me360Exp6motor_control - ME 360: FUNDAMENTALS OF SIGNAL...

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1 ME 360: FUNDAMENTALS OF SIGNAL PROCESSING, INSTRUMENTATION AND CONTROL Speed Control of a DC Electric Motor 1. CREDITS Experiment Originated: Professors T-C. Tsao, October, 1995, and Norman Miller, January, 1997 Updated: D. Block, September 2009 2. OBJECTIVE The objective of this experiment is to study proportional-integral control of the speed of a DC motor. A secondary objective is to become familiar with the use of SIMULINK as a system simulation tool. 3. KEY CONCEPTS (a) As we know from previous experiments, a DC motor with voltage as the input and speed as the output behaves as a quasi-linear, first-order system with steady-state gain K and time constant τ . For the motor- generator system used in our laboratory, K is typically between 1.1 and 1.2 depending on the motor and various factors such as bearing wear. τ is typically between 40 and 70 ms. (b) A quasi-linear system is one that can be modeled as linear for the purpose of control but with dynamic parameters (K and τ ) that vary with motor speed and motor age. (c) We can use the changes in K and τ as the motor ages as a means of diagnosing motor health (bearing condition). (d) Proportional-integral-derivative (PID) control is one of the most common control methods. A block diagram of PID control is given below. Special cases of PID control include: (i) P (only) control where K I and K D are both 0, (ii) PI control where K D is 0, and (iii) PD control where K I is 0. + re u y control block system block set point error state variable control action K D s 2 + K p s + K I s τ s + 1 K Controller (e) In this experiment, we only consider P and PI control. Derivative (D) control is not considered. (f) Proportional control is the primary workhorse of PID control. The proportional gain K p determines how quickly a system responds. (g) The system generally becomes more responsive (rise time is reduced) as proportional gain is increased. (h) A drawback of this increased responsiveness is that oscillations die away more slowly. Such oscillations may originate (i) in the system, (ii) in the input, or (iii) from other factors outside the system. (i) P-only control has nonzero steady-state error e ss = r / (1 + K K p ). PI control has zero steady-state error. (j) The primary benefit of adding integral control to this system is elimination of the steady-state error. 4. SYNOPSIS OF PROCEDURE In this experiment, we add speed control to the motor-generator system used in the previous experiment. We investigate both proportional (P) and proportional-integral (PI) control. We first simulate the motor-generator
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2 system on the computer using SIMULINK. We then add speed control to the simulation, and evaluate the performance of the control system. Finally, we test the speed control on the actual motor-generator system and document the differences between simulated and actual system performance.
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me360Exp6motor_control - ME 360: FUNDAMENTALS OF SIGNAL...

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