لخّصلي

Introduction In ancient times, thunder, lightning and electric fish [1] were the natural phenomena related to electricity.For instance, high-accuracy and high-frequency control methods based on single-chip solutions like Digital Signal Processors, Field Programmable Gate Arrays or Complex Programmable Logic Devices are applied to meet desired requirements and to gain better control of loads; more accurate mathematical methods to model power converters enable gaining better output features, reducing energy losses and increasing efficiency; and improved control algorithms are utilised to improve efficiency and robustness, to reduce complexity and to achieve better output features.The first power electronics device was the mercury arc rectifier developed in 1900, followed by other power devices, like metal-tank rectifier, grid-controlled vacuum tube rectifier, ignitron, phanotron, thyratron and magnetic amplifier, developed and deployed gradually for power-control applications until the 1950s.Since then, a series of great discoveries on the principles of electricity and magnetism has been achieved by Volta, Coulomb, Gauss, Henry, Faraday and others, leading to many inventions such as batteries (1800), generators (1831), electric motors (1831), telegraphs (1837) and telephones (1876), to name just a few.Included here are improved bipolar transistors (with fine structures, and also shorter switching times), metal-oxide-semiconductor field-effect transistors (MOSFETs), gate turn-off thyristors (GTOs) and insulated-gate bipolar transistors (IGBTs).Thereafter, G. Westinghouse applied transformers in AC distribution systems to transmit electricity efficiently over long distances, which has promoted the development of electrical engineering [5].Electric power deals with static and rotating power equipment for generation, transmission and distribution of electric power; while electronics is concerned with solid-state semiconductor power devices and circuits together with control systems for power conversion specified to meet the desired control objectives.It is now well known that electricity must be transmitted at high voltages and in the form of alternating current (AC), because DC voltage could not be increased or decreased by DC systems at that time [8].In practical applications, electric energy was expected to be converted from one form to another, for instance, between AC and DC, or just to different voltages or frequencies, or some combinations of those -- demands that cannot be fully met by transformers.Moreover, energy loss in transformers, magnetic radiations, huge volume and high cost of copper limited their wider use [9].

Introduction
In ancient times, thunder, lightning and electric fish [1] were the natural phenomena related to electricity. They were treated as myths, but not as energy until the discovery of electrostatic phenomena by Thales of Miletus in 640–540 BCE [2], [3]. Much later in 1752, B. Franklin discovered electricity [4], and in 1820 H.C. Örsted revealed electromagnetism [5]. Since then, a series of great discoveries on the principles of electricity and magnetism has been achieved by Volta, Coulomb, Gauß, Henry, Faraday and others, leading to many inventions such as batteries (1800), generators (1831), electric motors (1831), telegraphs (1837) and telephones (1876), to name just a few. In the early 19th century electricity has been established as a scientific discipline, and in the late 19th century the greatest progress has been witnessed in electrical engineering [6].

In 1882, the first power grid, which was a direct-current (DC) distribution system invented by T. Edison, was set up in New York to provide 110 V DC power supplying over 1000 bulbs in a short distance. At that time, the problem was how to transfer energy at a low loss from power plants to customers over a long distance through transmission lines [7]. It is now well known that electricity must be transmitted at high voltages and in the form of alternating current (AC), because DC voltage could not be increased or decreased by DC systems at that time [8]. In 1885, L. Gaulard and J.D. Gibbs developed a device named transformer, which can increase or decrease the electrical voltage of AC systems. Thereafter, G. Westinghouse applied transformers in AC distribution systems to transmit electricity efficiently over long distances, which has promoted the development of electrical engineering [5].

Transformers played a vital rôle in electricity transmission, especially in energy conversion between different voltages. Transformers can, however, only increase or decrease AC voltage (AC-AC) at the same frequency. Moreover, energy loss in transformers, magnetic radiations, huge volume and high cost of copper limited their wider use [9]. In practical applications, electric energy was expected to be converted from one form to another, for instance, between AC and DC, or just to different voltages or frequencies, or some combinations of those — demands that cannot be fully met by transformers. Therefore, novel techniques were required to solve those problems. With the development of semiconductor switches, power electronics has come into being [10].

Power electronics refers to electric power, electronics and control systems. Electric power deals with static and rotating power equipment for generation, transmission and distribution of electric power; while electronics is concerned with solid-state semiconductor power devices and circuits together with control systems for power conversion specified to meet the desired control objectives. Power electronics is one of the main technologies to realise energy conversion with high efficiency. It is known that about 70% of electric energy is converted by power electronics devices before it reaches the consumer. Nowadays, power electronics has become a fundamental technology critical for the development of energy conservation, especially for renewable energy [11].

The history of power electronics is linked to the breakthrough and the evolution of power-semiconductor devices. The first power electronics device was the mercury arc rectifier developed in 1900, followed by other power devices, like metal-tank rectifier, grid-controlled vacuum tube rectifier, ignitron, phanotron, thyratron and magnetic amplifier, developed and deployed gradually for power-control applications until the 1950s. The second electronics revolution began in 1958 with the development of the commercial-grade thyristor by the General Electric company (GE), indicating the beginning of a new era of power electronics. From 1975 to 1995, more turn-off power-semiconductor elements have been developed and implemented, which have vastly improved modern electronics. Included here are improved bipolar transistors (with fine structures, and also shorter switching times), metal-oxide-semiconductor field-effect transistors (MOSFETs), gate turn-off thyristors (GTOs) and insulated-gate bipolar transistors (IGBTs). Correspondingly, many different types of power-semiconductor devices and power-conversion techniques have been proposed and designed. The power electronics revolution has endowed us with the ability to convert, shape and control electrical power [10].

With the development of semiconductor devices, different kinds of control strategies have also been developed to realise specified purposes. For instance, high-accuracy and high-frequency control methods based on single-chip solutions like Digital Signal Processors, Field Programmable Gate Arrays or Complex Programmable Logic Devices are applied to meet desired requirements and to gain better control of loads; more accurate mathematical methods to model power converters enable gaining better output features, reducing energy losses and increasing efficiency; and improved control algorithms are utilised to improve efficiency and robustness, to reduce complexity and to achieve better output features.