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.

Sliding mode control of three-phase AC/DC converters using exponential rate reaching law

Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are involved in the SMC operation, namely reaching mode and sliding mode.In the reaching mode, the system state is forced to reach the sliding surface in a finite time.The major drawback of the SMC approach is the occurrence of chattering in the sliding mode, which is undesirable in most applications.Generally, the trade-off between chattering reduction and fast reaching time must be considered in the conventional SMC design.This paper proposes SMC design with a novel reaching law called the exponential rate reaching law(ERRL) to reduce chattering, and the control structure of the converter is designed based on the multiinput SMC that is applied to a three-phase AC/DC power converter.The simulation and experimental results show the effectiveness of the proposed technique.

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.

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.

薄盘工件加工过程中的不平衡量分析及去重方法研究

薄盘工件是转子机构上常见的零/部件,在装配调试前通常需要进行动平衡测试与校正。目前常用的不平衡校正方法存在加工与校正分离、平衡工艺复杂,以及效率低等问题。基于该问题提出在薄盘工件加工过程中不平衡量校正的方法,结合复合数控机床的主轴准停、刀具定位及去重控制等功能,进行薄盘工件不平衡量在线去重校正。同时,为了提高薄盘工件不平衡量在线去重校正精度,提出一种附加去重率的迭代控制方法,并从理论上证明了该方法的稳定性。通过仿真计算讨论了附加去重率的迭代控制方法优势,探讨了理想去重率的选取问题。研究内容可以在无动平衡机的情况下实现薄盘工件不平衡量在线去重校正,对创新性解决薄片工件平衡成本高、效率低等问题以及提高工件加工精度等方面具有重要的意义。

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.

利用换相开关治理低压台区三相不平衡问题的研究

在对换相开关治理低压台区三相不平衡的有效性进行研究的基础上,提出了一种基于分析三相不平衡节点电气参数等数据以确定换相开关安装位置及优先级的方法。通过工程实际应用换相开关,验证得出换相开关能够缓解三相不平衡问题的结论。通过对应用换相开关的典型台区进行仿真分析,得出换相开关能够降低线损率的结论。

某车型传动系剩余动不平衡引起轰鸣问题研究

以某前置后驱车为研究对象,针对客户抱怨的车内轰鸣问题进行了噪音和振动检测,解析数据后发现,传动系阶次噪音对车内轰鸣声贡献最大。文章对传动系阶次激励的来源、传递路径及车体响应进行了机理性分析,并根据轰鸣产生路径依次列出潜在解决措施并试制样件进行验证。结果表明,管控关键因子(隔振率、传动系模态)、抑制噪音因子(装配间隙产生的偏心量)对解决由传动系剩余动不平衡引起的车内轰鸣问题十分有效。

海洋沉积物光释光测年中环境剂量率测量方法对比分析

光释光测年作为一种沉积物绝对测年方法已在第四纪地质研究中得到了广泛应用,提高光释光测年精度和准确度一直是学术界关注的热点,长期以来人们对等效剂量测量程序和计算方法的研究十分丰富,而对环境剂量率的研究则相对较少。本文以琼西南海域ZBW钻孔岩心样品为例,利用电感耦合等离子质谱/发射光谱法(ICP-MS/OES)、中子活化分析(NAA)、γ谱仪法对海洋沉积物环境剂量率进行了对比测量。结果表明,在部分层段3种方法测量的结果存在差异,其原因为:(1)ICP-MS/OES前处理过程中重矿物中的U不完全溶解;(2)ICP-MS/OES测量结果为U、Th、K元素含量,包含了部分非放射性核素含量;(3)NAA测量用的样品量小,存在偶然性误差,样品中非放射性物质的稀释作用影响测量结果;(4)样品中存在铀系不平衡现象,结合研究区沉积环境和高纯锗γ谱仪测量结果进行对比分析表明,铀系不平衡主要来源于自生铀吸收,对环境剂量率的影响约为11%。

引入三相不平衡度的低压电网理论线损计算

提出采用均方根电流法计算低压电网理论线损,通过分析三相不平衡线路的线损,推导出线损与不平衡度的关系公式,并将该公式用于三相不平衡配电线路的理论线损计算。系统引入三相不平衡度采集装置,以单片机为主控制芯片,给出了系统结构框图。在采集三相电流时,使用该采集装置挂接在变压器出口端,定时实时采集和存储三相电流,以供计算三相不平衡度。以某台区实际运行为研究实例,介绍了计算步骤,计算结果表明所提出的计算系统是可行的。

荔枝采后生理与保鲜关系研究

研究了采后荔枝内源乙烯的动态变化规律与其果实的呼吸生理的关系和果皮褐变与果皮水分输导的关系。结果表明,荔枝果实内源乙烯合成的旺盛阶段在采后初期,峰值达0.195μl/kg·h,与呼吸强度的变化趋势一致;乙烯相对稳定释放时产量在0.04～0.09μl/kg·h之间。试验后期果实小部分褐变斑块产生,乙烯释放量微有上升,可能与其生理趋向衰竭有关。观察到果皮局部水分缺失难以从邻近获得补充,表明荔枝果皮的水分输导性较差,失水不平衡对果皮组织影响极大,果皮褐斑产生的最初原因可能是生理性的,而非病源性的,荔枝果实的采后保鲜首先应着重解决生理问题、其次才是病理问题。

三相不平衡对配电变压器损耗影响的研究

在配电网中,配电变压器三相不平衡运行状态普遍存在。三相不平衡会使配电变压器产生附加损耗,导致变压器局部过热,从而对变压器的绝缘寿命、带负荷能力产生很大影响。文章对常用的Dyn11和Yyn0联结方式的配电变压器建立了等效电路模型,研究其在三相不平衡状态下的损耗情况。仿真及试验结果表明,三相不平衡使变压器的损耗大幅增加,且随不平衡度的增加呈二次函数增长,不平衡度为50%时变压器损耗将增加一倍。为了保证变压器的运行安全及运行寿命,在不平衡情况下运行时,需要降低其负载率。

配电网三相负荷不对称的线损分析

线损率是供电企业的一项重要经济技术指标也是衡量企业综合管理水平的重要标志。配电网的线损占电网总线损的40%以上。当配网出现三相不平衡时占得比例将大大增加。因此研究降低配电网线损的措施就显得尤为重要。通过分析三相不平衡线路的线损。推导出了线损增加率与相不平衡度的关系公式。可以直接用于配电网三相负荷不对称的线损计算中,并大大简化了分析计算工作中,为后续的工作做好了铺垫。

变电站母线无功电量不平衡原因分析

变电站母线无功电量不平衡率计算及考核是变电站日常运行的一项重要工作。本文基于无功功率守恒理论提出了变电站母线无功电量平衡原理,同时结合无功电能测量理论,全面分析了变电站母线无功电量不平衡产生的各种原因,得出了只有在电能计量装置接线、互感器变比、电能表电量抄读、电能表四象限无功电能组合方式、母线无功电量不平衡率计算方法等五个方面均正确以及电能计量装置无功测量误差较小的条件下,才能确保变电站母线无功电量不平衡率处于合理范围之内的结论。

直流电阻和绝缘电阻对变压器运行状态的影响及故障判断研究

以在用10 kV变压器为测试对象,测量其直流电阻及绝缘电阻,研究其三相不平衡率,配合开展交流耐压试验,分析得到了测量对象的运行状态及潜在故障.

配出中性导体的IT系统带非线性负载研究

阐述了配出中性导体的IT系统应用于船舶岸电的条件及优越性,综合考虑电压畸变率、中性导体电流等因素,分析了配出中性导体的IT系统带非线性负载时谐波电流规律。在Simulink/MATLAB中建立了系统仿真模型,并搭建了原型系统进行试验,结果表明,配出中性导体的IT系统带非线性负载时满足现行国标对低压配电系统电能质量的相关要求。

环形生产线的生产率估算

环形生产线中的托盘数(在制品数)恒定,因此生产率指标不仅与工位中设备可靠性和工位间缓冲区容量有关,还与恒定的托盘数量相关.针对各工位作业时间确定、包含多种故障状态、故障率和修复率为负指数分布的有限缓冲区环形生产线,利用分解方法将整线分解为多个两工位单缓冲区的生产单元,并根据恒定的托盘数量划分故障传递区间,即界定每个生产单元的虚拟故障状态,再利用连续型生产线生产率计算方法获得两工位单缓冲区的生产率估算值,然后利用流失效与流修复方程迭代求解出整线生产率.最后,进行算例分析和实例求解,利用仿真软件进行对比分析,验证了本文方法的有效性,尤其是对于工位时间不同的非平衡生产线,该方法亦具有较高准确性.

500kV同塔四回线路电气不平衡度的研究

为有效提高单位走廊的输送容量,同塔多回路输电技术得到越来越广泛的应用,但是由于换位困难,一旦相序布置不当将造成线路电气不平衡情况更为严重。采用ATP-EMTP和MATLAB程序对500 kV同塔四回路3层横担和6层横担2种塔型的电气不平衡度展开了较为全面的研究。综合考虑负序电压电流不平衡度、杆塔的雷击跳闸率、电磁环境等指标,建议3层横担塔型采用推荐的相序布置方式、6层横担塔型上下两个双回路均采用逆相序布置。计算还表明,对500 kV同塔四回路,单回路停电检修时的感应电压和电流较高,选择接地开关时应予以特别关注。

空气源辅助吸收式地源热泵系统性能模拟

针对严寒地区集中供热系统存在能源利用效率低,地源热泵系统存在土壤吸/排热不平衡问题,提出空气源辅助吸收式地源热泵系统（AGSHPS）,该系统采用热管与蒸气压缩式复合的新型空气源热泵热水机组保障系统运行的可靠性。介绍系统的运行模式及运行控制策略,建立各主要部分的数学模型,选取乌鲁木齐地区的某办公建筑为对象,对该系统长期运行特性进行数值模拟。研究结果表明：系统全年综合性能系数约为1.18,相比蒸气压缩式地源热泵系统节能率为12.4%~24.0%,系统全年运行土壤取/排热量的不平衡率为7.8%,系统可保证长期高效稳定运行。