電氣工程及其自動化專業(yè)英語第三章section_3-1

1、Chapter 3Power Electronic Technology Section 1 Semiconductor Switchesn Textn New Words and Expressionsn Exercisesn Endn Transition of part of speechSection 1 Semiconductor Switches Semiconductor switches are very important and crucial components in power electronic systems. These switches are meant

2、to be the substitutions of the mechanical switches, but they are severely limited by the properties of the semiconductor materials and the process of manufacturing. Section 1 Semiconductor SwitchesSwitching losses Power losses in the power electronic converters are comprised of the switching losses

3、and the parasitic losses. The parasitic losses account for the losses due to the winding resistances of the inductors and transformers, the dielectric losses of capacitors, the eddy and the hysteresis losses. The switching losses are significant and can be managed. They can be further divided into t

4、hree components: (a) the on-state losses, (b) the off-state losses and the losses in the transition states. Section 1 Semiconductor SwitchesOn-State Losses The electrical switches conduct heavy current and have nonzero voltage across the switch in the on-state. The on-state power losses are given by

5、 fsononiuP (3-1) The uson and if are respectively the switch voltage in the on-state and the forward current through the switch. For example, the typical power diodes and the power transistors have nearly 0.5 to l volt across them in the on-state. The forward currents can be hundreds to thousands of

6、 amperes. The on-stateSection 1 Semiconductor Switchespower losses are very significant. Off-State Losses The electrical switches withstand high voltages and have nonzero leakage current through the switch in the off-state. The off-state power losses are given by rsoffoffiuP(3-2)Section 1 Semiconduc

7、tor Switches The usoff and ir are respectively the reverse bias voltage in the off-state and the reverse current through the switch. For example, the typical power diodes and the power transistors have high reverse voltages in hundreds to thousands of volts and microamps to milliamps through them in

8、 the off state. Transition-State Losses The practical switching devices have limited capabilities of rate of voltage transition and the rate of current steering. These nonabrupt transition ratesSection 1 Semiconductor Switchesgive rise to power losses in the switching devices. We will examine these

9、switching losses in two cases separately: the inductive and capacitive loads.Switching with Inductive Load The inductor is assumed to be large so that the current through it in steady state is nearly constant Io. Assume that initially the switch is off. The inductor current is +Io and freewheels thr

10、ough diode V1. When the switch is turned on, the current through the switch begins to build up linearly (an assumption) to +Io while the diode V1 is still on. Section 1 Semiconductor SwitchesThe on diode has zero voltage across it (an ideal diode), hence, the voltage on the switch is held constant a

11、t +Us. When the current buildup is over, the diode Vl ceases to conduct and the voltage on the switch ramps linearly (again an assumption) down to zero. When the switch is turned off, the voltage begins to build up linearly to +Us while the diode V1 is off. While the diode is off the current through

12、 the switch equals the inductor current, which is constant Io. After the switch voltage reaches zero, Section 1 Semiconductor Switchesthe current through the switch begins to decrease b e l o w I o , a s t h e remaining current is now steered through the diode V1, which has now turned on. The curren

13、t through the switch ramps down to zero ultimately. Switching waveforms with inductive load are shown in Fig.3-1. Fig.3-1 Switching waveforms with inductive load Section 1 Semiconductor Switches The switching losses are given by s2off1off2on1onossw21fttttIUP(3-3) The switching power losses increase

14、linearly with the switching frequency like in the resistive case but about six times more. The upper bound on the switching frequency is also about half. 2off1off2on1onmaxs1ttttf(3-4)Section 1 Semiconductor SwitchesSwitching with capacitive load The capacitor is assumed to be large so that the volta

15、ge through it in steady state is nearly constant Uo. Assume that initially the switch is on, hence, the current through the switch is IS. The capacitor voltage is Uo, the voltage across the switch is zero and the diode V1 is reverse biased. When the switch is turned off, the switch voltage begins to

16、 ramp up to + Uo while the diode V1 is still off. During this buildup, the current through the switch is held constant at IS . When the voltage buildup isSection 1 Semiconductor Switchesover, the diode Vl begins to conduct and the voltage on the switch is clamped at Uo, and the current through the s

17、witch ramps linearly (again an assumption) down to zero. When the switch is closed, the current begins to build up linearly to IS while the diode V1 is still on. The voltage on the switch remains clamped at UO. After the switch current reaches IS, the diode turns off and the voltage on the switch be

18、gins to ramp down to zero. Section 1 Semiconductor Switches The switching power losses in the case of capacitive load also have similar dependence as in the case of inductive loads. The switching losses can be usually minimized in two ways: divert the energy from the switch to a loss or non-loss cir

19、cuit or switch at either zero current or at zero voltage. The first is called snubbering and the later is known as zero-voltage and zero-current switching. ReturnNew Words and Expressionssemiconductor n. 半導(dǎo)體power electronicn. 電力電子lossn. 損耗，損失parasitic a. 寄生的，附加的windingn. 繞組，線圈 一圈，一轉(zhuǎn) transformer n 變壓

20、器，變換器，變量器dielectric n. 介質(zhì)，電介質(zhì)，絕緣材料；a. 絕緣的，介電的，介質(zhì)的，不導(dǎo)電的 New Words and Expressionseddyn. 渦流，旋渦； a. 渦流的，渦旋的；v. 渦流，起旋渦hysteresis n. 磁滯，滯后，遲滯on-state a. 通態(tài)的，接通的，開態(tài)off-state a. 關(guān)態(tài)的，斷開的，斷態(tài)的microamp n. 微安milliamp n. 毫安steering n. 轉(zhuǎn)向，操縱，控制，調(diào)整 New Words and Expressionsbuildupn. 形成，產(chǎn)生，出現(xiàn) 增加，增大，上升 建造，建起rampv. 斜

21、變，傾斜，直線上升waveform n. 波形clampv. 箝位，定位，使固定snubbering n. 緩沖zero-voltage 電壓過零的zero-current 電流過零的 ReturnTransition of Part of Speech 詞類轉(zhuǎn)換是指把原文語言中的某一詞類轉(zhuǎn)譯為漢詞類轉(zhuǎn)換是指把原文語言中的某一詞類轉(zhuǎn)譯為漢語的另一詞類。語的另一詞類。一、轉(zhuǎn)換為漢語動詞一、轉(zhuǎn)換為漢語動詞 1、名詞轉(zhuǎn)換成動詞、名詞轉(zhuǎn)換成動詞 英語中表達(dá)動作概念的動名詞、具有動作意義的抽英語中表達(dá)動作概念的動名詞、具有動作意義的抽象名詞、由動詞派生出來的名詞、動詞加名詞構(gòu)成的象名詞、由動詞派生出來的

22、名詞、動詞加名詞構(gòu)成的固定短語、介詞加名詞構(gòu)成的固定短語等，往往可以固定短語、介詞加名詞構(gòu)成的固定短語等，往往可以根據(jù)具體情況譯成漢語動詞。根據(jù)具體情況譯成漢語動詞。 (1) The application of electronic computers makes for a tremendous rise in labor productivity. 使用電子計(jì)算機(jī)可以大大提高勞動生產(chǎn)率。 Transition of Part of Speech(2) Computers can provide analyses of every operation in a factory. 計(jì)算機(jī)能對

23、工廠的每道工序進(jìn)行分析分析。(3) Primary forces have certain valuations that must be considered in any design. 在任何設(shè)計(jì)中，對于數(shù)值能確切計(jì)算計(jì)算的主要作用力都必須加以考慮。(4) Integrated circuits are fairly recent development. 集成電路是近年來發(fā)展起來發(fā)展起來的。 Transition of Part of Speech2、形容詞轉(zhuǎn)換成動詞、形容詞轉(zhuǎn)換成動詞 英語中某些由動詞轉(zhuǎn)換來的形容詞、同介詞搭配構(gòu)成句子表語或定語的形容詞、與連系動詞一起構(gòu)成復(fù)合謂語的形

24、容詞，通?？勺g成漢語中的動詞。(1) Copper wire is flexible. 銅線容易彎曲彎曲。(2) Television is different from radio in that it sends and receives pictures. 電視不同于不同于無線電在于能發(fā)送并接收圖像。 Transition of Part of Speech(3) If extremely low-cost power were ever to become available from large nuclear power plants, electrolytic hydrogen

25、would become competitive. 如能從大型核電站獲得獲得成本極低的電力，電解氫的競爭能力就會增強(qiáng)。(4) Heat is a form of energy into which all other forms are convertible. 熱是能的一種形式，其他一切能的形式都能轉(zhuǎn)化轉(zhuǎn)化為熱能。 Transition of Part of Speech3、介詞轉(zhuǎn)換成動詞、介詞轉(zhuǎn)換成動詞 英語中的介詞或介詞短語在許多情況下可以譯成漢語的動詞，尤其是當(dāng)它們用作表語或狀語時(shí)。(1) The letter E is commonly used for electromotive

26、force. 通常用字母E表示表示電動勢。(2) Except for atomic energy, all forms of energy used by man are from the sun. 除原子能之外，人類所利用的一切形式的能量都來來自自太陽。Transition of Part of Speech(3) So long as we have means of producing heat we can keep the steam engine at work. 只要能產(chǎn)生熱，就能使蒸汽機(jī)做做功。 Transition of Part of Speech4、 副詞轉(zhuǎn)換成動詞副詞

27、轉(zhuǎn)換成動詞 英語中有些作表語的副詞或復(fù)合賓語中的副詞，往往可譯成漢語的動詞。(1) The electric current flows through the circuit with the switch on. 如果開關(guān)接通接通，電流就流過線路。(2) Open the valve to let air in. 打開閥門，讓空氣進(jìn)入進(jìn)入。(3) We are through with our test report. 我們的試驗(yàn)報(bào)告寫寫完了。 ReturnExercises I. Choose the best answer into the blank 1. The switching

28、 losses are comprised of the on-state losses, and the losses in the transition states. A. the parasitic lossesB. the dielectric losses C. the off-state lossesD. the hysteresis losses2. The typical power transistors in the on-state have . A. 0.1 VB. 0.7 V C. 2VD. 5V Exercises I. Choose the best answe

29、r into the blank 3. The power transistors, as electrical switches, withstand voltages in the off-state. A. low forwardB. high forward C. low reverseD. high reverse4. The rate of voltage transition and the rate of current steering can produce in the switching devices. A. the switching losses B. the p

30、arasitic losses C. power losses D. the dielectric losses Exercises II. Answer the following questions according to the text 1. Which losses are power losses in the power electronic converters comprised of?2. How to determine the off-state power losses in the electrical switches?3. How do the switching power losses change with the switching frequency?4. How many ways to minimize the switching losses are there? Exercises III. Translate the following into Chinese Diodes in power electronic applications carry high currents, withstand high reverse volt