电力电子双语课翻译.docx

《电力电子双语课翻译.docx》由会员分享，可在线阅读，更多相关《电力电子双语课翻译.docx（8页珍藏版）》请在得力文库 - 分享文档赚钱的网站上搜索。

1、 _ Chapter Power Electronic Systems: An Overview . LAnmm OBJECTIVES： To become feimiliar with the power-electronic systems. To understand the overall systems view of power electronic converters. To introduce various power semiconductor devices. To consider the applications of power electronics. To i

2、ntroduce the simulation techniques for power electronic circuits. - 1.1 INTRODUCTION - - Generally, the electrical engineering field may be divided into three areas of specialization: Electronics Power Control Electronics essentially deals with the study of semiconductor devices and circuits for the

3、 processing of information at lower power levels. In this rapidly developing society, electronics has emerged as the most important branch of engineering. The power area deals with both rotating and static equipment for the generation, transmission, distribution and utilisation of vast quantities of

4、 electrical power. The transmission and distribution system is a very vital link between generation and utilisation of electrical power and the relative strength of this system indicates the quality of electric power in a country. In India, after successfully establishing capabilities of generating

5、electric power through various sources like hydel, thermal, nuclear, gas etc, a policy decision has been taken to give the highest priority to the transmission and distribution system in the 90s. The control area deals with the stability and response characteristics of closed- loop systems using fee

6、dback on either a continuous or sampled-data basis. Power electronics deals with the use of electronics for the control and conversion of large amounts of electrical power. The design of power electronics Scanned by CamScanner Power Electronics 2 Power Electronics . . kptween the source and the load

7、, and utilises equipment involves interactions betwe semiconductor devices. well as depends upon all other areas of e1ow： rdet has gone through rapid technological evolution . f alone with the the Technology is advancing and apparatus cost improvement ofreliability, their applications are expanding

8、in 肪 idential， miUtaiy， a咖印 ace 如 dutilityenvironments 二 :a: semiconductor devices, converter topologies, analytical an s rnntrihntino electrical machine drives, and control and estimation tec ques , , to this advancement. The frontier of the technology has been further advanced by the artificial in

9、telligence (AI) techniques, such as fuzzy logic and art cial neural networks, thus bringing more challenge to power electronic engineers. In the global industrial automation, energy generation, conservation ot the 21st century, the widespread impact of power electronics is mevita e. chapter, we will

10、 overview the power devices, converters and app ications o power electronics. 1.2 HISTORY OF POWER ELECTRONICS _ - DEVELOPMENTUntil 1956, the application of semiconductors was confined to low power circuits and electronic engineering was also called as light current engineering. In September 1956, f

11、our engineers of the Bell Telephone Laboratory, USA, published a paper entitled /WPiV transistor switches” in the proceedings of the Institute of Radio Engineers. This paper triggered intensive research on PNPN devices. In 1957, Gordon Hall of General Electric Company, USA, developed the three termi

12、nal PNPN silicon based semiconductor device called as silicon controlled rectifier (SCR). Continuous modifications and improvement in its design as well as fabrication techniques have made it more and more economical and suitable for various control purposes. Later on, many other power devices havin

13、g characteristics similar to that of an SCR were developed. Actually, the origin of power electronics can be traced back to the time when mercury arc devices were employed for the rectification of a.c. to d.c, or the inversion of d.c. to a.c. However, the rapidly increasing usage of power electronic

14、s nowadays has resulted from the development of solid state power devices. - 1.3 POWER ELECTRONIC SYSTEMS - - Block diagram of the generalised power electronics system is shown in Fig. 11 Power source may be an ac supply system or a dc supply system. In India, 1-phase and 3-phase 50 Hz ac supplies a

15、re readily available in most locations. Very low power drives (systems employed for motion control are called drives) are generally fed from 1-phase source. Rest of the drives are powered fron1 Sca nReed byiCimS6aenner Power Electronic Systems: An OverView 3 fed from 400 V supply; for high ratings,

16、motors may be rated at 3.3 kV, 6.6 kV, 11 kV and higher. In case of aircraft and space applications, 400 Hz ac supply is generally used to achieve high power to weight ratio for motors. In main line tractioi a high voltage supply is preferred because of economy. In India, 25 kV， 50 Hz supply is empl

17、oyed. _ Some loads are powered from a battery, e.g. fork lift trucks and milk vans. Depending on size, battery voltage may have topical values of 6 V, 12 V, 24 V, 48 V and 110 V dc. Solar powered drives wWch are used in space and water pumping applications are fed from a low voltage dc supply. Prese

18、ntiy, though these drives are very expensive but have a great future for rural water pumping and low power transport applications. Fig. 1.1 Block diagram of power electronic system Power modulator performs one or more of the following four functions: (i) Converts electrical energy of the source as p

19、er the requirement of the load. For example, if the load is a dc motor, the modulator output must be adjustable direct voltage. In case the load is a 3-phase induction motor, the modulator may have adjustable voltage and frequency at its output When power modulator performs this function, it is know

20、n as converter. (ii) Selects the mode of operation of the motor, i.e. motoring or braking. (iii) Modulates flow of power from the source to die motor in such a manner that motor is imparted speed-torque characteristics required by the load. (iv) During transient operations, such as starting, braking

21、 and speed reversal, it restricts source and motor currents within permissible values; excessive current drawn from source may overload it or may cause a voltage dip. Motors commonly used in power electronic systems are: (i) DC motors (shunt, series, compound and permanent magnet) (ii) Induction mot

22、ors (squirrel-cage, wound rotor and linear) (iii) Synchronous motors (woimd field and permanent magnet) (iv) Brushless dc motors (v) Stepper motors and (vi) Switched reluctance motors Scanned by CamScanner Power Electronics Power modulators are controlled by a control unit. Nature of the control uni

23、t for a particular system depends on the power modulator that is used. Control unit operates at much lower voltage and power levels. Sensing unit measures the I acj parameters, say speed in case of a rotating machine and compares it with the command. The difference of the two parameters processed by

24、 the control unit components now controls the tum-on of power semiconductor devices which are used in power modulators. As desired, the behaviour of the load circuit can be controlled over a wide range with the adjustment of the command. - 1.4 POWER SEMICONDUCTOR DEVICES - - The progress in power el

25、ectronics today has been possible primarily due to advances in power semiconductor devices. Of course, apart from device evolution, the inventions in converter topologies, pulse-width modulation (PWM) techniques, control and estimation techniques, digital signal processors, application specific inte

26、grated circuits (ASICs), control hardware and software, etc. also have contributed to this advancement. Modem era of solid-state power electronic began with the advent of thyristor (silicon controlled rectifiers) in the late 1957. Gradually, various types of power semiconductor devices were develope

27、d and became commercially available since 1970. Power semiconductor devices can be classified into three categories according to their degree of controllability. The categories are: (i) Uncontrolled tum-on and off devices (e.g. diode). (ii) Controlled tum-on and uncontrolled turn-off (e.g. SCR). (ii

28、i) Controlled tum-on and off characteristics e.g. Bipolar junction transistors (BJTs), MOSFETs, Gate-turn-off thyristors (GTOs), Static induction thyristor (SITH), Insulated-gate bipolar transistors (IGBTs), static induction transistors (SITs), mos-controlled thyristors (MCTs). The on and off states

29、 of diodes are controlled by power circuit. Thyristors are tumed-on by a control signal and are tumed-off by the power circuit whereas the controllable switches are tumed-on and off by controlled signals. The devices which behave as controllable switches are BJT, MOSFET, GTO, SITH, IGBT, SIT and MCT

30、. BJT, MOSFET, IGBT and MCT can withstand unipolar voltage whereas thyristors and GTOs can withstand bipolar voltages. BJT, MOSFET, IGBT and SIT requires continuous signal for keeping them in tum-on state but SCR, GTO, SITH and MCT requires pulse-gate signal for turning them ON and once these device

31、s are ON, gate-pulse is removed. Triac and RCT (reverse conducting thyristor) possess bidirectional current capability whereas all other remaining devices (diode, SCR, GTO, BJT, MOSFET, IGBT, SIT, SITH, MCT) are unidirectional current devices. As the evolution of new and advanced devices continued,

32、the voltage and current ratings and electrical characteristics of the existing devices begsn improving dramatically. In fact, the device evolution along with converter, control and system evolution was so spectacular in the last decade of 20tlLcentury, that Scanned by CamScanner Power Electronic Sys

33、tems: An Overview Thyristore are used for high power low frequency applications. Devices are available with 8000 V and 4000 A ratings. ABB recently introduced a monolithic ac switch that has the voltage ratings of 2.8 kV-6.5 kV and current ratings of 3000-6000 A. The advent of large GTOs push the th

34、yristor voltage-fed inverter from the market. Currently, GTOs are available with 6000 V, 6000 A (Mitsubishi) ratings for large voltage-fed inverter applications. Power MOSFET has grown in rating, but its primary popularity is in high- jfrequency switching mode power supply and portable appliances. T

35、he BJT appeared and then fell into obsolescence due to the advent of IGBT at the higher end and power MOSFET at the lower end. The invention of IGBT is an important milestone in the history of power semiconductor devices. Commercial IGBTs are available with 3500 V, 1200 A, but upto 6.5 kV and 10 kV

36、devices are under test in laboratory. Trench gate IGBT with reduced conduction drop is available upto 1200 V, 600A. IGBT intelligent power modules (IPM) from a number of vendors are available for 600 V, 50-300 A and 1200 V, 50-150 A to cover upto 150 hp ac drive applications. Integrated Gate-Commuta

37、ted Thyristor (IGCT) is basically a hard-driven GTO with built-in gate driver, and the device is available with 6000 V, 6000 A (10 kV devices are under test). Recently, ABB introduced reverse blocking IGCT (6000 V, 800 A) for use in current-fed inverter drives. Large band gap power semiconductor dev

38、ice with silicon carbide (SiC) that has high carrier mobility, high electrical and thermal conductivities and strong radiation hardness is showing high promise for next generation power devices. These devices can be fabricated for higher voltage, higher temperature, higher frequency and lower conduc

39、tion drop. SiC diodes are commercially available, and other devices are expected in future. Table 1.1 lists some power devices and shows their respective V-I characteristics and symbolic representation. We will study all these devices in Chapter 5. Table 1.1 Power devices, their characteristics and

40、symbolic representation Power devices _ Symbols _ VI characteristics _ (1) SCR (Silicon controlled rectifier) (Contd.) Scanned by CamScanner Power Electronic Systems: An Overview 1.5 POWER ELECTRONIC CONVERTERS 11 The great strides taken in the industrial applications of power electronics during rec

41、ent years have demonstrated that this versatile tool can be of great importance in increasing production, efficiency and control. Power Electronic Circuits are also called as power converters. A converter uses a matrix of power semiconductor switches to convert electrical power at high efficiency. T

42、he converter system is comprised of switches, reactive components L, C, and transformers. Switches include two terminal devices such as diodes and three terminal devices such as transistors or thyristors. These converters/controllers are generally classified into the following five broad categories:

43、 1. Phase Controlled Rectifiers (AC to DC Converters) These controllers convert fixed ac voltage to a variable dc oujut voltage. These converters takes power from one or more ac voltage/current sources of single or multiple phases and delivers to a load. The output variable is a low-ripple dc voltag

44、e or dc current. These controller circuits use line voltage for their commutation. Hence they are also called as line commutated or naturally commutated ac to dc converters. These circuits include diode rectifiers and single/three phase controlled circuits. These controllere are discussed in detail

45、in Chapter 6. Applications: High voltage dc transmission systems DC motor drives Regulated dc power supplies Static VAR compensator Wind generator converters Battery charger circuits 2. Choppers (DC to DC Converter) A chopper converts fixed dc input voltage to a variable dc output voltage. The dc ou

46、tput voltage may be different in amplitude than the input source voltage. Choppers are designed using semiconductor devices such as power transistors, IGBTs, GTOs, Power MOSFETs and thyristors. Output voltage can be varied steplessly by controlling the duty ratio of the device by low power signals f

47、rom a control unit. Chopper has either a battery, a solar powered dc voltage source or a line fiquency (50 60 Hz) derived dc voltage source. Choppers are discussed in Chapter 8. Applications: DC drives Subway cars Battery driven vehicles Electric traction Switch mode power supplies 3. Inverters (DC

48、to AC Converter) An inverter converts a fixed dc voltage to an ac voltage of variable frequency and of fixed or variable magnitude. A practical inverter has either a battery, a solar powered dc voltage source or a line frequency (50 Hz) derived dc voltage source (often unregulated). Inverters are widely used from very low-power portable electronic systems such as the flashlight discharge system in a photography camera to very high power industrial systems. Scanned by CamScanner 12 Power Electronics Inverters are designed using semiconductor devices such as power transi