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.”
integrated a digital signal controller from supplier
Instruments (Dallas, TX, U.S.) to help
create a quieter, energy-efficient, load-optimized
washing machine for its Ariston-branded Super
Silent product line.
Flexibility was something Texas
Instruments (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.”
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
“ 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.
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
digital signal controller chip provided by Texas
Instruments helps manage a three-phase a.c. motor
with Field Orientated Control (FOC). According
to the supplier, the chip allows motors to offer
higher efficiencies through algorithm-based speed
and torque control.
The success of the new controller and the benefits associated with
it did not come without a few challenges, however. According to Mr.
Frattesi, the main challenge the companies encountered while working
on the project dealt with the different torque speed behavior of the
three-phase motor compared to that of the typical universal motor. “The
motor’s acceleration performances and maximum torques were completely
different from the previous motor,” he tells APPLIANCE. “Adapting
this motor to the mechanical structure of our washing machine and to
the pre-existing wash cycles meant studying and implementing specific
algorithms.” The algorithms were based on an estimation of the
load inside the drum, controlled the speed profiles, and also limited
the mechanical stress and noise of the appliance.
Besides the motor performance, the control system was also different
than its predecessors. Because the mechanical structure of the washing
machine was changed, the control system had to be changed as well.
This included choosing which control parameters would suit the functions
in the most appropriate manner and also writing the computer software
needed to automate the task.
Also, because using FOC was new to Merloni, several adaptations and
modifications were made to tailor it to the functions of a washing
machine. The company says using the digital signal processor helped
to implement the necessary changes. “We had to think of different
methodologies to tune the control system and choose its parameters
for the different models of washing machines,” says Mr. Frattesi.
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.”