北京理工大学810自动控制原理考研课件8.pptVIP

* * 8. Non-minimum phase system A transfer function is called a minimum phase transfer function if all its poles and zeros lie in the left-hand s-plane. It is called a non-minimum phase transfer function if it has poles and zeros in the right-hand s-plane. The range of phase shift of a minimum phase transfer function is the least possible or minimum corresponding to a given amplitude curve. * 1. A unit of delay: Transfer function of a delay of Td seconds and the frequency response is * A time delay added into the loop does not change the magnitude but increases the phase lag of the frequency response. The main effects of time delay are to reduce phase margin and reduce the closed-loop bandwidth. * 2. Unstable unit * 6.4 Diagram of Complex Frequency Response Function * There have four different kinds of factors:Constant gain KbPoles (or zeros) at the origin (jw)Poles (or zeros) on the real axis (jwt+1)Complex conjugate poles (or zeros) * 1. Decompose transfer function to the elementary unit. * 2. Calculate the break frequencies. 　 3. Calculate the slope and gain of the low frequency(only consider the proportion and the integrators)　　　 * 4. Obtain the asymptotic magnitude plot for the complete transfer function. *5. Furthermore, obtain the actual curves only at specific important frequencies. * 6. Phase plot： (1). Write the phase angle equation. (2). Calculate the range and estimate the change direction. (3). List the phase angle of some points (the every corner frequency point and wc） (4). Draw the phase angle curve. * Example 6.1: The Bode diagram of the TF: 　　　　　　　　　　　　 1. 2. The break frequencies 3. * 4. Asymptotic magnitude plot slopes: ω0.4, -20dB/dec ω0.4, -40dB/dec ω2, -20dB/dec ω10, -40dB/dec ω20, -60dB/dec *5. revise. * 6. * 7. Phase plot Range from –90° to –270°. * 2 0.4 10 20 36 * Bode plot can be readily obtained by Matlab: num=[0 0 10]; den=[1 3 2 0]; b