Design and Construction of a 1kVA Automatic Voltage Regulator Using Solid State Devices
OBJECTIVES OF THE WORK
This AVR is constructed as a transformerless AVR for a stable and steady current. The device is designed to perform the following functions:
- To protect electrical and electronic gadgets from the consequences of over Voltage and under voltage thus lengthening their life span.
- To design an AVR that is cheaper, reduced in size and does not experience mechanical breakdown.
- To guarantee constant power supply of 220v at 50Hz
- To produce an AVR that can be easily conveyed from one place to another due to the absence of transformer.
Automatic AC voltage regulator or AVR is a wonderful invention of science, which is an electric device designed to regulate a constant voltage in a settable level. The main working of an AVR depends upon the laws of electromechanical physics. It is consist of many active and passive electrical components like adopters, capacitors, diodes and thermostats . The AVR device can serve as a rectifier since most electronic devices function on DC and as well as a potential divider to regulate the input voltage to a desired output voltage for the gadgets to function properly at the same time thus saving money.
Joseph Sola in 1938 invented CONSTANT VOLTAGE TRANSFORMER (CVT) which is the oldest method of combating the variations in ac line voltages. TheCVT (ferro) uses the unique principle of ferroresonance (operation of a transformer in the region of magnetic saturation) and oscillatory interchanges of energy between a capacitor and inductor. Core saturation causes the value of inductance to automatically adjust thereby maintaining an oscillating frequency equal to that of the main supply .The ferro voltage regulator, by its unique design, provides good isolation of load equipment from line noise and surges.Voltage regulators of this type can have electrical efficiencies up to 92% at full load and ideal conditions but at lighter loads the efficiency drops off substantially.
Further advancement led to the development of manual/Mechanical/Analog/Servo type AVR which has being in use for more than 50years and is themost popular type outside of North America for power quality applications. Thetwo primary methods of operation used by mechanical voltage regulators are: (A) by changing the turns ratio, or (B) by altering the magnetic induction between the primary and secondary coils of a transformer by physically changing their orientation.It is cheap, but has a big drawback, they need constant attention i.e. Mechanical drive components, brushes and contractors require regular maintenance and/or replacement, Speed of voltage correction correct may not be fast enough for electronic loads since the mechanical voltage regulator must physically move components thus there is no way to protect loads from sudden phase voltage changes and this can lead to damage of equipment [4 5].
The improvement in the 1940s in power semiconductors has led to the gradual displacement of mechanical voltage regulator by the electronic voltage regulator. In addition to, the introduction of semiconductor devices further enhanced the rectification of ac voltage. This helped to effectively control ac voltage using semi-conductors. Semiconductors are used to drive relays which automatically select voltage taps from auto transformer to a satisfactory output range . Its advantages include that the output voltage regulation ranges from good (tap switching) to very good (double conversion), Ultrafast voltage correction speed, very low or no regular maintenance. However, the sensitivity of AVR is of utmost importance. It largely depends either on the number of taps in the autotransformer for transformer type or the type of solid state devices for transformerless and also the type of voltage sensor that operates the relay if relays are used. Single relay AVR, though economical has some limitations. It works in only one step switching, therefore has a very limited input voltage range i.e. it will not give output at very low voltage and very high voltage, thus making it unsuitable for sensitive equipment like computers. Therefore in this work four MOSFETs were used to ensure a wider input voltage range.
REVIEW OF RELATED WORKS
As stated earlier in  with the growth of applications of power electronics, a large number of studies have investigated its application to the power system and its further development (including industries, commercial and domestic consumers). Most of these studies explored the use of switch mode converter topologies that areused in DC-DC conversion. Conversely, some studies have modified these DC regulators to use AC-AC conversion by using pulse width modulation (PWM) technique.Additionally, among all of these studies for AC-AC conversion, some significant proposals have already been made to control output voltage during input voltage fluctuation by using a switch mode AC voltage regulator with improved power quality [6, 7]. The following sections will provide a detailed review of these studies with its advantages as well as disadvantages.
REVIEW OF MOST SIGNIFICANT STUDIES ON VOLTAGE REGULATORS
Review of a 220V Voltage Stabilizer
Nafis Ahmed and Ariful Hoque,students of Department of Electrical & Electronic Engineering in Northern University Bangladesh in  worked on a 220v voltage stabilizer. In their work, they designed a simple automatic AC voltage stabilizer using active and passive devices, such as diodes, transformer(One step down transformer and one step up transformer), resistor, capacitor, relay, IC etc. Although the voltage stabilizer senses inappropriate voltage levels and corrects them to produce a reasonably stable output where the load is connected it is heavy, cannot be easily conveyed and unnecessarily expensive due to the presence of a transformer.
METHODOLOGY AND SYSTEMS DESIGN ANALYSIS
The method that is of paramount importance in conducting the research for the realization of any project has three major procedures which include:
A Design by Analysis: this involves determining the project to be worked on, its layout, specification, the functional blocks, the types of components to be used, making a list of those components and finally designing the project block by block.
B Design by Synthesis: this involves getting an already existing diagram of the project in question, making amendments, adding more parameters to the design to make it more functional.
C Design by Comparison: this involves comparing the work with an existing project which guides the designer to make decisions concerning the project.
SYSTEM IMPLEMENTATION, TESTING AND RESULT ANALYSIS
Once thorough analysis of the various sections mentioned in chapter three were carried out, all the components including the switches and IC were tested on a breadboard and the components which combined to give the best result were selected for use. After that, the microcontroller and the associated components were then transferred and soldered on a veroboard ensuring that precautions are properly taken during soldering. All safety measures are taken to prevent electric hazard. The whole arrangement was then housed in a metallic enclosure.
CONCLUSION AND RECOMENDATION
The system was tested and found to be working according to the design specification and so the objective of the project was successfully achieved. The construction of the automatic phase selector and change over system was very challenging but interesting and motivating. A lot of research work was done on the design and construction of a solid state automatic voltage regulator. The main purpose of the device is to sense inappropriate voltage levels and correct them to produce a stable output at the port where the load is to be connected. Also the purpose was to design a regulator with neither transformer nor relay but with solid state devices so as to improve its efficiency, for ease of control and to have a reduced size as well as a reduced cost and this was very much achieved.
As a result of the functionality value of this device, it is very suitable for deployment in any residential and commercial building such as offices. The device is very reliable, relatively cheap and can be mass produced economically. Thus the device is economically justifiable because it can be produced in commercial quantity since it is relatively cheap and operates at high efficiency. The device doesn’t have restriction when it comes to who to use it and who not to use it, where to use it and where not to use it.
In conclusion, this project has shown that there is the need for asolid state automatic voltage regulator in our industries and homes and that an efficient and reliable one can be designed locally. Thus it is advisable that the Nigerian government should take interest in the production of this device instead of importing it since it is more efficient than our conventional regulators and cost effective.
PROBLEMS ENCOUNTERED AND SOLUTIONS ADOPTED
- The greatest problem encountered was finding a means of regulating a 12V dc to power the oscillator from the high voltage dc, so I had to buy an external 12V dc supply source.
- Interruption of power supply: Due to the interruption in power supply, the soldering of the components and the testing of the system suffered some delay.
- During soldering some components were destroyed due to inexperience in soldering.
I suggest that:
- The packaging of the AVR should be improved on.
- When redesigning this project, the oscillator IC that will be used should be a pure sine wave oscillator to give a pure sine wave output.
- Future projects should implement a higher power rating in order to accommodate more home appliances.
- Supervisors and project topics should be given to students on time to prevent late completion of project and to give the students enough time to conduct proper research on the particular topic for a better result.
- Efforts should be made to ensure that a functional departmental library is made available as this will provide students with the adequate materials needed to carry out proper research on their project.
- Uniprojects.net “design and construction of an automatic voltage stabilizer” available at https://uniprojects.net/project-materials/design-and-construction-of-an-automatic-voltage-stabilizer/[accessed on 9th September,2016]
- Electronic circuit projects“Automatic Voltage Stabilizer Circuit for TV sets and Refrigerator” available at http://www.homemade-circuits.com/2011/12/how-to-make-small-homemade-automatic.html [accessed on 9th September, 2016]
- Neopower company “AC Automatic Voltage regulator(2010 09 20)” available at http://www.neo-industrial.com/knowledge-1.html [Accessed on 10th September, 2016]
- Nnamuma Anthony iloabuchi “Design and construction of an automatic voltage regulator (2010 June)” [Accessed on 10th September, 2016]
- UST company“AVR Guide: The Mechanical (Type) Voltage Regulator” Available at: http://www.ustpower.com/comparing-automatic-voltage-regulation technologies/avr-guide-mechanical-type-voltage-regulator/ [Accessed on 10th September, 2016]