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.

Energy-balanced clustering protocol for data gathering in wireless sensor networks with unbalanced traffic load

Energy-efficient data gathering in multi-hop wireless sensor networks was studied,considering that different node produces different amounts of data in realistic environments.A novel dominating set based clustering protocol (DSCP) was proposed to solve the data gathering problem in this scenario.In DSCP,a node evaluates the potential lifetime of the network (from its local point of view) assuming that it acts as the cluster head,and claims to be a tentative cluster head if it maximizes the potential lifetime.When evaluating the potential lifetime of the network,a node considers not only its remaining energy,but also other factors including its traffic load,the number of its neighbors,and the traffic loads of its neighbors.A tentative cluster head becomes a final cluster head with a probability inversely proportional to the number of tentative cluster heads that cover its neighbors.The protocol can terminate in O(n/lg n) steps,and its total message complexity is O(n2/lg n).Simulation results show that DSCP can effectively prolong the lifetime of the network in multi-hop networks with unbalanced traffic load.Compared with EECT,the network lifetime is prolonged by 56.6% in average.

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.

Unbalanced Load Simulation of Electronic Power Transformer in Distribution System

A control scheme of electronic power transformer (EPT) in a three-phase four-wire distribution system, which included an input section, an isolating section and an output section, was researched under unbalanced loads. The simple and appropriate control scheme was developed through analyzing the system requirements of the primary side and the load requirements of the secondary side. In the input section, a dual-loop control in synchronous rotating d-q coordinates was introduced, and in the output section, a dual-loop control based on instantaneous output voltage was used. Load characteristics of EPT were investigated by using Matlab/Simulink software. Simulation results showed that, with the proposed control scheme, the EPT has good performances and the sinusoidal input current and constant output voltage can be realized under both balanced and unbalanced loads.

Electromagnetic Performance Prediction for the Symmetrical Dual Three-phase Surface-mounted PMSM under Open-phase Faults Based on Accurate Subdomain Model

The paper presents an accurate analytical subdomain model for predicting the electromagnetic performance in the symmetrical dual three-phase surface-mounted permanent magnet synchronous machine(PMSM)under open-phase faulty conditions.The model derivations are extended from previous accurate subdomain models accounting for slotting effects.Compared with most conventional subdomain models for traditional three-phase machines with nonoverlapping winding arrangement,the subdomain model proposed in this paper applied for the 24-slot/4-pole dual three-phase machine with symmetrical overlapping winding arrangement.In order to investigate the postfault electromagnetic performance,the reconfigured phase currents and then current density distribution in stator slots under different open-circuit conditions are discussed.According to the developed model and postfault current density distribution,the steady-state electromagnetic performance,such as the electromagnetic torque and unbalanced magnetic force,under open-circuit faulty conditions are obtained.For validation purposes,finite element analysis(FEA)is employed to validate the analytical results.The result indicate that the postfault electromagnet performance can be accurately predicted by the proposed subdomain model,which is in good agreement with FEA results.

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.

补偿不平衡负载的HC-SVG相间电压平衡控制与直流电压取值分析

针对由中点钳位型(neutral-point clamped,NPC)功率单元和H桥级联型(cascade H-bridge,CHB)功率单元构成的混合级联型静止无功发生器(hybrid cascade static var generator,HC-SVG)在补偿不平衡负载时产生的CHB功率单元相间电压失衡问题,提出一种基于零序电压前馈的CHB功率单元相间电压平衡控制方法,并对零序电压注入后HC-SVG直流侧电压取值进行分析。首先,分析CHB功率单元承担基波电压分量与HC-SVG输出基波电压的关系。推导HC-SVG补偿不平衡负载时CHB功率单元相间电压平衡所需的零序电压,建立零序电压前馈控制。其次,基于零序电压与补偿电流的解析关系,讨论补偿电流不平衡度与HC-SVG直流侧电压取值之间的约束关系。以6 kV/3 Mvar装置为算例,进行直流侧电压的取值分析。并与星接CHB-SVG进行对比,揭示补偿不平衡负载时HC-SVG所需直流电压低的特点。仿真验证了相间电压平衡控制与直流电压取值分析的有效性。

实现配电变压器效率最大化的治理方法研究

铁损、铜损是影响配电变压器效率的基本损耗,尤其当三相负荷不平衡发生时还会带来附加损耗。为实现配电变压器效率最大化,结合低压供配电系统三相幅值和功率因数均不平衡的现状,通过数学建模对影响配电变压器效率的因素进行理论分析,并建立三相负荷不平衡度与配电变压器效率关系的度量式,基于联合机制提出实现配电变压器效率最大化算法。通过算例与实验法对所提理论进行验证分析,结果表明,通过治理中性线电流可以有效提高配电变压器效率。结合实验结果提出了实现配电变压器效率最大化的改良措施。

不平衡负载下改进光储VSG控制算法

这里提出了一种基于改进虚拟同步发电机(VSG)控制算法的不平衡负载储能系统优化方法,旨在提高电网输出电压稳定性。首先,建立了基于电机瞬态模型的储能系统数学模型。然后,提出了一种分序控制方案,该方案采用双二阶广义积分器(DSOGI)分离出三相电压的正序和负序分量,通过负序虚拟复阻抗技术抵消负序电流在连线阻抗上造成的电压降,从而使2倍频分量消除,避免负载三相电压失衡。通过Matlab/Simulink软件搭建相应的仿真模型,模拟光伏储能系统带不平衡负载时的运行工况,发现该算法能够使稳态过程电压不平衡度从2.7%降为0.6%,暂态过程电压不平衡度峰值从3.2%降低到2.1%,验证所提方法能够有效地优化不平衡负载储能系统的运行性能,提高微电网的电压质量。

不平衡负载下基于VSG的自适应负序控制策略

逆变器带不平衡负载时,逆变器输出电压不平衡度过大,为此提出一种三相不平衡负载下基于虚拟同步发电机(VSG)的自适应负序控制策略。首先,建立逆变器数学模型,分析输出电压不平衡度过大原因。其次,正序VSG控制正序电压幅值和相角,自适应负序VSG抑制输出电压的负序分量。然后,通过建立VSG小信号模型进行稳定性分析,得出正序和负序VSG的转动惯量和阻尼的取值范围。最后,通过实验结果得出,电压不平衡度降为0.05%,暂态过程电压不平衡度峰值降低到1.8%,说明所提控制策略能有效抑制不平衡负载引起的三相电压不平衡。

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。

基于深度学习的配电网三相不平衡负载自动控制方法

常规的配电网三相不平衡负载控制,更多采用负载监测进行控制,导致控制结果的网损降低量较小。为此,提出了基于深度学习的配电网三相不平衡负载自动控制方法。分析配电网三相拓扑结构的电流补偿能力,并计算三相不平衡度及负载率,根据计算结果判定配电网的三相状态,采用深度学习预测三相状态,并根据期望回报计算负载控制的补偿值,实现自动控制。结果表明,应用该方法后得出的控制结果表现出的网损降低量较高,均值为0.376 kW,控制效果较优,满足配电网的现实运行需求。

非平衡荷载下城市轨道交通车站深基坑变形特性分析

[目的]目前城市轨道交通非平衡荷载作用导致的地下工程病害、事故逐渐增多。为了解非平衡荷载对城市轨道交通车站深基坑变形的不利影响,减小施工风险,需要对该类型荷载作用下车站深基坑变形特性进行分析。[方法]基于理论分析和现场监测数据,研究了非平衡荷载下城市轨道交通车站深基坑的变形特性,分析了围护桩变形、深层土体水平位移及地面沉降的变化规律,探讨了围护桩变形同深层土体水平位移、地面沉降及开挖深度之间的关系。[结果及结论]围护桩水平位移曲线呈鱼腹状,且地层条件对围护桩变形影响明显;围护桩变形和深层土体水平位移大致呈线性关系,其中经验系数取1.30;由于偏载作用,深基坑周边地面沉降较大,围护桩最大水平位移δ_(hm)与地面最大沉降δ_(vm)存在δ_(vm)=(0.9~3.0)δ_(hm)的关系,且两者之间的比例系数大于对称荷载作用下的数值;岩层较强的抵抗变形能力限制了围护桩变形,δ_(hm)与H_(e)存在δ_(hm)=(0.009%~0.060%)H_(e)的关系,且两者之间的比例系数小于对称荷载作用下的数值;深基坑施工对周边环境影响区域主要划分为1区(主要影响区)、2区(次要影响区)和3区(无影响区),基坑施工影响区域约为(0~2.5)H_(e)。

永磁无刷轮毂电机轮对系统同步工况下的协调控制策略

针对双轮毂电机在负载不平衡工况下转速同步精度不够及同步响应速度不快的问题,该文提出速度环补偿PID交叉耦合同步控制和电流环补偿PID交叉耦合同步控制策略。首先,建立双轮毂电机的数学模型,采用双闭环六步方波控制。基于该模型,采用速度环补偿PID交叉耦合同步控制代替单增益交叉耦合控制器,使转速同步调节精度提升。在两侧电机负载不平衡工况下,用电流环补偿PID交叉耦合控制方法进一步提升转速同步精度,同时加快同步响应速度,并兼顾了转矩精度。仿真和实验验证了所提控制策略的正确性和有效性。

风机独立变桨减载模型预测控制研究

针对风力发电机组在额定风速以上运行时承受的不平衡载荷波动问题,提出了一种基于状态空间模型的独立变桨模型预测控制策略。首先基于风机仿真软件FAST对风电机组非线性系统线性化;然后将建立的线性时不变(LTI)模型与非线性风机系统对比验证预测模型的拟合度;最后建立FAST-MATLAB联合仿真的NREL5MW风机模型,在湍流风模式下进行仿真。所提出的控制策略与传统PI控制策略相比,在稳定功率的前提下有效地减少了不平衡载荷,提高了风电机组运行稳定性。

提升配网不平衡负载供电可靠性的VSC控制

配电网中存在的不平衡负载易使系统产生负序电流,严重时会影响配电网三相电压对称性,危害设备用电安全,利用电压源换流器(VSC)可对配电网中存在的负序电流进行抑制并提升配网供电可靠性。通过分析VSC输出接不平衡负载时的系统不平衡机理,提出在系统传统控制环路中引入谐振控制器,以抑制不平衡负载条件下控制环路中所存在的2倍工频脉动分量,所提出的控制策略免去常规控制中所需电压、电流正负序分离等控制环节,极大简化了系统控制结构。仿真和实验结果验证了所提出的系统控制策略能有效地抑制由不平衡负载引起的输出电压畸变,获得高质量的输出电压波形。

基于改进mSDFT算法的谐波信号提取方法

提出了一种改进mSDFT算法,该算法通过分解传统mSDFT算法的传递函数内含的梳状滤波器的结构,保留梳状滤波器中特定的零点,用于提取电网信号中指定次谐波,其余零点组成单独因子,用于指定次谐波频谱的幅值校正和相位校正。分解梳状滤波器的结构后,梳状滤波器中包含的零点减少,从而降低了算法的瞬态响应的延迟。进一步阐述了改进mSDFT算法的原理并完成了公式推导,仿真结果表明:该算法能够在谐波信号发生突变的情况下,快速跟踪提取出变化后的谐波信号,瞬态响应的延迟由10^(-2)s量级降低为10^(-3)s量级,同时具有无累计误差和稳定的优点。

不平衡负载下并网逆变器功率解耦控制方法

为了解决并网逆变器在不平衡负载下有功功率和无功功率为耦合影响状态、关联复杂,导致控制精度不佳、响应慢等问题,提出不平衡负载下并网逆变器功率解耦控制方法。根据并网逆变器拓扑结构获取并网逆变器功率,对并网逆变器有功功率与无功功率实行解耦,并通过带比例系数的双闭环功率控制器,完成并网逆变器功率解耦控制。在此基础上,通过遗传算法进行控制参数优化,获取比例系数的最优解,进一步提高并网逆变器功率解耦控制能力。实验结果表明:解耦后的控制方法在并网逆变器响应功率与给定功率上基本一致,解耦后的功率波动范围降低了8 kW,功率控制电流和功率波动最小,具有良好的控制效果。

基于改进TPDS长阵列的车辆超偏载检测研究

由于车辆超偏载检测过程中,受天气、路况等因素以及车辆行驶状态影响,导致信号组成的阵列过短,利用传统的TPDS车辆超偏载检测精度较低、耗时较长;提出基于改进TPDS长阵列的车辆超偏载检测研究;通过车辆运行品质轨边动态监测系统,利用测距传感器与数据采集仪将力学信号转换成电压信号,将其组合为长阵列输入到系统的测距传感器中;采用EDM算法对长阵列中的噪声点实施消除处理;将4个测距传感器安置到货运车辆底部,采用货运车辆动态称重方法,计算车辆上各弹簧组承载力的总和,并结合车辆有用信号,对车辆的载重情况展开测量,实现对车辆的超偏载检测;实验结果表明,利用长阵列改进TPDS系统后,其去噪效果好,在载重测量时,测量误差在5%以内,且平均耗时低、称重合格概率高,表明所提方法的测量精度、检测效率以及检测稳定性高。

基于C.P.Steinmetz平衡化原理PI控制方法的SVC系统研究

瞬时电流控制补偿策略来实现三相平衡化和功率因数的补偿,从理论上分析了这种方法的正确性;然后,用MATLAB/Simulink进行了仿真,通过仿真和实验发现,静止无功补偿控制系统具有一定的合理性和先进性,能够达到较快的响应和较好的补偿精度,可实现对三相不平衡负载的快速动态无功补偿,达到了预期的补偿效果。