Appliance Design - January 2008 - (Page 34)

MOTORS New Basis for Brushless Fig. 5. 1-Watt motor (top) with SingleSense PCB (right) and conventional PCB (left). Alternate technology changes cost/performance calculation. or a couple of decades, appliance makers have been trying to justify the added cost of brushless DC (BLDC) motor replacements for brush and AC motors. In general, only high cost/highreliability applications have been able to justify the change based on reliability and performance factors such as speed control, torque ripple, jitter, and EMI. Quadrant Systems Inc. (QSI) has taken a systems development approach to improving BLDC motor technology that has resulted in improved BLDC motors of all sizes from a few watts to hundreds of watts. The two following examples illustrate improvements in size, cost, and performance. F Commutation Existing commutation techniques utilize three Hall elements, three Hall ICs, or sensorless commutation. Sensorless systems eliminate the three required Halls sensors, saving a component cost of 10 cents to 45 cents, the mechanical placement of sensors, and a bundle of wires. Sensorless commutation systems require a much more complex chip, more discrete parts, and cannot generally start with a heavy load. However, by brad marshall and christian c. petersen Brad Marshall is president of USM-III, Bandera, Texas; and Christian C. Petersen is vice president engineering and development, Quadrant Systems, Inc., Bourne, Mass. 34 applianceDESIGN January 2008 sensorless technology is standard in HDD and other disk drive systems where space is at a premium, starting load is minimal, and speed/ jitter control is critical. In order to commutate a conventional 3-phase motor, three sensors are used. This requires three Hall sensors embedded in the motor with five to 12 wires and decoding logic. The Quadrant Systems, SingleSense® (1) method facilitates 3-phase commutation with no discrete Hall sensor. One sensor is combined with the control chip, so there is not a sensor component. In the SingleSense motor, the rotor is modified to contain magnetic signals, which allow one Hall sensor to control 3-phase commutation, utilizing simple logic. (6) A schematic drawing of one embodiment of the rotor magnet is shown in Fig. 1, where the A, B, and C black lines represent the stator poles. The radial magnetization provides the main rotor magnet poles. The small, axial magnetization implants and the radial magnet edge magnetization pattern provides the commutation signal. www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - January 2008 Contents Editorial Shipments/Forecasts News Watch Makers of Commercial Refrigeration Equipment Turn to Variable-Speed Motors to Improve Energy Efficiency. New Motor Design and Control Scheme Makes Brushless Motors More Economically Feasible for a Wider Range of Applications. External Gas Molding, a Relatively New Technique, Solves Many of the Challenges Associated with the Injection Molding of Large Plastic Parts. Plastic Housings Offer Many Benefits: EMI Protection Isn't One of Them. But, New Materials and Techniques are Solving that Problem. Choosing the Optimal Strategy for Effective EMI Shielding Depends on Both Mechanical and Electrical Requirements Ethernet-Enabled Microcontroller Makes Networking Schemes Easier and More Cost Effective to Implement The Ever-Changing Array of Microcontroller Memory Options Makes it Imperative to Keep Abreast of What's Available to Determine the Optimal Choice for an Application. A Vast Range of Components and Finished Products will be Exhibited at the Country's Preeminent HVAC/R Show, AHR Expo, which is Scheduled for Jan. 22-24 in New York. Advertiser's Index Association Report: PRBA

Appliance Design - January 2008

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