Get ready for the next wave of energy-efficient washers

The reason: A lot of callers might think their new machines aren't working properly because the wash water doesn't even cover the clothes in the tub.

Big surprise. The washing dynamics of many such machines are efficient enough to get clothes clean with a seemingly insufficient level of water. Makers of top-loaders, for example, can now precisely control both speed and action of agitators. This lets them use a minimum of water and still clean clothes.

Energy-efficient washers increasingly are adopting a front-loading format where the drum is driven directly by a specially built permanent-magnet synchronous motor with no intervening gearbox or belt drive. Wash dynamics in these new machines are such that clothes emerge clean after a wash and rinse with water levels that may not even cover the clothes. There are tough torque and speed requirements levied on the PM synchronous motors in such systems as becomes evident in a typical torque/speed graph as depicted by International Rectifier. New integrated circuits designed especially to drive PM washer motors can now synthesize such performance.

Most of the energy used in clothes washing goes into heating water and drying clean clothes. So getting the job done with less water attacks both problems.

But one of the challenges associated with realizing this kind of energy-efficient wash cycle lies with the washer motor. Energy-efficient washers put tough demands on their motors. Good washing dynamics demand precise control of drum or agitator movement with high torque at speeds that can be lower than 50 rpm. And washer makers are boosting their spin speeds to 1,000 rpm and more to wring out as much moisture as possible at the end of the cycle, thus minimizing drying time.

Washers have historically relied on split-phase induction motors and gearboxes to power the drum and agitator. But such setups don't give the kind of performance energy-efficient washers need at both ends of the speed range.

For this reason, next-generation washers are moving toward use of permanent-magnet synchronous motors. These motors not only generate the kinds of speed and torque needed for high-tech washing, they also do so without an intervening gearbox. The resulting direct-drive system is more efficient than mechanical drives and can be physically smaller besides.

Washer makers are also striving to get costs out of PM motors to make the approach economical enough for mid to lower-end washers. One avenue of investigation in this area is to eliminate Hall-effect sensors and associated electronics normally needed for motor commutation. The alternative is a sensorless, vector-control algorithm built into software. Control parameters for this technique must be tuned to work with specific motor types. So washer makers typically work with motor manufacturers to devise motors and controls optimized for specific washers.

Integrated circuits are now starting to emerge that will let PM motors synthesize the behavior needed for new washers. The most recent example is a sensorless control platform for direct-drive,synchronous PM motors recently developed by International Rectifier. The new chips feature a special field-oriented algorithm for high-dynamic torque control that is said to help washers reduce overall energy consumption by 70%.