Submitted By
R.PRASHANTH M.PRATHYUSH
K.PRAVEEN KUMAR
B.RADHIKA

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ABSTRACT
Due to efficient control methods, DC motors are widely used motors to drive the loads in industry. Among the different control techniques for the DC motor speed control, armature voltage control method using Pulse Width Modulation (PWM) technique is the best one. We can realize the PWM control method using a chopper, build with semiconductor switches, such as BJT, MOSFET, IGBT’s and also using an H-bridge built with MOSFET, IGBT switches. In our project, we design H-bridge with MOSFETs and control the input voltage of the DC motor using PWM technique. To generate PWM control signals, we use AT89C51 microcontroller, one of the popular 8051 microcontroller family members. According to the user’s required speed, AT89C51 based control circuit generates appropriate PWM pulses.
CHAPTER-1
INTRODUCTION
1.1: CONVENTIONAL METHODS OF SPEED CONTROL
The DC motors used in industrial applications have progressively gotten better over the years. Along with this, the way we control these motors has continued to improve. From the old rheostat which gave the way to solid state electronics and then the DCC and there after the PID controller.
A PID is a generic control loop feedback mechanism used to control the speed of the motor. It calculates the difference between a measured process variable and desired set point. It tries to minimize the error by adjusting the control inputs. As PID controllers require exact mathematical modeling, the performance is questionable if there is any parameter variation. It does not guarantee optimal control of the system. It is a time consuming process as we cannot get the required speed till the error produced equals to zero.
1.2: ADOPTED TECHNIQUE
In this project we are designing the H- Bridge with MOSFETs and controlling the input voltage of the DC motor by PWM technique.PWM is an effective method for adjusting the amount of power delivered to the load. PWM technique allows smooth speed variation without reducing the starting torque and eliminates harmonics. The MOSFET Bridge allows the bidirectional rotation of the DC motor. In PWM method, operating power to the motors is turned on and off to modulate the current to the motor. The ratio of on to off time is called as duty cycle. The duty cycle determines the speed of the motor. The desired speed can be obtained by changing the duty cycle.
1.3: BLOCK DIAGRAM
CHAPTER-2
DC MOTOR
2.1: WORKING PRINCIPLE OF A DC MOTOR
A DC motor is an electric motor that runs on DC electricity. It works on the principle of electromagnetism. A current carrying conductor when placed in an external magnetic field will experience a force proportional to the current in the conductor.
2.2: OPERATION OF A DC MOTOR
There are two magnetic fields produced in the motor. One magnetic field is produced by the permanent magnets and the other magnetic field is produced by the electrical current flowing in the motor windings. These two fields result in a torque which tends to rotate the rotor. As the rotor turns, the current in the windings is commutated to produce a continuous
Torque output this makes the motor to run.
2.3: SPEED CONTROL METHODS OF DC MOTOR
They are various methods used to control the speed of a DC motor. Some of them are:
1. Armature control method
2. Flux control method
3. Ward Leonard system.
Armature control method: Speed can be controlled by varying the voltage. As speed is directly proportional to the voltage. As voltage increases speed increases and vice-versa. A simple voltage regulation would cause lots of power loss on control circuit. So we are going for PWM. In this method the duty cycle determines the speed of the DC motor. Required speed can be attained by changing the duty cycles. PWM also allows smooth speed variation without reducing the torque. It also eliminates harmonics.
CHAPTER -3
POWER SUPPLY MODULE
Power Supply Circuit consists of following components:
• Printed circuit board(P.C.B)
• Operation
• Hardware description
3.1: DIAGRAM
3.2: OPERATION
A 1-phase 230v AC supply is given to a step down transformer; the output obtained is a 15v AC. The output obtained from the transformer is given to a diode bridge rectifier from which a rectified DC output is obtained. This DC output contains some ripples. To filter these ripples we use capacitors (1000uf, 100uf, 10uf). To maintain the steady state DC output the voltage is passed to the voltage regulators LM7805 which gives constant 5v DC and LM7812 which gives constant 12v DC
3.3: HARDWARE DESCRIPTION
STEP DOWN TRANSFORMER: Transformers are electrical devices that transform voltage through magnetic couplings, and they have no moving parts. There is a magnetic core with one winding of wire placed close to one or more windings, which can couple two or more alternating-current circuits together by employing the induction between the windings. The primary winding is connected to the power source and the other windings are known as secondary windings. If the secondary voltage wire is less than the primary wire, the transformer is called a
STEP DOWN TRANSFORMER. It steps down incoming voltage, which enables you to have the correct voltage input for your electrical needs.
DIODE BRIDGE RECTIFIER: It is used to rectify AC to DC. A diode bridge rectifier consists of four diodes D1, D2, D3 & D4. A sinusoidal input is given to the diodes. During the positive cycle of the supply diodes D1 & D2 are in forward bias and when the firing angle is applied, they conduct. During the negative cycle of the supply D3 & D4 are in forward bias and when the firing angle is applied, they conduct. In this way rectified DC output is obtained. For different firing angles different outputs can be obtained. The circuit diagram and waveforms of the diode bridge rectifier are shown as below.
LM7805: Usually having three legs, converts varying input voltage and produces a constant regulated output voltage. They are available in a variety of outputs. The most common part numbers start with the numbers 78 and finish with two digits indicating the output voltage. Therefore 7805 is a 5v regulator. It is a positive voltage regulator. They are immune to overload voltages.
LM7812: They are 3-terminal 1A positive voltage regulators. The last two digits of the voltage regulator indicate the output voltage. The output voltage of the LM7812 is 12v. They are immune to overload voltages. They accept only positive voltage as input.
FILTER CAPACITORS: They are any capacitors used for filtering. Glitch removal on DC power rails. They are used for suppressing the DC ripples. Capacitors used after the reservoir capacitor to further smooth DC power supplies.