27-10-2016, 03:47 PM
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INTRODUCTION:-
DC motors are one of the most used electrical machines, which are used in many industrial applications such as robots, welding and roll processes.
Speed control means intentional change of the drive speed to a value required for performing the specific work process. Speed control is a different concept from speed regulation where there is natural change in speed due change in load on the shaft. Speed control is either done manually by the operator or by means of some automatic control device.
The speed of DC motor can be controlled by many means like-using a variable dc voltage source(step down transformer),Armature control of dc motor,Field control of dc motor,
FPGA:-The FPGA stands for Field –Programmable Gate Array.It is an integrated circuit designed to be configured by a customer or a designer after manufacturing – hence field-programmable. The FPGA configuration is generally specified using a hardware description language (HDL), similar to that used for an application-specific integrated circuit (ASIC).
FPGAs contain an array of programmable logic blocks, and a hierarchy of reconfigurable interconnects that allow the blocks to be "wired together", like many logic gates that can be inter-wired in different configurations. Logic blocks can be configured to perform complexcombinational functions, or merely simple logic gates like AND and XOR. In most FPGAs, logic blocks also include memory elements, which may be simple flip-flops or more complete blocks of memory.Other applications of FPGAs include digital signal processing, software-defined radio, ASIC prototyping, medical imaging, computer vision, speech recognition, cryptography.
CHARACTERISTICS OF AN FPGA:-
FPGA are flexible, you can add subtract the functionality as required.
FPGAs are concurrent. You can take sequential functionality like adding soft processor core.
FPGAs are an increasingly attractive solution path for demanding applications due to their ability to handle massively parallel processing.
FPGAs are liked in military applications. There are two main reasons of that. The first is that FPGAs are hard-wired and the random attack of alpha rays can not destroy/corrupt the memory areas hence collapse the device functionality.
WORKING PRINCIPLE:
The speed of a dc motor can be controlled in various ways:
1.changing terminal voltage of the dc motor
2.varying the external resistance in armature
Here we are using the voltage changing method using Pulse Width Modulation.
is a method for binary signals generation, which has 2 signal periods (high and low). The width (W) of each pulse varies between 0 and the period (T). The main principle is control of power by varying the duty cycle. Here the conduction time to the load is controlled. Let for a time t1, the input voltage appears across the load i.e. ON state and for t2 time the voltage across the load is zero.
Pulse Width Modulation:
PWM is the modulator circuit which can change the width of the high pulse without changing the total time of that pulse. In PWM the comparator is the main equipment which gives the output in the form of high or low.
In comparator circuit there is a property, when the voltage applied to the non-inverting terminal of the op-amp is greater than the voltage applied to the inverting terminal then only the output of the op-amp will be high, for other case it will give zero voltage.According to the comparator output PWM gives the high signal. Thus the Ton time is changing consequently duty cycle also. According to the Ton time the voltage applied to the motor is changing.
DISCUSSION:-
DC motors are one of the most used electrical machines, which are used in many industrial applications such as robots, welding and roll processes.
Pulse-width modulation (PWM) of a signal or power source involves the modulation of its duty cycle, to either convey information over a communications channel or control the amount of power sent to a load.The use of pwm in control of dc motor is that the power dissipation is less.The amplitude of the motor also remains constant.