GB2071938A - Control system for AC induction motors - Google Patents

Control system for AC induction motors Download PDF

Info

Publication number
GB2071938A
GB2071938A GB8105779A GB8105779A GB2071938A GB 2071938 A GB2071938 A GB 2071938A GB 8105779 A GB8105779 A GB 8105779A GB 8105779 A GB8105779 A GB 8105779A GB 2071938 A GB2071938 A GB 2071938A
Authority
GB
United Kingdom
Prior art keywords
control system
connection
signal
power
wye
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8105779A
Other versions
GB2071938B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Borg Warner Corp
Original Assignee
Borg Warner Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Borg Warner Corp filed Critical Borg Warner Corp
Publication of GB2071938A publication Critical patent/GB2071938A/en
Application granted granted Critical
Publication of GB2071938B publication Critical patent/GB2071938B/en
Expired legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
    • H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
    • H02P1/26—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual polyphase induction motor
    • H02P1/32—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual polyphase induction motor by star-delta switching
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
    • H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
    • H02P1/26—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual polyphase induction motor
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
    • H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
    • H02P1/42—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
    • H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
    • H02P1/42—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor
    • H02P1/44—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor by phase-splitting with a capacitor
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
    • H02P25/04—Single phase motors, e.g. capacitor motors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/16—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using ac to ac converters without intermediate conversion to dc
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor

Abstract

A control system for reconnecting the primary windings of AC induction motor (14) into a wye-connection for coupling to a source of three-phase electric power at light loads to effect energy savings includes switching means (68), power sensing means (46), and differential comparator means (66). The comparator means is responsive to a control signal (64) and an adjustable reference signal (72) for generating an actuating signal (70) for operation of the switching means (68). Upon the occurrence of the control signal, which is directly proportional to the power applied to the induction motor, decreasing below a predetermined level, the differential comparator means deactivates the switching means to cause reconnection of the induction motor to the electric power source by a wye- connection.

Description

SPECIFICATION Control system for AC induction motors This invention relates generally to a control system for AC induction motors and more particularly, it relates to a control system for reconnecting the primary windings of an AC induction motor in a wye-connection at light loads to effect energy savings.
In U. S. Patent No.2,106,833 issued to W. F. Eames on February 1,1938, there is disclosed a motor and control system for operating a moving stairway by connecting the primary windings of the motor in a star connection for low speed and changing the primary windings from the star connection to a delta connection for high speed when needed for carrying passengers. A light-sensitive device was utilized to detect the presence of persons for controlling the stairway to operate at the low and high speeds.
In U. S. Patent No. 2,709,775 issued to A. Del Carlo on May 1955, there is disclosed an automatic regulation system for electric machines in which the motorwindings are switched from delta to star connection only for such load variations which are maintained for a certain length of time. The switching operation is in response to the amount of current supplied to the motor which corresponds to a predetermined load condition.
In U. S. Patent No.3,764,872 issued to W. K. Boice on October 9, 1973, there is disclosed an apparatus for damping motor speed oscillations in an a-c adjustable speed motor drive system which includes a current detector to provide an in-phase signal that varies in accordance with the variations in the speed of the motor.
In U. S. Patent No. 3,863,741 issued to Y. Mitsuishi on February 4, 1975, there is shown a control system for reel assembly winding and unwinding a power supply cable of an electrically powered earthmoving machine which includes a three-phase induction torque motor mechanically driving the reel assembly. The torque motor is selectively connected to an electric source by a wye-connection when the machine moves forward and by a delta-connection when the machine moves backward. A shift lever is utilized for changing the moving direction of the machine which is connected to the gear box.
In U. S. Patent No. 4,084,406 issued to D. A.
Brenneman on April 18, 1978, there is shown a solid state starter for a chiller compressor motor which includes a motor current sensing circuit which controllably switches a bank of silicon-controlled rectifiers to conduct current to the motor for starting and running.
In various applications of machines such as centrifugal turbocompressors driven byAC induction motors, the operation of the motors is subjected to a wide range of load conditions. It is known that such motors can be constructed to operate with high efficiency and power factor values during full load conditions, but when the motors are operated at reduced or light load conditions the efficiency and power factor are substantially decreased thus causing the waste of energy. It has been found that significant improvements in efficiency and power factor can be achieved by reconnecting the primary windings of such motors in a wye-connection for coupling to the electric source in response to the power delivered to the motor load dropping below a pre-selected level.
Accordingly, it is a general object of the present invention to provide a new and improved control system for reconnecting the primary windings of an electric motor in a wye-connection at light loads to effect energy savings.
It is another object of the present invention to provide a control system for reconnecting the prim arywindings of an electric motor in a wyeconnection for coupling to the electric source in response to the power delivered to the motor load dropping below a pre-selected level.
It is another object of the present invention to provide a control system for reconnecting the primary windings of an electric motor in a wyeconnection which includes a differential comparator circuit for generating an actuating signal to operate a switching device so as to establish alternately and selectively a first connection and a second connection between an electric motor and an electric source.
It is still another object of the present invention to provide a control system for reconnecting the primary windings of an electric motor in a wyeconnection which includes a wye-delta starter for connecting the electric motor to a source of electric power.
It is still another object of the present invention to provide a control system which includes a switching device, the power transducer, and a differential comparator circuit all operatively connected so as to reconnect the primary windings of an electric motor into a wye-connection for coupling to an electric source in response to the power delivered to the motor load dropping below a preselected level.
It is yet still another object of the present invention to provide a control system which is relatively simple in construction and easy to manufacture.
In accordance with these aims and objectives, there is provided in accordance with the instant invention a control system for reconnecting the primary windings of an electric motor into a wyeconnection for coupling to an electric source which includes a wye-delta switching device, a power transducer, and a differential comparator circuit. The switching device is operatively interconnected between an electric source and the electric motor. A power transducer generates a control signal proportional to the power applied to the electric motor.The differential comparator circuit includes an operational amplifierwhich is responsive to the control signal and an adjustable reference signal for generating an actuating signal which causes operation of the switching device so as to establish alternately and selectively a first position and a second position between the electric motor and the electric source.
Normally, in the operation during full load conditions the switching device is in the second position for connecting the electric motor to the electric source by a delta connection. Upon the occurrence of the power applied to the motor load decreasing below a pre-selected level, the switching device is actuated by the actuating signal for reconnecting the switching device back to the first position so as to connect the electric motor to the electric source by a wye connection.
These and other objects and advantages of the present invention will become more fully apparent from the detailed description when read in conjunction with the accompanying drawing in which there is shown a schematic block diagram of a control system for reconnecting the primary windings of an electric motor in a wye-connection for coupling to an electric source constructed in accordance with the present invention.
Referring now with particularity to the drawing, there is shown a schematic block diagram of a control system 10 constructed in accordance with the principles of the instant invention. The control system includes a switching device 12 such as a wye-delta controller or starter connected between a three-phase AC electric power source and a load circuit consisting of a three-phase AC induction motor 14. The power source is connectable to input terminals 16, 18, and 20 of the switching device 12 via the polyphase input lines L1, L2 and L3. The output terminals 22,24 and 26 of the switching device are joined to the respective polyphase lines 28,30, and 32. The terminals 14a, 14b, and 14c are each tied to one end of the respective primary windings of the motor 14 and also to the respective polyphase lines 28,30 and 32.Conductors 34,36 and 38 are connected between the respective output terminals 40,42, and 44 of the switching device and the respective terminals 14d, 14e, and 14fofthe motor 14. These terminals 14d, 14e and 14f are also joined to the other ends of the primarywindings of the motor 14.
The control system comprises power sensing means which includes a power or watt transducer 46, a wye-box 48, and a current transformer 50. For sensing the voltage from phase to neutral applied to the motor 14, the wye-box 48 is used to provide a pseudo-neutral point by having its input via lines 52 and 54 connected to the polyphase lines 30 and 28, respectively. For measuring the current drawn by the motor 14, the current transformer is disposed around the polyphase line 32. The power transducer 46 has its current input terminals connected to the current transformer 50 via conductors 56 and 58. The voltage input terminals of the power transducer 46 is connected to the output of the wye-box 48 via line 60 and to the polyphase line 32 via conductor 62.A control signal is generated on the output of the power transducer 46 on the conductor 64 which is directly proportional to the power applied to the induction motor 14.
The differential comparator circuit consist of an operational amplifier 66 and a three pole doublethrow relay 68 connected to the output of the amplifier 66 via line 70. The operational amplifier 66 has its inverting input terminal connected to a positive dc voltage via a potentiometer 72 so as to provide an adjustable threshold or reference signal.
The non-inverting input of the amplifier 66 is coupled to a fixed resistor 74 and a potentiometer 76.
The other end of the resistor 74 is connected to the output of the power transducer 46 via the line 64.
The other end of the potentiometer 76 is connected to the output of the operational amplifier 66. The relay 68 is provided with three normally opened contacts (not shown) which are operatively in a conventional manner for operating the switching device 12.
The watt transducer 46 is preferably of the type manufactured and sold by Ohio Semitronics, Inc.
under their designation of model number PC5-36D.
The wye-box 48 is formed by interconnecting appropriate resistance values with the voltage terminals of transducer 46 so as to produce a wye networkwith a pseudo-neutral point.Thewye-delta controller 12 can be of any conventional commercially available type, the specific current rating on the controller contacts being selected to be of suitable value for the desired motor load.
Initially, it is assumed that the electric power is applied to the polyphase lines L1, L2 and L3 and the operation of the induction motor 14 is to be at a reduced or light load. Thus, the control voltage on line 64 which is directly proportional to the power applied to the motor will be below the adjustable reference signal applied to the inverting input of the operational amplifier 66. Typically, this threshold or reference signal is set to a pre-selected value equal to approximately 40% of the full load condition. In this condition, the output of the amplifier 66 on the line 70 will be a low voltage thereby maintaining the relay 68 in its deenergized state. This causes the switching device to connect the electric power source to the primary windings of the motor 14 in the wye-connection.
Upon an increase in the control signal on line 64 due to a increase in the power applied to the load, the output of the amplifier 66 will change to a high voltage once the control signal exceeds the reference signal set by the potentiomotor 72. The high voltage on line 70 will cause the relay 68 to become energized so as to close the three not-shown normally open contacts. This causes the switching device to be switched selectively and alternately from the wye-connection to a delta-connection so that the motor can be operated for full load conditions. Once the power applied to the motor load decreases below a pre-determined value, the relay will become deenergized again and the switching device will automatically change back for reconnecting a primary windings of the motor into a wye-connection for coupling to the electric source. The potentiometer 76 provided in the feedback of the amplifier 66 defining a hysteresis adjustment is utilized to set this pre- - determined level. Generally, the reconnection is effected when the power drops to 30% of the full load power value, which avoids the rapid switching of back and forth between the wye and delta connections due to spurious load fluctuations or oscillations.
From the foregoing detailed discussion it can thus be seen that the present invention provides a new and improved control system which includes a power transducer for sensing the power applied to a motor load so as to cause reconnecting the primary windings of the electric motor into a wye connection at light loads to effect energy savings. Further, the control system includes a differential comparator circuit for generating an actuating signal which causes operation of a switching device so as to establish alternately and selectively a wyeconnection and a delta-connection between the induction motor and the electric power source.
While there has been illustrated and described what is at present to be a preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalence may be substituted for elements thereof without departing from the true scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the central scope thereof.
Therefore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (8)

1. A control system for reconnecting the primary windings of an AC induction motor into a wyeconnection for coupling to a source of three-phase electric power, said system comprising: switching means operatively interconnected between the induction motor and the electric power source; power sensing means for generating a control signal directly proportional to the power applied to the induction motor; and differential comparator means responsive to said control signal and an adjustable reference signal for generating an actuating signal which causes operation of said switching means so as to establish alternately and selectively a first connection and a second connection between said induction motor and said electric power source.
2. A control system as claimed in Claim 1, whereas said first connection is a wye-connection which is established when said actuating signal is below a first pre-selected level, and wherein said second connection is a delta-connection which is established when said actuating signal is above a second pre-selected level.
3. A control system as claimed in Claim 1, wherein said switching means comprises a wyedelta starter.
4. A control system as claimed in Claim 1, wherein said power sensing means comprises a power transducer having its inputs coupled to the output of a wye-box for sensing voltage and to the output of a current transformer for detecting current, said power transducer having an output on which the control signal is generated.
5. A control system as claimed in Claim 4, wherein said differential comparator means comprises an operational amplifier having its inverting input terminal connected to the adjustable reference signal and its non-inverting input terminal connected to the control signal, and a relay coupled to the output of the operational amplifier on which the actuating signal is generated.
6. A control system as claimed in Claim 5, wherein said operational amplifier includes a feedback potentiometer interconnected between its output and its non-inverting input for defining a hysteresis adjustment, thereby avoiding switching of the actuating signal due to spurious fluctuations in the load conditions.
7. A control system for AC induction motors constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
8. Induction motors including a control system in accordance with any preceding claim.
GB8105779A 1980-03-13 1981-02-24 Control system for ac induction motors Expired GB2071938B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US12995880A 1980-03-13 1980-03-13

Publications (2)

Publication Number Publication Date
GB2071938A true GB2071938A (en) 1981-09-23
GB2071938B GB2071938B (en) 1984-01-04

Family

ID=22442384

Family Applications (1)

Application Number Title Priority Date Filing Date
GB8105779A Expired GB2071938B (en) 1980-03-13 1981-02-24 Control system for ac induction motors

Country Status (7)

Country Link
JP (1) JPS56141795A (en)
AU (1) AU6807681A (en)
CA (1) CA1179010A (en)
DE (1) DE3108349A1 (en)
ES (1) ES8203176A1 (en)
FR (1) FR2478399A1 (en)
GB (1) GB2071938B (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3347792A1 (en) * 1983-02-22 1985-04-04 Hemag Maschinenbau, Ing. A. & F. Manasek Ohg, 6900 Heidelberg Method and device for controlling the drive motor of a wood-processing machine
DE3306061C2 (en) * 1983-02-22 1985-04-04 Hemag Maschinenbau, Ing. A. & F. Manasek Ohg, 6900 Heidelberg Device for controlling the drive motor of a woodworking machine
DE4018146A1 (en) * 1990-06-06 1991-12-12 Alber Karin Electronically-regulated electric drive - has star-delta switching device in supply path of asynchronous motor

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE536043A (en) * 1952-05-10
GB754066A (en) * 1953-09-15 1956-08-01 Licencia Talalmanyokat Automatic load-dependent y-delta change-over system for electric induction motors
FR1272762A (en) * 1959-10-31 1961-09-29 Device for automatic switching from the star assembly of an electric motor to delta assembly, and vice versa depending on the load of the electric motor
GB2009538B (en) * 1977-11-23 1982-09-02 Taylor P A Apparatus for controlling the speed and torque of a pumpjack motor

Also Published As

Publication number Publication date
AU6807681A (en) 1981-09-17
GB2071938B (en) 1984-01-04
CA1179010A (en) 1984-12-04
DE3108349A1 (en) 1982-01-21
ES500287A0 (en) 1982-02-16
JPS56141795A (en) 1981-11-05
FR2478399A1 (en) 1981-09-18
ES8203176A1 (en) 1982-02-16

Similar Documents

Publication Publication Date Title
US4425539A (en) Control system for AC induction motor
US4862053A (en) Motor starting circuit
US4307327A (en) Control arrangement for single phase AC systems
Bruce et al. Reduced-voltage starting of squirrel-cage induction motors
CA2088626C (en) Load-control circuit for a mains-powered asynchronous single-phase capacitor motor
US4482852A (en) Motor slip controller for AC motors
US4870339A (en) Variable-speed power generating system
CA1179010A (en) Control system for ac induction motors
US5880571A (en) Method of and system for controlling a variable speed induction motor
US4492911A (en) Static phase converter
US2367025A (en) Liquid slip regulator
US2958814A (en) Control system for alternating current motor
US2589277A (en) Motor control system
US3345550A (en) Hoist motor control
US2175935A (en) Motor control
US2478160A (en) System of electrical braking
GB2100894A (en) Motor slip controller for AC induction motor
US2704344A (en) Motor control system
US2877400A (en) Speed regulator for monophase and polyphase alternating-current motors
US2512322A (en) Wide speed range control
US1481905A (en) Motor-control system
US1640547A (en) Variable-speed induction-motor set
US2196041A (en) Electrical regulation
US2408217A (en) Control system
CA1113591A (en) Motor/brake transitioning for an inverter driven ac induction motor

Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee