一种电动汽车能量高效回馈制动方法

为提高电动汽车的能量利用率,提出了一种将可变电压系统作为电机驱动系统实现能量回馈的方法,利用可串并联切换的超级电容器组与双向直流功率变换器相结合,采用了2种回馈制动模式的控制策略,提高了电机到驱动系统电源之间能量流的传递效率和变换效率,实现了速度大范围变化的能量回馈。与常规制动方法相比,上述方法具有驱动系统体积小、成本低、能量回馈效率高的特点,通过计算机仿真对采用不同回馈制动方法时的3种情况进行了对比分析,仿真结果验证了该方法的可行性和有效性。     

谈谈电力系统无功补偿装置

变电站无功补偿装置是电力系统中重要设备之一,变电站并列电容器组是保证系统电压质量和降低电能损耗的重要设备,从理论上通过简单的计算,得出并联电容器组的各设备间的配合问题,为装置各元件的设计、安装设计,运行提供参考依据。     

对银行批扣电费工作的思考

分析了银行批扣电费系统的优越性和开展银行批扣电费的可行性,探讨了银行批扣电费方式的应用前景,认为这是使得用电客户、供电企业和银行三方都受益的工程,提出了积极推广银行批扣电费工作的实施措施。     

Numerical investigation of erosion on a staggered tube bank by particle laden flows with immersed boundary method

In the present paper, particle-laden flows past 10 × 11 staggered stainless steel tube banks in a duct and the caused erosion are investigated using point-particle Eulerian–Lagrangian method. The continuous gas flow field is obtained through direct numerical simulation. The coupling between fluid and the embedded tubes is handled through the multi-direct forcing immersed boundary method. Four types of coal ash particles with Stokes numbers 0.01, 0.1, 1.0, 10.0, are considered. The collision and erosion characteristics on the tubes located in the middle of the duct are analyzed in detail. It has been found that the global tube erosion of the first tube increases with the increment of the particle size, but particles with an intermediate Stokes number of 1.0 cause the most erosion to the other downstream tubes due to preferential accumulation effect. Results predict much more erosion to the second row of tubes in staggered tube banks than the first row of tubes. Global erosion to the tubes near the wall is much larger than the corresponding ones located in the center, especially far downstream. The maximum local tube erosion occurs within certain angle regions around the tubes, where more attention needs to be paid to prevent erosion.     

Frequency of Undulations on a Falling Water Film

An experimental study has been undertaken on the frequency of presented by the undulations occurring on the surface of a falling liquid film. The configuration of the film surface was observed by measuring the changes in the film thickness by means of a capacitometer. The flow regime was in the range of turbulent flow region, in which the undulations occur prominently and travel down along with the fluid film. The undulations proceed downward in an almost fixed pattern. The frequency of the passage of crests observed from a fixed point was evaluated from power spectral analysis to be about 20–30Hz, and this value changed very little with the Reynolds number and with heat flux applied to the falling liquid film. It is shown that this constancy of observed frequency is related to the fact that the large undulations move at the same velocity as the bulk of the fluid film, and that the speed of propagation is corresponding to a group velocity for ripples on the film surface.     

频变扩展重迭变换的快速算法

频变扩展重迭变换（FV-ELT）是一类具有灵活时频分辨率特性的非均匀滤波器组,适用于音频编码中时频映射处理部分。本文主要给出基于DCT-IV的FV-ELT快速算法,并给出复杂度计算公式。最后以几种典型滤波器组应用结构为例,给出了所需乘加运算次数。与直接计算模式相比,此快速算法能有效地降低FV-ELT的运算复杂度。     

Design of face-centred orthorhombic filter banks

In this paper, a method to design the two-channel FIR linear-phase (LP) face-centred orthorhombic (FCO) filter banks with equiripple magnitude responses and perfect-reconstruction (PR) is presented. The necessary conditions of lengths of LP FCO filter banks satisfying the PR constraint are derived. An interior-point algorithm is utilized to optimize the peak ripples of the analysis filters and a first-order approximation skill is introduced to satisfy the PR constraint. The simulation example is presented to illustrate the effectiveness of this proposed design technique.     

Nonlinear Discrete Wavelet Transforms over Finite Sets and an Application to Binary Image Compression

The discrete wavelet transform was originally a linear operator that works on signals that are modeled as functions from the integers into the real or complex numbers. However, many signals have discrete function values. This paper builds on two recent developments: the extension of the discrete wavelet transform to finite-valued signals and the research of nonlinear wavelet transforms triggered by the introduction of the lifting scheme by Sweldens. It defines discrete wavelet transforms as bijective, translation-invariant decompositions of signals that are functions from the integers into any finite set. Such transforms are essentially nonlinear, but they can be calculated very time efficiently since only discrete arithmetic is needed. Properties of these generalized discrete wavelet transforms are given along with an elaborate example of such a transform. In addition, the paper presents some ideas to find explicit examples of discrete wavelet transforms over finite sets. These ideas are used to show that, in case the finite set is a ring, there are much more nonlinear transforms than linear transforms. Finally, the paper exploits this increased number of transforms to do lossless compression of binary images.The research is sponsored (grant no. 613.006.570) by the Dutch Science Foundation (NWO).     

低温工况下结霜对翅片管蒸发器性能影响研究

翅片管蒸发器的结霜将增加空气压降，增大传热热阻，从而直接影响到蒸发器的效率及空气侧平均换热系数，本文就低温工况下，结霜对蒸发器性能的影响进行了测试研究，为翅片管蒸发器的设计应用提供了重要依据。