Electrical Engineering ⇒ Topic : Classifications of Control Systems

Daniel
 
CLASSIFICATIONS OF CONTROL SYSTEMS Natural control systems: The systems such as human physiology, living creatures, etc. are biological systems which are known as natural control systems. Manmade control systems: The various control systems that are designed and manufactured by human beings are known as manmade control systems. An automobile system is an example of manmade control system. Combination control systems: The combinations of natural control systems, as well as manmade control systems together are examples of combination control systems. Driver driving a car is an example combinational control systems. Timevarying and time invariant control systems: If the parameters of a control system vary with time, such a control system is termed as time varying control system. If the parameters of a control system are not varying with time, it is termed as time invariant control system. A space vehicle leaving earth is an example of timevarying control system. The elements of electrical networks such as resistance, inductance and capacitance are not time varying and which are examples of time invariant systems. Linear and nonlinear systems: A control system is known as linear if it satisfies the additive property as well as homogeneous property. Additive property: If x and y belong to the domain of the function f, we can write f(X + Y) = f(x) +.f(Y) ..........(1) (a) Homogenous property: For any x belonging to the domain of the function f and for any scalar constant β, we can write f(bx) = bf(x) ...........(2) (b) The principle of superposition is the combination of the above two properties. If a function satisfies the above two properties, it is said to be linear in nature Therefore, the function f(x) = x^{3} is nonlinear. All the physical systems are nonlinear in nature. If the presence of certain nonlinearity does not affect the performance of the system much, the presence of that nonlinearity can be neglected and the system can be treated as a linear system. Continuous time and discrete time control systems: If all the system variables of a control system are functions of time, it is termed as continuous control system. If one or more system variables of a control system are known at certain discrete time, it is termed as discrete control system. The speed control of a dc motor with tachogenerator feedback is an example of continuous time control systems. The microprocessor or computer based system is an example of discrete control systems Deterministic and stochastic control systems: If the response to input and behaviour to external disturbances of a control system are predictable and repeatable, the control system is known as deterministic control system. Any control system is called stochastic if such response is unpredictable. Lumped and distributed parameter of control systems: If a control system can be represented by ordinary differential equations, this control system is called lumped parameter control system. In case of electrical networks, the parameters such as resistance, inductance, etc. are lumped parameter systems. If a control system can be described by partial differential equations, such control system is known as distributed parameter control system. In a transmission line, the parameters such as resistance and inductance are totally distributed along its extent. Therefore, transmission line characteristics are always described by partial differential equations. Single input single output (SISO) and multiple input multiple output (MIMO) systems: If a control system has one input and one output, it is termed as single input and single output (SISO) system. If a control system has multiple input and multiple output, it is known as multiple input and multiple output (MIMO) system. Open loop and closed loop systems: This is another classification of control systems  
 
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