问题 问答题 简答题

换流站中交流侧和直流侧的特征谐波是如何产生的?

答案

参考答案:在换流站中产生谐波的主要元件为换流器。换流器在交直流转换的过程的同时,在交流侧它相当于一个谐波电流源,它畸变交流电流波形,向交流系统发出一系列的高次谐波电流,同时也畸变了交流电压波形。而在直流侧它相当于一个谐波电压源,它畸变直流电压波形,向直流侧发出一系列的谐波电压,在直流线路上产生谐波电流。

阅读理解

阅读理解。

Mr. Wise,

     I'm a slow (迟钝的) student. Most of my classmates are much better than me. So I usually get stressed

out. Although I spend much time studying for the tests, I can't get good grades, Sometimes my father gives

me some help. He tells me not to worry about it. But it doesn't work. What do you think I should do?

                                                                                                                                         Xiaoming

Dear Xiaoming,

     Many famous people were not so good when they were young. Edison, a famous scientist (科学家) did

poorly in his studies when he was a 12-year-old boy. But he did a lot for the people in the world at last.

When I was at your age, I didn't do well at school. But I kept working hard and I succeeded at last. You

should take it easy and try your best. Tomorrow is another day. I believe you can do better.

                                                                                                                                    Mr. Wise

1. Xiaoming feels worried because ________.

A. he has a headache

B. he doesn't want to work hard

C. he is not as good as most of his classmates

2. Xiaoming wrote this letter to ________.

A. ask for some help

B. find a pen pal

C. tell his father his problem

3. Mr. Wise wrote about a famous person to ________.

A. make Xiaoming angry

B. make Xiaoming feel better

C. show how much he knows

4. In Mr. Wise's letter,"tomorrow is another day" means ________.

A. a lot of hopes are in our lives

B. one can get good grades tomorrow

C. tomorrow is the same as today

5. From the second letter, we know Mr. Wise might be ________ before.

A. a doctor

B. a scientist

C. a slow student

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