Method and apparatus for determining motor speed using zero crossing times
AssigneeAllen-Bradley Company, Inc.
InventorsPeter J. Unsworth, Yuan Wang
Life of this patent
Estimating the term…
Abstract
A method and apparatus to be used with a motor controller for determining the speed of the motor rotor using current zero crossing times of the stator winding currents. An error signal set, consisting of phase angle errors between consecutive zero crossings over a sampling period, is generated and analyzed in a region of interest in either the time or frequency domain, producing a signal frequency, the signal frequency being the frequency of the motor rotor.
Claims15
A method to be used with a motor controller, the motor controller providing stator winding currents at a frequency of X Hz and indicating zero crossing times when each current is zero, the controller also providing a sampling period, the motor being of a design having p poles, the method determining the speed of a motor rotor, the method comprising the steps of:
- generating a plurality of error signals over the sampling period, each error signal indicating the deviation of consecutive current zero crossings from a constant interval, the plurality of error signals together forming an error signal sequence;
- and
- analyzing the error signal sequence to determine an error signal sequence spectrum, a region of interest within said spectrum comprising a back emf signal generated by said rotor.
An apparatus to be used with a motor controller, the motor controller providing stator winding currents at a frequency of X cycles per second and indicating zero crossing times when each current is zero, the controller also indicating a sampling period of time and a stator period, the motor being of a design having p poles, the apparatus for determining the speed of a motor rotor, the apparatus comprising:
- a period calculator which receives consecutive zero crossing times from the motor controller over the sampling period, subtracts each zero crossing time from a previous consecutive zero crossing time to produce a plurality of difference values, and subtracts 1/6th of the stator period from each difference value to produce a plurality of error signals indicating the period between consecutive current zero crossings, the error signals together forming an error signal set;
- and
- a frequency analyzer which analyzes the error signal set to determine a peak frequency component of said error signal set within a region of interest, the region of interest being between K((2Xp-n) and K(2X/p) Hz;
- wherein n is less than 2X/p, and K is an integer.
A method to be used with a motor controller, the motor controller providing stator winding currents at a frequency of 60 Hz and indicating zero crossing times when each current is zero, the controller also indicating a sampling period of approximately one second and a stator period, the motor being of a design having 4 poles, the method determining the speed of a motor rotor, the method comprising the steps of:
- receiving consecutive zero crossing times from the motor controller;
- subtracting each zero crossing time from a previous consecutive zero crossing time to produce a plurality of difference values;
- subtracting 1/6th of the stator period from each difference value to produce a plurality of error signals, the error signals together forming an error signal set;
- passing the error signal set through a bandpass filter having a bandpass between 27.0 and 30.0 Hz to produce a rotor component;
- determining a signal frequency of the rotor component, said signal frequency being the motor rotor frequency;
- and
- displaying the signal frequency.
Dependencies are inferred from the claim text.