Grid-Forming Inverter Negative-Sequence Current Control
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Solution Overview
Problem
Existing grid-forming control schemes for inverter-based resources, such as wind turbines, primarily focus on positive-sequence voltages and currents, failing to effectively manage negative-sequence currents, which can lead to voltage imbalances and stability issues in the power grid.
Innovation Solution
A method and system for providing grid-forming control that involves receiving negative-sequence feedback signals, determining control signals for desired negative-sequence impedance, and generating control commands to achieve the desired impedance, allowing the inverter-based resource to absorb negative-sequence current up to a dynamically set limit, thereby balancing grid voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grid-forming control schemes focus primarily on positive-sequence voltages and currents, then the control system remains simple and conventional, but negative-sequence currents are not effectively managed leading to voltage imbalances and stability issues
Solution Approach 1:
The control system is segmented into separate positive-sequence and negative-sequence control pathways. The negative-sequence current is extracted and controlled independently through a dedicated regulator, allowing targeted management of negative-sequence components without complicating the entire control system.
Solution Approach 2:
The patent applies local quality by implementing specific negative-sequence control only where needed - in the negative-sequence pathway - while leaving the positive-sequence control conventional. This localized enhancement improves grid stability without requiring complete system redesign.
2Reliability
If the inverter-based resource absorbs negative-sequence current up to a fixed limit, then voltage balance is improved, but the equipment may operate beyond its current capability during high negative-sequence conditions
Solution Approach 1:
The negative-sequence current limit is made dynamic rather than fixed. The regulator adjusts the allowable negative-sequence current based on real-time equipment capability and grid conditions, enabling maximum voltage balance support while preventing equipment overload through adaptive limit adjustment.
Solution Approach 2:
The patent changes the parameter of negative-sequence current limit from a static value to a dynamic parameter that adapts to operating conditions. This allows the system to optimize voltage balance while respecting equipment constraints under varying load and grid conditions.
3Device complexity
If conventional current source control is used assuming fundamental voltage waveforms with fixed frequency and magnitude, then the control system is simple, but wind power fluctuations cause increases in magnitude and frequency variations in grid voltage
Solution Approach 1:
The patent implements feedback by using a negative-sequence regulator that continuously monitors negative-sequence current and adjusts the control output accordingly. This closed-loop control detects voltage imbalances and automatically compensates, improving grid voltage stability without requiring complex open-loop control schemes.
Data Source
AI summary
A method for providing grid-forming control of an inverter-based resource includes receiving a negative-sequence voltage feedback of the inverter-based resource. The method also includes receiving at least one negative-sequence feedback signal of the inverter-based resource. The method also includes determining, via a negative-sequence regulator, one or more control signals indicative of a desired negative-sequence impedance of the inverter-based resource using the at least one negative-sequence feedback signal. Further, the method includes generating, via the negative-sequence regulator, a control command for the inverter-based resource based on the one or more control signals. Moreover, the method includes controlling the inverter-based resource based on the control command to achieve the desired negative-sequence impedance of the inverter-based resource.