[工学]北航自控原理课件13英文版.pptVIP

See the figure. 8.6 Design of sampled-data control systems 1. Root locus K G(s) H(s) C(s) R(s) The system characteristic equation is (1) (3). Pulse transfer function of components in cascade There is sampling switch between two components G2(s) D(z) d*(t) d(t) G1(s) r*(t) c(t) c*(t) C(z) R(z) r(t) G(z) The starred transform of Eq. above is where Note that in general Solving for from Eqs. above gives The starred transform obtained from Eq. above is The z transform is obtained by replacing each starred transform by the corresponding function of z: So when direct ideal impulse sequence input of continuous components, and avoiding the jump of the continuous output c(t), the condition must meet that 8.5 Analysis sampled-data control systems Ⅰ. Stability 1.mapping from the s plane to the z plane where So * Chapter8 sampled-data Control Systems 8-1 采样过程与采样定理 8-2 信号的恢复与零阶保持器 8-3 z变换与z反变换 8-4 脉冲传递函数 8-5 采样系统的性能分析 8-6 采样系统的数字校正 A/D : analog to digital converter D/A : digital to analog converter The advantages of digital control system 1.The capability to easily reconfigure the control algorithm. 2.It is inexpensive. 3.Reduced sensitivity to signal noise. A/D Digital computer D/A Plant sensor r(t) Digital control system actuator e(t) e(kT) 8.1 The sampling process and the sampling theorem e(kT) is obtained by sampling a continuous signal e(t). Definition A system that is continuous except for one or more sampling operations is called a sampled-data system. sampler hold plant e(t) e(kT) Sampled-data control system Where T is called the sampling period. Sampler: A switch the closes every T seconds for one instant of time. Continuous signal sampled signal e(t) ideal sampler t e(t) t 0 T 2T t e(t) e(t) real sampler t 0 T 2T So we have So the sampling operation can be expressed as or or where t 0 T 2T t 0 T 2T The continuous signal and its amplitude spectrum are 0