January 1999

INTRODUCTION

Brushless DC motors (BLDC) are becoming widely used in the field of control motors. These kind of syn-

chronous motors are used as servo drives in applications such as computer peripherals equipment, ro-

botics, and as adjustable-speed drives in load-proportional capacity-modulated heat pumps, large fans ,

compressors and so on.

Brushless DC motors are referred to by many aliases as brushless permanent magnet, permanent ma-

gnet AC motors, permanent magnet synchronous motors, etc. The confusion arises because a brush-

less motor does not directly operate off a dc voltage source. It is generally driven (supplied) from an in-

verter which converts a constant voltage to a 3-phase voltage with a frequency corresponding

instantaneously to the rotor speed.

One of the advantages of BLDC motor is the sparks absence. The brushes of a DC motor have several

problems as regards to brushes’ life and dust residues, maximum speed and electrical noise. BLDC mo-

tors are potentially cleaner, faster, more efficient, less noisy and more reliable. However, BLDC motors

require a more complex electronic control.

This application note will show how this complexity can be reduced by using ST52x301 Fuzzy controller.

AN OUTLINE OF BRUSHLESS MOTORS

The Brushless motor has the physical appearance of a 3-phase permanent magnet synchronous machi-

ne.

The brushes and commutator have been eliminated and the windings are connected to the control elec-

tronics. Electronics replaces the function of the commutator and energizes the proper winding. The ener-

gized stator winding leads the rotor magnet and switches just as the rotor aligns with the stator.

In synchronous motor drives, the stator is supplied with a set of balanced three-phase currents, whose

frequency is

f.

If

p is the number of the poles in the motor, then:

f

=

p

where

the rotor speed to the phases switching frequency of the electronic drive.

The above currents produce a constant amplitude flux

nous speed

winding current level to control the rotor torque.

From Brushless theory [3-4] it is possible to demonstrate that

phase linked flux

AN1113

APPLICATION NOTE

Brushless Motor Fuzzy Control by using ST52x301

Authors: G. Grasso, M. Di Guardo

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