In general, converter devices that transform DC power into AC power are called inverters at a desired output frequency and voltage, where the output voltage could be established at an alternative or variable frequency. They are low contorted sine-wave devices, where the output voltage of the inverters contain harmonics at whatever point it is non-sinusoidal. These harmonics can be lessened by using relevant control plans.

The output voltage waveform of the inverter can be in the form of a semisquare or a square. The voltage may be adequate for low- as well as medium-power applications. For high-power applications, low twisted sinusoidal wave structures are essential. The frequency response of the inverter circuit can be controlled by the proportion at which the power semiconductor switches are turned on and off by the inverter control setup.

In general, systems being utilized for control of movement are called drives. Drives might utilize any of the prime movers such as diesel motors, steam turbines and electric engines for supplying mechanical energy for movement control. Drives utilizing electric engines are called electrical drives. A drive can also be considered a combination of different systems consolidated together with the end goal of movement control. Electric drives for engines are utilized to draw electrical energy from the mains and supply the electrical energy to the engine at whatever voltage, current and frequency needed to accomplish the desired mechanical output. The basic block diagram of an electrical drive system is shown in Figure 9.1.

Gate Questions

Block Parameter Settings

The MATrix LABoratoy (MATLAB) is a high performance interactive multiparadigm numerical computing software system developed by MathWorks. Cleve Moler started developing MATLAB in the late 1960s and it was rewritten in C in 1984. MATLAB was first adopted by researchers and practitioners in control engineering; it has now spread to all domains. The MATLAB function is built roughly around the MATLAB language and the main use of MATLAB is the usage of the command window for execution of text files that includes functions or scripts. MATLAB provides a development environment for managing various sets of files, codes and multiple datasets. It is used to solve problems numerically; MATLAB is the best interactive tool for exploring the various levels of iterations, design, analysis and problem solving. In addition, MATLAB, which is a contemporary programming language, has its own stylish data structures that also contain built-in editing and debugging tools, and supports object-oriented programming.

Single-phase uncontrolled rectifiers are comprehensively used in different converters in the power electronics field. Power electronic converters are frequently used to give a moderate unregulated DC voltage source, which can be further changed to get a DC or AC output. Rectifiers are capable of changing power phase. The only real demerit of rectifiers could be a disability to govern the DC load voltage or current increase after the load parameters are settled. Converters are also unidirectional since they permit electrical power to flow from the AC to the DC side.

Generally, power diodes are used inside these converters. If these power diodes are replaced by thyristors, the resultant converters are referred to as fully-controlled converters. Fully controlled converters cannot be turned off from the gate terminals. Thus, they continue to display output voltage or current waveforms similar to their uncontrolled counterparts. However, in fully-controlled converters, the thyristor can create forward-biased voltage, the load voltage or current waveforms can be measured by governing its turn on of the thyristors. The working principle of thyristors is based on single-phase fully controlled converters with assorted loads supplying an R or RL load. Half-wave converters are also used inside rectifiers, although single-phase fully controlled rectifiers are the most standard setup. In this chapter, we will examine and execute rectifiers using MATLAB/ Simulink.

DC–DC converters are much required these days as numerous modern applications use DC voltage. The execution of these applications will be enhanced if we could utilize a variable DC supply. It will help enhance controllability of, for example, gears. Metro autos, trolley transports, battery worked vehicles are other appliances which may work better with variable DC supply. With a chopper, it is possible to control and fluctuate a consistent DC voltage. The chopper, which is a static power device, works by changing from settled power levels to variable levels. It is basically a high-speed switch, which connects and disconnects the load from source at a high rate to get the desired output.

In hardware, a chopper circuit is utilized to describe various sorts of electronic exchanging devices that are part of power control and signal applications. Basically, a chopper is an electronic switch that is utilized to intrude on one sign under the control of an alternate sign. Choppers can expand or diminish the DC voltage level at its inverse side. In this way, choppers fill the same need in DC circuit that rectifiers do if there should arise an occurrence of AC current. So, they are otherwise called DC transformers.

Introduction

In late 1880's after Faraday published his laws of electromagnetic induction, first alternator was manufactured. The alternator by principle cannot produce a non-variable voltage with respect to time unlike a voltaic cell. Here the electrical technology was going through a great dilemma. On one hand, all electric appliances and instruments were manufactured for fixed voltage or DC voltage and on other hand, the demand of new generation or alternative voltages was in questions. The famous war of current between the father of DC voltages Thomas Edison and American engineer and manufacturer of AC voltage George Westing House was the most discussed issue in late 1880's. For a short span of time we used to use a commutator to get DC out of an alternator. It was very soon that there was a great revolution in electrical engineering as such and all equipments were redesigned and redeveloped to function in AC environment.

What is AC?

In a voltaic cell the output voltage does not vary with time. For a fixed load (i.e. for a constant current) the output voltage is constant throughout the time. In other words the voltage does not change its polarity. The voltage of this kind is the direct current voltage or DC voltage. The current is proportional to the voltage. So a DC voltage always feeds a constant unidirectional current to the circuit. Whereas, an AC voltage source changes its polarity and thus the current changes its direction accordingly. We get a variable bidirectional current from an AC source.

Introduction

Let us look at the vast stary night sky. Let us think of the galaxy full of scintillating fire balls. Let us experience a ride on a high speed Maglev train in Miyazaki, Japan. We must find one thing common in these. Everything is so very balanced yet so moving. The equilibrium state or the multiple equilibrium states are adjoined by the consequent transient states of these events. They are characterized by different force fields. We can imagine our physical existence is situated and controlled by four major force fields. They are:

• a. Gravitational force field

• b. Electrical force field

• c. Magnetic force field

• d. Atomic or Nuclear force field

Out of these four the first three are governed by inverse square law. Bodies which are inversely proportional to the distance between them and directly proportional to their dimension (i.e. mass, charge, magnetic pole intensity). The gravitational force field is both attractive and repulsive. Electrical and magnetic field generally coexist. We can call them sister fields. In most of the cases we derive one as a result of another one. Thus we can easily establish a linear relationship between them. We as an electrical engineer mostly deal with these two sister fields and their combined network. Power system is an electro-magnetic system. Thus, we should have a profound study on electric and magnetic field with prior importance. This chapter will enlighten us how these two fields work and react to each other.

Introduction

Now we are almost at the verge of finish line of our course. Let us now reminisce what have we studied so far. Let us cultivate the purpose of our study. One part of achievement of our study is of course to know the nature and the natural law and how technology has been developed on these laws to make our lives easier. But the other part of our goal is to be socially responsible towards proper utilization of electrical energy. Society expects that engineers should understand the technology at work around us. In this chapter we shall conclude our study by knowing the basic electrical technology associated with our domestic and social lives. We hope we shall be able to understand and shall make awareness among others as a responsible engineer.

Cables and Wires

Electrical cables are made of wires. Two or many wires twisted or running side by side make a cable. The wires are made of Ohmic conductors, mainly copper or aluminium, to carry the current. To carry more amount of current we need less resistive wires in order to maintain a reasonably low I2R loss. To reduce the per unit length resistance of a wire we need to increase the diameter of the wire. In short, for higher current rating of a wire we must have more amount of conductive metal. The overhead cables are naked conductors. But the underground cables or overhead cable in densely populated areas are generally covered by non-conducting insulation. The insulators are dielectric materials, usually polyurethanes; prevent two wires to get short circuited.