AN863 Datasheet, PDF (11/22 Pages) STMicroelectronics – Improved sensorless control with the ST62 MCU for universal motor

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
11/22