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Zhanning Liu

Publications and source records attributed to Zhanning Liu.

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Permanent and Transient Synchronized Chaos in Large Arrays of Complex-Coupled Semiconductor Lasers

Synchronized chaos has previously been predicted and observed in a small number (3) of mutually coupled lasers. In this work, we demonstrate that this phenomenon can theoretically persist in significantly broader scenarios, extending to complex coupled arrays of up to 11 lasers and arrays with finite built-in disorder. We quantify the resulting high-dimensional dynamics by computing Lyapunov spectra and the associated Lyapunov dimension, confirming that the observed states are chaotic rather than quasi-periodic. Furthermore, we uncover a regime of transient synchronized chaos where the system eventually escapes from perfectly synchronized chaotic state into an asynchronous state. We find that the lifetime of these transient states follows a bi-exponential distribution.

physics.optics

Transient Stability Analysis for Grid Following Converters in Low-Inertia Power Systems by Direct Method

With the increased penetration of renewable energy and reduced proportion of synchronous generators, the low-inertia characteristics of todays power system become prominent, and the transient stability issue of grid following converter (GFLC) under low inertia system (LIS) condition becomes critical. There are two prominent problems in the transient stability analysis of GFLC-LIS. The angular dynamic of LIS increases the complexity of transient stability analysis, and the nonlinear, possibly negative damping of GFLC makes it difficult to guarantee the conservative of the traditional methods. These problems make the traditional methods inapplicable. In this paper, the transient stability analysis of GFLC LIS is investigated to provide an accurate estimation of the attraction boundary and critical clearance time (CCT). Firstly, a dynamic model of GFLC-LIS is constructed, considering the phase-locked loop (PLL)-based GFLC dynamics and swing equation-based LIS dynamics. The frequency mutation of PLL at fault occurrence and clearing time is also considered. Secondly, a Zubov based transient stability analysis method is proposed, which can construct the energy function in a way that is different from the traditional conservation of energy perspective and can address the negative damping issue. Moreover, the accuracy of the CCT estimation is analyzed, and the influences of LIS parameters on transient stability are illustrated. Finally, simulation experiments are carried out to verify the effectiveness of the proposed method

eess.SY