USOO6570778B2

(12) United States Patent (10) Patent No.: US 6,570,778 B2

Lipo et al. (45) Date of Patent: May 27, 2003

(54) ADJUSTABLE SPEED DRIVE FOR SINGLE- OTHER PUBLICATIONS

PHASE INDUCTION MOTORS Yr
P. Enjeti, et al., “Economic Single Phase to Three Phase
(75) Inventors: Thomas A. Lipo, Middleton, WI (US); Converter Topologies for Fixed Frequency Output.” IEEE
Miroslav Chomat, Prague (CZ) APEC Conf. Rec. 1991, pp. 88–94. No Date.
Chingchi Chen, et al., “Simple Topologies for Single Phase
(73) Assignee: Wisconsin Alumni Research AC Line Conditioning,” Conf. Rec. IEEE-IAS Annual
Foundation, Madison, WI (US) Meeting, Oct., 1991, pp. 911–917.
Chingchi Chen, et al., “A Single Phase to Three Phase Power
(*) Notice: Subject to any disclaimer, the term of this Converter for Motor Drive Applications,” Conf. Rec., IEEE
patent is extended or adjusted under 35 IAS, 1992, pp. 639-646. No Date.
U.S.C. 154(b) by 0 days. P. Enjeti, et al., “A Low Cost Single Phase to Three Phase
Static Power Converter.” IEEE Rural Electronics Confer
(21) Appl. No.: 09/943,417 CICC, May, 1992.
(22) Filed: Aug. 30, 2001 David K. Morgan, “COS/MOS Phase-Locked-Loop . . . A
Versatile Building Block for Micro-Power Digital and Ana
(65) Prior Publication Data log Applications, Texas Instruments Application Report,
US 2003/0043606 A1 Mar. 6, 2003 published prior to 2001. No Date.
Edward Randolph Collins, “Torque and Slip Behavior of
7 Single-Phase Induction Motors Driven from Variable-Fre
(51) Int. Cl." ............................. H02M 1/12; H02P 7/36 Ny Supplies,” IEEE Trans. on Industry Applications,
vol. 28, No. 3, May/Jun., 1992, pp. 710–715.
(52) U.S. Cl. .......................................... 363/41; 318/807
(List continued on next page.)
(58) Field of Search .............................. 363/41, 34, 39,
363/49; 318/708, 738, 700, 751, 259,441, Primary Examiner-Rajnikant B. Patel
442, 230, 807, 231 (74) Attorney, Agent, or Firm-Foley & Lardner
(56) References Cited (57) ABSTRACT
An adjustable speed drive for Single-phase induction motors
U.S. PATENT DOCUMENTS has a low-cost structure including a rectifier and a two
4,047,083 A * 9/1977 Plunkett ..................... 3.18/231 Switch inverter. During full-speed operation, power is Sup
4,060,754. A 11/1977 Kirtley, Jr. et al. plied directly from the AC power system to the main
4,401,933 A 8/1983 Davy et al. winding of the motor and from the inverter at line frequency
5,136.216 A * 8/1992 Wills et al. ................. 323/220 but phase-shifted from the line Voltage to an auxiliary
5,252.905 A * 10/1993 Wills et al. ................. 318/708 winding of the motor to develop start up torque for the
568 A ." E. B.N. N.
5566.219 A 10/1996 Volger ..........
so motor. In one or more lower speed operating modes, power
... 318/442 is Supplied from the inverter at a lower frequency directly to
5,796,234. A 8/1998 vionis. 318,751 the main winding and through a phase-shifting capacitor to
5,969.957 A 10/1999 Divan et al. the auxiliary winding of the motor. Low cost Switching
6,051,952. A 4/2000 Moreira et al. ............. 318/738 devices may be used in the inverter Since they are not
required to Switch the full-speed power of the motor.
FOREIGN PATENT DOCUMENTS
GB 2111326 6/1983 20 Claims, 10 Drawing Sheets
 US 6,570,778 B2
Page 2

OTHER PUBLICATIONS Do-Hyun Jang, et al., “Space Vector PWM Technique for
Alexander L. Julian, et al., “Multi-Speed Control of Single Two-Phase Inverter-Fed Single-Phase Induction Motors.”
-Phase Induction Motors for Blower Applications,” IEEE Conference Records IEEE/IAS Annual Meeting, 1999, pp.
47–53, No Date.
Trans. on Power Electronics, vol. 10, No. 1, Jan., 1995, pp. E.R. Benedict, et al., “Improved PWM Modulation for a
72-77.
Permanent-Split Capacitor Motor,” Conference Record
M.B.R. Correa, et al., “Single-Phase Induction Motor IEEE/IAS 2000, pp. 2004–2010. No Date.
Drives Systems,” Conference Records IEEE/APEC, vol. 1,
1999, pp. 403-409. No Date. * cited by examiner
U.S. Patent May 27, 2003 Sheet 1 of 10 US 6,570,778 B2

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 US 6,570,778 B2
1 2
ADJUSTABLE SPEED DRIVE FOR SINGLE may also be operated in multiple discrete Speed modes or
PHASE INDUCTION MOTORS continuously variable Speed modes if desired. The adjust
able Speed drive of the invention Supplies power to the motor
REFERENCE TO GOVERNMENT RIGHTS at higher efficiencies than can be obtained with conventional
low-cost drives that reduce the Voltage applied to the motor
This invention was made with United States government to reduce Speed.
support awarded by the following agency: NSF 9731677. The adjustable speed drive of the invention includes a
The United States government has certain rights in this rectifier which receives AC power at first and second AC
invention. input lines from the AC power mains and provides DC
FIELD OF THE INVENTION power acroSS DC bus lines, and a Single-phase two Switch
inverter which provides AC power at an output line at a
This invention pertains generally to the field of electrical Selected frequency and phase shift with respect to the input
power conversion Systems and particularly to power con power from the main power lines. The output of the inverter
verters for Supplying power to Single-phase induction is Supplied to a transfer Switch circuit which is also con
motorS. 15 nected to the Second of the input lines to receive AC power
from the AC power lines. The transfer Switch circuit also is
BACKGROUND OF THE INVENTION connected to a phase-shifting capacitor and has a main
Single-phase induction motorS typically include a main winding Supply line connectable to the main winding of the
Stator winding which provides the main drive power for the motor and an auxiliary winding Supply line connectable to
motor and an auxiliary winding which is Supplied with the auxiliary winding of the motor. Both the main and
power through a capacitor to provide Starting torque for the auxiliary windings are connected to the first of the AC input
motor. The auxiliary winding may be disconnected when the lines to complete the circuits through these windings. For
motor reaches operating Speed, as in a capacitor Start motor, full-speed mode operation, the inverter is operated to pro
or it may be Supplied with power constantly as in a perma vide an output Voltage that is at line frequency and approxi
nent Split capacitor motor. The capacitor connected in Series 25 mately 90° out of phase with the line voltage. The transfer
with the auxiliary winding provides the phase shift of the Switch circuit connects the inverter output to the auxiliary
Voltage applied to the auxiliary winding that allows starting winding and connects the Second input line to the main
torque to be developed. Such Single-phase induction motors motor winding. Operation in this mode provides relatively
are widely used in residential and commercial applications, high Starting torque, Superior to that obtainable by the use of
Such as in home appliances, fans, pumps, etc., and are a capacitor to provide the phase shift for the Voltage applied
manufactured in large Volumes at relatively low unit cost. to the auxiliary winding. After Start-up, the inverter may
continue to provide power to the auxiliary winding for
Single-phase induction motors inherently operate at a maximum efficiency. The torque capability of the motor is
constant speed determined by the AC power line frequency improved by the fact that a Voltage of correct amplitude and
(50 or 60Hz) and the load imposed on the motor. For various 35 90° phase shift is provided by the inverter, allowing opera
applications, Such as fan drives, it would be desirable to be tion over a wider range of loads than is available with a
able to operate the motor at Selectable speeds. The operating capacitor-run motor. Operation may also be in a mode
Speed of a fan drive motor can be reduced by Simply analogous to the operation of a capacitor Start motor, in
reducing the AC voltage applied to the motor. While this which the inverter may be disconnected or turned off so that
approach allows the use of inexpensive control circuitry, 40 power is Supplied only to the main winding through the
operating the motor at reduced Voltage levels lowers the transfer Switch circuit after the motor reaches operating
energy efficiency of the motor and generally does not result Speed as determined by the motor load and line frequency
in close control of the motor Speed. Another approach is the (e.g., 60 Hz). For operation at reduced speed, for example,
use of a variable frequency converter which receives AC for fan drives for heating, ventilating and air conditioning
power from the AC power System, rectifies it, and inverts the 45 Systems, the inverter may be operated to provide AC output
power to an approximately sinusoidal output voltage at a power at a frequency lower than line frequency (e.g., 30 Hz
Selected frequency that may be higher or lower than the for approximately half-speed operation), and the transfer
normal line frequency. While Such power conversion SyS Switch circuit is operated to Supply power from the inverter
tems can provide effective variable Speed drive of the motor, output directly to the main winding of the motor and through
the cost of the power converter itself is significant 50 the capacitor to the auxiliary winding of the motor, thereby
(particularly as compared to the low-cost induction machine providing phase-shifted voltage (at the lower frequency) to
it is driving) because of the complexity of the power the auxiliary winding to provide Start-up torque. Power may
converter and the need for several (typically at least Six) also be provided from the inverter through the capacitor to
semiconductor Switches which must be rated to handle the the auxiliary winding after the motor is up to Speed. The
maximum voltage and current to be Supplied to the motor. 55 inverter may also be operated at additional discrete or
Consequently, Such power converters have not been practi continuously variable frequencies to further expand adjust
cal for use in low-cost applications Such as Single phase fan able speed drive control of the induction motor in this mode.
motor drives. In a preferred adjustable Speed drive in accordance with
SUMMARY OF THE INVENTION the invention, the rectifier includes a pair of rectifying
60 diodes connected together at a node and connected acroSS
In accordance with the present invention, an adjustable DC bus lines. A pair of energy Storage capacitorS is also
Speed drive is provided having a simple, low-cost structure connected across the DC bus lines, with a node between the
that is well Suited for use with low-cost Single-phase induc capacitors connected to a first of the input lines, and with the
tion motors. The drive is capable of operating in a full-speed Second of the input lines connected to the node between the
mode with high Starting torque, and in at least one lower 65 pair of diodes. The diodes and capacitorS Serve to rectify AC
Speed mode which is well Suited for applications Such as fan Voltage from the main power System to a DC voltage acroSS
motor drives. The adjustable speed drive of the invention the DC bus lines. An inverter comprised of two gate con
 US 6,570,778 B2
3 4
trolled Switching devices is connected acroSS the DC bus at half-speed may utilize Switching devices which are rated
lines. A first output line is connected to the first input line, for only /s of the full speed motor power.
a Second output line is connected from the Second input line Although less torque is required due to the typical load
to the transfer Switch circuit, and a third output line is characteristics at lower Speed and lower excitation
connected from the node connecting the pair of controlled 5 frequency, the magnetic flux levels in the motor will increase
Switching devices to the transfer switch circuit. The first as excitation frequency decreases if winding Voltage remains
output line is connectable to both the main winding and the constant. To avoid Saturation, the invention can be adapted
auxiliary winding of a motor to be driven. A main winding to reduce inverter output voltage to maintain a fixed direct
Supply line extends from the transfer Switch circuit for proportionality relationship between winding Voltage and
connection to the main winding and an auxiliary winding excitation frequency. This is familiar to those skilled in the
Supply line extends from the transfer Switch circuit for art as “constant volts per hertz’ control.
connection to the auxiliary winding. A phase-shifting Further objects, features and advantages of the invention
capacitor is connected to the transfer Switch circuit. The will be apparent from the following detailed description
transfer Switch circuit can comprise a first Switch connected when taken in conjunction with the accompanying drawings.
on one Side to the Second and third output lines and on the 15
other Side to the main winding Supply line, the first Switch BRIEF DESCRIPTION OF THE DRAWINGS
Switchable between a position connecting the Second output
line to the main winding Supply line and a position con In the drawings:
necting the third output line to the main winding Supply line. FIG. 1 is a block diagram of an adjustable speed drive for
The transfer Switch circuit can further comprise a Second Single-phase induction motors in accordance with the inven
Switch connected on one side directly to the third output line tion.
and to the third output line through a phase-shift capacitor FIG. 2 is a Schematic circuit diagram of an embodiment
and with the auxiliary winding Supply line connected on the of an adjustable speed drive in accordance with the inven
other side of the second Switch. The second Switch is tion.
Switchable between a position connecting the third output 25
FIG. 3 is a block diagram of an embodiment of the
line to the auxiliary winding Supply line directly and a controller for an adjustable Speed drive in accordance with
position connecting the third output line to the auxiliary the invention.
winding Supply line through the phase-shift capacitor. The
first and Second Switches may be Switched together and may FIG. 4 is a block diagram of an embodiment of the
comprise a relay, in the first position of which the Second controller adapted for constant volts/hertz operation in
output line is connected directly to the main winding Supply accordance with the invention.
line to Supply power directly from the power System to the FIG. 5 are graphs showing motor torque-Speed character
main winding and the third output line is connected to istics in the main and auxiliary windings of a single phase
provide power from the inverter through the auxiliary wind induction motor driven at full-speed frequency of 60 Hz
ing Supply line to the auxiliary winding. In a Second position 35 using Standard operation from the AC power mains with a
of the transfer Switch, the third output line is connected phase-shift capacitor in Series with the auxiliary winding.
directly from the inverter to the main winding Supply line to FIG. 6 are graphs showing Stator currents as a function of
Supply power to the main winding and the third output line Speed in the main and auxiliary windings of a Single phase
is connected through the phase-shift capacitor to the auxil induction motor driven at full-speed frequency of 60 Hz
iary Supply line to Supply to the auxiliary winding power that 40 using Standard operation from the AC power mains with a
is phase-shifted from the power applied to the main winding. phase-shift capacitor in Series with the auxiliary winding.
A controller is connected to the Switching devices of the FIG. 7 are graphs showing motor torque-Speed character
inverter and to the transfer Switch circuit to respond to input istics in the main and auxiliary windings of a single phase
commands to change the two positions of the transfer Switch induction motor driven at full-speed frequency of 60 Hz
circuit and to appropriately control the Switching of the 45 using the adjustable Speed drive in accordance with the
Switching devices in the inverter to generate AC output invention.
power at the appropriate frequency and phase shift. The FIG. 8 are graphs showing Stator currents as a function of
circuit constructed in this manner can be utilized to operate Speed in the main and auxiliary windings of a Single phase
at discrete frequencies and thus discrete motor Speeds as induction motor driven at full-speed frequency of 60 Hz
well as allowing continuously variable driving of the motor, 50
using the adjustable Speed drive in accordance with the
if desired, utilizing a minimum number of components. The invention.
Switching devices of the inverter, e.g., Semiconductor FIG. 9 are graphs showing motor torque and Speed at
Switches Such as IGBTs or MOSFETs, can be devices which Start-up for full-speed mode operation utilizing the adjust
have a significantly lower rating, and thus lower cost, than able Speed drive in accordance with the invention.
devices which would be required to drive the motor at full 55
FIG. 10 are graphs showing main and auxiliary winding
speed. When the inverter is utilized to provide power to the
auxiliary winding during full-speed mode operation, the Stator currents at Start-up for full-speed operation of a motor
current drawn by the auxiliary winding is significantly leSS utilizing the adjustable Speed drive in accordance with the
than that drawn by the main winding, which is Supplied invention.
directly from the power lines through the transfer switch. In 60 FIG. 11 are graphs showing torque verSuS Speed charac
the lower speed (and lower frequency) mode or modes, the teristics of a motor driven at a half-speed frequency of 30 Hz
torque-producing currents drawn by the main winding and utilizing the adjustable Speed drive in accordance with the
auxiliary winding are generally Significantly less than cur invention.
rents drawn at full Speed. For example, the power required FIG. 12 are graphs showing main and auxiliary winding
to drive a fan increaseS as a cubic function. Thus, the power 65 Stator currents as a function of Speed for a motor driven at
required to drive the fan at half-speed is only vs that at full a half-speed frequency of 30 Hz utilizing the adjustable
Speed, and an inverter designed to operate in a Second mode Speed drive in accordance with the invention.
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FIG. 13 is a graph illustrating the Voltage across the AC the main winding Supply line 50 to provide power directly
phase-shifting capacitor for a motor driven at a half-Speed to the main winding. The transfer Switch circuit then also
frequency of 30 Hz utilizing the adjustable speed drive in connects the third output line 41 through the phase-shifting
accordance with the invention. capacitor 46 to the auxiliary winding Supply line 51 So as to
FIG. 14 are graphs illustrating torque and Speed at Start-up supply power from the inverter 30, phase-shifted by the
for a motor driven at a half-speed frequency of 30 Hz capacitor 46, to the auxiliary winding 37. The capacitor 46
utilizing the adjustable Speed drive in accordance with the serves to provide a phase shift of approximately 90 to the
invention. power Supplied to the auxiliary winding 37 as compared to
FIG. 15 are graphs illustrating main and auxiliary winding the power Supplied to the main winding 36 to allow Start-up
currents at Start-up of a motor driven at a half-Speed fre torque to be developed in the motor 35. The inverter 30 can
quency of 30 Hz utilizing the adjustable speed drive in be controlled by the controller 55 to produce a fundamental
accordance with the invention. frequency which is typically less than the frequency of the
power System 21, e.g., at 30 HZ. Depending on the Slip due
FIG. 16 are graphs illustrating the current through and to the load imposed on the motor 35, the output speed of the
Voltage acroSS the AC phase-shifting capacitor at Start-up for 15 motor with this lower input frequency will be at a speed
a motor driven at a half-speed frequency of 30 Hz utilizing lower than that of the motor when driven from line power at
the adjustable Speed drive in accordance with the invention. 60 Hz (e.g., about half-speed). If desired, the actual output
DETAILED DESCRIPTION OF THE Speed of the motor can be monitored, and the frequency of
INVENTION
the output voltage provided by the inverter 30 adjusted to
achieve the desired operating Speed.
With reference to the drawings, an adjustable Speed drive As shown in FIG. 2, the adjustable speed drive 20 may be
for Single-phase induction motorS is illustrated in block implemented with a simple circuit Structure having a mini
diagram form generally at 20 in FIG. 1. The drive 20 mum number of relatively inexpensive components. The
receives power from an AC power System 21 at input rectifier 26 may be implemented with a pair of rectifying
terminals 22. A first input line 24 and a second input line 25 25 diodes 60 and 61, connected together at a node 62 to which
are connected to a rectifier 26 which provides DC power on the Second input line 25 is connected, with the pair of diodes
DC bus lines 27 and 28. The DC voltage on the lines 27 and 60 and 61 connected across the DC bus lines 27 and 28. A
28 is provided to an inverter 30 which includes two con pair of capacitorS 64 and 65 are connected together at a node
trollable Switches 31 and 32. A first output line 34 is 66, which is connected to the first input line 24. The series
connected to the first input line 24 and extends to a single connected capacitorS 64 and 65 are also connected acroSS the
phase induction motor 35 where it is connected to a main DC bus lines 27 and 28 to filter the voltage rectified by the
winding 36 and an auxiliary winding 37 of the motor. A diodes 60 and 61 to provide a substantially constant DC
Second output line 38 is connected to the Second input line voltage across the bus lines 27 and 28. The inverter 30 may
25 and extends to a transfer switch circuit 40. A third output be implemented utilizing a pair of Solid-State Switching
line 41 is connected to the node 42 between the Switches 31 35 devices 31 and 32, Such as the IGBTs shown in FIG. 2,
and 32 in the inverter 30 and is connected to the transfer which receive gate control Signals at their gates from the
Switch circuit 40. A phase-shifting capacitor 46 is connected control lines 56. Other types of power Switching devices,
by lines 47 and 48 to the transfer Switch circuit 40. A main such as MOSFETs, may also be utilized. The transfer Switch
winding Supply line 50 extends from the transfer Switch circuit 40 may comprise a relay, as shown in FIG. 2, having
circuit 40 to the main winding 36 and an auxiliary winding 40 two single throw Switches 70 and 71 connected to Switch
supply line 51 extends from the transfer switch circuit to the together under the control of the signal on the control line 57
auxiliary winding 37. A controller 55 is connected by lines from the controller 55. Switches 70 and 71 are in a first
56 to the inverter 30 and by lines 57 to the transfer switch position to operate the motor in the full-speed drive mode,
circuit 40 to control the operation of the inverter and the and these Switches are in a Second position to operate the
transfer switch circuit. In a first, full-speed drive mode of the 45 motor in the lower-speed mode. The first relay switch 70 is
adjustable speed drive 20, Switches in the transfer Switch connected at an input Side to the Second output line 38 and
circuit 40 are in a position directly connecting the Second the third output line 41, and is connected at its output Side
output line 38 to the main.winding...Supply line 50 so that the to the main winding supply line 50. The Switch 70 Switches
main winding 36 of the motor is supplied directly with between a first position connecting the Second output line 38
power from the input line 25 connected to the main AC 50 to the Supply line 50 and a Second position connecting the
power system 21. The third output line 41 from the inverter third output line 41 to the main supply line 50 to provide
30 is connected through the transfer switch circuit directly to power from the inverter 30 to the main motor winding. The
the auxiliary winding Supply line 51 to Supply power to the relay Switch 71 is connected at an input side (to receive
auxiliary winding 37. The AC power system 21 typically power from the inverter) to the third output line 41 and to
provides power at 60 Hz in the United States (or 50 Hz in 55 receive power from the inverter through the capacitor 46 as
Europe and other areas), and the controller 55 operates the provided on the line 41, and is connected on its output Side
inverter 30 to provide output power on the line 41 at a to the line 51 to provide output power to the auxiliary
frequency of 60 Hz, but controlled to be approximately 90 winding 37. The Switch 71 switches from a first position
out of phase with the Voltage from the power System 21 So connecting the line 41 directly to the Supply line. 51 leading
that the power applied to the auxiliary winding 37 has the 60 to the auxiliary winding to a Second position connecting the
appropriate phase shift to develop start-up torque in the power from the inverter 30 through the capacitor 46 by
motor 35. When operation at a lower speed is desired, the connecting the line 48 to the auxiliary winding Supply line
operator provides a command to the controller 55 to Switch 51. The Switches 70 and 71 in the transfer Switch circuit.40
the positions of the transfer Switch circuit 40 such that the may also be implemented in other manners, e.g., by bilateral
Second input line 38 is disconnected from Supplying power 65 Semiconductor Switches, e.g., triacS or paralleled thyristors,
to the main winding 37, and the third output line 41 from the or any other device which provides appropriate Switching of
inverter is connected through the transfer Switch circuit to power. The controller 55 has a sense line 74 which is
 US 6,570,778 B2
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connected to the Second input line 25 to receive the Voltage order to, among other things, minimize ripple currents in the
on it from the AC power system. The controller monitors the inductive load. The comparator 124 typically has comple
AC power line Voltage to control the timing of Switching of mentary outputs 130 to control gate drive circuits 132 Such
the Switches 31 and 32 in the inverter 30, e.g., at 60 Hz with that both Switches 31 and 32 will not be in the on-state at the
an appropriate phase shift when Supplying power in the first same time. To Switch between the full-speed mode and the
mode to the auxiliary winding 37, and at a Selected lower lower-speed mode, the circuitry in controller 55 must gen
frequency (e.g., 30 Hz or half the power line frequency) erate the signal on control line 57 that commands the
when supplying power directly from the inverter 30 to the corresponding State of transfer Switch circuit 40. The opera
main winding 36 and through the capacitor 46 to the tor provides a command, using a Switch 140, or any equiva
auxiliary winding 37. Because the inverter 30 Supplies only lent means of controlling the logical State of the operating
the auxiliary winding 37 during full-speed operation and mode, to toggle as desired between full-speed mode and
both windings 36 and 37 in lower frequency half-speed lower-speed mode. Any Suitable control logic 142 can
operation, the adjustable Speed drive of the invention can be monitor the state of the Switch 140 and generate the appro
Smaller than conventional drives and have significantly priate control signal on line 57.
lower manufacturing costs. In addition, if desired, the trans 15 As shown in FIG. 4, the controller 55 of the invention can
fer Switch circuit 40 can be formed to allow operation in a be adapted to command a constant ratio between the inverter
default or failure mode bypassing the drive 20 entirely so fundamental Voltage on output line 41 and the fundamental
that power is Supplied directly from the power System 21 to frequency (volts/hertz), e.g., half Voltage at half frequency
the main winding 36 and through the capacitor 46 to the when the Switches 70 and 71 of FIG. 2 are in the lower
auxiliary winding 37. position. Such operation is known to optimize drive perfor
As shown in an exemplary embodiment in FIG. 3, the mance by, for example, avoiding Saturation at reduced
controller 55 has circuitry to generate Signals on control excitation frequency. In the preferred embodiment, with
lines 56 and 57. For inverter 30 to produce on output line 41 both a full-speed mode and a lower-speed mode, this con
a sinusoidal voltage which is shifted by 90 from the voltage stant volts/hertz operation would primarily benefit the
on the power system 21, the circuitry in controller 55 must 25 lower-speed mode in which motor excitation frequency can
generate the proper command Signals on control lines 56, be either fixed or variable. With reference to FIG. 4, F*
which together control the states of inverter Switches 31 and represents a desired excitation frequency command Signal,
32. The sense line 74 conducts sinusoidal voltage from the and V represents a voltage command Signal appropriately
AC power system 21 to a resistive voltage divider 90 which Scaled to conform to the desired ratio of volts/hertz. In the
Scales the Voltage to a level on the Voltage divider output line exemplary implementation, a digital-to-analog converter
92 that is appropriate for Signal processing. An analog-to (D/A) 150 generates a sinusoidal voltage signal on line 122
digital converter (A/D) 94 records and stores the most recent having an amplitude that is directly proportional to the
approximately 90 of the sinusoidal waveform of this volt excitation frequency, F. Comparator 124 then compares
age divider output line 92 for determination of waveform this sinusoidal waveform to a triangle wave to produce
characteristics, e.g. Voltage amplitude on the AC power 35 sinusoidal PWM Switching commands for Switches 31 and
system 21. The voltage divider output line 92 also feeds a 32 in the same manner as previously described.
comparator 96 that converts the Sinusoidal Signal to a logic The drive of the present invention may control a motor to
level Square wave on comparator output line 98. This operate at multiple discrete Speeds or at continuously vari
comparator output line 98 is an input to a phase-locked loop able speeds. The drive may also be used to control the
(PLL) 100 which produces on its output line 102 a square 40
auxiliary winding flux level in the full Speed mode, e.g., by
wave delayed with respect to the PLL input by 90. One low applying excitation Voltage to provide 20% of rated flux for
cost embodiment of Such a PLL uses an IC Such as Harris the winding to produce less torque ripple or to provide 100%
part number CD4046A. As depicted in FIG. 3, the key of the rated flux to maximize torque without incurring
elements of the PLL are the phase comparator 104, a Significant Saturation of machine flux paths.
low-pass loop filter formed by Series combination of a 45
The following illustrates an example of the adjustable
resistor 106 and a capacitor 108, and a voltage-controlled Speed drive of the invention as analyzed by computer
oscillator (VCO) 110. The phase comparator output drives Simulation. In this simulation, the parameters of a practical
the PLL output line 102. This output line feeds the low-pass % horsepower (HP) machine were used assuming a Supply
filter to produce an average value of the PLL Output wave voltage of 220 Vrms at the input of the drive. A steady-state
form on the VCO input line 112. The VCO 110 produces a 50
mathematical model was used in the computer modeling to
square wave on VCO output line 114 that is fed into the determine the operating points of the machine under various
Second input of the phase comparator 104 in Such a manner working conditions and.to calculate the optimal parameters
as to cause the PLL output line 102 to exhibit the same and Settings of the drive.
frequency as the Square wave on comparator output line 98
but shifted from it in phase by 90°. The phase-shifted square 55 First, Standard operation of the machine with a run
wave on PLL output line 102 provides timing and frequency capacitor of 10 uF, for which the motor was originally
information to a Square-to-Sine converter 120. Using this designed, was simulated to obtain a reference for the assess
information in conjunction with the approximately 90 of ment of the quality of the drive. FIG. 5 shows the torque
stored waveform sampled data from ADC 94, the square Speed characteristics. The Solid line denoted T. represents
to-Sine converter 120 generates on Signal line 122 a sinu 60 the resulting electromagnetic torque of the machine and the
soidal signal that is delayed by 90 from the sinusoidal dotted line denoted T shows the amplitude of the torque
signal on sense line 74 and the AC power system 21. This pulsations. FIG. 6 shows the dependencies of the current
phase-shifted Sinusoid on Signal line 122 is compared to a magnitudes in the main (I) and the auxiliary (I) windings.
triangle wave in a comparator 124 to produce Sinusoidal Second, full-speed operation was investigated. The
PWM switching commands for Switches 31 and 32. The 65 inverter Supplying the auxiliary winding was controlled to
triangle wave typically has much higher frequency than the generate a voltage of the same amplitude but shifted by 86
desired fundamental frequency of the inverter output in from the phase of the Voltage from the AC mains to achieve
 US 6,570,778 B2
10
phase quadrature of the currents. FIG. 7 shows the torque Compared to Simple Voltage reduction at a fixed excita
Speed characteristics of the drive. It can be noted that the tion frequency, an adjustable speed drive in accordance with
machine has quite high Starting torque when fed in this the invention can efficiently control motor rotational Veloc
manner. The relatively high value of the torque ripple is ity. Therefore, the invention can be incorporated into appli
mainly due to the limitation of the Voltage amplitude gen cations requiring motor Velocity regulation.
erated by the inverter. Balanced operation would require the The control algorithm for the controller 55 may be
magnitude of the Voltage for the auxiliary winding to be implemented in a universal control board based on a digital
approximately 30% above the magnitude of the voltage signal processor (e.g., TMS320 F240 from Texas
Supplying the main winding for this particular machine. This Instruments). The board may be connected to a PC computer
is, however, not achievable with a simple Suboscillation through the RS232 interface, which enables changes of
pulse-width-modulation (PWM) method as utilized in the control parameters in real time. The control algorithm may
Simulation. generate a PWM voltage waveform with variable amplitude
The dependencies of the magnitudes of currents in the and frequency with the ability to Synchronize the output with
main (I) and auxiliary (I) windings on the mechanical the line Voltage and to adjust the phase shift between the line
speed are presented in FIG.8. It can be seen that the current 15
and the generated waveform. Alternatively, the circuitry of
in the auxiliary winding is significantly lower than that in the the controller 55 may be substantially integrated as, for
main winding over the range of operating Speed considered example, in an application-specific integrated circuit
(with a slip of 6-8%), confirming that relatively low rated (ASIC).
inverter Switching devices may be used. It is understood that the invention is not confined to the
Comparison of FIGS. 7 and 8 with FIGS. 5 and 6 reveals particular embodiments Set forth herein as illustrative, but
that the drive provides in the full-speed mode significantly embraces all Such forms thereofas come within the Scope of
higher Starting as well as breakdown torques than the the following claims.
permanent split capacitor motor. On the other hand the What is claimed is:
produced torque ripple is higher for the drive. The Stator 1. An adjustable Speed drive for Single-phase induction
currents are comparable in both cases for the nominal 25
motorS having a main winding and an auxiliary winding
operating Speed. comprising:
Results of the numerical simulation of the start of the (a) first and Second input lines connectable to Single-phase
machine at full frequency (60 Hz) are illustrated in FIGS. 9 AC power lines,
and 10. A fan load characteristic was used in the Simulation. (b) a pair of DC bus lines;
FIG. 9 shows the resulting electromagnetic torque (T) and (c) a rectifier connected to the first and Second input lines
the mechanical speed (n) of the machine. The results confirm and to the DC bus lines: Such that, AC voltage applied
a higher content of torque pulsations in Steady-state opera to the input lines is rectified to a DC Voltage applied on
tion with the full load. This effect is, however, filtered to a the DC bus lines;
great extent by the moment of inertia of the machine and the (d) an inverter comprised of two gate controlled Switching
attached fan and has only a Small effect on the mechanical 35 devices connected together across the DC bus lines,
Speed. The waveforms of currents in the main. (I) and (e) a first output line connected to the first input line, a
auxiliary (I) windings are shown in FIG. 10. Second output line connected to the Second input line
Third, operation at a reduced Speed was analyzed. The and a third output line connected to a node between the
inverter produced a Voltage waveform with an amplitude of two gate controlled Switching devices, and
110 V, and a frequency of 30 Hz. A phase-shift capacitor 40 (f) a transfer Switch circuit connected to the Second and
of 30 uF was connected in Series with the auxiliary winding. third output lines, and connected to a main winding
The torque-Speed characteristic and the dependence of the Supply line and an auxiliary winding Supply line that
torque ripple on the speed are shown in FIG. 11. The value may be connected to the main winding and auxiliary
of the torque pulsations (T,) now has a local minimum near winding, respectively, of an induction motor, wherein
the expected operating point. FIG. 12 shows the currents in 45 the first output line may be connected to both the main
the main (I) and auxiliary windings (I) together with the winding and the auxiliary winding to complete the
overall current (I) drawn from the inverter. It can be noted circuit therethrough, and a phase-shifting capacitor
that the amplitude of the current supplied by the inverter is connected to the transfer Switch circuit, the transfer
comparable in both cases. The magnitude of the AC voltage Switch circuit having Switches Switchable between a
acroSS the phase-shifting capacitor plotted against the Speed 50 first position in which the Second output line is con
is shown in FIG. 13. nected directly to the main winding Supply line and the
The results of a simulated Start of the machine are given third output line is connected to the auxiliary winding
in FIGS. 14-16. FIG. 14 (torque T and speed n) and FIG. Supply line and a Second position in which the third
15 (stator currents I, and I) represent the quantities corre output line is connected directly through the transfer
sponding to those in FIGS. 9 and 10 for the full-speed 55 Switch circuit to the main winding Supply line and is
operation. FIG. 16 shows the resulting current (I, and I) also connected by the transfer Switch circuit through
Supplied by the inverter and the Voltage (V) across the the phase-shifting capacitor to the auxiliary winding
phase-shifting capacitor. Supply line.
Transitions between full-speed mode, lower-speed mode, 2. The adjustable speed drive of claim 1 further including
and other modes can be accomplished during operation of 60 a controller for the inverter connected to Switch the inverter
the motor 35. For example, after the motor is started by Switching devices to provide output power at a frequency
using the inverter 30 to drive the auxiliary winding 37, the corresponding to the input frequency from the AC Supply
invention can, for example, be adapted to Stop inverter 30 lines and at a phase shift of about 90 with respect to the AC
from Switching. In this way, the invention can provide power line power when the transfer Switch circuit is in its
enhanced Starting torque compared to Standard capacitor 65 first position.
Start motors and can disengage under electronic control 3. The adjustable speed drive of claim 2 wherein the
rather than through use of, for example, a centrifugal Switch. controller controls the inverter to provide a Voltage to the
 US 6,570,778 B2
11 12
auxiliary winding Supply line that will produce rated flux in complete the circuit therethrough, the transfer Switch
the auxiliary winding of a Selected motor. relay switchable between a first position in which the
4. The adjustable speed drive of claim 2 wherein the Second output line is connected by the first Switch
controller controls the inverter to Switch the Switching directly to the main winding Supply line and the third
devices to provide output power at a frequency lower than output line is connected by the Second Switch to the
the AC input line frequency when the transfer Switch circuit auxiliary winding Supply line and a Second position in
is in its Second position. which the third output line is connected by the first
5. The adjustable speed drive of claim 4 wherein the Switch directly to the main winding Supply line and is
controller controls the amplitude of the inverter Voltage to also connected by the Second Switch through the phase
vary in direct proportion to the variation in frequency of the shifting capacitor to the auxiliary winding Supply line.
inverter output power from the AC input line frequency. 11. The adjustable speed drive of claim 10 further includ
6. The adjustable speed drive of claim 4 wherein the ing a controller for the inverter connected to Switch the
controller controls the inverter Switching devices to Switch inverter Switching devices to provide output power at a
to provide output power at about 30 Hz when the transfer frequency corresponding to the input frequency from the AC
Switch circuit is in its Second position. 15 supply lines and at a phase shift of about 90 with respect to
7. The adjustable speed drive of claim 1 wherein the gate the AC power line power when the transfer Switch relay is
controlled Switching devices are Selected from the group in its first position.
consisting of IGBTs and MOSFETs. 12. The adjustable speed drive of claim 11 wherein the
8. The adjustable speed drive of claim 1 wherein the controller controls the inverter to provide a Voltage to the
transfer Switch circuit comprises a relay having two Single auxiliary winding Supply line that will produce rated flux in
throw Switches Switching together, a first of the Switches the auxiliary winding of a Selected motor.
connected to the Second output line and the third output line 13. The adjustable speed drive of claim 11 wherein the
on one side of the Switch and to the main winding Supply line controller controls the inverter to Switch the Switching
on another side of the Switch, a Second of the Switches devices to provide output power at a frequency lower than
connected to the third output line and connected to the third 25 the AC input line frequency when the transfer Switch relay
output line through the phase-shifting capacitor on one side is in its Second position.
of the Switch and to the auxiliary winding Supply line on 14. The adjustable speed drive of claim 12 wherein the
another side of the Switch. controller controls the amplitude of the inverter Voltage to
9. The adjustable speed drive of claim 1 wherein the vary in direction proportion to the variation in frequency of
rectifier comprises a pair of capacitors connected acroSS the the inverter output power from the AC input line frequency.
DC bus lines with a node between the capacitors connected 15. The adjustable speed drive of claim 12 wherein the
to the first of the input lines, and a pair of rectifying diodes controller controls the inverter Switching devices to Switch
connected together across the DC bus lines with a node to provide output power at about 30 Hz, when the transfer
between the diodes connected to the Second of the input Switch circuit is in its Second position.
lines. 35 16. The adjustable speed drive of claim 11 wherein the
10. An adjustable Speed drive for Single-phase induction gate controlled Switches are Selected from the group con
motorS having a main winding and.an auxiliary winding sisting of IGBTs and MOSFETs.
comprising: 17. The adjustable speed drive of claim 10 wherein the
(a) first and Second input lines connectable to Single-phase controller activates transitions of the relay in response to
AC power lines, 40 desired operation to achieve either full-speed mode in the
(b) a pair of DC bus lines; first position or lower-speed mode in the Second position.
(c) a pair of capacitors connected across the DC bus lines 18. An adjustable Speed drive for Single-phase induction
with a node between the capacitors connected to the motorS having a main winding and an auxiliary winding
first of the input lines; comprising:
45 (a) first and Second input lines connectable to Single-phase
(d) a pair of rectifying diodes connected together across AC power lines,
the DC bus lines, a node between the diodes connected
to the Second of the input lines Such that AC voltage (b) a pair of DC bus lines;
applied to the input lines is rectified by the diodes and (c) a rectifier connected to the first and Second input lines
applied on the DC bus lines to the capacitors, 50 and to the DC bus lines such that AC voltage applied to
(e) an inverter comprised of two gate controlled Switching the input lines is rectified to a DC voltage applied on
devices connected together across the DC bus lines, the DC bus lines;
(f) a first output line connected to the first input line, a (d) an inverter comprised of two gate controlled Switching
Second output line connected to the Second input line devices connected together across the DC bus lines,
and a third output line connected to a node between the 55 (e) a first output line connected to the first input line, a
two gate controlled Switching devices, and Second output line connected to the Second input line
(g) a transfer Switching relay having two Single throw and a third output line connected to a node between the
Switches that Switch together, a first of the Switches two gate controlled Switching devices, and
connected to the Second output line and the third output (f) a transfer Switch connected to the Second and third
line on one side of the Switch and to the main winding 60 output lines, and connected to a main winding Supply
Supply line on another side of the Switch, a Second of line that may be connected to the main winding of an
the Switches connected to the third output line and induction motor, wherein the first output line may be
connected to the third output line through a phase connected to both the main winding and the auxiliary
shifting capacitor on one side of the Switch and to the winding to complete the circuit therethrough, and a
auxiliary winding Supply line on another Side of the 65 phase-shifting capacitor connected between the third
Switch, wherein the first output line may be connected output line and the auxiliary winding Supply line, the
to both the main winding and the auxiliary winding to transfer Switch Switchable between a first position in
 US 6,570,778 B2
13 14
which the Second output line is connected to the main the AC power line power when the transfer Switch circuit is
winding Supply line and a Second position in which the in its first position.
third output line is connected to the main winding 20. The adjustable speed drive of claim 19 wherein the
Supply line. controller controls the inverter to Switch the Switching
19. The adjustable speed drive of claim 18 further includ devices to provide output power at a frequency lower than
ing a controller for the inverter connected to Switch the the AC input line frequency when the transfer Switch circuit
inverter Switching devices to provide output power at a is in its Second position.
frequency corresponding to the input frequency from the AC
supply lines and at a phase shift of about 90 with respect to k k k k k
 UNITED STATES PATENT AND TRADEMARK OFFICE
CERTIFICATE OF CORRECTION

PATENT NO. : 6,570,778 B2 Page 1 of 1

DATED : May 27, 2003
INVENTOR(S) : Lipo et al.

It is certified that error appears in the above-identified patent and that said Letters Patent is
hereby corrected as shown below:

Column 11
Line 2, please remove the period between the words "and.an" to read -- and an --.

Signed and Sealed this

Twenty-third Day of September, 2003

JAMES E ROGAN
Director of the United States Patent and Trademark Office