Sensorless Motor Control Simplifies Washer Drives

by Aengus Murray, Director iMOTION Products, Energy Savings Product Group, International Rectifier, El Segundo, Calif., Power Electronics Technology, Jun 01 2006

Focus:
In washing machine applications, direct-drive permanent-magnet (PM) motors offer higher performance than three-phase induction motors. However, the use of the PM motors is complicated by their need to measure the rotor position to synchronize the stator current with the rotor field. Hall-effect sensors may be used to measure rotor position, but they pose reliability concerns. One approach to eliminating Hall-effect sensors uses the stator winding's back EMF to determine rotor position. However, this approach poses problems in washing machine applications because it can produce high levels of acoustic noise and because it prohibits high-speed field weakening, which is necessary for high-speed spinning. A sensorless, field-oriented control (FOC) algorithm described here overcomes these limitations. This method determines rotor-flux position indirectly by measuring motor-winding-currents. Operation of the sensorless FOC algorithm is explained, a hardware implementation is described, and implementation issues are discussed.

What you’ll learn:

• How to implement sensorless control of direct-drive PM motors in washing machines
• How to overcome limitations of back-EMF sensing when implementing sensorless control of direct-drive PM motors

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