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issue: January 2005 APPLIANCE European Edition

Motors and Air-Moving Devices
Controlling Product Performance

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by Jill Russell, Associate Editor

When Italian appliance maker Merloni Elettrodomestici asked for a motor control that could make its products smart and advanced, supplier Texas Instruments (TI) answered.

Merloni integrated a digital signal controller from supplier Texas Instruments (Dallas, TX, U.S.) to help create a quieter, energy-efficient, load-optimized washing machine for its Ariston-branded Super Silent product line.

Utilizing TI’s TMS320LF2401A™ digital signal controller, Merloni was able to optimize its washing machines for the Ariston Super Silent product line by making the appliances quieter and more energy-efficient. “The technological content in Merloni’s appliances is very intensive and is continuously growing,” Stefano Frattesi of Merloni says. “The flexibility offered by our development systems was unexpected only a few years ago.”

Flexibility was something TI and Merloni had in mind when designing the controller and its functions. The two companies worked together to ensure the end result provided both Merloni and its consumers with a near silent, efficient washer machine. The OEM originally chose the supplier because it offered a controller that performed successfully and allowed options that Merloni could tailor to its likings.

In order to meet Merloni’s needs, TI formed a team of experts focused on the motor control and its appliance application. The supplier says doing so helped it develop the motor control solution while offering Merloni technical support and constant communication. “By developing [like this], we can maximize the benefit of using our technology,” says Jean-Claude Soroka, C2000 business development manager for TI’s European DSP Group. “It allows us to better understand our customers’ needs.”

Untraditional Technology

Unlike traditional washing machine motors, Merloni’s motor utilizes the supplier’s controller to provide a three-phase a.c. motor with field orientated control (FOC). This, according to TI, allows the implementation of smaller motors to run algorithm-based speed and torque control. According to TI, the use of the algorithms are what help the washing machine operate with both less noise and cost. “Benefits are not limited to better performance, but to also allow for optimization of the system design, driving to a system cost reduction,” Mr. Soroka tells APPLIANCE.

The digital signal control features a single-cycle multiplier, seven pulse width modulation (PWM) variable frequency, and dead-time ports. In addition, it also contains five ultra-rapid 10-bit analog to digital converters (ADCs), an impulse capture circuit with a 16-bit timer, and asynchronous serial communication. Integrated flash memory allows re-programmability during the development phase, contributing it to its low cost.

Both companies say the controller is the main contributor to the noise and energy benefits of the newly equipped washing machine. “Typical washing machine designs employ a universal motor and require only simple control algorithms and hardware that are noisier, bulkier, and characterized by poor dynamic performance,” Mr. Soroka explains. “Three-phase motors controlled by FOC, on the other hand, are smaller, run more quietly, and offer higher efficiency through algorithm-based speed and torque control based on the machine’s load.”

The supplier says that FOC treats the entire magnetic field of an a.c. induction motor as a single torque vector, which helps to maintain maximum rotor drive and eliminate torque ripple effects. “By using [the controller], the entire dynamic control algorithm cycle with feedback can be performed in less than 50 msec,” explains Mr. Soroka.

Flooding Out Noise

“During washing, the only noise that can be heard is the sound of water,” says Mr. Frattesi. According to Merloni, the newly controlled motor is combined with a suspension system and is “intrinsically more silent than the universal motor.” Mr. Frattesi attributes this to the absence of brushes in the motor and the sinusoidal driving method.

“High-performance, DSP-based controllers can perform the rotor positioning and speed calculations in real time without lookup tables,” adds Mr. Soroka of TI. “External sensors can be eliminated since the controllers can calculate the vectors from voltage and current feedback read by internal line sensors.” He says that the controller and microcontroller, enabled with FOC,
ripples and minimizes generated noise. This, combined with Merloni’s suspension system with sound-resistant materials is said to reduce the appliance’s noise level to only 10 dB.

Ensuring Efficiencies

Once installed, the motor reportedly improves both energy and washing efficiency of the appliance. Mr. Frattesi explains: “The power loss is lower, and the control algorithms enable the driving of the motor in the best efficiency point, varying the magnetic flux level as a function of the washing machine load.” Washing efficiency, according to Merloni, is also improved due to the dynamic responses of the motor drive, lower power loss, and consequently, lower operating temperature of the motor. “This,” says Mr. Frattesi, “allowed our experts to study washing cycles that remove stains in a far shorter time and in a better way.”

In addition, the motor is now said to be more energy efficient. This, according to Merloni, is due to the power loss of the motor, which is lower than other motors typically found in other washer machines. Besides this, the control algorithms are said to enable the driving of the motor at the best efficiency point at all times, varying the magnetic flux level as a function of the washing machine load.

“The digital signal controller is enabling drive manufacturers to design their drives with FOC, overcoming the traditional implementation challenges,” says Mr. Soroka. “This enables designers to implement the reference frame translations and the control implementations at higher sample rates, which results in very high current loop bandwidths and helps meet challenges like fast servo response time and precise control transients.”

As the motor control helped the appliance maker meet all of its product goals, Merloni plans to implement the technology on new washing machines within its Super Silent product line. “The technological content in Merloni’s appliances is very intensive and is continuously growing,” Mr. Frattesi says. “We will surely work together [with TI] in the future for further improvements in the performances of the Super Silent washing machines, and we will try to export this technology to other products, where power electronics and computational effort will make a big step toward performance.”

January 2005 APPLIANCE European Edition
Motors and Air-Moving Devices

Suppliers mentioned in this article:
Texas Instruments

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