WO2004038906A1

WO2004038906A1 - Load and speed sensitive motor starting circuit and method

Info

Publication number: WO2004038906A1
Application number: PCT/US2002/033750
Authority: WO
Inventors: Young-Kee Min
Original assignee: Young-Kee Min
Priority date: 2002-10-22
Filing date: 2002-10-22
Publication date: 2004-05-06
Also published as: CA2501432A1; EP1559189A4; JP2006504379A; CN1723605A; EP1559189A1

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).

Description

APPLICATION FOR UNITED STATES PATENT

SPECIFICATION

LOAD AND SPEED SENSITIVE MOTOR STARTING CIRCUIT AND METHOD

FIELD OF THE INVENTION

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

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.

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.

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. 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.

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.

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.

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

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.

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

predeteriΗined speed, the auxiliary winding will again be switched back into the

circuit to boost the speed of the main motor winding. 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.

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

Fig. 1 schematically shows a typical environment in which the

preferred embodiment of the invention is used.

Fig. 2 is a schematic block circuit diagram illustrating a motor

starting circuit in accordance with the invention. Fig. 3 is a detailed circuit diagram of the circuitry of Fig. 2.

Fig. 4 is a timing diagram illustrating operation of the circuitry of

Figs. 2 and 3.

Fig. 5 is another timing diagram illustrating operation of the

circuitry of Figs. 2 and 3 as it relates to RPM information.

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

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.

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.

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 VI, 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 VI, V2, V3, a window pulse PI, 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

II, 12, 13 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 II, 12, 13 in relation to the main voltage

window pulses PI, 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.

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.

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.

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.

Claims

CLAIMSThe principles of this invention having been fully explained inconnection with the foregoing, I hereby claim as my invention:

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

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

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.