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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 .sin

ωt 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 sin

ωt / (k.Ω + r)

If we do not neglect the inductance:

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