Home
Global Supplier Directory
APPLIANCE Engineer
Supplier Solutions
APPLIANCE Line
Whitepaper Library
Calendar of Events
Association Locator
Contents Pages
Market Research
Subscription Center


 
   
issue: December 2008 APPLIANCE Magazine

Appliance Engineer-Motor Technology
Powering Up for Less


 Printable format
 Email this Article
 Search

Ten new digital signal controllers (DSCs) give appliance engineers the ability to save power and have better performance at a reduced price.

New DSCs from Microchip help reduce overall system cost by reducing the external component requirements for power factor correction, fault detection, and analog signal conditioning.

Microchip Technology, Inc. (Chandler, AZ, U.S.; www.microchip.com) introduced 10 new 28- and 44-pin 16-bit DSCs for motor control designs requiring increased memory or performance, or enhanced peripherals, while obtaining cost and size savings associated with lower-pin-count devices. The devices are available in packages as small 6 × 6 mm, offer up to 128 KB of programmable Flash memory, and include on-chip, three-phase motor control pulse-width modulation (PWM), making them suitable for a wide range of appliance applications.

“If you take a snapshot today, most appliance engineers use the device with the smallest on-chip Flash memory possible for lowest cost,” Steve Marsh, strategic marketing manager, Digital Signal Controller Division, tells APPLIANCE. “Their need for memory will increase as they add additional functionality, such as power factor correction (PFC), driving multiple motors, sensor processing, or communication protocols.”

The new DSCs can operate the PFC algorithm and motor control algorithm on a single chip. “Many of our dsPIC DSCs have two additional PWM channels with an independent time base, which is important since the motor and PFC loops operate at different frequencies,” Marsh says. “Also, advanced algorithms are required to achieve increased efficiency—all against the backdrop of applications demanding faster response to changes in motor loading conditions.”

Two of the new motor control devices contain digital-to-analog convertors (DACs), which may be useful for motor noise reduction strategies or audio messages. A user-
selectable 10- or 12-bit analog-to-digital convertor (ADC) is available on chip. The 10-bit ADC mode features up to four “sample and holds” that can be triggered simultaneously, which can be useful for sensorless control strategies to gain improved loop performance from synchronized sampling strategies.

“One alternative [for appliance engineers] is to use a very fast ADC to get the time between samples to a minimum,” Marsh says. “However, this introduces an error in rotor position that degrades motor performance and efficiency. The second alternative is to employ a second ADC at additional cost. So, we put the sample and holds to improve performance and efficiency, and to lower system cost. Also, sensorless algorithms require the ADC to be in sync with the PWM, and many advanced algorithms require the sampling point to be modified on the fly. Additionally, the ADC can sample, capture, and store samples without CPU intervention, accommodating a broader range of algorithms and applications.”

With this combination of features, Marsh notes three key applications that could take advantage of the new DSCs:

• Washing Machines. According to Marsh, it is difficult to design motor control for front-load washing machines because they have significant load changes, often at a low motor speed. “This is caused by the action of wet laundry dropping with gravity during tub rotation,” he says. “Field-oriented control (FOC) on a permanent magnet synchronous motor (PMSM) is an
algorithm/motor combination that is well suited for this application. The DSCs can handle this algorithm with room left over for PFC and sensor processing for vibration monitoring, turbidity detection, or other advanced sensor functionality. Also, washing machines usually employ ‘sensorless’ rotor-position strategies—such as calculating the rotor position from the current sensed on noncommutated windings—which places more demand on the controller.”

• Air Conditioning. To meet efficiency demands, air-conditioner compressors are moving to variable-speed technologies. Marsh says this makes the compressor load complex over the speed range, which requires excellent torque control and resistance to stall. “Again, an advanced algorithm combination, such as FOC and PFC, is very desirable,” Marsh tells APPLIANCE. “These motors require sensorless control, since they are encapsulated in an oil-filled, sealed container. Sensorless control increases the demand on a controller, and simple controllers do not have the performance to pull off high-end sensorless FOC and PFC, whereas DSCs are more than capable.”

• Vacuum Cleaners. In vacuum design, Marsh says speed is key. “These applications require a fast ADC, fast internal comparators to detect zero crossing, and the fast ‘CPU plus DSP’ engine of a DSC to execute control loops,” he notes. “Some customers wish to run their motors at faster than their rated speed. Sensorless FOC of an ac induction motor using field weakening is a popular solution.”

Whatever the application, Marsh says the company’s application notes with free code make it easy for engineers to incorporate the controllers into appliance designs. “Since these are high-volume applications, and motors are customized for the application, we make the design stage where the algorithm is ‘tuned’ to the motor much faster with graphical tools,” he says. “Some manufacturers have their own approach to motor control. Motor control is one of the last bastions for assembly code, since the real-time requirements of the application discouraged high-level language utilization. Now that DSCs have more performance, C can be used for a larger portion of the motor-control algorithm. That makes transportation to a new controller easier. Some are just starting to consider C.”

ENGINEERING INNOVATIONS

Luran S BX 13042 was reportedly the first acrylonitrile-styrene-acrylate copolymer with antimicrobial properties. Silver compounds are incorporated into the plastic to impart its surface with a germicidal effect. Potential applications include hand dryers, soap dispensers, and public keyboards. The diagram shows the measured results after 24 hours in comparison with a plastic without an antimicrobial treatment. BASF, www.luran-s.com

 

Daily News

...........................................................

Apr 18, 2014: Spectrum Brands CEO Lumley Joins Husqvarna Board

Apr 17, 2014: GE Appliances 1Q Revenues Down 3%

Apr 17, 2014: Remodeling Growth Expected to Continue

Apr 17, 2014: HVAC/R Contractors Outlook Holds Steady

Apr 17, 2014: Appliance Store Sales Down Slightly in March

More Daily News>>

RSS Feeds
.........................................................
Appliance Industry
Market Research

...........................................................

March 2014: Market Research - 62nd Annual U.S. Appliance Industry Forecast
February 2014: Appliance Magazine Market Insight: December 2013
January 2014: Market Research - Appliance Historical Statistical Review: 1954-2012
January 2014: Appliance Magazine Market Insight: November 2013




 
Contact Us | About Us | Subscriptions | Advertising | Home
UBM Canon © 2014  

Please visit these other UBM Canon sites

UBM Canon Corporate | Design News | Test & Measurement World | Packaging Digest | EDN | Qmed | Pharmalive | Plastics Today | Powder Bulk Solids | Canon Trade Shows