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1、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
2、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 transforme
3、rs,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
4、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。 On-State Losses 通态损耗通态损耗： 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 Pon=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
5、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 amperes.The on-state p
6、ower 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 0.51 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 nonzero leakage current through the switch in the off-state.The off-state power lesses are given
7、 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 thousan
8、ds 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 转换损耗转换损耗： The practical switching devices have limited capabilities of rate of voltage transition and the rate of current ste
9、ering.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 接感性负载的开关接感性负载的
10、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 a
11、ssumption)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.
12、 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 th
13、rough 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
14、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 开关损耗的公式是开关损耗的公式是 Psw
15、=1/2UsIo.fsThe 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
16、载开关接有容性负载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
