Instantaneous Current Feedback Control Strategy on Buck Mode Inverter

Buck型逆变器的电感电流瞬时值反馈控制和电容电流瞬时值反馈控制存在本质区别。以差动正激直流斩波器型高频环节逆变器为例，采用理论推导方法，研究这两种电流控制逆变器的稳定性、输出外特性、短路能力、输出功率特性、带非线性负载能力及动态响应特性。研究结果表明，电感电流瞬时值反馈控制逆变器具有电感电流和输出功率受限、较强的过载和短路能力、较软的输出外特性、较弱的带非线性负载能力、较差的动态响应等特点；而电容电流瞬时值反馈控制逆变器具有电感电流和输出功率不受限、较弱的过载能力、无短路能力、硬的输出外特性、较强的带非线性负载能力、较好的动态响应等特点。研究成果为Buck型逆变器电流型控制策略的选择及其设计提供重要的理论依据。

A novel method to calculate the thrust of linear induction motor based on instantaneous current value

Because of the end effect, a linear induction motor （LIM） runs in an asymmetrical state even though the winding of each phase is symmetric. Based on the basic principle of the LIM, a new approach was proposed to calculate the thrust of the LIM using the instantaneous current value. A three-phase LIM model with 12 slots and a singlelayer winding was designed to validate this method. The experiments show that when the current is small, the calculated results basically agree with the experiments. The agreement becomes worse with the increase of the current because of the saturation of the primary iron core. The proposed formula is suitable when the iron core of the LIM primary is in an unsaturated state.

Study on the instantaneous protection reliability of low voltage circuit breakers

This paper outlines the significance of enhancing the instantaneous protection reliability of low voltage circuit breakers and describes their main failure modes. The instantaneous failure mechanism of low voltage circuit breakers was analyzed so that measures to improve instantaneous protection reliability can be determined. Furthermore, the theory of the instantaneous characteristics calibration device for low voltage circuit breakers and the method of eliminating the non-periodic component of test current are given in detail. Finally, the test results are presented.

Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

船舶永磁同步推进电机的优化I/f起动控制方法

为解决高转矩与高转动惯量的船舶推进电机在开环I/f控制中转速和转矩波动大、电机易失步、效率低的问题,提出一种I/f控制改进方法。通过建立转矩角观测器,调节给定电流矢量的幅值,使其跟随负载转矩变化,提高系统鲁棒性。同时,将电机运行状态推进至接近最大转矩电流比状态,提高电机的运行效率;通过瞬时有功功率调节电流矢量的角速度,降低电磁转矩波动,加快电机的转速收敛过程。最后,在Matlab/Simulink中进行仿真实验,实验结果表明该方法可以显著提高推进电机运行效率和稳定性。

瞬时电流预测的逆变器启动冲击负载的方法

针对通用逆变器启动冲击负载能力很弱的问题,此处提出一种利用瞬时负载电流预测来控制输出调制比的方法来增强逆变器启动冲击负载的能力。冲击性负载,通常是感性负载投入时会产生5~10倍的冲击电流,而通用逆变器抗冲击电流能力较弱,通常只能启动20%的额定负载。这里根据检测到的负载瞬时电流来瞬时减小逆变器的输出调制比,将负载电流控制在额定电流范围内,感性负载投入后会逐渐稳定,输出调制比也逐渐恢复到正常值,完成感性负载的启动。此方法已在油田储能电源上得到广泛应用,可将逆变器启动感性负载的能力从20%额定提高到70%额定。

基于对称分量法的调相机定子故障特征分析

传统同步调相机定子绕组匝间短路故障机理分析方法通常认为电机定子电流接近三相对称,并以此为基础建立同步调相机故障电流的数学表征。但是,一旦发生定子绕组匝间短路故障,同步调相机三相定子电流的对称性将遭到破坏,使得传统故障机理分析方法所建立的数学表征无法准确反映电机内部电气量的变化。文中通过引入对称分量法,建立故障后同步调相机瞬时有功/无功功率的数学模型,提出利用瞬时有功/无功功率中的2次谐波进行定子绕组匝间短路故障诊断。仿真和实验的结果表明:相较于利用定子电流3次谐波与基波幅值之比诊断故障的传统方法,文中方法在轻微故障状态下能提高至少7倍的诊断灵敏度,更易完成早期故障诊断。同时,所提方法中的故障特征量不受同步调相机工况和故障位置的影响,具有强鲁棒性。

COMPARISON AND EVALUATION OF CURRENT REFERENCE GENERATION STRATEGIES FOR ACTIVE POWER FILTERS IN THREE-PHASE FOUR-WIRE SYSTEMS

For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous active current （IAC） methods are analyzed and compared with each other. The interpretation of active and reactive currents in non-sinusoidal and unbalanced three-phase four-wire systems is given based on the generalized instantaneous reactive power theory. The performance and the characteristic are evaluated, and the application conditions of current reference generation strategies are concluded. Simulation results under different source voltages and loads verify the evaluation result.

Characteristics of Bi-2223 HTS Tapes Under Short-Circuit Current Impacts in Hybrid Energy Transmission Pipelines

A hybrid energy transmission pipeline is proposed with the aim of long-distance cooperative transmission of electricity and chemical fuels, which is composed of an inner high-temperature superconducting (HTS) power cable and outer liquefied natural gas (LNG) pipeline. The flowing LNG could maintain the operating temperature of the inner HTS power cable within the range of 85 K-90 K, thus the Bi-2223 superconductors in the HTS power cable produce little Joule loss with the transmission current below the critical current. Owing to the advantages of high power density, low transmission losses and economical manufacturing costs, the hybrid energy transmission pipeline is expected to be widely utilized in the near future. In order to ensure the safety of the HTS power cable and explosive LNG in case of short-circuit faults, this paper tests and analyzes the characteristics of Bi-2223 HTS tapes of the Type HT-CA, Type HT-SS and Type H models under short-circuit current impacts at the LNG cooling temperature (85 K-90 K). An experimental platform is designed and established for the ampacity tests of HTS tapes above LN2 cooling temperature (77 K). The AC over-current impact tests at 85 K-90 K are carried out on each sample of Bi-2223 tapes respectively, and the experimental results are analyzed and compared to evaluate their performances under different operating conditions. The results indicate that the Type HT-CA tape can withstand 50 Hz short-circuit current impact with the amplitude of 1108 A (10 times of critical current Ic ) for 100 ms at 90 K, and its resistance is the smallest of the three tested samples under similar current impacts. Therefore, the Type HT-CA Bi-2223 tape is the optimal superconductor of the HTS power cable in the hybrid energy transmission pipeline.

基于DSOGI-PLL与ANF-LPF的i_(p)-i_(q)三相谐波检测方法

随着分布式电源大规模接入电网,电力系统中频率波动、电压不平衡以及谐波畸变等问题日益严重。在这样不平衡和失真的电网条件下,传统i_(p)-i_(q)谐波检测法已不能满足工程需要。为解决这一问题,文中提出一种基于DSOGI-PLL与ANF-LPF的i_(p)-i_(q)三相谐波检测方法。一方面,采用DSOGI-PLL提高复杂电网下提取基波相位的能力;另一方面,采用一种具有选择性谐波滤波能力的改进结构LPF,来提高谐波检测的抗干扰能力。结果表明,所提方法能够在复杂电网条件下完成三相谐波检测。

考虑电流瞬时频率特性的水上浮吊供电系统定时限过流保护方法

水上浮吊供电系统中,通常含有多台大功率异步电动机,多个电动机在并网启动时会产生较大的启动电流,当各电机启动电流叠加,可能导致变压器电流激增,触发过电流保护误动,给工业生产带来巨大损失。本文首先基于异步电动机等效模型,揭示了冲击电流的产生机理和箱式变压器保护误动原因;接着针对水上浮吊电机断续周期工作场景,提出了随机运行场景生成方法,基于希尔伯特黄变换技术,对系统的故障短路和电机启动状态下变压器的电流信号进行瞬时频率特性分析,揭示不同状态下箱式变压器电流的瞬时频率特性差异,在此基础上构建定时限过电流主动闭锁模块,确保浮吊供电系统正常工作时的可靠供电;最后通过湖南省某水上浮吊系统的仿真模型对所提出的保护方案进行了验证。

一起500kV串补电容器组不平衡电流高定值旁路故障分析

近期网内某500kV串补站发生了数次串补电容器组不平衡电流高定值动作导致旁路故障的情况,本文通过研究该串补站电容器组不平衡电流动作机理及保护方式,结合故障录波分析,判断故障原因及故障类型,并通过故障模拟仿真进行了验证,然后针对该故障类型特点选择极间直流电压试验成功排查出故障电容器单元,并经解体检查证实。现场实际表明,该方法可有效排查出文中提到的瞬时性恢复故障,为日后运维人员处理该类型故障提供借鉴。

考虑瞬时功率特性的高压直流电网双极短路故障识别技术

高压直流电网运行过程中,由于受到负载特性和电压波动等因素影响,电容电流及谐波等瞬时功率特性较为复杂,增加了对电网系统故障的识别难度。为此,提出考虑瞬时功率特性的高压直流电网双极短路故障识别技术。通过建立高压直流电网拓扑结构模型,分析高压直流电网的双极短路故障;结合高压直流电网端点的瞬时功率特性判断出双极短路故障发生区域。利用双端故障电流最大值定位法获取双极短路故障定位,完成对高压直流电网双极短路的故障识别。实验结果表明,所提方法对高压直流电网双极短路故障定位识别精度较高,提升了故障识别效率。

基于改进瞬时对称分量法的STATCOM负序、零序电流优先补偿策略

为了提高三相四线制电力系统中静止同步补偿器(STATCOM)在补偿负荷中的利用率,基于改进的瞬时对称分量法提出了一种针对STATCOM的负序、零序电流优先补偿策略。该策略将系统参数分解成为正序、负序和零序网络后,得到实时的正序、负序和零序分量。利用控制负序电流和零序电流补偿三相负载不对称产生的负序分量和零序分量。利用控制正序电流补偿系统波动产生的谐波分量和无功分量。当STATCOM补偿容量不足时,优先补偿负序电流和零序电流,尽可能地补偿无功电流。结果表明,该补偿方法可以使STATCOM准确地动态补偿配电网三相负荷不平衡产生的负序、零序分量。

Placement optimization of Multi-Type fault current limiters based on genetic algorithm

The fault current limiter(FCL)is an effective measure for improving system stability and suppressing short-circuit fault current.Because of space and economic costs,the optimum placement of FCLs is vital in industrial applications.In this study,two objectives with the same dimensional measurement unit,namely,the total capital investment cost of FCLs and circuit breaker loss related to short-circuit currents,are considered.The circuit breaker loss model is developed based on the attenuation rule of the circuit breaker service life.The circuit breaker loss is used to quantify the current-limiting effect to avoid the problem of weight selection in a multi-objective problem.The IEEE 10-generator 39-bus system in New England is used to evaluate the performance of the proposed genetic algorithm(GA)method.Comparative and sensitivity analyses are performed.The results of the optimized plan are validated through simulations,indicating the significant potential of the GA for such optimization.

Research on Numerical Simulation of 3D Leakage Magnetic Field and Short-circuit Impedance of Axial Dual-low-voltage Split-winding Transformer

It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.

Single-phase earth fault current distribution between optical fiber composite overhead ground wire and ordinary ground wire in transmission system

It is important for the safety of transmission system to accurately calculate single-phase earth fault current distribution.Features of double sided elimination method were illustrated.Quantitative calculation of single-phase earth fault current distribution and case verification were accomplished by using the loop method.Influences of some factors,such as single-phase earth fault location and ground resistance of poles,on short-circuit current distribution were discussed.Results show that:1) results of the loop method conform to those of double sided elimination method;2) the fault location hardly influences macro-distribution of short-circuit current.However,current near fault location is evidently influenced;and 3) the short-circuit current distribution is not so sensitive to the ground resistance of poles.

CPT及IRPT多场景电流分解对比及分析

以新能源为主体的新型电力系统发展对系统计量装置、功率变换设备等提出了新要求,迫切需要革新的功率理论指导上述设备的设计与控制,以适应不同电气系统结构。通过构建多种含不同源荷类型的三相电气系统场景,针对守恒功率理论(CPT)及瞬时无功功率理论(IRPT),重点讨论二者在不同应用场景中电流分解的相似点及不同点。分析结果显示:IRPT仅在电压正弦条件下可以获得较好的电流分解结果,而基于CPT的电流分解,在正弦或非正弦等不同电压、负荷情况下均可较好地解释功率传输现象、分析负荷特性,其可作为有效的理论工具用于负荷特征识别、电费计量、滤波与补偿、功率变换器等领域中。

矿山电网瞬时电流速断保护整定策略

矿山电网作业环境较差,当井下供电系统发生短路故障时,使用复杂的防越级跳闸保护装置会使整个电网的可靠性降低、成本提高,并且矿山电网需要保证电流速断保护能够瞬时动作以切除短路故障,尤其是线路出口处的短路故障。目前矿山电网防越级跳闸保护方案不能兼顾保护速动性、供电可靠性和设备经济性。针对上述问题,根据矿山电网井下发生短路事故不能越级到井上的最低原则,提出了一种基于整体最优原则的矿山电网瞬时电流速断保护整定策略。分析了矿山电网短路电流与短路点位置的关系及线路首末端短路电流的分布特征,对比研究了传统单一整定方法存在的缺陷。定义了最小−最大系统阻抗比、最大系统阻抗与线路阻抗比、相邻线路阻抗比3个指标,用来表示不同短路电流分布场景的特征关系式和各整定方法满足要求的条件,从而判定不同短路电流分布场景下瞬时电流速断保护所适用的整定方法,并给出相应的最优整定策略流程。以典型矿山供电线路为例,根据所提整定策略对其各级保护开关进行整定计算,结果表明:采用该整定策略对矿山电网模型中5个存在越级跳闸风险的保护开关进行整定,可将其中4个保护开关的保护范围控制在2级线路之内,减少了越多级跳闸事故的次数,降低了矿山电网井下短路故障延伸到井上的概率。

瞬时功率下分布式电能计量自动计费方法研究

随着电力系统中各类非线性负载的使用日益增多,电能计量自动计费越来越受关注。对此,提出了瞬时功率下分布式电能计量自动计费方法。首先,分析瞬时功率下ADE7880芯片功能,利用单片机驱动与调用整体的功能模块,通过采集器模块采集电压与电流信号。然后,构建电能网关结构,通过电路调理模块调整并转换采集的电压、电流信号,输送至瞬时功率测量模块。最后,将瞬时有功功率传递至分布式电能计量模块,完成瞬时功率下电能计量自动计费方法研究。试验结果表明,所研究的瞬时功率下分布式电能计量自动计费方法的瞬时功率测量精度较高、功率测量稳定性较优,可精准计算用户使用电能的费用,具有较好的自动计费效果。