Converter-Controlled Wind Turbine Virtual Inertia Control
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Solution Overview
Problem
The increasing proportion of converter-controlled generating units in electrical supply grids complicates grid stabilization, especially during network restoration and sub-grid interconnection, as they behave differently from synchronous generators and require decentralized control.
Innovation Solution
Implementing a method that allows for the selection of control functions, such as normal and frequency hold control functions, to stabilize the grid frequency, where the frequency hold control function prioritizes maintaining a constant grid frequency by adjusting active and reactive power feed, emulating the behavior of a synchronous machine with a virtual rotating flywheel mass and increasing the virtual moment of inertia for enhanced frequency support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If converter-controlled generating units are used to increase flexibility and quick response capability, then the ability to react quickly to frequency and voltage changes is improved, but the stability and predictability of grid behavior deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the virtual moment of inertia parameter based on grid conditions. During normal operation, a lower virtual moment of inertia allows quick response to frequency changes. During grid restoration or islanded operation, the virtual moment of inertia is increased to provide stable frequency support, effectively changing the system parameters to resolve the contradiction between speed and stability.
Solution Approach 2:
The control device acts as an intermediary between the converter-controlled generating unit and the grid. It emulates synchronous generator behavior through virtual synchronous machine control, introducing a virtual moment of inertia that mediates between the fast response capability of power electronics and the stability requirements of the grid, particularly during critical operations like sub-grid interconnection.
2Adaptability or versatility
If converter-controlled generating units are deployed decentrally to improve distribution and flexibility, then the adaptability to local grid conditions is improved, but the complexity of coordinating control measures deteriorates
Solution Approach 1:
The patent implements self-service through autonomous control at each generating unit. The control device independently determines grid status (normal operation vs. grid restoration mode) and automatically adjusts the virtual moment of inertia and control parameters without requiring complex centralized coordination. Each unit serves itself by detecting local grid conditions and adapting its behavior, simplifying the overall control architecture.
Solution Approach 2:
The system dynamically adapts its control characteristics based on operating mode. During normal grid operation, units operate with standard control parameters. During grid restoration or islanded operation, the control parameters dynamically change to emulate synchronous generator behavior with increased virtual inertia, allowing decentralized units to automatically coordinate their behavior through dynamic parameter adjustment.
3Stability of the object's composition
If the virtual moment of inertia is increased to enhance frequency support capability, then the frequency stability is improved, but the response time to frequency changes may be slowed
Solution Approach 1:
The patent applies periodic action by switching between different virtual moment of inertia values based on operational phases. During frequency transients, the system provides strong frequency support with higher virtual inertia. Once frequency stability is achieved, the virtual inertia is reduced to allow faster response to new disturbances. This periodic adjustment of control parameters resolves the trade-off between stability and response time.
Data Source
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AI summary
The invention relates to a method for supplying electric power to an electric supply network (120, 300), which has a network frequency, at a network connection point (118) by means of a converter-controlled generator unit (100), in particular a wind turbine (100), having the steps of: supplying electric power depending on a control function, wherein the electric power can comprise active power and reactive power, and a normal control function and at least one frequency-maintaining control function which differs from the normal control function can be selected as the control function. The normal control function is selected if it has been detected that the electric supply network (120, 300) is operating in a normal state and the frequency-maintaining function is selected if a steady-frequency operating state is present or provided, said steady-frequency operating state describing in particular an electric supply network (120, 300) operating state in which the network frequency is maintained at a constant value.