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Control systems are designed to perform specific tasks. The requirements imposed on the
control system are usually referred as performance specifications. They generally relate to
accuracy, relative stability and speed of response.
Generally, the performance specifications should not be more stringent than necessary to
perform the given task. If the accuracy at steady-state operation is of prime importance in a given
control system, then we should not require unnecessarily rigid performance specifications on the
transient response since such specifications will require expensive components. We should
remember that the most important part of control system design is to state the performance
specifications precisely so that they will yield an optimal control system for a given purpose.
[1]
In this lesson, we are going to briefly introduce the design and compensation procedure of
single-input-single-output (SISO) , linear time-invariant (LTI) control systems by the frequency
response and root-locus approaches. Compensation is the modification of the system dynamics to
satisfy the given specifications.
Setting the gain is the first step in adjusting the system for satisfactory performance. In many
cases, increasing the gain value will improve the steady-state behavior but will result in poor
stability or even instability. Then it is necessary to redesign the system (by modifying the
structure or by incorporating additional devices or components) to alter the overall behavior so
that the system will behave as desired.
Fig. 8.1 shows the configuration where the compensator
C()Gs is placed in series with the plant. This scheme is
called series compensation. Another kind of compensation is
feedback compensation. Generally, series compensation may
be simpler than feedback compensation.
In discussing compensators, we frequently use terminology as lead network, lag network,
and lag-lead network. If a sinusoidal input ie is applied to the input of a network and the
steady-state output oe (which is also sinusoidal) has a phase lead, then the network is called a
lead network. Similarly, if the steady-state output oe has a phase lag, then the network is called
a lag network. In a lag-lead network, phase lag and phase lead both occur in the output but in
different frequency regions; phase lag occurs in the low-frequency region and phase lead occurs
in the high-frequency region.
Fig. 8.1 Series compensation
自动化专业英语 ·82·
·82·
Root-locus approach to control system design
The root-locus method is a graphical method for determining the locations of all closed-loop
poles from knowledge of the locations of the open-loop poles and zeros as some parameter
(usually the gain) is varied from zero to infinity. The method yields a clear indication of the
effects of parameter adjustment. In practice, the root-locus plot of a system may indicate that the
desired performance cannot be achieved just by the adjustment of gain. Then it is necessary to
reshape the root loci to meet the performance specifications.
In designing a control system, we may modify the original root loci by inserting a suitable
compensator ()CGs(as shown in Fig.8.1). Once the effects on the root locus of the addition of
the poles and/or zeros are fully understood, we can readily determine the locations of the pole(s)
and zero(s) of the compensator that will reshape the root locus as desired.
[2]
In the design by the
root-locus method, the root-loci of the system are reshaped through the use of a compensator so
that a pair of dominant closed-loop poles can be placed at the desired locations. (Usually, the
damping ratio and undamped natural frequency may be specified by the locations of a pair of
dominant closed-loop poles.)
[3]
The addition of a pole to the open-loop transfer function has the effect of pulling the root
locus to the right, tending to lower the system's relative stability and to slow down the settling of
the response.
[4]
The addition of a zero has the effect of pulling the root locus to the left, tending
to make the system more stable and to speed up the settling of the response.
The root-locus approach to design is very powerful when the specifications are given in
terms of time domain quantities, such as the damping ratio and undamped natural frequency,
maximum overshoot, rise time and settling time.
Let us consider a design problem. The original system either is unstable for all values of
gain or is stable but has undesirable transient response characteristics. In this case, the reshaping
of the root locus is necessary in order that the dominant closed-loop poles be at desired locations
in the complex plane. Inserting an appropriate lead compensator in cascade with the feed-
forward transfer function may solve this problem.
[5]
Frequency-response approach to control system design
It is important to note that in a control system design, transient-response performance is
usually most important. In the frequency-response approach, we specify the transient-response in
terms of the phase and gain margin, resonant peak magnitude, the gain crossover frequency,
resonant frequency and bandwidth.
[6]
Although the correlation between the transient response
and frequency response is indirect, the frequency domain specification can be met conveniently
by means of Bode diagram.
Design in the frequency domain is simple and straightforward. After the open loop has been
Lesson 8 System Design and Compensation Techniques ·83·
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designed by frequency response method, the closed loop poles and zeros can be determined. The
transient response characteristics must be checked to see whether the designed system meets the
requirements in the time domain. If it does not, the compensator has to be modified and the
analysis must be repeated until a satisfactory result is obtained.
Basically, there are two approaches in the frequency-domain design. One is the polar plot
approach and the other is the Bode diagram approach. It is more convenient to work with Bode
diagram. A Bode diagram of the compensator can be simply added to the original Bode diagram,
and thus plotting the complete Bode diagram is a simple matter.
[7] Also, if the open loop gain is
varied, the magnitude curve is shifted up or down without changing the slope of the curve, and
the phase curve remains the same.
A common approach to the Bode diagram is that we first adjust the open loop gain so that
the requirement on the steady state accuracy is met. Then we plot the magnitude and phase
curves of the uncompensated open loop. If the specification on the phase margin and gain margin
are not satisfied, then a suitable compensator that will reshape the open loop transfer function is
determined.
In many practical cases, compensation is essentially a compromise between steady-state
accuracy and relative stability. In order to have a high value of the velocity error constant and yet
satisfactory relative stability, we find it necessary to reshape the open loop frequency response
curve. The gain in the low-frequency region should be large enough to satisfy the steady-state
accuracy requirements. For the medium-frequency region (near the gain crossover frequency
Cωfrom both directions) , the slope of the log-magnitude curve in the Bode diagram should be
-20 dB per decade.
[8]
This slope should extend over a sufficient wide frequency band to assure a
proper phase margin. For the high-frequency region, the gain should be attenuated as rapidly as
possible to minimize the effects of noise.
The basic characteristics of lead, lag, and lag-lead compensation are as following. Lead
compensation essentially yields an appreciable improvement in transient response and a small
change in steady-state accuracy. It may accentuate high-frequency noise effects. On the other
hand, lag compensation yields an appreciable improvement in steady-state accuracy at the
expense of increasing the transient-response time. Lag compensation will suppress the effects of
high-frequency noise signals. Lag-lead compensation combines the characteristics of both lead
compensation and lag compensation.
New Words and Phrases
1. compensation [kCmpen5seiFEn] n. 补偿,调整,校正
2. impose [im5pEuz] v. 将……强加于,施加,使……负担
3. stringent [5strindVEnt] adj. 严厉的,迫切的
4. root-locus [5ru:t-5lEukEs] n. (pl. root-loci) 根轨迹
5. indication [indi5keiFEn] n. 指示,指出,显示,暗示
6. transient [5trAnziEnt] adj. 暂态的,瞬时的,过渡过程的
自动化专业英语 ·84·
·84·
7. magnitude [5mAgnitju:d] n. 量值,幅度
8. straightforward [streit5fC:wEd] adj. 直截了当的
9. accentuate [Ak5sentjueit] v. 加强,强调
10. attenuate [E5tenjueit] v. 削弱
11. approach [E5prEutF] n. 方法,途径
12. characteristic [7kAriktE5ristik] n. 特性,特征
adj. 特有的,典型的
13. prime [praim] n. 最初,青春,精华
adj. 主要的,最初的,有活力的,
最好的,根本的,素数的
14. rigid [5ridVid] adj. 刚硬的,刚性的,严格的,坚硬的,
僵直的,坚决的,固定的
15. transient response 暂态响应,过渡反应,瞬时 [瞬态]
反应,瞬时反应特性,瞬时特性
16. yield [ji:ld] vt. 出产,产生,生长,生产vi.(～to)
屈服,屈从,放弃
n. 产量,收益
17. time-domain 时域的
18. overshoot [5EuvE5Fu:t] vt. 打过头,飞过目标,超过,越过
vi. 射击越标,行动过火
n. 超调量
19. settling time 调整时间
20. phase margin 相位裕量
21. gain margin 增益裕度
22. resonant [5rezEnEnt] adj. (引起)共鸣的,响亮的,
共振的,深沉的
23. perk [pE:k] vi. 昂首,恢复,振作
vt. 竖起,打扮
24. resonant perk value 谐振峰值
25. bandwidth [5bAndwitW] n. 带宽,频带宽度
Notes
[1] We should remember that the most important part of control system design is to state the
performance specifications precisely so that they will yield an optimal control system for a given
purpose.
我们应该牢记,控制系统设计过程中最重要的一个环节就是把性能要求精确地表达出
来,这样才会设计出对于给定的目的而言最优的控制系统.
本句的结构比较复杂.在remember后面that所引导的从句是宾语从句,在该从句中
"to state…"是从句中的表语从句.在翻译这种英语长句时,不能够拘泥于原句的语法结
Lesson 8 System Design and Compensation Techniques ·85·
·85·
构,而应该在充分理解该语句意思的基础之上,重新组织,再用通顺的汉语表达出来.如
果过分拘泥于原来的语法结构,则翻译出来的汉语不通顺.科技英语翻译就是要在尽可能
忠实于原文的基础上,将通顺的英语(或汉语)所表达的意思转换成用通顺的汉语(或英语)
表达.
[2] Once the effects on the root locus of the addition of the poles and/or zeros are fully
understood, we can readily determine the locations of the pole(s) and zero(s) of the compensator
that will reshape the root locus as desired.
一旦我们完全理解了增加极点和/或零点对于根轨迹的影响,我们就可以很方便地确定
补偿器零点和极点的位置,以使得根轨迹改变成为我们所希望的形状.
Once引导条件状语从句,而且该条件状语从句是用被动语态.Compensator后面的
that…引导定语从句修饰the pole(s) and zero(s) of the compensator.
[3] In the design by the root-locus method, the root-loci of the system are reshaped through
the use of a compensator so that a pair of dominant closed-loop poles can be placed at the desired
locations. (Usually, the damping ratio and undamped natural frequency may be specified by the
locations of a pair of dominant closed-loop poles.)
在用根轨迹法设计的过程中,通过使用补偿器改变系统根轨迹的形状,以使闭环系统
一对主导极点位于理想的位置.(通常,阻尼比和无阻尼自然振荡频率是由闭环系统一对主
导极点的位置确定的.)
本句中有两个状语,In the design by…介词短语作状语表示场合;而so that a pair of…
状语从句表示结果.
[4] The addition of a pole to the open-loop transfer function has the effect of pulling the root
locus to the right, tending to lower the system's relative stability and to slow down the settling of
the response.
在开环传递函数中增加一个极点的效果是把根轨迹向右推,倾向于降低系统的相对稳
定性,并且降低系统的收敛速度.
介词短语The addition of a pole to the open-loop transfer function是句子的主语,现在分
词短语tending to lower…作状语,表示伴随状态.
[5] Inserting an appropriate lead compensator in cascade with the feed-forward transfer
function may solve this problem.
在前向传递函数中串联插入一个适当的超前补偿器,就可以解决这个问题.
动名词短语Inserting an…是句子的主语.
[6] In the frequency-response approach, we specify the transient-response in terms of the
phase and gain margin, resonant peak magnitude, the gain crossover frequency, resonant
frequency and bandwidth.
在频率响应法中,我们以相位裕量及增益裕量,谐振峰值幅度,增益穿越频率,谐振
频率和带宽来表征暂态响应.
在这个句子中,the phase and gain margin, resonant peak magnitude, the gain crossover
frequency, resonant frequency and bandwidth并列成为介词短语in terms of后面的宾语.
[7] A Bode diagram of the compensator can be simply added to the original Bode diagram,
自动化专业英语 ·86·
·86·
and thus plotting the complete Bode diagram is a simple matter.
补偿器的伯德图可以简单地加在原伯德图上,因此画完整的伯德图是很简单的事.
句子中and thus plotting…是一个并列句,其中动名词短语plotting the complete Bode
diagram作主语.
[8] For the medium-frequency region (near the gain crossover frequencyCωfrom both
directions) , the slope of the log-magnitude curve in the Bode diagram should be -20 dB per
decade.
在中频段(靠近幅频曲线的穿越频率Cω的两边),在伯德图中对数幅值曲线的斜率应该
为-20 dB/dec.
本句中括号内的部分是介词短语作为定语,用来修饰region.
Translating Skills 数词的译法
在专业英语中,数词出现的频率很高,对数词的翻译及读法的掌握程度会影响对专业
的学习,研究及交流.现分别介绍一些专业英语中常用的数词的译法和数学符号,公式的
读法.
1. 基数词的译法和读法
(1) 从1到12是单个单词: 十一 11 eleven 十二 12 twelve
(2) 从13到19加后缀-teen: 十三 13 thirteen 十九 19 nineteen
(3) 从20到90 加后缀-ty: 二十 20 twenty 二十三23 twenty-three
九十 90 ninety
百位数以上:
五百 500 five hundred
五百六十一 561 five hundred (and) sixty-one
五千六百六十一 5,661 five thousand six hundred (and) sixty-one
2. 序数词的译法和读法
序数词翻译时加"第……",如 twelfth 12th 第十二 thirtieth 30th 第三十
3. 数词的增加和减少的译法和读法
(1) The oxygen atom is nearly 16 times heavier than the hydrogen atom.
氧原子的重量几乎是氢原子的16倍.(如果把16用n代替,常译作"是……的n倍,
或"比……(大,多,长)n-1倍")
(2) The diode produces 5 times more radiant power than that one.
这只二极管的辐射功率比那只大4倍(是那只的5倍)(同上).
(3) The wire is twice as long as that one.
这根电线的长度是那根的两倍.(如果把twice用n代替,常译作"是……的n倍,或
"比……(大,多,长)n-1倍")
(4) The production of air-conditioners has increased three times this year.
Lesson 8 System Design and Compensation Techniques ·87·
·87·
今年空调的产量增加2倍(增加到3倍).(如果句中three用n表示,那么常译成"增加
了n-1倍或增加到n倍")
(5) The production of air-conditioners has increased by three times over the previous year.
今年空调的产量比上一年增加了3倍.
(6) The production of air-conditioners has decreased by three times over the previous year.
今年空调的产量比上一年减少了3倍.
(7) The production of air-conditioners has increased to three times this year.
今年空调的产量增加到了3倍.
(8) The production of air-conditioners has increased by a factor of three times this year.
今年空调的产量增加2倍.(如果句中three用n表示,那么常译成"增加了n-1倍"
类似减少的译法有:
(1) reduce by 10% 减少了10%
(2) reduce to 10% 减少到10%
(3) reduce by a factor of 10 减少了9/10(减少到 1/10)
(4) reduce 10 times 减少到1/10(减少了9/10)
4.分数,小数,时间等的译法和读法
(1) 简单的分数.
1/7 七分之一 one seventh 3/4 四分之三 three quarters
1/4 四分之一 a/one quarter 1/2 二分之一 a/one half
4
1
2
四又二分之一 four and a half 3
4
5
三又五分之四 three and four-fifths
(2) 复杂的分数.
24/9 九分之二十四 twenty-four over nine
20/83 八十三分之二十 twenty over eight three (twenty eighty-thirds)
7/20 二十分之七 seven twentieths
67/200 二百分之六十七 sixty-seven two hundredths
(3) 小数.
0.124 零点一二四 (nought) point one two four
0.24 零点二四 (nought) point two four
0.4 零点四 (nought) point four
16.789 十六点七八九 one six point seven eight nine
(4) 时间或其他.
60年代初期 in the early sixties
本世纪90年代 in the nineties of the century
20世纪90年代(1990s, 1990's) nineteen nineties
2005年10月10日 October 10th, 2005 (10 th October, 2005/ October 10, 2005/ 10 October
2005)
Fig.7 图7(直译)
14′59.38〃十五分五十九点三八秒 fourteen minutes fifty-nine point three eight seconds
自动化专业英语 ·88·
·88·
5. 数学符号,公式的读法
+ 加(上) plus/and
- 减(去) minus
× 乘以 times; multiplied by
÷ 除以 divided by/divided
= 等于 is equal to/equals
≈ 大约等于 is approximately equal to
( ) 圆括号 round brackets/parentheses
[ ] 方括号 squared brackets
/ 斜杠 slash
65% 百分之六十五 65 percent
109 十的九次方 the ninth power of ten/ten to the power nine/ten to the
ninth power
10-5 十的负五次方 en to the minus five
x′ x prime
x〃 x second prime
xe x sub e
2 根号2 the square root of 2
≥ 大于或等于 is more than or equal to
≤ 小于或等于 is less than or equal to
> 大于 is more than
δ delta
Φ Phi
Ω omega
ε epsilon
∝ 与……成比例 varies as/ is proportional to
ω omega
5 mm 5毫米 5 millimeters
x→∞ x approaches to infinity
Exercises
1. Translate the following into Chinese.
(1) Generally, we should adopt reasonable performance specifications while we are
designing a control system.
(2) We often use lead network, lag network, or lag-lead network to work as compensators in
control system compensation.
(3) Compensation for a closed-loop control system is essentially a compromise between
steady-state accuracy and relative stability of the system.
Lesson 8 System Design and Compensation Techniques ·89·
·89·
(4) The substance reacts three times as fast as the other one.
(5) The students who take part in physical activities have increased to 10,000.
(6) One in five women born in 1970 has suffered from depression and anxiety in their
thirties, twice the rate of those born in 1940, the University of London has found.
2. Translate the following into English.
(1) 使用根轨迹法设计控制系统补偿器,就是为了使闭环系统的一对主导极点位于左
半S平面中的理想位置.
(2) 超前补偿可以明显改善控制系统的暂态响应,对稳态精度没有影响.
(3) 用伯德图设计的常用方法是,我们首先调节开环增益,以使稳态精度的要求得到
满足.
(4) 那位警察要了比平常多一倍的罚款.
(5) 去年钢产量减少了20%.
(6) 这家造纸厂的产量比1980年增加两倍.
Reading Material An Eye on Reactor and Computer Control
A nuclear power plant operator stared at the computer screen and yawned. As the end of a
long shift approached, he was feeling very tired as he looked at icons of pumps, pipes, and
turbines. Even so, it was still early in the reactor startup sequence. When an indication that the
reactor had gone critical appeared on the screen, the operator tried to rouse himself. There was no
need for him or anyone else to be alarmed, however. Based on the way the operator looked at the
screen, the computer had already sensed that he was tiring and had begun to assist the operator in
reactor control. The computer zoomed in on the displays the operator needed to monitor
reactivity and highlighted the important data. It would even be capable of assuming partial
reactor control if necessary.
At a research laboratory, a cognitive scientist put a diskette in her computer and studied the
screen. The data indicated that a reactor operator had been glancing at a number of widely
scattered points in a short time on the computer screen in the reactor control room. "All these eye
movements," said the scientist, "tell me the operator is experiencing excessive mental work load.
It seems that several displays associated with reactor control must be redesigned to make it easier
for the operator to understand quickly what's going on."
A teenager who lost the use of both hands as a result of an automobile accident had found a
way to write again. His father bought him an "eye typewriter"——a computer that displays and
prints letters from a display of the alphabet on the screen in the order in which they are stared at.
The boy enjoyed his ability to control a computer simply by looking at it.
These futuristic scenarios suggest that information on eye gazes——the way people look at
an object——can be put to use to determine a person's mental work load and level of fatigue, to
guide the design of computer displays to speed human processing of information, and to control
自动化专业英语 ·90·
·90·
computers. Other applications include controlling camera positions on robots and guiding an
artificial intelligence system in recognizing enemy targets.
At ORNL computer software has been developed to make possible an improved eye-gaze
measurement technology. Such an innovation could be the basis for advanced eye-gaze systems
that may have applications such as those mentioned above.
New Words and Phrases
1. yawn [jC:n] v. n. 打哈欠,哈欠
2. turbine [5tE:bin] n. 涡轮机
3. critical [5kritikEl] adj. 危急的,临界的
4. scatter [5skAtE] v. 分散,散开,驱散
5. innovation [7inEu5veiFEn] n. 改革,创新
6. zoom in (镜头)放大
control system are usually referred as performance specifications. They generally relate to
accuracy, relative stability and speed of response.
Generally, the performance specifications should not be more stringent than necessary to
perform the given task. If the accuracy at steady-state operation is of prime importance in a given
control system, then we should not require unnecessarily rigid performance specifications on the
transient response since such specifications will require expensive components. We should
remember that the most important part of control system design is to state the performance
specifications precisely so that they will yield an optimal control system for a given purpose.
[1]
In this lesson, we are going to briefly introduce the design and compensation procedure of
single-input-single-output (SISO) , linear time-invariant (LTI) control systems by the frequency
response and root-locus approaches. Compensation is the modification of the system dynamics to
satisfy the given specifications.
Setting the gain is the first step in adjusting the system for satisfactory performance. In many
cases, increasing the gain value will improve the steady-state behavior but will result in poor
stability or even instability. Then it is necessary to redesign the system (by modifying the
structure or by incorporating additional devices or components) to alter the overall behavior so
that the system will behave as desired.
Fig. 8.1 shows the configuration where the compensator
C()Gs is placed in series with the plant. This scheme is
called series compensation. Another kind of compensation is
feedback compensation. Generally, series compensation may
be simpler than feedback compensation.
In discussing compensators, we frequently use terminology as lead network, lag network,
and lag-lead network. If a sinusoidal input ie is applied to the input of a network and the
steady-state output oe (which is also sinusoidal) has a phase lead, then the network is called a
lead network. Similarly, if the steady-state output oe has a phase lag, then the network is called
a lag network. In a lag-lead network, phase lag and phase lead both occur in the output but in
different frequency regions; phase lag occurs in the low-frequency region and phase lead occurs
in the high-frequency region.
Fig. 8.1 Series compensation
自动化专业英语 ·82·
·82·
Root-locus approach to control system design
The root-locus method is a graphical method for determining the locations of all closed-loop
poles from knowledge of the locations of the open-loop poles and zeros as some parameter
(usually the gain) is varied from zero to infinity. The method yields a clear indication of the
effects of parameter adjustment. In practice, the root-locus plot of a system may indicate that the
desired performance cannot be achieved just by the adjustment of gain. Then it is necessary to
reshape the root loci to meet the performance specifications.
In designing a control system, we may modify the original root loci by inserting a suitable
compensator ()CGs(as shown in Fig.8.1). Once the effects on the root locus of the addition of
the poles and/or zeros are fully understood, we can readily determine the locations of the pole(s)
and zero(s) of the compensator that will reshape the root locus as desired.
[2]
In the design by the
root-locus method, the root-loci of the system are reshaped through the use of a compensator so
that a pair of dominant closed-loop poles can be placed at the desired locations. (Usually, the
damping ratio and undamped natural frequency may be specified by the locations of a pair of
dominant closed-loop poles.)
[3]
The addition of a pole to the open-loop transfer function has the effect of pulling the root
locus to the right, tending to lower the system's relative stability and to slow down the settling of
the response.
[4]
The addition of a zero has the effect of pulling the root locus to the left, tending
to make the system more stable and to speed up the settling of the response.
The root-locus approach to design is very powerful when the specifications are given in
terms of time domain quantities, such as the damping ratio and undamped natural frequency,
maximum overshoot, rise time and settling time.
Let us consider a design problem. The original system either is unstable for all values of
gain or is stable but has undesirable transient response characteristics. In this case, the reshaping
of the root locus is necessary in order that the dominant closed-loop poles be at desired locations
in the complex plane. Inserting an appropriate lead compensator in cascade with the feed-
forward transfer function may solve this problem.
[5]
Frequency-response approach to control system design
It is important to note that in a control system design, transient-response performance is
usually most important. In the frequency-response approach, we specify the transient-response in
terms of the phase and gain margin, resonant peak magnitude, the gain crossover frequency,
resonant frequency and bandwidth.
[6]
Although the correlation between the transient response
and frequency response is indirect, the frequency domain specification can be met conveniently
by means of Bode diagram.
Design in the frequency domain is simple and straightforward. After the open loop has been
Lesson 8 System Design and Compensation Techniques ·83·
·83·
designed by frequency response method, the closed loop poles and zeros can be determined. The
transient response characteristics must be checked to see whether the designed system meets the
requirements in the time domain. If it does not, the compensator has to be modified and the
analysis must be repeated until a satisfactory result is obtained.
Basically, there are two approaches in the frequency-domain design. One is the polar plot
approach and the other is the Bode diagram approach. It is more convenient to work with Bode
diagram. A Bode diagram of the compensator can be simply added to the original Bode diagram,
and thus plotting the complete Bode diagram is a simple matter.
[7] Also, if the open loop gain is
varied, the magnitude curve is shifted up or down without changing the slope of the curve, and
the phase curve remains the same.
A common approach to the Bode diagram is that we first adjust the open loop gain so that
the requirement on the steady state accuracy is met. Then we plot the magnitude and phase
curves of the uncompensated open loop. If the specification on the phase margin and gain margin
are not satisfied, then a suitable compensator that will reshape the open loop transfer function is
determined.
In many practical cases, compensation is essentially a compromise between steady-state
accuracy and relative stability. In order to have a high value of the velocity error constant and yet
satisfactory relative stability, we find it necessary to reshape the open loop frequency response
curve. The gain in the low-frequency region should be large enough to satisfy the steady-state
accuracy requirements. For the medium-frequency region (near the gain crossover frequency
Cωfrom both directions) , the slope of the log-magnitude curve in the Bode diagram should be
-20 dB per decade.
[8]
This slope should extend over a sufficient wide frequency band to assure a
proper phase margin. For the high-frequency region, the gain should be attenuated as rapidly as
possible to minimize the effects of noise.
The basic characteristics of lead, lag, and lag-lead compensation are as following. Lead
compensation essentially yields an appreciable improvement in transient response and a small
change in steady-state accuracy. It may accentuate high-frequency noise effects. On the other
hand, lag compensation yields an appreciable improvement in steady-state accuracy at the
expense of increasing the transient-response time. Lag compensation will suppress the effects of
high-frequency noise signals. Lag-lead compensation combines the characteristics of both lead
compensation and lag compensation.
New Words and Phrases
1. compensation [kCmpen5seiFEn] n. 补偿,调整,校正
2. impose [im5pEuz] v. 将……强加于,施加,使……负担
3. stringent [5strindVEnt] adj. 严厉的,迫切的
4. root-locus [5ru:t-5lEukEs] n. (pl. root-loci) 根轨迹
5. indication [indi5keiFEn] n. 指示,指出,显示,暗示
6. transient [5trAnziEnt] adj. 暂态的,瞬时的,过渡过程的
自动化专业英语 ·84·
·84·
7. magnitude [5mAgnitju:d] n. 量值,幅度
8. straightforward [streit5fC:wEd] adj. 直截了当的
9. accentuate [Ak5sentjueit] v. 加强,强调
10. attenuate [E5tenjueit] v. 削弱
11. approach [E5prEutF] n. 方法,途径
12. characteristic [7kAriktE5ristik] n. 特性,特征
adj. 特有的,典型的
13. prime [praim] n. 最初,青春,精华
adj. 主要的,最初的,有活力的,
最好的,根本的,素数的
14. rigid [5ridVid] adj. 刚硬的,刚性的,严格的,坚硬的,
僵直的,坚决的,固定的
15. transient response 暂态响应,过渡反应,瞬时 [瞬态]
反应,瞬时反应特性,瞬时特性
16. yield [ji:ld] vt. 出产,产生,生长,生产vi.(～to)
屈服,屈从,放弃
n. 产量,收益
17. time-domain 时域的
18. overshoot [5EuvE5Fu:t] vt. 打过头,飞过目标,超过,越过
vi. 射击越标,行动过火
n. 超调量
19. settling time 调整时间
20. phase margin 相位裕量
21. gain margin 增益裕度
22. resonant [5rezEnEnt] adj. (引起)共鸣的,响亮的,
共振的,深沉的
23. perk [pE:k] vi. 昂首,恢复,振作
vt. 竖起,打扮
24. resonant perk value 谐振峰值
25. bandwidth [5bAndwitW] n. 带宽,频带宽度
Notes
[1] We should remember that the most important part of control system design is to state the
performance specifications precisely so that they will yield an optimal control system for a given
purpose.
我们应该牢记,控制系统设计过程中最重要的一个环节就是把性能要求精确地表达出
来,这样才会设计出对于给定的目的而言最优的控制系统.
本句的结构比较复杂.在remember后面that所引导的从句是宾语从句,在该从句中
"to state…"是从句中的表语从句.在翻译这种英语长句时,不能够拘泥于原句的语法结
Lesson 8 System Design and Compensation Techniques ·85·
·85·
构,而应该在充分理解该语句意思的基础之上,重新组织,再用通顺的汉语表达出来.如
果过分拘泥于原来的语法结构,则翻译出来的汉语不通顺.科技英语翻译就是要在尽可能
忠实于原文的基础上,将通顺的英语(或汉语)所表达的意思转换成用通顺的汉语(或英语)
表达.
[2] Once the effects on the root locus of the addition of the poles and/or zeros are fully
understood, we can readily determine the locations of the pole(s) and zero(s) of the compensator
that will reshape the root locus as desired.
一旦我们完全理解了增加极点和/或零点对于根轨迹的影响,我们就可以很方便地确定
补偿器零点和极点的位置,以使得根轨迹改变成为我们所希望的形状.
Once引导条件状语从句,而且该条件状语从句是用被动语态.Compensator后面的
that…引导定语从句修饰the pole(s) and zero(s) of the compensator.
[3] In the design by the root-locus method, the root-loci of the system are reshaped through
the use of a compensator so that a pair of dominant closed-loop poles can be placed at the desired
locations. (Usually, the damping ratio and undamped natural frequency may be specified by the
locations of a pair of dominant closed-loop poles.)
在用根轨迹法设计的过程中,通过使用补偿器改变系统根轨迹的形状,以使闭环系统
一对主导极点位于理想的位置.(通常,阻尼比和无阻尼自然振荡频率是由闭环系统一对主
导极点的位置确定的.)
本句中有两个状语,In the design by…介词短语作状语表示场合;而so that a pair of…
状语从句表示结果.
[4] The addition of a pole to the open-loop transfer function has the effect of pulling the root
locus to the right, tending to lower the system's relative stability and to slow down the settling of
the response.
在开环传递函数中增加一个极点的效果是把根轨迹向右推,倾向于降低系统的相对稳
定性,并且降低系统的收敛速度.
介词短语The addition of a pole to the open-loop transfer function是句子的主语,现在分
词短语tending to lower…作状语,表示伴随状态.
[5] Inserting an appropriate lead compensator in cascade with the feed-forward transfer
function may solve this problem.
在前向传递函数中串联插入一个适当的超前补偿器,就可以解决这个问题.
动名词短语Inserting an…是句子的主语.
[6] In the frequency-response approach, we specify the transient-response in terms of the
phase and gain margin, resonant peak magnitude, the gain crossover frequency, resonant
frequency and bandwidth.
在频率响应法中,我们以相位裕量及增益裕量,谐振峰值幅度,增益穿越频率,谐振
频率和带宽来表征暂态响应.
在这个句子中,the phase and gain margin, resonant peak magnitude, the gain crossover
frequency, resonant frequency and bandwidth并列成为介词短语in terms of后面的宾语.
[7] A Bode diagram of the compensator can be simply added to the original Bode diagram,
自动化专业英语 ·86·
·86·
and thus plotting the complete Bode diagram is a simple matter.
补偿器的伯德图可以简单地加在原伯德图上,因此画完整的伯德图是很简单的事.
句子中and thus plotting…是一个并列句,其中动名词短语plotting the complete Bode
diagram作主语.
[8] For the medium-frequency region (near the gain crossover frequencyCωfrom both
directions) , the slope of the log-magnitude curve in the Bode diagram should be -20 dB per
decade.
在中频段(靠近幅频曲线的穿越频率Cω的两边),在伯德图中对数幅值曲线的斜率应该
为-20 dB/dec.
本句中括号内的部分是介词短语作为定语,用来修饰region.
Translating Skills 数词的译法
在专业英语中,数词出现的频率很高,对数词的翻译及读法的掌握程度会影响对专业
的学习,研究及交流.现分别介绍一些专业英语中常用的数词的译法和数学符号,公式的
读法.
1. 基数词的译法和读法
(1) 从1到12是单个单词: 十一 11 eleven 十二 12 twelve
(2) 从13到19加后缀-teen: 十三 13 thirteen 十九 19 nineteen
(3) 从20到90 加后缀-ty: 二十 20 twenty 二十三23 twenty-three
九十 90 ninety
百位数以上:
五百 500 five hundred
五百六十一 561 five hundred (and) sixty-one
五千六百六十一 5,661 five thousand six hundred (and) sixty-one
2. 序数词的译法和读法
序数词翻译时加"第……",如 twelfth 12th 第十二 thirtieth 30th 第三十
3. 数词的增加和减少的译法和读法
(1) The oxygen atom is nearly 16 times heavier than the hydrogen atom.
氧原子的重量几乎是氢原子的16倍.(如果把16用n代替,常译作"是……的n倍,
或"比……(大,多,长)n-1倍")
(2) The diode produces 5 times more radiant power than that one.
这只二极管的辐射功率比那只大4倍(是那只的5倍)(同上).
(3) The wire is twice as long as that one.
这根电线的长度是那根的两倍.(如果把twice用n代替,常译作"是……的n倍,或
"比……(大,多,长)n-1倍")
(4) The production of air-conditioners has increased three times this year.
Lesson 8 System Design and Compensation Techniques ·87·
·87·
今年空调的产量增加2倍(增加到3倍).(如果句中three用n表示,那么常译成"增加
了n-1倍或增加到n倍")
(5) The production of air-conditioners has increased by three times over the previous year.
今年空调的产量比上一年增加了3倍.
(6) The production of air-conditioners has decreased by three times over the previous year.
今年空调的产量比上一年减少了3倍.
(7) The production of air-conditioners has increased to three times this year.
今年空调的产量增加到了3倍.
(8) The production of air-conditioners has increased by a factor of three times this year.
今年空调的产量增加2倍.(如果句中three用n表示,那么常译成"增加了n-1倍"
类似减少的译法有:
(1) reduce by 10% 减少了10%
(2) reduce to 10% 减少到10%
(3) reduce by a factor of 10 减少了9/10(减少到 1/10)
(4) reduce 10 times 减少到1/10(减少了9/10)
4.分数,小数,时间等的译法和读法
(1) 简单的分数.
1/7 七分之一 one seventh 3/4 四分之三 three quarters
1/4 四分之一 a/one quarter 1/2 二分之一 a/one half
4
1
2
四又二分之一 four and a half 3
4
5
三又五分之四 three and four-fifths
(2) 复杂的分数.
24/9 九分之二十四 twenty-four over nine
20/83 八十三分之二十 twenty over eight three (twenty eighty-thirds)
7/20 二十分之七 seven twentieths
67/200 二百分之六十七 sixty-seven two hundredths
(3) 小数.
0.124 零点一二四 (nought) point one two four
0.24 零点二四 (nought) point two four
0.4 零点四 (nought) point four
16.789 十六点七八九 one six point seven eight nine
(4) 时间或其他.
60年代初期 in the early sixties
本世纪90年代 in the nineties of the century
20世纪90年代(1990s, 1990's) nineteen nineties
2005年10月10日 October 10th, 2005 (10 th October, 2005/ October 10, 2005/ 10 October
2005)
Fig.7 图7(直译)
14′59.38〃十五分五十九点三八秒 fourteen minutes fifty-nine point three eight seconds
自动化专业英语 ·88·
·88·
5. 数学符号,公式的读法
+ 加(上) plus/and
- 减(去) minus
× 乘以 times; multiplied by
÷ 除以 divided by/divided
= 等于 is equal to/equals
≈ 大约等于 is approximately equal to
( ) 圆括号 round brackets/parentheses
[ ] 方括号 squared brackets
/ 斜杠 slash
65% 百分之六十五 65 percent
109 十的九次方 the ninth power of ten/ten to the power nine/ten to the
ninth power
10-5 十的负五次方 en to the minus five
x′ x prime
x〃 x second prime
xe x sub e
2 根号2 the square root of 2
≥ 大于或等于 is more than or equal to
≤ 小于或等于 is less than or equal to
> 大于 is more than
δ delta
Φ Phi
Ω omega
ε epsilon
∝ 与……成比例 varies as/ is proportional to
ω omega
5 mm 5毫米 5 millimeters
x→∞ x approaches to infinity
Exercises
1. Translate the following into Chinese.
(1) Generally, we should adopt reasonable performance specifications while we are
designing a control system.
(2) We often use lead network, lag network, or lag-lead network to work as compensators in
control system compensation.
(3) Compensation for a closed-loop control system is essentially a compromise between
steady-state accuracy and relative stability of the system.
Lesson 8 System Design and Compensation Techniques ·89·
·89·
(4) The substance reacts three times as fast as the other one.
(5) The students who take part in physical activities have increased to 10,000.
(6) One in five women born in 1970 has suffered from depression and anxiety in their
thirties, twice the rate of those born in 1940, the University of London has found.
2. Translate the following into English.
(1) 使用根轨迹法设计控制系统补偿器,就是为了使闭环系统的一对主导极点位于左
半S平面中的理想位置.
(2) 超前补偿可以明显改善控制系统的暂态响应,对稳态精度没有影响.
(3) 用伯德图设计的常用方法是,我们首先调节开环增益,以使稳态精度的要求得到
满足.
(4) 那位警察要了比平常多一倍的罚款.
(5) 去年钢产量减少了20%.
(6) 这家造纸厂的产量比1980年增加两倍.
Reading Material An Eye on Reactor and Computer Control
A nuclear power plant operator stared at the computer screen and yawned. As the end of a
long shift approached, he was feeling very tired as he looked at icons of pumps, pipes, and
turbines. Even so, it was still early in the reactor startup sequence. When an indication that the
reactor had gone critical appeared on the screen, the operator tried to rouse himself. There was no
need for him or anyone else to be alarmed, however. Based on the way the operator looked at the
screen, the computer had already sensed that he was tiring and had begun to assist the operator in
reactor control. The computer zoomed in on the displays the operator needed to monitor
reactivity and highlighted the important data. It would even be capable of assuming partial
reactor control if necessary.
At a research laboratory, a cognitive scientist put a diskette in her computer and studied the
screen. The data indicated that a reactor operator had been glancing at a number of widely
scattered points in a short time on the computer screen in the reactor control room. "All these eye
movements," said the scientist, "tell me the operator is experiencing excessive mental work load.
It seems that several displays associated with reactor control must be redesigned to make it easier
for the operator to understand quickly what's going on."
A teenager who lost the use of both hands as a result of an automobile accident had found a
way to write again. His father bought him an "eye typewriter"——a computer that displays and
prints letters from a display of the alphabet on the screen in the order in which they are stared at.
The boy enjoyed his ability to control a computer simply by looking at it.
These futuristic scenarios suggest that information on eye gazes——the way people look at
an object——can be put to use to determine a person's mental work load and level of fatigue, to
guide the design of computer displays to speed human processing of information, and to control
自动化专业英语 ·90·
·90·
computers. Other applications include controlling camera positions on robots and guiding an
artificial intelligence system in recognizing enemy targets.
At ORNL computer software has been developed to make possible an improved eye-gaze
measurement technology. Such an innovation could be the basis for advanced eye-gaze systems
that may have applications such as those mentioned above.
New Words and Phrases
1. yawn [jC:n] v. n. 打哈欠,哈欠
2. turbine [5tE:bin] n. 涡轮机
3. critical [5kritikEl] adj. 危急的,临界的
4. scatter [5skAtE] v. 分散,散开,驱散
5. innovation [7inEu5veiFEn] n. 改革,创新
6. zoom in (镜头)放大
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