DFIG Stator Voltage Control for Stable Weak-Grid Operation
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Solution Overview
Problem
Existing wind turbine generators, particularly double-fed induction generators, face challenges in providing stable grid-forming control, especially in weak grids where wind power penetration is high, leading to voltage and frequency fluctuations.
Innovation Solution
The implementation of a system and method that utilizes a converter controller with a stator voltage regulator to receive voltage commands, determine rotor current commands based on magnetizing current and stator current feedback, and control the rotor voltage to achieve the desired voltage commands, effectively providing grid-forming control for double-fed wind turbine generators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wind turbines operate in grid-following mode with conventional current source control, then the control structure is simple and relies on grid voltage as reference, but the system cannot maintain stability in weak grids with high wind power penetration where voltage and frequency fluctuations occur
Solution Approach 1:
The patent inverts the conventional control approach by switching from grid-following mode (where the converter adapts to grid voltage) to grid-forming mode (where the converter establishes the voltage reference). The stator voltage regulator generates voltage commands that serve as the reference for the entire system, rather than using grid voltage as the reference. This inversion enables the converter to stabilize weak grids by providing a stable voltage and frequency reference independent of grid conditions.
Solution Approach 2:
The patent introduces a stator voltage regulator as an intermediary component between the control system and the power converter. This regulator processes voltage commands and generates appropriate control signals for the converter, acting as a mediator that translates high-level voltage references into actionable control commands. This intermediary structure enables grid-forming control while maintaining a manageable control architecture.
2Speed
If wind turbines use grid-following control with fast current-regulation loops, then the response speed is fast, but the system becomes sensitive to voltage and frequency variations in weak grids, adversely affecting PLL and current control performance
Solution Approach 1:
The patent inverts the control hierarchy by making voltage regulation the primary control objective rather than current regulation. The stator voltage regulator generates voltage commands that are then translated into current references. This inversion changes the system from being sensitive to voltage variations (grid-following) to being the source of voltage stability (grid-forming), thereby eliminating the sensitivity problem while maintaining fast response through the regulated voltage reference.
3Adaptability or versatility
If wind turbines operate in isolated load or weak grid configurations, then the system must provide voltage and frequency support, but grid-following converters cannot establish voltage reference and require fast communication with external control systems
Solution Approach 1:
The patent implements self-service by enabling the converter to autonomously establish voltage and frequency references without requiring fast communication with external control systems. The stator voltage regulator generates voltage commands based on local measurements and control objectives, allowing the converter to serve itself as the voltage source. This self-service capability enables operation in isolated load configurations and weak grids where external communication may be slow or unavailable.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables double-fed wind turbine generators to provide stable grid-forming control, supporting voltage and frequency stability, and ensuring the generators can operate effectively in weak grids without requiring fast communication with external control systems.
Implementation Method 1
The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade.
Implementation Method 2
The lift force generates torque on the main rotor shaft, which is typically geared to a generator for producing electricity.
Data Source
AI summary
A method for providing grid-forming control of a double-fed generator of a wind turbine includes receiving, via a stator voltage regulator of a converter controller, one or more voltage commands from an external controller. Further, the method includes determining, via the stator voltage regulator, one or more rotor current commands as a function of a magnetizing current command and a stator current feedback signal of the double-fed generator. Thus, the method includes controlling a rotor voltage of the double-fed generator using the one or more rotor current commands to achieve the one or more voltage commands.