The Inverter system is an electrical system which accepts direct current (DC) as input and produces alternating current (AC) of appropriate voltage, frequency and phase as an output. The reliability of power company electricity service varies greatly due to many factors including the design of the power grid, protective features, power system maintenance practices and severe weather. This project aims to design a 1.5KVA inverter system with RF remote control using Pulse Width Modulation (PWM) switching scheme to supply AC utilities with emergency power and a frequency control. The system is also designed to automatically switch over to charging mode when the battery goes below a threshold value of 11v and to stop charging above a threshold value of 13.6V. The frequency control circuit maintains the operation frequency at 50hz even when the frequency tends to shift as a result of low battery. This feat is achieved using the LM741 IC which continually checks the voltage level of the battery and subsequently react accordingly by either switching off the inverter to recharge the battery or continue supplying the inverter.

TABLE OF CONTENTS
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
TABLE OF CONTENT
CHAPTER ONE
1.1       PROJECT BACKGROUND
1.2       PROBLEM STATEMENT
1.3       METHODOLOGY
1.4       OBJECTIVE OF THE PROJECT    
1.5       SIGNIFICANCE OF THE PROJECT
1.6       SCOPE OF THE PROJECT
1.7       PROJECT JUSTIFICATION
CHAPTER TWO
2.1     LITERATURE REVIEW
2.1       CONCEPT
2.2   METHOD/TOOLS USED FOR THE WORK
CHAPTER THREE
3.1     MODELLING
3.2       METHOD OF ANALYSIS
3.3      TOOLS APPLICATION
3.4       ANALYSIS/SIMULATION
CHAPTER FOUR
RESULT ANALYSIS
4.1       RESULT        
4.2       DISCUSSION
CHAPTER FIVE     
5.1       CONCLUSION
5.2       SUGGESTION
5.3       RECOMMENDATION
5.4       REFERENCES

 

CHAPTER ONE
1.1                                        BACKGROUND OF THE PROJECT
An inverter is an electrical power converter that changes direct current (DC) to alternating current (AC) [1]. It performs the opposite function of a rectifier which converts AC to DC. The inverter system has several electronic stages such as the oscillator, the amplifier, the switching and the transformer stages which work together to achieve the desired AC output. These stages of the inverter systems are so designed to produce output with the desired frequency, phase and voltage which are compatible with that required in household appliances and in industries.
Generally, Inverters are classified as the Voltage Source Inverter (VSI) and the Current Source Inverter (CSI)[2]. The Voltage Source Inverter (VSI) has the following characteristics: the input voltage to the inverter is constant, the voltage cannot reverse but the current can while in Current Source Inverter (CSI), the input current to the inverter remain constant and the input voltage can reverse, but the current cannot. Constant reliable electric power should be an integral part of everyday life whether at home or in the office as sudden power failure disrupts our daily activities.
Short term solution of power disruption could be addressed through this project work.
The system embraces the use of electronic means to generate electricity. It involves the conversion of direct current (DC) source from the battery to alternating current (AC) that can be used to power our house, offices, hospital, banks etc. This system also incorporates an AC to DC converter which serves as a charging system, responsible for recharging the batteries when they go below a threshold value of 11V
In work a modified sine wave type of inverter was constructed, the waveform in commercially available modified-sine-wave inverters is a square wave with a pause before the polarity transition, which only needs to cycle through a three-position switch that outputs forward, off, and reverse output at the pre-determined frequency. The peak voltage to RMS voltage does not maintain the same relationship as for a sine wave. The DC bus voltage may be actively regulated or the "on" and "off" times can be modified to maintain the same RMS value output up to the DC bus voltage to compensate for DC bus voltage variation.
The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a constant frequency with a technique called PWM. Harmonic spectrum in the output depends on the width of the pulses and the modulation frequency. When operating induction motors, voltage harmonics is not of great concern, however harmonic distortion in the current waveform introduces additional heating, and can produce pulsating torques.
Most AC motors will run on MSW inverters with an efficiency reduction of about 20% due to the harmonic content.

1.2                            PROBLEMS STATEMENT OF THE PROJECT

• Expensive when compared to traditional generators and other types of inverter because of the additional functions added to it, that is, remote control and frequency control circuits.
• There are no large capacity inverter in the markets
• The inverter can power a few appliances for a short period

1.3                                                DESIGN METHODOLOGY
The overall method employed in the design of this inverter system is the “push-pull” method of inverter design. This method involves the use of a “center-tapped” transformer, a pulse width modulated (PWM) sine wave source and the two banks of MOSFETs containing five (5) MOSFETs in each bank as it is the case with this design. The push-pull mechanism is the situation whereby one bank of the MOSFETs allows the passage of current through them upon receiving a gating signal from the oscillator while the other bank remains redundant for a period of time; this conduction state of the MOSFETs are reversed automatically to the other redundant MOSFETs bank at the frequency of 50Hz thereby supplying the transformer with the desired alternating input (12V AC). The transformer steps-up this 12V AC input supplied from the output of the MOSFETs to 230V AC at the same frequency of 50Hz.
The method used in actualizing the oscillatory unit of the project is the pulse width modulation techniques. This technique is made possible in this project by the use of a custom made integrated circuit (IC) chip SG3524N which when energized with a direct current of 5V to 24V, will output the alternating current (AC) equivalent of the supplied input but of lower amplitude. The output of this oscillatory unit otherwise called the “gating signal” is now used to bias the gate of the MOSFETs in each bank. The method used in the transformer winding is the centre-taped winding method. This method involves the winding of the primary side of the transformer with the 12V -0 -12V AC ratio while that of the secondary side is 240V AC.
This implies that the center tap of the of the primary side of the transformer with respect to the any of its side tapings will give the output of 12V while the side tapings of the both sides will give the output of 24V.
The system is also designed to automatically switch over to charging mode when the battery goes below a threshold value of 11v and to stop charging above a threshold value of 13.6V.

These modules are coupled with the encoder and decoder IC for a proper transmission and reception of signal which is used in controlling the switch relay. The frequency control circuit maintains the operation frequency at 50hz even when the frequency tends to shift as a result of low battery. The frequency controlled circuit is set with a variable resistor.

1.4                                           OBJECTIVE OF THE PROJECT

Specific objectives of this project are as follows:
1.         To design and construct a circuit that converts dc power to an ac power for various appliances used in laboratories, theatres and rural areas that is rated 1.5kva.
2.         To provide a noiseless source of electricity generation and also power with low maintenance cost and zero fuel cost
3.         To have a source of generating electricity that has no negative effect on the environment.
4.         To design an automatic battery charging system capable of recharging the battery source when it goes below a threshold value 0f 11V.
5.         To design a  frequency control circuit that maintains the operation frequency at 50hz even when the frequency tends to shift as a result of low battery.

1.5                                     SIGNIFICANCE OF THE PROJECT
In the recent years,  power  inverter has become a major power source due to its environmental and economic benefits and proven reliability. Since the solar power system does not have moving parts, virtually it does not require any kind of maintenance once installed.
Power inverter is produced by connecting the device on the 12VDC battery as the input to produce 230VAC as the required output. It can also be connected to solar panel.
Second, the whole energy conversion process is environmentally friendly. It produces no noise, harmful emissions or polluting gases. The burning of natural resources for energy can create smoke, cause acid rain and pollute water and air. Carbon dioxide, CO2, a leading greenhouse gas, is also produced in the case of burning fuels. Power inverter uses only the power of the battery as its fuel. It creates no harmful by-product and contributes actively to the reduction of global warming.
The system is also designed to automatically switch over to charging mode when the battery goes below a threshold value of 11v and to stop charging above a threshold value of 13.6V.

1.6                                              SCOPE OF THE PROJECT
A power inverter is a power conversion device. It converts fixed direct current (DC) voltage to frequency sinusoidal alternating current (AC) voltage output.
Power inverters are used to power and control the speed, torque, acceleration, deceleration, and direction of the motor. The use of inverter has become prevalent in wide range of industrial applications; from motion control applications to ventilation systems, waste water processing facilities to machining areas, and many others. Though power inverters offer lower operating costs and higher efficiency, they are not without their problems.
The frequency control circuit maintains the operation frequency at 50hz even when the frequency tends to shift as a result of low battery.
This inverter system is designed in such a way that it can be operated manually using a switch.

1.7                                      PROJECT JUSTIFICATION

Inverter will be of immense importance to all people in an area where there is irregular supply of electricity by way of serving as a substitute to power supply of electricity from big generating plants. The device is relatively reliable, risk free, portable, and cheap compared to other means of power generation.

The design and construction of a 1.5KVA inverter which converts 12Vdc from a battery to 230Vac, 1.5KVA output which can be used to power essential circuits such as computers, surgical equipments, security doors, home appliances e.t.c.  Also the integration of the wireless control to the system adds automation to it and reduces the stress involved in manual switching of the inverter.

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