Grid-Connected Inverter Dual-Mode Control for Weak-Grid Stability
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Solution Overview
Problem
Conventional grid-connected inverters face instability and wideband oscillation in high-impedance and low-inertia weak grids due to nonlinear factors like plug-and-play and free switching, with existing dual-mode switching methods lacking accurate real-time impedance sensing and robustness under complex conditions.
Innovation Solution
A passivity-based dual-mode integrated control method for grid-connected inverters using a port-controlled Hamiltonian model with weighted passivity-based feedback control laws for both grid-following and grid-forming modes, eliminating the need for grid impedance identification and ensuring stable operation across varying grid conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If virtual admittance method is used to improve GCI stability in weak grid, then stability is improved, but accurate real-time grid impedance identification becomes complex and difficult
Solution Approach 1:
The patent extracts and eliminates the impedance identification link from the control system. Instead of requiring accurate real-time measurement of grid impedance, the control method is designed to be inherently robust against impedance variations, directly addressing the contradiction by removing the complex measurement requirement while maintaining stability improvement
Solution Approach 2:
The patent changes the control parameters and strategy to achieve robustness against impedance variations. By adopting a control method that does not depend on precise impedance values but rather on robust control laws, the system maintains stability without requiring complex impedance identification
2Adaptability or versatility
If dual-mode switching control is implemented to adapt to grid variations, then adaptability is improved, but coupling between PLL and grid impedance causes instability risk
Solution Approach 1:
The patent introduces a robust control law as an intermediary between the grid variations and the PLL system. This control law acts as a buffer that decouples the PLL from direct sensitivity to grid impedance changes, allowing the system to adapt to grid variations while maintaining stability through the mediating control strategy
Solution Approach 2:
The patent implements dynamic control strategies that can adapt to changing grid conditions. The control parameters and laws are designed to dynamically respond to grid variations without creating harmful coupling effects, enabling the system to maintain stability while adapting to different operating conditions
3Device complexity
If conventional single-mode GCI control is used, then control simplicity is maintained, but wideband oscillation and stability problems occur in weak grid
Solution Approach 1:
The patent merges grid-following and grid-forming control modes into a unified robust control framework. This integration allows the system to maintain the simplicity of a single control structure while incorporating the stability benefits of multiple modes, eliminating wideband oscillation without requiring complex mode switching
Data Source
AI summary
A passivity-based dual-mode integrated control method for a grid-connected inverter (GCI) is provided. In view of the insufficient robustness of the conventional single-mode GCI in a high-impedance and low-inertia weak grid, and the problem of wideband oscillation of the grid voltage and grid current or even system instability in nonlinear application scenarios such as grid structure/parameter variation, and plug-and-play of the inverter, the dual-mode integrated control method performs modeling on the GCI based on a port-controlled Hamiltonian (PCH) model, thereby obtaining integrated control with a weighted passivity-based feedback control law for the GCI based on a grid-following (GFL) mode and a grid-forming (GFM) mode. Based on the dual-mode integrated control method, the stable operation of the GCI in severe grid conditions with large fluctuation of the impedance, and desirable robustness of the GCI in nonlinear working scenarios can be ensured.