insight - Computer Networks - # Cross-Forming Control for Grid-Forming Inverters

Cross-Forming Control for Grid-Forming Inverters: Enabling Fault Current Limiting and Grid-Forming Ancillary Services

Q: How can the proposed cross-forming control be extended to handle more complex grid fault scenarios, such as unbalanced faults or faults with varying fault impedances

The proposed cross-forming control concept can be extended to handle more complex grid fault scenarios by adapting the control strategies to accommodate unbalanced faults or faults with varying fault impedances. For unbalanced faults, the control algorithms can be modified to consider the asymmetrical nature of the fault and adjust the current references accordingly. This may involve incorporating negative-sequence control strategies to address the unbalanced conditions effectively. By extending the cross-forming control to include provisions for negative-sequence components, the inverter can respond appropriately to unbalanced faults. In the case of faults with varying fault impedances, the cross-forming control can be enhanced by incorporating adaptive algorithms that can dynamically adjust the control parameters based on the changing fault conditions. This adaptability can help the inverter maintain stability and performance even when faced with varying fault impedances. Overall, by enhancing the cross-forming control strategies to account for these more complex grid fault scenarios, grid-forming inverters can improve their resilience and effectiveness in diverse grid conditions.

Q: What are the potential challenges and limitations of the cross-forming control approach, and how can they be addressed in future research

While the cross-forming control approach offers several advantages in terms of current limiting, fault ride-through capabilities, and stability, there are potential challenges and limitations that need to be addressed in future research. One challenge is the complexity of tuning the control parameters for optimal performance, especially in dynamic grid conditions. Future research could focus on developing advanced tuning algorithms or machine learning techniques to automate the tuning process and enhance the robustness of the control strategy. Another limitation is the potential for instability or oscillations in the control system, especially during rapid changes in grid conditions. Addressing this limitation may involve implementing advanced control techniques such as predictive control or model predictive control to improve the transient response and stability of the system. Furthermore, the scalability of the cross-forming control approach to larger grid systems or interconnected networks could be a challenge. Future research could explore distributed control strategies or hierarchical control architectures to ensure the scalability and efficiency of the control approach in complex grid environments. Overall, by addressing these challenges and limitations through further research and development, the cross-forming control approach can be optimized for a wide range of grid-forming inverter applications.

Q: Given the focus on grid-forming inverters, how can the cross-forming control concept be adapted or extended to other types of power electronic converters, such as grid-following inverters or hybrid converter systems

The cross-forming control concept, initially designed for grid-forming inverters, can be adapted or extended to other types of power electronic converters, such as grid-following inverters or hybrid converter systems, by modifying the control strategies to suit the specific requirements of these systems. For grid-following inverters, the cross-forming control concept can be adjusted to prioritize voltage magnitude and frequency tracking while still incorporating current limiting capabilities. By integrating elements of both grid-forming and grid-following control strategies, the cross-forming concept can enable grid-following inverters to maintain stability and performance during grid disturbances. In the case of hybrid converter systems, which combine features of both grid-forming and grid-following inverters, the cross-forming control concept can be customized to switch between different operating modes based on the grid conditions. This flexibility allows hybrid converter systems to adapt to varying grid requirements and optimize their performance accordingly. By tailoring the cross-forming control concept to suit the specific characteristics and operational needs of different types of power converters, it can enhance the overall efficiency, stability, and reliability of these systems in diverse grid environments.

Core Concepts

The proposed cross-forming control concept enables grid-forming inverters to fast-limit fault current while preserving voltage angle forming for grid synchronization and dynamic ancillary services provision during fault ride-through.

Abstract

The paper presents a novel "cross-forming" control concept for grid-forming inverters operating against grid faults. Cross-forming refers to voltage angle forming and current magnitude forming, differing from classical grid-forming and grid-following concepts.

The key highlights are:

The cross-forming control is motivated by device security requirements for fault current limitation and grid code requirements for voltage angle forming preservation. It aims to address the technical challenges in limiting fault current, maintaining transient synchronization stability, and providing fault ride-through (FRT) ancillary services simultaneously.
Two feasible control strategies are developed to realize the cross-forming concept - angle-enforcing and current-enforcing cross-forming control. These strategies result in an equivalent system featuring a constant virtual impedance, differing from prior results.
An equivalent representation of the cross-forming inverter system is derived, which conforms to the normal form of current-unsaturated grid-forming systems. This allows extending existing transient stability analysis approaches and results to current-saturated conditions.
Simulation and experimental validations demonstrate the efficacy of the proposed cross-forming control in fast current limiting, preserving grid-forming synchronization, and providing FRT ancillary services.

The cross-forming control is fast-acting, able to fully utilize the overcurrent capability, adaptable to various disturbances, simple to implement, easy to tune, and robust in stability performance, serving as a promising candidate for future grid-forming product development.

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arxiv.org

Stats

The paper does not provide any specific numerical data or metrics. It focuses on the conceptual development and theoretical analysis of the cross-forming control.

Quotes

"Cross-forming refers to voltage angle forming and current magnitude forming, differing from classical grid-forming and grid-following concepts, i.e., voltage magnitude-and-angle forming and current magnitude-and-angle forming, respectively."
"Unlike purely grid-forming or grid-following paradigms, the cross-forming concept is motivated by device security requirements for fault current limitation and meanwhile grid code requirements for voltage angle forming preserving."
"The cross-forming control yields an equivalent system featuring a constant virtual impedance and an "equivalent normal form" of representation, making transient stability analysis tractable."

Key Insights Distilled From

Cross-Forming Control and Fault Current Limiting for Grid-Forming Inverters

by Xiuq... at arxiv.org 04-23-2024

https://arxiv.org/pdf/2404.13376.pdf

Cross-Forming Control and Fault Current Limiting for Grid-Forming Inverters

Deeper Inquiries

How can the proposed cross-forming control be extended to handle more complex grid fault scenarios, such as unbalanced faults or faults with varying fault impedances

The proposed cross-forming control concept can be extended to handle more complex grid fault scenarios by adapting the control strategies to accommodate unbalanced faults or faults with varying fault impedances.
For unbalanced faults, the control algorithms can be modified to consider the asymmetrical nature of the fault and adjust the current references accordingly. This may involve incorporating negative-sequence control strategies to address the unbalanced conditions effectively. By extending the cross-forming control to include provisions for negative-sequence components, the inverter can respond appropriately to unbalanced faults.
In the case of faults with varying fault impedances, the cross-forming control can be enhanced by incorporating adaptive algorithms that can dynamically adjust the control parameters based on the changing fault conditions. This adaptability can help the inverter maintain stability and performance even when faced with varying fault impedances.
Overall, by enhancing the cross-forming control strategies to account for these more complex grid fault scenarios, grid-forming inverters can improve their resilience and effectiveness in diverse grid conditions.

What are the potential challenges and limitations of the cross-forming control approach, and how can they be addressed in future research

While the cross-forming control approach offers several advantages in terms of current limiting, fault ride-through capabilities, and stability, there are potential challenges and limitations that need to be addressed in future research.
One challenge is the complexity of tuning the control parameters for optimal performance, especially in dynamic grid conditions. Future research could focus on developing advanced tuning algorithms or machine learning techniques to automate the tuning process and enhance the robustness of the control strategy.
Another limitation is the potential for instability or oscillations in the control system, especially during rapid changes in grid conditions. Addressing this limitation may involve implementing advanced control techniques such as predictive control or model predictive control to improve the transient response and stability of the system.
Furthermore, the scalability of the cross-forming control approach to larger grid systems or interconnected networks could be a challenge. Future research could explore distributed control strategies or hierarchical control architectures to ensure the scalability and efficiency of the control approach in complex grid environments.
Overall, by addressing these challenges and limitations through further research and development, the cross-forming control approach can be optimized for a wide range of grid-forming inverter applications.

Given the focus on grid-forming inverters, how can the cross-forming control concept be adapted or extended to other types of power electronic converters, such as grid-following inverters or hybrid converter systems

The cross-forming control concept, initially designed for grid-forming inverters, can be adapted or extended to other types of power electronic converters, such as grid-following inverters or hybrid converter systems, by modifying the control strategies to suit the specific requirements of these systems.
For grid-following inverters, the cross-forming control concept can be adjusted to prioritize voltage magnitude and frequency tracking while still incorporating current limiting capabilities. By integrating elements of both grid-forming and grid-following control strategies, the cross-forming concept can enable grid-following inverters to maintain stability and performance during grid disturbances.
In the case of hybrid converter systems, which combine features of both grid-forming and grid-following inverters, the cross-forming control concept can be customized to switch between different operating modes based on the grid conditions. This flexibility allows hybrid converter systems to adapt to varying grid requirements and optimize their performance accordingly.
By tailoring the cross-forming control concept to suit the specific characteristics and operational needs of different types of power converters, it can enhance the overall efficiency, stability, and reliability of these systems in diverse grid environments.