Three-Phase Unbalance Prediction of Electric Power Based on Hierarchical Temporal Memory

The difference in electricity and power usage time leads to an unbalanced current among the three phases in the power grid.The three-phase unbalanced is closely related to power planning and load distribution.When the unbalance occurs,the safe operation of the electrical equipment will be seriously jeopardized.This paper proposes a Hierarchical Temporal Memory(HTM)-based three-phase unbalance prediction model consisted by the encoder for binary coding,the spatial pooler for frequency pattern learning,the temporal pooler for pattern sequence learning,and the sparse distributed representations classifier for unbalance prediction.Following the feasibility of spatial-temporal streaming data analysis,we adopted this brain-liked neural network to a real-time prediction for power load.We applied the model in five cities(Tangshan,Langfang,Qinhuangdao,Chengde,Zhangjiakou)of north China.We experimented with the proposed model and Long Short-term Memory(LSTM)model and analyzed the predict results and real currents.The results show that the predictions conform to the reality;compared to LSTM,the HTM-based prediction model shows enhanced accuracy and stability.The prediction model could serve for the overload warning and the load planning to provide high-quality power grid operation.

Research of Three-Phase Unbalanced Treatment in Low-Voltage Distribution Network Based on New Commutation Switch

Low-voltage distribution systems in our country are mostly used in agricultural loads and household loads. The value and using time of these kinds of loads are uncontrollable, which lead to the three-phase imbalance in low-voltage distribution system, and seriously affect the quality of power supply. A new type of the commutation system and an improved quantum genetic algorithm (IQGA) are proposed in the paper. At last, the rationality and the efficiency of the method are verified by a practical example.

Performance Analysis of Unbalance Radial Feeder with Time Varying Composite Load

The focus of this paper is to present performance indices for unbalance radial feeder having different characteristic and composition of time varying static ZIP load models. These provide a framework for benchmarking of distribution automation projects. 15 minutes characteristics time interval for load flow and load modeling are considered to meet smart grid implementation criterion. A forward-backward sweep method is employed for load flow solution. Developed performance indices were illustrated on modified IEEE 37 node test feeder. Performance indices are useful for analysis, operational, planning and integration of stochastic renewable sources.

Research on a New Control Strategy of Three Phase Inverter for Unbalanced Loads

One of the very important functions of three-phase inverter is to maintain the symmetric three-phase output voltage when the three-phase loads are unbalanced. Although the traditional symmetrical component decomposing and superimpose theory can keep the voltage balance through compensating the positive-, negative- and zero-sequence components of the output voltage of inverter, however, this method is time-consuming and not suitable for control. Aiming at high power medium frequency inverter source, a P+Resonant (Proportion and Resonant) controller which ensured a balanced three phase output voltage under unbalanced load is proposed in this paper. The regulator was proved to be applicable to both three-phase three-wire system and three-phase four-wire system and developed two methods of realization. The simulation results verified that this method can suppressed effectively the output voltage distorted caused by the unbalanced load and attained a high quality voltage waveforms.

Unbalance Level Regulating Algorithm in Power Distribution Networks

The paper dwells on the unified power quality indexes characterizing the phenomenon of voltage unbalance in three-phase systems. Voltage unbalance is one of the commonest occurrences in the town mains of 0.38 kV voltage. The phenomenon describes as inequality of vector magnitude of phase voltage and shearing angle between them. Causes and consequences of the voltage unbalance in distribution networks have been considered. The algorithm, which allows switching one-phase load, has been developed as one of the methods of reducing the unbalance level. The algorithm is written in the function block diagram programming language. For determining the duration and magnitude of the unbalance level it is proposed to introduce the forecasting algorithm. The necessary data for forecasting are accumulated in the course of the algorithm based on the Function Block Diagram. The algorithm example is given for transforming substation of the urban electrical power supply system. The results of the economic efficiency assessment of the algorithm implementation are shown in conclusion. The use of automatic switching of the one-phase load for explored substation allows reducing energy losses (active electric energy by 7.63%;reactive energy by 8.37%). It also allows improving supply quality to a consumer. For explored substation the average zero-sequence unbalance factor has dropped from 3.59% to 2.13%, and the negative-sequence unbalance factor has dropped from 0.61% to 0.36%.

The Control Technology Research of the Z-source Three-phase Four-bridge Arm Inverter

Z-source inverter can boost the voltage of the DC-side, allow the two switches of the same bridge arm conducting at the same time and it has some other advantages. The zero-sequence current flows through the fourth leg of the three-phase four-leg inverter so the three-phase four-leg inverter can work with unbalanced load. This paper presents a Z-source three-phase four-leg inverter which combines a Z-source network with three-phase four-leg inverter. The circuit uses simple SPWM modulation technique and the fourth bridge arm uses fully compensated control method. The inverter can maintain a symmetrical output voltage when the proposed scheme under the unbalanced load.

Three-Phase Optimal Power Flow for Study of PV Plant Distributed Impact on Distribution Systems

This paper presents a TOPF （three-phase optimal power flow） model that represents photovoltaic systems. The PV plant is modeled in the TOPF as active and reactive power source. Reactive power can be generated or absorbed using the available capacity and the adjustable power factor of the inverter. The reduction of unbalance voltage and losses in the distribution systems is obtained by actions of reactive power control of the inverter. The TOPF is formulated by current balance equations and the PV systems are modeled via an equivalent circuit. The primal-dual interior point method is used to obtain the optimal operating points for the systems for different scenarios of solar irradiance and temperature, thus providing a detailed view of the impact of photovoltaic distributed generation.

一种三相线电压级联单位功率因数整流器负载不均衡特性分析及电压均衡控制策略

该文对一种由三个三相单开关整流器线电压级联构成的三相单位功率因数整流器的负载不均衡特性和输出电压均衡控制策略进行分析和研究,首先详细阐述此类整流器在三个直流侧负载不均衡时,交流输入端电流能自动保持均衡的独特特性及相应工作机理;然后研究系统整体分层控制策略。在传统的基于电压外环PI控制、电流内环PR控制的上层控制基础上,针对各整流模块参数不一致及负载功率不一致引起的各模块输出电压不均衡问题,通过加入偏差因子调制波补偿的底层控制,实现了对每个模块输出功率的独立调节,进而实现了各整流模块输出电压的均衡控制。仿真和实验结果验证了所研究拓扑结构的优越性和控制策略的可行性。

基于中性线电流离散分析治理三相负荷不平衡

当三相负荷不平衡时,必然会引起中性线电流的产生。针对三种不同三相负荷不平衡条件下中性线电流的变化情况,建立与之对应的三相负荷不平衡度算法模型。采用中性线电流的离散分析建立三相负荷不平衡度算法,作为三相负荷不平衡治理的有效判据,结合试验分析,得到了三相负荷不平衡度与中性线电流的变化规律,并应用于低压供配电系统三相负荷不平衡的治理分析。结果表明:所提三相负荷不平衡度算法对低压供配电系统三相负荷不平衡的治理具有较强的实用性。提出的以三相负荷不平衡度为自适应变量,以中性线电流为过程监测量,采用有功调配与无功补偿相结合策略,能够有效反映三相负荷不平衡的治理情况。

单相PET级联整流SVPWM均压边界及拓展方法

电力电子变压器(power electronic transformer,PET)是交直流配电系统互联的重要接口设备,然而后级等效负载不平衡将造成前级整流器各模块的电压偏移。针对单相级联H桥整流器空间矢量调制均压失效问题,推导出基于最优矢量选择均压策略的边界计算方法。根据计算所得的负载不平衡度限制边界与级联模块数、调制度以及功率因数的关系,提出了变调制度和功率因数的控制策略以增加均压能力。该策略通过改变直流电压或降低功率因数来重建更宽的均压工作范围,确保原不平衡度均压极限的系统稳定运行。最后,通过三模块级联整流器的仿真与实验验证了该均压边界的正确性,以及所提均压拓展方法保障极端不平衡负载条件下均压的有效性。

Optimal Planning of Hybrid AC/DC Low-voltage Distribution Networks Considering DC Conversion of Three-phase Four-wire Low-voltage AC Systems

The increasing integration of distributed household photovoltaics(PVs)and electric vehicles(EVs)may further ag gravate voltage violations and unbalance of low-voltage distribu tion networks(LVDNs).DC distribution networks can increase the accommodation of PVs and EVs and mitigate mutilple pow er quality problems by the flexible power regulation capability of voltage source converters.This paper proposes schemes to es tablish hybrid AC/DC LVDNs considering the conversion of the existing three-phase four-wire low-voltage AC systems to DC op eration.The characteristics and DC conversion constraints of typical LVDNs are analyzed.In addition,converter configura tions for typical LVDNs are proposed based on the three-phase four-wire characteristics and quantitative analysis of various DC configurations.Moreover,an optimal planning method of hybrid AC/DC LVDNs is proposed,which is modeled as a bi-level programming model considering the annual investments and three-phase unbalance.Simulations are conducted to verify the effectiveness of the proposed optimal planning method.Sim ulation results show that the proposed optimal planning method can increase the integration of PVs while simultaneously reduc ing issues related to voltage violation and unbalance.

偏载作用下菱形负刚度隔振系统的刚度特性

为探究偏载对菱形负刚度隔振系统刚度的影响,课题组基于力学分析方法,建立了偏载作用下隔振系统的数学模型,得到其无量纲刚度-位移非线性曲线,分析了偏载对其准零刚度特性的影响。利用Simulink进行仿真实验,给偏载作用下的隔振系统振动基座施加激励,得到了不同激励下隔振系统的时变刚度;结合傅里叶变换,探讨了隔振系统刚度的时变特性和幅频特性。结果表明:偏载越大,低刚度区间越窄,准零刚度特性越弱;时变刚度波动范围与峰值随偏载的增加而变大,但时变刚度的波动趋势不受偏载的影响;时变刚度幅值主要集中在低频区间,随频率的增加而减小,最终趋近于0。研究表明偏载对隔振系统的刚度会产生一定的影响。

铁路集装箱超偏载检测装置溯源研究

在阐述铁路集装箱超偏载检测装置计量特性的基础上,分别从总重、横向偏移量、纵向偏重量的定义及示值误差等方面,分析铁路集装箱超偏载检测装置的主要计量性能要求。结合铁路集装箱超偏载检测装置量值溯源工作,探讨铁路集装箱超偏载检测装置的量值溯源方法及注意事项,以便理解铁路集装箱超偏载检测装置的量值溯源本质和要求。

搭接-叠片式箔片气体动压轴承转子动力学特性实验研究

本文研制了由搭接式径向轴承和叠片式推力轴承组成的一套搭接-叠片式箔片气体动压轴承,同时设计并搭建了相应的箔片气体动压轴承转子实验台,通过多组转子降速对比实验研究了所提出箔片气体动压轴承的起飞特性,分析了转子不平衡量和外部载荷对该轴承-转子系统的转子动力学影响。起飞实验结果表明,本文所研制的搭接式径向箔片气体动压轴承的起飞转速约为7500 r/min,最大起飞转矩约为220 N·mm。转子降速实验研究结果表明,随着转子不平衡量的增加,转子系统1X频振动幅值逐渐增大、二阶临界转速逐渐降低、次频振动发生频率逐渐提前;随着转子转速的增加,转子系统1X频振动呈现先增大后减小的趋势、次频振动幅值整体逐渐增大;在减小顶箔结构的圆心距后,转子系统稳定性增加。不平衡量与外部载荷加载耦合实验结果表明,不平衡量与外部载荷都会激起系统的次频振动,次频振动幅值随转速升高而增大;并且在激起次频振动方面,不平衡量与外部载荷之间存在着相互放大作用。

主燃油泵轴承剥落故障探究

【目的】查明某型发动机配套主燃油泵所用滚子轴承内外滚道剥落的原因,可以提高主燃油泵寿命和可靠性。【方法】本文对主燃油泵所用滚子轴承的结构组成、配合间隙、滚道受力等进行仿真分析。【结果】导致滚道剥落的原因为偏载引起的局部应力超出材料的许用范围。本研究还查出了轴承偏载的原因。针对偏载原因制定了控制间隙和滚子修形的措施。经仿真分析和试验验证,证明了措施的可行性。【结论】该问题的解决提高了主燃油泵的寿命和可靠性,同时为同类滚动轴承的设计和剥落故障分析提供了依据和参考方案。

解析TB/T 3096-2023《铁路货车超偏载检测装置》

介绍TB/T 3096—2023《铁路货车超偏载检测装置》的修订背景。从术语和定义、环境条件、总体技术要求、主要部件技术要求、安装技术要求、控制室要求、计量性能要求、计量性能试验方法等方面,解析TB/T 3096—2023的主要内容,以便标准使用者更好地理解该标准。

四极电子式RCD用于单相负荷的缺陷探讨

研究了四极电子式RCD用于单相负荷理论上的可行性。运用实例和理论分析,证明了单相负荷不平衡并不影响四极电子式RCD的动作特性。运用实例分析了单相负荷接地故障受自然泄漏电流干扰的情况,得知导致四极电子式RCD误动作的原因是自然泄漏电流。提出四极RCD接单相负荷易出现“断零”事故,并提出采用“3P+N”极RCD可避免此种事故。

采用双剪力传感器的铁路货车超偏载检测装置设计

针对在既有线安装铁路货车超偏载检测装置存在的施工周期长、成本高、对线路条件要求高等问题,设计一种采用双剪力传感器的铁路货车超偏载检测装置。在介绍采用双剪力传感器的铁路货车超偏载检测装置设计原理的基础上,分析这种铁路货车超偏载检测装置的总体技术要求及设计方案,评定其测量不确定度,并进行检定和应用验证。结果表明,采用双剪力传感器的铁路货车超偏载检测装置各秤量点的重量测量结果不确定度均小于称重最大允许误差的1/3,满足计量性能要求;重量、偏重和偏载率检定结果均满足设计要求;与现有铁路货车超偏载检测装置测得的货车重量、偏重差、偏载率相比,采用双剪力传感器的超偏载检测装置测得的货车重量、偏重差、偏载率的偏差均较小,检测结果准确度满足货运安全检测要求。

Control strategy for microgrid under three-phase unbalance condition

Microgrid(MG) is generally developed at utility terminal which contains lots of unbalanced loads and distributed generations(DGs). The interaction between MG and the unbalance loads or DGs will degrades the control performance of interfaced inverter in MG and dramatically leads to MG voltage unbalance. In this paper, a negative-sequence compensation based three-phase voltage unified correction strategy is proposed. While MG operates in islanded mode, a positive virtual impedance control is used to eliminate the negative voltage resulted from the negative-sequence current,and then a positive-sequence voltage control loop and negative-sequence control loop are used to improve the inverter control performance. While MG operates in grid-tied mode,the inverter operates as a negative-sequence current source to compensate the negative-sequence currents of loads to guarantee the point of common coupling(PCC) voltage balance.By using the proposed strategy, the voltage control performance of inverter can be improved;the MG power quality can be enhanced significantly. Simulation and experimental results verify the effectiveness of the proposed method.

适用于双负载模式的Vienna整流器调制方法

在工程应用中,Vienna整流器常处于双负载模式给串联电池组充电以提高效率和降低成本,此时,上、下直流侧的输出电压和功率不再相等,矢量的合成变得非常复杂。文中从载波的角度进行分析,通过注入零序电压实现了上、下直流侧输出功率的解耦和中点电压的主动控制,简化了计算过程。基于Vienna整流器拓扑的输出电平约束和调制约束分析了零序电压的约束条件,并基于上述约束条件给出了不同运行状态下Vienna整流器的上、下直流侧可输出的极限功率,为工程参数设计提供参考。此外,分析了双负载运行状态下Vienna整流器的电流过零畸变问题,提出了抑制电流过零畸变的方法,并直接给出了三相调制电压。实验结果验证了理论分析的正确性和所提方法的优越性。