离散时间控制系统ch1.pptx

Computer-Controlled Systems ;Course Information;Chapter 1 Introduction to Discrete-Time ;4;1-1 Introduction;Digital Controller The trend is due to Digital control can achieve optimal perfor- mance, have Decision-making capability and flexibility in the control program Availablity of low-cost digital computers Advantages of digital signals;Types of Signals Continuous-time signal: A signal defined over a continuous range of time Analog signal: A signal defined over a continuous range of time whose amplitude can assume a continuous range of values A continuous-time quantized signal Discrete-time signal: A signal defined only at discrete instants of time;Sampled-data signal: A discrete-time signal if the amplitude can assume a continuous range of values Digital signal: A discrete-time signal with quantized amplitude Comparison Discrete-time, digital, sampled data signal (control system) Continuous-time, analog signal (control system);1-1 Introduction;Systems Dealt With in This Book Linear and time invariant Discrete-Time Control Systems one or more variables can change only at discrete instants of time. These instants may specify the times at which some physical measurement is performed or the memory of a digital computer is read out Described in linear difference equations with constant coefficients ;;S/H and A/D (A/D) Sample-and-Hold (S/H) Sampling Processes, replace original continuous-time signal by a sequence of values at discrete-time time points a circuit that receives analog input signal and holds this signal at a constant value for a specified period of time. Analog-to-Digital Converter (A/D) Also called an encoder, is a device that converts an analog signal into a digital signal, usually a numerically coded signal. A S/H circuit is often an integral part of a commercially available A/D converter.;Types of Sampling Operations Periodic sampling tk = kT (k = 0, 1, 2, …) Multiple-order sampling tk+r - tk = constant Multiple-rate sampling A digital control syste