电气工程及其自动化专业英语第三章翻译Semiconductor switches are very important and crucial components in power electronic systems.these switches are meant to be the substitutionsof the mechanical switches,but they are severely limited by the propertiesof 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 windingresistances of the inductors and transformers,the dielectric lossesofcapacitors,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 lossesin 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。
On-State Losses：The electrical switches conduct heavy current and have nonzero voltageacross the switch in the on-state.The on-state power losses aregiven byPon=Uson if.这个电子开关能导通大电流，并且在通态时有非零的压降。
这个通态功率损耗的公式为Pon=Uson if.The Uson and If are respectively the switch voltage in the on-state and the forward current through the switch.For example,the typical powerdiodes and the power transistors have nearly 0.5 to l volt across themin the on-state.The forward currents can be hundreds to thousands of amperes.The on-state power losses are very significant. 其中Uson是通态时开关上的压降，if是流过开关的电流。
例如，典型的功率二极管和功率晶体管有近似0.5~1伏的通态压降。
而电流会有数百到数千安培。
这个通态损耗非常重要。
Off-State Losses断态损耗The electrical switches withstand high voltages and have nonzeroleakage current through the switch in the off-state.The off-state powerlesses 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 voltagesin hundreds to thousands of volts and microamps to milliamps through themin 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：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 switchingdevices.Wewill examine these switching losses in two cases separately:the inductiveand 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：The indutor is assumed to be large so that the current through it in steady state is nearly constant Io.Assume that initially the switchisoff.The inductor current is +Io and freewheels through diode V1.When theswitch is turned on,the current through the switch begins to builduplinearly(an assumption)to+Io while the diode V1 is still on.The on diode has zero voltage across it(an ideal diode),hence,the voltageon theswitch is held constant at+Us.When the current buildup is over,the diodeV1 ceases to conduct and the voltage on the switch rampslinearly(againan 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 linearlyto +us while the diode V1 is off. while the diode is off the current throughthe switch equals the inductor current,which is constant I0 After theswitch voltage reaches aero, the current through the switch begins todecrease below I0,as the remaining current is now steered through thediode V1 which has now turned on The current through the swithch rampsdown to zero ultimately. Switching waveforms with inductive load are shownin 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3-1The switching losses are given by : Psw=1/2UsIo[……….]fsPsw=1/2UsIo[……….]fsThe switching power losses increase linearly with the switchingrequency like in the resistive case but about six times more. The upperbound 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 LoadThe capacitor is assumed to be large so that the voltage through is in stedy state is nearly constant U0.Assume that initially the switch ison,hence,the cuttent through the switch is IS.The capacitor voltage isU the voltage across the switch is zero and the diode V1is reverse biased.When the switch is turned off,the switch voltage begins to rampup to+U0 while the diode V1 is still off.During this buildup,the currentthrough the switch is held constant at Is.Wheng the voltage buildup isover,the diode V1begins to conduct and the voltage on the switch is clampedat 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。