Introduction:
A recent world-wide interest in the environmental friendliness, water consumption, and energy saving particularly impinges on the home appliance area. The actual regulatory standards and recommendations, either multination (EU standards) or nation-wide, enforce basic demands for a new generation of home appliances and particularly washing machines, dryers, dish washers and refrigerators. To meet such home appliance requirements and recommendations while reducing cost, enhanced microcontrollers equipped with appropriate software must be employed.
For this particular purpose, a digital signal controller based solution is proposed in order to combine the processing power of a digital signal processor with the functionality and ease of use of a microcontroller on a single chip. A flexible set of peripherals allows the designers to realize numerous functions such as standard motor drive algorithms, advanced control algorithms, sophisticated feedback signal sensing, power factor correction schemes, and communication to external environment.
Employing variable speed motor drives gives an opportunity to have more sophisticated control programs. This enhances the appliance performance and increases overall energy efficiency. Thus home appliances equipped with variable speed drives and intelligent controls consequently out-perform electronically uncontrolled motor drives and improve home appliance performance over motor drives with fixed speeds.
The majority of electric motor drives in home appliances are generally controlled very simply by fixing the motor speed at pre-defined levels or running directly from the AC main supply without additional control electronics " electronically uncontrolled motor drives.
The AC mains-supplied single"phase induction motor (ACIM) is the widely accepted solution and has gained wide acceptance due to suc advantages as low cost, reliability, and robustness; but along with advantages there are significant drawbacks such as low efficiency and low effective speed control. These drawbacks hinder control improvements to single-phase induction motors to meet mandatory regulatory features, customer attractiveness, and product flexibility. In contrast to single"phase ACIM, the variable speed drives address energy-efficiency requirements by maintaining precise torque control and improve overall appliance efficiency.
In the case of a refrigerator, the conventional control turns the compressor on and off to maintain the temperature in a predefined range. The washing machine operates in two basic cycles: tumble-wash and spin-dry. During the tumble wash cycle, the motor drive operates at low speed with high torque; during spin "dry cycle, the motor drive works at high speed for short time periods.
AC Motor Choice
There are different motor categories applicable to driving home appliances such as AC induction motors (ACIM), Permanent Magnent (PM) motors or switched reluctance (SR) motors. The overall efficiency is given by the product of the electronic drive efficiency and the motor efficiency.
In general, to achieve variable speed operation of an ACIM, a variable frequency and a variable voltage needs to be supplied to the ACIM. This mode of operation is referred to as constant volt per Hz control. The ACIM speed drive efficiency can be further improved by using vector control. This requires accurate velocity information sensed by a speed or position sensor attached to the rotor. However, an additional extra sensor, connector, and wire increase the cost of the motor drive.
