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HIGH-PERFORMANCE MOTOR SYSTEM FOR WASHING MACHINES

4 APPLICATION OF A DIGITAL SLIP CONTROL DEVICE TO A

WASHING MACHINE

4.1 EFFICIENCY IMPROVEMENT

The use of an automatic control device for maintaining the slip at its optimum value means an

optimum performance of the motor regardless of its load. This is implemented with the

ST92141 dedicated microcontroller that comes with a complete software library. All the soft-

ware needed to performed high efficiency operation is available in this library.

The curve shown in Figure 4., measured on a test bench, shows in abscissa the load torque

at the wash-cycle speed, and in ordinate the value of the motor + drive efficiency (lower

curve), as well as the mains input current and Power (upper curves). Note that the total effi-

ciency of the system is almost independent of the load in the useful speed range and optimum

for this very low operating speed.

universal motor with that of a 3-phase brush less induction motor. The induction motor was

used in compliance with the conditions specified in section 4 and highlighted a substantial gain

in consumption.

One of the benefits of this excellent efficiency is reflected by the small and cheap heatsink re-

sulting from the low level of power losses.

4.2 REDUCTION OF ACOUSTIC NOISE

It is well-known that the use of a brushless motor effectively eliminates noise related to its op-

eration, especially during high-speed spin cycles.

Moreover, the slip control device is used to limit the instantaneous motor flux to a low or

middle rate while keeping it independent from voltage variations of the mains supply. This

means a perfectly silent operation of the motor; free of all 100 Hz noise and torque peak noise

that may be encountered in vectorial control devices. The noise of the motor / pulley / drum as-

sembly is therefore substantially reduced.

Finally, these motors have high torque capabilities, and the transmission ratio of the pulley can

be significantly reduced as well as the associated noise.