design and construction of a 4.8kva pure sinewave inverter (2nd edition)

Description

ABSTRACT

The aim of this project is to design and implement a single phase pure sine wave inverter which can convert DC voltage to AC voltage at high efficiency and low cost. Solar and wind powered electricity generation are being favored nowadays as the world increasingly focuses on environmental concerns. Power inverters, which convert solar-cell DC into domestic-use AC, are one of the key technologies for delivering efficient AC power. A low voltage DC source is inverted into a high voltage AC source in a two-step process. First the DC voltage is stepped up using a boost converter to a much higher voltage. This high voltage DC source is then transformed into an AC signal using pure sine wave modulation. Another method involves first transforming the DC source to AC at low voltage levels and then stepping up the AC signal using a transformer. A transformer however is less efficient and adds to the overall size and cost of a system. Therefor the former method is the one used to implement this project.

CHAPTER ONE

1.0                                                          INTRODUCTION

1.1                                                    BACKGROUND STUDY

 

Electronic devices run on AC power, however, batteries and some forms of power generation produce a DC voltage so it is necessary to convert the voltage into a source that devices can use. Hence a need for power rating inverter to smoothly operate electrical and electronic appliances. Most of the commercially available inverters are actually square wave or quasi square wave inverters. Electronic devices run by this inverter will damage due to harmonic contents [1]. Available sine wave inverters are expensive and their output is not so good. For getting pure sine wave we’ve to apply sinusoidal pulse width modulation (SPWM) technique. This technique has been the main choice in power electronics because of its simplicity and it is the mostly used method in inverter application [2]. To generate this signal, triangular wave is used as a carrier signal is compared with sinusoidal wave at desired frequency.

Advances in microcontroller technology have made it possible to perform functions that were previously done by analog electronic components. With multitasking capability, microcontrollers today are able to perform functions like comparator, analog to digital conversion (ADC), setting input/output (I/O), counters/timer, among others replacing dedicated analog components for each specified tasks, greatly reducing number of component in circuit and thus, lowering component production cost. Flexibility in the design has also been introduced by using microcontroller with capability of flash programming/reprogramming of tasks [3].

The proposed approach is to replace the conventional method with the use of microcontroller. In this project PIC16F877A microcontroller was used. It has low cost and reduces the complexity of the circuit for the single phase full bridge inverter [4]. The focus of this report is on the design and prototype testing of a DC to AC inverter which efficiently transforms a DC voltage source to a high voltage AC source similar to the power delivered through an electrical outlet (240Vrms, 50Hz) with a power rating of approximately 4.8kW.

The method in which the low voltage DC power is inverted is completed in two steps. The first being the conversion of the low voltage DC power to a high voltage DC source, and the second step being the conversion of the high DC source to an AC waveform using pulse width modulation. Another method to complete the desired outcome would be to first convert the low voltage DC power to AC, and then use a transformer to boost the voltage to 240 volts

 

 

[5]. This paper focused on the first method described and specifically the transformation of a high voltage DC source into an AC output.

This project builds upon the work of another project which mandated to build the DC to DC boost. In this report, it is detailed how the inverter’s controls are implemented with a digital approach using a microprocessor for the control system and how effective and efficient a 3- level PWM inverter can be. The inverter device will be able to run more sensitive devices that a modified sine wave may cause damage to such as: laser printers, laptop computers, power tools, digital clocks and medical equipment [1]. This form of AC power  also reduces audible noise in devices such  as  fluorescent  lights  and  runs  inductive  loads, like motors, faster and quieter due to the low harmonic distortion

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 24V 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                                        LIMITATION OF THE PROJECT

• Expensive when compared to traditional generators or modified sine wave inverters
• The input is limited to 24VDC, output to 230VAC and the frequency to 50Hz

1.8                                      APPLICATION OF THE PROJECT

The applications and uses of a power inverter are as follows:

1. DC power source utilization
2. Uninterruptible power supplies

• Induction heating

1. HVDC power transmission
2. Variable-frequency drives
3. Electric vehicle drives

• Air conditioning
• Electroshock weapons