Uninterruptible Power Supply Systems

Recently, there has been a sharp increase in a number of so-called critical equipment of electrical power. Both separated units and complex objects, whose normal operation is strongly influenced by the parameters of electrical power, are included in this equipment.

Energy and Energy Efficiency

Originally, coal was the main source of energy. It remains so throughout the 18th century during the period of the rapid industry development. Later on, oil and naphtha began to be used as energy sources and their usage expanded especially in 19th century. A special feature of the above mentioned fossil fuels is their long creation period – requiring millennia. They are a result of rotting of different plant and animal kinds. In comparison to the period of their formation, the period of their utilization is far shorter. In accordance with a number of existing statistics about 2050 year it may be talked about a depletion of the liquid fossil fuels, also, the world coal supplies are considered to last within the next 200 years. Therefore, the development of nuclear power engineering is considered to be one of the alternatives to generate energy. Recently, the nuclear power energy generation has been denied in many countries because of the risks associated with its generation and because these risks have been confirmed by serious accidents throughout the World. The storage of worked nuclear waste is also a problem and risky. The renewable energy sources are another possibility to generate energy.

State-of-the-Art Review on Power Electronics

During 1991-2004 years, International Workshop on the Future of Electronic Power Processing and Conversion (FEPPCON) held four times with the support of IEEE Power Electronics Society. The main purpose is to outline the possibilities of development in different fields during the next period as a result of the discussions. At the last meeting held in Italy, the tendency to increase the role of Power Electronics during the next 25-30 years in the processes of energy conversion has been confirmed (Blaabjerg, 2005). Special attention is paid to the role of Power Electronics at a system energy conversion level, because it is not in the position to dictate the trends in the development of this level. Nevertheless, without the power electronics tools, future serious achievements in power processing are impossible. Therefore, the power electronics implantation at a system level at a system energy conversion level is an issue of the efforts of the specialists in this field (Agrawal, 2001). This, of course, imposes also some changes and adaptation towards Power electronics role also in the process of schooling of specialists paying attention mainly to multidisciplinary of Power Electronics. For example, a necessity of further tuition in electrochemistry, mechanics, physics (especially electromagnetic and thermal processes), etc, is outlined. Remote access to complex power electronics laboratory equipment and the possibility of remotely driving experiments and measurement is represented (Rodriguez, 2009). Power Electronics takes a significant part in the following systems: Generic Systems; Energy Storage; Power Systems, including Alternative Energy Supply; Automotive Systems (Bose, 2009).

Conversion of Electrical Power from Renewable Energy Sources

Towards the end of the previous century, the humanity understood very clearly two facts – first, the World supplies of fossil fuels (coal, oil, gas, uranium) are limited, and, second, industrial development and classical generation of electrical energy seriously endanger the environment. Renewable energy sources (sun energy, wind energy, bio fuels, etc.) are based on the use of natural fluxes of energy (Masters,2004). That is why they are considered to be inexhaustible. In specific cases of implementations, for example in lighting, a direct generation of electrical energy using photovoltaics is outlined as a long-term one.

Power Electronics and Its Role in Effective Conversion of Electrical Energy

As it has been clarified by information provided in the previous chapters, there is a necessity to convert electrical energy from one input kind into other output kind of energy.

Conversion of Electrical Energy in the Processes of Its Generation and Transmission

Electrical energy can be obtained by burning coal (thermal power plant), by using nuclear fuel (nuclear power plant) or by using the power of water (hydro power plant). In these cases, the energy obtained by the sources put a shaft of an electrical generator in motion. The generator generates electrical energy – see Figure 1. In the installation, excitation system for the generator is used. The system turns on an uncontrolled rectifier, thyristor-controlled rectifier or AC thyristor regulator dependent on the generator type. The obtained energy is transmitted using a transmission system towards consumers. The transmission yet is made mainly in high-voltage AC energy form (HVAC). In different parts of the transmission network the voltage value may be different. There are so-called high-voltage (420 kV, 220 kV, 110 kV, etc) and medium voltage (20 kV, 6.6 kV, etc.) systems. General consumers consume electrical energy from so-called low-voltage systems (230V, 50Hz or 110V, 60Hz). During the transmission the type of energy does not change, only the value of the voltage changes using transformers.

DC/AC Conversion

The operational principle of converters from DC into AC electrical powers, so-called inverters, is based on the idea studied in Chapter 3. In this chapter, the autonomic or independent inverters are studied, whose operational frequency is determined in general by their control system (Bedford, 1964).

AC/DC Conversion

Figure 1 displays a power electronic converter connected to the mains. In general, a power electronic converter is an electrical power converter – controlled or uncontrolled rectifier, AC regulator, compensator of reactive power, converter of phase number, active power filter. The converter supplies a load with power Pout, and in the same time it loads the mains with active power P and total power S.

DC/DC Conversion

The basic idea of converting DC into DC voltages has been studied in Section 1 Chapter 3. There also has been mentioned that to separate DC component a smoothing filter is connected between the output of the converter and the load. The filter consists of passive elements – inductances and capacitors, and in several cases it is included in the converters circuit (Williams, 2008). Figure 1 displays the waveform of the output voltage as the block of the converter contains and the smoothing filter. Using the figure the basic indicators of the converter will be defined.

Other Applications of Converters and Systems of Converters

The industrial application of power electronic converters and systems of converters are varied (Motorola, 1991, 1993). Power electronic converters of electrical energy for electrical engineering technologies have a wide spread in industry.