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DESIGN AND CONSTRUCTION OF A 10KVA PURE SINEWAVE POWER INVERTER SYSTEM

 

ABSTRACT

This project is titled the design and construction of a pure sine wave inverter system. Pure sine wave inverters produce a pure sine wave output.  This means the power output from a pure sine wave inverter is the same as the mains supply.

What you may not know is that not all inverters are created equal. The output from many inverters is a modified sine wave, inferior to the 220 volt mains power supply. Pure sine wave inverters produce a pure sine wave output.

A pure sine wave is not only critical for the correct functioning of high end electronic equipment, it will also ensure that appliances run more smoothly, producing less heat and noise.
Pure sinewave inverter take up 12v DC from battery and inverts it to an output of 220v, 50H2 AC. It makes no noise during operation and no hazardous carbon monoxide is generated in the surrounding.   
This is a feature that makes it safe to use any where when compared to generator. Also, the circuit is capable of charging the battery (i.e 12v source) when the power from the supply authority is on. This greatly reduces the cost of operation of the system. 

TABLE OF CONTENTS
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
TABLE OF CONTENT

CHAPTER ONE
1.0      INTRODUCTION
1.1      OBJECTIVE OF THE PROJECT
1.2      PURPOSE OF THE PROJECT
1.3     SIGNIFICANCE OF THE PROJECT
1.4      LIMITATION OF THE PROJECT
1.5      PROBLEM OF THE PROJECT
1.6      APPLICATION OF THE PROJECT
1.7      INVERTER RATING
1.8      IMPORTANT CONSIDERATION OF INVERTER
1.9      DIFFERENCE BETWEEN CONVENTIONAL GENERATOR AND INVERTER

CHAPTER TWO
2.0     LITERATURE REVIEW
2.1      HISTORITICAL BACKGROUND OF AN INVERTER
2.2         TYPES OF INVERTER
2.3          SATETY OF INVERTER
2.4      INVERTER CAPACITY
2.5      REVIEW OF EARLY INVERTERS
2.6      HOW TO CHOOSE AN INVERTER
CHAPTER THREE
3.0     CONSTRUCTION
3.1      BASIC DESIGNS OF A PURE SINE WAVE
3.2      BLOCK DIAGRAM OF THE SYSTEM
3.3      DESCRIPTION OF PURE SINE WAVE INVERTER UNITS
3.4      SYSTEM CIRCUIT DIAGRAM
3.5      CIRCUIT OPERATION
3.6      DESCRIPTION OF COMPONENTS USED
3.7      HOW TO CHOOSE THE BEST INVERTER BATTERY

CHAPTER FOUR
RESULT ANALYSIS
4.0      CONSTRUCTION PROCEDURE AND TESTING
4.1      CASING AND PACKAGING
4.2      ASSEMBLING OF SECTIONS
4.3      TESTING OF SYSTEM OPERATION
4.4      COST ANALYSIS
CHAPTER FIVE     
5.0      CONCLUSION
5.1      RECOMMENDATION
5.2      REFERENCES

 

CHAPTER ONE
1.0                                                      INTRODUCTION
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:

  • High efficiency
  • Low standby losses
  • High surge capacity
  • 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                                            OBJECTIVE OF THE STUDY
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. The objective of this project is to design and construct a to design a device that will produce a sine wave-form of the mains / utility voltage which is rated  10KW which can be powered from the source of 12V battery.

1.2                                                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 10kW which can be powered from the source of 12V battery.

1.3                          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.

1.4                                         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 10KVA.
  • 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.

1.5                                              PROBLEM OF THE PROJECT
Battery Under/Over-Charge: Every battery has its charge/discharge cycle. A permanently under-charged or over-charged battery cannot maintain its rated lifespan. Many of the modern days intelligent Inverters have over-discharge cut-off sensor that ensures that the batteries are not unduly over-charged or discharged. However, some of the cheap Inverters in the market are not equipped with this intelligent device, which causes the batteries to boil when over-charged or cause suffation to set up when the batteries are over-discharged and are not constantly kept at full charge. For batteries to serve their stated lifespan successfully without premature failure, they must be maintained at full or near full charge at all times.
Another thing to consider is that, batteries must not be over-discharged. In-fact, batteries are not expected to be discharged below 0.5 per cell, i.e. for a 12V battery, minimum voltage to discharge the battery must be around 10.8V. Once it is below this, most intelligent Inverters will begin to beep to alert that the battery is low and after sometimes shut itself down completely to prevent damaging the battery. At this point, it must be fully re-charged before use, even if the machine fails to shut itself down.
Over-Load: Basically, most domestic or industrial Inverters are designed for light loads- such as lighting, electronics appliances, and fan. Heavy high wattage equipment, like refrigerators, heating appliances, ovens, Air conditioners and pumping machine are not practically suitable for Inverters. While many of these appliances draw very heavy current from the battery causing it to run down quickly, they can also be too heavy for the capacity of the Inverter, causing it to shutdown under over-load condition or even burn the machine. When calculating the loads to be connected to the Inverter, the total demand load must not exceed the rating of the Inverter. Consideration must also be made to the difference between the Wattage rating of the appliances normally written on the name plate and the KVA rating of the Inverter. Since there is a difference between (Kilowatt (KW) Volt Ampere (VA) and Kilovolt Ampere (KVA), and most of the appliances are rated in KW while most Inverters are either rated in VA or KVA, some mathematical conversion has to be done to arrive at the actual capacity of the machine.

Wiring Circuit and Cable Sizing: While it is true that any road side technician can buy any Inverter sold in the market place and connect it, as long as it is seen to be working, care must be taken to the theoretical calculations involved in cable sizing for a particular installation and how the machine is connected to the load and the supply source. Wrong cable size is a potential fire disaster, loose termination and wrong wiring is another accident waiting to happen. Most fire incidents in homes and industries are caused by loose termination or wrong cable sizing.

Capacitor wear: The first reason for inverter failure is electro-mechanical wear on capacitors. Inverters rely on capacitors to provide a smooth power output at varying levels of current; however electrolytic capacitors have a limited lifespan and age faster than dry components. This in itself can be a cause of inverter failure.
Overuse: Using inverters beyond their operating limit, either by choice or due to oversight or lack of knowledge, can contribute to inverter bridge failure. Using any component at a rating higher than its operating limit will decrease its lifespan and lead to failure, so avoiding this issue simply comes down to checking that all inverters are being run correctly.
Ultrasonic vibrations: The final problem on the list is one that contributes to the mechanical stress placed on an inverter. Ultrasonic vibrations originating in the cores of inductive components cause friction, adding to the unwanted heat generated by the device and further damaging components in the inverter.

1.6                                       APPLICATION OF THE PROJECT
This study exposes me the applications and uses of a pure sine wave inverter which are as follows:
DC power source utilization
Inverter designed to provide 240 VAC from the 12 VDC source provided in an automobile. The unit shown provides more than 20 amperes of alternating current, or enough to power up to 10KW load.
An inverter converts the DC electricity from sources such as batteries, solar panels, or fuel cells to AC electricity. The electricity can be at any required voltage; in particular it can operate AC equipment designed for mains operation, or rectified to produce DC at any desired voltage.
Uninterruptible power supplies
An uninterruptible power supply (UPS) uses batteries and an inverter to supply AC power when main power is not available. When main power is restored, a rectifier supplies DC power to recharge the batteries.
Induction heating
Pure Sine wave Inverters convert low frequency main AC power to higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power.
HVDC power transmission
With HVDC power transmission, AC power is rectified and high voltage DC power is transmitted to another location. At the receiving location, an inverter in a static inverter plant converts the power back to AC. The inverter must be synchronized with grid frequency and phase and minimize harmonic generation.
Variable-frequency drives
A variable-frequency drive controls the operating speed of an AC motor by controlling the frequency and voltage of the power supplied to the motor. An inverter provides the controlled power. In most cases, the variable-frequency drive includes a rectifier so that DC power for the inverter can be provided from main AC power. Since an inverter is the key component, variable-frequency drives are sometimes called inverter drives or just inverters.
VFDs that operate directly from an AC source without first converting it to DC are called cyclo-converters. They are now commonly used on large ships to drive the propulsion motors.
Electric vehicle drives
Adjustable speed motor control inverters are currently used to power the traction motors in some electric and diesel-electric rail vehicles as well as some battery electric vehicles and hybrid electric highway vehicles. In vehicles with regenerative braking, the inverter also takes power from the motor (now acting as a generator) and stores it in the batteries.
Air conditioning
An inverter air conditioner uses a variable-frequency drive to control the speed of the motor and thus the compressor.
Electroshock weapons
Electroshock weapons and tasters have a DC/AC inverter to generate several tens of thousands of V AC out of a small 12V DC battery. First the 12VDC is converted to 400–2000V AC with a compact high frequency transformer, which is then rectified and temporarily stored in a high voltage capacitor until a pre-set threshold voltage is reached. When the threshold (set by way of an air gap or TRIAC) is reached, the capacitor dumps its entire load into a pulse transformer which then steps it up to its final output voltage of 20–60 kV. A variant of the principle is also used in electronic flash and bug zappers, though they rely on a capacitor-based voltage multiplier to achieve their high voltage.

1.7                               INVERTER RATINGS

 The ratings that you should look at when buying an inverter (depending on the type) are:

  • Continuous Rating: This is the amount of power you could expect to use continuously without the inverter overheating and shutting down.
  • Half Hour Rating: This is handy as the continuous rating may be too low to run a high energy consumption power tool or appliance, however if the appliance was only to be used occasionally then the half hour rating may well suffice.
  • Surge Rating: A high surge is required to start some appliances and once running they may need considerably less power to keep functioning. The inverter must be able to hold its surge rating for at least 5 seconds. TVs and refrigerators are examples of items that require only relatively low power once running, but require a high surge to start.
     
  • IP rating - defines the ability of the inverter seals to prevent water and dust ingress. Although some inverter manufacturers claim high IP ratings suitable for outdoor installation, the quality and location of the seals and ventilation will greatly affect the ability of the inverter to outlast the many years solar installations are expected to work. 
  • Peak efficiency - represents the highest efficiency that the inverter can achieve.

1.8                        IMPORTANT CONSIDERATION FOR INVERTERS

Before going into construction of an inverter, students must know the following:

OUTPUT FREQUENCY
The AC output frequency of a power inverter device is usually the same as standard power line frequency, 50 or 60 hertz
If the output of the device or circuit is to be further conditioned (for example stepped up) then the frequency may be much higher for good transformer efficiency.
OUTPUT VOLTAGE
The AC output voltage of a power inverter is often regulated to be the same as the grid line voltage, typically 220 VAC, even when there are changes in the load that the inverter is driving. This allows the inverter to power numerous devices designed for standard line power.
Some inverters also allow selectable or continuously variable output voltages.
OUTPUT POWER
A power inverter will often have an overall power rating expressed in watts or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. Smaller popular consumer and commercial devices designed to mimic line power typically range from 150 to 3000 watts.
Not all inverter applications are solely or primarily concerned with power delivery; in some cases the frequency and or waveform properties are used by the follow-on circuit or device.
BATTERIES
The runtime of an inverter is dependent on the battery power and the amount of power being drawn from the inverter at a given time. As the amount of equipment using the inverter increases, the runtime will decrease. In order to prolong the runtime of an inverter, additional batteries can be added to the inverter.
When attempting to add more batteries to an inverter, there are two basic options for installation: Series Configuration and Parallel Configuration.
Series configuration
If the goal is to increase the overall voltage of the inverter, one can daisy chain batteries in a Series Configuration. In a Series Configuration, if a single battery dies, the other batteries will not be able to power the load.
Parallel configuration
If the goal is to increase capacity and prolong the runtime of the inverter, batteries can be connected in parallel. This increases the overall Ampere-hour(Ah) rating of the battery set.
If a single battery is discharged though, the other batteries will then discharge through it. This can lead to rapid discharge of the entire pack, or even an over-current and possible fire. To avoid this, large paralleled batteries may be connected via diodes or intelligent monitoring with automatic switching to isolate an under-voltage battery from the others.

1.9     DIFFERENCE BETWEEN CONVENTIONAL GENERATOR AND INVERTER

 

CONVENTIONAL GENERATOR

 

INVERTER GENERATOR

Conventional generators have been around for quite a while, and the basic concept behind them has remained essentially unchanged. They consist of an energy source, usually a fossil fuel such as diesel, propane or gasoline, which powers a motor attached to an alternator that produces electricity. The motor must run at a constant speed (usually 3600 rpm) to produce the standard current that most household uses require (in Nigeria, typically 220 Volts AC @ 50 Hertz). If the engine’s rpm fluctuates, so will the frequency (Hertz) of electrical output.

Inverters are a relatively recent development, made possible by advanced electronic circuitry. It inverter draws power from a fixed DC source (typically a comparatively fixed source like a car battery or a solar panel), and uses electronic circuitry to “invert” the DC power into the AC power. The converted AC can be at any required voltage and frequency with the use of appropriate equipment, but for consumer-level applications in Nigeria, the most common combination is probably taking the 12V DC power from car, boat or RV batteries and making it into the 220V AC power required for most everyday uses.

Conventional generators always bigger and heavier than inverter

The compact size, relatively light weight and resulting portability of inverter generators make them the clear winner in this category.

Conventional generators always noisy

Inverters are often designed from the ground up to be comparatively quiet

Conventional generators are often designed simply to get a certain amount of power where it is needed, and to keep the power on. Factors like the size of the unit have not been a major consideration. This has meant that conventional designs can often accommodate sizeable fuel tanks, with the obvious result being relatively long run times. This means that it uses fuel for it to operate.

Inverters draws power from DC source, either from battery or solar panel.

Conventional  generators emit smoke which causes pollution

Inverter produces no smoke

A conventional generator is nothing more than an engine connected to an alternator and run at a speed that produces the desired AC frequency, regardless of the load on it (as the load increases the engine throttles up to keep the engine speed the same). The output of the alternator is connected directly to the load, without any processing.

With an inverter generator, a rectifier is used to convert the AC power to DC and capacitors are used to smooth it out to a certain degree. The DC power is then “inverted” back into clean AC power of the desired frequency and voltage

Many inverters can be paired with another identical unit to double your power capacity. This type of parallel capability means you can use two smaller, lighter generators to provide the same wattage and amperage of one much larger generator – without sacrificing all the benefits of the smaller, lighter, quieter, more portable inverter units.

Conventional units simply can’t offer this feature. Note that you will need a special cable to connect your generators, which is generally not

 

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.

 

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