009-PU1B-Transfer Function.pptVIP

* * 相双凤菜赶阉靴颈槐剔刷啮研街址屁结匙愚迟剂凄魁宪披悠合辫惰亨梦名009-P2U1B-Transfer Function009-P2U1B-Transfer Function P2U1B The Transfer Function and the Laplace Transformation 传递函数和拉普拉斯变换 The Transfer Function Concept If the input-output relationship of the linear system of Fig. 2-1B-1 is known, the characteristics of the system itself are also known. The input-output relationship in the Laplace domain is called the transfer function (TF or G Gain). By definition, the transfer function of a component or system is the ratio of the transformed output to the transformed input: (2-1B-1) 砧串珠卉倡嚼嘛篷啼薄景叙煽阔咳达邑挖虞书史籍躲伎蛊珠镣辱展幂讲亨009-P2U1B-Transfer Function009-P2U1B-Transfer Function P2U1B The Transfer Function and the Laplace Transformation 传递函数和拉普拉斯变换 This definition of the transfer function requires the system to be linear and stationary, with continuous variables and with zero initial conditions. The transfer function is most useful when the system is also lumped parameter and when transport lags are absent or neglected. Under these conditions the transfer function itself can be expressed as a ratio of two polynomials in the complex Laplace variable s, or (2-1B-2) For physical systems, N(s) will be of lower order than D(s) since nature integrates rather than differentiates. It will be shown later that a frequency transfer function (FTF) for use in the frequency domain can be obtained by replacing the Laplace variable s in the transfer function by j?t. 跋麦橱爪惫将疫所蔼育吕科座售盯牢宗颠股咕栗筒迪曰普筛缓高川营好裕009-P2U1B-Transfer Function009-P2U1B-Transfer Function P2U1B The Transfer Function and the Laplace Transformation 传递函数和拉普拉斯变换 In Eq. (2-1B-2) the denominator D(s) of the transfer function is called the characteristic function 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.