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Synchronous control on inverter system of grid connected high-power wind generators with nonlinear and pulse disturbance#br#
LIU Jiang, ZHANG Long, JIANG Zhong-chuan, LI Yan-qing
Applied Mathematics A Journal of Chinese Universities, 2017, 32(4): 388-402.
A kind of synchronization control problems of grid system connected high-power wind generators with nonlinear pulse disturbance was investigated in this paper. By using the Kirchhoff's law, a class of mathematical model of grid side converter system of wind generators was established. Meanwhile, an appropriate feedback synchronization controller was designed. By the theory of Lyapunov stability, the e?ectiveness of synchronous controller was validated. In order to restrain the nonlinear pulse disturbance in grid system connected with wind generators, make the current generated by wind generators synchronize the current in grid, an optimal algorithm was obtained. Finally, the theoretical results were demonstrated by the Simulink in Matlab.
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Complex oscillation of solutions of some second order non-homogeneous linear di?erential equations#br#
YUAN Rong, LIU Hui-fang
Applied Mathematics A Journal of Chinese Universities, 2017, 32(4): 431-436.
In this paper, the growth and the distribution of zeros of solutions to some second order non-homogeneous differential equations $f''+A\text{e}^{az^n}f'+(B_1\text{e}^{bz^n}+B_0\text{e}^{dz^n})f=F(z)$ are investigated, where $F$ is a nonzero entire function with order less than $n$, $A, B_1, B_0$ are nonzero polynomials. Under an appropriate assumption on complex numbers $a, b, d$, the precise estimations on the hyper order and the hyper convergence exponent of zeros of solutions of such equation are obtained.
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High accuracy analysis of a new low order nonconforming mixed finite element method for the EFK equation
ZHANG Hou-chao, SHI Dong-yang
Applied Mathematics A Journal of Chinese Universities, 2017, 32(4): 437-454.
With the help of $EQ^{rot}_1$ element and zero order Raviart-Thomas(R-T) elements, a new nonconforming mixed finite elements approximation scheme is proposed for the extended Fisher-Kolmogorov equation(EFK). Firstly, a priori estimate of approximation solutions is proved and the existence and uniqueness are also derived for semi-discrete scheme. Based on the high accuracy analysis of two elements and the priori estimate of the finite element solutions, the superclose properties of order $O(h^{2})$ for the primitive solution $u$ and the intermediate variable $v=-\Delta u~$in~$H^{1}$-norm and flux $\vec{p}=\nabla u$ in $(L^{2})^{2}$-norm are obtained without the boundedness of numerical solution $u_{h}$ in $L^{\infty}$-norm, respectively. Meanwhile, the global superconvergent error estimates for above variables of order $O(h^{2})$ are proved through interpolated postprocessing technique. Secondly, a new linearized backward Euler full-discrete scheme is established, the existence and uniqueness of approximation scheme are proved. On the other hand, the superclose properties of order $O(h^{2}+\tau)$ for variable $u,v$ in $H^{1}$-norm and $\vec{p}$ in $(L^{2})^{2}$-norm are obtained respectively through a new splitting technique for consistent error estimate and nonlinear term, which have never been considered in the previous literature. Furthermore, the global superconvergent estimates for above variables are deduced by interpolated postprocessing technique.~Here,~$h,~\tau$~are parameters of the subdivision in space and time step, respectively. Finally, numerical results are provided to confirm the theoretical analysis.
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Arc-disjoint Hamiltonian cycles and paths in positive-round digraphs#br#
LI Rui-juan, HAN Ting-ting
Applied Mathematics A Journal of Chinese Universities, 2017, 32(4): 487-492.
In 2012, Bang-Jensen and Huang (\emph{J. Combin. Theory Ser. B}. 2012, {\noindent\bf 102}: 701-714) proved that every $2$-arc-strong locally semicomplete digraph has two arc-disjoint strongly connected spanning subdigraphs, and conjectured that every $3$-strong local tournament has two arc-disjoint hamiltonian cycles. In this paper, the arc-disjoint hamiltonian paths and cycles in positive-round digraphs are discussed, and the following results are proved: every 3-arc-strong positive-round digraph contains two arc-disjoint hamiltonian cycles and every 4-arc-strong positive-round digraph contains one hamiltonian cycle and two hamiltonian paths, such that they are arc-disjoint pairwise. A round digraph must be positive-round, thus those conclusions on positive-round digraphs can be generalized to round digraphs. Since round digraphs form the subclass of local tournaments, Bang-Jensen and Huang's conjecture holds for round digraphs which is the subclass of local tournaments.
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12 articles
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