stator and a rotor. This motor is widely used because of its strong features and reasonable cost. A sinusoidal voltage is applied to the stator, in the induction motor, which results in an induced electromagnetic field. A current in the rotor is induced due to this field, which creates another field that tries to align with the stator field, causing the rotor to spin. A slip is created between these fields, when a load is applied to the motor. Compared to the synchronous speed, the rotor speed decreases, at higher slip values. The frequency of the stator voltage controls the synchronous speed. The frequency of the voltage is applied to the stator through power electronic devices, which allows the control of the speed of the motor. The research is using techniques, which implement a constant voltage to frequency ratio. Finally, the torque begins to fall when the motor reaches the synchronous speed. Thus, induction motor synchronous speed is defined by following equation, (24) Where f is the frequency of AC supply, n, is the speed of rotor; p is the number of poles per phase of the motor. By varying the frequency of control circuit through AC supply, the rotor speed will change. A. Control Strategy of Induction Motor Power electronics interface such as three-phase SPWM inverter using constant closed loop Volts l
  • 8. 45 International Journal for Modern Trends in Science and Technology Adaptive Control Scheme for PV Based Induction Machine Hertz control scheme is used to control the motor. According to the desired output speed, the amplitude and frequency of the reference (sinusoidal) signals will change. In order to maintain constant magnetic flux in the motor, the ratio of the voltage amplitude to voltage frequency will be kept constant. Hence a closed loop Proportional Integral (PI) controller is implemented to regulate the motor speed to the desired set point. The closed loop speed control is characterized by the measurement of the actual motor speed, which is compared to the reference speed while the error signal is generated. The magnitude and polarity of the error signal correspond to the difference between the actual and required speed. The PI controller generates the corrected motor stator frequency to compensate for the error, based on the speed error. VII. SIMULATION RESULTS Fig 5 Matlab/simulation circuit of Adaptive Control Scheme for Pv Based system Fig 6 Performance under standard atmospheric conditions (Blue line—grid voltage, red line—grid current with the RPFBLSS, and green line—grid current with the PFBLS) Fig 7 Performance under changing atmospheric conditions (Blue line—grid voltage, red line-grid current with the RPFBLSS, and green line—grid current with the PFBLS). Fig 8 Performance under a three-phase short-circuit fault (Red line—grid current with the RPFBLSS, and green line—grid current with the PFBLS). Fig 9 Matlab/simulation circuit of Adaptive Control Scheme for Pv Based system with Induction Motor Fig 10 simulation wave form of line output voltage with IM Fig 11 simulation wave form of line output current with IM Fig 12 simulation wave form of phase voltage with IM
  • 9. 46 International Journal for Modern Trends in Science and Technology Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST Fig 13 simulation wave form of stator current, speed and torque VIII. CONCLUSION In this paper, a robust stabilization scheme is considered by modeling the uncertainties of a three phase grid-connected PV system based on the satisfaction of matching conditions to ensure the operation of the system at unity power factor. In order to design the robust scheme, the partial feedback linearization approach is used, and with the designed scheme, only the upper bounds of the PV systems’ parameters and states need to be known rather than network parameters, system operating points, or nature of the faults. The resulting robust scheme enhances the overall stability of a three-phase grid connected PV system, considering admissible network uncertainties. Thus, this stabilization scheme has good robustness against the PV system parameter variations, irrespective of the network parameters and configuration. Future work will include the implementation of the proposed scheme on a Induction machine system to study the characteristics of speed, torque. REFERENCES [1] S. Jain and V. Agarwal, ―A single-stage grid connected inverter topology for solar PV systems with maximum power point tracking,‖ IEEE Trans. Power Electron., vol. 22, no. 5, pp. 1928–1940, Sep. 2007. [2] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, ―A review of single-phase grid-connected inverters for photovoltaic modules,‖ IEEE Trans. Ind. Appl., vol. 41, no. 5, pp. 1292–1306, Sep./Oct. 2005. [3] T. Esram and P. L. Chapman, ―Comparison of photovoltaic array maximum power point tracking techniques,‖ IEEE Trans. Energy Convers., vol. 22, no. 2, pp. 439–449, Jun. 2007. [4] I. Houssamo, F. Locment, and M. Sechilariu, ―Maximum power point tracking for photovoltaic power system: Development and experimental comparison of two algorithms,‖ Renewable Energy, vol. 35, no. 10, pp. 2381–2387, Oct. 2010. [5] U. Zimmermann and M. Edoff, ―A maximum power point tracker for long-term logging of PV module performance,‖ IEEE J. Photovoltaics, vol. 2, no. 1, pp. 47–55, Jan. 2012. [6] E. Koutroulis and F. Blaabjerg, ―A new technique for tracking the global maximum power point of PV arrays operating under partial-shading conditions,‖ IEEE J. Photovoltaics, vol. 2, no. 2, pp. 184 190, Apr. 2012. [7] L. F. L. Villa, D. Picault, B. Raison, S. Bacha, and A. Labonne, ―Maximizing the power output of partially shaded photovoltaic plants through optimization of the interconnections among its modules,‖ IEEE J. Photovoltaics, vol. 2, no. 2, pp. 154–163, Apr. 2012. [8] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, ―Overview of control and grid synchronization for distributed power generation systems,‖ IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1398–1409, Oct. 2006. [9] A. Kotsopoulos, J. L. Darte, and M. A. M. Hendrix, ―Predictive DC voltage control of single-phase PV inverters with small dc link capacitance,‖ in Proc. IEEE Int. Symp. Ind. Electron., Jun. 2003, pp. 793–797. [10]C. Meza, J. J. Negroni, D. Biel, and F. Guinjoan, ―Energy balance modeling and discrete control for single-phase grid connected PV central inverters,‖ IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2734–2743, Jul. 2008. [11]R. Kadri, J. P. Gaubert, and G. Champenois, ―An improved maximum power point tracking for photovoltaic grid-connected inverter based on voltage-oriented control,‖ IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 66–75, Jan. 2011. [12]J. Selvaraj and N. A. Rahim, ―Multilevel inverter for grid-connected PV system employing digital PI controller,‖ IEEE Trans. Ind. Electron., vol. 56, no. 1, pp. 149–158, Jan. 2009. [13]N. A. Rahim, J. Selvaraj, and C. C. Krismadinata, ―Hysteresis current control and sensorless MPPT for grid-connected photovoltaic systems,‖ in Proc. IEEE Int. Symp. Ind. Electron., 2007, pp. 572–577. [14]A. Kotsopoulos, J. L. Duarte, and M. A. M. Hendrix, ―A predictive control scheme for DC voltage and AC current in grid-connected photovoltaic inverters with minimum DC link capacitance,‖ in Proc. IEEE Ind. 27th Annu. Conf. Electron. Soc., 2001, pp. 1994–1999. [15]I. Kim, ―Sliding mode controller for the single-phase grid connected photovoltaic system,‖ Appl. Energy, vol. 83, pp. 1101 1115, 2006. [16]A. O. Zue and A. Chandra, ―State feedback linearization control of a grid connected photovoltaic interface with MPPT,‖ in Proc. IEEE Electr. Power Energy Conf., Oct. 2009. [17]D. Lalili, A. Mellit, N. Lourci, B. Medjahed, and E. M. Berkouk, ―Input output feedback linearization control and variable step size MPPT algorithm of a grid-connected photovoltaic inverter,‖ Renewable Energy, vol. 36, no. 12, pp. 3282–3291, Dec. 2011. [18]M. A. Mahmud, H. R. Pota, and M. J. Hossain, ―Dynamic stability of three-phase grid-connected photovoltaic system using zero dynamic design
  • 10. 47 International Journal for Modern Trends in Science and Technology Adaptive Control Scheme for PV Based Induction Machine approach,‖ IEEE J. Photovoltaics, vol. 2, no. 4, pp. 564–571, Oct. 2012. [19]I.-S. Kim, ―Robust maximum power point tracker using sliding mode controller for the three–phase grid–connected photovoltaic system,‖ Sol. Energy, vol. 81, no. 3, pp. 405–414, Mar. 2007. [20]C.-C. Chu and C.-L. Chen, ―Robust maximum power point tracking method for photovoltaic cells: A sliding mode control approach,‖ Sol. Energy, vol. 83, no. 8, pp. 1370–1378, Aug. 2009. [21]M. J. Hossain, T. K. Saha, N. Mithulananthan, and H. R. Pota, ―Robust control strategy for PV system integration in distribution systems,‖ Appl. Energy, vol. 99, pp. 355–362, Nov. 2012. [22]A. Yazdani and P. P. Dash, ―A control methodology and characterization of dynamics for a photovoltaic (PV) system interfaced with a distribution network,‖ IEEE Trans. Power Del., vol. 24, no. 3, pp. 1538–1551, Jul. 2009. [23]Y.-K. Chen, C.-H. Yang, and Y.-C. Wu, ―Robust fuzzy controlled photovoltaic power inverter with Taguchi method,‖ IEEE Trans. Aerosp. Electron. Syst., vol. 38, no. 3, pp. 940–954, Jul. 2002. [24] S. Behtash, ―Robust output tracking for nonlinear systems,‖ Int. J. Control, vol. 51, no. 6, pp. 1381–1407, 1990.