Validation of D.C Motor Speed Control Model Using PIC 16F628A Microcontroller

Validation of D.C Motor Speed Control Model Using PIC 16F628A Microcontroller

Validation of D.C Motor Speed Control Model Using PIC 16F628A

Microcontroller

Ayoade Benson OGUNDARE

Lagos State Polytechnic, Ikorodu, Lagos

Abstract

Bulk of energy used in industrial facilities is consumed by electric motors and drives. This demonstrates the reason for using energy efficient electric drives. It is imperative to investigate the effect of the voltage on the speed of these drives for industrial application. In this paper, an electric drive is designed constructed which is controlled using Programmable Integrated Controller (PIC) 16F628A and the theoretical model investigated experimentally. The results showed that a good correlation exists between the standard and well-known theoretical model presented and the experimental results. The experimental results are displayed in both tabular and graphical forms.

Keywords: D.C motor, Microcontroller, Voltage dip, electric drive, Inrush current, speed control.

1.0 Introduction

Full voltage applied across the terminals of motors during starting can produce objectionable voltage flicker, mechanical stress to gear boxes or belt drive systems and create pressure surges or water hammer in pumping applications if not properly monitored and controlled [1]. Even though, the motor controller can have different features and complexity depending on the task that the motor will be performing, the controller may be a relay type or contactor type, which may have several positions to select different connections of the motor, connected to some form of sensor to automatically start and stop the motor [1]. This allows a reduced-voltage at starting for the motor and hence, reversing control or selection of multiple speeds. More complex motor controllers may be used to accurately control the speed and torque of the connected motor and may be part of closed loop control systems for precise positioning of a driven machine [2]. Therefore, controlling the speed of the motor at a reduced voltage can help reduce or overcome these problems

coupled with right selection of electric motors for various applications as well as selecting the appropriate starting methods and speed control for the electric motors [3]. Speed control of dc motor has been achieved through several means by different researchers and lots of works have been published in that regards [4, 5, 6-11]. In [12], Fuzzy Logic Controller model is proposed for the control of dc motor. The validity of this is tested and the simulation results presented to show the effectiveness and performance of the model.

Reference [13] showed a DC Motor using MATLAB. It presented the design, control method and simulation of PIC 16F877A microcontroller and MOSFET using Real peak and MP LAB.Application of Multilayer Neural Network and PID Controllers is demonstrated in reference [6]. The results of the work demonstrated the contribution of ANNs in controlling the DC motor in MATLAB and SIMULINK R2009b.Reference [2] considered the estimation of speed and controlling the separately excited DC motor by developing Artificial Neural Network. The validity of the new developed controllers is verified using simulation from the MATLAB/SIMULINK package

.Reference [7] presented a fuzzy neural network controller which is based on the mathematical model of brushless DC motor (BLDCM). Good robustness, excellent flexibility, adaptability as well as high Precision are obtained by the proposed model.In this paper, the speed control of the electric drives has been achieved and determined with the help of PIC 16F628A microcontroller.

2.0 Necessity for microcontroller

It is necessary to include microcontroller in the operation of DC motor control due to the following reasons: The motor speed is zero when stationary. This means that, the motor has no back e.m.f Eb when it is at rest. If connected directly to the supply mains, a heavy current will

flow through the armature conductors because armature resistance is very small [1,12,13] .

High reactive power consumed by the motor. In such a case, the rating of the upstream equipment may need to be rated higher than the steady-state condition. The reactive power during start up is closely related to the voltage dip. [14]

Heavy inrush current. This can cause heavy sparking at the commutator and even flashover. Damage of armature winding either by the heat develop in the armature windings, or by mechanical force set up by electromagnetic action. Damage to the rotating parts of the motor and load due to development of large starting torque and quick acceleration Large dip in the supply voltage.

The need for motor controller therefore, is not conversely enough, to provide starting but to reduce heavy starting currents and provide overload and no- voltage protection [1, 15]. The ratio of starting current or running current of an electric motor varies greatly with the size and type of motor, for any given motor the ratio depends on the kind of machinery the motor is driving. The starting current will be higher when the load is heavy. [16,17] The microcontrollers are applied to control electric motor, protect the motor against fault current and over-current so as to minimize the effect of starting current and smooth running of the electric motor.

In addition to starting, controller units can also be used for stopping the motor, by ramping the voltage down. This is particularly useful where sudden loss of driving torque would create mechanical shock on the load.

3.0 Reduced Voltage Starter

The generated e.m.f, E, is proportional to the speed N of the motor according to the expression given by

E kN —————————– (2)

Where k is the machine constant, N is the speed and

is the flux.

Substituting equation (2) in equation (1), we have V =

kN + Ia Ra

N = V ( Ia Ra ) / k (3)

Since Ia Ra is far less than V

equation (3) can be written as)

N = V / k (4)

Equation (4) Shows that the speed of an electric motor is approximately proportional to the applied voltage. This equation is known as the empirical model for d.c motors. Therefore, variation of supplied voltage to the motor is for manual or automatic control of speed over a wide range and in both direction of rotation.

5.0 Construction and Simulation

I/P O/P

AC

U1

16 RA7/OSC1/CLKIN RA0/AN0 17

15 RA6/OSC2/CLKOUT RA1/AN1 18

U1

16 RA7/OSC1/CLKIN RA0/AN0 17

15 RA6/OSC2/CLKOUT RA1/AN1 18

R4

R4

4

4

RA5/MCLR RA3/AN3/CMP1

RA5/MCLR RA3/AN3/CMP1

1k

1k

Application of full voltage to the terminals of a D. C motor will cause high inrush current. To reduce the inrush current in this work, variation of supplied voltage (other than the full voltage) to the motor was carried out. This was accomplished by reducing the voltage applied to the motor. This minimized voltage dips to the power supply. Electrical power is supplied to both the field and the armature windings. The field of the motor is connected permanently to a fixed exciting voltage of PIC 16F628A but the armature is supplied with variable voltages. The armature speed was found to be approximately proportional to the difference between two voltages.

4.0 Empirical Model

The generated e.m.f E, in armature is smaller than the terminal voltage V, for a motor and it is given by

VSS VDD VEE

RS RW E

D0 D1 D2 D3 D4 D5 D6 D7

VSS VDD VEE

RS RWE

D0 D1 D2 D3 D4 D5 D6 D7

RA2/AN2/VREF 1

RA2/AN2/VREF 1

1

2

3

1

2

3

4

5

6

4

5

6

7

8

9

10

11

12

13

14

7

8

9

10

11

12

13

14

Figure 1.0 Experimental circuit diagram

LCD1

LM016L

LCD1

LM016L

R5

4.7k

R5

4.7k

SW1

SW-SPST REED

SW 1(COM)

SW1

SW-SPST REED

SW 1(COM)

R1

4.7k

R3

4.7k

R1

4.7k

R3

4.7k

MEM

MEM

RELAY

2

2

RA4/T0CKI/CMP2 3

RB0/INT 6

RB1/RX/DT 7

RB2/TX/CK 8

RB3/CCP1 9

RB4 10

RB5 11

RB6/T1OSO/T1CKI 12

RB7/T1OSI 13

RA4/T0CKI/CMP2 3

RB0/INT 6

RB1/RX/DT 7

RB2/TX/CK 8

RB3/CCP1 9

RB4 10

RB5 11

RB6/T1OSO/T1CKI 12

RB7/T1OSI 13

PIC16F628A

PIC16F628A

V E Ia Ra

————————- (i) where Ra is

the armature resistance and Ia is the armature current.

Figure 2.0 Simulation circuit of Programmable Integrated Controller 16F628A

igure 3.0 Experimental Set-up (Front view)

6.0 Experimental Procedure.

speed inRPM

speed inRPM

Figure 1.0 shows the circuit diagram used for the experiment in this work. The experimental set-up is shown in figure 3.0. The motor was made to rotate by varying the voltage supply to the circuit. The input voltage was rectified and its variable output voltage was applied to the electric motor. The speed of the motor was determined by using a PIC 16F628A micro controller figure 1. A magnetic metal was attached to the pulley and an electronics card was placed at a distance of 2cm away from the rotating pulley that carried the magnet figure 2. The card is made of bi-metallic strip separated from each other, whenever a revolution is made, the magnetic spot on the rotating pulley focuses on the card and a pulse is generated in the circuit which gives a count of one revolution based on the program that has been added to the micro-controller. The two separate metals on the card are brought together by the magnetic force of attraction from the rotating pulley per revolution

7.0 Results and Discussion

Table 1.0. Input voltage/ Operating speed.

1800

1600

1400

1200

1000

800

600

400

200

0

90 110 140 180 220

1800

1600

1400

1200

1000

800

600

400

200

0

90 110 140 180 220

Figure 4.0 Plot of Voltage against speed

Figure 4.0 shows that as the applied voltage to the motor is increasing, the speed is also gradually increasing. From 80V to 140V the rate at which the speed is increasing is linearly constant. Between 140v to 200V the speed is almost constant. At 140V the speed is 1370rpm which represent 80% of full load speed. Therefore, at 140V of the supply voltage the starting equipment can be disconnected since it has already achieved 75% and above of the rated speed.

8.0 Conclusion

Validation of DC Motor speed control using PIC 16F628A Microcontroller is presented in this paper. The theoretical background model to show the direct relationship of voltage on the speed of dc drives in order to control the speed of a DC machine is discussed and presented. A DC machine is designed and constructed in this work. Speed measurements of the constructed DC machine were obtained. The results were presented in both tabular and graphical forms. It is shown that as the terminal voltage is increasing, the speed gradually increases.

Results of the constructed DC machine presented validate the theoretical model.

9.0 References:

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2. Amit Kumar Singh, Dr. A.K. Pandey, Intelligent PI Controller for Speed Control of SEDM using MATLAB, International Journal of Engineering Science and Innovative Technology (IJESIT), January 2013, Volume 2, Issue 1.

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4. G. Madhusudhana Rao, B. V. Sanker Ram, A Neutral Network Based Speed Control for D.C Motor, International Journal of Recent Trends in Engineering, November 2009, Volume 2, No 6, pp. 121-124.

5. Boumeddiene Alloua, Abdellah Laoufi, Brahim Gasbaoui, and Abdessalam Abderrahmani, Setting Up PID DC Motor Speed Control Alteration Parameters Using Particle Swarm Optimization Strategy, Leonardo Electronic Journal of Particles and Technologies, January-June 2009, Issue 14, pp 19-32.

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