Power_Electronics_Supplement - SUPPLEMENT 1 INTRODUCTION TO...

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1 SUPPLEMENT 1 INTRODUCTION TO POWER ELECTRONICS O ver the last 40 years, a revolution has occurred in the application of electric motors. The development of solid-state motor drive packages has progressed to the point where practically any power control problem can be solved by using them. With such solid-state drives, it is possible to run dc motors from ac power supplies or ac motors from dc power supplies. It is even possible to change ac power at one frequency to ac power at another frequency. Furthermore, the costs of solid-state drive systems have decreased dramati- cally, while their reliability has increased. The versatility and the relatively low cost of solid-state controls and drives have resulted in many new applications for ac motors in which they are doing jobs formerly done by dc machines. DC motors have also gained flexibility from the application of solid-state drives. This major change has resulted from the development and improvement of a series of high-power solid-state devices. Although the detailed study of such power electronic circuits and components would require a book in itself, some familiarity with them is important to an understanding of modern motor applications. This chapter is a brief introduction to high-power electronic components and to the circuits in which they are employed. It is placed at this point in the book because the material contained in it is used in the discussions of both ac motor controllers and dc motor controllers. S1.1 POWER ELECTRONIC COMPONENTS Several major types of semiconductor devices are used in motor-control circuits. Among the more important are
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2 ELECTRIC MACHINERY FUNDAMENTALS 1. The diode 2. The two-wire thyristor (or PNPN diode) 3. The three-wire thyristor [or silicon controlled rectifier (SCR)] 4. The gate turnoff (GTO) thyristor 5. The DIAC 6. The TRIAC 7. The power transistor (PTR) 8. The insulated-gate bipolar transistor (IGBT) Circuits containing these eight devices are studied in this chapter. Before the cir- cuits are examined, though, it is necessary to understand what each device does. The Diode A diode is a semiconductor device designed to conduct current in one direction only. The symbol for this device is shown in Figure S1–1. A diode is designed to conduct current from its anode to its cathode, but not in the opposite direction. The voltage-current characteristic of a diode is shown in Figure S1–2. When a voltage is applied to the diode in the forward direction, a large current flow re- sults. When a voltage is applied to the diode in the reverse direction, the current flow is limited to a very small value (on the order of microamperes or less). If a large enough reverse voltage is applied to the diode, eventually the diode will break down and allow current to flow in the reverse direction. These three regions of diode operation are shown on the characteristic in Figure S1–2.
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This note was uploaded on 04/01/2012 for the course ECE 341 taught by Professor Keyhani during the Fall '08 term at Ohio State.

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Power_Electronics_Supplement - SUPPLEMENT 1 INTRODUCTION TO...

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