Method and apparatus for grid impedance detection
AssigneeEnphase Energy, Inc.
InventorsAndrew Barnes, Brian Acker
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Abstract
A method and apparatus for monitoring an AC line for impedance change. In one embodiment, the method, comprises superimposing a tone on an AC current coupled to the AC line, wherein the tone is a higher frequency than an AC voltage waveform on the AC line; applying a correlation over a sampled AC voltage waveform, obtained by sampling the AC voltage waveform, to generate a correlated signal; and determining whether at least one change in characteristic of the correlated signal occurs.
Claims20
A method for monitoring an AC power grid, comprising one or more distributed generation systems, for impedance changes, comprising:
- superimposing a tone on an AC current flowing in an AC line of a distributed generation system connected to the AC power grid, wherein the tone has a higher frequency than a frequency of an AC voltage waveform of the power grid;
- applying a correlation between a sampled AC voltage waveform and a copy of the superimposed tone to generate a correlated signal, wherein the sampled AC voltage waveform is obtained by sampling the AC voltage waveform subsequent to superimposing the tone on the AC current
- determining whether at least one change in a characteristic of the correlated signal occurs, thereby detecting a change in the grid impedance.
An apparatus for monitoring an AC power grid, comprising one or more distributed generation systems, for impedance changes, comprising:
- a grid impedance detection module that:
- (i) superimposes a tone on an AC current flowing in an AC line of a distributed generation system connected to the AC power grid, wherein the tone has a higher frequency than a frequency of an AC voltage waveform of the power grid,
- (ii) applies a correlation between a sampled AC voltage waveform and a copy of the superimposed tone to generate a correlated signal, wherein the sampled AC voltage waveform is obtained by sampling the AC voltage waveform subsequent to superimposing the tone on the AC current, and
- (iii) determines whether at least one change in a characteristic of the correlated signal occurs, thereby detecting a change in the grid impedance.
A system for monitoring a power grid, comprising one or more distributed generation systems, for impedance changes, comprising:
- a photovoltaic (PV) module;
- and
- a power converter, coupled to the PV module and to the power grid, for generating an AC current that is coupled to the power grid, wherein the power converter comprises a grid impedance detection module that
- (i) superimposes a tone on the AC current, wherein the tone has a higher frequency than a frequency of the AC voltage waveform of the power grid,
- (ii) applies a correlation between a sampled AC voltage waveform and a copy of the superimposed tone to generate a correlated signal, wherein the sampled AC voltage waveform is obtained by sampling the AC voltage waveform subsequent to superimposing the tone on the AC current, and
- (iii) determines whether at least one change in a characteristic of the correlated signal occurs, thereby detecting a change in the grid impedance.
The system of claim17, wherein determining whether the at least one change occurs comprises:
- averaging the correlated signal over an averaging period to generate an averaged correlation signal value;
- determining a difference between the averaged correlation signal value and a previous averaged correlation signal value;
- and
- comparing the difference to a threshold.
Dependencies are inferred from the claim text.