System and method for anti-islanding, such as anti-islanding for a grid-connected photovoltaic inverter
AssigneePV Powered, Inc.
InventorDal Y. Ohm
Life of this patent
Estimating the term…
Abstract
A system and method for detecting islanding in a Distributed Generation utility grid is described. In some examples, the system, via an inverter, injects a frequency disturbance to a location of the utility grid associated with a DG generator, measures both the frequency error due to the disturbance and the frequency drift of the location of the utility grid, and determines islanding based on a maximum value of the frequencies. In some cases, the system is able to reduce or minimize the Non-Detection Zone of the inverter by detecting islanding without always relying on a detectable frequency error due to an injected waveform.
Claims25
A method for detecting islanding at a location of a utility grid associated with a distributed generation system, the method comprising:
- receiving a frequency of the location of the utility grid associated with the distributed generation system;
- determining a frequency bias based on a greater of (1) a first value based on a frequency error associated with the frequency of the location of the utility grid, and (2) a second value based on application of a sign of the frequency error to a disturbance value;
- and
- injecting a generated waveform into the location of the utility grid associated with the distributed generation system, wherein the waveform is generated based on the frequency bias.
A method in an inverter for detecting islanding at a location of a utility grid associated with a photovoltaic array, the method comprising:
- measuring a frequency of the location of the utility grid associated with the photovoltaic array;
- and
- injecting a frequency disturbance into the location of the utility grid associated with the photovoltaic array;
- wherein the frequency disturbance is based on a greater of (1) a value of a frequency error due to the measured frequency and (2) a value of a frequency drift to a resonant frequency of the utility grid, wherein the value of the frequency error due to the measured frequency includes a value for loop gain times a value for a difference between the measured frequency and an average frequency for the utility grid.
A system for detecting islanding at a location of a utility grid receiving power from one or more power generation sources via one or more inverters, the system comprising:
- a waveform generation module configured to generate a waveform based on a calculated frequency bias, wherein the calculated frequency bias includes an inverter frequency component and a frequency bias component, and wherein the frequency bias component is based on a greater of
- 1) a first value based on a frequency error associated with a frequency of the utility grid, and
- 2) second value based on a direction of the frequency error and a disturbance value;
- a waveform injection module configured to inject the generated waveform into the utility grid;
- and
- a frequency comparison module configured to compare the frequency of the utility grid with a threshold frequency and provide an indication of islanding if the frequency of the utility grid meets or exceeds the threshold frequency.
An inverter configured to supply power to a utility grid, the inverter comprising:
- a power reception subsystem configured to receive generated direct current power from a power generation source;
- a current inverter subsystem configured to convert the received direct current power to alternating current power;
- and
- an anti-islanding subsystem configured to cause the supply of power to the utility grid to be interrupted, wherein the anti-islanding subsystem includes:
- a waveform injection module configured to inject a waveform into the utility grid;
- and
- a frequency module configured to determine a frequency bias based on a greater of 1) a first value based on a frequency error associated with a frequency of the utility grid and 2) a second value based on a direction of the frequency error and a disturbance value,
- wherein the injected waveform is based on the determined frequency bias.
A method of generating an output waveform, the method comprising:
- determining a grid frequency of an electrical grid;
- determining a first frequency bias based on a greater of 1) a first value based on a frequency error associated with the grid frequency, and 2) a second value based on a disturbance value;
- determining a second frequency bias of a power-producing system coupled to the electrical grid;
- determining an output frequency bias based on the first frequency bias and the second frequency bias;
- and
- generating, by the power-producing system, a output waveform based on the output frequency bias.
Dependencies are inferred from the claim text.