Điều khiển số động cơ một chiều qua mạch thyristor công suất

Huy Ngoc Vu et al Journal of SCIENCE and TECHNOLOGY 127(13): 87 - 91

87

THYRISTOR-BASED DIGITAL CONTROL OF DC MOTORS

Huy Ngoc Vu*

, Tuan Manh Tran, Huong Thi Mai Nguyen, Hung Tien Nguyen

University of Technology – TNU

ABSTRACT

DC motors have been widely used in the industry because of high mechanical power density,

simplicity and cost effectiveness as well as of their versatile control characteristics. Speed of the DC

motor can be controlled by regulating its armature voltage using some of the thyristor-based circuits.

In the past, the speed control of DC motors was accomplished with analog technology due to simple,

and low cost constraints. However, this technique exhibits many drawbacks since it can not guarantee

the drift of device parameters in a desired range when working conditions are changed. This paper

proposed the speed control of DC motors using a digital signal processor (DSP) which has the special

features for digital motor control. The velocity control loop uses PI controller that has been

implemented by programming in the DSP core. According to the input command, feedback command

and control algorithm, the PWM pulses generated by the DSP are given to gates of thyristors.

Keywords: DC motor, digital signal processing, DSP, PWM.

INTRODUCTION*

Currently in DC motor drive systems are still

widely used because it has the following

advantages: High starting torque, ability to

adjust the speed is relatively simple, even for

the high power motor, easy to reverse

rotation, stabilizing the speed easily, the

structures of the power circuit and the control

circuit are relatively simple, can achieve high

adjustable quality in wide speed range.

Most of the drive systems using DC motors

are required to adjust the speed. In fact there

are two basic methods to adjust the speed of

DC motors: Adjustable voltage for the motor

armature and adjustable voltage for motor

excitation circuit.

The controlled rectifier is in the power circuit

of the drive system to adjust the motor speed.

These converters’ outputs apply to the motor

armature circuit or motor excitation circuit.

The converters, the circuits and the control

algorithms can be implemented using analog

or digital techniques. In particular, the use of

analog techniques has the advantage of being

relatively simple, efficient and has developed

completely. Basic drawback of this technique

depends heavily on parameters’ drift of the

elements in the system making the stability of

* Tel: 0983169582; Email: [email protected]

the system sometimes not be guaranteed over

time and be difficult to response to the

different working conditions.

The drive system of the DC motor typically

uses two adjustable loops. In the outer loop is

the velocity regulation, the inside loop is the

current regulation. Current regulation loop

required to response faster than the velocity

regulation loop that depends heavily on

mechanical inertia of the motor and the load.

Therefore, the design requirements for the

current loop have more stringent

requirements. To get the optimal parameters

for the current regulation loop, there must be

the exact parameters of the motor. Then, the

controller in analog technique of the current

loop is adjusted according to the parameters

have been synthesized by changing the value

of the variable resistor, variable capacity or

the gain of the amplifiers. However, in the

operation, the parameters of the motor may be

altered due to their dependences on working

conditions (resistance of the armature varies

with temperature, inertia varies with the

load...), the electronic components themselves

as well as operational amplifiers also changes

with temperature, humidity... Therefore, the

quality of the controller in analog technique is

very difficult to ensure over time and the

different working modes.