永磁同步电机无位置传感器

Performance Comparison of Permanent Magnet Synchronous Motors and Controlled Induction Motors in Washing Machine Applications using Sensorless Field Oriented Control

Aengus Murray, Marco Palma and Ali Husain

Energy Saving Products Division

International Rectifier

El Segundo, CA 90245

Abstract—This paper describes two alternative variable speed motor drive systems for washing machine applications. Three phase induction motors with tachometer feedback and direct drive permanent magnet synchronous motors with hall sensor feedback are two drive systems commonly used in North American washers today. Appliance manufacturers are now evaluating sensorless drive systems because of the low reliability and high cost of the speed and position feedback sensors. A Field Oriented Control Algorithm with an embedded rotor flux and position estimation algorithm enables sensorless control of both permanent magnet synchronous motors and induction motors. The estimator derives rotor shaft position and speed from rotor flux estimates obtained from measured stator currents and the applied voltages. Sampling of currents in the dc link shunt simplifies stator current measurement and minimizes cost. Field oriented control algorithm allows good dynamic control of torque and enables an extended speed range through field weakening. The digital control algorithm runs on a unique hardware engine that allows algorithms to be designed using graphical tools. A common hardware platform can run either the PMSM or IM using sensorless field oriented control in a front loading washer application. Test results are presented for both drives in standard wash cycles.

Keywords-component; Advanced Control; Field Oriented Control Algorithm;, Appliance control architecture;

I.I NTRODUCTION

Accurate control of drum speed is required in both horizontal and vertical axis washer machines [1]. In front loading horizontal axis washers, the drum speed determines the washing action. There is a critical drum RPM, depending on the drum radius, above which the clothes stick to the inside edge of the drum. At this speed, the centrifugal force due to rotation balances the weight of the wet clothes. At speeds below this, the clothes will stick to the side of the drum until the component of the weight acting along the radius is greater than the centrifugal force. Once this angle is reached, the clothes fall back down into the base of the drum. The speed of the drum determines how vigorously the clothes are washed and allows a gentle wash cycle to be selected for delicate items. In the spin mode, the water is drained and the drum speed is increased well beyond the critical speed and the water forced out of the cloths by the centrifugal force. In traditional top loading vertical axis machines, the agitation action is produced mechanically using a gearbox and clutch. However, the introduction of speed control systems not only simplifies the mechanical system but also allows for wash cycle control. The control of the speed and angle of stroke allows the system designer to better manage the washing action and so develop wash cycles that use less water.

European front-loading washers have used variable speed control for many years and typically use a universal ‘brush type’ motor. However, the American washer uses a larger drum size, which requires a motor with a power range beyond that of the universal motor solution. The front-loading drive solutions on the market today include direct drive permanent magnet synchronous motor drives or a belt drive using an induction motor. Appliance manufacturers are now evaluating these two drive types in top-loading machine to reduce cost and improve performance. However, both these drive systems use shaft feedbacks sensors. The direct drive PMSM typically uses a Hall Effect sensor for position feedback while the induction motor drive typically uses an analog or digital tachometer for speed feedback. The ideal universal drive can run either a PMSM or an induction motor without shaft feedback sensors. However, a single hardware platform can efficiently run either a PMSM or an induction motor using sensorless field oriented control algorithm. In both cases, speed and position estimates derive from motor terminal voltages and currents.

Induction motors were initially preferred for washing machine drives because of the ease of running in high speed field weakening mode even with simple scalar control methods. However, the PMSM is now becoming a viable solution because field oriented control approach enables high speed field weakening. In an induction motor, the torque producing current flows in both the rotor and stator windings while the air gap field generation needs additional field current. Therefore, in washing mode, the total copper losses are more than double