arXiv subjects

Jingyang Fang

Publications and source records attributed to Jingyang Fang.

4 recordsLinked to original sources

arXiv2026

The role of symmetries on the stability of power grids

The stability of power grids principally depends on the synchronization of multiple generating units. So far, the relationship between grid stability and symmetries remains unclear. This article fills in the research gap by innovatively using the mathematical tool of group theory. We find that grid symmetries involve two aspects-network and component symmetries, which reflect the homogeneities of network structures and generating units, respectively. As disclosed, the stability of power grids has a tight bearing on network and component symmetries, where corresponding automorphism group and symmetric subgroup orders reflect their levels of symmetries, respectively. In the perspective of network symmetries, where grid stability and synchronization speed are dictated by the algebraic connectivity, the stability ranking list of grids with four generators is K4 > C4 > K13 > R4 > P4 > X4, which fully agrees with that of network symmetries. In terms of component symmetries, the stability of power grids largely benefits from improved component symmetries yet with R4 as an exceptional case, where it is recommended to avoid the centralized effort of a single generator. These conclusions have significant implications for the control of modern power grids with distributed resources and controllable generators, including energy storage and renewable power generators interfaced by grid-following/-forming converters.

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arXiv2024

Generalized Averaging Method for Power Electronics Modeling from DC to above Half the Switching Frequency

Modeling power electronic converters at frequencies close to or above half the switching frequency has been difficult due to the time-variant and discontinuous switching actions. This paper uses the properties of moving Fourier coefficients to develop the generalized averaging method, breaking though the limit of half the switching frequency. The paper also proposes the generalized average model for various switching signals, including pulse-width modulation (PWM), phase-shift modulation, pulse-frequency modulation (PFM), and state-dependent switching signals, so that circuits and modulators/controllers can be modeled separately and combined flexibly. Using the Laplace transform of moving Fourier coefficients, the coupling of signals and their sidebands at different frequencies is clearly described as the coupling of moving Fourier coefficients at the same frequency in a linear time-invariant system framework. The modeling method is applied to a PWM controlled boost converter, a V2 constant on-time controlled buck converter, and a PFM controlled LLC converter, for demonstration and validation. Experimental results of the converters in different operating modes show that the proposed models have higher accuracy than exiting models, especially in the frequency range close to or above half the switching frequency. The developed method can be applied to almost all types of power electronic converters.

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arXiv2024

Dynamic Phasor Modeling of Single-Phase Grid-Forming Converters

In modern power systems, grid-forming power converters (GFMCs) have emerged as an enabling technology. However, the modeling of single-phase GFMCs faces new challenges. In particular, the nonlinear orthogonal signal generation unit, crucial for power measurement, still lacks an accurate model. To overcome the challenges, this letter proposes a dynamic phasor model of single-phase GFMCs. Moreover, we linearize the proposed model and perform stability analysis, which confirm that the proposed model is more accurate than existing models. Experimental results validate the improved accuracy of the proposed dynamic phasor model.

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arXiv2019

A Simplified Dynamical Model for Tuned Wireless Power Transfer Systems

Dynamical models of wireless power transfer (WPT) systems are of primary importance for the dynamical behavior studies and controller design. However, the existing dynamical models usually suffer from high orders and complicated forms due to the complex nature of the coupled resonances and switched-mode power converters in WPT systems. This letter finds that a well-tuned WPT system can be accurately described by a much simpler dynamical model. Specifically, at the tuned condition, the existing dynamical model can be decomposed into two parts. One is controllable and the other one is uncontrollable. The former should be considered in the modeling while the latter can be ignored because it always exponentially converges to zero. For illustration, the recently proposed zero-voltage-switching full-bridge pulse-density modulation WPT system is modeled as an example since such a system can efficiently operate at the tuned condition with soft switching and control capabilities. The derived model was verified in experiments by time-domain and frequency-domain responses.

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