Appliance Design - April 2008 - (Page 44)

MOTORS Fig. 4. Ideal trapezoidal commutation. Fig. 5. Sinusoidal commutation. of thermal loads in both the inverter and commutation is that sinusoidal commutathe motor. Trapezoidal commutation is tion delivers absolutely smooth torque at any rotational angle or speed. Torque disdepicted in Fig. 4. In contrast, for a sinusoidally commutat- turbances due to commutation, combined ed PMAC motor, each of the three phases with magnetostriction in the stator generof the inverter is modulating (PWM) all the ate acoustical commutation noise in BLDC time, driving three out-of-phase sinusoi- motors. This effect is absent in sinusoidally dal currents into each winding. Sinusoidal commutated PMAC motors, making them commutation is depicted in Fig. 5. From an virtually silent (except for possible PWM AD05062Therm 4/7/06 2:11 PM Page 1 application standpoint, the biggest differ- noise). Quiet operation is often a very ence between trapezoidal and sinusoidal important consideration for appliances. Controlling synchronous motors Based on the previous paragraph, it may seem that sinusoidal commutation would always be the preferred choice because of the smooth torque and lack of commutation noise. However, there is an additional control burden to consider as well. Simply put, trapezoidal control is simpler to implement than sinusoidal control. This added complexity must be considered in the deci- For more Information Enter 114 44 applianceDESIGN April 2008 AD04081Exmek.indd 1 For more Information Enter 115 www.applianceDESIGN.com 3/10/08 10:17:35 AM http://www.exmek.com http://www.thermtrol.com http://www.thermtrol.com http://www.exmek.com http://www.appliancedesign.com

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Appliance Design - April 2008 Contents Editorial Shipments/Forecasts News Watch A Variant of Thermoacoustic Refrigeration Known as Acoustic-Stirling is Expanding Its Range Outside Cryocooling Into More Conventional Applications Such As Refrigeration and Air Conditioning Free-Piston, Stirling Coolers Are Now Showing Up in Mainstream Applications As Costs Come Down and Heat Transport Solutions Are Devised Heat Exchanger Innovations Are Helping To Improve the Overall Efficiency of Vapor Compression Systems Environmental Concerns Have Once Again Ignited a Debate Over Refrigerants A New Glass Ceramic Material for Induction Cooktops Can Be Decorated In a Variety of Glimmering Metallic, 3-D Looks That Can Employ a Number of Shades, Patterns, Styles, Colors, Intensities, and Textures Colorful, Reflective Coatings for Glass Create a Variety of Design Options To Help Designers Establish a Unique Look for Their Products Appliance Designers Faced With Different Motor and Drive Options Need To Understand the Differences and Tradeoffs Before Choosing A New MEMS Valve Offers a Number of Advantages Over Solenoids In Certain Applications, Including the Opportunity To Cut Energy Use The AHR Expo Set Attendance Records and Showcased Thousands of Innovative New Products Classifieds Design Marts Advertiser’s Index Association Report: CEA

Appliance Design - April 2008

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