力电效应

物体受力后,其电参数将要发生变化。这种变化因物体(材料)性质和种类不同而不同。这些力转换成电的种种物理现象,称为力电效应。力电效应是将机械能转换为电能的物理效应。

不同作用点下压电测力仪灵敏度规律及其预测

为了测量作用位置可变的大量程矢量力,设计了多点支撑式压电测力仪。对不同作用点下测力仪的灵敏度差异性进行分析和预测,以实现精准测量变作用位置的大量程矢量力的目标。对造成测力仪不同测试位置的灵敏度差异的影响因素进行分析,得到测力仪工作面域内不同作用点下的灵敏度与测力单元力电转换系数之间的关系。进行三向变加载点标定实验,获得不同作用点下测力仪的灵敏度实验值。建立LS-SVM预测模型,利用变加载点实验结果对模型进行训练。验证实验表明,该模型预测的不同作用点下的测力仪灵敏度值与真实值的偏差小于3%。采用LS-SVM模型对不同作用点下的多点支撑式压电测力仪灵敏度进行预测具有快速、可靠和高精度的特点,该方法用于定量分析复杂关系量是有效的。

四支点压电测力仪输出稳定性提高方法研究

针对四支点测力仪中各传感器存在性能差异,导致在不同测试位置输出结果不一致的问题,提出了一种优化传感器布置次序的改善方法。根据测试时测力仪中各传感器的力分配关系,推导出了三向输出电压差异量的解析式,提出了4个布置位置所安装的传感器的各向力电转换系数差异性要求,通过标定实验进一步确定了传感器优化布置方案。在排除其他干扰因素的基础上进行了验证实验,结果表明,依照优化布置次序组装的测力仪的输出差异量降低了48%,验证了方法的可行性。

基于双层晶组的压电式四维力传感器静态特性分析与仿真

在现有压电式四维力传感器结构基础上,选用石英作为敏感元件,并根据不同切型石英的特点按特定方式进行排列组合,设计了双层晶组式传感器。通过有限元分析方法,对优化的压电式四维力传感器进行仿真,从而得到新型传感器力电转换效率、维间干扰等静态特性指标,证明了该传感器能够有效提高测量的精度。

两种由薄片式压电元件构成的换能器对比测试

为简化压电换能器制作工艺和减小结构尺寸,利用薄片式压电元件良好的力电转换特性,根据压电换能器结构不同的能量转换方式,设计并制备了冲击型和弯曲型两种换能器。通过建立对比试验,分析了两种结构的工作原理以及换能器的发电性能,并研究了加载条件的变化对换能器输出性能的影响规律。测试结果表明:弯曲型换能器在有限位移下,低频率加载时的发电性能和工作稳定性强于冲击型换能器。最后,根据对比结果提出了一种弯曲型换能器的有效封装结构。

演示“电子秤的简明原理”的教具制作

采用了学生熟悉的器材和常见的材料制作了与电子秤组成相同且原理一致的教具,该装置的力电转换部分采用了分压电路,可较好地演示电子秤的工作原理.

A new high-performance AC/DC power factor correction switching converter based on one-cycle control technology and active floating-charge technology

A new family of converters,high-performance AC/DC power factor correction(PFC) switching converters with one-cycle control technology and active floating-charge technology,was derived and experimentally verified.The topology of a single-phase CCM and DCM Boost-PFC switching converter was also analyzed.Its operating prniciples and control methods were expounded.Based on these,a new type of AC/DC switching converter circuits for PFC combined with one-cycle control technology was presented herein.The proposed AC/DC switching converter significantly helps improve the converter efficiency and its power factor value.

Comparison of the Performance of Two Direct Wave Energy Conversion Systems: Archimedes Wave Swing and Power Buoy

Many wave energy conversion devices have not been well received. The main reasons are that they are too complicated and not economical. However, in the last two decades direct conversion systems have drawn the attention of researchers to their widely distributed energy source due to their simple structure and low cost. The most well-known direct conversion systems presently in use include the Archimedes Wave Swing (AWS) and Power Buoy (PB). In this paper, these two systems were simulated in the same conditions and their behaviors were studied in different wave conditions. In order to verify the simulations, results of the generator of the finite element computations were followed. An attempt was made to determine the merits and drawbacks of each method under different wave conditions by comparing the performance of the two systems. The wave conditions suitable for each system were specified.

A study on the electrical property of HgSe under high pressure

Using a microcircuit fabricated on a diamond anvil cell, we have measured in-situ conductivity of HgSe under high pressures, and investigated the temperature dependence of conductivity under several different pressures. The result shows that HgSe has a pressure-induced transition sequence from a semimetal to a semiconductor to a metal, similar to that in HgTe. Several discontinuous changes in conductivity are observed at around 1.5, 17, 29 and 49GPa, corresponding to the phase transitions from zinc-blende to cinnabar to rocksalt to orthorhombic to an unknown structure, respectively. In comparison with HgTe, it is speculated that the unknown structure may be a distorted CsCl structure. For the cinnabar-HgSe, the energy gap as a function of pressure is obtained according to the temperature dependence of conductivity. The plot of the temperature dependence of conductivity indicates that the unknown structure of HgSe has an electrical property of a conductor.

New energy power generation-wind power generation

This paper introduced the status quo of wind power and wind power generation technology. Focusing on the introduction of wind power generating system ibrational self-consistent field（VSCF）, program implementation included Alternating Current （AC）-Direct Current （DC）-AC conversion system, magnetic field modulation generator system, doubly-fed generator system etc. Among these, doubly-fed generator system is the trend. Where to build the wind farm is very important, so a perfect site is needed. Wind power generation will have a bright future. As long as the wind power can be linked to the grid in large scale.

Theoretical Studies of Electron Paramagnetic Resonance Parameters for Cr^4＋ Ions in Ca2GeO4 Crystals

The electron paramagnetic resonance (EPR) parameters (zero-Geld splitting Dand g factors g_‖, g_⊥) of Cr~(4+) ions in Ca_2 GeO_4 crystals have been calculated from thecomplete high-order perturbation formulas of EPR parameters for a 3d~2 ion in trigonal MX_4clusters. In these formulas, in addition to the contributions to EPR parameters from the widely usedcrystal-field (CF) mechanism, the contributions from the charge-transfer (CT) mechanism (which areoften neglected) are included. From the calculations, it is found that for the high valence state3d~n ions in crystals, the reasonable explanation of EPR parameters (in particular, the g factors)should take both the CF and CT mechanisms into account.

A Review of Direct Driven PMSG for Wind Energy Systems

This paper presents a comprehensive overview study of the DDPMSG （direct driven permanent magnet synchronous generator） for wind energy generation system. Wind turbine controls are provided. The PMSG （permanent magnet synchronous generator） is introduced as construction and model. Configurations of different power converters are presented for use with DDPMSG in wind systems at variable speed operation and maximum power capture. Control techniques for the system are discussed for both machine-side and grid-side in details. Grid integration is provided with focus on how to insure power quality of the system and the performance at disturbances.

Fault Ride-Through Capability of Full-Power Converter Wind Turbine

In order to ensure power system stability, modern wind turbines are required to be able to endure deep voltage dips. The specifications that determine the voltage dip versus time are called fault r/de-through （FRT） requirements. The purpose of this paper is not only to examine the FRT behavior of a full-power converter wind turbine but also to combine the power system viewpoint to the studies. It is not enough for the turbine to be FRT capable; the loss of mains （LOM） protection of the turbine must also be set to allow the FRT. Enabling FRT, however, means that the LOM protection settings must be loosen, which may sometimes pose a safety hazard. This article introduces unique real-time simulation environment and proposes an FRT method for a wind turbine that also takes the operation of LOM protection relay into account. Simulations are carried out using the simulation environment and results show that wind turbine is able to ride-through a symmetrical power system fault.

Study on ultracapacitor-battery hybrid power system for PHEV applications

For the battery only power system is hard to meet the energy and power requirements reasonably, a hybrid power system with uhracapacitor and battery is studied. A Topology structure is analyzed that the uhracapacitor system is connected with battery pack parallel after a bidirectional DC/DC converter. The ultracapacitor, battery and the hybrid power system are modeled. For the plug-in hybrid electric vehicle （PHEV） application, the control target and control strategy of the hybrid power system are put forward. From the simulation results based on the Chinese urban driving cycle, the hybrid power system could meet the peak power requirements reasonably while the battery pack＇ s current is controlled in a reasonable limit which will be helpful to optimize the battery pack＇ s working conditions to get long cycling life and high efficiency.

Large power analysis of switched reluctance machine system for coal mine

The conventional structures in the Switched Reluctance machines are introduced, such as three-phase 12/8 structure Switched Reluctance machine, three-phase 6/4 structure Switched Reluctance machine, four-phase 16/12 structure Switched Reluctance machine, and four-phase 8/6 structure Switched Reluctance machine. Three-phase 12/8 structure Switched Reluctance machine is the best choice for the large power Switched Reluctance machine system in coal mines. The asymmetric bridge power converter main circuit and the bifilar winding power converter main circuit are also introduced. Three-phase asymmetric bridge power converter main circuit is the best choice for the large power Switched Reluctance machine system in coal mines. The magnetic paths of the designed large power motor are given with one phase excitation and double phases excitation. The phase current waveforms are also given.

Numerical Study of Thermoelectric Generation within a Reciprocal Flow Porous Media Burner

A numerical study based on direct thermal to electric energy conversion was performed in a reciprocal flow porous media burner embedded with two layers of thermoelements. The burner lean combustibility limit was sought in order to maximize global efficiency of thermal to electrical energy conversion by minimizing fuel consumption. Once the pairs of operational variables, composition and filtrational velocity of gas inlet mixture were found, the optimal length and placement of thermoelectric elements within the reactor high thermal gradients were sought to maximize the electric current, thermoelements and system overall efficiency. A two temperature-resistance model for finite time thermodynamics was developed for the thermoelectric elements energy fluxes. Results indicate a distribution of current and efficiencies that presents a maximum at different themoelements length. Maximum values for current and system efficiency obtained were 44.3 m A and 2.5%, respectively.

How the Orbital System of Particles Consolidates Gravity and Electromagnetism

There is an actual reality that underlies the relative reality of physics. The orbital system is shown to be the principle by which motion transforms space into matter. The support of the universe is the absolute three-stage hierarchy of particles, atoms, and gravitational systems. Below 1/c waves are dissociated into strands and neutrinos are separated as points of charge. The electron and positron are single strands with opposed helical turns. Protons and neutrons have a nucleus of positrinos and negatrinos surrounded by concentric shells of strands in 2＂~ resonance. The orbital strands reverberate into space creating a field with gravitational and electromagnetic aspects. The orbital system defines matter, energy, motion, and time based on composition. The three stages have a constant field content but differ by field density and components.

Short Term Load Forecast Using Wavelet Neural Network

This paper presents a wavelet neural network (WNN) model combining wavelet transform and artificial neural networks for short term load forecast (STLF). Both historical load and temperature data having important impacts on load level were used in the proposed forecasting model. The model used the three-layer feed forward network trained by the error back-propagation algorithm. To enhance the forecast- ing accuracy by neural networks, wavelet multi-resolution analysis method was introduced to pre-process these data and reconstruct the predicted output. The proposed model has been evaluated with actual data of electricity load and temperature of Hunan Province. The simulation results show that the model is capable of providing a reasonable forecasting accuracy in STLF.

On Impulse Switching Functions of Inverters as an Orthogonal System

The paper deals with impulse switching function which are used as exciting functions of one- and multidimensional state-space models of power electronic converters. Obviously, these functions are harmonic but using power converters they can be strongly non-harmonic, sometimes piecewise constants with zero spaces between them. Then, one deals with power series of time pulses. The impulse switching functions which are orthogonal ones can be derived from these series. The new impulse switching functions are created using Z-transform, inverse Z-transform and numerical series/sequences. The impulse switching functions created this way can be used for both steady- and transient state investigation of converters.

Reliability Comparison of MPPT Converter in DCM and CCM Operation

The reliability plays an important role in power electronic systems by which the number of system failures, repair costs, guarantee and etc. are estimated. In this paper first, a boost Maximum Power Point Tracker （MPPT） converter is simulated in Discontinues Conduction Mode （DCM） and Continuous Conduction Mode （CCM） under different output power ratings. For these simulations, all of the inherent parameters of MOSFET and diodes are applied according to the actual types. Then, reliability calculation is done based on MIL-HDBK-217 handbook. Results have shown that the MPPT converter would have better performance from reliability point of view in CCM operating mode.