ABSTRACT
This project proposes a new type of voltage regulator based on single-phase converter otherwise known as transformerless AVR that compensates wide range voltage variations. This is not only capable of compensating variations at a much higher bandwidth but also does not experience mechanical wear down and is cost effective. The proposed device employs a pulse width modulation (PWM) z-source ac–ac converter along with a simple closed loop control. High speed MOSFETs are used as bi-directional switch of the ac–ac converter and the circuit ultimately can easily and steadily maintain regulated voltage supply to the end user. The whole system operating principle and analysis are provided.
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE WORK
In the world today for example our country Nigeria, the electricity power delivered to consumers either at their homes or offices is not upheld at an agreed voltage approximately 220volts as a result of voltage fluctuation from the supply of the power system. This voltage fluctuation occurs as a result of sudden changes in the real and reactive power drawn by loads. This fluctuating current that is drawn from the supply causes an additional voltage drops in the power system leading to fluctuation in the supply voltage [1]. Nevertheless, it is relevant to maintain a constant voltage level so as to protect and elongate the life span of the various delicate electrical and electronic gadgets used in our homes and offices from the effect of over voltage and under voltage that may occur as a result of faults arising in the power system through the use of an automatic voltage regulator [1].
According to [2], an Automatic voltage regulator is an electrical device that is used to sense inappropriate voltage levels and correct them to produce a stable output at the port where the load is to be connected. However, this project was designed and constructed using double conversion electronic voltage regulator (EVR) method that uses a rectifier to convert AC power toDCpower and then uses an inverter to convert the DC power back to AC. The voltage regulation here is achieved by supplying the inverter with a constant DC voltage and regulating the voltage level during conversion back to AC in the inverter. The time delay obtainable here is inexpensive and a reliable circuit for protecting equipment such as freezers, refrigerators and air conditioners from damage. Each time power is switched on it gets connected to the appliance only after a delay of a fixed time. On the other hand, this AVR is also built with an undelay function for use with home appliances such as televisions, stereos, CD/DVD players, modems and telephone equipment. This AVR was designed and constructed so as to provide a constant voltage supply (220v) to our electrical and electronic gadgets irrespective of the power fluctuations that occurs in the power system.
1.2 AIM OF THE WORK
The aim of this work is to design and construct a device that will help to protect and lengthen the life span of various delicate electrical and electronic gadgets used in our homes and offices from the consequences of over Voltage and under voltage that may occur as a result of faults arising in the power system.
1.3 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.
1.4 PROBLEM STATEMENT
The problem to be solved in this work is that ofbringing the voltage fluctuations to a required output of 220volts that will ensure the steady performance of the electrical gadgets that containelectrical and electronic components thatmay be susceptible to over voltages and under voltages. Examples of which are flat screen TV’s, audio/video equipment, PCs, Fridges/refrigerators, etc.
1.5 MOTIVATION
To solve the power quality related problems that take place in our homes, offices and industry due to under voltage and overvoltagewith the use of AVR thus eradicating its negative impact on the domestic appliances and industrial efficiency.
1.6 SIGNIFICANCE OF THE WORK
Most electrical or electronic equipment are designed and constructed to operate at a harmless limit of 220volts, but in Nigeria and other small countries, power supply authorities often find it so difficult to achieve or preserve this voltage range due to the evolving nature of the society in addition to not giving room todevelopmentin our power stations.In most areas due to overloading, voltage supply falls below 220v for example 100 volts and sometimes due to fault also, voltage rises to about 315volts for only one phase which is a wide abnormality from the normal supply voltage and is of great danger to the life span of our electrical gadgets such as refrigerators, PCs, freezers, air conditioners, television sets, etc. Excessive high/low voltage supply to our appliances leads to excessive current which afterwards leads to overheating and insulation failure or even burnout of the electronic components in the electrical gadgets. It will be of our interest to know that in electrical equipment, most semiconductor devices have very narrow voltage tolerance and could be easily damaged. So, it is important to protect these electrical gadgets from the effect of over or under voltages by making use of AVR so as to increase the life span of our electrical equipment.
1.7 SCOPE OF THE WORK
The design and construction of an automatic voltage regulator is the project I am working on. I am working on this AVR because I have some ideas on how it can be constructed and also how it works. I am also doing this because I want to learn more about it.As we have mentioned in [2], this device is a protective device that protects our electrical and electronic appliances from the effect of current and voltage fluctuation. This is how it works, when this system is plugged into a socket or mains supply, it will receive a minimum voltage of 100V which is AC then it converts the AC to a high voltage DC with the use of rectifiers and also uses the inverter control to convert the High voltage DC to AC which our electrical and electronic gadgets requires for its safe operation.
So, I am designing and constructing this device to reduce the risk, damages that occurs in our appliances as a result of fluctuation of current/voltage caused by power and also to develop the knowledge acquired from the technical knowhow so as to reduce the large amount of automatic voltage regulators that are being imported into the country.
1.8 JUSTIFICATION OF THE PROJECT
There are various types of automatic voltage regulators in the market, but this transformerless voltage regulator is well suited to the voltage requirement (220v) andoperating frequency (50Hz) of gadgets used in our country Nigeria. Since it was constructed without the use of transformer, it makes the AVR to be less bulky, lighter in weight and portable to carry about. However, there is an absence of relay in this AVR thereby avoiding sparks (noise) that may occur as a result of switching ON/OFF of the relays. Relays however, are far slower than transistors, typically 50ms to switch ON and probably more. Furthermore, the MOSFET used in this work can switch ON in Pico seconds. This transformerless AVR does not consume a lot of current on the ON-state due to the transistor (MOSFET) it was built with. Moreover, this transformerless AVR is durable and can withstand high voltage surge. There is absence of brush in this AVR that will lead to mechanical wears and tears in the device and as a result of that, the need for regular maintenance of the AVR will not be needed.
1.9 LIMITATIONS OF THE WORK
The project has certain limitations which are mentioned below
- It can only be used indoors.
- The device has a stipulated frequency range of operation to avoid breakdown.
- The input to the AVR cannot exceed the specified minimum or maximum set points for a programmable time period, otherwise the AVR shall electronically shut off and would require manual restart even when the electrical parameters are within acceptable range.
- The device is rated 1000VA which limits the amount or type of load it can carry.
- The double conversion AVR method can fail in a matter of hours or days when put in an application with high inrush or over load currents without exercising due precautions such as sizing for the peak currents.
1.10 PROJECT OUTLINE
Chapter one is the introduction of this work. It comprises of the background of the project, aim of the project, objective of the project, problem statement, motivation,and significance of the work, the scope of the work, justificationand the limitations of this work.
Chapter two is the literature review of this work. It consists of the historical background and theoretical background of this work and accounts of what has been published by scholars and researches about it.
Chapter three consists of the methodology used in this project. It comprises of the theoretical analysis and model of this work.
Chapter four entails of the design and implementation of this project. It contains the block diagram which is made up of power supply unit, rectification unit, filtration circuit, inverter unit and the feedback circuit. It also comprises of the principle of operation of this transformerless AVR and bill of engineering specification.
Chapter five consist of the recommendation, conclusion and references with regards to this work.
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