Virtual Impedance for Grid-Forming Inverter Control
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Solution Overview
Problem
Conventional inverter-based resources face challenges in grid-forming control due to the drastic nonlinearity of current changes during grid disturbances, leading to chaotic behavior and inadequate support to the grid, especially in systems with multiple similar resources, where the effective impedance is tied to physical hardware characteristics.
Innovation Solution
The introduction of virtual impedance allows for configuring effective impedance independently of physical characteristics, enabling flexible tuning of system dynamics by providing virtual impedance values that can be adjusted based on measured grid conditions, reducing nonlinearity during faults and enhancing grid support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional current source control is used with physical impedance, then the system structure is simple and hardware is straightforward, but the effective impedance is tied to physical hardware characteristics causing drastic nonlinearity during grid disturbances
Solution Approach 1:
The patent creates a virtual copy of the physical impedance through software modeling. The virtual impedance controller replicates the electrical characteristics of physical impedance components (reactors, transformers) in the control algorithm, allowing the inverter to behave as if it has the desired impedance without being physically constrained by hardware limitations. This enables flexible impedance tuning while maintaining simple physical system architecture.
Solution Approach 2:
The patent enables dynamic adjustment of impedance parameters through software control. The virtual impedance values can be modified in real-time based on grid conditions, allowing the system to adapt its effective impedance characteristics without physical reconfiguration. This resolves the contradiction by decoupling impedance parameters from fixed hardware characteristics while adding computational control complexity.
2Adaptability or versatility
If virtual impedance is introduced to enable flexible impedance tuning, then adaptability improves, but control algorithm complexity increases
Solution Approach 1:
The patent introduces virtual impedance as an intermediary layer between the physical inverter and the grid. This virtual impedance model acts as a mediator that translates control objectives into appropriate current/voltage references, simplifying the overall control architecture despite the added computational elements. The virtual impedance serves as a bridge that enables flexible adaptation without requiring complex direct control of physical parameters.
3Adaptability or versatility
If physical impedance hardware is used, then the system structure is straightforward, but the impedance cannot be adjusted independently of hardware characteristics
Solution Approach 1:
The patent replaces physical impedance hardware (reactors, transformers) with virtual impedance implemented through software control algorithms. This substitution eliminates the need for additional physical components while achieving the same electrical effect, thereby maintaining ease of manufacture and installation while dramatically improving impedance adjustability. The control system computes virtual impedance effects through mathematical models rather than physical components.
Data Source
AI summary
A method for providing grid-forming control of an inverter-based resource connected to an electrical grid includes providing, via a processor, at least one virtual impedance value of the inverter-based resource. The method also includes determining a voltage drop across the at least one virtual impedance value of the inverter-based resource using at least one current feedback signal, the voltage drop comprising a voltage magnitude and a voltage angle. Further, the method includes receiving one or more voltage or current signals of the inverter-based resource. Moreover, the method includes determining a control command for the inverter-based resource as a function of the voltage drop across the virtual impedance value(s) of the inverter-based resource and the one or more voltage or current signals.