EP0055856A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Power factor control systems for polyphase induction motors
Assignee: Individual
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Filing: 1981-12-29
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Granted: —
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Expires: 2001-12-29
Abstract
Abstract Improved power factor control systems for polyphase induction motors operate the same at improved efficiencies. In one embodiment, voltages applied across each of the three motor windings are uniformly and sequentially phase controlled, and in another are applied in phase controlled fashion across only two of the three windings. In other embodiments, where the motor is always lightly loaded full sine waves of voltage are initially applied across all of the windings during motor startup, whereafter phase control is exercised over only two of the windings and the third is disconnected, while for motors which are usually lightly loaded, but may occasionally be subjected to heavier loads, power is selectively connected to the third winding in accordance with motor load conditions. To prevent motor instability when significant phase angle control is exercised over the winding voltages, it is also contemplated that the winding voltages be sequentially, cyclically and unevenly phase controlled to operate the motor in an unbalanced condition.
Inventors
- 👤 Joseph E. Pascente
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 00:46
CPC Classifications
H; H02; H02J; H02J3/00; H02J3/18; H02J3/1892; H02P; H02P23/00; H02P23/26
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
267 words
A power factor control system for improving the operating efficiency of a three-phase a.c. induction motor by varying the form of input voltages coupled thereto, the motor having first, second and third stator wind- .ings for being energized by a three-phase sine wave voltage source through respective first, second and third lines and a rotor for being coupled to a load, said power factor control system comprising first and second switching means positionable in respective ones of the first and second lines, each said switching means having a control input and being responsive to signals at said control input to establish and interrupt a circuit path through its associated line; sensing circuit means adapted for connection to the lines for sensing the phase angle between the voltage across and the current through the stator windings as it varies in response to motor loading, said sensing circuit means having an output for generating a control signal having a value representative of the sensed phase angle; and means for coupling said sensing circuit means output to said control inputs to said first and second switching means to control the same in a manner to vary the electrical angle of the phases of voltage from the voltage source which are actually coupled to the windings through said first and second switching means to decrease the sensed phase angle for values thereof which are greater than an optimum value, whereby the average current supplied to the stator windings from the power source is a function of the actual load on the motor and the operating efficiency of the motor is improved.
Claim 2
Dependent Claim
267 words
A power factor control system for improving the operating efficiency of a three-phase a.c. induction motor by varying the form of input voltages coupled thereto, the motor having first, second and third stator wind- .ings for being energized by a three-phase sine wave voltage source through respective first, second and third lines and a rotor for being coupled to a load, said power factor control system comprising first and second switching means positionable in respective ones of the first and second lines, each said switching means having a control input and being responsive to signals at said control input to establish and interrupt a circuit path through its associated line; sensing circuit means adapted for connection to the lines for sensing the phase angle between the voltage across and the current through the stator windings as it varies in response to motor loading, said sensing circuit means having an output for generating a control signal having a value representative of the sensed phase angle; and means for coupling said sensing circuit means output to said control inputs to said first and second switching means to control the same in a manner to vary the electrical angle of the phases of voltage from the voltage source which are actually coupled to the windings through said first and second switching means to decrease the sensed phase angle for values thereof which are greater than an optimum value, whereby the average current supplied to the stator windings from the power source is a function of the actual load on the motor and the operating efficiency of the motor is improved.
Claim 3
Dependent Claim
150 words
A system as in claim 1, including a signal delay circuit and a voltage phase shift circuit, said sensing circuit means having a current monitoring input coupled to the winding side of said first switching means; a first voltage monitoring input coupled to the voltage cource side of said first switching means and a second voltage monitoring input coupled through said voltage phase shift circuit to one of the voltage source side of said second switching means or the third line, said voltage phase shift circuit shifting the phase of the voltage applied to said second voltage monitoring input by an amount such that said sensing circuit means monitors voltage signals representative of the current through and the voltage across the first winding and of the phase angle therebetween, said sensing circuit means output being coupled to the control input to said second switching means through said signal, delay circuit.
Claim 4
Dependent Claim
73 words
A system as in claim 1, including circuit means coupled with the control inputs to said first and second switching means and responsive upon application of voltage on the lines to apply a signal to said control inputs to render said first and second switching means conductive to couple full sine waves of voltage -to the first and second lines for a time sufficient to enable the motor to reach normal running speed.
Claim 5
Dependent Claim
117 words
A system as in claim 1, including third switching means positionable in the third line and having a control input coupled to said sensing circuit means output for being controlled in a manner to establish and interrupt a path through the third line, including circuit means for cyclically coupling control signals at said sensing circuit means output with said first, second and third switching means control inputs to control the same in a manner to vary the electrical angle of the phases of voltage which are actually coupled to two windings by a first amount and to the remaining winding by a different amount, whereby the motor is operated in an unbalanced condition for improved operating stability.
Claim 6
Dependent Claim
57 words
A system as in claim 13, wherein said circuit means, in response to cycles or half cycles of the voltages, sequentially and cyclically controls said switching means to sequentially and cyclically apply.through said first, second and third switching means and to the windings phases of voltage the electrical angle of which is varied by the different amount.
Claim 7
Dependent Claim
174 words
A system as in claim 1, including third switching means positionable in the third line and having a control input, and microprocessor circuit means coupled with said sensing circuit means, said microprocessor circuit means and sensing circuit means being coupled at inputs thereto with the winding sides and the voltage source sides of said first, second and third switching means for sensing the phase angles between the currents through and the voltages across the first, second and third windings and having outputs coupled with the control inputs to said first, second and third switching means for applying control signals thereto to control the same to sequentially and cyclically, in response to each cycle or half cycle of the voltages, vary by a first amount the electrical angle of each phase of voltage which is actually coupled to the windings through two of said switching means and to vary by a second and lesser amount the electrical angle of the phase of voltage which is actually coupled to the windings through the remaining switching means.
Claim 8
Dependent Claim
51 words
. A system as in claim 1, wherein said second switching means is nonconductive in response to said control signal having less than a predetermined value, and including means for rendering said first and second switching means fully conductive in response to said control signal having at least said predetermined value.
Claim 9
Dependent Claim
80 words
A system as in claim 1, including circuit means coupled with said sensing circuit means and responsive to a change in phase angle from the optimum value to sequentially control said sensing circuit means so that it momentarily causes full phases of voltage to be applied across the windings and so that it then successively increments the electrical angles of the phases of voltage coupled to the windings until the sensed phase angle is again decreased to the optimum value.
Claim 10
Independent Claim
206 words
A method of operation of the system defined in any of the preceding claims to improve the power factor and operating efficiency of a three-phase a.c. induction motor by varying the form of input voltages coupled thereto, the motor having first, second and third stator windings for being energized by a three-phase sine wave voltage source through first, second and third lines and a rotor for being coupled to a load, comprising the steps of sensing the phase angle between the voltage across and the current through the windings as it varies in response to motor loading; generating a control signal having a value representative of the sensed phase angle; and selectively interrupting the circuit paths through the first and second lines in accordance with the value of the control signal to vary the electrical angle of the phases of voltage from the voltage source which are actually coupled to the windings through the first and second lines to decrease the sensed phase angle for values thereof which are greater than an optimum value, whereby the average current supplied to the stator windings from the power source is a function of the actual load on the motor and the operating efficiency of the motor is improved.
Claim 11
Dependent Claim
109 words
A method as in claim 9, wherein said sensing step includes the steps of monitoring the current flow through the first line, monitoring the voltage between the first line and one of the second or third lines, phase shifting the phase of the monitored voltage by an amount such that the phase shifted voltage is in phase with the voltage across the first winding, and comparing the phases of the monitored current flow and the phase shifted voltage, and wherein the step of selectively interrupting includes the step of delaying interruption of the circuit path through the second line after interruption of the circuit path through the first line.
Claim 12
Dependent Claim
57 words
A method as in claim 9, including the step of inhibiting operation of said interrupting step for a predetermined time upon application of the three phases of voltage on the lines, whereby upon application of voltage on the lines to start the motor full sine waves of voltage are coupled with the windings for said predetermined time.
Claim 13
Dependent Claim
104 words
A method as in claim 9, wherein said selectively interrupting step also interrupts the circuit path through the third line in accordance with the value of the control signal, and including the step of cyclically controlling said selectively interrupting step to vary the electrical angle of the phases of voltage which are actually coupled to the windings through two of the lines by a first amount and to vary the electrical angle of the phase of voltage which is actually coupled to the windings through the remaining lines by a different amount, whereby the motor is-operated in an unbalanced condition for improved operating stability.
Claim 14
Dependent Claim
55 words
A system as in claim 9, wherein said controlling step, in response to cycles or half cycles of the voltages, controls said selectively interrupting step to sequentially and cyclically apply through the first, second and third lines, and to the windings, phases of voltage the electrical angle of which is varied by the different amount.
Claim 15
Dependent Claim
68 words
A method as in claim 9, wherein said selectively interrupting step comprises selectively interrupting the circuit path through the first line and continuously interrupting the circuit path through the second line in response to the control signal having less than a predetermined value, and inhibiting interruption of the circuit paths through the first and second lines in response to the control signal having at least said predetermined value.
Claim 16
Independent Claim
68 words
A method as in claim "9, including the steps, in response to a sensed change in phase angle from the optimum value, of sequentially controlling the selectively interrupting step so that full phases of voltage are momentarily applied across the windings and so that the electrical angles of the phases of voltage are then incrementally varied until the sensed phase angle is again decreased to the optimum value.
References Cited (Backward Citations)
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