1.1 Introduction
An inverter is a device that can convert electrical energy of DC form into that of Ac, the inverting process can be achieved with the help of transistors, silicon controlled rectifier (SCR), tunnel diodes etc for low and medium power outputs transistorized inverters are suitable but silicon controlled rectifier (SCR) are suitable for higher power outputs. The working principle of an inverter can be explained with the help of a complete circuit diagram. This is a voltage driven inverter because the voltage source is connected through semi-conductor switches directly to the primary of the transformer.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the Study. Others are Significance of the Study, Scope of work, Limitation of the Study and Definition of technical terms.
1.2 Background of Study
Currently almost all the inverters available in the market use the PWM (Pulse Width Modulation) technology. PWM based inverters are superior in many ways compared to the inverters based on traditional technology. PWM based inverters use MOSFET devices in-its output section. So, these inverters are also known as PWM MOSFET inverter. These PWM MOSFET inverters contain many protection circuits to protect the inverter, inverter battery, load at the inverter output and the user from various fault conditions. Some of the special control/protection circuits used in the PWM MOSFET inverter is:
- Battery charging current sensing circuit
- Battery voltage sensing circuit
- AC mains sensing circuit
- Soft start circuit
- Low battery cut circuit.
- Changeover circuit
- Overload protection circuit o Shutdown section
- PWM section to regulate output supply.
Other than these protection/control circuits, the PWM MOSFET inverters contain the following sections: Oscillator, Driver, Output and Battery Charging Section.
This is a fully automatic PWM technology based inverter, which provides very good performance. PWM or Pulse Width Modulationis mainly used to keep the AC supply output by the inverter to a constant 220V. In an ordinary inverter, the inverter output changes with any change in the value of the load connected at the inverter output. To solve this problem the PWM based inverter correct the output value based on the value of the load connected at the inverter output socket. In the PWM inverter this is done by changing the width of the switching frequency generated by the oscillator. In a PWM based inverter, the AC supply at the inverter output depends on the width of the oscillator frequency generated by the oscillator section.
In this inverter, a small part of the inverter output is given as reference voltage to the PWM controller 1C. Based on this reference voltage, the PWM section will increase “or reduce the width of the oscillation pulse generated by oscillator section. This change in the width will compensate any change in the inverter output, and the inverter output will always stay constant, even if there is any change in the load at the inverter output. When the inverter comes into AC mains mode, from the battery off mode, i.e. When the AC mains return after a power cut, the battery charging does not start immediately. It starts after a delay of about 8-10 seconds. This is done to protect the MOSFET at the output section. If the charging is started immediacy, when the AC mains return, the MOSFET at the output section will receive high current and could get damaged.
Therefore, to protect the MOSFET at the output, the battery charging is delayed for 8-10 seconds after the AC mains return. This is known as Soft-Start or Mains Delay. This section informs about the availability of the AC main supply to the inverter circuit. When the battery voltage reduces from 12V to 10V, the battery is considered discharged. When the battery becomes discharged, the inverter should be switched off, otherwise the battery will go into Deep Discharge State and the battery life will get reduced.
1.3 Statement of Problem
Problem Statement and Need for Inverters In the market of power inverters, there are many choices;
- They range from the very expensive to the less expensive with varying degrees of quality, efficiency and power output.
- Capability along the way, High quality combined with high efficiency exists but it is often at high cost.
- There are many problems that has limited the output power and low energy an inverter can produce this include finance time access to some necessary destined component etc.
1.4 Aim and Objective of the Study
The aim of this research work is to design and construct a 1.5kva (Kilovolt-amps) Inverter. In achieving this aim, the following specific objectives were laid out as follows:
- To design an electrical system capable of producing power from a D.C battery that will produce an output of 500 - 1000 watts, 50Hz - 240v which Will be used to drive electrical appliances.
- To expose the student in electrical /electronic engineering to be able to design and build electrical /electronic circuits
- To understand the basic principles of operation of an inverter circuit and its relevance in the society.
- To introduce the principle of circuit analysis during construction of 1.5kva Inverter.
1.5 Motivation of Study
I was motivated by the need to generate electrical power through a noiseless, portable and inexpensive source that has no negative effect on the environment. I also took up the challenge to carry out this project because of my quest to know more about power generation.
1.6 Significance / Relevance of Study
Inverter works noiselessly. Inverters provided completely automatic switch over function. When the mains supply fails the inverter immediately switches the output to its internal battery and when the mains supply returns the inverter shuts down its operation and provides the mains AC supply-at its output. Inverter does not require any special starting process and the switching of output from mains to inverter and inverter to mains is done automatically.
Inverter does not require any special starting process and the switching of output from mains to inverter and inverter to mains is done automatically. Inverter works on battery which works noiselessly without producing any ‘smell or other harmful emissions etc. As the inverter is an electrical device it does not require any special maintenance. Only the battery used with the inverter will require some routine service such as topping it with distill water once in 15-20 days.
1.7 Limitations of the Study
Every design has it scope and limitation. In this study (Pulse Width Modulated inverter) it scope depend on the inverter rating & design which is the capacity. The inverters depend on the direct current from the battery of which if the current in the battery is been exhausted the inverter will stop automatically. How long the power supply of the inverter will last also depend on the battery. The inverter also needs power supply from main power source to be able to charge the battery when its current has been exhausted. The limitations of this works are:
- Inferol battery in the market
- Inferol component in the market
- Main power fluctuation
- Main power supply interruption
1.8 Definition of Terms
Inverter:
An inverter is a system that converts a direct current to an alternating current.
…
