Grid-Forming Inverter Voltage Control Loop Mitigating Flicker

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Solution Overview

Problem

Wind turbines, especially those with grid-forming inverters, experience voltage disturbances known as flicker due to frequency variations, which can destabilize the grid and violate connection requirements, particularly in weak grids with high wind power penetration.

Innovation Solution

A method and system that utilize a dynamic controller within the voltage control loop of a grid-forming inverter-based resource to mitigate flicker effects by generating a current vector reference signal containing a frequency component of voltage disturbances, adjusting the transfer function of the regulator, and regulating a voltage vector command to stabilize the grid connection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If wind turbines operate in grid-forming mode with conventional current source control, then they can inject specified current into the grid based on fundamental voltage waveforms, but voltage disturbances known as flicker occur due to frequency variations, especially in weak grids with high wind power penetration

Engineering Contradiction:

Improvewind power penetrationVSAvoidvoltage disturbances (flicker)

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent implements a feedback mechanism where the controller continuously monitors the frequency component of voltage disturbances at the point of interconnection and dynamically adjusts the transfer function of the voltage regulator based on this feedback signal, enabling the system to respond to and mitigate flicker effects in real-time

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent transforms the static voltage regulator into a dynamic system by making the transfer function adjustable based on detected frequency components. The controller dynamically modifies regulator parameters according to the detected voltage disturbance characteristics, allowing adaptive mitigation of flicker effects across varying operating conditions

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If wind turbines are located in weak grids, then wind power can be integrated into the grid, but wind turbine power fluctuations lead to increased magnitude and frequency variations in grid voltage, adversely affecting PLL and current control performance

Engineering Contradiction:

Improvegrid integration capabilityVSAvoidcontrol system stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The system uses feedback from voltage disturbance detection to continuously adjust control parameters, ensuring stable operation of the phase-locked loop and current control even when grid conditions vary due to power fluctuations in weak grids

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the parameters of the voltage regulator (transfer function) based on detected frequency components of voltage disturbances, allowing the control system to adapt to varying grid conditions and maintain stability despite power fluctuations

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If the proportion of synchronous machines is reduced in favor of asynchronous machines, then grid flexibility and wind power integration increase, but stability margins decrease, leading to grid collapse when subjected to voltage and frequency disturbances

Engineering Contradiction:

Improvegrid flexibilityVSAvoidgrid stability margins

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The patent converts the harmful flicker effects and voltage disturbances into useful information by detecting their frequency components and using this information to dynamically adjust the controller transfer function, thereby improving grid stability in systems with high asynchronous machine penetration

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

By implementing feedback control that detects voltage disturbance frequency components and adjusts regulator parameters accordingly, the system enhances stability margins in grids with reduced synchronous machine presence, preventing grid collapse under disturbance conditions

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS11689022B2Voltage control loop for mitigating flicker in a grid-forming inverter-based resource

Publication Date: 2023.06.27 GENERAL ELECTRIC RENOVABLES ESPANA SL

AI summary

A method for mitigating voltage disturbances at a point of interconnection (POI) of a grid-forming inverter-based resource (IBR) due to flicker includes receiving a voltage reference command and a voltage feedback. The voltage feedback contains information indicative of the voltage disturbances at the POI due to the flicker. The method also includes determining a power reference signal for the IBR based on the voltage reference command and the voltage feedback. Moreover, the method includes generating a current vector reference signal based on the power reference signal, the current vector reference signal containing a frequency component of the voltage disturbances. Further, the method includes generating a transfer function of a regulator based on the frequency component to account for the flicker effect. In addition, the method includes generating a current vector based on a comparison of the current vector reference signal and a current vector feedback signal. Thus, the method includes regulating a voltage vector command using the current vector to mitigate the voltage disturbances.