ST ST62 User Manual
APPLICATIONNOTE
ST62 MICROCONTROLLERS DRIVE HOME APPLIANCE
MOTOR TECHNOLOGY
By Bruno MAURICE
INTRODUCTION
Most domestic appliances are driven by an electric motor; for the most part, these motors are
controlled in a simple and rudimentary fashion, and electronics isonly nowbeginning to be applied.This article describes the three main motor families – Universal, Induction and Electronically Commutated – as well as the relevant electronic control techniques, now possible
thanks to the intrinsic characteristics of STMicroelectronics ST62 Family of microcontrollers.
ST62 MCUs, with their wide range of on-chip peripherals, their wide supply voltage range,
their built-in ruggedness and their legendary noise immunity allow truly low total system cost,
thus favouring the technological advancement of electrical motor design.
Basic electrical topologies are described, together with their associated power and signal
electronics. The relative strengths and weaknesses are explored, usingpractical examples, in
order to illustrate the advantages of electronic control using ST62 MCUs.
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Table of Contents
INTRODUCTION . . . . . . . . . . . . . . . . . ......................................1
1 ELECTRIC MOTORS IN DOMESTIC APPLIANCES . . ........................3
2THERIGHTMOTORFORTHEJOB ......................................4
2.1 CONVENTIONAL ELECTRIC MOTORS . ..............................4
3UNIVERSALMOTORCONTROL .........................................6
3.1 PHASE ANGLE CONTROL MODE . . .................................6
3.2 CHOPPERCONTROLMODE .......................................8
3.3 HARMONICS AND POWER DRAWN FROM THE MAINS . . . . . . . . . . . . . . . . . 9
4INDUCTIONMOTORCONTROL ........................................10
4.1 INDUCTION MOTOR SUPPLIED BY MONOPHASE AC . .................10
4.2 VARIABLE SPEED CONTROL FOR MONOPHASE INDUCTION MOTORS . . 11
5ELECTRONICMOTORS ..............................................12
5.1 PERMANENT MAGNET SYNCHRONOUS MOTOR (PMDC) . . . . . . . . . . . . . . 13
5.2 SWITCHED RELUCTANCE MOTOR(SRM) . ..........................14
5.3 SIMPLIFIED TOPOLOGY FOR SWITCHED RELUCTANCE MOTORS . . ....15
5.4 ST6260 OFFERS THE SIMPLEST SRM DRIVER . . . . . . . . . . . . . . .........17
5.5 ST62:LOWESTTOTALSYSTEMCOST..............................17
6 STMICROELECTRONICS APPLICATION NOTES . . .......................18
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AN885 - ELECTRIC MOTORS IN DOMESTIC APPLIANCES
1 ELECTRIC MOTORS IN DOMESTIC APPLIANCES
In hom e appliances and light household equipment, electronics is commonly found in the
man-machine interface (dashboards, control panels, remote controls, etc...), as well as in the
management of complex operating sequences, such as in washing machines; however, it is
only just beginning to be used to control the electric motors which power them.
Energy saving,silence, flexibility and simplicity are requirements of growing importance: in applications such as drills, vacuum-cleaners and refrigerators, variable speed control is the principal means of obtaining such performance features.
Up to 46 motors are to be found in the variousitems of domestic equipment in a typical American home
of home appliance motors.
Electronics will initially become more common in the control of conventional electric motors,
and will subsequently lead to the popularisation of brushless electronic motors, which offer the
advantages of beingmore rugged and of requiring lower cost mechanical parts. These motors
naturally require more complex electronic control systems, which will become increasingly viable as the cost of electronic systems falls, thanks to the use of STMicroelectronics ST62
Family of MCUs and low-cost integrated power ICs.
(*)
Emerson in Appliance Manufacturer August ’94
(*)
. This illustrates the important role that electronics is bound to play in the control
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AN885 - THE RIGHT MOTORFOR THE JOB
2 THE RIGHT MOTOR FOR THE JOB
2.1 CONVENTIONAL ELECTRIC MOTORS
Three main families of electric motors are commonly used in home appliances. Their power
can range from 50W to 1.5 kW. The first two families, Brush Motors (i.e. Universal Motors)
andBrushless Motors (i.e. Induction Motors) are the most popular and these cheap and well
known motor designs may be connected directly to the AC mains.
Figure 1. Features and typical applications of the three main types of electric
applicance motors
BRUSHLESS ELECTRONIC
WITH BRUSHES
BRUSHLESS
COMMUTATION
UNIVERSAL
– AC or DC supplied
– High torque at starting
– Washing machine (EU)
– Hand tools
– AC supplied
– Robust
– Washing machine (WW)
– Heating-Ventilation-Air
conditioning
INDUCTION
FEATURES
APPLICATIONS FIELDS
AUTOCOMMUTATED
Perm. Magnet or Var. Reluctance
– Electronic replaces brushes
– High torque at starting
– Washing machine
– H.V.A.C.
– Pump / Fan
– Immersed pump / Com-
pressor / Fan
– Food processor
– Vacuum cleaner
– Dish washer / Tumble drier
– Freezer / Refrigerator
– Food processor
– Vacuum cleaner
– Freezer / Refrigerator
– Universal (Brush) Motors are used in applications where high torque and/or variable speed
are required (e.g. drills, food-processors, hand-tools, vacuum cleaners, etc.). They can be
powered either by an AC or DC supply, and are currently the most popular motors in appliances. Dueto their poor efficiency and relatively limited life, universal motors are tending to
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AN885 - THE RIGHT MOTOR FOR THE JOB
be replaced by newertypes when the cost of the necessary electronic controlsystems drops
to sufficiently low levels.
– Induction (Brushless) Motors are mainlyused in applications requiring silent operation, long
life and high safety levels (i.e. pumps, compressors, refrigerators, fans, etc.). These motors
are AC supplied and rotational speed does not vary easily, since it is synchronised with the
electrical mains frequency.
In the third family, electronic acts as an electronic commutator and takes the place of brushes.
– These Electronically Commutated Brushless Motors include Permanent Magnet Syn-
chronous Motors and Switched Reluctance Motors. Both types are controlled by electronically switching the current in the windings. Electronically Commutated Brushless Motors
combine the high torque and variable speed performance of the universal motor withtheabsence of brushes and the intrinsic ruggedness of the induction motor.
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AN885 - UNIVERSAL MOTOR CONTROL
3 UNIVERSAL MOTOR CONTROL
3.1 PHASE ANGLE CONTROL MODE
Universal motor speed may be simply and economically varied by phase angle control using
a TRIAC: this is therefore a very popular solution [1]. The motor current is directly drawn from
the mains and, because of its large peak to peak value, power losses in the iron are high.
When the TRIAC conduction angle is less than full wave, the current drawn from the mains
contains low frequency harmonic components with high amplitudes which can easily exceed
the authorised IEC levels.
Figure 2. Universal brush motor driven by phase-angle triggered TRIAC switched AC
supply.
ST6210 MCU
strength
Directly on the mains
Cheap solution
Variable speed
TRIAC
M
Umot
Imot
weakness
High current ripple
Brushes Noise
Sparkes, RFI pertubations
Low life time (3000hrs)
t
∆
Ι
t
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