"Ref" value from AD Channel0 and the instantaneous Hall signal period by means of a digital port. A

software task performs the "error" calculation

error

= VREF − speed.

The variable "

Error" also forms the Fuzzy Input for the "Fuzzy Controller" block. A Fuzzy algorithm uses

three rules to compute the fuzzy-out, achieving an incremental variable to drive the inverter in real-time

mode.

This incremental method allows to manage the speed in a closed loop real-time control, since software

task time is very short.

The first rule is fully activated when "error" value is "neg", i.e. when Vref <<speed. This implies that the

actual speed of the shaft is higher than "Ref". Then the action to carry out is to reduce the phase current

Figure 6. Fuzzy algorithm

I. To achieve this, it is necessary to decrease the PWM duty-cycle. The displayed value "-10" is a good

compromise between system stability and step response of the system. This value was assigned after

some trials by using only human reasoning. Instead, If the duty step is higher, for example "-20", the sy-

stem will sooner reach the "Speed_Ref" but the overshoot in a step response could lead to instability.

The above explanation is similar for the other rules.

The implemented 3-rules fuzzy algorithm is the simplest way to control the speed. A more accurate con-

trol could be done by using first derivative of the speed to improve the action strenght by means of other

rules.

HARDWARE DESCRIPTION

®

Brushless Motor Fuzzy Control by using ST52x301

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