Modeling, Simulation and Implementation of Speed Control of DC Motor Using PIC 16F877A

Transcription

1 Modeling, Simulation and Implementation of Speed Control of DC Motor Using PIC 16F877A Payal P.Raval 1, Prof.C.R.mehta 2 1 PG Student, Electrical Engg. Department, Nirma University, SG Highway, Ahmedabad, Gujarat, India. 2 Asst. Prof. Electrical Engg. Department, Nirma University, SG Highway, Ahmedabad, Gujarat, India. 1 10meep15@nirmauni.ac.in 2 chintanmehta@nirmauni.ac.in Abstract The Microcontroller based adjustable closed-loop DC motor speed controller systems has already become an important drive configuration for many applications across a wide range of powers and speeds. This is due to their simple control, high reliability, low cost and fast response. Control System Design and Analysis technologies are widely suppress and very useful to be applied in real-time development. Some can be solved by hardware technology and by the advance used of software, control system are analyzed easily. Fractional HP DC Motors can be used in various applications and can be used as various sizes and rates. The designed circuit is stimulated using Real peak and MP LAB. In this paper, control techniques of PIC 16F877A microcontroller and MOSFET, mechanism assignments of analyzed by mainly focusing with the Modeling and Simulation of DC Motor using MATLAB. Keywords DC Motor, MATLAB/ Simulink, PIC. I. INTRODUCTION Traditionally, the DC Motors and the associate close loop control systems used to drive them have been modeled using classic control theory techniques, based on transfer functions. Control system design and analysis technologies are widely suppress and very useful to be applied in real-time development. Some can be solved by hardware technology and by the advance used of software, control system are analyzed easily and detail. DC Motors can be used in various applications and can be used as various sizes and rates. The microprocessor computes the actual speed of the motor by sensing the terminal voltage. It then compares the actual speed of the motor with the reference speed and generates a suitable control signal which is fed into the triggering unit. This unit drives a Power MOSFET amplifier, which in turn supplies a PWM voltage to the dc motor. The objective of this paper is to explore the approach of designing a microcontroller based closed loop controller. The interface circuit and the software are all designed to achieve a better performance. The microcontroller system is equipped with an LCD display and a keypad and software was written to monitor the registers on the LCD and read commands from the keypad. Thus, by using the User Interface Module (UIM) the operator can view and/or change all the control and monitoring variables of the controller program. II. MODELING A DC MOTOR For modeling and simulation of a DC Motor, simple circuit of its electrical diagram as shown in Figure 1 is to be considered. A. Closed-Loop System Consideration To perform the simulation of the system, an appropriate model needs to be established. Therefore, a model based on the motor specifications needs to be obtained. Figure-1 shows the DC motor circuit with Torque and Rotor Angle consideration. Fig.1.Schematic Diagram of a DC Motor 146

2 B. System Equation The motor torque T is related to the armature current, i, by a torque constant K; From the block diagram in Fig. 2, it is easy to see that the transfer function from the input voltage, V(s), to the angular velocity is: The generated voltage, e a, is relative to angular velocity by From Fig. 1 we can write the following equations based on the Newton s law com bined with the Kirchoff s law: (1) (2) (3) + b = Ki (4) D. MATLAB Representation (11) To represent the model with m-file, we can perform the Fig. 2 data as follows; Power P = 0.37 kw Speed N = 1500 rpm, Rotor Inertia J is assumed to be 0.01 Supply voltage = 220 volts. Calculate the torque constant K; C. Transfer Function +RI =V - K (5) Using the Laplace transform, equations (3) and (4) can be written as: (6) K=1.4 By using equation (3) for (12) (13) (7) Where s denotes the Laplace operator. From (7) we can express I(s): At the steady state (used as analyzed data), both I and ω are stabilized; and substitute it in (5) to obtain: (8) And (14) (9) This equation for the DC motor is shown in the block diagram in Fig. 2. From equation (8), the transfer function from the input voltage, V(s), to the output angle θ, directly follows: (10) (15) Following value are assigned to be used for our desire DC Motor Model: V t = 220v; J=0.01; b=0.02; k=1.4; R a =13.5 Ω; L a =132.5 mh. By calculating and assuming the require data as above. 147

3 III. SIMULINK MODEL The block diagram of Fig. 2 can be represented and created as a model as shown in Fig. 4. The approaching to construct this model can easily be done by using Simulink Library. The M- file and Simulink model can be combined by the following commands and these are commands used in M-file which can be solve it. Figure.2 Closed loop system that Representing the DC motor D. Analysis We plot the step, impulse and frequency responses of the given motor model: Figure.4 Model created in SIMULINK Toolbox of MATLAB Fig.3(a) Step response using simulink model. Fig. 3(b) Impulse response using simulink model. 148 Figure.5. Final results using simulink model (with Step response)

4 IV. SYSTEM DESCRIPTION The input from the stable power supply unit (230 V AC) is converted into 12v AC by means of a step down transformer, the output of this is used as input to bridge rectifier circuit. Here in this system bridge rectifier will generate 5 V DC with the help of regulator The output of the 7805 regulator is used as an input to the PIC. The PIC will generate pulses to drive the DC motor according to the requirement. As the output voltage of the PIC is in mv, driver circuits are used to drive the DC motor An optical encoder is used to measure the speed of the motor. The output of the encoder is a stream of pulses with variable frequency according to the speed of the motor. The optocouplers were used to isolate the high voltage circuits from the low voltage controlling signals. The rating of the motor should be chosen according to the rating of the power circuit. A. Microcontroller PIC16F877A. Peripheral Interface Controller (PIC) is a term introduced by Microchip technology. PIC 16F877A is a family of CMOS 8-bit Flash microcontrollers[3]. Power consumption is very low. PIC16F877A is a 40/44-pin device which can operate at up to 20 MHz clock speed. It has 8K * 14 words flash program memory, 368*8 RAM data memory, 64bytes of EEPROM nonvolatile data memory, 8-bit timer with pre-scalar, watchdog timer, Only 35 single-word instructions to learn, external and internal interrupt sources and large sink and source capability. The architecture is shown in Fig.3[3] For this study a dc shunt motor with ratings 1500 rpm, 220 V, 2.3 A, 0.37 kw is used. The entire operation of the blocks is explained briefly as follows with the diagram as shown in figure.6 below. Fig.7.Architecture of PIC16F877A Microcontroller B. Driver Circuit This driver circuit is designed based on the DC motor current ratings, The current rating of the DC motor is 2.3 Amp So driver circuit is needed. It is the most popular and cost effective drive circuits for driving MOSFETs. A bipolar, non-inverting totem-pole driver as shown in Fig 4. Transistors can be used to supply higher current to the motor. This circuit handles the current spikes and power losses making the operating conditions for the PWM controller more favorable. Fig.6.Circuit diagram for DC Motor speed control. Fig.8 Driver Circuit 149

5 V. SIMULATION RESULTS The proposed control circuit is implemented using software module like Real PIC Simulator as shown in Fig 9. For the purpose of coding the software package used is MPLAB. If any suddenly jerk is coming our PIC IC will not damage. Two pins are also used for ground. In chips with 40pins and more, it is common to have multiple pins for V cc and GND. This will help reduce the noise (ground bounce) in high-frequency systems. The PIC 16F has many options for the clock source. Most often a quartz crystal oscillator is connected to input pins OSC1 & OSC2. PIC 16F877A microcontroller can have speed of 0 Hz to 20 MHz. LCD Driver ckt PIC Power supply Fig.9(a) Output pulses of PIC16F877A through MPLAB IDE for ω=500rpm Figure.10 PIC 16F877A Hardware Connection with Power Supply, Driver circuit and LCD Display B. Bridge Rectifiers, Regulator and Driver circuit The bridge rectifiers,regulator and driver circuit used to convert 230 V AC to 12 V DC and 5 V DC to give as input to the PIC 16F877A controller is shown in Fig.11 Bridge ckt Driver circuit Fig.9 (b) Output pulses of PIC16F877A through MPLAB IDE for ω=1500 rpm VI. HARDWARE SETUP AND RESULTS A. Minimum Hardware connections of PIC16F877A The results shown are for the motor having parameters: V = 220 V, ω=1500 rpm, P = 0.37 kw, I=2.3 A. The minimum hardware connections circuit board is as shown in Fig.10. Two pins are used to provide supply voltage tochip. The stable power supply of +5 V is used. 150 Fig.11. Bridge rectifiers, Regulators and driver circuit C. Optical Encoder and Rotating disk The most popular type of encoder is the optical encoder, which consists of a rotating disk, a light source, and a photo detector (light sensor). The disk.which is mounted on the rotating shaft, has coded patterns of opaque and transparent sectors.

6 As the disk rotates, these patterns interrupt the light emitted onto the photo detector, generating a digital or pulse signal output. It is shown in fig. 12. Rotating disk Fig.14.Practically Actual & Ref. speed on LCD ω = 750 rpm Optical encoder Figure.12.Optical Encoder and rotating disc (8 Number of Slots) which is mounted on the rotating shaft The corresponding output pulse of PIC is as shown in Fig 13 on CRO and Fig 14 on LCD VII. CONCLUSION The DC machine is considered to be basic electric machines. The aim of this paper is to introduce Technicians to the modeling of power components and to use computer simulation as a tool for conducting transient and control studies. The Microcontroller based adjustable closed-loop DC motor speed controller system has been developed.. The results showed that the microcontroller is a reliable instrument to control the motor. This system is applicable to different sizes of motors and capable of controlling the speed of the motors with very high precision. VIII. REFERENCES [1] Wai Phyo Aung, Analysis on Modeling and Simulink of DC Motor and its Driving System Used for Wheeled Mobile Robot, PWASET VOLUME 26 DECEMBER 2007 ISSN [2] Gopal K. Dubey, Fundamentals of Electrical Drives, 2nd edition, Narosa Publishing House, New Delhi Fig.13Practical output pulse of pic16f877a in CRO [3] Muhammad Ali Mazidi, PIC Microcontroller and Embedded systems using Assembly and C for PIC16, Pearson Education, [4]Ajay V. Deshmukh, Microcontrollers: Theory and applications, Tata McGraw-Hill [5] 7805 and 7812 Voltage Regulator ICs-Data sheets. [6] PIC16F877A Data sheet from Microchip Corporation. [7] MPLAB IDE Software-Microchip technology. 151