Design And Construction Of A 7.5KVA Pure Sinewave Power Inverter System

1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
An inverter converts DC power to standard AC power. Inverters are used to operate electrical equipment from the power produced by a car or boat battery or renewable energy sources, like solar panels or wind turbines. DC power is what batteries store, while AC power is what most electrical appliances need to run so an inverter is necessary to convert the power into a usable form. For example, when a cell phone is plugged into a car cigarette lighter to recharge, it supplies DC power; this must be converted to the required AC power by a power inverter to charge the phone. There are different types of inverters with different sine wave, but in this work we are focusing on the pure sine wave type of inverter.
In pure sine-wave, the output voltage of a sine-wave inverter has a sine wave-form like the sine wave-form of the mains / utility voltage. In a sine wave, the voltage rises and falls smoothly with a smoothly changing phase angle and also changes its polarity instantly when it crosses 0 Volts.
Sine wave inverters are used to operate sensitive electronic devices that require high quality waveform with little harmonic distortion. In addition, they have high surge capacity which means they are able to exceed their rated wattage for a limited time. This enables power motors to start easily which can draw up to seven times their rated wattage during start up. Virtually any electronic device will operate with the output from a pure sine wave inverter.
Sine wave inverter has the following characteristics:
1. High efficiency
2. Low standby losses
3. High surge capacity
4. Low harmonic distortion
To get a sinusoidal alternating current from the output of our transformer, we have to apply a sinusoidal current to the input. For this we need an oscillator. An amplifying transistor can be made to oscillate by feeding some of the amplified output back to its input as positive feedback. The positive feedback in an electronic circuit can be tuned using extra components to produce the frequency we require (generally either 50 or 60 cycles per second to mimic mains electricity).

1.2 STATEMENT OF PROBLEM
Electricity is the major source of power for country’s most of the economic activities. But in our country Nigeria, we have been suffering due to electricity crisis for a long time. To reduce this problem, there are some alternative ways which can help in this purpose. But among all of the methods using an inverter which can be powered with solar energy or battery system may be an easy and effective one especially in the rural areas where the electricity has not reached yet.
This solar energy is a renewable energy which is inefficiently exploited. The importance of solar energy is that it’s free, clean and with very high potentials in the future [2]. Photovoltaic systems (PV) are used to convert the solar energy into electrical energy using photovoltaic panels which can then be used into domestic electrical applications.
An important piece of solar power supply is the DC to AC inverter which converts the DC voltage from a battery to an AC voltage that is necessary to operate electronic components. Due to the delicate nature of this equipment, an inverter which is capable of producing a pure sine wave is necessary to avoid noise and wear on delicate and expensive gear. Many of these devices are very expensive so it is the goal of this project to design a DC/AC inverter capable of producing a pure sine wave for use with domestic equipment. In this project, pure wave inverter circuit was designed that can supply an electrical load of up to 4.8kilo-watts was implemented and realized.

1.3 AIM AND OBJECTIVES
The main aim of this project is to design an inverter that can be derived by 12V battery and can be used to operate AC loads while minimizing the conventional inverter cost and complexity using Microcontroller. The system’s objectives are;
• Generation of a pure sine wave signal from a solar panel reducing the dependency on the fossil fuels and limited energy source .
• Reduction of circuit’s complexity by using micro-controller to generate modulating signal.
• To provide a noiseless source of electricity generation.
• To have a source of generating electricity that has no negative effect on the environment (i.e. no greenhouse effect).

1.4 PROJECT MOTIVATION
Pure sine wave Inverters are the best when it comes to back-up since they can come up very fast and they generate little or no noise unlike generator. Even in an area with constant power supply, power outage due to natural cause and faults are usually unannounced. It is therefore very important to prevent causalities and loss of goodwill by having a reliable back-up power installed.

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.
Power inverter is produced by connecting the device on the 24VDC battery as the input to produce 220VAC 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.

1.6 SCOPE OF THE PROJECT
The scope of this work focused on building a conversion device. It converts fixed direct current (DC) voltage to 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. In this work, application of sinusoidal pulse width modulation (SPWM) technique was used to generate sine wave output.

1.7 PURPOSE OF THIS WORK
The purpose of this work is to design an electrical device that converts direct current (DC) to alternating current (AC); the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits. The output of this work produces a sine wave-form of the mains / utility voltage which is rated 500W which can be powered from the source of 12V battery.

1.8 SIGNIFICANCE OF THE PROJECT
• Some electronic devices may pick up inverter noise while operating with modified sine waveform. Using fluorescent lighting can be problematic when using modified sine wave inverters. Most of the equipment on the market is designed for use with sine waves. Some appliances, such as microwaves, drills, clocks or speed motors will not produce full output if they don’t use sine wave current, moreover they may damage the equipment. Some loads, such as light dimmers will not work without sine wave at all. It’s safe to say any electronic device that requires sensitive calibration can only be used with pure sine wave inverters
• Pure Sine Wave output is the most compatible AC power from an inverter, and it is the best waveform for all AC electrical appliances.
• Pure Sine Wave output eliminates interference, noise, and overheating.
• Reduces audible and electrical noise in fans, fluorescent lights, electronics gear and magnetic circuit breakers.
• Prevents glitches and noise in monitoring equipment.
• It can be efficiently electronically protected from overload, over voltage, under voltage, and over temperature conditions.
• Inductive loads like microwave ovens and variable-speed motors operate properly, quieter and cooler. Some appliances will not produce full output if they do not use Pure Sine Wave power.
• Some appliances, such as variable speed drills and bread makers, will not work properly without Pure Sine Wave power.

1.9 LIMITATION OF THE PROJECT
• More expensive than Modified Sine Wave power inverters. Physically larger than their Modified Sine Wave counterparts.
• The built-in circuit becomes far more complex due to multiple conversions from AC (Alternating Current) to DC (Direct Current) and back to AC (Alternating Current). 3-DC, 4-D or All DC inverter ACs have even more conversions taking place as there are more components working on DC.
• Repair costs increase as components are more sophisticated and as a result, more expensive. They require more effort to build or repair.
• Response Time: The inverter shall respond to any line voltage variation in 1/2 cycle while operating linear or non-linear loads, with a load power factor of 0.60 of unity. Peak detection of the voltage sine wave shall not be permitted to avoid inaccurate tap switching due to input voltage distortion.
• Operating Frequency: The inverter shall be capable of operating at +10% to -15% of the nominal frequency, 50Hz.
• Rating: this device shall be rated at 7.5KVA.
• Access Requirements: The inverter shall have removable panels on the front, rear and sides as required for ease of maintenance and/or repair.
• Metering: An input meter is provided to display line voltages.
• Ventilation: The inverter isolation transformer shall be designed for convection cooling. Fan cooling is required for the MOSFET used.

1.10 PROJECT WORK ORGANISATION
The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:
Chapter one of this works is on the introduction to pure sine wave power inverter. In this chapter, the background, significance, objective limitation and problem of pure sine wave power inverter were discussed.
Chapter two is on literature review of pure sine wave power inverter. In this chapter, all the literature pertaining to this work was reviewed.
Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.
Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.
Chapter five is on conclusion, recommendation and references.