# US 2025/0096572 A1 · Systems and methods for synchronising islanded power grids with a main power grid

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- Number: US 2025/0096572 A1
- Document ID: US20250096572A1
- Status: Published application
- Kind: A1
- Application number: 18/885,929
- Filed: 2024-09-16
- Published: 2025-03-20
- Earliest claimed: 2023-09-19
- Assignees: Smart Power Networks Ltd
- Applicants: Smart Power Networks Ltd
- Inventors: Anastasios Rousis; Dimitrios Tzelepis; Angelos Patsidis
- Web page: https://patentgrep.com/patent/US20250096572A1

## CPC

- H02J 3/34: Arrangements for transfer of electric power between networks of substantially different frequency
- H02J 3/388: Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power
- H02J 3/00142: {Oscillations concerning frequency}
- H02J 3/00144: {using phasor measuring units [PMU]}
- H02J 3/381: {Dispersed generators}
- H02J 3/40: Synchronisation of generators for connection to a network or to another generator
- H02J 3/44: with means for ensuring correct phase sequence
- Y02E 40/70: Smart grids as climate change mitigation technology in the energy generation sector
- Y02E 60/00: Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y04S 10/22: Flexible AC transmission systems [FACTS] or power factor or reactive power compensating or correcting units
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y04S: SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS

## Abstract

A system for synchronising islanded power grid (IPG) with main power grid (MPG), the system includes first phasor measurement unit(s) (PMU(s)) that collects first phasor data associated with MPG; second PMU(s) that collect second phasor data associated with IPG; main controller of IPG that is communicably coupled to first PMU(s) and second PMU(s). The main controller is configured to: receive first and second phasor data; receive command from device; execute frequency correction process iteratively using first and second phasor data, to match frequency of IPG to frequency of MPG; execute phase and voltage magnitude correction process iteratively using first and second phasor data, to match phase and voltage magnitude of IPG at connection point to phase and voltage magnitude of MPG; and send activation signal to electrical element(s) arranged at connection point to establish electrical connection between IPG and MPG upon receiving activation signal.

## Claims

### Claim 1

A system for synchronising an islanded power grid with a main power grid, the system comprising:
at least one first phasor measurement unit (PMU) that in use, collects first phasor data associated with the main power grid, wherein the first phasor data comprises time-stamped voltage phasors and frequency values at an electrical node within main power grid close to a connection point;
a plurality of second PMUs that in use, collect second phasor data associated with the islanded power grid, wherein the second phasor data comprises time-stamped voltage phasors and frequency values at a plurality of electric nodes which at least include a plurality of energy sources in the islanded power grid;
a main controller of the islanded power grid that is communicably coupled to the at least one first PMU and at least one of the plurality of second PMUs, the main controller being configured to:
receive the first phasor data and the second phasor data;
receive a command from a device associated with an operator of the system; and then
execute the frequency correction process iteratively using the first phasor data and the second phasor data, to match a frequency of the islanded power grid to a frequency of the main power grid;
execute a phase and voltage magnitude correction process iteratively using the first phasor data and the second phasor data, to match a phase and voltage magnitude of the islanded power grid at the connection point to a phase and voltage magnitude of the main power grid; and
send an activation signal to at least an electrical element arranged at the connection point, causing the electrical element to establish an electrical connection between the islanded power grid and the main power grid upon receiving the activation signal.

### Claim 2 (depends on 1)

The system of claim 1, wherein when executing the frequency correction process iteratively, at each iteration, the main controller is configured to:
determine a first average value of the frequency values in the first phasor data;
determine a second average value of the frequency values in the second phasor data;
determine whether a difference between the first average value and the second average value is greater than or equal to a first predefined threshold;
when the difference between the first average value and the second average value is greater than or equal to the first predefined threshold, determine a frequency correction value based on the first average value and the second average value;
determine frequency correction setpoints according to the frequency correction value taking into account stability metrics of the islanded power grid; and
send the frequency correction setpoints to converters of the plurality of energy sources for realisation,
wherein the iterative execution of the frequency correction process terminates upon matching of the frequency of the islanded power grid with the frequency of the main power grid.

### Claim 3 (depends on 2)

The system of claim 2, wherein at each iteration, the main controller is further configured to:
determine a first confidence value indicative of a reliability of the frequency values in the first phasor data;
determine a second confidence value indicative of a reliability of the frequency values in the second phasor data;
determine an overall frequency confidence value as a product of the first confidence value and the second confidence value; and
determine whether the overall frequency confidence value is greater than or equal to a second predefined threshold,
wherein when the overall frequency confidence value is greater than or equal to the second predefined threshold, the frequency correction value is determined.

### Claim 4 (depends on 2)

The system of claim 2, wherein when determining the frequency correction setpoints according to the frequency correction value, the main controller is configured to:
determine tentative frequency correction setpoints for the converters of the plurality of energy sources, according to the frequency correction value; and
process the tentative frequency correction setpoints using compensation filter functions and stability metrics, to produce the frequency correction setpoints.

### Claim 5 (depends on 1)

The system of claim 1, wherein a given time-stamped voltage phasor comprises at least a phase value, and when executing the phase correction process iteratively, at each iteration, the main controller is configured to:
determine a third average value of phase values in the first phasor data and a fourth average value of voltage magnitude values in the first phasor data;
determine a fifth average value of phase values in the second phasor data and a sixth average value of voltage magnitude values in the second phasor data;
determine a phase correction value based on the third average value and the fifth average value and a voltage magnitude correction value based on the fourth average value and the sixth average value;
determine phase and voltage magnitude correction setpoints according to the phase and voltage magnitude correction value taking into account stability metrics of the islanded power grid; and
send the phase and voltage magnitude correction setpoints to the converters of the plurality of energy sources for realisation,
wherein the iterative execution of the phase and voltage magnitude correction process terminates upon matching of the phase and voltage magnitude of the islanded power grid at the connection point with the phase and voltage magnitude of the main power grid.

### Claim 6 (depends on 5)

The system of claim 5, wherein at each iteration, the main controller is further configured to:
determine a third confidence value indicative of a reliability of the phase values in the first phasor data and a fourth confidence value indicative of a reliability of the voltage magnitude values in the first phasor data;
determine a fifth confidence value indicative of a reliability of the phase values in the second phasor data and a sixth confidence value indicative of a reliability of the voltage magnitude values in the second phasor data;
determine an overall phase confidence value at the connection point as a product of the third confidence value and the fifth confidence value, and determine an overall voltage magnitude confidence value at the connection point as a product of the fourth confidence value and the sixth confidence value; and
determine whether the overall phase confidence value and the overall voltage magnitude confidence value is greater than or equal to a third predefined threshold,
wherein when the overall phase confidence value and the overall voltage magnitude confidence value is greater than or equal to the third predefined threshold, the phase and voltage magnitude correction values are determined.

### Claim 7 (depends on 5)

The system of claim 5, wherein when determining the phase and voltage magnitude correction setpoints according to the phase correction value and the voltage magnitude correction value, the main controller is configured to:
determine tentative phase and voltage magnitude correction setpoints for the converters of the plurality of energy sources, according to the phase and voltage magnitude correction value; and
process the tentative phase and voltage magnitude correction setpoints using compensation filter functions and stability metrics, to produce the phase and voltage magnitude correction setpoints.

### Claim 8 (depends on 5)

The system of claim 5, wherein when determining the phase and voltage magnitude correction value, the main controller is further configured to:
employ an artificial intelligence (AI)-based software application for identifying whether there exists any electrical device or operating condition that introduces a phase and voltage magnitude deviation, in any of the plurality of electric nodes including the plurality of energy sources in the islanded power grid;
when it is determined that there exists an electrical device or operating condition that introduces the phase and voltage magnitude deviation in any of the plurality of electric nodes, determine a value of the phase and voltage magnitude deviation; and
update the phase and voltage magnitude correction value that is determined using the third average value, the fourth average value, the fifth average value, and the sixth average value, by using information from phase and voltage magnitude deviation value.

### Claim 9 (depends on 1)

The system of claim 1, wherein a given PMU comprises a PMU-based controller, the PMU-based controller being configured to:
receive information indicative of a plurality of timing sources in the islanded power grid and the main power grid;
determine an efficiency of each of the plurality of timing sources, based on a plurality of metrics associated with each of the plurality of timing sources; and
select a timing source having a highest efficiency amongst the plurality of timing sources as a timing reference.

### Claim 10 (depends on 1)

The system of claim 1, further comprising a data repository communicably coupled to the main controller, wherein the main controller is configured to store, at the data repository, at least one of: network parameters of the main power grid, network parameters of the islanded power grid, network parameters of devices in the islanded power grid, synchronisation criteria of the islanded power grid and the main power grid.

### Claim 11 (depends on 1)

The system of claim 1, wherein the electrical element is at least one of: a circuit breaker, a relay, a switch.

### Claim 12

A method for synchronising an islanded power grid with a main power grid, the method comprising:
receiving a first phasor data from at least one phase measurement unit (PMU) and a second phasor data from a plurality of second PMUs, wherein the first phasor data comprises time-stamped voltage phasors and frequency values at an electrical node within main power grid close to a connection point, and the second phasor data comprises time-stamped voltage phasors and frequency values at a plurality of electric nodes which at least include a plurality of energy sources in the islanded power grid;
receiving a command from a device associated with an operator of the system; and then
executing the frequency correction process iteratively using the first phasor data and the second phasor data, for matching a frequency of the islanded power grid to a frequency of the main power grid;
executing a phase and voltage magnitude correction process iteratively using the first phasor data and the second phasor data, for matching a phase and voltage magnitude of the islanded power grid at the connection point to a phase and voltage magnitude of the main power grid; and
sending an activation signal to at least an electrical element arranged at the connection point, causing the electrical element to establish an electrical connection between the islanded power grid and the main power grid upon receiving the activation signal.

### Claim 13 (depends on 12)

The method of claim 12, wherein the step of executing the frequency correction process iteratively, at each iteration, comprises:
determining a first average value of the frequency values in the first phasor data;
determining a second average value of the frequency values in the second phasor data;
determining whether a difference between the first average value and the second average value is greater than or equal to a first predefined threshold;
when the difference between the first average value and the second average value is greater than or equal to the first predefined threshold, determining a frequency correction value based on the first average value and the second average value;
determining frequency correction setpoints according to the frequency correction value taking into account stability metrics of the islanded power grid; and
sending the frequency correction setpoints to converters of the plurality of energy sources for realisation,
wherein the iterative execution of the frequency correction process terminates upon matching of the frequency of the islanded power grid with the frequency of the main power grid.

### Claim 14 (depends on 12)

The method of claim 12, wherein a given time-stamped voltage phasor comprises at least a phase and voltage magnitude value, and the step of executing the phase and voltage magnitude correction process iteratively, at each iteration, comprises:
determining a third average value of phase values in the first phasor data and a fourth average value of voltage magnitude values in the first phasor data;
determining a fifth average value of phase values in the second phasor data and a sixth average value of voltage magnitude values, in the second phasor data;
determining a phase correction value based on the third average value and the fifth average value and a voltage magnitude correction value based on the fourth average value and the sixth average value;
determining phase and voltage magnitude correction setpoints according to the phase and voltage magnitude correction value taking into account stability metrics of the islanded power grid; and
sending the phase and voltage magnitude correction setpoints to the converters of the plurality of energy sources for realisation,
wherein the iterative execution of the phase and voltage magnitude correction process terminates upon matching of the phase and voltage magnitude of the islanded power grid close to the connection point with the phase and voltage magnitude of the main power grid.