AN863 Datasheet, PDF (4/22 Pages) STMicroelectronics – Improved sensorless control with the ST62 MCU for universal motor

IMPROVED SENSORLESS CONTROL WITH THE ST62 MCU FOR UNIVERSAL MOTOR
2 SENSORLESS REGULATION PRINCIPLE
The above equations were first order equations, assuming DC operation, or average
values for voltage and current. The real, instantaneous equation is the following:
While the triac is off:
i=0
While the triac is on (after firing time td, and until current comes back to zero; see
Figure 2):
v = e + z.i
with: e = back electromotive force (bemf) = k. Ω. i
z = motor impedance = r + j.L.ω
k = constant dependent upon motor characteristics
Ω = motor speed
i = instantaneous motor current
v = instantaneous motor voltage
L = motor inductance
r = winding resistance
ω = mains frequency
v = (k.Ω + r) i + j.L.ω.i
Figure 2. First Order Model (resistive only): Constant Speed, Variable Load
Vmains
i(t0)
Imotor
td
t0
In the time domain, v(t) is the mains voltage: v(t) = V0 .sinωt (V0 = mains peak
voltage).
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