分析智能电能表出现反向有功电能量的原因及预控措施

本文分析了智能电能表出现反向有功电能量的原因,并论述了智能电能表出现反向有功电能量的预控措施。

低压配电网中单相动态电压恢复器与电力系统之间的能量流动

动态电压恢复器(DVR)工作时流经全部负载电流,其输出能量的大小则会影响储能单元充放电时间的长短。详细分析了同相位补偿、故障前补偿和最小能量补偿3种方式下DVR能量流动的规律。同相位补偿时,输出的电压最小,但在大多数时候可能输出的能量较大;故障前电压补偿方式下只要是电压发生暂降,必然需要向系统提供有功和无功才能满足控制的需求,这就对储能单元的功率输出提出了较高的要求;最小能量补偿方式下,指定补偿角的选取是关键。能量流动中有功功率的确定是配置储能单元额定储能量的前提,同时也是控制单元实现和执行补偿策略的理论依据。Matlab的仿真结果证明了以上结论。

中点钳位式三电平D-STATCOM的鲁棒电流和中点电位控制策略研究

中点电位的平衡控制是中点钳位式三电平拓扑安全可靠运行的关键,但现有文献均未能通过建立精确的数学模型对中点电位漂移的物理机理进行精确分析,控制参数整定困难。该文建立了考虑未知干扰和参数摄动影响的中点钳位式三电平D-STATCOM的精确数学模型,利用重复控制与无源性控制相结合的方法实现了基于鲁棒L_2性能准则的电流控制器设计,精确分析了参数摄动导致的有功能量分配不均是中点电位漂移的根本原因。通过零序分量注入,利用直流侧上下端电容器之间的有功能量交换实现了中点电位的平衡控制。通过仿真以及1.14 k V,±400 k Var煤矿供电系统的工程应用,验证了该文所建立模型的准确性以及所提控制算法的可行性和有效性。

APF控制及检测电路实现方法综述

有源电力滤波器APF(active power filter)是补偿电力系统谐波及无功功率的重要装置,其控制的实时性和准确性是实现有效补偿的一个关键,就目前所研究的几种有代表性的单相APF方法进行了一一分析,阐述了它们的原理,并指出了它们的缺点和优点。其中逆变器输出电压恒定控制,单周控制,基于有功能量平衡原理的并联型有源滤波器由于能够保持逆变器输出端电压恒定,并且电流畸变率(THDi)能保持在5%以下,因而具有广阔的发展前景,就最后一种方法在Matlab7.0中进行了仿真,仿真结果表明,此种方法实现的APF具有很好的谐波补偿效果。

基于三维调制的级联H桥整流器控制策略

在无工频变压器式级联式功率变换器中,级联H桥整流器直流侧电容电压平衡是变换器控制的关键问题。本文提出一种基于三维调制的级联H桥整流器直流侧电容电压平衡控制策略,通过各桥在单位时间内吸收的有功能量调节,实现直流侧电容电压平衡控制。引入有功电流和无功电流双闭环的方法对输入电流进行解耦,实现系统的单位功率因数运行。仿真实验表明,该控制策略有效地提高了直流侧电容电压平衡的控制效果。

有源电力滤波器自适应电网电流滞环控制

简要介绍了基于有功能量平衡原理的控制方法,将自适应电网电流滞环控制方法应用于三相四线制有源电力滤波器。该方法主要根据电网电压、有源电力滤波器接入点电压和电网电流的微分改变滞环电流宽度,从而实现开关频率的稳定;通过改变补偿电流的波形实现电网电流的正弦化,且在负载变化时,电网电流能实现动态稳定。该方法的特点是不需要传统的谐波电流检测,可实现数字化控制。使用Matlab仿真,其结果证明了该方法对三相四线制有源电力滤波器进行定频控制是可行的。

单相智能电表中电能计量方法的研究

如今全球智能电网的发展趋势迅猛,其核心技术也是逐步进步,同时我国政府为了刺激经济,加大力度发展智能电网。智能电表对广大用电消费者的生活非常贴近,其应用技术也在居民中广泛普及。通过智能电网的发展,作为它智能终端的智能电表已相当普及,不同于以往使用的电表,它除了一些基本的电量计算功能,更多为了适用于新能源的发展以及智能电网要求具备了新的智能化功能,如双向数据通信,用户端控制技术,多种费率双向接受计量及防窃电等。主要对单相智能电表对电能的计量方法进行了研究。通过将电压信号和电流信号分别经过高精度模数转换器,由模拟信号转化为数字信号。然后通过高通滤波器和采样滤波器,滤去直流增益与高频噪声,从而得到需要的电压和电流采样数据。将电压和电流数据相乘,可得到瞬时有功功率,经过低通滤波器输出平均有功功率。另外,电压和电流采样数据分别通过平方电路,低通滤波器,开平方电路,可以得到电压和电流的有效值。将有功功率通过时间的积分,还可以获得有功能量。

An Energy Efficient Transmission Scheme for OFDM Systems in LTE

In orthogonal frequency division multiplexing(OFDM) systems,for given total transmit power,insertion of the noninformation bearing cyclic prefix(CP) will reduce the effective energy per information bit.Generally,the energy loss is proportional to the ratio of CP length to the symbol duration.If the CP is too long,the energy loss will be considerable high.In this paper,we propose an energy efficient transmission scheme for OFDM systems in Long Term Evolution(LTE) which is developed based on reduction of the CP energy.Simulation results show that the proposed method can save up to about10%of the total energy,while keeping almost the same bit-error-rate(BER) performance in some applications.

Analysis on electric energy measuring method based on multi-resolution analysis

Along with the massive applications of the non-linear loads and the impact loads, many non-stationary stochastic signals such as harmonics, inter-harmonics, impulse signals and so on are introduced into the electric network, and these non-stationary stochastic signals have had effects on the accuracy of the measurement of electric energy. The traditional method like Fourier Analysis can he applied efficiently on the stationary stochastic signals, hut it has little effect on non-stationary stochastic signals. In light of this, the form of the signals of the electric network in wavelet domain will he discussed in this paper. A measurement method of active power based on multi-resolution analysis in the stochastic process is presented. This method has a wider application scope compared with the traditional method Fourier analysis, and it is of good referential value and practical value in terms of raising the level of the existing electric energy measurement.

基于整体能量分配的级联整流级电压平衡控制的研究

本文介绍了新一代无工频变压器大功率变换器的结构及特点,分析简化了该变换器级联整流级的电路模型。引入单相坐标变换的理论,对级联整流级在该坐标变换下的数学模型进行了详细的推导。提出了一种系统整体有功能量分配的控制方法,用于平衡级联整流级各模块直流侧的电压。仿真结果表明,该平衡策略能够较好平衡级联整流级各模块直流侧的电压,有效控制系统的有功和无功,实现整流系统单位功率因数的要求。

Research Progress of Soil Microbiology

This paper aims at summarized the research progress of soil microbes,in amount of soil microbes including bacteria,fungi and actinomycetes,soil microbial biomass,including microbial biomass carbon,microbial biomass nitrogen and microbial biomass phosphorus,function of microbial and screening and application of beneficial microorganisms etc.,and future research are discussed combined with our project team for many years of work.

Energy Efficient Power Allocation Scheme for Distributed Antenna Systems with Target BER Constraint

The energy efficiency(EE) of distributed antenna system with quality of service(Qo S) requirement is investigated over composite Rayleigh fading channel,where the shadow fading,path loss and Rayleigh fading are all considered. Our aim is to maximize the EE which is defined as the ratio of the transmission rate to the total consumed power subject to the maximum transmit power of each remote antenna constraint and Qo S(target BER) requirement. According to the definition of EE and using the upper bound of average EE,the optimized objective function is provided. Based on this,utilizing Karush-KuhnTucker conditions and numerical calculation,a suboptimal energy efficient power allocation(PA) scheme is developed,and the closedform expression of PA coefficients is derived. The scheme may obtain the EE performance close to the existing optimal scheme. Moreover,it has relatively lower complexity than the existing scheme because only the statistic channel information and less iteration are required. Simulation results show the presented scheme is valid and can meet the target BER requirement,and the EE can be increased as target BER requirement decreases.

An Integrated System for Active Filter and Photovoltaic Energy Conversion

This paper focuses on the implementation of a three-phase four-wire current-controlled Voltage Source Inverter （CC-VSI） as both power quality improvement and Photovoltaic （PV） energy extraction. For power quality improvement, the CC-VSI works as a grid current-controller shunt active power filter. Then, the PV array supported by the Hill- Climbing maximum power point tracking （MPPT） controller is coupled to the DC bus of the CC-VSI. The output of the MPPT controller is a DC voltage that determines the DC-bus voltage according to the PV maximum power. From computer simulation results, the CC-VSI is able to compensate for the harmonic and reactive power as well as to extract the PV maximum power.

Microbial D-amino acids and marine carbon storage

In nature, there are two conformational types of amino acids: L- and D-isomers. The L-amino acids are the predominant form and are used mainly for protein synthesis, while the D-amino acids are few in quantity but more diverse in terms of their biological functions. D-amino acids are produced by many marine microbes, which are important players in carbon and energy cycles in the ocean. As the major constituent of the marine organic carbon pool, D-amino acids can persist in the water column for a long time before being further transformed by chemical or biological processes or transported through physical processes(such as absorption and aggregation). This article reviews the microbial synthesis of D-amino acids, their physiological function and metabolism in microbes, and the contribution of D-amino acids as a carbon source to the oceanic carbon reservoir.

Increased working voltage of hexamine-coated porous carbon for supercapacitors

Highly porous carbon, both unmodified and hexamine-coated on the pore surfaces, is tested at high working voltages in organic electrolyte for supercapacitors in order to enhance the energy density and power density.Sol–gel processing allows for excellent control of the porous structure and chemical composition of carbon,resulting in a material with high surface area and a low level of impurities. This porous carbon can be modified using a simple solution-based method to enhance capacitance. Increasing the working voltage from 2.0 to 3.0 V significantly improves performance for both unmodified and hexamine-coated carbon. The energy density and power density increase at higher working voltage, and under certain conditions, the capacitance increases as well.Cyclic stability is also investigated, with hexamine-coated carbon retaining more of its initial capacitance than unmodified carbon at all working voltages.

Theoretical methods for excited state dynamics of molecules and molecular aggregates

This contribution provides a summary of proposed theoretical and computational studies on excited state dynamics in molecular aggregates, as an important part of the National Natural Science Foundation (NNSF) Major Project entitled "Theoretical study of the low-lying electronic excited state for molecular aggregates". This study will focus on developments of novel methods to simulate excited state dynamics of molecular aggregates, with the aim of understanding several important chemical physics processes, and providing a solid foundation for predicting the opto-electronic properties of organic functional materials and devices. The contents of this study include: (1) The quantum chemical methods for electronic excited state and electronic couplings targeted for dynamics in molecular aggregates; (2) Methods to construct effective Hamiltonian models, and to solve their dynamics using system-bath approaches; (3) Non-adiabatic mixed quantum-classic methods targeted for molecular aggregates; (4) Theoretical studies of charge and energy transfer, and related spectroscopic phenomena in molecular aggregates.