11-05-2012, 10:56 AM
Dc Motor Speed Controller a fuzzy approach
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ABSTRACT:
This paper presents an insight into the speed control of D.C motor using a fuzzy logic controller to meet the desired speed. Fuzzy logic is one of the most successful applications of fuzzy set in which the variables are linguistic rather than numeric. A fuzzy logic controller (FLC) is based on a set of control rules (fuzzy rules) among linguistic variables. The personal computer provides the necessary flexibility in setting any speed profile with the use of fuzzy packages. Basically a D.C shunt motor has drooping speed-torque characteristics. The proposed fuzzy controller results in a better response compared to the basic fuzzy controller and normal response of D.C motor. The step response parameters can be closely controlled with the help of simple operations within the controller. The simulation is carried out and the simulation results present the flexibility of the motor speed control.
KEY WORDS: fuzzy controller, speed-torque characteristics, fuzzification,
De- fuzzification.
INTRODUCTION:
DC motor converts electrical energy into mechanical energy. DC motor is used in applications where wide speed ranges are required. DC shunt motor exhibits a drooping speed-torque characteristic. The speed of the DC motor is given by
Hence, the speed can be controlled by varying,
i) Flux/pole (). Field Control Method
ii) Voltage of armature circuit, by varying Ra, Armature Control Method.
FIELD CONTROL METHOD:
The speed is inversely proportional to flux. By decreasing the flux, the speed can be increased and vive versa. The flux of the DC motor is changed by changing
field current with help of a shunt field rheostat.
ARMATURE CONTROL METHOD:
This method is used when speeds below base speed are required. As supply voltage is normally constant, the voltage across the armature is varied by inserting a variable resistance in series with the armature circuit. As resistance is increased, armature voltage is decreased, thereby decreasing the armature speed.
FUZZY LOGIC CONTROL SYSTEM:
A fuzzy logic controller (FLC) is based on a set of control rules (fuzzy rules) among linguistic variables. Usually these rules are expression in the form of conditional statements (if x is small, then y is large). The execution of these rules is given by the compositional title. A basic architecture of FLC is shown in Fig 1. This structure consists of following four modules: