现代控制工程CH05-3Open-loopfrequencycharacteristicgraph.ppt

CH.5 frequency response Frequency characteristics have clear physical meaning, can be measured by experiments and be used to induce the transfer function in black-box situation. 1. frequency response experiments A kind of instruments, called signal analyzer can perform frequency response measurements, generating the sine wave with different frequency, measuring the amplitude and phase variation. 2. transfer function identification * 5-1 Concept of frequency characteristics 5-2 Frequency response of typical elements 5-4 Stability criterion of control system in frequent domain 5-5 Relationship between the frequency characteristics of open-loop system and the performance of closed-loop system 5-3 Plotting for the open-loop transfer function 5-3 Open-loop frequency characteristic graph Open-loop Bode diagram General OL transfer function is Bode diagram can be easily obtained by adding plots of typical elements. The principal characteristics of frequency method is analyzing the performance of a closed-loop system by utilizing the open-loop frequency characteristics. The whole process is simplified. write the transfer function as: The frequency characteristics are: thus finally Example 4 Plot the open-loop Bode diagram of the following system Solution: Transform the open-loop frequency characteristics to the standard form (the constant item of inertia, 1-order differential, oscillation and 2-order differential changed to be 1). (3) Plot the asymptotic curves of each element; (4) Superposing all the asymptotic curves: first superposing the elements without break frequency, then the ones with break frequency. (2) Figure out the typical elements and arrange them according to the break frequency except the proportional and integral elements; 40db 0.1 1 10 Example 5 Transfer function is 20db 100 0db -20db -40db 30 2 [-20] [-40] [-20] [-40] Lower： , 38db Break Frequency：0.5 2 30 slope： -40 -20