4996031888215ECN-5-00| Application Note
www.ecnmag.com ECN May 2000
Technological
DSP Motor Control In Domestic Appliance Applications
DSP-based motor control systems offer the control bandwidth required to make possible the development of advanced motor drive systems for domestic appliance applications .
by Dr. Aengus Murray, Analog Devices, Inc.
E
lectric motors are the major components in electric appliances such as refrigerators, washing machines. The energy consumed by the electric motor is a very significant portion of the total energy consumed by the machine. Controlling the speed of the appliance motor can both directly and indirectly reduce the total energy consumption of the appliance. In many major appliances advanced three phase variable speed drive systems provide the performance improvements needed to meet new energy consumption targets. DSP based motor control systems offer the control bandwidth required to make possible the development of advanced motor drive systems for domestic appliance applications.
DSP Motor Control In Domestic Refrigeration Applications
System Requirements: Energy efficient compressors require the motor speed to be controlled in the range from 1200 rpm to 4000 rpm. In fractional horsepower applica-
tions, the motor of choice with the highest efficiency is an electronically controlled three phase permanent magnet motor. Motor Control Strategy: In order to run the permanent magnet motor efficiently, it is important to synchronize the frequency of the applied voltage to the position of the permanent magnet rotor. A very effective control scheme is to run the motor in a six-step commutation mode with only two windings active at any one time. In this case, the back emf on the unconnected winding is a direct indication of the rotor position. The rotor position is estimated by matching a set of back emf waveform samples to the correct segment of the stored waveform profile. This technique averages the data from a large number of samples giving a high degree of noise immunity. The control system, outlined below, has an inner position control loop which adjusts the angles of the applied stator field to keep the rotor in synchronization. Integrator input tracks the motor velocity when the rotor position error is
forced to zero. The outer velocity loop adjusts the applied
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