Method and apparatus for determining motor speed using zero crossing times

Claim 1

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.

Claim 2

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.

Claim 10

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.

Claim 11

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.

Claim 16

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.

Claim 17

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.