Grid-Forming Inverter Control Using Virtual Reactance Tuning
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Solution Overview
Problem
Inverter-based resources, such as wind turbines, face challenges in providing stable grid-forming control due to increased wind power penetration, leading to grid voltage and frequency fluctuations, which can destabilize phase-locked loops and current control, exceeding equipment capabilities and requiring improved methods to maximize grid-supporting functions within design limits.
Innovation Solution
A method and system for tuning the reactance of inverter-based resources to adjust active power responses to grid events by changing frequency or angle of the IBR voltage relative to grid voltage, mimicking an active power response with a desired impedance, using a phase-locked loop to estimate grid frequency and angle, and integrating these estimates with inertial power regulators to generate an internal angle reference for grid-forming control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wind power penetration into the grid is increased, then the grid-supporting function of inverter-based resources is improved, but grid voltage and frequency fluctuations increase causing instability
Solution Approach 1:
The patent changes the control parameters of inverter-based resources from grid-following mode to grid-forming mode. Specifically, it modifies the voltage and frequency reference generation mechanism, allowing IBRs to actively regulate grid voltage and frequency rather than passively following grid signals. This parameter change enables IBRs to stabilize the grid even at high penetration levels by providing inertial response and voltage support.
Solution Approach 2:
The patent inverts the traditional control architecture where the grid provides references to IBRs. Instead, IBRs generate their own voltage and frequency references and provide these to the grid, effectively reversing the master-slave relationship. This inversion allows IBRs to become grid-forming resources that can stabilize voltage and frequency rather than being destabilized by them.
2Ease of operation
If conventional current source control is used with PLL, then wind turbines can inject specified current into the grid, but the control becomes unstable when grid voltage and frequency vary significantly
Solution Approach 1:
The patent introduces an intermediary voltage-source control layer between the current control and the grid. Instead of directly controlling current based on PLL-detected grid voltage, the system first generates an internal voltage reference that accounts for grid conditions, then uses this voltage reference to control current injection. This intermediary voltage control layer isolates the current control from grid disturbances, maintaining stability.
Solution Approach 2:
The patent replaces the mechanical PLL-based synchronization mechanism with an electronic voltage-source control mechanism. Instead of relying on the mechanical analogy of phase-locking to grid frequency, the system uses electronic generation of voltage references with inherent frequency and voltage control, substituting a more robust electronic control mechanism for the vulnerable PLL mechanism.
3Reliability
If inverter-based resources operate in grid-forming mode, then they can provide voltage and frequency support to the grid, but the equipment may be pushed beyond design capabilities
Solution Approach 1:
The patent implements dynamic control that adjusts the grid-forming behavior of IBRs based on real-time grid conditions and equipment capabilities. The control system dynamically modulates voltage and frequency references, and actively manages reactive power and current limits, allowing IBRs to provide maximum grid support within their design capabilities rather than operating at fixed conservative limits.
Solution Approach 2:
The patent incorporates feedback mechanisms that continuously monitor grid voltage, frequency, and IBR operating conditions. This feedback is used to adjust control parameters in real-time, ensuring that IBRs provide grid-supporting functions while remaining within their design capabilities. The feedback loop allows the system to respond to changing conditions and prevent equipment overload.
Data Source
AI summary
A method and associated system for providing grid-forming (GFM) control of an inverter-based resource (IBR) connected to an electrical grid include monitoring the electrical grid for grid events that cause a change in one or both of grid frequency and angle. Via a controller, an active power response of the IBR to the grid event is controlled by changing an angle of the IBR voltage relative to grid voltage in a manner so as to mimic an active power response of an IBR having a certain desired impedance that may similar to or different from a hardware impedance of the IBR itself.