11-10-2012, 04:18 PM
Modeling and Simulation of DC motor and H Bridge
Modeling and Simulation of DC Motor and H Bridge .doc (Size: 468.5 KB / Downloads: 29)
Abstract
Our training commenced at infrared camouflage group of Defence Laboratory, Jodhpur. The present work aims with modeling and simulation of DC motor and H Bridge circuit with Pulse width modulation (PWM) for speed control and study the motor parameters.
DC Motors are widely used motors to drive the loads in industry. Among the different control techniques for the DC Motor speed control is armature voltage control method using PWM. PWM is commonly used as excitation for controlling power to inertial electrical devices.
In our project, Simulation and modeling of a DC motor and H Bridge circuit was carried out using PSpice ORCAD software. PWM control method has been realized using an H- Bridge built with four transistor switches for speed as well as direction control. The H-Bridge allows the bi-directional rotation of the DC Motor. The operating power to the motors is turned on and off to modulate the current to the motor
PWM is an effective switching method for adjusting the amount of power delivered to the load. This technique allows smooth speed variations without reducing the starting torques and eliminates harmonics.
DC Motor
INTRODUCTION:-
A DC motor is an electric motor that runs on direct current (DC) electricity. DC motors were used to run machinery, often eliminating the need for a local steam engine or internal combustion engine. DC motors can operate directly from rechargeable batteries, providing the motive power for the first electric vehicles. Now a day's DC motors are still found in applications as small as toys and disk drives, or in large sizes to operate steel rolling mills and paper machines. Modern DC motors are nearly always operated in conjunction with power electronic devices.
Principle of DC motor:-
A DC motor works by converting electric power into mechanical work. This is accomplished by forcing current through a coil and producing a magnetic field that spins the motor. The simplest DC motor is a single coil apparatus, used here to discuss the DC motor theory. The process can be explained in further detail by observing the diagram below.
CHARACTERISTICS AND DEPENDENCE OF DC MOTOR ON VARIOUS FACTORS
Moment of inertia:-
Moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, (SI units kg•m², imperial/US units Lbm ft²) is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation. The moment of inertia plays much the same role in rotational dynamics as mass does in linear dynamics, describing the relationship between angular momentum and angular velocity, torque and angular acceleration, and several other quantities. The symbols I and sometimes J are usually used to refer to the moment of inertia or polar moment of inertia.
Back e.m.f:-
The counter-electromotive force also known as back electromotive force is the voltage, or electromotive force, that pushes against the current which induces it. e.m.f is caused by a changing electromagnetic field. It is the effect of Lenz's Law of electromagnetism. Back electromotive force is a voltage that occurs in electric motors where there is relative motion between the armature of the motor and the external magnetic field. In a motor using a rotating armature and, in the presence of a magnetic flux, the conductors cut the magnetic field lines as they rotate. The changing field strength produces a voltage in the coil; the motor is acting like a generator. (Faraday's law of induction.) This voltage opposes the original applied voltage; therefore, it is called "counter-electromotive force" (by Lenz's law). With a lower overall voltage across the armature, the current flowing into the motor coils is reduced. It is expressed as “Eb” .