Digital Control Systems Waseem Gulsher BS (Evening) 11 & 18 Sep, 17 Introduction Lecture – 1 & 2 Digital Control Systems Waseem Gulsher

MS (Electronics) in progress from PAF-KIET Waseem Gulsher MS (Electronics) in progress from PAF-KIET Email: waseemgulsher@yahoo.com Contact: 0333-5454993

Digital Control Systems Recommended Text Book Digital Control Systems Philips, Nagle

Grading Midterm Paper Final Term Paper 25 10 5 50 100 Assignments Quizzes Class Participation Attendance Final Total 25 10 5 50 100 Midterm Paper Three out of five questions Final Term Paper Five out of Eight questions

General Guidelines No need to take permission while entering or leaving the class during lecture. There will be three assignments during semester and average of best two will be taken for sessional marks. There will be five quizzes during semester and average of best four will be taken for sessional marks. Assignments are to be submitted in a file / folder.

General Guidelines No marks will be given for copy work. Assignments must be submitted within one week. If assignment is submitted with one week delay, it will marked out of 5 marks instead of 10 No assignment will be accepted after 2 weeks.

General Guidelines All lectures will be delivered on multimedia. Lectures (including assignments) will be email on your addresses within 24 hours. If not received, you can text me on my cell phone. There will be no compromise on attendance in any case.

Introduction

Closed Loop Systems This course is concerned with analysis and design of closed-loop physical systems that contains digital systems. The computers are placed within the systems to modify the dynamics of the closed-loop system such that a more satisfactory system response is obtained. The closed-loop system is one in which certain system forcing functions (inputs) are determined, at least in part, by response (outputs) of the system (i.e., the input is function of output).

Closed Loop Systems A simple closed-loop system is illustrated below.

Closed Loop Systems The physical system (process) to be controlled is called the plant. Usually a system, called the control actuator, is required to drive the plant. The sensor (or sensors) measures the response of the plant, which is then compared to the desired response. The difference system initiates actions that result in the actual response approaching the desired response, which drives the difference signal towards zero.

Closed Loop Systems Generally, an unacceptable closed-loop response occurs if the plant input is simply the difference in the desired response and the actual response. Instead, this difference signal must be processed (filtered) by another physical system, which is called a compensator, a controller, or simply a filter. One problem of the control system designer is the design of a compensator.

Closed Loop Systems An example of a closed-loop system is the case of a pilot landing an aircraft. For this example, the plant is the aircraft and the plant inputs are the pilot’s manipulations of the various control surfaces and of the aircraft velocity. The pilot is the sensor, with his visual perceptions of position, velocity, instrument indications and so on. The desired response is the pilot’s concept of the desired flight path.

Closed Loop Systems Hence, for this example, the compensation, the sensor and the generation of the desired response are all functions performed by the pilot. It is obvious from this example that the compensation must be a function of plant (aircraft) dynamics. A pilot trained only on a fighter aircraft is not qualified to land a large passenger aircraft even if he can manipulate the controls.

Closed Loop Systems Almost, all control-system techniques developed (in this course) are applicable to linear time-invariant discrete-time system model. A linear system is one for which the principal of superposition applies. Suppose that input of a system is x1(t) produces a response (output) y1(t), and the input x2(t) produces the response y2(t).

Closed Loop Systems Then if the system is linear, the principal of superposition applies and the input [a1x1(t) + a2x2(t)] will produce the output [a1y1(t) + a2y2(t)] where a1 and a2 are any constant. All physical systems are inherently non-linear, however in many systems, if the system signals do not vary over too wide a range, the system responds in a linear manner.

Closed Loop Systems When the parameters of a system are constant with respect to time, the system is called a time- invariant system. An example of time-varying system is the booster stage of a space vehicle, in which fuel is consumed at a known rate; for this case mass of the vehicle decreases with time.

Closed Loop Systems A discrete-time system has signal that can change values only at discrete instants of time. We will refer to the systems in which all signals can change continuously with time as continuous- time or analog, system.

Closed Loop Systems The compensator, or controller is a digital filter. The filter implements a transfer function. Once the transfer function is known, algorithms for its realization must be programmed on a digital computer, or the algorithms must be implemented in special-purpose hardware.

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