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WORKBOOK SILICA | The Engineers of Distribution.
www.silica.com
Linecard
Table of Content 1. Abstract
4
2. System Level Problem
8
2.1
Motor Topologies and Drives
9
2.1.1
PMDC – Permanent Magnet DC Motor
10
2.1.2
DC Motor Driver
12
2.1.3
Asynchronous Motor
12
2.1.4
Synchronous Motor
13
2.1.5
BLDC – Brushless DC
14
2.1.6
SRM – Switched Reluctance Motor
15
2.1.7
Bi-Polar Stepper Motor
15
2.1.8
AC Motor Driver
18
2.2
Motor Selection Criteria
19
2.3
Applications Summary and Overview
20
3. Solutions
21
3.1
Analog Devices
21
3.2
Freescale Semiconductor
23
3.3
International Rectifier
48
3.4
Infineon Technologies
70
3.5
Maxim
80
3.6
Microchip Technology
84
3.7
ON Semiconductor
98
3.8
Renesas Technology
100
3.9
STMicroelectronics
110
3.10
Texas Instruments
118
4. Glossary
144
3
The Engineers of Distribution.
1. Abstract Going back in time over 30 or 40 years, brush
theory that was developed long before anyone knew
motors were the typical motor use. Most of the
how to build a control around it. Consequently,
control electronics were analog components, SCR
electrical drives are currently used in a variety of
rectifiers for the power stage, control amplifiers
applications, as it had been pointed out in the 2005
were often built with discrete components and
IMS report The WW Market for AC & DC Motor
transistor amplifiers. Then, variable speed drives
Drives1):
were built with standard electronic system blocks combined with computer drives. As an example linear amplifiers were often used rather than
Estimated 2004 Motor Units/Industry 3%
switching amplifiers. Typical applications were in areas where drives could be afforded, such as
1 2 3
12
industrial servo drives, machine tools and computer
3% 4
7%
6 7
18% 11
8%
8 10
Then there were a number of improvements
4%
5
disk drives; there were also a number of very high power drive systems.
1 – Cranes & Hoists 2 – Textiles
3%
3% 21%
11%
9%
9
10%
3 – Pulp and Paper 4 – Rubber & Plastics 5 – Metals & Mining 6 – Packaging 7 – Utilities 8 – Petro-chem 9 – Food & Beverage 10 – Pumps & Pumping 11 – Other 12 – HVAC
that brought about the different power switches. Bipolar transistors became available for power switching and motors started to be available beyond
Obviously, the biggest portion of the business (42%)
the standard brush DC motor. Permanent magnet
can be assigned to HVAC2), Pumps & Pumping
synchronous motors and AC induction motors
as well as the Food & Beverages Industries, so
became available and on the power electronics
traditional industrial applications.
side IGBTs, high performance micro processors and integrated amplifiers; the result was more
On the other hand, with the increase of potential
sophisticated control.
application fields and a general increase of energy consumption world wide, the efficiency of electric
Nowadays there is a whole selection of motors as
appliances such as motors become more and
well as a lot more control technology such as DSPs
more an issue. In 2007 the International Energy
and micros, ASICs, etc. A lot of the mathematical
Agency (IEA) issued an Energy Efficient Electrical
models that were developed to simulate AC
End-Use Equipment3) report where the general
machines 40-50 years ago all of a sudden become
electricity consumption worldwide was outlined in
relevant: the field oriented control is based on
the following way:
1) 2) 3)
4
http://www.aceee.org/conf/mt05/i4_offi.pdf HVAC - Heating, Ventilating and Air Conditioning http://www.iea.org/Textbase/work/2007/ia/Motors.pdf
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Unit
Value
Electricity production global (2006)
PWh/a
18.6
Electricity production from fossil energy
PWh/a (%)
12.4 (67%)
Electricity for industrial motors (not included household appliances, consumer electronics, office equipment, vehicles)
PWh/a (%)
7.4 (40%)
Capacity for electric motors (peak)
TWe
1.6...2.3
Motor electricity, greenhouse gas emissions
G t CO2/a
4.3
Motor system energy efficiency improvement potential (average within life cycle 10...20 years)
min max
20% 30%
Electricity savings potential (industry and buildings)
PWh/a min max G t CO2/a min max Euro/kWh
Greenhouse gas emission reductions potential Average electricity price (industrial end-users) Electricity cost saveings potential (industry end-users)
Billion Euro/a min max
1.5 2.2 0.9 1.4 0.05 75 110
As above breakdown points out, the energy
significant increase of energy prices, especially
improvement potential in 2007 for electric drives
during the last couple of months.
was being considered to be between 20...30% (or in absolute values 1.5 – 2.2 PWh/a)4). One of the
Broken down into geographical regions, the
reasons that forced the change up in mind in the
same report points out the following distribution
way to deal with available energy was probably the
characteristic:
Population
4)
GDP
Electricity
Mio
% cumul
Mio US $
% cumul
TWh/a
% cumul
1
China
1’322
20.0%
2229
5.0%
2475
13.6%
2
India
1’130
37.1%
785
6.8%
679
17.3%
3
United States of America
301
41.7%
12455
34.9%
4239
40.7%
4
Indonesia
235
45.3%
287
35.5%
123
41.3%
5
Brazil
190
48.1%
794
37.3%
405
43.6%
6
Pakistan
165
50.6%
111
37.5%
96
44.1%
7
Bangladesh
150
52.9%
60
37.7%
23
44.2%
8
Russia
141
55.0%
581
39.0%
952
49.5%
9
Japan
127
57.0%
4506
49.1%
1134
55.7%
10
Mexico
109
58.6%
768
50.9%
233
57.0%
11
Germany
82
59.9%
2782
57.1%
619
60.4%
12
Thailand
65
60.9%
176
57.5%
575
63.5%
13
France
64
61.8%
2193
62.5%
399
65.7%
14
United Kingdom
61
62.7%
2193
67.4%
399
67.9%
15
Italy
58
63.6%
1723
71.3%
301
69.6%
16
Korea, South
49
64.4%
788
73.1%
395
71.8%
17
South Africa
44
65.0%
240
73.6%
245
73.1%
18
Spain
40
65.6%
1124
76.1%
292
74.7%
19
Australia
20
66.0%
701
77.7%
243
76.0%
MEPS
20
Canada
33
66.5%
1115
80.2%
594
79.3%
MEPS
Total
4’388
35’610
MEPS MEPS MEPS
MEPS
MEPS
14’422
1 PWh/a = 105 Wh/a
5
The Engineers of Distribution.
Above table shows that countries like the US with
Although China’s productivity may be far away from
a population of 301 Million people (5% of the ww
above mentioned scenario a 20 – 30% world wide
population) but a total energy consumption of
efficiency improvement may sound pointless if we
4.239 PWh/a represent almost 23% of the total
take into consideration the consumption growth
energy consumption worldwide, while on the other
rate of some countries over time. As an example
hand a country like China with 1300 Million citizens
we can take an official report issued in 2002 by
(representing 21% of the total global population)
U.S. Department of Energy5) where the expected
consumes a bit more then half the amount of the
Midrange Savings where lined out to be 14.8%
energy the US are currently needing (13.3%). If
(as compared to 20 – 30% setup in 2006); yet the
China’s productivity was to be the same like the
total power consumption for 2002 only represented
US’ (annual energy consumption per population →
1.085 PWh/a, hence 31.39% of the consumption of
18.67 PWh/a !!!) one can see that a 20 – 30% world
2007, meaning that the US national energy demand
wide electrical efficiency improvement (hence 1.5 –
almost tripled within a period of time of 5 years.
2.2 PWh/a in absolute values) are probably just an initial step to the right direction with much bigger problems to be expected in the future.
Measure
Potential Energy Savings GWh/Year
Midrange Savings as Percent of
Low**
Total Motor System GWh
Midrange**
High**
System-Specific GWh
Motor Efficiency Upgrade* Upgrade all integral AC motors to EPAct Levels***
13,043
2.3%
Upgrade all integral AC motors to CEE Levels***
6,756
1.2%
Improve Rewind Practices
4,778
0.8%
Total Motor Efficiency Upgrade
24,577
4.3%
System Level Efficiency Measures Correct motor oversizing
6,786
6,786
6,786
1.2%
Pump Systems: System Efficiency Improvements
8,975
13,698
19,106
2.4%
9.6%
Pump Systems: Speed Controls
6,421
14,982
19,263
2.6%
10.5%
Pump Systems: Total
15,396
28,681
38,369
5.0%
20.1%
Fan Systems: System Efficiency Improvements
1,378
2,755
3,897
0.5%
3.5%
Fan Systems: Speed Controls
787
1,575
2,362
0.3%
2.0%
Fan Systems: Total
2,165
4,330
6,259
0.8%
5.5%
Compressed Air Systems: System Eff. Improvements
8,559
13,248
16,343
2.3%
14.6%
Compressed Air Systems: Speed Controls
1,366
2,276
3,642
0.4%
2.5%
Compressed Air Systems: Total
9,924
15,524
19,985
2.7%
17.1%
Specialised Systems: Total
2,630
5,259
7,889
0.9%
2.0%
Total System Improvements
36,901
60,579
79,288
10.5%
Total Potential Savings
61,478
85,157
103,865
14.8%
* Potential savings for Motor Efficiency Upgrades calculated directly by applying engineering formulas to Inventory data. ** High, Medium and Low savings estimates for system efficiency impriovements reflect the range of expert opinion on potential savings. *** Includes savings from upgrades of motors over 200 HP not covered EPAct standards.
5)
6
http://www1.eere.energy.gov/industry/bestpractices/pdfs/mtrmkt.pdf
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Therefore, some of the market trends predicted for the next couple of years become obvious by now: the demand for higher Reliability as well as Power Density are continuously increasing as a
Initial costs Maintenance costs
result of price vs. demand shift, hence cost/unit as well as cost/kW are steadily decreasing. A variety of standards like the European CE or the National Electric Code are addressing specific issues like
Energy costs
EMC filtering or thermal protection solutions. Other costs
Consequently, there is a great many of other costs on top of the typical initial costs (purchase, parts, etc.) which need to be taken into account when it comes to the selection of a specific motor type. As an example we can take a standard pumping
Maintenance and Energy Costs (→ electrical
application, with the following cost breakdown :
efficiency) seem to be - besides performance
6)
specific requirements - the driving factors with LCC = Cic + Cin + Ce + Co + Cm + Cs + Cenv + Cd
respect to technology improvements and finally
when it comes to the selection of a motor.
C = cost element
IC = initial cost, purchase price (pump, system, pipes, auxiliaries)
The objective of this workbook will therefore be to
IN = installation and comissioning
point out the main selection criteria for the most
E = energy costs
usual motor types, point out the principles of
O = operating cost (labor cost of normal
operation, provide an overview about the typical
system supervision)
applications where a given motor is traditionally
M = maintenance cost (parts, man-hours)
seen nowadays and finalize it with a set of selected
S = downtime, loss of production
best fitting SILICA system solutions.
ENV = environmental costs
D = Decommissioning
Axel Kleinitz, PhD Poing, 20-Apr-09
In above equation LCC stays for the total Life Cycle Cost; on percentage level, the relationship between all above mentioned parameters can be weighted through the following high-level diagram:
6)
http://www1.eere.energy.gov/industry/bestpractices/pdfs/variable_speed_pumping.pdf
7
The Engineers of Distribution.
2. System Level Problem
7)
In general terms, electric drives an motors
Although the complexity of above system block
are appliances used to convert electrical into
may vary with the application, a motor drive system
mechanical (kinetic) energy. The power ranges
will always require some sort of power conversion
start at a couple of mW and can go up to a several
stage (which will be depending upon the available
hundreds of MW per unit, meaning therefore a
power source), combined with an open – and in
variety of potential applications. However, although
case of more complex systems – a closed loop
the power ranges may significantly change from
control unit.
motor to motor the principles of operation seem to be always the same.
Since neither the motor itself nor the energy buffer system are intended to be a main matter of
Within the context the typical block diagram of such
discussion of the workbook, the focus will therefore
an energy conversion system (electric → mechanic/
primarily be the Power Conversion stage and –
kinetic) could be drawn in the following way:
up to a certain extent – the Closed Loop Control circuitry in the context of a given motor topology.
(Closed Loop) Control
Measurement Parameters
Control Quantity & Signals
(Elect.) Power Source
Converter
Motor
Processing Machine
Energy Buffer
7)
8
FAE Training – Elektrische Maschinen, Labor für Leistungselektronik, Maschinen und Antriebe, Dr.-Ing. Johannes Teigelkötter
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2.1 Motor Topologies and Drives Depending upon the principles of operations, following types of motors can be classified8):
The Complete Family of Electric Motors AC
DC
Asynchronous
Induction
Single Phase
Synchronous
BLDC
Sine
Poly Phase
Capacitor Start
Cast Rotor
Capacitor Run
Inserted Rotor
Shaded Pole
Wound Rotor
Hysterisis
Commutator
Step
Reluctance
PMDC
Homopolar Wound Field
PSM
Permanent Magnet
SRM
Shunt
Wound Field
Hybrid
Synchronous Reluctance
Compound
Variable Reluctance
Series
Universal
Of course, each motor type can be combined with
initial costs are concerned, however with a much
another one mentioned in above table, significantly
better performance (efficiency) and almost no
blowing up this overview; however, the most
maintenance costs. However, the complexity of the
common once used nowadays would probably be
electrical control is significantly higher then in case
those highlighted in red. Out of those the most
of a DC motor.
commonly used DC motor is the mechanically commutated
permanent
magnet
“PMDC”9),
predominantly due to the relative low initial costs.
In the following comparison some of the key selection parameters for those red highlighted motors have been put together providing an
Yet, electrical efficiency as well as maintenance
overview of the most typical applications where
costs seem to be relatively high as compared
they can be seen today.
to AC synchronous and asynchronous motors. These two last once are rather cheap as far as the
8) 9)
Motor, Drive and Control Basics, International Rectifier Corp. by Eric Persson & Michael Mankel PMDC - Permanent Magnet DC Motor
9
The Engineers of Distribution.
2.1.1 PMDC – Permanent Magnet DC Motor10)
The opposite polarities of the energized winding and the stator magnet attract and the rotor will rotate until it is aligned with the stator. Just as the
The DC motor is a rotating electric
rotor reaches alignment, the brushes move across
machine designed to operate from source of direct
the commutator contacts and energize the next
voltage. The basic type is a permanent magnet DC
winding.
motor. The stator of a permanent magnet DC motor
In order to understand the principles of operation,
is composed of two or more permanent magnet
we will start with a permanent magnet, mechanically
pole pieces. The rotor is composed of windings
commutated DC motor and use the terminology
that are connected to a mechanical commutator.
used in following block diagram11):
Communication of a Single-Loop DC Machine
The main windings rotate (rotor) while the
T = 2NBrlI0 = KT · I0
magnetic field is fixed, usually through a
and
permanent magnet. DC voltages and currents
e = 2NBrlω = Ke · ω
(1) (2)
are provided though brushes. With N wires per coil and multiple commutator bars, following mathematical relationships are know to be valid:
10) 11)
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10
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with
Two other types of DC motors are series wound
KT: Torque Constant
and shunt wound DC motors. These motors also
T: Magnetic Torque
use a similar rotor with brushes and a commutator.
Ke: emf Constant
However, the stator uses windings instead of
e: “emf” Induced Voltage (“electromotive force”)
permanent magnets. The basic principle is still
B: Constant Magnetic Field, generated by the
the same. A series wound DC motor has the stator
permanent magnet
windings in series with the rotor. A shunt wound DC motor has the stator windings in parallel with the
The relationship between Torque and rpm “n” leads
rotor winding. A series wound motor is also called
to following mathematical expression12):
a universal motor. It is universal in the sense that
n = n0 -
R
it will run equally well using either an AC or a DC M
(3)
kM = cϕ
(4)
M = T - MR
(5)
2π · kM2
voltage source.
with M: Torque n0: Idle Speed R: Total Resistance (rotor and brushes) c: Engine’s Constant ϕ: Magnetic Flux, constant in case B is constant (permanent magnet!) MR: Friction Losses
12)
Handbuch Elektrische Antriebe, Hans-Dieter Stölting & Eberhard Kallenbach
11
The Engineers of Distribution.
2.1.2. DC Motor Driver
commutator voltage; the speed itself through a PWM duty cycle, using a classic H-bridge circuit.
The traditional way to control the sense of rotation
With this approach 4 different operational modes
would be by changing the polarity of the DC
can be defined13):
H-Bridge Motor Drive (be-directional)
For obvious reasons, the H-bridge driver requires 4 switches, hence 2 less then the traditional 3-pahes
2.1.3. Asynchronous Motor14)
driver. The current flow – and therefore the torque, see equation (1) – can be driven in either direction.
In an induction motor (asynchronous)
The control strategy can be designed for 4-quadrant
the stator (3 phase) windings are fixed while the
operation modes: 1 forward and 2 reverse motoring
magnetic field rotates. AC voltages and currents
as well as 3 forward and 4 reverse braking using
are provided to the stator while the AC currents
the “emf” induced voltage as a breaking effect.
on rotor experience a slip at frequency; the
These last two once may require shunt regulator for
speed is always a little less than the synchronous
braking (regeneration). With respect to modulation
speed and speed drops with increasing load
there are a variety of strategies available, with PWM
(~5% max.).
as the most usual one.
The AC induction motor is a rotating electric machine designed to operate from a three-phase source of alternating voltage. The stator is a classic three phase stator with the winding displaced by 120°. The most common type of induction motor has a squirrel cage rotor in which aluminum
13) 14)
Motor, Drive and Control Basics, International Rectifier Corp. by Eric Persson & Michael Mankel http://www.freescale.com/webapp/sps/site/homepage.jsp?nodeId=02nQXG
12
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conductors or bars are shorted together at both
between Torque, synchronous speed and rotor
ends of the rotor by cast aluminum end rings. When
speed is been expressed through the following
three currents flow through the three symmetrically
equation:
placed windings, a sinusoidally distributed air gap flux generating the rotor current is produced. The interaction of the sinusoidally distributed air gap
Pδ P M= = 2πn 2πnS
flux and induced rotor currents produces a torque
with
on the rotor. The mechanical angular velocity of the
P: Output Power
rotor is lower then the angular velocity of the flux
Pδ: Rotor Loss
(8)
wave by so called slip velocity. In adjustable speed applications, AC motors are The valid block diagram looks as follows15):
powered by inverters. The inverter converts DC power to AC power at the required frequency and amplitude. The inverter consists of three halfbridge units where the upper and lower switches are controlled complimentarily. As the power device’s turn-off time is longer than its turn-on time, some
Starconnection
dead-time must be inserted between the turn-off
Deltaconnection
of one transistor of the half-bridge and turn-on of its complementary device. The output voltage is
The slip, hence the difference between the rotor-
mostly created by a pulse width modulation (PWM)
speed and the rotational-speed of the rotating-
technique. The 3-phase voltage waves are shifted
field is been expressed through the following
120° to each other and thus a 3-phase motor can
relationship:
be supplied.
nS - n s = nS
(6)
2.1.4. Synchronous Motor16)
and ƒ1 nS = p
(7)
In a synchronous motor the speed is synchronised to the stator voltage frequency;
representing
the
synchronous
speed
as
a
relationship between ƒ1, the stator current and p,
speed is therefore directly proportional to stator frequency. Since ns = n, s = 0.
the number of pole-pairs. Therefore the relationship
15) 16)
Handbuch Elektrische Antriebe, Hans-Dieter Stölting & Eberhard Kallenbach http://www.freescale.com/webapp/sps/site/homepage.jsp?nodeId=02nQXG
13
The Engineers of Distribution.
The PM Synchronous motor is a rotating electric
BLDC motors. The power stage utilizes six power
machine where the stator is a classic three phase
transistors with independent switching. The power
stator like that of an induction motor and the rotor
transistors are switched in the complementary
has surface-mounted permanent magnets. In this
mode. The sine wave output is generated using a
respect, the PM Synchronous motor is equivalent
PWM technique.
to an induction motor where the air gap magnetic field is produced by a permanent magnet. The use of a permanent magnet to generate a substantial air gap magnetic flux makes it possible to design
2.1.5. BLDC – Brushless DC17)
highly efficient PM motors. A PM Synchronous motor is driven by sine wave voltage coupled with
A
the given rotor position. The generated stator flux
motor is a rotating electric
brushless
DC
(BLDC)
together with the rotor flux, which is generated by
machine where the stator is a classic three-phase
a rotor magnet, defines the torque, and thus, speed
stator like that of an induction motor and the rotor
of the motor. The sine wave voltage output have to
has surface-mounted permanent magnets. In this
be applied to the 3-phase winding system in a way
respect, the BLDC motor is equivalent to a reversed
that angle between the stator flux and the rotor flux
DC commutator motor, in which the magnet rotates
is kept close to 90° to get the maximum generated
while the conductors remain stationary. In the DC
torque. To meet this criterion, the motor requires
commutator motor, the current polarity is altered
electronic control for proper operation.
by the commutator and brushes. On the contrary, in the brushless DC motor, the polarity reversal
The relationship between Torque and Rotor Speed
is performed by power transistors switching in
can be expressed through following term:
synchronization with the rotor position. Therefore, BLDC motors often incorporate either internal or
M - ML = J
(9)
1 δω ω = p · Ω p δt
(10)
external position sensors to sense the actual rotor position or the position can be detected without sensors.
with
The BLDC motor is driven by rectangular voltage
ML: Load torque
strokes coupled with the given rotor position. The
J: Total Moment of Inertia
generated stator flux interacts with the rotor fluxes,
Ω: Mechanical Radial Frequency
which is generated by a rotor magnet, defines the torque and thus speed of the motor. The voltage
For a common 3-phase PM Synchronous motor,
strokes must be properly applied to the two phases
a standard 3-phase power stage is used. The
of the three-phase winding system so that the angle
same power stage is used for AC induction and
between the stator flux and the rotor flux is kept
17)
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14
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close to 90° to get the maximum generated torque.
being implemented, according to the number of
Due to this fact, the motor requires electronic
motor phases and the desired control algorithm. A
control for proper operation.
power stage with two independent power switches per motor phase is the most used topology. This particular topology of SR power stage is fault
2.1.6. SRM – Switched Reluctance Motor18)
tolerant - in contrast to power stages of AC induction motors - because it eliminates the possibility of a rail-to-rail short circuit. The SR motor requires position feedback for motor phase commutation. In
A Switched Reluctance Motor is a rotating electric
many cases, this requirement is addressed by using
machine where both stator and rotor have salient
position sensors, like encoders, Hall sensors, etc.
poles. The stator winding is comprised of a set
The result is that the implementation of mechanical
of coils, each of which is wound on one pole. SR
sensors increases costs and decreases system
motors differ in the number of phases wound on
reliability. Traditionally, developers of motion
the stator. Each of them has a certain number of
control products have attempted to lower system
suitable combinations of stator and rotor poles.
costs by reducing the number of sensors. A variety of algorithms for sensorless control have been
The motor is excited by a sequence of current
developed, most of which involve evaluation of the
pulses applied at each phase. The individual
variation of magnetic circuit parameters that are
phases are consequently excited, forcing the motor
dependent on the rotor position.
to rotate. The current pulses need to be applied to the respective phase at the exact rotor position relative to the excited phase. The inductance profile
2.1.7. Bi-Polar Stepper Motor
of SR motors is triangular shaped, with maximum inductance when it is in an aligned position and
In a bi-polar stepper motor, the stator poles change
minimum inductance when unaligned. When the
polarity by varying current through each of the two
voltage is applied to the stator phase, the motor
coils. The rotor’s magnetic poles, however, fixed
creates torque in the direction of increasing
relative to the rotor itself. By definition, the bi-
inductance. When the phase is energized in its
polar stepper motor has one phase per stator pole
minimum inductance position the rotor moves to
which requires advanced circuitry such as a driver
the forth coming position of maximal inductance.
and H-bridge circuit to cause rotation and torque
The profile of the phase current together with
by switching the poles by alternately changing the
the magnetization characteristics defines the
current direction in each phase. The resolution of
generated torque and thus the speed of the motor.
a stepper motor is determined by arrangement of
The SR motor requires control electronic for its
the “teeth”.
operation. Several power stage topologies are 18)
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The Engineers of Distribution.
Stator – Phase 1
Stator – Phase 1
N
S
S N
N S
Rotor
Stator – Phase 2
S
Stator – Phase 2
Stator – Phase 2
N
Stator – Phase 2
Stator – Phase 1
Stator – Phase 1
Step 3 – P hase 1 energized with negative current Step 1 – P hase 1 energized with positive current Phase 2 not energized
Phase 2 not energized Rotor rotates 90 degrees to align with north
Stator – Phase 1
S Stator – Phase 2
Stator – Phase 1
N
NS
Stator – Phase 2
N Stator – Phase 2
Stator – Phase 1
Step 2 – Phase 1 is de-energized while
16
S
SN
Stator – Phase 2
Stator – Phase 1
Step 4 – P hase 1 is de-energized while
Phase 2 is energized with positive current
Phase 2 is energized with negative current
Rotor rotates 90 degrees to align with
Rotor rotates 90 degrees to align with
north
north
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As a simplified example of how a stepper motor
Stator – Phase 1
operates, one can imagine a stepper motor with only
N
four teeth or two phases each controlling two poles (Figure 1). When such a stepper motor is in full-step mode, the rotor rotates 90-degrees by sequentially changing the current in each phase. For example,
of the phase 1 stator pole. If phase 1 is then deenergised and a ‘positive’ current is then applied
S
N
N
south pole of the roor to align with the north pole
r to Ro
‘positive’ current which causes the permanent
S
in Step 1 of Figure 1, Phase 1 is energised with a
S
Stator – Phase 2
to phase 2, the position of the north pole changes
Stator – Phase 2
causing the rotor to align its south pole, therefore rotating 90-degrees clockwise in this example
Stator – Phase 1
(Step 2 of Figure 1). In order to get the rotor to continue in a clockwise motion, phase 1 is then
Step 1 – B oth phases 1 and 2 energised with
energised with a ‘negative current’ which switches
positive current resulting in the rotor
the north and south poles from Step 1 causing the
aligning between full-steps
rotor to align itself and turn 90-degrees clockwise (Step 3, Figure 1). Phase 1 is then de-energised
Very simply, micro-stepping is accomplished by
and phase 2 is energised with a ‘negative’ current,
partially energising both phases allowing the rotor
once again rotating the rotor one quarter turn. The
to stop between steps as shown in Figure 2. By
cycle then starts over by de-energising phase 2 and
energizing both phases using the same current
energising phase 1 with a positive current, which
magnitude, the rotor is equally attracted to both
puts the motor back to Step 1. This simple example
north poles which causes it to stop in-between the
represents a stepper motor with 90-degree re-
two and resulting in a half-step, or as referred to in
solution, which for practical purposes is not typical.
most literature, a one-half microstep. By applying currents to both phases in different ratios, advanced
The resolution of a stepper motor is determined
stepper motor drivers can further reduce micro-
by the number of teeth and alignment and a
stepping increments to ¼, 1/8, 1/16, 1/32 and even
1.8-degree step provides motion with much less
1/64 microsteps. For the designer, this means that a
vibration caused by the overshoot than our fictional
stepper motor specified to be capable of 1.8-degree
90-degree motor example above.
However, the
steps, or 200 steps per rotation, is now capable of
vibration experienced in a stepper motor with only
stepping in increments of 0.028-degrees or 12,800
1.8-degree incremental steps, or full-steps, can
steps per rotation. Not only does this allow finer
be even further reduced by utilising stepper motor
resolution in stepping, it also drastically reduces
drivers capable of micro-stepping.
vibration.
Although
the
increased
resolution
17
The Engineers of Distribution.
typically comes at a cost of 10% to 20% of torque,
Depending upon the application, above 3-Phase-
the increase resolution has many applications
Bridge can be realized with IGBTs like in above
when the trade-offs are considered.
example or with power MOSFETs. Performance criteria mainly like power and heat dissipation will determine which solution to go for. Yet, due
2.1.8 AC Motor Driver
to the system, topology and circuitry architecture peculiarities a further detailed discussion will be
Since AC motors require three AC phases to be
performed in the context of specific solutions.
independently driven, the solution would be to control – both, synchronous and asynchronous motors – through a 3-Phase-Bridge-Driver like the one represented in the following illustration19):
AC-DC
DC link
DC-AC AC out
AC in
19)
Motor
Motor Control Basics, International Rectifier Corp. by Aengus Murray
18
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2.2. Motor Selection Criteria
Finally, logistics and costs will be an issue that will require a dedicated focus, especially if we remember
When it comes to the selection of a specific motor
the analysis in the introduction. In specific those
for a given application, the criteria based upon the
criteria like annual usage and unit cost target will
decision will have to be founded on, may significantly
have to be carefully considered. Within this context
complicate the decision process.
the question about making or buying the complete system (or part of it) will be depending on risk
At a first stage the designer has to understand the
factors like availability of suppliers, time to market,
load requirements, meaning those parameters like
development cost and technology risk.
speed range, continuous and peak torque as well as starting requirements, which will provide a first
Due to the complexity of this approach, the selection
decision base to deal with.
of a specific motor for a given application may become more sophisticated then initially expected;
Besides that it is fundamental to understand those
taking into consideration all above mentioned
performance requirements like efficiency, dynamic
parameters, the overview presented on page 10
performance, speed accuracy, torque and speed
reflects a selection of those motor commonly used
ripple, acoustic noise, hence those parameters
for specific applications at the moment. Although
that will have a direct impact on the application’s
meant to be used as a guidance, it will still require
performance quality.
individual adaption to a given problem.
At a next step these needs will have to be put in line with important Supply Considerations (AC or DC, Voltage and current, connections, EMI/RFI) which in many cases narrow down the applicability of a potential candidate. Once above criteria had been carefully taken into consideration, the designer will have to determine Mechanical and Environmental Issues like size &
weight,
temperature,
reliability,
explosion
proof, integration of drive and control and safety issues, hence those kind of parameters that may significantly limit the usage of a selected solution depending upon their importance in a given application.
19
20
SRM – Switched Reluctance Motor
M - ML = J
1 ·Ì p ·t
P P = · 2Ãn 2ÃnS low
low
low
high
AC – Synchronous
M=
R M 2÷ kM2
Cost (CIC)
PSM – Permanent Magnet Synchronous Motor
AC – Asynchronous
Cast Motor – Squirrel Cage Rotor
n = n0 -
Characteristics
moderate
DC – Commutator
PMDC – Permanent Magnet DC
Mathematical Relationship
BLDC – Brushless DC
Functional Principle
Type
very good
good
very good
good
low
Motor Efficiency
low
middle
middle
high
high
Motor Technology Stage of Development
no
yes
no
no
yes
Maintenance Costs (Cm)
moderate
high
high
high
low
Complexity Electronic Circuit
Industrial: 110...240 V Automotive: 12...24 V
110...240 V
4...240 V
220...440 V
100...103 V
Voltage Ranges
100.000
10.000
50.000
20.000
20.000
Speed Ranges [rpm]
16, 30, 66, 96, 106
13, 33, 66, 106
Fans, Appliances, Emering Automotive Applications
12, 24, 67, 97, 109
Washing Machines, Electrical Power Steering, Electrical vehicle traction drive, Refrigerators, AC, PC-Fan, Ceiling Fan, Blowers
Servo Drives, Electronic Power Steering
10, 16, 26, 84, 102, 118
8, 96 ff
Hand Tools, Washers & Dryers, Starters, Wipers, Power Windows
Pumps, Fans, HVAC, White Goods, Heavy Traction Machinery
Page
Typical Applications
The Engineers of Distribution.
2.3 Applications Summary and Overview – Electric Motor Topologies
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3.
Solutions
3.1 Analog Devices The ADM3251E in Motion Control Applications
A basic architecture of a motion control system is depicted in Figure 1. To improve system reliability
Introduction
within a noisy environment and protect against
For many years, communications in Motion Control
voltage spikes and ground loops, isolation is
Systems has typically been implemented via an
required between the RS-232 cable network and
RS-232 interface. The RS-232 bus standard has
the systems connected to it. Analog Devices Inc.
proven itself to be a robust communication protocol,
have developed the ADM3251E integrated isolated
particularly suited to noisy environments. Recent
RS-232 transceiver to solve these problems. Until
enhancements in serial communication design
recently, transferring power across an isolation
include the isolation of the RS-232 port from the
barrier required either a separate dc-to-dc
motion controller itself. The ADM3251E offers the
converter, which is relatively large, expensive, and
latest level of innovation, by combining both power
has insufficient isolation, or a custom discrete
and data isolation in a single package.
approach, which is not only bulky but also difficult to design. The ADM3251E combines iCoupler technology
RS-232 Port
with isoPower, which results in a complete Motion Controller
AMP/ Drive
MOTOR
MECHANICAL
isolation solution within a single package. Not only does the ADM3251E offer state of the art digital
Feedback Device
signal isolation, having substantial advantage over optocouplers in terms of power, size and performance, but it also eliminates the need for
Figure 1. Block Diagram of a Typical Motion Control Application
a separate isolated power supply. The ADM3251E provides functional integration that can dramatically reduce the complexity, size and total cost of an isolated system.
21
The Engineers of Distribution.
Figure 2.
ADM3251E Features
rather than the LEDs and photodiodes used in
The ADM3251E is a high speed, 2.5 kV fully isolated,
optocouplers. By fabricating the transformers
singlechannel RS-232 transceiver device that
directly on chip using wafer level processing
operates from a single 5V power supply. Due to the
iCoupler channels can be integrated with other
high ESD protection on the RIN and TOUT pins the
semiconductor functions as low cost. Transfer
device is ideally suited for operation in electrically
of the digital signal is realised through the
harsh environments or where RS-232 cables are
transmission of short pulses approximately routed
frequently being plugged and unplugged.
to the primary side of a given transformer. These pulses couple from one transformer coil to another
C1 0.1µF 16V
C3 0.1µF 10V
C1+ C1– V+
ADM3251E VCC
OSC
VISO
0.1µF
C2+ C2–
VOLTAGE DOUBLER
RECT
C2 0.1µF 16V
C4 0.1µF 16V
and are detected by the circuitry on the secondary side of the transformer. The circuitry then recreates
V–
the input digital signal.
VOLTAGE INVERTER
REG
0.1µF
TIN
ENCODE
ENCODE
DECODE
R
T
RIN* TOUT
Another novel feature of iCoupler technology is that the transformer coils that are used to isolate data signals may also be used as the transformers
GND *5kΩ PULL-DOWN RESISTOR ON THE RS-232 INPUT.
GNDISO
07388-001
ROUT
DECODE
Figure 3. ADM3251E Functional Block Diagram
in an isolated DC-DC converter, this extension of iCoupler technology is termed isoPower. The result is a total isolation solution.
Complete isolation of both signal and power is achieved using iCoupler technology. iCoupler
For further information, please visit:
technology is based on chipscale transformers
www.analog.com/ADM3251E
22
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3.2 Freescale Semiconductor
Freescale delivers solutions that have wide ranging banks of flash and RAM memories, configurable
Freescale Solutions for Motor Control
timer options, pulse width modulators (PWMs),
Technologies
and some even offer an enhanced Time Processing
Comprehensive 8-, 16- and 32-bit systems with
Unit (eTPU). Freescale supports these devices with
advanced sensor and analog/mixed signal devices
motor control-related application notes, hardware/ software tools, drivers, algorithms and helpful
Freescale offers complete solutions for every motor
Web links including our motor control Web site at
control application. Our superior portfolio and
www.freescale.com/motorcontrol.
breadth of devices includes: • 8-bit microcontrollers (MCUs) • 16-bit digital signal controllers (DSCs) • 32-bit embedded controllers • Acceleration and pressure sensors • Analog and mixed signal devices
Freescale Motor Control Solutions A full range of products, technology, services and tools
23
The Engineers of Distribution.
Expertise
Application Notes
Demos
Freescale's Complete Motor Control Solution
MCUs, MPUs and DSCs
Analog and Sensors
Development Tools Software and Drivers
Reference Designs
Online Training
Website
Technical Support
We are dedicated to providing comprehensive
Freescale provides microcontrollers and develop-
system solutions that not only improve motor
ment tool solutions for all of your motor control
efficiency but also minimise system updates,
needs.
development time and maintenance costs.
24
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A Roadmap for Your Future Design Needs
control for an incredible variety of applications.
Intelligent solutions driving new generations of
The product roadmaps demonstrate that new
motor control applications
feature integration and software compatibility will continue to drive future generations of embedded
Freescale MCUs, MPUs and DSCs, when coupled
motor
control
solutions.
Freescale
provides
with analog/mixed-signal and power integrated
microcontrollers and development tool solutions
circuits, are designed to provide system solutions
for all of your motor control needs.
for motor control, motion control and static load
