Accurate Dynamic Phasor Modeling and Stability Analysis of Single-Phase Grid-Forming Converters

Core Concepts

This letter proposes an accurate dynamic phasor model of single-phase grid-forming converters that captures the dynamics of the orthogonal signal generation unit, enabling improved stability analysis compared to existing models.

Abstract

The key highlights and insights from the content are:

Modern power systems are transitioning from centralized fossil-fuel-based generation to distributed renewable energy generation, where renewable energies are coupled to the grid through grid-tied converters. Grid-forming converters (GFMCs) have emerged as an enabling technology, especially for single-phase applications.

Existing modeling approaches, such as impedance and state-space modeling, have limitations in accurately describing the dynamics of single-phase GFMCs. The dynamics of the nonlinear orthogonal signal generation unit, crucial for power measurement, have been ignored in previous models, leading to inaccuracies.

The letter proposes a dynamic phasor model of single-phase GFMCs that captures the dynamics of the orthogonal signal generation unit. The model is derived rigorously and linearized for small-signal stability analysis.

The stability analysis using the proposed model reveals that some eigenvalues are located in the right half plane, indicating system instability, which is not captured by existing models. This demonstrates the improved accuracy of the proposed dynamic phasor model.

Experimental results validate the accuracy of the proposed dynamic phasor model, showing that the single-phase GFMC operates unstably with a low damping coefficient (Dg = 4) and stably with a higher damping coefficient (Dg = 10), consistent with the theoretical analysis.

Stats

The following sentences contain key metrics or important figures used to support the author's key logics:
The grid is modelled as a serial connection of the inductor Ls, resistor Rs, and voltage source vs.
The grid-forming converter is coupled to the grid via an LCL filter (including Lgi, Cgf, and Lgg).
The system parameters are listed in Table I, including the rated/grid voltage (V0/Vs), rated power/frequency (S0/f0), active/reactive power reference (pg_ref/qg_ref), line inductance/resistance (Lgs/Rs), reactive power droop gain (kq), and inertia/damping coefficient (Hg/Dg).

Quotes

"The dynamics of orthogonal signal generation units have been ignored, leading to the inaccuracy of existing models. As a result, the instability of GFMCs will be hidden."
"The stability analysis results verify that the proposed dynamic phasor model can accurately predict the system stability, while other existing models fail to do so."

Key Insights Distilled From

Dynamic Phasor Modeling of Single-Phase Grid-Forming Converters

by Wenjia Si,Ch... at arxiv.org 04-18-2024

https://arxiv.org/pdf/2404.11304.pdf

Deeper Inquiries

How can the proposed dynamic phasor modeling approach be extended to three-phase grid-forming converters to capture their unique dynamics

The proposed dynamic phasor modeling approach for single-phase grid-forming converters can be extended to three-phase grid-forming converters by considering the additional complexities and dynamics inherent in three-phase systems. One key aspect would be to incorporate the dynamics of the three-phase system, including the interactions between phases and the impact of unbalanced conditions.
To capture the unique dynamics of three-phase converters, the modeling approach would need to account for the interconnection between the phases, the presence of zero-sequence components, and the interactions between the different control loops in a three-phase system. Additionally, the modeling should consider the spatial distribution of power and the effects of asymmetrical loading on the system's stability and performance.
By extending the dynamic phasor modeling approach to three-phase grid-forming converters, a more comprehensive understanding of the system's behavior can be achieved, enabling better control strategies and improved stability analysis for complex three-phase power systems.

What are the potential limitations of the dynamic phasor modeling technique, and how can it be further improved to address more complex power converter topologies and control structures

While dynamic phasor modeling offers a valuable framework for capturing the dynamics of grid-forming converters, there are potential limitations that need to be addressed for more complex power converter topologies and control structures.
One limitation is the assumption of linearity in the modeling approach, which may not fully capture the nonlinear behavior of certain power converters under varying operating conditions. To address this, nonlinear elements can be incorporated into the model to improve accuracy.
Another limitation is the simplification of certain components in the model, which may overlook important dynamics that could impact system performance. Enhancements can be made by including more detailed models of individual components, such as the LCL filter, to better represent their behavior.
To further improve the dynamic phasor modeling technique, advanced control strategies, such as predictive control or model predictive control, can be integrated into the model to enhance the system's response to dynamic grid conditions. Additionally, incorporating real-time data feedback and adaptive algorithms can make the model more robust and adaptable to changing system requirements.
Overall, by addressing these limitations and incorporating more advanced modeling techniques, the dynamic phasor modeling approach can be enhanced to better accommodate complex power converter topologies and control structures, improving the accuracy and effectiveness of the models.

Given the importance of accurate modeling for the stability and control of grid-forming converters, how can the insights from this work be applied to the design and optimization of renewable energy integration systems

The insights gained from the dynamic phasor modeling of grid-forming converters can be applied to the design and optimization of renewable energy integration systems to enhance their stability and performance.
By accurately modeling the dynamics of grid-forming converters, system designers can better understand the interactions between renewable energy sources and the grid, enabling the development of more effective control strategies for power flow management and grid support.
The modeling approach can be used to optimize the sizing and placement of renewable energy systems within the grid, ensuring maximum efficiency and reliability while maintaining grid stability. By simulating different operating scenarios and grid conditions, system designers can assess the impact of renewable energy integration on grid stability and identify potential issues before deployment.
Furthermore, the insights from the modeling work can inform the development of advanced control algorithms for renewable energy systems, enabling them to provide grid support services, such as frequency regulation and voltage control, in a more dynamic and responsive manner.
Overall, by leveraging the findings from the dynamic phasor modeling of grid-forming converters, designers and operators of renewable energy integration systems can enhance their understanding of system behavior and improve the overall performance and reliability of renewable energy integration into the grid.