During the tumble-wash
phase, the motor works at low speed and high torque, and although
power consumption during the tumble-wash phase is comparatively
low, this phase lasts much longer than the spin-dry phase.
Therefore, driving the motor correctly during the tumble-wash
phase is mandatory in order to reduce total power consumption.
Also, balancing the load before fast spinning is very important
because it reduces power consumption during acceleration.
And finally, in order to achieve a rapid, power-saving spin-dry
phase, maximum drum speed is essential as well.
issue: June 2003 APPLIANCE Magazine
Engineering Washer Drives
Three-Phase A.C. Motor Drive and Controller for Clothes Washers
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by Andrea Bianchi and Mr. Luciano Buti, MagneTek S.p.A.
Because a complete washing cycle for domestic clothes washers consists of two phases - tumble-wash and spin-dry - it calls for very different motor characteristics.
This paper describes
a clothes washer controller with integrated DSP-based, three-phase
a.c. motor drive. The results and estimates included herein
are based on a front-loading 230-V a.c. clothes washer, but
they are equally indicative for top- and front-loading 115-V
a.c. clothes washers.
The paper will
describe how, when compared with single-phase 50/60-Hz a.c.
induction motors or universal (brush-type) motors, using this
controller to drive a three-phase a.c. motor results in improved
washer efficiency, less water consumption, less acoustic noise
and electromagnetic interference (EMI), and enhanced reliability.
typical front-loading clothes washerÕs duty cycle is
shown in Figure 1. Generally, there are two sequential phases:
tumble-wash and spin-dry.
1. Two-Speed Washing Cycle
The tumble-wash phase
is typically three to four times as long as the spin-dry phase.
During the tumble-wash phase, the drum turns slowly, typically
at 40 rpm, first clockwise (CW), then stops, then counter clockwise
(CCW), then stops, and so on. Turning time can last 20 to 120
sec, depending on the load (delicate, light, heavy, etc.) and
the washer manufacturerÕs specifications. The drum turns
one way or the other 50 to 90 percent of the time, again, depending
on the load and the washer manufacturer. An example of a 90-percent
turn time in a 100-sec interval is shown in Figure 2. This example
is given to illustrate the complexity of washing machine protocol.
2. Example of Tumble-Wash Period.
During the spin-dry
phase, the washer drum turns at high speed, typically 400
to 600 rpm, for brief intervals. Between these high-speed
intervals, the drum turns at low speed for longer intervals.
In the example shown in Figure 1, the drum turns for 1 min
at 400 rpm, then turns at low speed for 4 to 5 min. Then there
is the second 400-rpm spin (2-min long) followed by another
low-speed spin for 4 to 5 minutes. Finally, there is a high-speed
spin 3 to 4 min long.
When a variable
speed motor is used, the whole washing cycle can become more
sophisticated, enabling better washing performance and improving
energy efficiency. An example of such a washing cycle is shown
in Figure 3.
The tumble-wash phase in Figure 3 can have different speeds
(two or more), and the drum can turn at slower speeds than
the typical 40 rpm. The spin-dry phase has three different
speeds, and all of them are higher than the spin-dry phase
of two-speed washers.
3. Improved Washing Cycle
As noted above,
there are two approaches widely used by washing machine manufacturers
to provide the performance requested by consumers. The first
and older method uses a two-speed a.c. motor driven by an
electro-mechanical commutator on a relay board. The second
approach uses an a.c. universal motor (brush-type) electronically
controlled with a triac.
In the European
washing machine market, only 10 to 20 percent still use two-speed,
single-phase a.c. motors. These motors are cheaper than universal
motors, so they are sold primarily to the low-price market
segment. However, the market in general now demands improved
washer performance. Typically, the motor is a single-phase
permanent split capacitor (PSC) type that can run in both
directions in low-speed operation, which can be easily controlled
by electro-mechanical commutators or relays. During the tumble-wash
phase, when the drum reverses direction (CW, OFF, CCW, OFF,
and so on), the motor accelerates to running without any ramp-up.
This means that, even if you are using a high-efficiency PSC
motor, the total tumble-wash phase efficiency cannot be high.
also is reached without any ramp-up. This results in high
power consumption during acceleration and, since there is
no load-balancing, spinning consumes a great deal of energy
due to unbalanced loads, and maximum spin speed cannot be
In the European
market, 80 to 90 percent of all washing machines use universal
motors with controlled circuit boards containing triacs. These
boards are microprocessor-based and usually control the whole
washing cycle. The electro-mechanical commutator is gradually
disappearing from the market.
Universal motor speed can be controlled easily with a triac
using feedback from a speed sensor, so the motor turns the
drum at variable speeds, enabling improved tumble-wash performance.
And higher spin speeds are possible due to load-balancing
are more complicated and expensive than two-speed a.c. motors,
but their variable-speed capability has made them successful
in the European market. The biggest drawbacks of universal
motors are their limited speed range, low top-speed, acoustic
noise, and the brush wear. In order to improve motor performance,
d.c. ÒchopperÓ motor drives are sometimes used
Some washing machines
also use three-phase a.c. motors, but these motors are used
only in very expensive models, and due to their high cost,
their market share is low. Three-phase motors themselves are
more simple and less expensive than two-speed, single-phase
a.c. motors, or universal motors.
The motor drive is more complicated, sophisticated, and expensive
with respect to the others. This technology allows for good
performance in terms of motor efficiency, maximum speed, and
With respect to
a three-phase motor washing machine, the motor efficiency
during the washing phase could be further improved by using
DSP-based, field-oriented control algorithms.
Most washing machines
available on the European market have electronic controllers
inside. They work like electro-mechanical commutators, controlling
the water-heating resistor relay, the water pump relay, and
several valve triacs, while on-board microprocessors improve
washing performance based on sensor feedback.
The proposed washing
machine controller accomplishes that and more. A dedicated
microprocessor controls all washer functions, user interface
displays, and actuators. A motor drive DSP carries out real-time
calculations in order to maximize motor efficiency. Since
the microprocessor controls the entire washing cycle, it works
as a master in the serial link, and the DSP runs the motor
according to the microprocessorÕs requirements.
Figure 4 is a
block diagram of the integrated board control logic. The hardware
arrangement is shown in Figure 5.
4. Integrated Washing Machine Control Logic
5. Integrated Washing Machine Hardware Arrangement
Looking at Figure
5, there are two EMI issues to addressÑhigh-frequency
electromagnetic conducted noise and low-frequency input current
harmonics. In compliance with European standards, a small
EMI filter is used on the washerÕs a.c. input bus, and
a choke is used to remove input current harmonics. The input
choke also is useful in reducing ripple current in the inverter
As shown in Figure
6, the inverter d.c. bus is obtained by rectifying a.c. input
power with a diode bridge and an electrolytic bulk capacitor.
The three motor output voltages are generated using six electronic
In order to apply
field-oriented control (FOC), the motor currents must be known.
Three shunts are used because this method yields the best
performance in the fast spin-dry phase. The six electronic
switches are controlled by means of space vector pulse-width
in excess of 95 percent is attained in the spin-dry phase
because the motor is applying high power to the load. Efficiency
declines at low drum speeds because the motor is applying
less voltage and more current to the load, and inverter losses
are determined by motor current.
6. Motor Drive Circuit Topology
The motor drive
power supply also powers the microprocessor, DSP, insulated
sensors, and user interfaces, so it must be a multi-output
switch mode power supply (SMPS) providing three different
sets of outputs for the following components:
- Motor drive.
Since the microprocessor drives triacs and relays, it calls
for both 5 V and 12 V d.c. Since the triacs have to be driven
with a negative gate signal, the microprocessor positive
supply input is connected to the line and the microprocessor
negative input is connected to the -5 V. The relays are
connected between -5 V and +7 V.
and DSP. The DSP requires 3.3 V, and the three-phase inverter
requires 15 V. Both return paths are connected to the negative
d.c. link (or ÐDC link, as shown in Figure 6).
- Sensors and
user interfaces. The insulated sensors and the user interfaces
require a 5 V SELV supply voltage (8-mm clearance).
and Relays Section
uses the relays and triacs to control the water pump, valves,
and heating resistors. The relays switch the larger loads
(heating resistors, pump), and the triacs control the valves,
fans, and other smaller loads.
In the European
market, washer performance parameters must be stated on the
appliance label based on a standard 60¡C washing cycle.
Test results are indicated with letters from A to G (A = best).
The main parameters are energy consumption, washing performance,
and spinning efficiency. In addition, the appliance producer
must indicate the acoustic noise level in decibels.
The energy consumption parameter is a measurement of kWh during
the standard 60-degree tumble-wash phase related to water
heating and motor operation. The energy required for drying
the clothes is not included in this measurement.
is the more important parameter. By improving washing characteristics,
it is possible to save both water and energy. In order to
optimize washing performance, it is also important for the
motor to operate efficiently below 40-rpm drum speed (15 to
is the measurement of the water content still in the clothes
after the spin-dry phase. The faster the drum speed, the less
water is left in the clothes. The better the spin-dry phase,
the more energy is saved in the dryer.
Since so much
energy is consumed by the heating resistors, using a more
efficient motor by itself does not solve the overall efficiency
problem. However, by using an efficient motor and controlling
its operation correctly, we are able to attain excellent washing
performance at low water temperatures. In order to do this,
the motor must be able to work efficiently across a broad
range of speeds. The maximum-minimum speed ratio may be greater
Table 1 shows
a cost/performance matrix comparison between different motors.
There are two rows regarding the three-phase motor because
of two different control methods. As previously mentioned,
the field-oriented control method improves the energy efficiency
of the motor because the inverter feed always has the optimum
voltage. Since the minimum speed is reduced, the washing performance
is improved as well. Moreover, thanks to the tight torque
control, efficient ramp is possible and, therefore, the highest
drum speed can be achieved.
1. Cost/Performance Matrix Comparison
This paper has
described a cost-effective integrated washing machine controller.
By correctly driving a three-phase a.c. motor, it is possible
to improve washing performance and reduce water and energy
consumption. Acoustic noise is reduced as well.
gain is reached when the washer drum turns slowly during the
tumble-wash phase, meaning that the motor controller algorithm
enables the motor to run efficiently even well below the nominal
As noted, although
the spin-dry phase has no great impact on the total energy
consumption, very high drum speed during spin-dry is mandatory
in order to minimize the dryer power consumption. It is important
to control in-rush current during drum acceleration as well.
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Vector control and Dynamics of AC Drives. Oxford science publication,
2. P. Vas. Sensorless Vector and Direct Torque Control. Oxford
science publication, 1998.
3. Aengus Murray, AE. Dash DSP Simplifies Washing Machine
4. Frattesi, R. Petrella, M. Tursini. An Efficient Induction
Motor Vector Controller for Washing Machine Applications.
Energy Efficiency in Household Appliances and Lighting. Naples,
is an edited version of a paper presented at the 2003 International
Appliance Technical Conference, held March 10-12.