Wind Turbine Voltage Source Control for Weak Grid Stability
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Solution Overview
Problem
Wind turbine power fluctuations in weak grids cause significant grid voltage and frequency variations, destabilizing phase locked loop (PLL) control and current regulation in conventional current source controlled systems, especially with high wind power penetration.
Innovation Solution
Implementing a voltage source control system for wind turbines, using a controller to generate voltage commands with an internal frequency reference from power imbalances and a second controller to limit converter current, allowing the grid side converter to respond to grid changes as a voltage behind reactance, and incorporating a current limiter to prevent overcurrent during transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional current source control is used in wind turbines, then the control system is simple and relies on grid frequency reference, but the system becomes unstable when wind power penetration is high causing grid voltage and frequency variations
Solution Approach 1:
The patent inverts the conventional control approach by switching from current source control to voltage source control. Instead of controlling the wind turbine generator to output a specified current based on grid frequency reference, the system controls it to output a specified voltage with an internal frequency reference. This inversion resolves the stability issue in weak grids with high wind power penetration.
Solution Approach 2:
The patent changes the control parameters from current-based to voltage-based control. The voltage source control system uses voltage magnitude reference and internal frequency reference as control parameters, replacing the conventional current magnitude and grid frequency reference. This parameter change enables stable operation in weak grids.
2Reliability
If voltage source control is implemented to improve stability in weak grids, then the system responds better to grid changes, but the device complexity increases with additional controllers and control mechanisms
Solution Approach 1:
The voltage source control system performs multiple functions: it provides voltage magnitude control, frequency reference generation from power imbalance, and converter current limiting. By integrating these functions into a unified control architecture, the system achieves improved reliability without excessive complexity increase.
Solution Approach 2:
The patent introduces a second controller as an intermediary component that limits converter current. This intermediary controller protects the system during transients while working cooperatively with the first controller that generates voltage commands, distributing the control complexity across specialized components.
3Productivity
If the wind turbine generates electrical power quickly to respond to load changes, then the productivity increases, but the converter may experience overcurrent conditions causing system failure
Solution Approach 1:
The patent implements preliminary protective action by incorporating a current limiter in the control system before overcurrent conditions can cause damage. The second controller continuously monitors and limits converter current, preventing overcurrent conditions during rapid power response to load changes.
Solution Approach 2:
The voltage source control system uses feedback from power imbalance to generate internal frequency reference and adjust voltage commands. This feedback mechanism enables quick response to load changes while the current limiter provides real-time monitoring and protection against overcurrent conditions.
Data Source
AI summary
A system for controlling a grid connected power generating system is provided. The system includes a wind turbine, a converter, a first controller and a second controller. The wind turbine supplies electrical power to a power grid and the converter couples the wind turbine to the power grid. The first controller calculates voltage commands to emulate a phasor back electromotive force behind an inductance. The controller further generates converter switching commands from the voltage commands. The voltage commands include a voltage magnitude reference and an internal frequency reference calculated from a power imbalance between an active power reference and the electrical power. The second controller is used to limit a converter current.