Apparatus and method for high slip operation of an AC electric motor at substantially zero rotation and substantially zero torque
First Claim
1. A substantially zero rotation and substantially zero torque apparatus for an AC electric motor drive system having an AC electric motor producing a rotation in response to a drive current of variable magnitude and frequency comprising:
- (a) means for establishing a rotation reference signal proportional to a desired level of motor rotation;
(b) means for generating an actual rotation signal proportional to the rotation of the motor;
(c) means for generating a rotation difference signal as a function of any difference between said rotation reference signal and said actual rotation signal;
(d) means for supplying a torque command signal in accordance with said rotation difference signal, and for producing a frequency control signal and a current control signal as functions of said torque command signal;
(e) means for supplying drive current to the motor at a frequency controlled in response to said frequency control signal and at a magnitude varied in accordance with said current control signal;
(f) means for furnishing an idle control signal when said torque command signal and at least two of said rotation reference signal, said actual rotation signal, and said rotation difference signal are less than respective predetermined values; and
(g) first and second modifying means each responsive to said idle control signal for, respectively, changing the magnitude and rapidly raising the frequency of the drive current to cause the motor to produce a substantially zero rotation and substantially zero torque at high slip.
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Abstract
Apparatus and method for high slip operation of an AC electric motor at substantially zero rotation and substantially zero torque in an AC electric motor drive system is disclosed. The electric motor produces a rotation in response to an outgoing signal, such as a drive current, of variable magnitude and frequency supplied by the drive system. An idle control signal is furnished when the drive system is in a substantially zero rotation and substantially zero torque state, where the frequency of the current is approximately zero. The idle control signal causes substantially simultaneously an adjustment of the magnitude of the current to a predetermined magnitude level and a rapid raising of the frequency of the current to a higher frequency value to produce per-unit slip s=(n1 -n)/nb greater than 0.1, where n1 is the synchronous rotation of the stator field of the motor, n is the rotation of the rotor of the motor, and nb is the synchronous speed of the stator field at motor rated rpm. The adjustment in the magnitude and the rapid increase in the frequency of the current causes the motor to produce substantially zero rotation and substantially zero torque because the motor is operating in the high slip region of its torque-rotation curve. The apparatus and method of the present invention allows the motor to accelerate rapidly on command from the substantially zero rotation and substantially zero torque high slip mode.
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Citations
29 Claims
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1. A substantially zero rotation and substantially zero torque apparatus for an AC electric motor drive system having an AC electric motor producing a rotation in response to a drive current of variable magnitude and frequency comprising:
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(a) means for establishing a rotation reference signal proportional to a desired level of motor rotation; (b) means for generating an actual rotation signal proportional to the rotation of the motor; (c) means for generating a rotation difference signal as a function of any difference between said rotation reference signal and said actual rotation signal; (d) means for supplying a torque command signal in accordance with said rotation difference signal, and for producing a frequency control signal and a current control signal as functions of said torque command signal; (e) means for supplying drive current to the motor at a frequency controlled in response to said frequency control signal and at a magnitude varied in accordance with said current control signal; (f) means for furnishing an idle control signal when said torque command signal and at least two of said rotation reference signal, said actual rotation signal, and said rotation difference signal are less than respective predetermined values; and (g) first and second modifying means each responsive to said idle control signal for, respectively, changing the magnitude and rapidly raising the frequency of the drive current to cause the motor to produce a substantially zero rotation and substantially zero torque at high slip. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A substantially zero rotation and substantially zero torque apparatus for an AC electric motor drive system having an AC electric motor producing a rotation in response to a drive current of variable magnitude and frequency comprising:
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(a) means for establishing a torque reference signal proportional to a desired level of motor torque; (b) means for generating an actual rotation signal proportional to motor rotation; (c) means for generating a torque command signal as a function of said torque reference signal, and for producing a frequency control signal and a current control signal as functions of said torque command signal; (d) means for supplying drive current to said motor at a frequency controlled in response to said frequency control signal and at a magnitude varied in accordance with said current control signal; (e) means for furnishing an idle control signal when said torque reference signal and said actual rotation signal are less than respective predetermined values; and (f) first and second modifying means each responsive to said idle control signal for, respectively, changing the magnitude and rapidly raising the frequency of said drive current to cause the motor to produce a substantially zero rotation and substantially zero torque at high slip. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21)
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22. A method of producing substantially zero rotation and substantially zero torque from an AC electric motor producing rotation and torque in response to a motor drive current of variable magnitude and frequency supplied by an AC electric motor drive system comprising the steps of:
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(a) producing a motor drive current of controllable magnitude and frequency; (b) furnishing an idle control signal when the drive system is in a substantially zero rotation and substantially zero torque state where the magnitude and frequency of said motor drive current are below preselected levels; and (c) substantially simultaneously, in response to said idle control signal, changing the magnitude of said motor drive current to a predetermined magnitude level and raising rapidly the frequency of said motor drive current to a higher frequency value to produce a per-unit slip greater than 0.1.
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23. A method of producing substantially zero rotation and substantially zero torque from an AC electric motor producing rotation and torque in response to a drive current of variable magnitude and frequency supplied by an AC electric motor drive system comprising the steps of:
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(a) establishing a rotation reference signal proportional to a desired level of motor rotation; (b) generating an actual rotation signal proportional to the motor rotation; (c) generating a rotation difference signal as a function of any difference between said rotation reference signal and said actual rotation signal; (d) producing a torque command signal in accordance with said rotation difference signal; (e) producing a frequency control signal and a current control signal as functions of said torque command signal; (f) supplying to the motor drive current at a frequency controlled in response to said frequency control signal and at a magnitude varied in accordance with said current control signal; (g) furnishing an idle control signal when said torque command signal and at least two of said rotation reference signal, said actual rotation signal, and said rotation difference signal are less than respective predetermined values; and (h) substantially simultaneously, in response to said idle control signal, changing the magnitude of said drive current to a preselected magnitude level and raising rapidly the frequency of said drive current to a higher frequency value to cause the motor to produce a substantially zero rotation and substantially zero torque at high slip. - View Dependent Claims (24)
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25. A method of producing substantially zero rotation and substantially zero torque from an AC electric motor producing rotation and torque in response to a drive current of variable magnitude and frequency supplied by an AC electric motor drive system comprising the steps of:
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(a) establishing a torque reference signal proportional to a desired level of motor torque; (b) generating an actual rotation signal proportional to motor rotation; (c) generating a torque command signal as a function of said torque reference signal; (d) producing a frequency control signal and a current control signal as functions of said torque command signal; (e) supplying to the motor drive current at a frequency controlled as a function of said frequency control signal and at a magnitude varied in accordance with said current control signal; (f) furnishing an idle control signal when said actual rotation signal and said torque reference signal are less than respective predetermined values; (g) substantially simultaneously, in response to said idle control signal, changing the magnitude of said drive current to a lower preselected magnitude level and raising rapidly the frequency of said drive current to a higher frequency value to cause the motor to produce a substantially zero rotation and substantially zero torque at high slip.
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26. In a drive system for controlling the operation of an AC electric motor, apparatus for effecting a mode of motor operation at substantially zero rotation and substantially zero torque comprising:
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(a) means for developing an outgoing signal of controllable magnitude and controllable frequency, said outgoing signal acting to supply electrical power to the motor; (b) means for furnishing a command for placing the motor in a substantially zero rotation and substantially zero torque mode of operation; (c) means for furnishing an idle control signal in response to said command; (d) first modifying means responsive to said idle control signal for changing the magnitude of said outgoing signal to a predetermined magnitude level; and
,(e) second modifying means responsive to said idle control signal for rapidly raising the frequency of said outgoing signal to a higher frequency to effect, in said motor, a pre-unit slip of greater than a predetermined value. - View Dependent Claims (27, 28, 29)
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Specification