DC Motor Speed Control System - ED4400B

Control Engineering Laboratory Electrical Engineering Department Faculty of Electrical Technology Institut Teknologi Sepuluh Nopember

EXPERIMENT 1 DC MOTOR SPEED CONTROL SYSTEM OBJECTIVE Doing experiment of control system is essential to know comparison between control theories and practical. DC motor speed control system can show response of first order system and also second order system. Adjusting gain controller will change behavior of the system. REFERENCE Ogata, K. Modern Control Engineering. 2010. Anonym. DC Servo Trainer User’s Manual ED-4400B ED -4400B EXPERIMENT EQUIPMENT In this experiment, will used some equipment as shown in Table 1.

Table 1 Equipment of DC Motor Speed Control System Experiment Quantity Designation Description 1 U-151 Dual Attenuator 1 U-152 Summing Amplifier 1 U-153 Pre-Amplifier 1 U-154 Motor Driven Amplifier 1 U-155 Tacho Amp Unit 1 U-156 DC Power Supply 1 U-157 Potentiometer (Reference) 1 U-158 Potentiometer (Motor Coupling) 1 U-159 Tachometer 1 U-161 Servo Motor 13 U-163 Magnet Brake 5 Power Cable 50 Jumper Cable PRE-EXPERIMENT TASK 1. Draw block diagram of speed control system! 2. How speed control of DC motor works? INTRODUCTION The purpose of this laboratory experience is to provide an introduction to control systems and give explanation application of control system. In this e xperiment, will give explanation about DC motor speed control system. First experiment will do error investigating, the second is simple position control system the last is closed loop control system.

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The Components of the Control System The basic goal of a control system is to produce an output as a response to an input signal or command and keep it this way in the presence of external interference, disturbances, etc. Control systems can be basically classified as open-loop systems or closed-loop systems depending on how they are built. This introductory lab experience will explore both types of systems. Voltage Regulation For permanent magnet DC motors, the magnetic field value is constant. Then you only need to set the magnitude of the voltage at the motor terminals. Current passing through the armature will cut the magnetic field of permanent magnet. According to the Lorentz law, if there is a current-carrying conductor in a magnetic field then, there will be a force that moves the conductor. The magnitude of the force is proportional to the current through conductors. The amount of current is affected by the voltage received by conductor. A force that emerged later converted into a rotation force by mechanical rings. The equivalent circuit of the motor can be seen in Figure 1. While armature resistance is constant, by regulating the voltage at the terminals, it will regulate the speed of the motor. Where  is voltage terminal,  is induction voltage, is  armature resistance, and  is armature current.

Figure 1. Equivalent Circuit of Permanent Magnet DC Motor

Increasing the value  will increase the speed of DC motor. If the rotor of the DC motor attached to output potentiometer is increased the value of  and suddenly decrease it to the zero value will bring the shaft of motor in the certain position. Equipment: Here are the components used in lab module of DC motor speed control system: 1) Dual Attenuator Components consisting of a dual rotary potentiometer which consists of 10 steps and each step is reduced to 10%. The total resistance of the po\tentiometer is 100 kOhm. 2


2) Summing Amplifier This consists of a series of inverting summing amplifier, so do the operations of addition and be able to take the role of the gain.

Figure 2. Dual Attenuator

Figure 3. Summing Amplifier

3) Pre-amplifier This module is designed to perform a DC voltage offset settings. Scope of the offset is set on module capable of approaching + 5 V with a gain of 20 dB. 4) Motor driver amplifier A component that serves as a protection circuit and servo motor drive. The series consists of 10 W DC differential amplifier.

Figure 4. Pre-ampliflier

Figure 5. Motor Driven Amplifier

5) Tacho Amp Unit Equipment that works to change the output frequency becomes rpm tachogenerator be proportional to the DC voltage and polarity (+) or (-), which represents the direction of rotation of the motor. 6) DC Power supply Equipment that serves to provide a DC voltage supply equipment amounted to + 15V 0.2A for modules and + 15V 0.5A to the motor with the input of 220V 50 / 60Hz.

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Figure 7. DC Power Supply

Figure 6. Tacho Amplifier Unit

7) Potentiometer (Reference and Motor coupling) The module consists of precision potentiometer with a scale of 360 ° swivel that can be used to set and detect the position. The potentiometer input resistance is 1/10 kOhm with 1/1000 resolution section. 8) Tachometer The measuring equipment used in conjunction with Amp Tacho Unit a nd used to the speed indicator derived from tachogenerator output.

Figure 8. Potentiometer

Figure 9. Tachometer

9) DC servo motors This module consists of a DC motor, gear speed reducer, and tachogenerator. Input voltage used is 12 V DC with a max power of 4-5 W is the maximum motor speed of 5000 rpm. 10) Magnet brake These devices have a load coming from eddy currents (eddy current) generated by the magnetic field on the electric brake and affect slabs installed in a DC motor.

Figure 10. Servo Motor

Figure 11. Magnet Brake

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EXPERIMENT Experiment 1. Motor Speed and Input Characteristics In general, a motor is a machine that converts electrical energy into mechanical rotation. The key elements of a DC motor are a field winding and an armature winding. As electric currents flow through the windings, torque is developed between these two windings. In ED-4400B trainer system, the field winding is replaced by permanent magnets. The permanent magnets provide constant lines of magnetic flux and therefore, the motor speed becomes only a function of the voltage applied to the armature winding. A. Operational Procedure 1. Referring to Figure 12, place the modules needed in the experiment on a flat surface or on top of the ED-4400B cover, and connect modules as indicated in the Figure 12. 2. Connect Tacho-meter U-159 across U-155 meter and GND. 3. Set the angle on U-157 to 180 degrees. 4. Verify that line voltage is correct (220V). Plug U-156 line cord to the power outlet, and turn the power switch ON. 5. Turn U-157 slowly counter-clockwise until the motor begins to move. Record the U-157 position and the input voltage. 6. Increase the input voltage by slowly turning the U-157 clockwise. For every on volt increment of the input voltage (1V, 2V, 3V ...), record the U-159 indication and motor current in Table 2.

Figure 12. Wiring Diagram of Experiment 1

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B. Experimental Data The value that get from Step 6 in operational procedure of Motor Speed and Input Characteristics write in motor current and speed column as shown in Table 2.

No

1 2 3 4 5 6

Table 2. Experiment of Motor Speed and Input Characteristics Input Voltage Input Potentiometer Motor Current Motor Speed (Volt) (Degree) (A) (RPM) 0

180

0.5 1 1.5 2 2.5

C. Analysis and Experimental Task 1. Make a graph on input voltage vs. motor speed using above measurement data! 2. Why there exist a “dead band” input voltage range in a motor? 3. Make a graph on motor speed vs. motor current using data obtained in Step 5 and 6! Review relationships between these two parameters! Experiment 2. Motor Speed and Load Characteristics Typical output ratings of permanent magnet based DC motors range from a few watts t o several hundred watts, and this type of motors exhibit an excellent power efficiency. As was mentioned earlier, permanent magnets in the motor provide constant magnetic flux (). Therefore, the torque () generated in the motor becomes a function of only the input current ( ). Also, the counter  (electromotive force) of a motor (  ) is generated by the action of the armature conductors cutting lines of force, and is proportional to the speed of the motor ( ). The input voltage and speed of the motor are related to other parameters according to the following equations:

 =  +  .   =

 . 

−

 .  (. )2

Where  is input voltage and  is resistance of armature coil. It should be noted that input current increase as mechanical load of motor is increased, resulting in increased input power. A. Operational Procedure 1. Referring to Figure 13, arrange the modules and connect them together. Attach aluminum disk to high-speed shaft of U-161 as show in Figure 13. 2. Set U-151 attenuator to “8”, and turn the power switch of U -156 ON. Adjust U-157 to obtain maximum speed on U-159 without saturation.

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3. Raise magnet brake setting on U-163 from 0 to 10 by one step each time, and push the button and measure the RPM on U-159. Record corresponding motor current for each step readings as indicated on U-156 power supply module in Table 3. 4. Repeat measurements in Step 3 by starting from 10 to 0. Record the corresponding motor current for each step readings as indicated on U-156 power supply module in Table 4.


B. Experimental Data The value that get from Step 3 and 4 in operational procedure of Motor Speed and Load Characteristics, write in Table 3 and Table 4.

Table 3. Experiment of Motor Speed and Load Characteristics 0-10 Magnetic Brake Tacho Voltage Motor Current Motor Speed (V) (A) (RPM) Scale 0 2 4 6 8 10

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Table 4. Experiment of Motor Speed and Load Characteristics 10-0 Magnetic Brake Tacho Voltage Motor Current Motor Speed (V) (A) (rpm) Scale 10 8 6 4 2 0 C. Analysis and Experimental Task 1. Make a graph that showing the relationships between brake setting, motor speed, and motor currents! 2. What is the effect of overloading a motor? Experiment 3. Closed Loop Motor Speed Control Techniques Quite often, when a motor is used as a source of mechanical force, motor is required to provide constants speed regardless of the change in loads. A closed loop speed control system is a self-regulating system in which measured speed of motor is compared to preset value to produce an error output. Detected error voltage is, then, amplified and feedback to the control circuit to compensate the difference between actual and preset speed. This self-correcting process continues until the detected error voltage becomes zero. At this point, actual speed of motor is equal to preset speed, and motor maintains a constant speed. A. Operational Procedure 1. Referring to Figure 14, arrange the required modules and connect them together. 2. Set the selector switch of Summing Amp U-152 to “a”. 3. Set ATT-2 of the U-151 to “10” to prevent Tacho output from entering the system. Set ATT1 to “5”. 4. Turn the power of U-156 ON. 5. Adjust U-157 to obtain about one half of the maximum speed. This is same as setting for 2500 RPM on U-159 meter. 6. Attach a magnet brake U-163. With the brake’s setting increased by one notch at a time, record the RPM reading at each setting. 7. Measure the error voltage at each brake setting (Note: There is no feedback signal at this point). 8. Set ATT-2 of U-151 to “5”. Adjust U-157 to obtain the same speed as in Step 5 (around 2500 RPM). 9. Measure Tacho output and error voltage at different brake points. 10. Change ATT-2 setting to “0”. Adjust U-157 to obtain 2500 RPM. 11. Measure the speed and error voltage at each brake setting.

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B. Experimental Data The value that get from Step 6, 7, 9, and 11 from operational procedure of Closed Loop Motor Speed Control Techniques, write in Table 5.

Table 5. Closed Loop Motor Speed Control Techniques Magnet Brake Motor Speed Voltage Error ATT-2 Position Scale (RPM) (V) 0 2 4 10 6 8 10 0 2 4 5 6 8 10 0 0 2 9


4 6 8 10 C. 1. 2. 3.

Analysis and Experiment Task Make a graph that showing the relationships between brake scale and error voltage! Make a graph that showing the relationships between brake scale and motor speed! Draw DC motor speed control system block diagram and explain each component according to DC servo trainer modules! 4. Explain the mechanism of summing amplifier that can produce error of DC motor speed control system!

Experiment 4. System Gain and Motor Speed Control System In a practical system, maintaining a high system gain means reduction of the dead band, as well as desensitizing motor speed to the load changes. Although large system gain is desired in general, the gain should be limited to an acceptable level. When gain is beyond acceptable level, transient characteristics of system will suffer, and it will cause irregular motor rotation. A. Operational Procedure 1. Referring to Figure 15, arrange all the modules and an oscilloscope and connect them together. 2. Set the selector switch of U-152 to “a”. 3. Set ATT-1 of U-151 to “9” and ATT-2 to “10”. This will minimize reference setting, and feedback will be almost zero. 4. Turn the power of U-156 ON. Adjust U-157 to approximately one half of the maximum motor speed (2500 RPM). 5. Attach disk brake to high-speed shaft of servo motor, and set brake selector to “0”. Raise brake setting by one increment, and each time, press the brake button and measure the motor speed and associated error signal. 6. Set U-151 ATT-2 to “5”. Adjust motor speed to 2500 RPM, and repeat Step 5. 7. Using U-157, set motor speed to 2500 RPM. Set U -151 ATT-2 to “5”. Adjust ATT -1 from 0 to 0, and measure the error voltage at each point. 8. For each point of ATT-1 setting, hold high-speed motor shaft by hand and repeat experiments in Step 7. Compute error deviation ratio as defined by the following equation:

   =

  ℎ     ℎ  

*Note : The higher ATT-1 setting means lower s ystem gain.

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B. Experimental Data The value that get from step 5, 7, and 9 from operational procedure of System Gain and Motor Speed Control System, write in Table 6.

Table 6. System Gain and Motor Speed Control System Magnetic Brake Motor Speed Error Voltage ATT-2 (RPM) Scale (V) 0 2 4 10 6 8 10 0 2 4 5 6 8 10

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ATT-1

Table 7. System Gain and Motor Speed Control System Motor Speed Error Voltage Error Voltage Error Deviation (RPM) Running (V) Stalled (V) Ratio

0 1 2 3 4 5 6 7 8 9 C. Analysis and Experiment Task 1. Make a graph that showing the relationships between brake scale, motor speed and error voltage! 2. Make a graph that showing the relationships between ATT-1 positions, error voltage and error deviation! Experiment 4. PID Controller in DC Motor Speed Control System We will first investigate the effect of proportional, integral and derivative forms of control on a very simple system. The motor in a speed control loop is effectively a single-lag system, since mechanical lag dominates any others, and there is no integration in direct path around loop. A. Operational Procedure 1. Connect the apparatus as shown in Figure 5, Make the following settings of the controls. 2. On the signal generator Set the generator to deliver a 5 Vp-p square wave at 0.1 Hz. 3. On the operational amplifier U-152 Select 100k Ω resistive feedback. On the PID module Y-165B Integrator out  

Proportional in, x1, maximum gain

Derivative out. 4. With the magnetic brake removed from the brake disc, switch on the power supply. The motor should start to run, first one way and then the other. 

Proportional Control 1. Observe the output of the operational amplifier unit on the oscilloscope. This is the deviation signal, and will be perhaps ±100mV, with superimposed ripple from tachogenerator. (The large initial error at each reversed may be ignored for the moment).

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Figure 16. The Block Diagram of PID Speed Control

2. Apply a load by setting the brake magnet around the braking disc and adjusting so that the current indicated on the power supply is about 0.5A. 3. Because more signal is needed to drive the servo amplifier harder, the deviation has now increased. Make a note of its magnitude, together with PID settings which correspond. 4. An obvious way of reducing the deviation is to integrate the gain. Try setting the proportional gain switch to x10. Record the new value of deviation and any comment about the general nature of the performance. It will probably be found that tachogenerator noise swamps the servo amplifier, giving rise to rather large random deviations. 5. Adjustment of the proportional gain may bring about some improvement, but probably not much. Record the best deviation figure you can achieve this way. Proportional + Integral Control 6. Leave the magnetic brake undisturbanced 

Integrator in T = 0.5 x 10s



Proportional in x1, max gain



Derivative out 13


7. It should now be possible to see that after each reversal the deviation is progressively reduced as the integrator builds up its component of the correcting signal. The effect is exponential in waveform, because less deviation less the rate at which integrator output changes. 8. If the integrator gain is greatly increased, by switching  ×1, the speed will be found to overshoot, giving an unsatisfactory response to the step speed demands. Find a value of , giving a satisfactory step response and record it, together with the other PID settings. Find out whether it is as satisfactory when magnetic brake is removed, recording your findings. Addition of derivative term It will be found that switching the derivative term ‘in’ w ill give little benefit, whatever the settings of the derivative time constant controls. This is largely because the derivative action increases the effect of the tachogenerator noise. Derivative control is mainly useful for cancelling one of the lags in a system with two significant lags, as we shall see in the next equipment. B. Experimental Data The value that get from step number four from operational procedure of PID Controller in DC Motor Speed Control System, write in Table 7.

Table 7. PID Controller in DC Motor Speed Control System Error Motor Voltage Speed    (V) (RPM) 0.1 1.1 1.1 0.1 0.1 1.1 1.1 0.1 2 1.1 22 0.1 2 0.1 22 2 1.1 22 1.1 2 0.1 22 C. Analysis and Experiment Task 1. What is your conclusion about the effect of each component of proportional-integralderivative controller in DC motor speed control system? 2. Why integral control can minimize error? Explain it!

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DC Motor Speed Control System - ED4400B

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