电力电子复习题

电力电子复习题

1. 已知 ，选择 。

2. What’s the conditions of triggering thyristors into on - state?

Answer : The thyristor can be triggered into the on state by applying a pulse of positive gate current for a short duration provided that the device is in its forward-blocking state.

3. What’s the conditions of keeping thyristors on? And how to turn off the thyristors? Answer : Only when the anode current tries to go negative, under the influence of the circuit in which the thyristor is connected ,does the thyristor turn off and current go to zero, ususlly applying a negative voltage for a short duration.a

4. What are the conditions for the inverter mode operation of controlled rectifiers?

1）There must be DC EMF in the load and the direction of the DC EMF must be enabling current flow in thyristors.

2）

3） α>π/2 so that the output voltage Ud is also negative.

5. In Single-Phase bridge fully-controlled rectifier and three-phase fully-controlled rectifier with R load or RL load, what’s the range of triggering delay angle respectively?

6. 什么是逆变失败？如何防止逆变失败？

逆变运行时，一旦发生换流失败，外接的直流电源就会通过晶闸管电路

形成短路，或者使变流器的输出平均电压和直流电动势变为顺向串联，

由于逆变电路内阻很小，形成很大的短路电流，称为逆变失败或逆变颠

覆。

防止逆变失败的方法有：采用精确可靠的触发电路，使用性能良好的晶闸

管，保证交流电源的质量，留出充足的换向裕量角β等。

7. Description: Classifications and features of power semiconductor devices according to their degree of controllability.

8. Definitions: pulse width modulation (PWM) and switch duty ratio D.

9. Requirements of thyristor gate trigger control circuit ?

10. Description: PWM with bipolar switching and PWM with unipolar switching.

11. Which elements are included in the total power loss on power electronic devices?

12. Description ：two types of soft-switching.

13. Comparing the hard switching with soft switching techniques?

14. Definitions ：voltage source inverters and current source inverters.

15.三相全控桥式整流电路，当—只晶闸管短路时，电路会发生什么情况？

• 1．In a single-phase diode bridge rectifier with zero Ls, R load, if vs is a sinusoidal voltage with Vs=50V at 50Hz, calculate the average output voltage ( )

a ．100V

b ．45V

c ．90V

d ．50V

• 2. During the commutation interval of three-phase half-wave rectifier with Ls, thyristor 1 (phase a) and 2 (phase b) conduct simultaneously, and the dc output voltage vd equal to

( ).

a. 0

b. ua

c. ub

d.

e.

A I d 100=)(av T I H A i i >

• 3. When an ideal controllable switch is on, it ( )

a blocks current with a small forward voltage drop

b blocks current with a large forward or reverse voltage

c conducts large current with a large forwar

d voltag

e drop

d conducts larg

e current with zero voltage drop

• 4. Step-down (Buck) converter can convert ( )

a DC to higher voltage DC

b DC to lower voltage DC

c DC to higher or lower DC

d DC to higher or lower AC

5. In the following controllable switches, ( b ) has the fastest switching speed, and ( c ) has the highest power properties.

a. BJT

b. MOSFET

c. GTO

d. IGBT

• 6. Which does not satisfy the conditions for the inverter mode operation of controlled rectifiers? （）

a．with a feedback diode to conduct current b．a >π/2

c．|EM|>|Ud| d．with a filter inductance

•7. In PWM Switching Scheme, carrier（载波）frequency means ( )

a. the inverter switching frequency

b. output frequency

c. modulating frequency

d. sinusoidal frequency

•8. Effects of transformer leakage inductance on three-phase half-wave rectifier include: current commutation between thyristors can not happen instantly, but take a corresponding ( ); and the average output voltage is ( ).

• a. commutation interval (or commutation angle) b. triggering delay angle

• c. reduced d. increased

• 1.实际整流电路中，变压器绕组总存在一定的漏电感LB，那么LB越小，则换相重叠角γ 。

• 2. 若晶闸管电流有效值是157A，则不考虑安全裕量，其额定电流为。

• 3.双窄脉冲触发是在触发某一号晶闸管时，触发电路同时给______________一号晶闸管补发一个脉冲。

• 4.电力电子器件的损耗包括三方面，一是；

•二是，三是。

• 5.在晶闸管的电流上升到其维持电流后，去掉门极触发信号，晶闸管是否仍能维持导通(能/不能)。

• 1. 单相交流调压电路，画出原理图，在阻性负载条件下，分析电路工作过程，绘制出相应的波形。

• 2.单相交流调压电路，画出原理图，在阻感负载条件下，分析电路工作过程，绘制出相应的波形。

• 3. 画出单相半桥逆变电路原理图，采用PWM调制方式，分析其工作过程，绘制出相应的输出波形。

• 4. 画出单相全桥逆变电路原理图，采用PWM调制方式，分析其工作过程，绘制出相应的输出波形。

•画出降压式斩波电路的原理图，采用脉宽调制控制方式，稳态时在电感电流连续情况下，通过分析工作原理推导输入输出之间的关系。

•三相全控桥变流器，反电动势阻感负载，R=1Ω，L=∞，U2=220V，L B=1mH，当

E M=-400V，β=60°时求U d、I d与γ的值，此