11/22

IMPROVED SENSORLESS CONTROL WITH THE ST62 MCU FOR UNIVERSAL MOTOR

If we note with index (n) the variables related to the nth mains cycle, the complete PI

(proportional-integral) algorithm can be expressed by:

i_err(n) = it0(n-1) + table(td(n-1))

- icalc0

sum(n)

= sum(n-1) + KI * i_err(n)

td(n)

= VITMIN - [ sum(n) + KP * i_err(n) ]

table(td(n-1)) is the current compensation coefficient extracted from the table, and as-

sociated to the corresponding value of the firing delay td, td(n-1).

sum(n) is the integral term, and KP * i_err(n) the proportional term. VITMIN is a con-

stant equal to the maximum firing delay (150 x 48

μS = 7.2 mS in the example).

This is expressed in the program by:

i_err

<- it0 + table(td) - icalc0

sum

<- sum_old + KI * i_err

temp1

<- sum + KP * i_err

td

<- VITMIN - temp1

sum_old <- sum