《西北工业大学自动化学院科技英语英语3》由会员分享，可在线阅读，更多相关《西北工业大学自动化学院科技英语英语3（19页珍藏版）》请在金锄头文库上搜索。
1、西北工业大学自动化学院科技英语英语西北工业大学自动化学院科技英语英语 3 3本文由 guoxing241 贡献doc 文档可能在 WAP 端浏览体验不佳。建议您优先选择 TXT，或下载源文件到本机查看。1、By definition, the transfer function of a component or system is the ration of the transformed output to the transformed input:G( s) =output ( s ) C ( s ) = input ( s ) R( s )(2-1B-1)This definitio
2、n of the transfer function requires the system to be linear and stationary, with continuous variables and with zero initial conditions. 按照定义，元件或系统的传递函数表示为输出量与输入量的比值：(2-1B-1)这个定义要求系 统是线性的、稳定的、有连续变量和零初始条件。 2、 Eq.(2-1B-2) the denominator D(s) of the transfer function is called the characteristic functi
3、on In since it contains all the physical characteristics of the system. The characteristic equation is formed by setting D(s) equal to zero. The roots of the characteristic equation determine the stability of the system and the general nature of the transient response to any input. The numerator pol
4、ynomial N(s) is a function of how the input enters the system. Consequently, N(s) does, however, along with the specific input, determine the magnitude and sign of each transient mode and thus establishes the shape of the transient response as well as the steady-state value of the output. 在等式.(2-1B-
5、2)中，传递函数的分母多项式 D(s)被称为特征函数，因为它包含了系统的所有 物理特性。使 D(s)=0 则得到特征方程。特征方程的根决定了系统的稳定性和任何输入的瞬 态响应的一般性质。传递函数的分子多项式 N(s)是确定输入如何输入系统的函数。从而， N(s)与典型输入一起决定每个瞬态的幅值和符号，并确定了瞬态响应的形式和稳态响应的 值。 3、A known input (sinusoids and steps are commonly used) is apply to the system, the output is measured, and the transfer functio
6、n is constructed from operating data and combination of the known transfer functions of the individual elements. This combination or reduction process is termed block diagram algebra. 给系统送入一个已知的输入（通常是正弦阶跃信号） ，其输出是可测量的，传递函数是由有 效数据和已知的传递函数的组合构成， 这些传递函数的成分独立。 这种合并和约简过程是用 方框图运算来实现的。 4、 Analytical techni
7、ques require mathematical models. The transfer function is a convenient model form for the analysis and design of stationary linear systems with a limited number of differential equations and by block diagram algebra. From the deferential or intergro-differential equations describing the behavior of
8、 a particular plant（对象）, process, or component, using the Laplace transformation and its properties can develop the transfer functions. 解析技术需要数学模型。 传递函数就是一种简便的模型， 它适用于通过方块图代数来分析和 设计具有有限个微分方程的静态线性系统。通过描述特指的被控对象的行为、过程、元件的 微分或微积分方程，或者，通过拉氏变换和性质可以导出传递函数。5、The stability of a continuous or discrete-time s
9、ystem is determined by its response to inputs or disturbance. Intuitively, a stable system is one that remains at rest (or in equilibrium) unless excited by an external source and returns to rest if all excitation are removed. The output will pass through a transient phase and settle down to a stead
10、y-state response that will be of the same form as, or bounded by, the input. If we apply the same input to an unstable system, the output will never settle down to a steady-state phase; it will increase in an unbounded manner, usually exponentially or with oscillations of increasing amplitude. 离散或连续
11、系统的稳定性由其对输入或扰动的响应决定。 直观的来讲， 一个稳定的系统会保 持静止（或者处于平衡态） ，除非受到外部干扰。一旦消除干扰， （系统）将恢复静止状态。 输出将会经历一个瞬态阶段，最终达到静态响应，其响应形式将和输入一致，或受到输入限 制。如果我们给不稳定系统一个同样的输入，输出永远不会达到稳态。它将会以一种无限制 的方式增加，通常是指数形式，或者增幅震荡。6、It can be shown that the transient response for n distinct roots in the Laplace domain isCtr ( s ) =And in the ti
12、me domain isC C C1 C + 2 + 3 +L + n s + r1 s + r2 s + r3 s + rn(2-2A-4)Ctr ( t ) = C1e ? r1t + C2 e? r2t + C3e ? r3t + L + Cn e? rnt(2-2A-5)Each term in the last equation is called transient mode. There is a transient mode for each root with a shape determined solely by the location of the root in t
13、he s plane. So, a necessary and sufficient condition for the system to be stable is that the roots of the characteristic equation have negative real parts. This ensures that the impulse response will decay exponentially with time. 可以看出，在拉普拉斯域，n 个相异根的瞬态响应为式(2-2A-4)。并且在时域有式(2-2A-5)。 上一个方程的每一项都被称为瞬态模式。
14、每个根都对应一个瞬态模式，根的形式（实根/共 轭复根）仅由跟在拉氏平面中位置来决定。 所以， 系统稳定的充分必要条件是特征等式的所有根都有负的实部。 这就确保了脉冲响应是 随时间而以指数方式衰减的。 7、 Routh Criterion: All the roots of the characteristic equation have real parts if and only if the The elements of the first column of the Routh table have the same sign. Otherwise, the number of roo
15、ts with positive real parts is equal to the number of changes of sign. The Hurwitz criterion is another method for determining whether all the roots of the characteristic equation of a continuous system have negative real parts. It has the same principle with the Routh criterion in substantial altho
16、ugh their forms or patterns are different, so they are commonly called Routh-Hurwitz criterion. 劳斯判据： 特征方程的所有根都有实部， 并当且仅当劳斯矩阵的第一列元素符号相同。 否则，有正实部的根的个数要和符号的变化次数相同。 赫尔维茨判据是另一种判定连续系统特征方程的所有根是否有负实部的方法。 尽管他们的形 式或模式不同， 但它实质上和劳斯判据有相同的原理，所以它们统称为劳斯-赫尔维茨判据。 8、 transient of firstorder system is seen to be a decaying exponential, and the commonly used The measure of the speed of decay is the time constant. The time constant （T） the time in seconds for is the decaying exponential transient to be reduced to
