自动化研究生专业外语——第三讲.pptVIP

电气与自动化工程学院 研究生专业外语 研究生专业外语 电气与自动化工程学院 电气与自动化工程学院 研究生专业外语 信息与电气工程学院 自动控制原理经典部分 电气与自动化工程学院 研究生专业外语 * 第一章 自动控制理论 * * 第一章 自动控制理论 1-1 自动控制系统概述 1-2 经典控制理论 1-3 现代控制理论 * * 4. 稳定性（Stability） The stability of a continuous or discrete-time system is determined by its response to inputs or disturbance. Intuitively, a stable system is one that remains at rest ( or in equilibrium) unless excited by an external source and returns to rest if all excitations are removed. The output will pass through a transient phase and settle down to a steady-state response that will be of the same form as, or bounded by, the input. * 任何系统在扰动作用下都会偏离原平衡状态产生初始偏差。所谓稳定性，是指系统在扰动消失后，由初始偏差状态恢复到原平衡状态的性能。 线性系统的稳定性是系统在外界扰动消失后，自身具有的一种恢复能力，也就是说系统的稳定性取决于系统自身的固有特性，即系统的结构和参数，而与外界条件（输入信号）无关。 设线性定常系统在初始条件为零时，以理想单位脉冲为输入，这相当于系统在零平衡状态，受到一个外界扰动信号，若t→∞时，系统输出响应c(t)收敛到原零平衡状态，即 ，系统是稳定的。 * In a mathematical manner, the definition of stability may be stated: if the zero-input of the linear time-invariant system, subject to nonzero initial condition, approaches zeros as time approaches infinity, i.e., then the system is said to be stable; otherwise the system is unstable. A necessary and sufficient condition for a feedback system to be stable is that all the poles of the system transfer function have negative real parts. * The stability is of utmost importance when the analysis and design of control systems are considered. From a practical point of view an unstable system is of little value. In practical operation, almost all control system are subject to extraneous or inherent disturbances, such as fluctuation of load or power source, variation of system parameters or circumstance. utmost， 极度的、最远的 fluctuation， 起伏、波动 * Many physical systems are inherently open-loop instable. Introducing feedback is useful to stabilize the unstable plant and then adjust the transient performance with an appropriate controller. For open-loop stabl