Introduction

This chapter is mainly focused on the objectives, basic block diagram, applications and limitations of our project.

OBJECTIVES OF THE PROJECT

• To understand the function and working of inverter as a power electronic converter or modulator.
• To design the topology and control strategy of cascaded multilevel inverter.
• To perform simulation of cascaded multilevel inverter.
• To design proper filter for reduction of harmonics and its effect.
• To design power switches for inverter circuit.
• To design batteries for input of inverter.
• To construct an inverter that can be used as main power sources for domestic level application.

HYPOTHESIS

• Gobinath.K, Mahendran.S, Gnanambal.I

This paper focuses on improving the efficiency of the multilevel inverter and quality of output voltage waveform. Seven level reduced switches topology has been implemented with only seven switches. Fundamental Switching scheme and Selective Harmonics Elimination were implemented to reduce the Total Harmonics Distortion (THD) value. Selective Harmonics Elimination Stepped Waveform (SHESW) method is implemented to eliminate the lower order harmonics. Fundamental switching scheme is used to control the power electronics switches in the inverter. The proposed topology is suitable for any number of levels. The harmonic reduction is achieved by selecting appropriate switching angles. It shows hope to reduce initial cost and complexity hence it is apt for industrial applications. In this paper third and fifth level harmonics have been eliminated. Simulation work is done using the MATLAB software and experimental results have been presented to validate the theory.

• Zhong Du, Leon M. Tolbert, John N. Chiasson, and Burak Ozpineci

A method is presented showing that a cascade multilevel inverter can be implemented using only a single DC power source and capacitors. A standard cascade multilevel inverter requires n DC sources for 2n + 1 levels. Without requiring transformers, the scheme proposed here allows the use of a single DC power source (e.g., a battery or a fuel cell stack) with the remaining n−1 DC sources being capacitors. It is shown that one can simultaneously maintain the DC voltage level of the capacitors and choose a fundamental frequency switching pattern to produce a nearly sinusoidal output. A cascade multilevel inverter topology has been proposed that requires only a single DC power source. Subject to specified constraints, it was shown that the voltage level of the capacitors can be controlled while at the same time choosing the switching angles to achieve a specified modulation index and eliminate harmonics in the output waveform.

BLOCK DIAGRAM

Basic Block diagram of our project is shown in the figure. 1.1

• Input Source

For inverter circuit input source is DC in nature. The DC input can be supplied by batteries, solar cell or by rectifier. As our project is focused on utilization of solar energy so in that case input source must be solar panel.

• Power electronic modulator

Power electronic modulator is heart of all power electronic system that consists of power semiconductor switches. For our system the PEM is cascaded connection of three H-bridges.

• Harmonic Filter

Power electronic devices have tendency to generate harmonics in circuit waveforms. Harmonics filter is used to filter out higher order harmonics that will make the output waveform nearer to sinusoidal waveform. A wide variety of filters are available to improve the output waveform. The following are the normally used filter:

(i) LC filters

(ii) Resonant-arm filter

(iii) OTT filter

• Load

This type of Inverter is used to fulfill only the domestic applications used in homes as load.

• Controller and Driver

Controller is used to generate pulses for power switches for modulation of power flow. Driver is used to drive the switch from the pulses available from controller.

APPLICATIONS

• This inverter is designed only for domestic application. With increasing ratings the same inverter can be designed for commercial applications.
• The hybrid combination of power available from this inverter and the power available from substation can be made so that both energies can be utilized simultaneously.
• The other combination can also be made such that during day time only le from inverter is utilized and during night the power available from substation is utilized.
• For small industrial applications that are based on single phase supply this inverter can be used although with improved ratings.
• In industry for monitoring system the required power is not so high so that such inverters can be used as separate power supply for such systems.

LIMITATIONS

• The main problem with this inverter is that it does not generate pure sinusoidal waveform that means some amount of harmonic distortions is present that increases the losses.
• With increase in level number of switches the switching loss are also increase.
• The power available from solar panel is not constant because the intensity of solar radiation is not constant for whole day and during night time those are completely unavailable.
• For hybrid combination with substation power the synchronization must require that need some extra efforts.
• For inverter fed by batteries the main problem is in input, we must have some charging system that can charge the batteries.