Method and apparatus to limit motor current at low frequencies
AssigneeRockwell Automation Technologies, Inc.
InventorBrian Seibel
Life of this patent
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Abstract
A method and apparatus for use with an induction machine system including a controller and d and q-axis current feedback loops, the controller receiving a frequency command signal and generating d and q-axis voltage command signals, the method for limiting load current to a level below a limit current at low operating frequencies, the method comprising the steps of identifying an operating frequency as a function of the d and q-axis feedback currents, where the operating frequency is below a low threshold value: comparing a feedback current to the limit current; and where the feedback current exceeds the limit current, reducing the q-axis voltage command value.
Claims20
A method for use with an induction machine system including a controller and d and q-axis current feedback loops, the controller receiving a frequency command signal and generating d and q-axis voltage command signals, the method for limiting load current to a level below a limit current at low operating frequencies, the method comprising the steps of:
- identifying a system operating frequency;
- where the operating frequency is below a low threshold value:
- comparing a feedback current to the limit current;
- and
- where the feedback current exceeds the limit current, reducing the q-axis voltage command value.
A method for use with an induction machine system including a controller and d and q-axis current feedback loops, the controller receiving a frequency command signal and generating d and q-axis voltage command signals, the method for limiting load current to a level below a limit current at low operating frequencies, the method comprising the steps of:
- identifying a system operating frequency;
- where the operating frequency is below a low threshold value:
- mathematically combining the d-axis feedback current and the limit current to generate a maximum q-axis feedback current;
- comparing the q-axis feedback current the maximum q-axis current;
- and
- where the q-axis feedback current exceeds the maximum q-axis current, reducing the q-axis voltage command value.
An apparatus for use with an induction machine system including a controller and d and q-axis current feedback loops, the controller receiving a frequency command signal and generating d and q-axis voltage command signals, the apparatus for limiting load current to a level below a limit current at low operating frequencies, the apparatus comprising:
- a processor running a pulse sequencing program to perform the steps of:
- identifying a system operating frequency;
- where the operating frequency is below a low threshold value:
- comparing a feedback current to the limit current;
- and
- where the feedback current exceeds the limit current, reducing the q-axis voltage command value.
Dependencies are inferred from the claim text.