Analysis and design of grid connected photovoltaic systems

2. ABSTRACT
In this paper describes the architecture of multiple-integrated converter
modules sharing an unfolding full-bridge inverter with a pseudo dc link (MIPs) is
proposed for grid-connected photovoltaic systems in this paper. The proposed
configuration can improve the power conversion, the control circuit complexity,
and the cost competitiveness. The proposed MIP is composed of distributed
flyback dc–dc converters (DFCs) and an unfolding full-bridge inverter with an ac
filter.
The DFCs can eliminate the shading effect by using the individual
maximum power point tracking. In conventional flyback-type single-phase
utility-interactive inverters, discontinuous conduction mode and boundary
conduction mode are popular because of the inherent constant current-source
characteristics more desirable for grid connection and of the simple procedures
for the controller design.

3. However, the operating mode suffers from a large current stress of the
circuit components, which leads to the low power efficiency. To avoid this, the
DFCs operate under continuous conduction mode that allows reduced current
stresses and increased power efficiency, as well as low material cost.
The current control loop of the converters employs primary-side
regulation contributing to improvement of dynamics as well as the cost reduction
significantly due to the elimination of the high-linearity photo coupler device.
Development of a new dc-current loop that maintains the level of dc-current
injection into the grid within the levels stipulated will be dealt as well. The
performance validation of the proposed design is confirmed by experimental
results.

4. INTRODUCTION
The Maximum Power Point Tracker (MPPT) is needed to optimize the
amount of power obtained from the photovoltaic array to the power supply. The
output of a solar module is characterized by a performance curve of voltage
versus current, called the I-V curve. See Figure 1. The maximum power point of a
solar module is the point along the I-V curve that corresponds to the maximum
output power possible for the module. This value can be determined by finding
the maximum area under the current versus voltage curve.
The objective of the project is to design a Maximum Power Point Tracking
(MPPT) charge collecter which operate with photovoltaic module and produce
maximum power to solar power collector. This component optimized the amount
of power obtained from the photovoltaic array and charged the power supply.

5. The maximum power point tracker (MPPT) is now prevalent in grid-tied PV
power systems and is becoming more popular in stand-alone systems. It should not be
confused with sun trackers, mechanical devices that rotate and/or tilt PV modules in the
direction of sun. MPPT is a power electronic device interconnecting a PV power source and
a load, maximizes the power output from a PV module or array with varying operating
conditions, and therefore maximizes the system efficiency. MPPT is made up with a
switch-mode DC-DC converter and a controller. For grid-tied systems, a switch-mode
inverter sometimes fills the role of MPPT. Otherwise, it is combined with a DC-DC
converter that performs the MPPT function.
In addition to MPPT, the system could also employ a sun tracker. According to
the data in reference, the single-axis sun tracker can collect about 40% more energy than a
seasonally optimized fixed-axis collector in summer in a dry climate. In winter, however, it
can gain only 20% more energy. The effect of sun tracker is smaller because a larger fraction
of solar irradiation is diffuse. It collects 30% more energy in summer, but the gain is less
than 10% in winter.

6. HOW DOES IT WORK?
The inputs of the MPPT consisted of the photovoltaic voltage and current
outputs. The adjusted voltage and current output of the MPPT charges the
power supply. See Figure.
A microcontroller was utilized to regulate the integrated circuits (ICs) and
calculate the maximum power point, given the output from the solar array.
Hardware and software integration was necessary for the completion of this
component.

7. LITERATURE SURVEY
1. T. V. Thang, N. M. Thao, Jong-Ho Jang, and Joung-Hu Park, Senior
Member, IEEE “Analysis and Design of Grid-Connected Photovoltaic
Systems With Multiple-Integrated Converters and a Pseudo-DC-Link
Inverter:” IEEE Transactions On Industrial Electronics, VOL. 61, NO. 7,
JULY 2014.
2. P.Dhandayuthabaani*, M.Hemalatha*, V.Gowtham*, M.Suresh, “An
Improved Flyback Inverter for Photovoltaic Applications”
International Journal of Advanced Research in Electrical, Electronics
and Instrumentation Engineering, Vol. 4, Issue 3, March 2015.
3. Ali Ajami, Hossein Ardi, and Amir Farakhor, “A Novel High Step-up
DC/DC Converter Based on Integrating Coupled Inductor and
Switched-Capacitor Techniques for Renewable Energy Applications”,
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 30, NO. 8,
AUGUST 2015.

8. EXISTING SYSTEM
Existing system described an procedure to design a sliding controller for the
PV system, which drives the PV voltage to follow a reference provided by an
external MPPT algorithm.
System used high power components so overall efficiency increased.
The combination of the input capacitor current and the PV voltage error had
occurred.
The control system obtained in the sliding analysis indicated that a low-pass
pre-filter had to be inserted between the MPPT module and the controller
input, so that the usually large power was consumed and dissipated power
increased.
The controller parameters were calculated by solving a nonlinear set of
equations.

9. PROPOSED SYSTEM
In this paper, small-signal analysis and design guidelines of a MIP with a
CCM flyback converter and an unfolding full bridge inverter have been proposed.
A desirable feature of the work is the material-cost reduction from a new
architecture of the dc-link multi module structure with the current and from a
new analog-circuited dc-rejection controller.
The output has two loads first one CFL bulb operates in AC and second
one DC water pump motor has been used. The analog-circuited MPPT
performance of the hardware prototype was mostly over 99%. Another issue is dc-
current injection. To overcome the problem, a dc-rejection circuit that introduces
a current reference waveform based on measurement of the dc component at grid
current has been proposed.
As a result, a dc-rejection circuit is applied to the MIP circuit, using
costly persuasive devices. The proposed scheme achieves an acceptable dc-current
level at the output of the MPPT system.

10. Proposed Block Diagram

11. Circuit Diagram

12. DESCRIPTION
The input of our design MPPT system is the DC power supply
from the solar panel. The output of this system is the output voltage to the
load supplying 80 W to the DC motor. The power that is harvested from
solar panel is maximized using the MPPT system by using P&O
algorithm. Basically, to have the maximum power transfer to the load, an
impedance matching circuit design is required. Hence, our overall design
can be divided into four simple stages as shown. The input solar panel is
fed into the MPPT system and impedance matching to have the desired
output at the load.

13. 1.INVERTER
Most standard appliances are designed to accept only AC
(alternating current) voltages because that's how electricity is supplied from
the grid. In order to run an electronic device from a DC (direct current)
source you obviously need to transform it into AC. A device that converts
electricity from DC form to AC form using electronic circuits is known in
power industry as inverter. Note that the same term is used in digital
electronics for a circuit that switches the logic level of a signal.
To avoid confusion, the device we are talking about is a power
inverter. Its typical application is to convert a battery voltage into
conventional residential AC.
Inverters are used in a wide variety of applications from small car
adapters to large grid-tie systems that can supply electricity to an entire
home.

14. 2.BUCK AND BOOST CONVERTER
A buck converter is a step-down DC to DC converter. Its design is
similar to the step-up boost converter, and like the boost converter it is a
switched-mode power supply that uses two switches (a transistor and a diode), an
inductor and a capacitor. The operation of the buck converter is fairly simple,
with an inductor and two switches (usually a transistor and a diode) that
control the inductor.
It alternates between connecting the inductor to source voltage to store energy in
the inductor and discharging the inductor into the load. For the purposes of
analysis it is useful to consider an idealised buck converter. In the idealised
converter all the components are considered to be perfect.
Specifically the switch and the diode have zero voltage drop when on
and zero current flow when off and the inductor has zero series resistance.
Further it is assumed that the input and output voltages do not change over the
course of a cycle (this would imply the output capacitance being infinitely large).

15. INVERTOR AND BUCK BOOST
CONVERTOR

16. 3.KA3525 PULSE WIDTH MODULATOR
The KA3525 regulating pulse width modulator contains all of the
control circuit necessary to implement switching regulators of either polarity
transformer coupled DC to DC converters, transformer less polarity converters
and voltage doublers, as well as other power control applications. This device
includes a 5V voltage regulator capable of supplying up to 50mA to external
circuit, a control amplifier, an oscillator, a pulse width modulator, a phase
splitting flip-flop.
FEATURES
Complete PWM power control circuit
Operation beyond 100KHz
2% frequency stability with temperature
Total quiescent current less than 10mA
Single ended or push-pull outputs
Current limit amplifier provides external component protection
On-chip protection against excessive junction temperature

17. COMPARISION: MPPT vs NON-MPPT

18. CONCLUSION
In order to charge a power source at its maximum efficiency, a
Maximum Power Point Tracker (MPPT) device is utilized. The MPPT design
incorporated three systems – the Voltage Divider, Buck convertor, Solar
Charging Unit, and Solar Array Protection. Although the final MPPT
completely function as planned, so Maximum Power Point voltage was
obtained. As the project came to an end, various changes could have been
made which could benefit the design and implementation process. A smaller
output range of the solar array would have helped to design a more efficient
MPPT. Many problems with the component purchasing and software were
encountered.

19. FUTURE WORK
The non-renewable energy is running out nowadays, such as fossil
fuels are depleting on earth. Therefore, changing to renewable energy source
is a necessity. Solar energy will be the choice and it is easily acquired.
However, most solar panel has low efficiency, so the MPPT system will help
maximizing the power absorbed from the solar panel. Fast-switching
components are necessary to operate the device intended for solar
applications. The component choice is key in the design of the MPPT. High
power efficiency is attained by carefully researching and selected the right
components.

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