WAVE SUPERPOSITION METHOD BASED ON VIRTUAL SOURCE BOUNDARY WITH COMPLEX RADIUS VECTOR FOR SOLVING ACOUSTIC RADIATION PROBLEMS

By virtue of the comparability between the wave superposition method and the dynamic analysis of structures, a general format for overcoming the non-uniqueness of solution induced by the wave superposition method at the eigenfrequencies of the corresponding interior problems is proposed. By adding appropriate damp to the virtual source system of the wave superposition method, the unique solutions for all wave numbers can be ensured. Based on this thought, a novel method-wave superposition method with complex radius vector is constructed. Not only is the computational time of this method approximately equal to that of the standard wave superposition method, but also the accuracy is much higher compared with other correlative methods. Finally, by taking the pulsating sphere and oscillating sphere as examples, the results of calculation show that the present method can effectively overcome the non-uniqueness problem.

Finite Control Set Model Predictive Current Control of a Five-Phase PMSM with Virtual Voltage Vectors and Adaptive Control Set

This paper presents an improved finite control set model predictive current control(FCS-MPCC)of a five-phase permanent magnet synchronous motor(PMSM).First,to avoid including all the 32 voltage vectors provided by a two-level five-phase inverter into the control set,virtual voltage vectors are adopted.As the third current harmonics can be much reduced by virtual voltage vectors automatically,the harmonic items in the cost function of conventional FCS-MPCC are not considered.Furthermore,an adaptive control set is proposed based on voltage prediction.Best control set with proper voltage vector amplitude corresponding to different rotor speed can be achieved by this method.Consequently,current ripples can be largely reduced and the system performs much better.At last,simulations are established to verify the steady and transient performance of the proposed FCS-MPCC,and experiments based on a 2 kW five-phase motor are carried out.The results have validated the performance improvement of the proposed control strategy.

Editing Vector Graphics in the Virtual Simulation Environment

We present a method to represent multi-resolution vector graphics such as road networks or railway networks in virtual environment. These vector data can be interactively edited and the landscape and be explored in real time at any altitude from flight view to car view. We design a context-focused vector description of linear can areal features, with associated customized definition painter to specify their appearance （color and material） and their display mode （detailed mode or simplified mode）. There are some special problems in drawing vector graphics in virtual environment. Floating-point round-off error appear when we use a low view point to observe the scene, and it leads to scene jittering. Drawing 3D wide lines turns into a problem on 3D terrain. We design a view-based self-adaptive interpolation algorithm and an offset line generating algorithm to solve it. Our results show high performance with good visual quality.

Vector Control of the Single-Phase Inverter Based on the Extended and Virtual Circuits

A vector control based on the extended equivalent circuit and virtual circuits is proposed for the single-phase inverter.By the extended circuit,the other two phase voltages can be extended by the output voltage of the single-phase inverter so as to construct the voltage vector.The voltage outer-loop is to control the voltage vector in dq coordinate system,and the output voltage can track the target value without deviation in steady state.By designing the virtual circuit,the voltage inner-loop can achieve approximate decoupling and improve the dynamic response under the changeable load.Compared with the traditional dual closed-loop control,the proposed dual closed-loop control scheme only needs to detect and control the voltage without the current.It not only can achieve good control effect,but also reduce the complexity of the hardware.Finally,the simulation and experimental results show that the single-phase inverter has good static and dynamic characteristics regardless of stable load or changeable load.

虚拟场景中基于Motion Vector的人群图像绘制算法

针对虚拟场景中大规模人群图像绘制时由于采集图像数量有限,在视点连续变化时出现跳变的问题,提出了一种基于Motion Vector的图像绘制算法,该算法通过移动原始图像的像素位置生成相邻视点位置的图像,使得各个离散采样之间能够连续过渡,很好地解决了由于采样不足而引起的跳变问题,同时保证了绘制系统的实时性,实验结果验证了该算法的有效性。

基于Vector Panel Designer的车辆虚拟总线仪表开发

基于Vector Panel Designer平台,建立并实现了虚拟总线仪表的动态仿真。在该虚拟仪表建立的仿真环境下,可以在车辆仪表设计方案阶段对设计进行检查和仿真测试,从而降低设计成本、缩短设计周期。

Spin Supercurrent in Phenomena of Quantum Non-Locality (Quantum Correlations, Magnetic Vector Potential) and in Near-Field Antenna Effect

It is shown that such phenomena as quantum correlations (interaction of space-separated quantum entities), the action of magnetic vector potential on quantum entities in the absence of magnetic field, and near-field antenna effect (the existence of superluminally propagating electromagnetic fields) may be explained by action of spin supercurrents. In case of quantum correlations between quantum entities, spin supercurrent emerges between virtual particles pairs (virtual photons) created by those quantum entities. The explanation of magnetic vector potential and near-field antenna effect is based on contemporary principle of quantum mechanics: the physical vacuum is not an empty space but the ground state of the field consisting of quantum harmonic oscillators (QHOs) characterized by zero-point energy. Using the properties of the oscillators and spin supercurrent, it is proved that magnetic vector potential is proportional to the moment causing the orientation of spin of QHO along the direction of magnetic field. The near-field antenna effect is supposed to take place as a result of action of spin supercurrent causing secondary electromagnetic oscillations. In this way, the electromagnetic field may spread at the speed of spin supercurrent. As spin supercurrent is an inertia free process, its speed may be greater than that of light, which does not contradict postulates of special relativity that sets limits to the speed of inertial systems only.

3D Vector Reconstruction of the Neck Skeleton from the Anatomical Sections of Korean Visible Human at the Anatomical Laboratory of Paris Descartes

Aim: To perform a vector 3D reconstruction of the neck skeleton from the anatomical sections of the “Korean Visible Human” for educational purposes. Material and Methods: The anatomical subject was a 33-year-old Korean male who died of leukemia. It measured 164 cm and weighed 55 kgs. The anatomical cuts were made in 2010 after an MRI and a CT scan. A special saw (cryomacrotome) made it possible to make cuts on the frozen body of 0.2 mm thick or 5960 slices. Sections numbered 1500 to 2000 (500 neck sections) were used for this study. Manual contouring segmentation of each anatomical element of the anterior neck area was done using Winsurf software version 3.5 on a PC. Results: Our vector 3D neck model includes the following: cervical vertebrae, hyoid bone, sternum manubrium and clavicles. This vector model has been integrated into the virtual dissection table Diva3d, a new educational tool used by universities and medical schools to learn anatomy. This model was also put online on the Sketchfab website and printed in 3D using an ENDER 3 printer. Conclusion: This original work is a remarkable educational tool for the study of the skeleton of the neck and can also serve as a 3D atlas for simulation purposes for training therapeutic gestures.

3D Vector Reconstruction of the Muscles of the Ventral Region of the Neck from Anatomical Sections of Korean Visible Human at the Paris Descartes Anatomy Laboratory

Objective: To carry out a 3D vector reconstruction of the muscles of the ventral region of the neck from anatomical sections of the “Korean Visible Human” for educational purposes. Materials and Methods: The anatomical subject was a 33-year-old Korean man who died of leukemia. He was 164 cm tall and weighed 55 kgs. The anatomical sections were made in 2010 after an MRI and a CT scan. A special saw (cryomacrotome) made it possible to make cuts 0.2 mm thick on the frozen body, i.e. 5960 cuts. Sections numbered 1500 to 2000 (or 500 cuts covering the neck) were used for our study. A segmentation by manual contouring of each anatomical element of the anterior neck region was done using Winsurf version 3.5 software on a laptop PC running Windows 7 equipped with an 8 gigabyte RAM. Results: We modeled the sternocleidomastoid muscles, the supra-hyoid muscles, the infra-hyoid muscles and the muscle structures of the anterior neck region, the aero-digestive axis of the anterior neck region and the vasculo-nervous axis of the neck. This model is easily manipulated using the Acrobat 3Dpdf interface. Each item accessible in a menu can be displayed, hidden or made transparent, and 3D labels are available as well as educational menus for learning anatomy. This vector model has been integrated into the Diva3d virtual dissection table, a new educational tool used by universities and medical schools to learn anatomy. This model was also uploaded to the Sketchfab? website and 3D printed using an ENDER? pro 3 printer. Conclusion: This original work constitutes a remarkable educational tool for the anatomical study of the anterior neck region and can also be used as a 3D atlas for simulation purposes for training in therapeutic gestures.

基于简化有限集模型预测电流控制的五相PMSM统一容错控制

在五相永磁同步电机(permanent-magnet synchronous motor,PMSM)中,有限集模型预测容错控制(finite control set model predictive fault tolerant control,FCS-MPFTC)存在计算量大、电流谐波含量高等问题。因此,该文提出一种简化FCS-MPFTC来实现相开路和短路故障情况下的统一容错控制。首先,将模型预测电流控制的电流代价函数等效转化为电压代价函数,并采用无差拍方法通过电流模型计算出参考电压。然后,基于抑制三次谐波电流为0的原则合成虚拟电压矢量(virtual voltage vector,V^(3));通过重构V^(3)和扇区,以直接获得参考电压矢量对应的最优电压矢量。最后,对传统和简化FCS-MPFTC在开路和短路故障下进行对比实验。结果表明,所提策略能够有效减小故障后计算量、转矩脉动以及电流谐波含量。

永磁同步电机模型预测转矩控制共模电压抑制研究

针对永磁同步电机模型预测转矩控制共模电压较大的问题,对比分析了磁链、转矩和共模电压共同控制、直接去除零电压矢量和虚拟零电压矢量三种抑制共模电压的方法。仿真结果表明,三种方法均可有效抑制共模电压。前两种方法均未采用零电压矢量,导致磁链脉动和转矩脉动增大;虚拟零电压矢量方法既保留了零电压矢量,又有效抑制了共模电压,但开关频率有所增大;动态虚拟零电压矢量选择开关次数最小的零电压矢量生成方式,可在控制性能基本相当的前提下,有效减小开关频率,综合性能最优。

基于虚拟电压矢量的双三相直线磁通切换永磁电机容错SVPWM策略

高可靠性是电梯驱动系统的首要指标。针对双三相直线磁通切换永磁(dual-three-phase linear flux switching permanent magnet,DTP-LFSPM)电机单相开路故障,提出一种基于虚拟电压矢量的容错空间矢量脉宽调制策略。首先,基于单相开路故障下的五维变换矩阵计算得到故障后的32个空间电压矢量分布。然后,筛选部分空间电压矢量,以z子空间电压幅值为零且每个扇区产生对称的脉宽调制波形为目标,重构得到12个虚拟电压矢量,相邻的2个虚拟电压矢量都由3个基本电压矢量组成,并用于合成参考电压矢量,不仅可以减少单相开路故障容错控制时的电流谐波,而且具有计算简单,易于硬件实现等优点。最后,搭建DTP-LFSPM电机驱动控制系统仿真与实验平台,仿真和实验测试结果证明所提容错策略的正确性和有效性。

基于新型VLMZVM的ANPC型三电平并网逆变器环流抑制方法

为解决广泛应用在大功率分布式发电系统中的多机有源中点钳位(ANPC)型三电平并网逆变器间的低频零序环流问题,提出一种基于虚拟大矢量的新型十三矢量调制(VLMZVM)策略。通过建立多机ANPC型三电平并网逆变器零序环流模型,分析零序环流产生机理和影响因素,通过检测零序环流状态,实时选择虚拟大矢量或实际大矢量合成方法来抑制零序环流,并提出区分奇偶扇区的矢量分配方法快速选择合成矢量。实验结果验证了新型VLMZVM策略能在电流突变、参数不一致、全功率因数范围都具有很好的环流抑制效果。

基于人工智能的非高斯风压预测虚拟仿真实验教学

利用有限的随机风场时程数据预测未知点位置的随机风场时程,以实现虚拟仿真实验教学的目的,可在一定程度上节省实验费用和资源,降低实验测试难度。利用Matlab仿真软件建立基于支持向量机(SVM)非高斯风压预测仿真方法。仿真结果表明,SVM核函数的选择对非高斯风压预测仿真影响较大,线性核函数模型对非高斯风压的预测仿真效果优于高斯核函数与指数核函数。基于SVM线性核函数模型能有效预测非高斯风压,为风洞试验或风场实测的虚拟仿真教学提供借鉴。

基于贪婪算法的云计算数据块节能存储仿真

针对云数据储存能量消耗大的问题,提出基于贪婪算法的云计算数据块节能存储方法。建立具有用户访问层、核心服务层和服务管理层的云计算架构,了解数据块产生过程和储存环境;将物理机利用率、能源消耗量和主机储存能力作为节能储存的约束条件,将待储存的数据块封装为虚拟机,利用贪婪算法描述虚拟机部署问题,构建贪婪算法下虚拟机分配环境;计算单个物理机和整个数据中心的数据块储存能力和资源请求能力,综合考虑虚拟机分配的相关向量,运算数据储存时的能量消耗;以总体能量最小为目标函数,将虚拟机分为主模块与备用模块,通过设置虚拟机状态转换规则来减少储存开销,实现节能储存。实验结果表明,上述方法在数据储存过程中能够有效减少服务器开启数量,节省储存功率,达到节能目的。

上市公司影子银行化对金融稳定的影响与机制研究

影子银行因其规模的日益扩大及其带来的巨大影响而受到政府与学术界的广泛关注。本文基于上市公司财务数据和金融稳定相关数据,运用CRITIC指数构建法和误差修正模型,对上市公司影子银行化对金融稳定的影响与机制进行了理论分析与实证检验。研究发现:上市公司影子银行化提高了经济金融化程度,进而增加金融脆弱性而影响金融稳定。金融稳定更多受到东部、中部地区上市公司影子银行化的影响。相较于规模较小与盈利能力较弱上市公司,规模较大上市公司与盈利能力较强上市公司影子银行化对金融稳定造成的影响更大。研究结果有助于深化影子银行发展对金融稳定影响的理解,对强化上市公司金融化行为监管,维护金融稳定,实现金融高质量发展具有重要的政策意义。

一种适用三电平并联系统的虚拟矢量调制策略

直流侧中点电位平衡和零序环流抑制是保证三电平逆变器并联系统正常运行的重要问题,然而基于冗余小矢量对调节的环流抑制方案进一步增加空间矢量脉宽调制(space vector pulse width modulation,SVPWM)中点电流无法对称消除的场景,加剧双机系统中点电位不平衡程度。该文基于虚拟矢量合成思路,提出一种满足零序环流抑制和中点电位平衡需求的双机虚拟矢量调制方法。该方法重新定义虚拟中矢量,通过缩短中矢量作用时间和增加参与合成的对称冗余小矢量以减少中点电流不平衡场景;分析不同扇区不同控制目标下虚拟矢量合成规则,利用相占空比法优化虚拟矢量的作用顺序,减少矢量合成过程中的开关次数。与传统SVPWM策略下中点电压变化量的对比分析表明,所提方法能够削弱环流抑制和中点电位平衡的耦合关系。最后,利用Starsim平台实验验证该策略的有效性。

基于自然容错开关表的五相永磁同步电机直接转矩控制

五相永磁同步电机(permanent-magnetsynchronous motor,PMSM)传统直接转矩控制(direct torque control,DTC)存在相电流畸变严重、共模电压(common-modevoltage,CMV)高、转矩和磁链脉动大等问题,且无法实现相开路故障情况下的无扰运行。为解决上述问题,提出一种基于自然容错开关表的DTC策略。该策略根据PMSM开路故障前后基电压矢量的特点以及三次平面合成电压矢量为零的原则,构建虚拟矢量(virtual vector,VV),设计故障前后同一套自然容错开关表,进而不但抑制了故障导致的转矩脉动,而且在故障前后均能降低三次谐波电流、减小转矩和磁链脉动、抑制CMV。实验结果验证所提策略的可行性。

永磁同步电机低共模电压和低复杂度无差拍预测控制

针对永磁同步电机无差拍预测控制共模电压较大的问题,在一个控制周期内采用相位相反的基本电压矢量来生成虚拟零电压矢量抑制共模电压,并采用动态选择虚拟电压矢量生成方式来减小开关频率。为了提升无差拍预测控制性能,构造12个虚拟非零电压矢量来增加备选电压矢量。仿真结果表明:与7个基本备选电压矢量相比,基于19个备选电压矢量的无差拍预测控制降低转矩脉动6.89%,降低磁链脉动13.33%,同时共模电压也得到有效抑制。相较固定生成方式,动态选择虚拟电压矢量生成方式可降低开关频率25.89%。虽然该方法可有效提升系统性能,但增加遍历次数,极大增大计算量。为提高算法实时性,提出一种通过判断理想电压矢量所在区域来确定最优电压矢量简化确定方法,无需遍历计算,减小运算负担。基于STM32H743IIT6单片机实时性试验表明:相较于7个基本电压矢量,采用19个电压矢量算法执行时间增大273.40%,最优电压矢量简化确定方法执行时间减小88.09%。