Control and designing of the DC motor drive using p-i controllers with the help of matlab simulation

Abstract

The paper describes the designing of a closed loop model of the dc motor drive for controlling speed. Accuracy and the dynamic responses are better in a closed loop system. In the closed loop system, acceleration and the deceleration of the motor can be controlled according to the requirement. In order to regulate drives automatically, the controlled variables are measured. A tachogenerator is used for this purpose. The output of the tachogenerators is compared with a preset reference voltage. The differences between these two signals are fed as an actuating signal to control the elements of the system. Control amplifiers are used as both comparators and amplifiers. As a small change in the voltage can cause a large change in the motor current and lead to a particular drive control feature. There are two closed paths in the dc control scheme. One is the outer speed control loop and the other is the inner current control loop. Both the loops are controlled with the help of P-I controllers having their own gains and the time constants according to the requirement of the system. The output of the speed P-I controller which is the function of the speed error is used to command for current P-I controller and compared with armature current. The current P-I controller output control the triggering circuit of the converter. The armature current tends to increase to a large value when the motor is accelerating. A current limit can be obtained in this system by limiting the maximum current command voltage. If the motor speed drops below the set point, the resulting error signal causes the gate pulse generator to advance the firing pulses, and increase the rectifier output voltage. Consequently the speed rises to the desired level