AN863 Datasheet, PDF (15/22 Pages) STMicroelectronics – Improved sensorless control with the ST62 MCU for universal motor

IMPROVED SENSORLESS CONTROL WITH THE ST62 MCU FOR UNIVERSAL MOTOR
7 REFERENCES
[1] Power control with triacs and ST6210 MCU
AN392 - P. Rabier and L. Perier (SGS-THOMSON Microelectronics)
[2] Digital control for brush DC motor
T. Castagnet and J. Nicolai (SGS-THOMSON Microelectronics)
PCIM Nuremberg, June 93
[3] Sensorless motor drive with the ST62 MCU + TRIAC
AN416 - T. Castagnet (SGS-THOMSON Microelectronics)
8 ANNEX
ANNEX 1 MOTOR CURRENT CALCULATION
The motor voltage equation is: v(t) = (k.Ω + r) i(t) + L di/dt
v(t) = 0 while the triac is off (before turn on at time td, and after the turn off caused
by the motor current reaching 0)
v(t) = V0 .sinωt while the triac is on
The solution to the differential equation is:
i(t) = 0 while the triac is off
While the triac is on:
If we neglect the inductance L: i(t) = V0 sinωt / (k.Ω + r)
If we do not neglect the inductance:
i(t) = - exp(-A(t-td)/L) [ B sin ωtd + C cos ωtd] + B sin ωt + C cos ωt
with: A = k.Ω + r
B = AV0 / (A ² + L² ω²)
C = - L ω V0 / (A ² + L² ω²)
td = triac firing delay measured from mains zero-crossing
Figure 10 is a plot of i(t0) versus td at constant speed. Modifying the speed parameter
generates a family of curves. In Figure 11, t0 equals 10 mS: the current i(t0) is meas-
ured at the mains voltage zero crossing.
Figure 11 is a plot of i(t) versus t at constant speed. Modifying the parameter td (triac
firing delay) generates a family of curves
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