Unbalance Vibratory Displacement Compensation for Active Magnetic Bearings

As the dynamic stiffness of radial magnetic bearings is not big enough, when the rotor spins at high speed, unbalance displacement vibration phenomenon will be produced. The most effective way for reducing the displacement vibration is to enhance the radial magnetic bearing stiffness through increasing the control currents, but the suitable control currents are not easy to be provided, especially, to be provided in real time. To implement real time unbalance displacement vibration compensation, through analyzing active magnetic bearings （AMB） mathematical model, the existence of radial displacement runout is demonstrated. To restrain the runout, a new control scheme-adaptive iterative learning control （A1LC） is proposed in view of rotor frequency periodic uncertainties during the startup process. The previous error signal is added into AILC learning law to enhance the convergence speed, and an impacting factor/3 influenced by the rotor rotating frequency is introduced as learning output coefficient to improve the rotor control effects, As a feed-forward compensation controller, AILC can provide one tmknown and perfect compensatory signal to make the rotor rotate around its geometric axis through power amplifier and radial magnetic bearings. To improve AMB closed-loop control system robust stability, one kind of incomplete differential PID feedback controller is adopted. The correctness of the AILC algorithm is validated by the simulation of AMB mathematical model adding AILC compensation algorithm through MATLAB soft. And the compensation for fixed rotational frequency is implemented in the actual AMB system. The simulation and experiment results show that the compensation scheme based on AILC algorithm as feed-forward compensation and PID algorithm as close-loop control can realize AMB system displacement minimum compensation at one fixed frequency, and improve the stability of the control system. The proposed research provides a new adaptive iterative/earning control algorithm and control strategy for AMB displacement minimum compensation, and provides some references for time-varied displacement minimum compensation.

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.

Compensation of Unbalanced Impedance of Asymmetric Wind Power PMSG Compensated by External Circuits in Series

The unbalanced impedance of the asymmetric 3-phase wind power permanent magnet synchronous generator(PMSG)compensated by external circuits in series with the 3-phase windings is investigated in this paper.The asymmetric impedance includes the unbalanced resistances,unbalanced self-inductances,and unbalanced mutual inductances.From the perspective of the second harmonic inductances in dq-frame and from the perspective of the second harmonic power,it is theoretically demonstrated that the original asymmetric 3-phase system with asymmetric impedance can be modified to a balanced system by external circuits consisting of resistances and inductances.Therefore,the second harmonic power and DC bus voltage due to the asymmetries can be suppressed naturally without any software modifications.The feasibility of this compensation method is validated by elaborate experiments at different speeds and under different load condition,although the effectiveness might be slightly affected by the non-linearity of the compensation inductance in practice.

Mitigation of Unbalanced Voltage Sags and Voltage Unbalance in CIGRE Low Voltage Distribution Network

Any problem with voltage in a power network is undesirable as it aggravates the quality of the power. Power electronic devices such as Voltage Source Converter (VSC) based Static Synchronous Compensator (STATCOM) etc. can be used to mitigate the voltage problems in the distribution system. The voltage problems dealt with in this paper are to show how to mitigate unbalanced voltage sags and voltage unbalance in the CIGRE Low Voltage (LV) test network and networks like this. The voltage unbalances, for the tested cases in the CIGRE LV test network are mainly due to single phase loads and due to unbalanced faults. The compensation of unbalanced voltage sags and voltage unbalance in the CIGRE distribution network is done by using the four STATCOM compensators already existing in the test grid. The simulations are carried out in DIgSILENT power factory software version 15.0.

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.

带自适应谐波补偿功能的谐波阻抗控制策略

针对工业园区高比例电力电子负荷接入带来的电能质量问题,提出一种基于APF的带自适应谐波补偿限流功能的谐波阻抗控制策略。谐波阻抗控制策略可以对系统的指令电流进行无差控制并对各谐波分量进行独立控制,自适应谐波补偿限流可以有针对性地进行谐波补偿,两者相结合后可以对选取的各谐波分量进行单独控制,使限流后的谐波补偿效果明显提高。该控制策略在系统容量不超限时在Matlab/Simulink中搭建仿真模型,结果表明,该控制策略响应速度快,治理后的谐波总畸变率为2.91%,减少了27.08%,三相不平衡度为8.52%,减少了16.15%,补偿效果明显。

三相电压不平衡下DDSRF-PLL与DSOGI-PLL的锁相误差检测与补偿方法

由于高渗透的分布式电源、多样化的负荷类型以及电网故障等因素,并网点三相电压不仅存在幅值不平衡,而且会出现相位不平衡现象。这种情况下,广泛应用的解耦双同步坐标系锁相环(DDSRF-PLL)和双二阶广义积分器锁相环(DSOGI-PLL)无法获得精确的同步信息。为此,该文在论证这两种锁相环具有理论等价性的基础上,阐释三相电压不平衡与锁相误差的内在关系,进而提出一种锁相误差的补偿方法,实现幅值和相位不平衡下的准确锁相。所提方法仅需对电压采样值进行简单计算即可获得不平衡相位和锁相误差,实现开环相位补偿,无需修改原有锁相结构,具有良好的拓展性。最后,通过仿真和实验验证了所提方法的有效性。

特高压换流站交流滤波电容器组不平衡保护故障研究

交流滤波器作为特高压直流输电工程关键组成部分,扮演着调节电压、提供无功补偿的角色,其安全稳定运行至关重要。针对某换流站交流滤波器组发生不平衡保护动作,通过介绍该站交流滤波器配置情况,结合故障电流的分布特点,对交流滤波器C1电容器不平衡异常进行了分析。为了提高现场运维人员处理故障效率,提出了一种故障电容器组定位方法,该方法可精确定位双H桥的1/6区域,解决了电容器组不平衡保护的故障定位难题,对特高压换流站可靠运行具有实际参考价值。

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.

Distributed Cooperative Secondary Voltage Control in an Unbalanced Microgrid

The negative-sequence reactive power-conductance(Q^(−)-G) droop control strategy is a conventional method to compensate for the output unbalanced voltages in an islanded MG.Nevertheless, the conflict between unbalanced voltage compensation and negative-sequence reactive power sharing, caused bythe impedance mismatching of distribution lines and distributedgenerators, has not been solved only by Q^(−)-G droop control.In this paper, a distributed cooperative secondary unbalancedvoltage control strategy is proposed to decrease the outputvoltage unbalance factor (VUF) of each droop-controlled DG,as well as to further enhance the negative-sequence reactivepower sharing effectiveness among DGs by properly shiftingup and down the Q^(−)-G droop characteristics of each DG.An algorithm for adaptive VUF weight coefficient is proposedto better suppress VUF under severe imbalance conditions.Furthermore, a negative-sequence small-signal model of an MGunder an unbalanced condition, considering the communicationdelay time of the proposed SUVC, is established to analyze thesystem’s stability and transient performance under the influenceof some critical parameters. Finally, the effectiveness of theproposed strategy is validated by the simulation results froma real-time emulator of StarSim HIL.

Coordinated Control of Parallel Three-phase Four-wire Converters in Autonomous AC Microgrids

The coordinated control of parallel three-phase fourwire converters in autonomous AC microgrids is investigated in this paper.First,based on droop control,virtual impedance is inserted in positive-,negative-and zero-sequences to enhance system damping and imbalance power sharing.Then,to facilitate virtual impedance design,small signal models of the three-sequence equivalent circuits are established respectively.Corresponding indexes are proposed to comprehensively evaluate the impact of sequence virtual impedance on current sharing accuracy,voltage quality at the point of common coupling(PCC)and system stability.In addition,constraint of DClink voltage is also considered to avoid over modulation when subjected to unbalanced loads.Furthermore,to address the PCC voltage degradation resulting from virtual impedance,a voltage imbalance compensation method,based on low-bandwidth communication,is proposed.Finally,simulation and experimental results are provided to verify the correctness of the theory model,indicating that the proposed method can achieve PCC voltage restoration while guaranteeing the current sharing accuracy with desirable dynamics.

工厂分布式光伏电能质量综合治理分析

装备制造业工厂用电负荷较高,建设屋面分布式光伏项目能产生较好的经济效益和社会效益,但工厂电力供应系统由于增加了光伏发电设备,导致用电系统电能质量下降,表现为功率因数过低、产生力调电费等,故工厂迫切希望对此类用电系统进行电能质量治理,以解决电费罚款问题。

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.

Voltage Unbalance Compensation in Distribution Feeders Using Soft Open Points

Soft open points(SOPs)are power electronic devices that may replace conventional normally-open points in distribution networks.They can be used for active power flow control,reactive power compensation,fault isolation,and service restoration through network reconfiguration with enhanced operation flexibility and grid resiliency.Due to unbalanced loading conditions,the voltage unbalance issue,as a common problem in distribution networks,has negative impacts on distribution network operation.In this paper,a control strategy of voltage unbalance compensation for feeders using SOPs is proposed.With the power flow control,three-phase current is regulated simultaneously to mitigate the unbalanced voltage between neighboring feeders where SOPs are installed.Feeder voltage unbalance and current unbalance among three phases are compensated with the injection of negative-sequence and zero-sequence current from SOPs.Especially in response to power outages,three-phase voltage of isolated loads is regulated to be balanced by the control of SOPs connected to the feeders under faults,even if the loads are unbalanced.A MATLAB/Simulink model of the IEEE 13-bus test feeder with an SOP across feeder ends is implemented,and experimental tests on a hardware-in-the-loop platform are implemented to validate the effectiveness of the proposed control strategy.

Comparative study of semiconductor power losses between CSI-based STATCOM and VSI-based STATCOM,both used for unbalance compensation

In this paper,we present a detailed procedure to determine the semiconductor losses for both structures of a shunt STATCOM(Static Compensator),STATCOM based on Current Source Inverter(CSI)and STATCOM based on Voltage Source Inverter(VSI),both used for voltage unbalance compensation.As a first step,we study the VSI-based STATCOM and the CSI-based STATCOM used in high speed railway substations.Then we analyze the design and the sizing of the unbalance compensator in order to obtain an unbalance factor that does not exceed the limits imposed by the standards or by the energy provider.Following that,we compare the performances obtained with both structures VSI-STATCOM and CSI-STATCOM,after calculating the semiconductor power losses in the STATCOM converters.Finally,we validate our approach by simulation over real data of unbalance compensation caused by the new high-speed railway in Morocco.We use the tools MATLAB/Simulink/Simpowersys for performing our simulations.

一种用于主动磁轴承不平衡补偿的切换控制法

为了改善主动磁轴承转子在质量不平衡影响下的动力学性能,本文提出了一种基于I&I控制法和自适应陷波滤波器不平衡补偿切换控制方法。首先,本文考虑了转子的质量不平衡,建立了三极磁轴承转子系统的动力学模型。然后,本文分别设计了适用于该系统的I&I参数更新律、控制律及自适应陷波滤波器,并设计了合适的切换点,实现了对磁轴承不平衡转子的切换控制。仿真结果表明,该控制方法结合了I&I控制法的高精度和自适应陷波滤波器的低铜损优势,能够在保证转子振幅不超出安全范围的同时获得较低的能量损耗。

计及电网电压不平衡的储能型铁路功率调节器负序优化补偿策略

针对偏远地区电网电压不平衡条件下牵引供电系统负序补偿及再生制动能量回收利用问题,基于储能型铁路功率调节器,提出一种在补偿装置容量有限时,计及电网电压不平衡条件的再生制动能量利用及负序综合补偿优化策略。分析了电网电压不平衡时储能型铁路功率调节器负序完全补偿机理,引入储能系统补偿系数,有功、无功电流补偿系数,以负序补偿度和牵引变电所补偿容量及供电臂负荷平衡度作为优化目标,提出储能型铁路功率调节器优化补偿模型。采用序列二次规划法对优化模型进行求解,最后通过仿真验证,表明该策略可以在电网电压不平衡时,使电网侧负序不平衡度降低的同时提高再生制动能量利用率,减少牵引负荷对牵引变电所的能量需求。

无速度主动磁悬浮轴承系统全频域不平衡控制

为了解决无转子角频率信息下主动磁悬浮轴承系统的不平衡振动问题,研究了一种无速度反馈的全频域转子同步振动力抑制算法。首先,根据主动磁悬浮轴承系统结构和转子质量偏心特征,建立含不平衡量时主动磁悬浮转子系统的动力学模型,然后,通过设计二阶广义积分锁频环对转子旋转角频率进行精确辨识。为保证全频域下转子的不平衡控制效果,提出变增益系数和位移前馈补偿环节对同步振动控制环路进行优化,利用根轨迹法证明所设计闭环控制系统的稳定性,并给出稳定性条件。最后,分别在恒定转速、变转速和不同采样噪声环境3种条件下进行仿真验证,结果表明,所提方法可在全频域范围下实现准确的频率估计,获得良好的同步振动力抑制效果。

主动电磁轴承–柔性转子系统过多个临界转速区的同频振动抑制

为了对电磁轴承(active magnetic bearings,AMBs)–柔性转子系统在多阶弯曲临界转速范围内的同频不平衡振动行有效控制,首先建立AMBs–柔性转子系统的动力学模型,分析线性自抗扰控制器和相位偏移最小均方(least mean square,LMS)算法。然后,提出一种基于相位偏移LMS的扰动跟踪补偿方法,并将相位偏移LMS算法用在同频扰动的跟踪中,以解决扩展状态观测器不能准确估计高频同频不平衡扰动的问题。接着,从补偿方法、补偿有效性和闭环系统稳定性等方面分析相位偏移LMS的补偿特性。最后,在AMBs–多盘柔性转子系统试验台上进行试验。结果表明,所提出的基于相位偏移LMS扰动补偿策略无需切换极性和相位,就能够有效地抑制柔性转子在跨越系统的刚体平动、刚体锥动、一阶弯曲和二阶弯曲临界转速区的同频不平衡振动,使转子系统在高于二阶弯曲临界转速的转速区稳定工作。