Grid-Forming Inverter Control for Seamless Power Recovery
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Solution Overview
Problem
Current solutions lack a unified control architecture for voltage source inverters (VSIs) to operate effectively in both on-grid and off-grid modes, ensuring seamless transitions and stable power supply to critical infrastructure during grid failures, while minimizing communication burden and practical implementability.
Innovation Solution
A novel mode-dependent droop control framework that allows VSIs to operate in grid-forming mode always, regulating output active and reactive power based on minimal grid status information, enabling seamless transitions between on-grid and off-grid operations without interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If VSIs operate in grid-following mode during on-grid operation, then they can supply power to the grid, but they cannot maintain autonomous operation and seamless transition capability when grid failure occurs
Solution Approach 1:
The VSI is designed to operate in grid-forming mode universally, whether connected to the grid or not. The same control architecture handles both on-grid and off-grid operations, eliminating the need for separate grid-following and grid-forming control modes. This universal approach enables seamless transitions while maintaining reliability.
Solution Approach 2:
Instead of using conventional grid-following mode during on-grid operation and switching to grid-forming mode during off-grid operation, the invention inverts this approach by always operating in grid-forming mode. This inversion simplifies the control architecture and ensures autonomous operation capability is always present, enabling seamless transitions.
2Reliability
If VSIs remain synchronized and connected to the grid during on-grid mode, then seamless power restoration is enabled, but significant challenges arise in VSI operation and CI normal operation
Solution Approach 1:
The invention extracts the synchronization and grid-connection requirements from the VSI control during on-grid mode. By operating in grid-forming mode, the VSI maintains its own voltage and frequency references independently, taking out the burden of grid synchronization and simplifying operation while ensuring seamless restoration capability.
Solution Approach 2:
The VSI performs preliminary action by maintaining grid-forming capability and synchronization readiness even during on-grid operation. This preliminary preparation ensures that when grid failure occurs, the VSI can immediately take over power supply without interruption, enabling seamless restoration.
3Extent of automation
If conventional droop control is used for multiple inverters in off-grid mode, then autonomous operation is achieved, but control over output active and reactive power is challenging during on-grid mode
Solution Approach 1:
The droop control is designed to be universal, working effectively in both on-grid and off-grid modes. By always operating in grid-forming mode with droop control, the same autonomous control mechanism manages both active and reactive power output regardless of grid connection status, simplifying operation while maintaining automation.
Data Source
AI summary
A method and system of maintaining electrical power to one or more designated loads connected to an electrical bus that is selectively connected to an electric power grid as a first source of power and to an inverter for providing power to the bus from a second source of electrical power. A controller receives an input indicating if the bus is connected to the grid. The inverter is operated to be synchronized with the grid and provide a selected amount of active and reactive electrical power from the second source of electrical power while the one or more designated loads receive electrical power from the grid. Connection of the bus to the grid is monitored and at the time the electrical bus is no longer receiving power from the grid, the inverter is operated to provide required power without interruption to the one or more designated loads of the bus.