U.S. patent application number 10/532557 was filed with the patent office on 2006-08-10 for load and speed sensitive motor starting circuit and method.
Invention is credited to Young-Kee Min.
Application Number | 20060175999 10/532557 |
Document ID | / |
Family ID | 36779281 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060175999 |
Kind Code |
A1 |
Min; Young-Kee |
August 10, 2006 |
LOAD AND SPEED SENSITIVE MOTOR STARTING CIRCUIT AND METHOD
Abstract
A circuit and method measures the voltage at the main motor
winding (1) and detects the points in the electromagnetic wave
cycle at which this voltage "crosses" zero. The method and circuit
also measures the voltage at the auxiliary motor winding (2). The
voltages measured in the main winding (1) and in the auxiliary
winding (2) are compared by the circuit (13) as a means for
starting and restarting the auxiliary winding (2). The circuit and
method also detects the points in the electromagnetic wave cycle
where the current in the auxiliary winding "crosses" zero and
compares the phase of these current zero crossing points with a
window pulse (11) that is generated when the main voltage crosses
zero. When the zero current crossing points fall within the window
pulse, the auxiliary winding (2) is up to proper operating speed
and the auxiliary winding (2) is disconnected by the starting
circuit. If the load on the main motor winding (1) increases or the
main motor winding (1) speed decreases below a certain
predetermined speed, the auxiliary winding (2) is switched back
into the circuit to boost the speed of the main motor winding
(1).
Inventors: |
Min; Young-Kee; (Elm Grove,
WI) |
Correspondence
Address: |
JOSEPH S. HEINO, ESQ.;DAVIS & KUELTHAU, S.C.
111 E. KILBOURN
SUITE 1400
MILWAUKEE
WI
53202-6613
US
|
Family ID: |
36779281 |
Appl. No.: |
10/532557 |
Filed: |
October 22, 2002 |
PCT Filed: |
October 22, 2002 |
PCT NO: |
PCT/US02/33750 |
371 Date: |
April 22, 2005 |
Current U.S.
Class: |
318/437 ;
318/108 |
Current CPC
Class: |
H02P 1/44 20130101 |
Class at
Publication: |
318/437 ;
318/108 |
International
Class: |
H02K 23/16 20060101
H02K023/16 |
Claims
1. In an AC motor having a main winding and an auxiliary winding
both connectable to an AC power source, and having a switch for
disconnecting said auxiliary winding from said AC source, an
improved control circuit for said switch comprising main voltage
detector means for sensing the magnitude of the AC main winding
voltage, main voltage zero crossing detector means for sensing the
points at which main winding voltage polarity is instantaneously
reversed, window pulse generating means for generating a pulse at
the points at which main winding voltage polarity is reverse,
auxiliary voltage detector means for sensing the magnitude of the
AC auxiliary winding voltage, voltage comparator means for sensing
the difference in voltage magnitude between the main winding and
the auxiliary winding, auxiliary current zero crossing detector
means for sensing the points at which auxiliary current flow
changes direction, and phase comparator means for sensing the phase
shift between the main voltage zero crossing points and the
auxiliary current zero crossing points, wherein said phase
comparator means operates to disconnect said auxiliary winding when
the phase shift of the auxiliary winding current zero crossing
falls within the main voltage pulse as a function of motor
speed.
2. The control circuit of claim 1 wherein said voltage comparator
means operates to connect or reconnect said auxiliary winding when
the magnitude of the voltage of the auxiliary winding decreases
below a predetermined value relative to the magnitude of the
voltage of the main winding as a function of motor load and motor
speed.
3. The control circuit of claim 2 wherein said voltage comparator
includes pulse shape generating means for generating a first logic
pulse and said phase comparator includes pulse shape generating
means for generating a second logic pulse.
4. The control circuit of claim 3 wherein said first and second
logic pulses are used by a logic controller to turn said switch on
and off.
5. The control circuit of claim 4 wherein said switch comprises a
triac device that is triggered by a negative voltage value.
6. In an AC motor having a main winding and an auxiliary winding
both connectable to an AC power source, and having a switch for
disconnecting said auxiliary winding from said AC source, an
improved method for controlling said switch comprising the steps of
sensing the magnitude of the AC main winding voltage, sensing the
points at which main winding voltage polarity is instantaneously
reversed, generating a pulse at the points at which main winding
voltage polarity is reversed, sensing the magnitude of the AC
auxiliary winding voltage, sensing the difference in voltage
magnitude between the main winding and the auxiliary winding,
sensing the points at which auxiliary current flow changes
direction, and sensing the phase shift between the main voltage
zero crossing points and the auxiliary current zero crossing
points, wherein said phase shift operates to disconnect said
auxiliary winding when the phase shift of the auxiliary winding
current zero crossing falls within the main voltage pulse as a
function of motor speed.
7. The method of claim 6 including the step of connecting or
reconnecting said auxiliary winding when the magnitude of the
voltage of the auxiliary winding decreases below a predetermined
value relative to the magnitude of the voltage of the main winding
as a function of motor load and motor speed.
8. The method of claim 7 including the steps of generating a first
logic pulse as a result of voltage comparison and generating a
second logic pulse as a result of phase comparison.
9. The method of claim 8 wherein said first and second logic pulses
are used by a logic controller to turn said switch on and off.
10. The method of claim 9 including the step of providing a triac
device that is triggered by a negative voltage value as the
switch.
11. In an AC motor having a main winding and an auxiliary winding
both connectable to an AC power source, and having a swithch for
disconnecting said auxiliary winding from said AC source, an
improved control circuit for said switch comprising main voltage
detector means for sensing the magnitude of the AC main winding
voltage, main voltage phase detector means for provision of a
reference for phase comparison of main winding current phase
sensing. auxiliary voltage detector means for sensing the magnitude
of the AC auxiliary winding voltage, voltage comparator means for
sensing the difference in voltage magnitude between the main
winding and the auxiliary winding, auxiliary current phase detector
means for measuring the main winding phase shift, and phase
comparator means for sensing the phase shift between the main
voltage and the main winding current, wherein said phase comparator
means operates to disconnect said auxiliary winding when the phase
shift of the main winding falls within a predetermined value of the
phase relative to the main voltage as a function of motor
speed.
12. The control circuit of claim 11 wherein said voltage comparator
means operates to connect or reconnect said auxiliary winding when
the magnitude of the voltage of the auxiliary winding decreases
below a predetermined value relative to the magnitude of the
voltage of the main winding as a function of motor speed.
13. The control circuit of claim 12 wherein said voltage comparator
includes pulse shape generating means for generating a first logic
pulse and said phase comparator includes pulse shape generating
means for generating a second logic pulse.
14. The control circuit of claim 13 wherein said first and second
logic pulses are used by a logic controller to turn said switch on
and off.
15. The control circuit of claim 14 wherein said switch comprises a
triac.
16. In an AC motor having a main winding and an auxiliary winding
both connectable to an AC power source, and having a switch for
disconnecting said auxiliary winding from said AC source, an
improved method for controlling said switch comprising the steps of
sensing the magnitude of the AC main winding voltage, sensing the
points at which main winding voltage polarity is instantaneously
reversed, generating a pulse at the points at which main winding
voltage polarity is reversed, sensing the magnitude of the AC
auxiliary winding voltage, sensing the difference in voltage
magnitude between the main winding and the auxiliary winding,
sensing the points at which main current flow changes direction,
and sensing the phase shift between the main voltage zero crossing
points and the main current zero crossing points, wherein said
phase shift operates to disconnect said auxiliary winding when the
phase shift of the main winding current zero crossing falls outside
the main voltage pulse as a function of motor speed.
17. The method of claim 16 including the step of connecting or
reconnecting said auxiliary winding when the magnitude of the
voltage of the auxiliary winding decreases below a predetermined
value relative to the magnitude of the voltage of the main winding
as a function of motor speed.
18. The method of claim 17 including the steps of generating a
first logic pulse as a result of voltage comparison and generating
a second logic pulse as a result of phase comparison.
19. The method of claim 8 wherein said first and second logic
pulses are used by a logic controller to turn said switch on and
off.
20. The method of claim 9 including the step of providing a triac
device that is triggered by a negative voltage value as the
switch.
21. In an AC motor having a main winding and an auxiliary winding
both connectable to an AC power source, and having a switch for
disconnecting said auxiliary winding from said AC source, an
improved control circuit for said switch comprising main voltage
detector means for sensing the magnitude of the AC main winding
voltage, main current phase detector means for provision of a
reference for phase comparison of auxiliary current phase sensing.
auxiliary voltage detector means for sensing the magnitude of the
AC auxiliary winding voltage, voltage comparator means for sensing
the difference in voltage magnitude between the main winding and
the auxiliary winding, auxiliary current phase detector means for
measuring the auxiliary winding phase shift, and phase comparator
means for sensing the phase shift between the main current and the
auxiliary current, wherein said phase comparator means operates to
disconnect said auxiliary winding when the phase shift of the
auxiliary winding current falls within a predetermined value of the
phase relative to the main winding current as a function of motor
speed.
22. The control circuit of claim 21 wherein said voltage comparator
means operates to connect or reconnect said auxiliary winding when
the magnitude of the voltage of the auxiliary winding decreases
below a predetermined value relative to the magnitude of the
voltage of the main winding as a function of motor speed.
23. The control circuit of claim 22 wherein said voltage comparator
includes pulse shape generating means for generating a first logic
pulse and said phase comparator includes pulse shape generating
means for generating a second logic pulse.
24. The control circuit of claim 23 wherein said first and second
logic pulses are used by a logic controller to turn said switch on
and off.
25. The control circuit of claim 24 wherein said switch comprises a
triac.
26. In an AC motor having a main winding and an auxiliary winding
both connectable to an AC power source, and having a switch for
disconnecting said auxiliary winding from said AC source, an
improved method for controlling said switch comprising the steps of
sensing the magnitude of the AC main winding voltage, sensing the
points at which main winding voltage polarity is instantaneously
reversed, generating a pulse at the points at which main winding
voltage polarity is reverse, sensing the magnitude of the AC
auxiliary winding voltage, sensing the difference in voltage
magnitude between the main winding and the auxiliary winding,
sensing the points at which the main current flow changes
direction, sensing the points at which auxiliary current flow
changes direction, and sensing the phase shift between the main
current zero crossing points and the auxiliary current zero
crossing points, wherein said phase shift operates to disconnect
said auxiliary winding when the phase shift of the auxiliary
winding current zero crossing is within a predetermined time
relative to the main current zero crossing as a function of motor
speed.
27. The method of claim 26 including the step of connecting or
reconnecting said auxiliary winding when the magnitude of the
voltage of the auxiliary winding decreases below a predetermined
value relative to the magnitude of the voltage of the main winding
as a function of motor speed.
28. The method of claim 27 including the steps of generating a
first logic pulse as a result of voltage comparison and generating
a second logic pulse as a result of phase comparison.
29. The method of claim 28 wherein said first and second logic
pulses are used by a logic controller to turn said switch on and
off.
30. The method of claim 29 including the step of providing a triac
device that is triggered by a negative voltage value as the switch.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to alternating
current (AC) motors and to disconnect switches and circuits for use
with AC motors. More specifically, the present invention relates to
a circuit and method used with the start, or auxiliary, winding of
an AC motor wherein the auxiliary winding is energized when
starting the motor from rest and then disconnected at a given motor
speed. The present invention also relates to such a circuit and
method used with both split-phase and capacitor-start motors.
BACKGROUND OF THE INVENTION
[0002] It is well known that a single-phase AC motor produces an
alternating magnetic field, one pulling first in one direction,
then in the opposite direction as the polarity of the magnetic
field changes. This is because the single-phase AC motor is
energized by a single alternating current source. The major
distinction between the different types of single-phase AC motors
is how they go about starting the motor in a particular direction.
Motor start is usually accomplished by some device or circuit that
introduces a phase-shifted magnetic field on one side of the motor
shaft, or rotor.
[0003] Split-phase motors achieve their starting capability by
having two separate windings wound in the motor stator. The two
windings are separated such that one winding is used only for
starting. The starting, or auxiliary, winding is wound with a
smaller wire size having higher electrical resistance than the main
windings. Both windings are energized when the motor is started.
The starting winding produces a field that appears to rotate. This
rotation causes the motor to start. A centrifugal switch then
disconnects the starting winding when the motor reaches a
predetermined speed.
[0004] The winding and centrifugal switch arrangement of a
capacitor-start motor is similar to that used in a split-phase
motor. In the capacitor-start motor, a capacitor is used in series
with the starting winding to produce a phase shift and the
appearance of a rotating field. Here again, when the motor
approaches a predetermined running speed, the starting switch opens
thereby disconnecting the starting winding and the motor continues
to run. One starting circuit for use with a motor of this type is
disclosed in U.S. Pat. No. 4,622,506. The method and apparatus of
the present invention is an improvement of that starting
circuit.
[0005] Various types of switches, and controls therefor, are also
well known in the electrical arts. This includes the mechanical
switch and the centrifugal actuator mounted on the motor rotor, as
alluded to previously. Mechanical switches of the centrifugal type
are subject to problems such as limited life, fatigue, friction,
vibration, mounting position, contact wear, among others. Also, the
centrifugal switch includes a radial member that blocks axial
airflow through the motor, which may impair cooling. This radial
member also requires additional room in the motor housing, which
may be objectionable in various applications.
[0006] In another known start winding disconnect system, Hall
effect sensors or pick-up coils are used to detect motor speed to
actuate a disconnect switch. This approach may be objectionable
because of the requirement of adding an extra element such as a
magnet on the motor shaft, and the pick-up coil to sense speed.
These extra parts and the assembly required may be cost
objectionable.
[0007] In another known disconnect system, a timer is started upon
initial energization of the motor. When the timer times out, the
disconnect switch is actuated to disconnect the auxiliary winding.
This approach is not load or speed sensitive, but rather
disconnects the auxiliary winding only after a preselected time
regardless of motor speed and regardless of load. This approach is
limited to dedicated applications where the load on the motor is
known beforehand, and the delay time set accordingly. If the load
on the motor is increased, the motor speed will not be up to the
desired threshold at the noted cutout time. On the other hand, if
the load on the motor is decreased, the motor will accelerate
faster, and full voltage will be applied across the capacitor for a
longer time than is desired, which in turn may damage the motor
and/or the capacitor. Capacitor burn-out is a significant problem
when reducing the loading of the motor in timed disconnect
systems.
[0008] Another known approach is to sense current through the main
winding and then actuate the disconnect switch at a designated
condition. This requires a current sensor in series with the main
winding and the start or auxiliary winding, which is objectionable
to many manufacturers because of the cost of the extra components
and the assembly cost of modifying the circuit and inserting such
components in series in the circuit. This approach may also be
objectionable due to the extra wattage and heat because current is
still flowing through the sensor in the run mode after
starting.
SUMMARY OF THE INVENTION
[0009] The present invention addresses and solves the above noted
and other problems in a particularly simple and effective
electronic control system for an auxiliary winding disconnect
switch. The invention is load and speed sensitive, and is AC line
voltage fluctuation insensitive. The invention eliminates the need
for extra components on the motor shaft, around the shaft, or in
series in the motor circuit. There is no need for physical
modification of the motor components or the windings.
[0010] The present invention provides a new and useful circuit and
method for measuring the voltage at the main motor winding and
detecting the points in the electromagnetic wave cycle at which
this voltage "crosses" zero. In other words, it detects the points
at which the main motor winding voltage switches instantaneously
from positive to negative and vice versa. The method and circuit
also measures the voltage at the auxiliary motor winding. The
voltages measured in the main winding and in the auxiliary winding
are each compared by the circuit as a means for starting and
restarting the auxiliary winding. The circuit and method also
detects the points in the electromagnetic wave cycle where the
current in the auxiliary winding "crosses" zero and compares the
phase of these current zero crossing points with a window pulse
that is generated when the main voltage crosses zero. When the zero
current crossing points fall within the window pulse, this means
that the auxiliary winding is up to proper operating speed and the
auxiliary winding is disconnected by the starting circuit. If the
load on the main motor winding increases thereby causing the motor
rotor speed to decrease below a certain predetermined speed, the
auxiliary winding will again be switched back into the circuit to
boost the speed of the main motor winding.
[0011] As previously alluded to, the present invention provides an
improvement over the circuit disclosed and claimed in U.S. Pat. No.
4,622,506. In the circuit of that embodiment, one was always
measuring the voltage across the auxiliary winding. In the circuit
of the present invention, one is always measuring the current zero
crossing points in the auxiliary winding. More specifically, when
the switch to the auxiliary winding is closed, the voltage of the
auxiliary winding has no meaning because it contains no information
as to motor speed, or RPM. This is why the auxiliary current is
measured at this condition. When the switch is open, no current is
passing through the auxiliary winding and there is no current
information that is available. This is why the auxiliary winding
voltage is measured at this condition, based on RPM information
available.
[0012] Other aspects and advantages of the new and useful circuit
and method will be apparent to those having skill in the art upon
review of the attached drawings and the following detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 schematically shows a typical environment in which
the preferred embodiment of the invention is used.
[0014] FIG. 2 is a schematic block circuit diagram illustrating a
motor starting circuit in accordance with the invention.
[0015] FIG. 3 is a detailed circuit diagram of the circuitry of
FIG. 2.
[0016] FIG. 4 is a timing diagram illustrating operation of the
circuitry of FIGS. 2 and 3.
[0017] FIG. 5 is another timing diagram illustrating operation of
the circuitry of FIGS. 2 and 3 as it relates to RPM
information.
DETAILED DESCRIPTION
[0018] Referring now to the drawings in detail wherein like
numbered elements represent like elements throughout, FIG. 1 shows
a main winding 1 and auxiliary winding 2 of an AC motor that are
each connected to an AC power source 3. When the motor reaches a
given threshold speed, a switch 5 that is connected in series with
the auxiliary winding 2 is opened to disconnect the auxiliary
winding 2 from the power source 3. A current detection means 6 is
also provided for detecting and measuring the current flow through
the auxiliary winding 2 when it is energized. The current detection
means 6 provides the circuit of the present invention with the
capability of detecting the points in the sinusoidal AC current
waveform at which the current of the auxiliary winding 2 "crosses"
the zero point. This will also be called the "current zero
crossing" of the auxiliary winding 2. The significance of this will
become more apparent later in this detailed description.
[0019] FIG. 2 shows a control circuit, generally identified 10,
including main voltage detecting means 7 for sensing the magnitude
of voltage across the main winding 1, and auxiliary voltage
detector means 8 for sensing the magnitude of voltage across the
auxiliary winding 2. A voltage comparator means 13 is provided
which is responsive to the main and auxiliary voltage detectors 7,
8, respectively, and responds to a given relation between the
magnitudes of the main and auxiliary winding voltages. A main
voltage zero crossing means 9 is provided which senses the
sinusoidal AC voltage waveform of the main winding voltage and the
points at which the main winding voltage "crosses" zero or switches
polarity. Window pulse means 11 responds to the main voltage zero
crossing means 9 and generates a window pulse. The width of the
window pulse that is generated is not a limitation of the present
invention. An auxiliary winding current zero crossing means 12 is
provided which senses the current flow through the auxiliary
winding 2 and the points at which the auxiliary winding current
also "crosses" zero or switches flow direction, as was mentioned
previously. A phase comparison means 14 is provided which senses
the auxiliary current zero crossing points in relation to the main
voltage window pulse that has been generated. The voltage
comparison means 13 generates a pulse shape 15 and the phase
comparison means 14 generates a pulse shape 16 as well. Logic means
17 is provided to respond to the pulse shapes 15, 16 to turn "off"
or to turn "on" the switch 5. This can be done, for example, by
means of a triac driver 18 to disconnect or reconnect,
respectively, the auxiliary winding 2 from the AC power source 3.
In effect, the triac driver 18 is switched on and off by negative
voltage, which will become apparent later in this detailed
description.
[0020] FIG. 3 shows the detailed circuitry for the schematic shown
in FIG. 2 and like reference numerals are used to facilitate
clarity. There are various portions of the detailed circuitry that
correspond to the various functions illustrated in FIG. 2. For
example, the final logic 17 portion of the schematic shown in FIG.
2 corresponds to the NAND gate 86 shown in FIG. 3. The gate 86 is
used with other circuit components to trigger the triac 90 and to
turn the auxiliary winding 2 on and off. A pair of windings 91, 92
are transformer windings that effectively provide current sensing
means for the auxiliary winding 2.
[0021] Again referring to FIG. 3, a power supply portion of the
circuit includes a pair of transistors 55, 56 that are connected to
other components including a pair of zener diodes 78, 79, a
resistor 44 and a capacitor 67. The voltage across the main winding
1 is the same as the potential as across the resistor 43, the
capacitor 69 and the diode 77. The main voltage sensing 7 portion
of the circuit includes other resistors 36, 37, 38, capacitor 64,
and a diode 73. The auxiliary voltage sensing 8 portion of the
circuit includes the resistors 39, 40, 41, 42, the capacitor 65,
the diode 74 and the transistor 53. Voltage comparison 13 is
accomplished by use of a comparator 81. In actuality, the
comparator 81 is one-fourth of a quad comparator chip, or other
integrated circuit, which provides access to other comparators 80,
82, 83. Specifically, the input pin 6 of the comparator 81 senses
the main winding voltage 7 and the input pin 7 of the same
comparator 81 senses the auxiliary winding voltage 8. The output
pin 1 of the comparator 81 feeds into the resistor 45 and the input
pin 6 of the NAND gate 85. Depending upon the input at the input
pin 5 of the gate 85, a pulse shape 15 is generated at the output
pin 4 of the gate 85. The significance of this will be discussed
later in this detailed description.
[0022] Referring now to the main voltage zero crossing 9 and the
auxiliary current zero crossing 12 portions of the circuit 10, it
will be seen that the voltage 7 across the main motor winding 1 is
at the same potential as that across the resistors 20, 21 of the
circuit shown in FIG. 3. Also included in the main voltage zero
crossing 9 portion of the circuit are two transistors 50, 51, a
resistor 22 and a capacitor 60. A delay portion of the circuit is
also provided by the resistors 23, 24, 25, 26, the diode 70, the
transistor 52 and the capacitor 61. As previously discussed,
another comparator 80 is provided, the output pin 2 of which feeds
into a pulse shape generator 11 portion of the circuit. The pulse
shape generator 11 portion of the circuit includes the resistors
27, 46 and the capacitor 68.
[0023] The auxiliary winding current zero crossing 12 portion of
the circuit includes the remaining pair of comparators 82, 83, a
number of resistors 28, 29, 30, 31, 32, 33, 34, 35, a pair of
capacitors 62, 63 and a pair of diodes 71, 72. As shown, the output
pins 13, 14 of the comparators 82, 83, respectively, feed into one
of the input pins 2 of a phase comparator gate 84. The output pin 3
of the phase comparator gate 84 generates a pulse 16 on the "stop"
side of the circuit by means of the resistor 47, the capacitor 66
and the diode 75. This output is fed into the input gate 8 of the
final logic gate 86. In this fashion, the pulse shapes 15, 16 are
used to turn the triac driver 18 "on" and "off" as required. The
triac switching circuit is provided by virtue of the resistors 48,
49 and the transistor 57 at the output pin 10 of the logic gate 86.
By use of this configuration, the triac driver 18 is switched on
and off by negative voltage. See FIG. 2.
[0024] The initial starting of the motor on application of line
voltage 3 is activated by means of the voltage comparison 13. The
voltage comparison 13 senses the low auxiliary winding voltage
relative to the main winding voltage and initiates the triac turn
on through logic 17. Immediately after the first turn on, the
auxiliary winding 2 is kept energized by the phase comparison 14.
The voltage comparison 13 cannot be used to maintain the starting
condition because, after the first energization of the auxiliary
winding 2, the voltage on the auxiliary winding 2 is that of the
line voltage source 3, and does not represent the motor speed by
means of induced voltage from the main winding 1 through the rotor.
The maintenance of the auxiliary energization by means of winding
current phase controls is explained in following paragraphs.
[0025] Referring now to FIG. 4, it will be demonstrated how the
main voltage detecting means 7 in the circuit of the present
invention views the magnitude of the main winding voltage, shown in
the top graph as a generally sinusoidal waveform. The graph below
it shows the points V1, V2, V3 at which the main winding voltage
crosses zero. That is, the points at which voltage polarity is
instantaneously reversed. The next graph illustrates that, at each
of these voltage zero crossing points V1, V2, V3, a window pulse
P1, P2, P3, respectively, is generated by the window pulse means
11. As the speed of the motor "ramps up" or increases, the
auxiliary winding current zero crossing means 12 senses the current
flow through the auxiliary winding 2 and the points I1, I2, I3 at
which the auxiliary winding current "crosses" zero or switches flow
direction. Phase comparison means 14 is provided to sense the
auxiliary winding current zero crossing points I1, I2, I3 in
relation to the main voltage window pulses P1, P2, P3. As the
auxiliary current zero crossing point 13, for example, falls within
the window pulse P3, the phase comparator 14 generates a pulse
shape 16 to be received by the logic control 17 and turn off the
triac driver 18. If, because of load increase causing a reduction
of motor speed, the auxiliary winding 2 needs to be reenergized,
the voltage comparison means 13 is activated to the restart
condition, which is the same as the initial motor start condition.
The starting sequence is thereby reactivated to connect the
auxiliary winding 2. The sequence is that voltage comparison 13 is
activated by the sensing of a low auxiliary winding voltage 2
relative to the main winding voltage 1. This sensing is used for
initial turn on the triac 18 after which the phase comparison means
14 is used to maintain the auxiliary winding 2 reenergization until
the motor speed increases to the desird auxiliary winding
denergization speed.
[0026] Referring now to FIGS. 1 and 5, it will be seen that
function of the circuit is derived from the accessibility of RPM
information of the motor. For example, when the switch 5 is open,
the auxiliary voltage provides RPM information and there is no
auxiliary current available. That is, the auxiliary winding voltage
is really a function of the voltage across the main winding 1 and
the motor RPM. The voltage across the auxiliary winding 2 has a
direct relationship to the motor RPM. When the switch 5 is closed,
the auxiliary voltage is the same as the line voltage and it
contains no RPM information. On the other hand, the auxiliary
current zero crossing does have RPM information. This is translated
as shown in the uppermost figure showing the switch 5 "on" and
"off" positions. As the switch 5 is initially closed, the speed of
the motor "ramps up" to the point that the auxiliary winding 2 can
be "cut out" of the circuit and the switch 5 opened up. During this
time, auxiliary current zero crossing is determined by the circuit.
After the switch 5 opens up, there is no current flowing through
the auxiliary winding 2 and the voltage across the auxiliary
winding 2 is a function of the voltage across the main winding 1
and the motor RPM. As the motor continues and RPM decreases due to
load imposed on the motor, the switch 5 again needs to be closed to
increase the motor torque to try and regain speed. This switch 5
closure "boosts" the motor so that the RPM increases to the point
that the auxiliary winding 1 no longer needs to be energized. This
continues throughout the operation cycle of the motor.
[0027] Accordingly, it will be apparent that there has been
provided a new and useful circuit and method for measuring the
voltage at the main motor winding and detecting points in the
electromagnetic wave cycle where the main winding voltage "crosses"
zero. The method and circuit also measures the voltage at the
auxiliary motor winding. The voltages measured in the main winding
and the auxiliary winding are each compared by the circuit as a
means for starting and restarting the auxiliary winding. The
circuit and method also detects the points in the electromagnetic
wave cycle at which the current in the auxiliary winding "crosses"
zero and compares the phase of these current zero crossing points
with a window pulse that is generated when the main winding voltage
crosses zero. When the zero current crossing point falls within the
window pulse, the auxiliary winding is up to proper operating speed
and the auxiliary winding is disconnected by the switching circuit.
If the load on the motor increases causing the motor speed to
decrease below a certain level, the auxiliary winding will again be
switched back into the circuit to boost the speed of the main motor
winding.
[0028] The scope of this invention is to include deenergization of
the auxiliary winding based on current phase changes with motor
speed of the main winding and/or the auxiliary winding current.
With the auxiliary winding energized, both the main winding and
auxiliary winding current phases change with motor speed during the
motor starting or slowing. The disclosed circuit functions on the
phase shift of the auxiliary winding relative to the line voltage
phase. The main winding current phase shift with motor speed change
is in the opposite direction as found for the auxiliary current. A
change in logic and the circuit location of the current sensor from
the auxiliary winding to the main winding could have been made to
activate the deenergization of the auxiliary winding on the phase
shift of the main winding current relative to the line voltage.
Further, with two current sensors, the deactivation could have been
activated by comparison of the phase of the auxiliary winding
relative to the main winding. The circuit previously described in
detail is an embodiment based on an attempt to minimize the cost of
achieving the desired control. it is to be understood that the
scope of the disclosure and appended claims are not limited to the
specific embodiments described and depicted herein.
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