Fostering microgeneration in power systems: The effect of legislative limitations

The large-scale integration of microgeneration (MG) can bring several technical benefits, such as: improving the voltage profile, reducing power losses and allowing for network capacity investment deferral. Furthermore, it is now widely accepted that introducing new renewable MG, such as wind turbines, photovoltaic panels or biomass can help control carbon emissions, reduce our dependence on oil and contribute to a sustainable energy growth. This paper presents an empirical analysis of the benefits of MG on avoided losses, voltage profiles and branch congestion. The main goal is to clarify whether the current regulatory framework allows for obtaining all the MG potential gains. The main conclusion is that some legal constraints should be removed, or at least relaxed, in order to promote the growth of distributed power generation, particularly, for domestic MG.     

Assessing the contribution of microgrids to the reliability of distribution networks

The emergence of microgeneration has recently lead to the concept of microgrid, a network of LV consumers and producers able to export electric energy in some circumstances and also to work in an isolated way in emergency situations. Research on the organization of microgrids, control devices, functionalities and other technical aspects is presently being carried out, in order to establish a consistent technical framework to support the concept.     

人工神经网络预测技术在微网运行中的应用

针对微网中用电高峰时期电能短缺的问题,提出根据预测系统控制微网的运行模式可以充分发挥分布式电源的优势,最大限度地利用网内资源供电,减轻主网压力。文中借助人工神经网络算法,预测微网中的微电源和负荷,以此分析和规划微网的运行方式。实测数据的仿真结果表明在配网高负荷时期引入预测系统后,微网的供电可靠性和节能减排效果都得到了极大地提高,可为微网的运行方式提供可行的建议。     

微电网规划评价指标体系构建与应用

为了更客观地评价规划阶段中不同结构微电网的优劣,针对微电源组合方式多样、运行方式灵活等特点,将微电网评价指标分为可靠性、经济性、市场运营和环保性4个方面,对各指标进行展开说明,并构建了树状结构。结合实际算例,先利用微分进化算法对构建的目标函数进行优化求解,得到多种微电网组合,再利用层次分析法对得到的微电网进行综合评价决策。介绍了采用该方法进行微电网综合评价决策的计算过程。实例表明,提出的方法合理地避免了微电网规划阶段因决策因素可能导致的不确定性和专家评判的主观性,是一种较实用的微电网规划综合评价问题的解决方法。     

Analysis of the World Experience of Smart Grid Deployment: Economic Effectiveness Issues

Despite the positive dynamics in the growth of RES-based power production in electric power systems of many countries, the further development of commercially mature technologies of wind and solar generation is often constrained by the existing grid infrastructure and conventional energy supply practices. The integration of large wind and solar power plants into a single power grid and the development of microgeneration require the widespread introduction of a new smart grid technology cluster (smart power grids), whose technical advantages over the conventional ones have been fairly well studied, while issues of their economic effectiveness remain open. Estimation and forecasting potential economic effects from the introduction of innovative technologies in the power sector during the stage preceding commercial development is a methodologically difficult task that requires the use of knowledge from different sciences. This paper contains the analysis of smart grid project implementation in Europe and the United States. Interval estimates are obtained for their basic economic parameters. It was revealed that the majority of smart grid implemented projects are not yet commercially effective, since their positive externalities are usually not recognized on the revenue side due to the lack of universal methods for public benefits monetization. The results of the research can be used in modernization and development planning for the existing grid infrastructure both at the federal level and at the level of certain regions and territories.     

Fast harmonic simulation method for the analysis of network losses with converter-connected distributed generation

The use of distributed generation (DG) in low voltage grids is becoming more common. The impact of the DG units is considered, with an emphasis on the effect of DG on the network losses. These losses consist of fundamental and harmonic losses. The converter-connected DG units have a different influence on these two terms of the total losses. The aim of this paper is to present a fast harmonic simulation model that can be applied to study the influence of a DG unit on the total losses and elucidate the importance of the harmonic losses in proportion to the total losses.     

Optimization-based method of dividing the network development costs

Paper presented the main aspect in efficiency of distribution of network. Losses are inevitably connected with the flow of energy, however not all of them are direct function of the flow. Calculation of losses requires firstly their breakdown according to their source of origin. Technical load losses can be divided into three levels: “real losses i.e. the ones that really exist in the network, justified losses i.e. the ones that may be achieved at efficient operation of the network, optimal losses i.e. the ones, at which level the costs of distribution and supply are the lowest”. Calculation of real losses in the distribution network is not sufficient for the evaluation of this network. Comparison of losses, even as percentage of the total energy in the network between different areas e.g. regions doesn’t lead to meaningful conclusions. One has to compare real losses with justified or optimal losses. It has to be stressed that unjustified losses i.e. the difference between real losses and justified losses are insignificant, in the range of 2–3% i.e. approx. 10–15% of real losses on average. In case of a single region, the difference may be larger. Presentation of the network as a set of elements enables its optimisation as a whole. The cost factors from the optimisation of network development point of view are: (1) deprecation costs of construction of the station, (2) deprecation costs of construction of the line and, (3) costs of losses.     

A novel nucleolus-based loss allocation method in bilateral electricity markets

The situation of current research on power losses allocation in bilateral electricity markets is presented. Based on cooperative game theory, a novel nucleolus theory-based method for power losses allocation under the bilateral-transactions model is put forward and compared in detail with the Shapley-value-based allocation method. The impacts of different market players on network power losses are taken into account. With the new method, network power losses can be allocated to each transaction reasonably. The allocation results would not be affected by the sequence that each transaction is formed and be active. The method answers for the open, equal, and impartial principles of electricity market and can be easily understood and accepted by market players. Numerical tests validated the equity and validity of the method.     

基于叠加定理和Aumann-Shapley法的发电权交易网损分摊

发电权交易使得电网的潮流以及损耗发生变化,对电网的运行成本产生影响,因此如何有效计及这种影响并对电网进行相应的补偿是亟待解决的问题。为解决此问题,首先针对断面网损进行研究,在断面下将输电网等效为线性电路,发电机和负荷等效为电流源,通过叠加原理确定各支路潮流及功率损耗与各电流源的关系式,进而确定发电权交易量与网损变化量的关系式。其次,将网损分摊看作一个合作博弈问题,即网损是由所有参与者共同合作的结果。应用Aumann-Shapley法对支路的互耦合功率损耗进行分摊,可保证结果公平合理,且具有经济一致性。最后,通过IEEE9节点标准算例进行仿真,验证了所提方法的正确性和有效性。     

Optimal voltage profiles in transmission networks taking into account the phenomenon of corona

This paper is devoted to the study of corona losses and their influence on the optimization of voltage profiles and reactive flows in transmission networks. It is shown that the influence of corona on an optimal voltage profile obtained by minimization of the total active losses in the lines is very important under foul-weather conditions. The results of the study have motivated the proposal that, under conditions of extremely intensive corona, a different voltage strategy, opposite to the usual one, should be applied. The new strategy consists in setting consumer bus voltages to some reasonable low value, which is contrary to the usual operating practice where all generator bus voltages are set to the maximum allowable value. Such an inverse voltage strategy appears to be an efficient measure for reducing the total active losses (resistance losses plus corona losses) in the operation of transmission networks, without jeopardizing the security of the system operation.     

Assessment of energy distribution losses for increasing penetration of distributed generation

High levels of penetration of distributed generation (DG) are a new challenge for traditional electric power systems. Power injections from DGs change network power flows modifying energy losses. Although it is considered that DG reduce losses, this paper shows that this is not always true. This paper presents an approach to compute annual energy losses variations when different penetration and concentration levels of DG are connected to a distribution network. In addition, the impact on losses of different DG technologies, such as combined heat and power, wind power, photovoltaic, and fuel-cells, is analyzed. Results show that energy losses variation, as a function of the DG penetration level, presents a characteristic U-shape trajectory. Moreover, when DG units are more dispersed along network feeders, higher losses reduction can be expected. Regarding DG technologies, it should be noted that wind power is the one that shows the worst behavior in losses reduction. Finally, DG units with reactive power control provide a better network voltage profile and lower losses.     

基于谐波损耗的干式变压器降容研究

IEEE Std C57.110中给出了计算电流畸变情况下变压器损耗的计算方法,其利用绕组涡流谐波损耗因子和杂散谐波损耗因子计算变压器的涡流损耗和杂散损耗,但忽略了绕组高频交流情况下集肤效应和邻近效应引起的附加损耗,计算精度受到一定影响。为了精确计算变压器谐波情况下的损耗,引入了绕组电阻谐波损耗因子,考虑了谐波情况下绕组集肤效应引起的损耗,并据此计算变压器最大负荷电流。在此基础上,研究了电流畸变率对干式变压器降容率的影响,计算结果表明谐波对干式变压器最大负荷电流及带负载能力有较大影响,当谐波畸变率达到60%时,变压器带负荷能力减小一半。     

Quantitative evaluation of perpendicular‐field losses in stacked high‐Tc superconducting tapes

The influence of stacks of Bi‐2223 multifilamentary tape‐shaped wires without twisting on AC losses observed in an external magnetic field perpendicular to their wide faces is investigated. The perpendicular‐field losses decrease with increasing number of tapes in the range of small field amplitudes. At larger amplitudes, on the other hand, the AC losses have little dependence on the stack number. This can be attributed to the effect of magnetic interaction between wires. By taking into account effective demagnetization factors on the basis of theoretical consideration, the perpendicular‐field losses are plotted on a master curve for the maximum magnetic field applied to the wires. Furthermore, the perpendicular‐field losses measured as a function of the field amplitude are well reproduced by the numerical evaluation of AC losses for a slab with infinitely wide surfaces. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 50–57, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10050     

高频电感气隙布置与绕组损耗的分析

针对高频电感的绕组损耗问题,利用有限元数值分析,研究了气隙位置的变化对电感器绕组损耗的影响,比较了不均匀分布气隙与均匀分布气隙对绕组损耗的影响,并对分布气隙参数提出了合理的设计原则.结果表明：气隙位置开在拐角处会增加绕组损耗.相对于不均匀分布气隙,均匀分布气隙有利于减小绕组损耗,且可以将分布气隙个数增加到使绕组距气隙的避让距离控制在3～5个气隙距之间,同时分布气隙间磁柱的长度大于6个气隙距,以得到较小的绕组损耗.     

计及变频器和电机损耗的全变速泵站效率优化控制

针对已有研究泵站效率优化的文献均未涉及变频器和电机损耗的现状,提出计及变频器和电机损耗的全变速泵站效率优化模型,利用枚举法和约束变尺度优化算法求解模型,得到最佳控制策略.对比不计变频器和电机损耗的全变速泵站优化模型,进行大量的仿真实验和经济效益分析.结果表明,在相同给水指标下,变频器和电机损耗不影响全变速泵站效率优化控制的优化决策,在仅以求得优化决策为目的的情况下,可不予考虑,以简化建模和求解过程;但在评估泵站的节能效果时,必须考虑.     

反激式电源设计中MOSFET的选择与功耗验证

讨论了反激电源设计的另外一个方面,即MOSFET场效应管的选择和功耗验证,提出了相应的计算公式与验证流程。该思想也可用于其它电路设计中的MOSFET检验。     

开关磁阻电机铁损的双频法有限元计算研究

文中对1台三相12/8结构开关磁阻电机进行了四分之一域的二维(2D)电磁场有限元分析,得到了大小和方向都随时间变化的铁心磁密矢量的X和Y分量,从而更细致地描述了电机铁心各单元磁密随时间(转子位置角度)的变化周期和规律。在无需知道电机铁心材料的损耗系数(即涡流修正因子和局部磁滞回线因子)的情况下,以磁密的计算信息和铁心材料单位体积的铁损密度数据为基础,通过双频法分离出铁损中的涡流损耗和磁滞损耗,再用频率分解法和最大磁密法分别计算这2种损耗,并对占电机铁心铁损较大比例的涡流损耗进行了离散傅里叶分解,比较各次谐波分量对铁损的影响。由间接法计算出铁损的实验值,近似地分离了铁损和杂散损耗,实验验证了该铁损计算方法的准确性。     

Loss analysis based on constant gate current for MOSFET selection of CCM boost converter

Predicting the power losses in a semiconductor is an essential design process to determine the converter's size. In the continuous conduction mode (CCM) boost converter, the power loss of MOSFETs can be divided into the loss not depending on the gate current (the conduction loss) and losses depending on the gate current (the switching losses) leading to I_DS transition period and V_DS transition period. Therefore, analysis of both conduction and switching losses based on constant gate current can realize the MOSFET selection to improve the efficiency of the CCM boost converter.     

Assignment of turn-on and turn-off power and energy losses in a GTO

The authors discuss the turn-on and turn-off losses in a gate turn-off (GTO) thyristor which must be properly accounted for because they can comprise upwards of 60% of the total losses. The authors attempt to discuss and clarify the definitions of power loss and energy per pulse for the turn-on and turn-off intervals. It is shown that prior work defining turn-on and turn-off power and energy losses does not adequately include all losses associated with the turn-on and turn-off events. Thus, it will be difficult to account for all those losses determining the heating effects of the GTO unless improvements are made. An example shows that the error can be substantial (8 to 15%). For this reason, improved definitions that have an underestimation of only 1 to 2% of the switching losses have been proposed. It was also found that the gate losses during the turn-off event must be accounted for and that improved measuring techniques and instrumentation are both necessary and possible     

提高小型电机效率的方法

介绍提高小型电机效率的主要途径和降低各种损耗应采取的措施,通过性能分析阐述降低各种损耗对提高电机效率的影响,为高效电机的发展提供一些技术参考。