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Graduation Project

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Alaa Mekky

on 18 August 2014

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Transcript of Graduation Project

PV System with Pure Sine Wave Inverter

Presented by
Alaa Ahmed Mekky
Mohamed Ahmed Ameen
Eslam Ahmed Aly
Saleh Mirghany
Abdullrahman Ghanem

Supervised by
Dr. Mohamed Al-Harouny
Dr. Ahmed Hamdy

Grid PV System:
PV Cell
Solar panel electricity systems, also known as solar photovoltaic (PV), capture the sun's energy using photovoltaic cells.
A PV cell is a device that directly converts the energy in light into electrical energy through the process of photovoltaic.
These cells don't need direct sunlight to work – they can still generate some electricity on a cloudy day.
PV Cells Structure
How it Works
A solar cell is an electronic device which directly converts sunlight into electricity.
Light shining on the solar cell produces both a current and a voltage to generate electric power.

This Process requires:
A material in which the absorption of light raises an electron to a higher energy state,
The movement of this higher energy electron from the solar cell into an external circuit.
The electron then dissipates its energy in the external circuit and returns to the solar cell.

In practice nearly all photovoltaic energy conversion uses semiconductor materials in the form of a p-n junction
Types of Photovoltaic - PV Cells
PV cells are manufactured from a variety of different types of materials. The most significant is crystalline silicon.
There are 4 main types of commercially available cells
- Mono-Crystalline Silicon PV
- Poly-Crystalline Silicon PV
- Amorphous Silicon PV
- Hybrid PV

Mono-Crystalline Silicon PV
To produce mono-crystalline silicon a crystal of silicon is grown from highly pure molten silicon.
Poly-Crystalline Silicon PV
Polycrystalline silicon is also produced from a molten and highly pure molten silicon, but using a casting process.
Amorphous "Thin Film" PV
Amorphous silicon is non-crystalline silicon. Cells made from this material are found in pocket calculators
Hybrid PV
Hybrid photovoltaic cells are classified as PV cells that use two different types of PV technology. It comprises a mono-crystalline PV cell covered by an ultra-thin amorphous silicon PV layer.
Comparison Between PV Cells Types
Charge Controller
A charge controller is used to maintain the proper charging voltage on the batteries.As the input voltage from the solar array rises, the charge controller regulates the charge to the batteries preventing any overcharging.
Multi-Stage Charge Controllers
Most quality charge controller units have what is known as a 3 stage charge cycle that goes like this:
- Bulk
- Absorption
- Float
Maximum Power Point Tracking - MPPT
They match the output of the solar panels to the battery voltage to insure maximum charge "amps".


The Charge Controller is installed between the Solar Panel array and the Batteries where it automatically maintains the charge on the batteries using the 3 stage charge cycle just described.
Multi-Stage Charge Controllers
Storage Batteries
They are the fuel tank solar power system. Without batteries to store energy you would only have power when the sun was shining or the generator was running
Power Inverter
The function of the power inverter is to efficiently transform the DC power coming from the PV system to a high voltage AC source, similar to power that would be available at an electrical wall outlet.
Inverting circuit
The method, in which the low voltage DC power is inverted, is completed in two steps:
The First: the conversion of the low voltage DC power to a high voltage DC source.
The Second step being the conversion of the high DC source to an AC waveform using sinusoidal pulse width modulation.
Inverting Circuit
Another method to complete the desired outcome would be, also in two steps
The First: convert the low voltage DC power to AC.
The Second: use a transformer to boost the voltage up to 220 volts.
DC/AC inverters on the market today are essentially two different forms of AC output generated
Modified sine wave
Pure sine wave
Problem is
High quality inverters combined with high efficiency exists, though it is often at a high monetary cost.
The high end pure sine wave inverters tend to incorporate very expensive, high power capable digital components.
The modified sine wave units can be very efficient, as there is not much processing being performed on the output waveform, but this results in a waveform with a high number of harmonics, which can affect sensitive equipment such as medical monitors.
Our Goal
Our goal is to fill a niche which seems to be lacking in the power inverters market, one for a fairly efficient, inexpensive inverter with a pure sine wave output.
These inverters differ in their outputs, providing varying levels of efficiency and distortion that can affect electronic devices in different ways.
Basic Block diagram
Control circuit
Sinusoidal Pulse Width Modulation - SPWM
In electronic power converters and motors, PWM is used extensively as a means of powering alternating current (AC) devices with an available direct current (DC) source or for advanced DC/AC conversion.
Variation of duty cycle in the PWM signal to provide a DC voltage across the load in a specific pattern will appear to the load as an AC signal.
The pattern at which the duty cycle of a SPWM signal varies can be created through simple analog components, or a digital micro-controller.
Control circuit
Sinusoidal Pulse Width Modulation - SPWM
Control circuit
Sinusoidal Pulse Width Modulation - SPWM
Analog SPWM control
Analog SPWM control requires the generation of both reference and carrier signals that feed into a comparator which creates output signals based on the difference between the signals.
The reference signal is sinusoidal and at the frequency of the desired output signal, while the carrier signal is often either a triangular wave at a frequency significantly greater than the reference.
Digital SPWM control
Digital SPWM control requires only a digital microcontroller, such as PIC16F877A used in this project.
In order to source an output with a SPWM signal, transistor or other switching technologies are used to connect the source to the load when the signal is high or low.
Full or half bridge configurations are common switching schemes used in power electronics.
Control circuit
Sinusoidal Pulse Width Modulation - SPWM
Advantages of SPWM
Low power consumption.
High energy efficient up to 90%.
High power handling capability.
No temperature variation-and ageing-caused drifting or degradation in linearity.
Easy to implement and control.
Compatible with today’s digital microprocessors.
Control circuit
Sinusoidal Pulse Width Modulation - SPWM
Bubba Oscillator
The Bubba Oscillator is a circuit that provides a filtered sine wave of any frequency the user desires based upon the configuration of resistors and capacitors in the circuit.
Why ?!
It offers a few features that other oscillators cannot, the biggest factor is that the frequency stability holds while still giving a low distortion output.
Control circuit
Sinusoidal Pulse Width Modulation - SPWM
Digital Microcontroller
It is an Embedded System used to control non-digital electronic systems.
Switching Circuit
H-Bridge Configuration
An H-Bridge or full bridge converter is a switching configuration composed of four switches in an arrangement that resembles an H shape.
By controlling different switches in the bridge, a positive, negative, or zero potential voltage can be placed across a load.
Driving Circuit
MOSFET Drivers
When utilizing N-Channel MOSFETs to switch a DC voltage across a load, the drain terminals of the high side MOSFETs are often connected to the highest voltage in the system.
This creates a difficulty, as the gate terminal must be approximately 10V higher than the drain terminal for the MOSFET to conduct.
integrated circuit devices known as MOSFET drivers are utilized to achieve this difference through charge pumps or bootstrapping techniques.
Voltage amplification
Step up Transformer
A transformer is a device that converts one AC voltage to another AC voltage at the same frequency.
Step up transformers are used to step up the AC voltage coming from the H-Bridge to the desired level.
Voltage amplification
Step up Transformer
Despite the widely use of power transformers in DC to AC inverters, they have some very annoying
disadvantages
such as:
Bulky size: As we're operating in low frequency, and with high power, the transformer size would be relatively large.
Limited efficiency: From 50% to 90% according to loads.
Need cooling.
Due to these disadvantages, we will use another technique to amplify the voltage,
The DC converter
.
Voltage amplification
DC Boost Converter
A DC Boost Converter is a type of power converters which converts a source of Direct Current (DC) from one voltage level to another, by storing the input energy momentarily and then releasing that energy to the output at a different voltage.
The storage should be in electric field storage components or in magnetic field storage components.
There are three basic types of converter:
- Buck Converter
- Boost Converter
- Buck-Boost Converter
Voltage amplification
DC Boost Converter
we used a DC Boost Converter to successfully amplify PV arrays voltage into the required level.
This power converter is controlled by Pulse Width Modulation (PWM) and applied through transistor.
To achieve desired output from power converter, the duty cycle of the PWM should be large.
Voltage amplification
DC Boost Converter
The DC Boost Converter is used to convert the 12 VDC coming from the batteries to a 340 VDC to feed the H-Bridge.
Advantages of using DC Boost Converter
Small size compared to power transformer.
Higher efficiency.
PV System Block Diagram
Methodology and Implementation
The following sections detail each specific part of the project as well as how each section is constructed and interacts with other blocks to result in the production of a 220V pure sine wave power inverter.
Inverter Block Diagram
DC Boost Converter
In boost regulator the output voltage is greater than the input voltage-hence the name of the converter is "Boost".
DC Boost Converter
When Switch is ON
DC Boost Converter
Current Path with MOSFET OFF
DC Boost Converter
Current Path with MOSFET ON
SPWM Using Micro-controller
In our inverter we need to generate SPWM from MCU, but in fact the MCU does not generate SPWM directly, it generates normal PWM, and we've to adjust the frequency and duty cycle the PWM signal to obtain SPWM, and this is the outcome of our code.
Flow Chart
Output of the micro-controller
H-Bridge and Drivers
Generating a sine wave centered on zero volts requires both a positive and negative voltage across the load, for the positive and negative parts of the wave, respectively.
This can be achieved from a single source through the use of four MOSFET switches arranged in an H-Bridge configuration.
H-Bridge
H-Bridge and Drivers
H-Bridge
There are four possible switch positions that can be used to obtain voltages across the load. These positions are outlined in next Table
H-Bridge and Drivers
H-Bridge
The use of P-Channel MOSFETs on the high side and N-Channel MOSFETs on the low side is easier, but using all N-Channel MOSFETs and a FET driver, lower "on" resistance can be obtained resulting in reduced power loss.

BUT
, The use of all N-Channel MOSFETs requires a driver, in order to turn on a high side N-Channel MOSFET, there must be a voltage higher than the switching voltage.
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