Fault-tolerant grid frequency measurement algorithm during transients

Patent metadata

Field	Value
Publication number	US-11882889-B2
Application number	US-202117204494-A
Country	US
Kind code	B2
Filing date	Mar 17, 2021
Priority date	Apr 16, 2020
Publication date	Jan 30, 2024
Grant date	Jan 30, 2024

Abstract

A system determines the frequency of grid signals corresponding to an electrical grid in real time. The system includes a transient detector that monitors a grid signal from a voltage meter or a current meter connected to the electrical grid. The system produces, in real time and at a sampling rate, a deviation signal indicative of a periodicity of the monitored grid signal. The system determines, over one or more cycles of the monitored grid signal, a measurement signal corresponding to the deviation signal. The system determines a frequency signal that corresponds a frequency estimation of the monitored signal by applying a frequency estimation when values of the measurement signal are less than a deviation threshold and maintaining the frequency signal at a constant value when values of the measured signal equal or exceeds the deviation threshold.

First claim

What is claimed is:

1. An apparatus that determines in real time frequency of grid signals x(t) corresponding to an electrical grid comprising:
a transient detector configured to:
monitor a signal indicative of a grid signal x(k) from a voltage meter or current meter connected to the electrical grid, where the grid signal is expected to include a periodic signal with a nominal frequency f o and a sampling rate f s ;

produce, in real time and at the sampling rate of the monitored signal, a deviation signal X dev indicative of whether or not the monitored signal includes the periodic signal; and
determine, over one or more cycles, a measurement signal corresponding to the deviation signal; and
a frequency estimator communicatively linked with the transient detector, the frequency estimator configured to:
determine a frequency signal fe that corresponds to a frequency estimation of the monitored signal while values of the measurement signal are less than a deviation threshold; and
maintain the frequency signal at a constant value while values of the measured signal equal or exceed the deviation threshold;
where the transient detector is configured to transmit a flag to the frequency estimator indicating that the monitored signal:
comprises a periodic signal when values of the measurement signal are less than a deviation threshold expressed as γ<thr, where γ comprises a measurement of the deviation signal and thr comprises the deviation threshold; and
exhibits a transient when values of the measurement signal equal or exceed the deviation threshold expressed as γ≥thr.

2. The apparatus of claim 1 , where the transient detector is configured to determine the measurement signal by integrating the deviation signal over one or more monitored signal cycles.

3. The apparatus of claim 2 , where integrating the deviation signal over one or more cycles is executed according to:

γ
⁡
(
k
)

=

❘
"\[LeftBracketingBar]"

∑

n
=
0

N
-
1

(

x
dev

(

k
+
n

)

)

❘
"\[RightBracketingBar]"

where γ comprises the measurement of the deviation signal, k is a sample index, and N is a number of sampled values in one or more cycles that varies with estimated grid frequency.

4. The apparatus of claim 1 , where the flag is transmitted in response to a transient event comprising a phase angle jump and/or a magnitude jump.

5. The apparatus of claim 1 , where the deviation signal comprises x dev (k)=x(k+n)−x(k), where k is a sample index, and N is a number of sampled values in one or more cycles that varies with estimated grid frequency.

6. The apparatus of claim 1 , where the frequency estimation that determines the frequency signal while values of the measurement signal are less than the deviation threshold comprises one of at least:
a discrete Fourier transform-based frequency-measurement algorithm; or
a model-based frequency-measurement algorithm.

7. The apparatus of claim 1 , where the grid signal comprises a single-phase grid signal or a three-phase grid signal.

8. The apparatus of claim 1 , where the transient detector and the frequency estimator comprises a unitary part of:
a protection relay,
a distributed energy resources (DER) device,
a phasor measurement unit (PMU),
a smart meter,
a digital fault detector, or
a power quality analyzer.

9. The apparatus of claim 1 , where the transient detector and the frequency estimator comprises a unitary part of:
a solar inverter;
a power generator;
a wind turbine; or
a flexible alternating current transmission system.

10. The apparatus of claim 1 , where the transient detector and the frequency estimator comprise a plurality of software instructions stored on a non- transitory computer-readable medium executed by a processor.

Assignees

• Ut Battelle Llc

Inventors

• Zhan Lingwei
• King Jr Thomas J
• Li Fuhua
• Liu Yilu
• Yao Wenxuan
• Yin He
• Xiao Bailu

Classifications

• H02J3/17

  Demand-responsive operation of AC power transmission or distribution networks · CPC title

• A41D13/1184 Primary

  with protection for the eyes, e.g. using shield or visor · CPC title

• A61B5/01

  Measuring temperature of body parts {; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue} (clinical contact thermometers G01K13/20) · CPC title

• A61F9/045

  Eye-shades or visors; Shields beside, between or below the eyes (caps with means for protecting the eyes A42B1/018) · CPC title

• H02J3/003

  Load forecast, e.g. methods or systems for forecasting future load demand · CPC title