现代控制教学PPT英语版.ppt

fundamentals of control engineering lecture 3 feiyun xu email: /jmp/jpkc2006/kczd/index.htm,机械工程测试与控制技术,chapter 2: mathematical models of systems,2.4 the laplace transform and its inverse transform,laplace transform and its inverse transform,chapter 2: mathematical models of systems,the inverse laplace transform for the function f(s) is :,chapter 2: mathematical models of systems,laplace transform of some typical functions,the unit step function,chapter 2: mathematical models of systems,the unit ramp function,chapter 2: mathematical models of systems,the unit parabolic function,chapter 2: mathematical models of systems,the unit impulse function,chapter 2: mathematical models of systems,the damping exponential function,(a is constant),chapter 2: mathematical models of systems,the sine and cosine function,by euler fomula:,chapter 2: mathematical models of systems,therefore:,similarly：,chapter 2: mathematical models of systems,properties of laplace transform,linearity,chapter 2: mathematical models of systems,real differential theorem,chapter 2: mathematical models of systems,chapter 2: mathematical models of systems,this means the laplace variable s can be considered as a differential operator.,chapter 2: mathematical models of systems,integral theorem,if,integral operator,chapter 2: mathematical models of systems,delay theorem,provided that f(t) = 0 while t0, exists,chapter 2: mathematical models of systems,translational theorem,initial value theorem,chapter 2: mathematical models of systems,final value theorem,chapter 2: mathematical models of systems,chapter 2: mathematical models of systems,convolution theorem,chapter 2: mathematical models of systems,chapter 2: mathematical models of systems,scale transform,example：,chapter 2: mathematical models of systems,find the inverse laplace transform with partial fraction expansion,partial fraction expansion,if f(s)=f1(s)+f2(s)+fn(s),chapter 2: mathematical models of systems,in control engineering, f(s) can be written as:,where -p1, -p2, , -pn are the roots of the characteristic equation a(s) = 0, i.e. the poles of f(s). ci=bi /a0 (i = 0,1,m),chapter 2: mathematical models of systems,partial fraction expansion for f(s) with different real poles,where the constant coefficients ai are called residues at the pole s = -pi.,therefore：,how to find the coefficients ai ?,chapter 2: mathematical models of systems,example1: find the inverse laplace transform,chapter 2: mathematical models of systems,i.e.,chapter 2: mathematical models of systems,partial fraction expansion for f(s) with complex poles,supposing f(s) only has one pair of conjugated complex poles -p1 and -p2, and the other poles are different real poles. then,where,chapter 2: mathematical models of systems,or:,where a1 and a2 can be calculated with the following equation.,chapter 2: mathematical models of systems,example 2: find the inverse laplace transform,given,chapter 2: mathematical models of systems,i.e.,chapter 2: mathematical models of systems,therefore,chapter 2: mathematical models of systems,finally,the inverse laplace transform will be:,chapter 2: mathematical models of systems,partial fraction expansion for f(s) with repeated poles,where the coefficients ar+1,an can be found with the forenamed single pole residue method.,chapter 2: mathematical models of systems,chapter 2: mathematical models of systems,therefore,from the laplace transform table, we obtain,chapter 2: mathematical models of systems,example 3: find the inverse laplace transform,chapter 2: mathematical models of systems,chapter 2: mathematical models of systems,using laplace transform to solve the differential equations,image function of output in s-domain,algebraic equation in s-domain,chapter 2: mathematical models of systems,example 5: solving a differential equation with laplace transform,chapter 2: mathematical models of systems,do the laplace transform to the left-hand of the differential equation, we have,i.e.,chapter 2: mathematical models of systems,since we obtain,chapter 2: mathematical models of systems,chapter 2: mathematical models of systems,therefore:,from the laplace transform table, we obtain,chapter 2: mathematical models of systems,comments:,the final solution of a differential equation is obtained directly with laplace transform method. no need for finding the general and the particular solution of the differential equation.,if the initial conditions is zero, the transformed algebraic equation in s-domain can be gotten simply with replacing the dn/dtn operator with variable sn.,chapter 2: mathematical models of systems,note that the output response x0(s) includes two parts: the forced response determined by the input and the natural response determined by the initial conditions.,chapter 2: mathematical models of systems,obviously, the transient response of the system will be decreased to zero with time t.,chapter 2: mathematical models of systems,2.5 the transfer function of linear systems,transfer function,the transfer function of a linear system is defined as the ratio of the laplace transform of the output variable to the laplace transform of the input variable, with all initial conditions assumed to be zero.,the system is in steady-state, i.e. output variable and its derivative of all order are equal to zero while t0.,chapter 2: mathematical models of systems,example 1: finding the transfer function of the spring-mass-damper system,chapter 2: mathematical models of systems,example 2: finding the transfer function of an op-amp circuit,i.e.,chapter 2: mathematical models of systems,example 3: finding the transfer function of a two-mass mechanical system,chapter 2: mathematical models of systems,if the transfer function in terms of the position x1(t) of mass m1 is desired, then we have,mini-test: please write the differential equation of the two-mass mechanical system.,chapter 2: mathematical models of systems,example 4: transfer function of dc motor,chapter 2: mathematical models of systems,the transfer function of the dc motor will be developed for a linear approximation to an actual motor, and second-order effects, such as hysteresis and the voltage drop across the brushes, will be neglected.,the air-gap flux of the motor is proportional to the field current, provided the field is unsaturated, so that,the torque developed by the motor is assumed to be related linearly to and the armature current as follows:,chapter 2: mathematical models of systems,field current controlled dc motor (ia=ia is constant),where km is defined as the motor constant.,the field current is related to the field voltage as,chapter 2: mathematical models of systems,the load torque for rotating inertia as shown in the figure is written as,therefore the transfer function of the motorload combination, with td(s) = 0, is,chapter 2: mathematical models of systems,armature current controlled dc motor (if=if is constant),the armature current is related to the input voltage applied to the armature as,where vb(s) is the back electromotive-force voltage proportional to the motor speed. therefore we have：,chapter 2: mathematical models of systems,the armature current is,therefore the transfer function of the motorload combination, with td(s) = 0, is,chapter 2: mathematical models of systems,range of control response time and power to load for electro-mechanical and electrohydraulic devices.,chapter 2: mathematical models of systems,general form of transfer function,chapter 2: mathematical models of systems,remarks,the transfer function of a system (or element) represents the relationship describing