This book on ‘Electrical Machines’ has been written for under-graduate students of Electrical Engineering (EE) and Electrical & Electronics Engineering (EEE) belonging to various Indian and Foreign Universities. It will also be useful to candidates appearing for AMIE, IETE, GATE, UPSC Engineering Services and Civil Services Entrance Examinations.

We know that electrical energy has a wide range of applications where electrical machines play a vital role in industrial production and many other areas of science and technology. Accordingly, this book has been designed so that it be useful not only to students pursuing courses in electrical engineering but also for practising engineers and technicians.

‘Electrical Machines’ is taught at various universities under different titles such as Electrical Machines-I, Electrical Machines-II, DC Machines and Transformers, Electromagnetic Energy Conversion Devices, Special Purpose Machines, etc. All the topics in such courses have been covered in this single unit. As such, the book covers the revised syllabi of all Indian and Foreign Universities.

Generally, students find Electrical Machines to be one of the most difficult subjects to understand, despite the availability of a large number of text books in this field. Keeping this fact in mind, this text has been developed in a systematic manner giving more emphasis on basic concepts.

Each chapter of the book contains much needed text, supported by neat and self-explanatory diagrams to make the subject self-speaking to a great extent. A large number of solved and unsolved examples have been added in various chapters to enable students to attempt different types of questions in examination without any difficulty. Section Practice Problems have been added in all the chapters to maintain regular study and understanding. At the end of each chapter sufficient objective type questions, short-answer questions, test questions and unsolved examples have been added to make the book a complete and comprehensive unit in all respects.

The author lays no claim to original research in preparing the text. Materials available in the research work of eminent authors have been used liberally. But the author claims that he has organised the subject matter in very systematic manner. He also claims that the language of the text is lucid, direct and easy to understand.

MATLAB Functions

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.