Virtual Impedance Grid-Forming Control for DFIG Stability

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Solution Overview

Problem

Double-fed wind turbine generators face challenges in grid-forming control due to their reliance on hardware-imposed impedance, which limits flexibility and stability, especially in weak grids with high wind power penetration, leading to voltage and frequency fluctuations.

Innovation Solution

Implementing a virtual impedance system that allows for configurable impedance settings independent of physical equipment characteristics, enabling dynamic tuning of the grid-forming control for double-fed wind turbine generators to stabilize grid voltage and frequency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If grid-following control mode is used with hardware-imposed impedance, then the wind turbine generator can operate with simple control structure, but the flexibility and stability are limited especially in weak grids with high wind power penetration

Engineering Contradiction:

Improveflexibility of grid-forming controlVSAvoidcontrol structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent changes the impedance parameter from fixed hardware-imposed values to configurable virtual impedance values that can be dynamically adjusted. The controller synthesizes a voltage source behind a configurable impedance, allowing the impedance parameter to be optimized for different grid conditions without changing physical hardware, thus improving flexibility while maintaining control structure simplicity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical hardware impedance with a virtual impedance implemented through control algorithms. Instead of relying on physical reactors, transformers, or rotating machine impedances, the system uses a controller to synthesize the impedance characteristic, substituting mechanical/electrical hardware constraints with flexible software-based control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If hardware-imposed impedance is used, then the system structure is simple, but the ability to tune grid-forming control dynamically is limited

Engineering Contradiction:

Improvedynamic tuning capabilityVSAvoidsystem configuration flexibility

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent introduces dynamic tuning capability by implementing virtual impedance that can be adjusted in real-time based on grid conditions. The controller continuously adapts the impedance parameters to optimize grid-forming performance, transforming a static hardware system into a dynamic controllable system that responds to changing operational requirements.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The virtual impedance system serves multiple functions: it provides grid-forming control, enables dynamic tuning, stabilizes voltage and frequency, and adapts to different grid conditions all through a single configurable parameter set, replacing the need for multiple hardware configurations.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If conventional current source control is used assuming fixed grid voltage, then the control is simple, but the system becomes unstable when wind power penetration is high causing voltage and frequency fluctuations

Engineering Contradiction:

Improvegrid stabilityVSAvoidcontrol system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements a feedback mechanism where the controller monitors grid conditions and adjusts the virtual impedance parameters accordingly. This feedback loop enables the system to maintain stability under varying wind power penetration levels by dynamically adapting to voltage and frequency fluctuations rather than assuming fixed grid conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary action by proactively adjusting the virtual impedance before instability occurs. The controller anticipates grid conditions and pre-configures the impedance parameters to prevent voltage and frequency fluctuations, rather than reacting after problems arise.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11506173B2System and method for providing grid-forming control for a double-fed wind turbine generator using virtual impedance

Publication Date: 2022.11.22 GE INFRASTRUCTURE TECH LLC

AI summary

A method for providing grid-forming control of a double-fed wind turbine generator connected to an electrical grid includes receiving at least one control signal associated with a desired total power output or a total current output of the double-fed wind turbine generator. The method also includes determining a contribution of at least one of power or current from the line-side converter to the desired total power output or to the total current output of the double-fed wind turbine generator, respectively. The method also includes determining a control command for a stator of the double-fed wind turbine generator based on the contribution of at least one of the power or the current from the line-side converter and the at least one control signal. Further, the method includes using the control command to regulate at least one of power or current in the stator of the double-fed wind-turbine generator.