Grid-Forming Inverter Synchronization Under Current Limiting
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Solution Overview
Problem
Grid-forming inverters face challenges in maintaining synchronism during abnormal operating conditions such as grid faults, overloading, or phase jumps, as they are prone to losing stability due to current limiting, and existing solutions are inadequate in addressing frequency and voltage jumps, especially in inverter-dominated networks.
Innovation Solution
The implementation of an imaginary power compensation control method that introduces virtual power and voltage terms to stabilize grid-connected power electronics, mimicking the behavior of a synchronous generator, allowing the inverter to predict and respond to non-ideal conditions by calculating a fictitious power term that accounts for the power not injected due to current limiting, thereby maintaining synchronism and grid stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If grid-forming inverters operate during abnormal conditions, then power delivery continues, but stability is lost due to current limiting
Solution Approach 1:
The patent introduces a fictitious power term as an intermediary variable that mediates between the actual current-limited power output and the reference power. This fictitious term allows the inverter to maintain stability by compensating for the power deficit caused by current limiting, enabling continuous power delivery without losing stability during abnormal conditions
Solution Approach 2:
The patent dynamically adjusts the fictitious power term parameter based on the difference between reference power and actual power output. By changing this parameter in response to operating conditions, the system maintains stability while continuing to deliver power during abnormal conditions such as grid faults or overloading
2Strength
If current limiting is applied to protect the inverter, then device safety is improved, but synchronism is lost
Solution Approach 1:
The patent implements a feedback mechanism where the fictitious power term is continuously updated based on the power deficit (difference between reference and actual power). This feedback loop ensures that when current limiting occurs, the system automatically compensates to maintain synchronism with the grid while protecting the inverter
Solution Approach 2:
The fictitious power term acts as a mediator between the current limiting protection mechanism and the synchronism maintenance requirement. It allows the system to apply current limiting for device safety while simultaneously maintaining synchronism by compensating for the power deficit through this intermediary parameter
3Ease of operation
If existing synchronization methods are used, then normal operation is maintained, but transient stability deteriorates during faults
Solution Approach 1:
The patent transitions from static synchronization methods to a dynamic approach where the fictitious power term adapts in real-time to changing conditions. During normal operation, the system operates as before, but during faults, the dynamic adjustment of the fictitious power term provides transient stability while maintaining ease of operation
Solution Approach 2:
The patent changes the operational parameters by introducing the fictitious power term that is activated during abnormal conditions. This parameter change allows the system to maintain normal operation characteristics during steady-state while improving transient stability during faults without complicating normal operation
Data Source
AI summary
A device includes at least one processor configured to determine a reference quantity based on a difference between a reference output power for a power inverter and an actual output power of the power inverter and cause the power inverter to control its power output based on the reference quantity. The at least one processor may be further configured to, responsive to the power inverter entering current-limiting operation, determine a non-zero power term that represents an additional amount of power that the inverter would have outputted if not current-limited; and determine the reference quantity based further on the non-zero power term.