International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016
A NOVEL METHOD TO EXTRACT
MAXIMUM POWER FROM SOLAR PANEL OF
A GRID CONNECTED PHOTOTVOLTAIC
SYSTEM USING PHASE ANGLE CONTROL
AND HYSTERESIS CURRENT CONTROL
Devika Menon M.K
Department of Electrical and Electronics Engineering
devika.menon@christuniversity.in
Abstract- Categorized as one of the renewable energies,
photovoltaic (PV) system has great potential due to the
availability of the sun in most part of the world. This project
proposes a high performance, single stage single phase inverter
topology for grid connected PV systems. The proposed
configuration converts the solar panel’s dc power into high
quality ac power for feeding into mains, while tracking maximum
power from the PV array. The power transferred to the mains is
controlled by using two different control strategies viz phase
angle control and current control. At the same time the THD of
inverter output voltage will have the values as specified by IEEE
standards for grid interconnection and the frequency of
generated inverter output voltage is synchronized with the grid
frequency.
certain applications, grid connected PV systems usually
employ two stages to appropriately condition the available
solar power for feeding into the grid. While the first stage is
used to boost the PV array voltage and track the maximum
solar power, the second stage inverts this dc power into high
quality ac power. Typically, the first stage comprises of a
boost or buck-boost type dc–dc converter topology. Such twostage configurations are time tested and work well, but have
drawbacks such as lower efficiency, lower reliability, higher
cost and larger size. This can be overcome by going for a
single power electronic stage between the PV array and the
grid to achieve all the functions namely the electrical MPPT
and inversion leading to a compact system.
Keywords—current control; phase angle control; PV system; THD.
Such compact systems are also in line with the modern
day need to have highly integrated systems built into modules
having high reliability, high performance (e.g., intelligence,
protection, low electromagnetic interference (EMI), etc.),
reduced weight and low cost . Lesser is the number of (power)
stages, easier is the module integration required. Single phase
inverter which is used as an interface between PV module and
grid in such a system has to control various parameters like
frequency, voltage, current, active and reactive power etc.
Sinusoidal pulse width modulation technique and hysteresis
current control technique are the two different control
strategies adapted in this project work to control the above
mentioned parameters.
I. INTRODUCTION
Recently, there are many researches about the alternate
energy sources with the increase of the concern about the
global environment protection and the demand for the
pollution-free natural energy. Especially, the solar energy is
one of the positive choices. Solar Photovoltaic (PV) cells
convert the light energy from the sun to electrical energy.
Many PV cells are connected in series and parallel to rise the
output voltage and current and thus the output power. Solar
PV systems can either be stand-alone or connected to utility
grid.
High initial investment and limited life span of a
photovoltaic (PV) array makes it necessary for the user to
extract maximum power from the PV system. The nonlinear i–
v characteristics of the PV array [1] and the rotation and
revolution of the earth around the sun, further necessitate the
application of maximum power point tracking (MPPT) [2] to
any PV system that can either be stand alone or grid
connected. In this context, grid connected PV systems have
become very popular because they do not need battery backups whereas stand-alone systems need suitable battery backups. Though, multistage systems [1] have been reported for
978-1-4673-9939-5/16/$31.00 ©2016 IEEE
II. NEED FOR MAXIMUM POWER POINT TRACKING
FROM A PV ARRAY
The maximum power extracted from PV array depends
strongly on three factors namely irradiance, load impedance
and cell temperature assuming fixed cell efficiency. When a
PV system is directly connected to the load, the system will
operate at the intersection of I-V curve and load line, which
can be far from maximum power point (MPP). So PV array
must be oversized to meet the load requirements and hence it
makes the entire system expensive. As the cost per watt of a
solar PV system ie very high, the power generated has to be
harnessed so as to make the system cost effective.To
overcome this problem, a switched mode power converter
called maximum power point tracker (MPPT) can be used to
maintain the PV array’s operating point at MPP. The MPPT
does this by controlling array’s voltage and current
independently of the load. MPP production is therefore based
on the load-line adjustment under varying atmospheric
conditions as shown in the figure 1 below.
Figure 1: Operating point of PV array for different load
conditions.
The variation of the output I-V characteristics of
commercial P-V module as a function of temperature and
irradiance shows that the temperature changes mainly affect
the output voltage, while the irradiation changes affect the P-V
output current. Nevertheless, PV systems should be designed
to operate at their maximum output power levels for any
temperature and solar irradiation levels at all times. Another
significant factor which determines the PV power is the
impedance of the load. However, the load impedance is not
constant. To adapt the load resistance to PV modules and to
extract maximum power from them, the duty cycle is set to its
optimal value which corresponds to its optimal operating point
MPP. Thus the tracker can maintain the operating point under
all conditions to lie on the maximum power point.
III.
TWO STAGE TOPOLOGY APPROACH FOR
MAXIMUM POWER POINT TRACKING IN GRID
CONNECTED P-V SYSTEM.
The maximum power point is obtained by introducing a
dc/dc converter in between the load and solar PV module. The
duty cycle ‘D’ of the converter is changed till maximum
power point is obtained. The output impedance Ro remains
constant and by changing the duty cycle the input-impedance
seen by the source changes. So the impedance
Ri
corresponding to the maximum power point is obtained by
changing the duty cycle. Consider a step down converter, the
output voltage is given by the expression given below
VO=D*Vi
(1)
Where Vo is the output voltage and Vi is the input voltage and
D is the duty ratio.
Solving for the impedance transfer ratio gives
(2)
Ri = Ro/D2
Where R0 is the load impedance and Ri is the input impedance
as seen by the source and D is the duty ratio. For a step up
converter the above relation becomes
Ri = Ro(1- D2)
(3)
and for up down converter the above relation becomes
Ri= R0(1-D)2 /D2.
(4)
Where R0 is the load impedance and Ri is the input
impedance as seen by the source and D is the duty ratio. Thus
it is understood that by including a dc-dc converter between
the panel and load maximum power is delivered to the load
under all possible conditions of ambient/load conditions by
varying the duty ratio of the converter.
Now question arises how to vary the duty cycle and in
which direction so that maximum power point is reached.
Whether manual tracking or automatic tracking? Manual
tracking is not possible. So automatic tracking is preferred to
manual tracking. An automatic tracking can be performed by
utilizing various control algorithms as shown in the figure 2.
The commonly used MPPT control algorithms are [4]
(a)Perturb and observe (P&O)
(b)Incremental conductance (INC)
(c)Parasitic capacitance (PC)
(d)Constant voltage (CV)
Figure 2: Two stage topology for maximum power point
tracking in a grid connected PV system.
In the two stage topology maximum power point tracking
and DC/AC conversion is achieved in two separate stages. The
makes the whole system expensive and the overall losses
associated will be more. To overcome this a single stage
topology is proposed in this paper where in dc to ac
conversion and maximum power point tracking is achieved in
one stage.
IV. SINGLE STAGE TOPOLOGY APPROACH FOR
MAXIMUM POWER POINT TRACKING IN GRID
CONNECTED P.V SYSTEM.
The most important design constraints of a PV system are
low mass and size, high efficiency and better reliability.
Selection of single stage topology for the proposed grid
connected photovoltaic system (PV) as shown in the figure 3
below ensures all these factors.
Figure 3: Single stage topology for maximum power point
tracking in a grid connected PV system.
Simulations of all the selected control strategies for
MPPT as well as power control were done in MATLABSIMULINK to evaluate the performance of proposed system.
The selected control strategies for this project were (i). Phase
angle control (ii) Hysteresis current control .
IV. CONTROL ALGORITHM
The single phase inverter in the proposed grid connected
photovoltaic system is expected to do the following controls
like active power delivered, maintaining the power factor, the
output frequency to be the same as that of the grid and finally
the MPPT. In this paper two different control strategies are
taken up for implementation, which are phase angle control
and hysteresis current control.
Phase Angle Control - Consider a system shown in the figure
below
Figure 4: system with inverter and grid.
The equivalent circuit and its phasor diagram
showing the phase shift δ is as shown below in the figure 4
and figure 5 respectively.
Figure 5: Phasor diagram showing the phase shift δ.
But the power flow changes are more sensitive to δ than
Vinv. Thus it is decided to choose δ as the control parameter
for varying the power flow. The phase angle δ controls active
and reactive power between two sources. Every time the
updation of δ is done, the power delivered by the inverter is
also updated. The updation of δ can be done in every cycle,
but in this project it updated once in every five cycles, because
the typical insolation change on the PV panel will be in
seconds whereas the five cycle time period is in milliseconds.
As δ is selected as the control parameter it is to be
estimated accurately depending on the available power from
the PV panel, which necessitates accurate measurement of the
available power. The measurement of power to be delivered
can be done at two points viz., the output of the PV panels,
output of the inverter. If the calculations are carried out on the
DC side it will be tedious, because it is only the instantaneous
power which is continuously varying. So, the averaging is
moved to the output of the inverter.
The average power at nth instant (Pn) is first measured and
after introducing an updation of δ, the average power is
measured at n+1thinstant (Pn+1) . The difference between Pn
and Pn+1decides whether the power delivered to be increased
from the present value or decreased. Accordingly the direction
and the magnitude of δ decided. This algorithm continues
until the power delivered is equal to the maximum power
available i.e. Pn is equal to Pn+1. A PLL which senses the grid
voltage generates a unit sine wave signal in phase with the
grid voltage having the same frequency as that of grid. Phase
angle δ which is obtained as mentioned above is added to the
unit sine wave, thus generating the reference signal for the
PWM generator. This reference signal will have a frequency
equal to the grid frequency and is phase shifted by a value of δ
decided by the amount of power available from the PV
module. A LC filter is used after single stage inverter to
remove the harmonics at switching frequencies or multiples of
switching frequencies.
The algorithm for implementing MPPT using phase angle
control in a single stage grid connected PV system is as shown
below in figure 6. The block diagram for implementing
maximum power point tracking using phase angle control is
shown below in the figure 7.
Hysteresis current control - In this system current injected
from the inverter is made in phase with the grid voltage using
hysteresis current controller. Here Iref is selected as the control
parameter to control active and reactive power between two
sources. Every time the updation of Iref is done, the power
delivered by the inverter is also updated. The updation of Iref
can be done in every cycle, but in this project it updated once
in every five cycles, because the typical insolation change on
the PV panel will be in seconds whereas the five cycle time
period is in milliseconds.
As Iref is chosen as the control parameter it is to be estimated
accurately depending on the available power from the PV
panel, which necessitates accurate measurement of the
available power. The measurement of power to be delivered
can be done at two points viz., the output of the PV panels,
output of the inverter. If the calculations are carried out on the
DC side it will be tedious, because it is only the instantaneous
power which is continuously varying. So, the averaging is
moved to the output of the inverter. The average power at nth
instant (Pn) is first measured and after introducing an updation
of δ, the average power is measured at n+1thinstant (Pn+1) .
The difference between Pn and Pn+1decides whether the power
delivered is to be increased from the present value or
decreased. Accordingly the direction and the magnitude of Iref
decided. This algorithm continues until the power delivered is
equal to the maximum power available i.e. Pn is equal to
Pn+1.
A PLL which senses the grid voltage generates a unit sine
wave signal in phase with the grid voltage having the same
frequency as that of grid. Reference current Iref which is
obtained as mentioned above is multiplied to the unit sine
wave, thus generating the reference signal for the Hysteresis
current controller which is having a predefined hysteresis
band. Hysteresis controller compares reference current and
actual current with in hysteresis band and gives switching
pulses for the inverter which always injects a current in phase
with grid voltage. The algorithm for implementing maximum
power point tracking using hysteresis current control is as
shown in the flow chart of figure 7 given below.
Figure7:Algorithm for implementing hysteresis current
control.
Figure 6: Algorithm to implement MPPT using phase
angle control
Figure 7: Block diagram representation for implementing
MPPT using phase angle control
The block diagram for implementing MPPT using hysteresis
current control is as shown in the figure 8 given below.
Figure 8: Block diagram representation for implementing
MPPT using hysteresis current control.
IV. SIMULATION RESULTS.
Phase Angle Control – (i) Unit sine wave having the grid
frequency of 50Hz generated by PLL is as shown in the figure
9 below.
Figure 9: Unit sine wave generated by PLL at grid frequency
of 50Hz.
(ii) Variation of phase angle to track maximum power from
PV array is as shown in the figure 10 below.
Figure 11: Current THD at PCC.
Hysteresis current control- (i) Waveforms of actual and
reference current is as shown in the figure 12 below.
Figure 12: Waveforms of actual and reference current.
Figure 10: Variation of phase angle to track maximum power
from PV array.
(iii) Inverter and grid voltage is as shown in the figure 11
given below.
(ii) Variation of reference current to track maximum power
from PV panel is as shown in the figure 12 below.
Figure 11: Inverter and grid voltage.
(iv) Current THD at PCC (6.5%) is as shown in the figure 12
given below.
Figure 13:Variation of reference current to track maximum
power from PV array.
(iii) Current THD at PCC- The current THD at PCC is 0.5%
as shown in figure 14 below.
other at PCC in phase angle control strategy discussed in the
paper. For achieving upf current controller is implemented
with same power rating. For hysteresis band of ±0.5A the
switching frequency observed was 22 KHz. The current and
voltage were found in phase with each other and hence
reactive power delivered was observed to be zero. The novel
method discussed in this paper to extract maximum power
from a grid connected photovoltaic system has law losses and
hence more efficient since conversion of dc supply from solar
panel to ac as well as maximum power point tracking is
achieved in single stage.
VI. REFERENCES
[1] Achary, B.S.; Mishra, S.; Kumar, A., "Real time hardware
in loop testing of single phase grid connected PV system," in
Power Systems Conference (NPSC), 2014 Eighteenth National
, vol., no., pp.1-6, 18-20 Dec. 2014
[2] Ding Li; Feng Gao; Poh Chiang Loh; Peng Wang; Yi Tang,
Figure 14: Current THD at PCC
(iv)Voltage THD at PCC –The voltage THD at PCC is 0.02%
as shown in the figure 15 below.
"Transient maximum power point tracking for single-stage
grid-tied inverter," in Energy Conversion Congress and
Exposition, 2009. ECCE 2009. IEEE , vol., no., pp.313-318,
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[3] Zhigang Liang; Rong Guo; Huang, A., "A new cost-
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[4] Kang-Hoon Koh; Ju-Sung Kang; Doo-Sung Hong; HyunWoo Lee; Matsui, M., "Analysis and Design of Simple Limit
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[5] Shuai Jiang; Dong Cao; Peng, F.Z.; Yuan Li, "Grid-
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Figure 15: Voltage THD at PCC.
V. CONCLUSION
Grid connected photovoltaic system is designed and
system validation is done using MATLAB simulation. The
current THD at PCC observed in phase angle control is 6.5%
and the voltage THD and the current THD observed at PCC in
hysteresis current control are 0.02% and 0.5% respectively.
The current and voltage were found not in phase with each
Analysis of a Grid-Connected Photovoltaic Power System," in
Power Electronics, IEEE Transactions on , vol.25, no.4,
pp.992-1000, April 2010
[7] Murtaza, A.F.; Sher, H.A.; Chiaberge, M.; Boero, D.; De
Giuseppe, M.; Addoweesh, K.E., "Comparative analysis of
maximum power point tracking techniques for PV
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[8] El Aamri, F.; Maker, H.; Mouhsen, A.; Harmouchi, M., "A
new MPPT using Gradient Method for grid-connected PV
inverter," in Renewable and Sustainable Energy Conference
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Oct. 2014.
Devika Menon M.K received B.Tech degree from Kerala Univerity
in 2009 and M.Tech from Amritha University in 2011. Currently she
is working as Assistant Professor in the department of electrical and
electronics engineering at Christ University Faculty Of Engineering ,
Bengaluru. Her research areas are power electronics, control systems,
renewable energy and power quality.