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电气工程及其自动化专业英语翻译ppt素材

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这是一个关于电气工程及其自动化专业英语翻译ppt素材,主要介绍电路基本原理、电子学、电机等相关内容。欢迎点击下载哦。

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电气工程及其自动化专业英语翻译ppt素材

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第一章  电路基本原理
第一节  电流和电压
Exercises(41)
           模拟电子电路是关于其中电压和电流是对物理量进行模拟的且连续变化那些系统。复制音乐的电子电路必须具有与声音成正比的电压和电流。一个高保真的放大系统要尽可能保持模拟量不失真,我们要仔细地设计模拟电子电路以使电压和电流反映输入信号。如果输入信号在幅值上增大一倍,输出的电压和电流也应增大一倍。这是可能的。因为为了保证线性(度)我们使电路元件工作在限定范围内。
一、背景知识
模拟信号和数字信号
   (1)模拟信号    信号波形模拟着信息的变化而变化。其特点是幅度连续(连续的含义是在某一取值范围内可以取无限多个数值)。
   (2)数字信号    其特点是幅值被限制在有限个数值之内,即幅值不是连续的而是离散的。
一、背景知识
布尔代数也称为逻辑代数。它是英国数学家乔治-布尔(1815-1864)于1849年创立的。在当时,这种代数纯粹是一种数学游戏。在布尔代数里,布尔构思出一种关于0和1的代数系数,用基础的逻辑符号系统描述物体和概念。这种代数不仅广泛于概率和统计等领域,更为重要的是,它为数字计算机开关电路设计提供了最重要的数学方法。
布尔代数应用于三种基本类型的逻辑门的运算:一种是或门,一种是与门,还有一种是反相器(非门)。逻辑门的符号和真值表如图2-3所示,真值表显示与门对应于乘,或门对应于加,而反相器产生其输入变量的补码。
           我们已经算出对于与门来说  AB=“A AND B”
    而对与或门来说 A+B=“A OR B”
          对于“与”,即逻辑乘,以及“或”,即析取,它们的代数形式必须遵循代数组合的三个法则。在接下来的等式中,读者可以把变量A,B,C设为两个
可能的值0和1来证明每个表达式的正确性。例如采用A=0,B=0,C=0,或A=1, B=0,C=0等等,在每个表达式中,结合律表明如何把变量进行重组。
第三章   
Semiconductor switches are very important and crucial components in power electronic systems.these switches are meant to be the substitutions of the mechanical switches,but they are severely limited by the properties of the semiconductor materials and process of manufacturing. 在电力电子系统,中半导体开关是非常重要和关键部件。半导体开关将要替换机械开关,但半导体材料的性质和生产过程严重限制了他们。
Switching losses开关损耗
Power losses in the power eletronic converters are comprised of the Switching losses and parasitic losses. 电力电子转换器的功率损耗分为开关损耗和寄生损耗
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. 寄生损失的绕组电感器、变压器的阻力、介电损耗的电容器,涡流和磁滞损耗
the switching losses are significant and can be managed. 这个开关损耗是非常重要的,可以被处理。they can be further divided into three components:(a)the on-state losses,(b)the off-state losses and the losses in the transition states. 他们可以分为三个部分: 通态损耗,断态损耗和转换过程中产生的损耗。
Off-State Losses断态损耗
The electrical switches withstand high voltages and have nonzero leakage current through the switch in the off-state.The off-state power lesses are given by Poh=Uoff ir在关断状态时,电子开关到经受得起高电压,并会有非零的漏电流。断态损耗的公式为Poh=Uoff ir.
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 the off state. 其中Uoff在断态时的反向偏置电压,ir是流过开关的反向漏电流。例如,典型的功率二极管和功率晶体管有很高的反向压降几百到几千伏和几微安到几毫安的漏电流。
Transition-State Losses转换损耗:
The practical switching devices have limited capabilities of rate of voltage transition and the rate of current steering.These nonabrupt transition rates give rise to power losses in the switching devices.We will examine these switching losses in two cases separately:the inductive and capacitive loads. 在实际的开关装置限制了电压变换率和电流变化率。非突变引起了开关装置的功率损耗。我们测试开关损耗时分两种情况:感性负载和容性负载。
Switching with Inductive Load接感性负载的开关:
The indutor 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 through 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.The on diode has zero voltage across it(an ideal diode),hence,the voltage on the switch is held constant at+Us.When the current buildup is over,the diode V1 ceases to conduct and the voltage on the switch ramps linearly(again an assumption)down to zero. 假设电感无穷大,即在稳定时流经电感的电流是恒定的Io,假定开始时开关处于关断状态。电感电流为+Io惯性流过二极管V1。当开关闭合后,电流流经开关开始建立线性上升+Io此时二极管扔导通。二极管压降为0,此时开关两端电压维持在+Us当电流建立完成后,二极管V1截止,开关两端电压线性下降为0。
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 the switch equals the inductor current,which is constant I0 After the switch voltage reaches aero, the current through the switch begins to decrease below I0,as the remaining current is now steered through the diode V1 which has now turned on The current through the swithch ramps down to zero ultimately. Switching waveforms with inductive load are shown in Fig.3-1开关打开后,开关两端电压线性上升至Us。此时二极管仍截止,二极管截止,流过开关的电流相当于流过电感的电流,维持在恒定的Io。开关电压到0时,通过开关的电流开始上升到Io以下。此时余留的电流正转向二极管V1,V1导通。最终通过开关的电流下降到0,开关过程的波形的电感负载波形见图3-1
  The switching losses are given by : Psw=1/2UsIo[……….]fs
开关损耗的公式是Psw=1/2UsIo[……….]fs
  The switching power losses increase linearly with the switching requency like in the resistive case but about six times more. The upper bound on the switching frequency is also about half. 开关功率损耗线性增加随着开关频率 此时的损耗要比阻性负载损耗的6倍还多。当f取最大时  Psw=1/2UsIo。
Switching with capacitive Load开关接有容性负载
The capacitor is assumed to be large so that the voltage through is in stedy state is nearly constant U0.Assume that initially the switch is on,hence,the cuttent through the switch is IS.The capacitor voltage is U the voltage across the switch is zero and the diode V1is reverse biased.When the switch is turned off,the switch voltage begins to ramp up to+U0 while the diode V1 is still off.During this buildup,the current through the switch is held constant at Is.Wheng the voltage buildup is over,the diode V1begins to conduct and the voltage on the switch is clamped at U0,and the current through the switch ramps linearly(again an assumption)down to zero. 假设电容器很大,致使在稳定状态下其两端电压接近为常数Uo。假使开关初始状态为闭合,则通过开关的电流为Is。电容器的电压为Uo开关两端的电压为零,二极管V1反向偏置。当开关打开后,开关两端电压开始上升到Uo,此时二极管一直关断。当电压等于Uo时,二极管V1开始导通并且开关两端电压被钳位在Uo。流过开关的电流线性下降到零。
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 U0.After the switchcurrent reaches Is ,the diode turns off and the voltage on the switch begins to ramp down to zero. 当开关闭合,电流开始上升至Is,此时V1仍然导通,开关两端电位被钳位在Uo。当开关电流等于Is时,二极管关断并且开关两端电压线性下降至0。
The switching power losses in the case of capacitive load also have similar dependence as in the case of inductive loads. 当开关闭合,电流开始上升至Is,此时V1仍然导通,开关两端电位被钳位在Uo。当开关电流等于Is时,二极管关断并且开关两端电压线性下降至0。
The switching power losses in the case of capacitive load also have similar dependence as in the case of inductive loads. 接容性负载情况下的开关功率损耗的决定因素与感性负载情况下有相似之处。
The switching losses can be usually minimized in two ways; 1divert the energy from the switch to a loss or non-loss circuit or 2switch at either zero current or at zero voltage.The first is called snubbering and the later is known as zero-voltage and zero-current swithching. 开关损耗一般被归为两点:1。开关的能量转化成了损耗或无损耗电流或开关的过0电流或过0电压,第一个被称为缓冲,最后一个被成为过0电流或过0电压的开关。
专业英语期末复习
划出下列句中的从句,并说出其名称,然后将句子译成汉语。

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