Apparatus used with AC motors for compensating for turn on delay errors
AssigneeAllin-Bradley Company, LLC
InventorLuis J. Garces
Life of this patent
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Abstract
An apparatus for compensating for turn on delay distortions generated by a PWM controller. When turn on delay compensation is added to a PWM controller command signal and current zero crossings are inaccurately determined, compensation at the zero crossings causes further distortion which is reflected in a d and q-axis current vector frequency. Deviations from an ideal vector frequency are identified and used to modify command voltages to eliminate the zero crossing errors.
Claims17
An apparatus to be used with a PWM controller which generates terminal voltages as a function of command voltages and thereby produces associated currents in three separate stator windings of an induction motor, the currents representable by a current vector which rotates at a vector frequency, the apparatus for substantially eliminating turn on delay distortions in terminal voltage by modifying command voltages, the apparatus comprising:
- a zero crossing identifier for approximately identifying stator winding current zero crossings;
- a first compensator for modifying the command voltages by a first correction voltage, the first compensator increasing a command voltage between zero crossings when an associated current is positive and decreasing a command voltage between zero crossings when an associated current is negative;
- a frequency deviation identifier for identifying irregularities in the vector frequency;
- a second compensator for increasing or decreasing the command voltage associated with the next stator current to cross zero by a second correction voltage, the second correction voltage being a function of the vector frequency irregularity magnitude.
A method to be used with a PWM controller which generates terminal voltages as a function of command voltages and thereby produces associated currents in three separate stator windings of an induction motor, the currents representable by a current vector which rotates at a vector frequency, the method for substantially eliminating turn on delay distortions in terminal voltage by modifying command voltages, the method comprising the steps of:
- approximately identifying stator winding current zero crossings;
- modifying the command voltages by a first correction voltage which increases a command voltage between zero crossings when an associated current is positive and decreases a command voltage between zero crossings when an associated current is negative;
- identifying irregularities in the vector frequency;
- increasing or decreasing the command voltage associated with the next stator current to cross zero by a second correction voltage, the second correction voltage being a function of the vector frequency irregularity magnitude.
Dependencies are inferred from the claim text.