MMC的稳态相量模型及功率运行区间计算方法

模块化多电平换流器(MMC)的控制器输出量与MMC内部电气量之间存在复杂的耦合关系,难以确定影响其输出功率范围的关键因素及计算功率运行区间的边界。为此,首先以dq坐标相量的形式,推导出一种新的MMC的交流侧稳态等效模型,该模型为1个等效电容与等效电压源串联。模型参数可完全由控制器输出量和直流电压确定,从而将控制输出量与运行电气量解耦;等效电容直观地反映了MMC子模块电容充放电过程造成的换流器内部耦合特性对交流侧输出特性的影响。利用所提模型可以方便地计算得到MMC输出功率的P-Q曲线。然后,通过计算P-Q曲线族的包络线,提出一种确定MMC稳态运行区域边界的方法,并研究了环流抑制控制和交流系统短路比对运行区域的影响。最后,在PSCAD/EMTDC平台上搭建单端MMC仿真模型,验证了所提模型及稳态运行区间计算方法的正确性。

基于自适应移频分析法的Voltage-Behind-Reactance异步电机多时间尺度暂态建模与仿真

为满足对电力系统多时间尺度暂态过程准确、快速仿真的需要,提出了一种基于自适应移频分析法的voltage-behind-reactance(VBR)异步电机多时间尺度模型。首先,基于希尔伯特变换,将传统电气信号转换为相应的解析信号;进一步,引入灵活的移频变换,利用解析信号构建异步电机暂态仿真模型。这样,移动频率成为可调节的模型参数。所提出的电机模型通过设置不同的移动频率,能够同时实现准确的高频暂态过程仿真和高效的低频暂态过程仿真。当移动频率等于零时,该模型与传统电磁暂态电机模型等价,可刻画高频暂态过程。当移动频率等于系统基波频率时,该模型适用于大步长仿真,获得低频暂态包络曲线。仿真结果表明,所提出的模型可实现准确和高效的异步电机多时间尺度暂态仿真。

Energies and Transition Rates of Low-Lying Excited States for Beryllium

Low lying excited states of beryllium are calculated with multiconfiguration interaction method. The relativisitic corrections and mass polarization are included. The oscillator strength and radiation rates are also calculated. Our results are in good agreement with other theoretical data.

Influence of the Interaction Between Phonons and Coulomb Potential on the Properties of a Bound Polaron in a Quantum Dot

The properties of a bound polaron in a parabolic quantum dot with weak electron-LO-phonon coupling under a Coulomb field are studied. The ground state energy of the bound polaron is derived by using a linear combination operator and the perturbation method. The influence of the interaction between phonons with different wave vectors in the recoil process on the ground state energy of the bound polaron is discussed. Numerical calculations are performed,and the results show that the ground state energy increases significantly as the effective confinement length of the quantum dot decreases,considering of the interaction between phonons. When l0〉1.0, the influence of the interaction between phonons on the ground state energy cannot be ignored.

Analysis on the Essential Characters and Biological Yield Change of Purple-fleshed Sweetpotato Xuzishu 3

Objective] This study was performed to investigate the trait changes and their correlations as wel as the dynamic changes of biological yield of Xuzishu 3, which wil help to enhance the yield and anthocyanin content of sweetpotato by cul-tivation. [Method] We systematical y measured the agronomic traits, qualitative char-acters and biological yield of Xuzishu 3 during six growing periods to investigate the dynamic changes of its essential characters and yield accumulation. [Result] The characters of Xuzishu 3 appeared most prosperous after the 90th d except for an-thocyanin content. Extremely significant positive correlations were found between ev-ery two of the dry matter rates of above-ground parts （including leaf petioles, leaves and stems）, reducing sugar content and potato weight per plant. Assimilated product distributed more in stems and leaves than in storage roots before the 90th d in growing period. Photosynthetic capacity and net assimilation rate gradual y de-creased after the 90th d, but the assimilated product distributing to storage roots in-creased quickly and maximized in the 135th d. [Conclusion] Xuzishu 3 is a late ma-turing variety requiring more fertilizer, and the accumulation of anthocyanin fluctuates during the growth period of Xuzishu 3. So yield of Xuzishu 3 can be increased by applying more fertilizer and extending the growth period reasonably, meanwhile the anthocyanin content can be increased by means of control ing temperature, light, water and phytohormone within 60 d after planting.

Teleportation of Two-Particle Entangled State via Cluster State

In this paper, two schemes for teleporting an unknown two-particle entangled state from the sender （Alice） to the receiver （Bob） via a four-particle entangled cluster state are proposed. In these two schemes, the unknown twoparticle entangled state can be teleported perfectly. The successful probabilities and fidelities of the schemes can reach unity.

New Damage Detection Index Based on Mid-span Displacement and Its Application to Simply Supported Beam

This study presents a new idea of using only mid-span displacement measurement for damage detection of simply supported beams. Equivalent element concept is introduced at the beginning. In order to relate the damage detectability by means of mid-span dlsplacement measurement with the damage-eaused local stiffness change, a novel index termed as symmetrical mid-span displacement difference index （SMDDI） is proposed. The proposed method based on SMDDI is sensitive to tiny damage and comparatively small quantities of measurements are required during the application process. Another significant attraction of this method is putting aside the knowledge a-priori of the intact state. An example using simulated data has been conducted to examine the suitability of this method and assess its comparative advantages over the previous modal method.

Quantum Secure Direct Intercommunication with Superdense Coding and Entanglement Swapping

A quantum secure direct intercommunication scheme is proposed to exchange directly the communicators＇ secret messages by making ase of swapping entanglement of Bell states. It has great capacity to distribute the secret messages since these messages have been imposed on high-dimensional Bell states via the local unitary operations with superdense coding. The security is ensured by the secure transmission of the travel sequences and the application of entanglement swapping.

Quantum Properties of Two-Mode Squeezed Even and Odd Coherent States

Two new types of quantum states are constructed by applying the operator s（ξ） = exp（ξ＊ ab - ξa＋b＋） on the two-mode even and odd coherent states. The mathematical and quantum statistical properties of such states are investigated. Various nonclassical features of these states, such as squeezing properties, the inter-mode photon bunching, and the violation of Cauchy-Schwarz inequality, are discussed. The Wigner function in these states are studied in detail.

Generalized Bargmann Representation of Spin Coherent State

Based on the conclusion that the generalized Bargmann representation of a two-mode Fock state is a two-variable Hermite polynomial function /Hong-Yi Fan and Jun-hua Chen,Phys.Lett.A303(2002)311] we derive the generalized Bargmann representation of the spin coherent state and some new relations in the generalized function space.

Study of Concurrence and D-Concurrence on Two-Qubits Resulted in Pair Coherent States in Language of SU(2) Coherent States

Pair coherent state, is a state of a two-mode radiation field that is known as a state with non-gaussian wave function. In this paper, study on the pair coherent state, we notice that with superposition of two first terms of this states, one two-qubits formed. Because of the importance of two-qubits in theory of quantum entanglement, with two different measures with the title of concurrence and D-concurrence, we have studied the amount of entanglement and discussed its details. At the end, we describe these measures for pair coherent states as a function of the amplitude of the SU（2） coherent states.

A Scheme for Teleportation of an Unknown Entangled Coherent State via Raman Interaction

A scheme is reported for the teleportation of entangled coherent states through the degenerate Raman interaction. The scheme uses an entangled state of an atom and two coherent states as a quantum channel. It makes lull use of coherent cavity fields. Furthermore, it does not need any classical field to transform the atom states.

Conditional Generation of Multiparticle Entanglement via Cavity QED

We propose a simple scheme to not only generate GHZ states and W states of the multiparticle but also form a new category of multiparticle entangled states by letting the A-type three-level atoms simultaneously interacting with a coherent cavity field followed by the selective measurements on the cavity mode. We investigate the influence of the cavity dissipation on the generated entangled state and discuss the experimental feasibility of our scheme. It is shown that the intensity of the coherent cavity field plays an instructive role in contribution to state preparation process while the cavity decay and the detuning between the atoms and cavity mode result in the deterioration of the generated entangled state.

Properties of Coherent State for Hydrogen Atom

We construct the coherent state for the two-dimensional hydrogen atom,for which the averaged motion of position describes a Kepler ellipse.The coherent state can be expanded with respect to the eigenstates of 2D hydrogen atom,from which we evaluate the binding energy of the wave packet for this state.

New Formulation of Weyl Quantization Scheme in Coherent State Representation

By virtue of the technique of integration within an ordered product of operators we present a new formulation of the Weyl quantization scheme in the coherent state representation, which not only brings convenience for calculating the Weyl correspondence of normally ordered operators, but also directly leads us to find both the coherent state representation and the Weyl ordering representation of the Wigner operator.

Influence of substituting Ni with Co on hydriding and dehydriding kinetics of melt spun nanocrystalline and amorphous Mg_2Ni-type alloys

In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys,Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox (x=0,0.1,0.2,0.3,0.4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied with an X-ray diffractometer (XRD) and a high resolution transmission electronic microscope (HRTEM). An investigation on the thermal stability of the as-spun alloys was carried out with a differential scanning calorimeter (DSC). The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results demonstrate that the substitution of Co for Ni does not alter the major phase of Mg2Ni but results in the formation of secondary phase MgCo2. No amorphous phase is detected in the as-spun Co-free alloy,but a certain amount of amorphous phase is clearly found in the as-spun Co-containing alloys. The substitution of Co for Ni exerts a slight influence on the hydriding kinetics of the as-spun alloy. However,it dramatically enhances the dehydriding kinetics of the as-cast and spun alloys. As Co content (x) increases from 0 to 0.4,the hydrogen desorption capacity increases from 0.19% to 1.39% (mass fraction) in 20 min for the as-cast alloy,and from 0.89% to 2.18% (mass fraction) for the as-spun alloy (30 m/s).

Preparation of Highly Squeezed States and Multi—component Entangled Coherent States via the Raman Interaction

A method is presented for generating highly squeezed states of a cavity field via the atom-cavity field interaction of the Raman type. In the scheme a sequence of three-level -type atoms interacts with a cavity field, displaced by a classical source, in a Raman manner. Then the atomic states are measured. By this way the cavity field may collapse onto a superposition of several coherent states, which exhibits strong squeezing. The scheme can also be used to prepare superpositions of many two-mode coherent states for two cavity fields. The coherent states in each mode are on a straight line. This is the first way for preparing multi-component entangled coherent states of this type in cavity QED.

A random forest algorithm based on similarity measure and dynamic weighted voting

The random forest model is universal and easy to understand, which is often used for classification and prediction. However, it uses non-selective integration and the majority rule to judge the final result, thus the difference between the decision trees in the model is ignored and the prediction accuracy of the model is reduced. Taking into consideration these defects, an improved random forest model based on confusion matrix (CM-RF)is proposed. The decision tree cluster is selectively constructed by the similarity measure in the process of constructing the model, and the result is output by using the dynamic weighted voting fusion method in the final voting session. Experiments show that the proposed CM-RF can reduce the impact of low-performance decision trees on the output result, thus improving the accuracy and generalization ability of random forest model.

Entanglement Involved in Pair Coherent State Studied via Wigner Function Formalism

We calculate Wigner function, tomogram of the pair coherent state by using its Sehmidt decomposition in the coherent state representation. It turns out that the Wigner function can be seen as the quantum entanglement （QE） between two two-variable Hermite polynomials （TVHP） and the tomogram is further simplified as QE of two single-variable Hermite polynomials. The Husimi function of pair coherent state is also calculated.

Dynamical Suppression of Nonlocal Decoherence in Two-State Quantum Systems

Nonlocal decoherence of two qubits due to pure phase damping has been investigated.We have proposeda scheme to keep the entanglement of two qubits from nonlocal decoherence.By applying a series of±π pulses,nonlocaldecoherence can be thoroughly suppressed.