METHOD OF SENSING GENERATOR SPEED
CLAIM OF PRIORITY
This application claims the benefit of priority of U.S. Patent Application
Serial No. 13/289,524, entitled "METHOD OF SENSING GENERATOR
SPEED," filed on November 4, 2011, which application is incorporated by
reference herein in its entirety.
TECHNICAL FIELD
Embodiments pertain to a method of sensing generator speed using
amplitude threshold detection.
BACKGROUND
Sensing generator frequency is commonly done in order to determine if
the generator is operating within normal parameters. The frequency of an AC
waveform produced by a generator is typically determined by measuring the
elapsed time between zero crossings of the AC waveform.
One of drawbacks with measuring the elapsed time between zero
crossings of the AC waveform is that with a low signal to noise ratio, phantom
zero crossing may be undesirably detected resulting in potentially incorrect
frequency measurement. This problem arises only at low voltage amplitudes
which is not a typical operating condition of a generator.
These problems do not occur at higher levels because there is a high
signal to noise ratio. Therefore, the noise does not cause the signal to
inadvertently pass the zero crossing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an example wave form plot that illustrates basic threshold
detection.
FIG. 2 is an example schematic illustrating implementation of basic
threshold detection.
FIG. 3 is a partial section view of an example alternator showing winding
locations.
FIG. 4 is a block diagram that illustrates a diagrammatic representation
of a machine in the example form of a computer system 400 within which a set
of instructions for causing the machine to perform any one or more of the
methodologies discussed herein may be executed.
DETAILED DESCRIPTION
The following description and the drawings sufficiently illustrate specific
embodiments to enable those skilled in the art to practice them. Other
embodiments may incorporate structural, logical, electrical, process, and other
changes. Portions and features of some embodiments may be included in, or
substituted for, those of other embodiments. Embodiments set forth in the
claims encompass all available equivalents of those claims.
An example method of sensing generator speed will now be described
with reference to FIGS. 1-3. In one example embodiment, the method includes
detecting an AC waveform 20 produced by a generator (not shown) and
determining a threshold voltage 22 from the AC waveform 20 produced by the
generator. The method further includes determining generator speed by
comparing timing of the threshold voltage 22 with the AC waveform 20.
It should be noted that the generator speed may be determined by a time
period between cycles of an output of the generator. With reference to FIG. 1,
the speed is determined using the equation:
(1) generator speed = 1/Tl; or 1/T2
In some embodiments, detecting an AC waveform 20 produced by a
generator includes scaling the voltage through a resistor divider network 25 to
signal voltage levels. As an example, a differential amplifier 27 may be used to
scale an unreferenced AC waveform 20 to a lower DC-referenced level 26.
Embodiments are also contemplated where determining a threshold
voltage 22 from the AC waveform 20 produced by the generator includes
determining an average rectified AC voltage. As an example, the full-waverectified
AC signal 29 may be scaled using a differential amplifier 28 to a lower
DC-referenced level 31.
It should be noted that determining generator speed by comparing the
threshold voltage 22 with the AC waveform 20 includes measuring the amount
of time T betweens instances of the AC waveform 20 exceeding the threshold
voltage 22. As examples, determining generator speed by comparing the
threshold voltage 22 with the AC waveform 20 may include measuring the
amount of time T betweens instances of the average AC voltage (i) dropping
below the threshold voltage 22; or (ii) exceeding the threshold voltage 22. As
shown in FIG. 2, the scaled DC-referenced level 26 of the AC waveform 20 is
compared to the scaled DC-referenced level 3 1 of the full-wave-rectified AC
signal 29 using comparator 32 to establish a square wave output 15 useful for
determining generator speed.
In some embodiments, detecting an AC waveform 20 produced by a
generator may include detecting an AC waveform 20 produced by an alternative
stator winding 40 within the generator.
Another example method of sensing generator speed will now be
described with reference to FIGS. 1-3. In one example embodiment, the method
includes detecting an AC waveform 50 produced by an alternative stator winding
40 within the generator. The method further includes measuring a frequency of
the AC waveform 50 to determine generator speed.
Sensing generator speed based on the AC waveform 20 produced by an
alternative stator winding 40 may be beneficial since the voltage on a correctly
phased alternative stator winding 40 will not collapse under a short circuit
condition of the AC output of the generator which is produced by the main stator
winding 58 (see FIG. 3). The ability to sense generator speed while the main AC
output is short circuited may permit extended sourcing of current to the fault.
Extended sourcing of current to the fault may allow downstream over current
protection to isolate the fault.
In some embodiments, detecting an AC waveform 20 produced by an
alternative stator winding 40 may include detecting an AC waveform 20 that is
produced by an auxiliary winding that provides energy to excite an alternator
field 54. It should be noted the auxiliary winding may be placed out of phase
with the main winding 58 which provides the AC output of the generator.
Changing the phase between the auxiliary winding and the main winding
58 may allow (i) the excitation control system to continue to source current to
the alternator field 54; and (ii) continued sensing of the generator speed.
Note that generator speed is related to rotor 60 speed by a ratio, as the
rotation of the rotor 60 provides the AC frequency. Varying the number of
magnetic poles on the rotor 60 will change the ratio between the rotor speed and
the AC frequency. As an example, FIG. 3 depicts a 2-pole rotor, although other
embodiments are contemplated where there is different than 2 rotor poles.
In other embodiments, detecting an AC waveform produced by an
alternative stator winding 40 includes detecting an AC waveform that is
produced by a stator winding that only performs speed sensing. As long as the
alternative stator winding 40 is out of phase with the main winding 58, the
voltage sensed from the alternative stator winding 40 will not collapse in a short
circuit condition.
As shown in FIGS. 1-3, embodiments are contemplated where measuring
a frequency of the AC waveform 20 to determine generator speed may include
(as discussed above) (i) detecting an AC waveform 20 produced by the
generator; (ii) determining an average AC voltage 29 from the AC waveform 20
produced by the generator to establish a threshold voltage 22; and (iii)
determining generator speed by comparing the threshold voltage 22 with the AC
waveform 20.
The method of sensing generator speed described herein may reduce the
problems associated with measuring frequency having a low signal to noise ratio
where phantom zero crossings might otherwise be undesirably detected to cause
potentially incorrect frequency measurement. Therefore, the method of sensing
generator speed may permit accurate frequency measurement at low voltage
amplitudes which is not a typical operating condition of a generator.
Example Machine Architecture
FIG. 4 is a block diagram that illustrates a diagrammatic representation
of a machine in the example form of a computer system 400 within which a set
of instructions for causing the machine to perform any one or more of the
methodologies discussed herein may be executed. In some embodiments, the
computer system 400 may operate in the capacity of a server or a client machine
in a server-client network environment, or as a peer machine in a peer-to-peer
(or distributed) network environment.
The computer system 400 may be a server computer, a client computer, a
personal computer (PC), a tablet PC, a set-top box (STB), a Personal Digital
Assistant (PDA), a cellular telephone, a Web appliance, a network router, switch
or bridge, or any machine capable of executing a set of instructions (sequential
or otherwise) that specify actions to be taken by that machine. Further, while
only a single machine is illustrated, the term "machine" shall also be taken to
include any collection of machines that individually or jointly execute a set (or
multiple sets) of instructions to perform any one or more of the methodologies
discussed herein.
The example computer system 400 may include a processor 460 (e.g., a
central processing unit (CPU), a graphics processing unit (GPU) or both), a main
memory 470 and a static memory 480, all of which communicate with each other
via a bus 408. The computer system 400 may further include a video display
unit 410 (e.g., liquid crystal displays (LCD) or cathode ray tube (CRT)). The
computer system 400 also may include an alphanumeric input device 420 (e.g., a
keyboard), a cursor control device 430 (e.g., a mouse), a disk drive unit 440, a
signal generation device 450 (e.g., a speaker), and a network interface device
490.
The disk drive unit 440 may include a machine-readable medium 422 on
which is stored one or more sets of instructions (e.g., software 424) embodying
any one or more of the methodologies or functions described herein. The
software 424 may also reside, completely or at least partially, within the main
memory 470 and/or within the processor 460 during execution thereof by the
computer system 400, the main memory 470 and the processor 460 also
constituting machine-readable media. It should be noted that the software 424
may further be transmitted or received over a network (e.g., network 380 in FIG.
3) via the network interface device 490.
While the machine-readable medium 422 is shown in an example
embodiment to be a single medium, the term "machine-readable medium" should
be taken to include a single medium or multiple media (e.g., a centralized or
distributed database, and/or associated caches and servers) that store the one or
more sets of instructions. The term "machine-readable medium" shall also be
taken to include any medium that is capable of storing, encoding or carrying a
set of instructions for execution by the machine and that cause the machine to
perform any one or more of example embodiments described herein. The term
"machine-readable medium" shall accordingly be taken to include, but not be
limited to, solid-state memories and optical and magnetic media.
Thus, a computerized method and system are described herein. Although
the present invention has been described with reference to specific example
embodiments, it will be evident that various modifications and changes may be
made to these embodiments without departing from scope of the invention.
Accordingly, the specification and drawings are to be regarded in an illustrative
rather than a restrictive sense.
The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)
requiring an abstract that will allow the reader to ascertain the nature and gist of
the technical disclosure. It is submitted with the understanding that it will not be
used to limit or interpret the scope or meaning of the claims. The following
claims are hereby incorporated into the detailed description, with each claim
standing on its own as a separate embodiment.
CLAIMS
What is claimed is:
1. A method of sensing generator speed comprising:
detecting an AC waveform produced by a generator;
determining a threshold voltage from the AC waveform produced by the
generator; and
determining generator speed by comparing the threshold voltage with the
AC waveform.
2. The method of claim 1, wherein detecting an AC waveform produced by
a generator includes scaling the voltage through a resistor divider network to
signal voltage levels.
3. The method of claim 1, wherein determining a threshold voltage from the
AC waveform produced by the generator includes determining an average
rectified AC voltage.
4. The method of claim 1, wherein determining generator speed by
comparing the threshold voltage with the AC waveform includes measuring the
amount of time betweens instances of the average AC voltage exceeding the
threshold voltage.
5. The method of claim 1, wherein determining generator speed by
comparing the threshold voltage with the AC waveform includes measuring the
amount of time betweens instances of the average AC voltage dropping below
the threshold voltage.
6. The method of claim 1, wherein detecting an AC waveform produced by
a generator includes detecting an AC waveform produced by an alternative stator
winding within the generator.
7. A method of sensing generator speed comprising:
detecting an AC waveform produced by an alternative stator winding
within the generator; and
measuring a frequency of the AC waveform to determine generator
speed.
8. The method of claim 7, wherein detecting an AC waveform produced by
an alternative stator winding includes detecting an AC waveform produced by an
auxiliary winding that provides energy to excite an alternator field.
9. The method of claim 7, wherein detecting an AC waveform produced by
an alternative stator winding includes detecting an AC waveform produced by a
stator winding that only performs speed sensing.
10. The method of claim 7, wherein measuring a frequency of the AC
waveform to determine generator speed includes:
detecting an AC waveform produced by a generator;
determining an average AC voltage from the AC waveform produced by
the generator to establish a threshold voltage; and
determining generator speed by comparing the threshold voltage with the
AC waveform.