ST ST62 User Manual

APPLICATION NOTE

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 is only now beginning 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, using practical 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 2 THE RIGHT MOTOR FOR THE JOB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 CONVENTIONAL ELECTRIC MOTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 UNIVERSAL MOTOR CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 PHASE ANGLE CONTROL MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 CHOPPER CONTROL MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3 HARMONICS AND POWER DRAWN FROM THE MAINS . . . . . . . . . . . . . . . . . 9

4 INDUCTION MOTOR CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1 INDUCTION MOTOR SUPPLIED BY MONOPHASE AC . . . . . . . . . . . . . . . . . . 10 4.2 VARIABLE SPEED CONTROL FOR MONOPHASE INDUCTION MOTORS . . 11 5 ELECTRONIC MOTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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: LOWEST TOTAL SYSTEM COST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6 STMICROELECTRONICS APPLICATION NOTES . . . . . . . . . . . . . . . . . . . . . . . . . 18

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AN885 - ELECTRIC MOTORS IN DOMESTIC APPLIANCES

1 ELECTRIC MOTORS IN DOMESTIC APPLIANCES

In home 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 various items of domestic equipment in a typical American home(*). This illustrates the important role that electronics is bound to play in the control 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 being more 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

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AN885 - THE RIGHT MOTOR FOR 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) and Brushless 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	INDUCTION	AUTOCOMMUTATED
		Perm. Magnet or Var. Reluctance

FEATURES

±AC or DC supplied

±High torque at starting

±Washing machine (EU)

±Hand tools

±Food processor

±Vacuum cleaner

± AC supplied	± Electronic replaces brushes
± Robust	± High torque at starting
APPLICATIONS FIELDS
± Washing machine (WW)	± Washing machine
± Heating-Ventilation-Air	± H.V.A.C.
conditioning	± Pump / Fan

±Immersed pump / Compressor / Fan

±Dish washer / Tumble drier ± Food processor

± Freezer / Refrigerator	± 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. Due to 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 newer types when the cost of the necessary electronic control systems drops to sufficiently low levels.

±Induction (Brushless) Motors are mainly used 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 Synchronous 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 with the absence 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.

		Umot
ST6210 MCU	M	t

		Imot	Ι
	TRIAC		t
	strength	weakness
		High current ripple
	Directly on the mains
		Brushes Noise
	Cheap solution
		Sparkes, RFI pertubations
	Variable speed
		Low life time (3000hrs)

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