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Microcontroller based solar power system with grid synchronization
Conference Paper · November 2016
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Microcontroller based solar power system with
grid synchronization
Amish Chauhan
Enggenius, Vadodara
Gujarat, India
Chauhan_amish@yahoo.in
Anand Panchbhai
Dr. Hiren Shah
Enggenius, Vadodara
Gujarat, India
anand.panchbhai@yahoo.com
Abstract- Maximum power point tracking (MPPT) techniques
are employed in photovoltaic (PV) systems to make full
utilization of the PV array output power which depends on
solar irradiation and cell temperature. This paper proposes
simulation and hardware of a grid connected photovoltaic
system which is interfaced with the power system network
through a DC-DC boost converter. The maximum power
point tracking is achieved by using perturb and observe
algorithm having minimum converging iterations. The DCDC converter is operated in a closed loop mode for tracking
the reference voltage generated by the MPPT algorithm to
ensure maximum power extraction. The controlling of boost
converter and grid connected inverter is done with
microcontroller AT89S52. The performance of the
photovoltaic system is observed using MATLAB and then
implemented on hardware.
M S University of Baroda
Gujarat, India
microxpt@gmail.com
hardware implementation, sensors required, cost, and
implementation complexity. These methods are mostly
based on derivative calculation and are more sensitive to
signal fluctuations and sensor noise.
A PV system for grid connected application mainly
consists of five main components as shown in Fig.1. They
are;1)a PV array that converts solar energy into electrical
energy, 2) a DC-DC boost converter with MPPT, 3) an
inverter which converts dc voltage to single phase or three
phase ac voltage, 4) AT89S52 controller for maximum
power extraction algorithm and for inverter control, 5) a
filter that absorbs the harmonics generated by the system.
Keywords— AC-DC power converters, DC-DC power
converters, Inverters, AT89S52, MATLAB, Photovoltaic cells,
Solar energy
I.
INTRODUCTION
Solar Energy is being selected as one of the most
important source of energy because as opposed to the nonrenewable sources such as coal, gasoline etc. It is a clean,
inexhaustible and free source of energy. PV is the most upto-date technique to address the energy problems.
Initially, Photovoltaic generation was mainly used in
restricted applications such as remote areas where grid
power was inaccessible but nowadays grid connected
applications are used to reduce the energy demand from
grid, which saves the peak load demand with greater
efficiency. The power supplied by the solar cell varies with
irradiation level and the cell temperature. For a given
irradiation level and cell temperature maximum power is
supplied by the photovoltaic cell at a particular operating
point, that point is termed as Maximum Power Point
(MPP). This MPP varies with irradiance and temperature
therefore Maximum Power Point Tracking (MPPT)
techniques are used for extracting maximum power from
the system.
Mainly MPPT circuits are realized by means of switch
mode DC-DC converters used with Pulse Width
Modulation (PWM) techniques. There are various
techniques of MPPT such as Constant Voltage (CV), Open
Circuit Voltage, Short Circuit Current, Perturb and
Observe (P&O), Incremental Conductance (IC)
Temperature method. These techniques vary in many
aspects like PV array dependence, convergence speed,
978-1-4673-8962-4/16/$31.00 ©2016 IEEE
Fig.1 Block diagram of a photovoltaic system.
II.
MODELLING OF PV SYSTEM
A photovoltaic array is formed when large numbers of
Solar cells are connected in series or parallel or both. An
Equivalent model of a PV cell is formed by a p-n junction
Semiconductor, which produces current by photovoltaic
effect. An equivalent model of PV cell is shown in Fig.2.
Fig. 2 Equivalent model of PV cell
Fig 3(a) shows a comparison of the I-V and power
characteristics at different values of irradiance.
The PV output current is given by equation below,
I = Ipv − Io
Vt =
exp(V + RsI)
V + RsI
−1 −
Rp
Vta
(Ns ∗ K ∗ T)
q
(1)
(2)
Vt = thermal voltage of array,
Ns = number of cells connected in series,
T = cell temperature,
q = electron charge (1.60217646 x 10-19 C),
K = Boltzmann constant (1.3806503 x10-23 J/K),
a = ideality factor of diode (1 to 1.5),
The light generated current of PV cell depends linearly
on irradiance and is also influenced by temperature.
S
Ipv =
Ipvn + Ki(T − Tn)
(3)
Sn
III.
MAXIMUM POWER POINT TRACKING
(MPPT)
To maximize power produced by solar panels, a
Maximum power point tracking (MPPT) controller which
is an electronic system is used to track the maximum
power point of PV systems. A typical MPPT controller
consists of a DC-DC boost converter and a
microcontroller. The maximum power point (MPP) which
shown in Fig. 3(b) of a PV module can be detected by a
microcontroller which is driven by an MPPT algorithm.
Once the MPP is obtained, a triggering signal with a
specific duty cycle is generated and used to trigger the
boost converter switches in order to ensure that the
converter operates as close as possible to the PV MPP.
Ipv = light generated current at nominal condition (usually
25℃ and 1000 W/m2),
Tn = nominal temperature,
S = irradiance on device surface (W/m2),
Sn = nominal irradiance (W/m2),
Ki = temperature coefficient of short circuit current,
The diode saturation current Io and its dependence on
temperature is given by equation below :
qEg 1 1
Tn
exp
−
(4)
Io = Ion
aK Tn t
T
Ion =
Iscn
exp
−1
(5)
Eg = the band gap energy of semiconductor (Eg is 1.12eV
for polycrystalline at 25℃),
Ion = nominal saturation current,
Vtn = thermal voltage at nominal condition.
Using the above equations (1)-(5), an computation
program in MATLAB is developed for obtaining the
operating characteristics of the PV array. These
characteristics serve as a representation of PV array in
simulation.
Fig. 3(a) PV characteristics
978-1-4673-8962-4/16/$31.00 ©2016 IEEE
Fig.3 (b) Maximum Power Point
The perturb-and-observe method, also known as
perturbation method, is the most commonly used MPPT
algorithm in commercial PV products. The principle of
P&O is to create a perturbation by decreasing or increasing
the duty cycle of boost converter and then observing the
direction of change of PV output. If at any instant k, the
output PV power P(k) & voltage V(k) are greater than the
previous computed power P(k−1) & V(k-1), then the
direction of perturbation is maintained, otherwise it is
reversed. The flow chart of the P&O algorithm is shown in
Fig.4.
Fig.4 flow chart of P & O algorithm
The algorithm given in fig.4 is implemented in
MATLAB and its simulation shown in fig.5. The output of
MPPT algorithm is a PWM signal generated by comparing
the carrier power with the reference triangular waveform
shown in fig.6.
This PWM signal used for the switching of IGBT
(switch) of Boost converter, for extracting maximum
energy from panel.
By using the above formulae on a required voltage
level, the designed boost converter in MATLAB is shown
in fig.7.
Fig.7 Simulation of Boost converter
TABLE I
Fig.5MATLAB simulation of MPPT algorithm
Parameters used in above MATLAB simulation
Fig.6 Generated PWM signal from MPPT
IV.
DC-DC Boost converter
A DC-to-DC is an electronic circuit which converts a
one level of voltage value to the other level voltage values.
Parameter Selection for Boost converter for the required
output DC voltage is given by following formulae.
1) Selection of duty cycle according to Input and
Output Voltages :
V
D=1−
V
2) Selection Of Value Of Inductor :
The results of the simulation of DC-DC Boost
converter with MPPT is shown in Fig.8. In Fig.8 (a),
variation of the duty cycle is shown with respect to the
variation in solar power. As solar power decreases, duty
cycle increases to extract maximum power from solar
panel. In the same way as solar power increases, duty cycle
decreases to maintain the maximum power from the solar
panel. In fig.8(b), the output current and voltage of Boost
converter is shown.
(1 − D)
R
×
2
F
3) Selection of the value of capacitor:
L=
C=
D
F ×R ×
∆
Fig.8(a) Output of MPPTDuty cycle With Power
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Fig. 8(b)Output of boost Converter (I&V)
V.
C. GATE DRIVER
A gate driver is a power amplifier circuit that allows
the microcontroller to control the switching of inverter and
converter power electronics. Since the microcontroller
cannot generate enough current and voltage to drive the
power transistors, a gate driver will be used to amplify the
microcontroller signal. Here TLP250 IC is used as gate
driver shown in fig 9. The requirements for the gate driver
design will be determined by the maximum switching
frequency and by the power transistors gate input
requirements. With higher switching frequency or a larger
gate capacitance, a larger drive current is required.
GRID CONNECTED INVERTER
The DC/AC inverter will convert the DC power,
supplied by the DC/DC converter, to AC power. The
implementation of the inverter will consist of a DC-link
capacitor, power electronics switching circuit, and filter
and. Furthermore, control algorithms implemented in the
microcontroller will synchronize the inverter's output with
the grid signal. The power electronics circuit of the inverter
will have two inputs: one is output of DC-DC converter
and the other is a switching control signal generated by the
microcontroller.
A. FILTER
The output waveform from the power electronics
circuit is rich with harmonic components. Therefore, to
obtain a clean sinusoidal waveform the output must be
filtered. A filter will be designed such that the total
harmonic distortion injected into the grid is less than 5%.
The filter circuit will be simulated in MATLAB Simulink
software. Then, based on the simulation results, circuit
components will be further optimized if necessary.
B. GRID SYNCHRONIZATION
Frequency, voltage and phase of the inverter output
signal must be synchronized with the waveform of the grid.
First, a Phase Locked Loop (PLL) algorithm will be used
to synchronize the inverter output frequency with the grid
signal. Second, a Proportional Integral Derivative (PID)
controller will be used to continuously adjust the voltage
and phase of the inverter output to match the grid. In
addition, the PID controller will be responsible for
adjusting the reactive output power to the desired level.
Both the PLL algorithm and the PID controller will be
implemented in the microcontroller. But in this paper,
output of inverter is synchronized with grid in term of
frequency only by detecting the zero crossing of grid and
then switching of switches of inverter using SPWM control
technique.
978-1-4673-8962-4/16/$31.00 ©2016 IEEE
Fig.9 Gate driver circuit for MOSFET & IGBT
Fig.10 shows the MATLAB simulation of whole
system with 3 major parts, 1) DC-DC converter with
MPPT, 2) DC-AC inverter, 3) Grid synchronization.
Fig. 10 MATLAB simulation of whole system
D. INVERTER TOPOLOGY
The most commonly used inverter topology is a fullbridge or H-bridge inverter which is built with four
switches. The conversion of DC to AC is achieved by
using a switching mechanism that directs current through
the load in both the positive and negative directions. As a
consequence, a pulse width modulated (PWM) signal with
an amplitude equivalent to the DC input source is
generated at the output terminals of the inverter.
TABLE II
Switching of Inverter topology
E. SWITCH SELECTION
There are two types of switches considered for the Hbridge inverter: Metal-Oxide-Semiconductor Field-Effect
Transistors (MOSFETS) and Insulated-Gate Bipolar
Transistors (IGBTs).
IGBTs tend to be used in very high voltage
applications, nearly always above 200V, and generally
above 600V. They do not have the high frequency
switching capability of MOSFETs, and tend to be used at
frequencies lower than 20kHz and have very good thermal
operating ability, being able to operate properly above 100
Celsius.
MOSFETS have a much higher switching frequency
capability than IGBTs, and can be switched at frequencies
higher than 200 kHz. They do not have as much capability
for high voltage and high current applications, and tend to
be used at voltages lower than 250V and less than 500W.
In this paper, MOSFETs are used as we are not working
with large power ratings
VI.
Fig. 12 Gate driver interfaced with 8051 for INVERTER
Fig. 13 Full hardware with LCD display
MICROCONTROLLER-AT89S52
The 8052 microcontroller(8-bit) with its high capability
of control using Boolean processor operates on single bits
(210 bit-addressable locations), four basic Input/output
ports (P0,P1,P2 and P3) and three internal 16-bit timers
(TMR0, TMR1, TMR2) is used as a base unit. 8052 used
for MPPT implementation and switching of inverter
switches shown in Fig. 11 & Fig. 12 respectively.The gate
pulses for six IRF840 MOSFETs are generated with the
help of AT89S52 microcontroller.
Fig. 11 ADC0809 interfaced with 8051 for MPPT
978-1-4673-8962-4/16/$31.00 ©2016 IEEE
Fig. 14 Hardware
VII.
RESULTS ANALYSIS
Fig. 15 Gate signals for S1 & S4
Fig. 16 Gate signals for S1 & S3
Fig. 20 Zero crossing detection of voltage (grid matching)
VIII.
Fig. 17 Dead band between switching of S1 & S3
This paper presents that the interfacing of solar power
with grid taking frequency into consideration. The
maximum power of the PV cell is tracked with an adjusted
P&O MPPT algorithm based on Boost DC/DC converter.
A DC/AC inverter has been used to connect the PV cell to
the grid and regulate the output voltage of DC/DC
converter. The whole photovoltaic grid-connected system
is simulated in MATLAB/Simulink. Special situations
such as sudden change of temperature and solar radiation
have been simulated and analyzed.
IX.
Fig. 18 Inverter waveform (without grid synchronization)
Fig. 19 Inverter waveform (with grid synchronization)
978-1-4673-8962-4/16/$31.00 ©2016 IEEE
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CONCLUSION
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