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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

In the time domain, v(t) is the mains voltage: v(t) = V0 .sin

ωt (V0 = mains peak

voltage).

Vmains

Imotor

td

i(t0)