PCB型Rogowski线圈的设计与特性分析

设计了一种新型的电流传感头-PCB型Rogowski线圈,介绍了其工作原理及增大互感的方法.基于MATLAB软件,对影响线圈动态性能的参数进行了数学分析,得出了线圈优化设计的规律.在此基础上,优选线圈参数,设计了由PCB型Rogowski线圈和积分器组成的测量系统,并对其灵敏度和频率特性进行了分析计算.结果表明,该系统具有较高的灵敏度和良好的频率特性,能满足电力系统中对大电流的测量要求.     

A spectral estimation method for nonstationary signals analysis with application to power systems

In this paper we analyze a new method for estimating the spectral content of frequency and amplitude modulated waveforms in the context of power line signals where, as well known, the frequency of the fundamental component (50 Hz or 60 Hz) slightly changes over time. The method, proposed here in two distinct implementations, is based on a different choice of the harmonic functions that are usually used in the DFT as a basis to analyze signals. Indeed their frequency is allowed to change over time, according to the output of an instantaneous frequency detector. The orthogonality of the basis is preserved by performing a change of reference in the time. The theory is developed in continuous time and subsequently implemented in discrete time. Simulations and experimental results are provided in order to verify and characterize preliminarily the proposed method.     

Effect of geometrical parameters on high frequency performance of Rogowski coil for partial discharge measurements

Partial discharges (PD) in a power system component is a sever threat, indicating a high likelihood of the imminent and complete failure of the insulation. The reliability of partial discharge diagnostics depends upon the design and accuracy of the measuring sensors. In this paper the Rogowski coil is employed as a PD measuring sensor. The selection of suitable geometrical parameters has been identified as an important aspect regarding the proper operation and installation of the coil around the under test power component. These parameters significantly affect the measuring performance of the coil in terms of its sensitivity and bandwidth. The measurement performance of different geometrical designs for the high frequency Rogowski coils is evaluated. The variation in parameters such as core and coil diameter, diameter of the copper wire used for winding and number of turns, has been experimentally investigated. In addition the return winding, as a non-conventional method of creating a return loop for the Rogowski coil, is compared with a return wire (loop) to analyze sensor performance. The comparative study of variation in mechanical design features provides a brief guideline to select the optimal design of the coil.     

基于延时补偿的电网谐波电流信号跟踪控制方法研究

针对电力系统中谐波污染严重等问题,以注入式混合的有源电力滤波器IHAPF作为研究对象,提出了基于延时补偿的谐波电流信号跟踪控制方法。该方法主要由π补偿Smith预估器与神经网络PI控制组成,π补偿Smith预估器使系统延时过程中从控制的闭环内部转换到外部,从而减小了控制延时对系统的影响;通过PSO-BP算法对PI控制器参数进行优化处理,最后对所提方法进行了仿真验证。仿真结果表明,与传统方法相比,本研究所提方法具有更好动态响应特性和更高的稳态补偿精度。     

A new concept of harmonic current detection for shunt active power filters control

The paper deals with measurement and control aspects of active power filtering in ship systems. The main focus of the paper is concentrated on improvement of harmonic current measurement algorithms based on i_p–i_q method with application of low-pass filter (LPF) module and, alternatively, on i_p–i_q method with application of mean value module.     

Arbitrary waveform generator for harmonic distortion tests on compact fluorescent lamps

This paper presents an experimental method to perform tests on compact fluorescent lamps operated with distorted voltage waveform conditions. The voltages used for the tests are obtained from an arbitrary waveform generator. It consists of a computer, a multifunction card and the software package. The characteristics of the voltage are entered from the computer that loads the required waveform into the card. The output of the card is driven to a voltage amplifier to supply the lamps. Samples of the voltage across the load and of the circulating current are recorded and transferred to the computer for harmonic analysis. The user supervises the tests through several virtual instruments that have been developed especially for this application. The system facilitates the performance evaluation of various appliances for distorted supply voltages. The cost of the system is very low compared with a conventional system consisting of an arbitrary waveform generator, a digital oscilloscope, a spectrum analyzer or/and a computer for harmonic analysis and a true rms multifunction meter. The experimental results show that the distribution of the harmonics of some lamp types does not alter linearly under distorted supply voltages.     

A method for discriminating original pulses in online partial discharge measurement

Partial discharge (PD) measurement is a promising method for condition assessment of insulation systems in high voltage equipments. Conventional PD measuring systems have some difficulties in the measurements especially in online conditions and noisy environments. There is a growing tendency to use new measuring systems for separation of PD pulses from different sources and rejection of external noises. In this investigation a new ultra wideband PD measuring system and relevant methodology are discussed. The proposed system uses an efficient detection method for extracting PD pulses embedded in noisy signal, meanwhile, a wavelet multiresolution analysis is applied to reduce background and communication noise level. In this paper some new and modified features for pulse classification procedure have been proposed. The proposed system, methodology and features have been implemented on a hydrogenerator and also a power transformer. Finally performance of the system is discussed.     

面向相对导航的UWB测距误差估计与补偿方法

基于无人飞行器和智能机器人等载体构成的智能集群是当前的研究热点,相邻或相近集群成员之间精确的相对距离是密集集群实现协同控制的关键信息。超宽带(UWB)无线传输技术能传输信息,同时具有厘米级的理论测距精度,在集群的协同导航与控制中具有广阔的应用前景。面向集群成员间相对导航的厘米级测距需求,阐述了UWB的测距方案,分析了实际环境中UWB天线的时钟偏移、节点之间有相对速度和非视距环境引起的测距误差的特性,研究了UWB距离测量的状态检测和误差补偿、估计的方法,采用DW1000超宽带模块构建了实验环境,对所研究的方法进行实验验证。结果表明,所研究的方法可显著提高UWB在实际应用中的测距精度,与传统的测距算法相比,在空旷环境(LOS)状态下误差降低了70%,在非视距环境(NLOS)状态下误差降低了50%。     

中性点经消弧线圈接地的电网脱谐度微机测试装置

本文采用新的补偿电网脱谐度测量原理,提出了脱谐度的外加扫频信号自动测量方法。并结合微机系统迅速、准确的特点,无需其它参数,即可完成对脱谐度的直接测量。测量结果准确,误差不大于0.64％;测量速度快,历时不足20S;可在-156％～64％大范围内实时监测脱谐度,并实现了测试过程与电网运行双方互不相扰,为在此基础上进行消弧线圈的自动跟踪调谐奠定了良好的基础。     

Novel current sensing method for mass production of power converters

Orthogonal least squares estimation algorithm is applied for the identification of unknown relationship between the drain current, the voltage across the drain and source of a fully on metal–oxide semiconductor field-effect transistor (MOSFET) under different temperatures. Very low loss current sensing can be derived based on the fitted model, the sensed temperature and voltage across the drain and source of the MOSFET. The model can easily be denormalized to cater for MOSFETs of the same model so that it is not necessary to test individual MOSFET in power converters. The proposed method could be useful for testing power converters during the manufacturing process. It could also be embedded into the controller to implement current control or over-current protection for power converters. Experiments and procedures to carry out the model fitting are presented.     

Precision compensation method for tooth flank measurement error of hypoid gear

When measuring the tooth flank of hypoid gear, the measurement datum surface (the large end surface of the gear) does not always coincide with the design bases (the theoretical mounting distance), and this non-coincidence error would affect the tooth flank measurement results. Based on the measurement theory of the hypoid gear tooth flank, a precision matching method of the theoretical tooth surface and the measured tooth surface is designed, the objective function of the tooth flank matching method is established, and the search iterative method was used to calculate the compensation value of the measurement error of the tooth flank, when the two gear tooth surface is most accurately matched. As the mounting distance of the hypoid gear changes, two experiments are done to verify the proposed method. The experiment results show that, for different tooth flank of the measured gear, the measuring error of the tooth flank along Z-axis dropped significantly after compensated by this method, more than 80% of the error along Z-axis are compensated. It is obvious that this method could improve the measurement accuracy of the tooth flank form of hypoid gear.     

A robust parametric method for power harmonic estimation based on M-Estimators

Power harmonic estimation is essential for evolving suitable protection and control strategies of power networks. Parametric approaches exhibit super-resolution and have been gradually applied in practice. However, they are susceptible to the presence of noise in the signals. The analysis accuracy will be abruptly reduced and even ineffective under non-Gaussian or impulsive noise environment. In this paper, a novel approach based on M-Estimators for harmonic estimation is proposed to overcome the above shortcomings. The derivation of Gauss–Newton iteration equations of harmonic frequency, amplitude and phase is presented. Further, the ESPRIT algorithm is also employed to acquire the initial values of harmonic frequencies, which avoids the objective function of M-Estimator to be stuck in local minima and improves the convergence rate of optimization. The numerical simulations and experimental results verify the feasibility and effectiveness of the proposed method.     

A new combined method in active filter design for power quality improvement in power systems

The voltage & current harmonics produced by nonlinear loads in power systems cause a reduction in power quality. In order to improve the power quality, active power filters (APFs) can be used. In this paper, a new control system for designing active filters despite nonlinear loads of electric arc furnaces (EAFs) is presented. The system is composed of three main parts: computation of reference currents, regulation of DC capacitor voltage, and production of firing pulses. In the first part, the active filter control system is presented based on the combination of the synchronous detection method and instantaneous power theory. In the second part, the DC capacitor voltage regulator is applied, producing a reference current and a proper voltage regulator is developed. For the third part of the control system, we use a PI controller to provide some conditions that follow the reference current in a complete cycle, and generate firing pulses by the hysteresis method. The proposed control system not only reduces the voltage and current harmonics in power systems but can also improve the power quality indices. The above design was implemented in the EAF system of the Mobarakeh steel complex (Isfahan, Iran). The simulation results show the effectiveness of the APFs in improving the power quality indices.     

DAQs-based wattmeters for high accuracy measurements. Comparison with the Italian power primary standard

This paper is focused on the use of data acquisition boards (DAQs) for the development of high accuracy PC-based instruments for the measurements of electrical power. The proposed systems are simple, portable and low cost because they are based on commercial data acquisition boards (DAQs) connected to a common personal computer. Data processing is carried out by a commercial software based on an interpolating windowed FFT. In the paper it is shown how the voltage can be sensed directly, thanks to the DAQ input range, thus avoiding expensive voltage dividers. The set up of the DAQs-based solutions is described and the evaluation of their metrological features is made by means of a comparison with the Italian power primary standard, which was built at INRIM with a complex solution and expensive with two high precision digital voltmeters.     

An integrated error compensation method based on on-machine measurement for thin web parts machining

Thin webs are widely used in the aerospace industry for the advantages of compact structure, light weight and high strength-to-weight ratio. Due to its low rigidity, serious machining error may occur, therefore, Finite Element method and mechanism analysis are usually utilized to modeling its deformation. However, they are very time-consuming and only suitable for elastic deformation error. In this study, an integrated error compensation method is proposed based on on-machine measurement (OMM) inspection and error compensation. The OMM inspection is firstly applied to measure the comprehensive machining errors. The Hampel filtering is then used to eliminate outliers, followed by the triangulation-based cubic interpolation as well as a machine learning algorithm which are used to establish the compensation model. At last, the real time compensation of high-density cutting points is realized by developing the compensation system based on External Machine Zero Point Shift (EMZPS) function of machine tool. Three sets of machining experiment of a typical thin web part are conducted to validate the feasibility and efficiency of the proposed method. Experiment results revealed that after compensation, the comprehensive machining errors were controlled under different machining conditions and 58.1%, 68.4% and 62.6% of the machining error ranges were decreased, respectively. This method demonstrates immense potential for further applications in efficiency and accuracy improvement of thin-walled surface parts.     

A precise scheme for detection of current transformer saturation based on time frequency analysis

Current Transformers (CTs) are prone to saturation due to large amplitude of fault current and existence of decaying Direct Current (DC) offset. Since the CT saturation leads to mal-operation of protective relays, detection and correction of saturated currents is one of the most important challenges in the power systems protection. In this paper, a new algorithm is presented for detection of CT saturation time interval by using the Improved S-Transform (IST). Simultaneously, IST can yield a complete visualization of signal in both time and frequency domains. An index based on instantaneous power of the CT secondary current is calculated using the IST output matrix. Then, the saturation region is estimated by determining the maximum and minimum values of the proposed index in the time domain. Comprehensive simulations are implemented using PSCAD/EMTDC software. Main parameters which have direct effect on the saturation levels are considered in simulation studies. As extremum points of the proposed index are determined for detection of saturation regions, the proposed method is not affected by CT parameters. The obtained results show that the proposed algorithm can precisely detect CT saturation time intervals even in noisy conditions.     

A web-based distributed measurement system for electrical power quality assessment

Industries’ systems are shifting toward almost entirely sophisticated electronic devices. Power Quality (PQ) analysis is getting importance for the economy because this equipment is highly sensitive to PQ events. Control and supervision of an industrial process has mainly been focused on the electrical protection, and little attention has been paid to the quality of the electrical supplies. Nowadays, measurement and communications systems have advanced to enable the installation of web-based sensors within a PQ assessment scenario. In this sense, this paper presents an innovative low-cost measurement system, as well as investigates the challenges and trends in the development of distributed PQ measurement systems using smart sensors.     

Magnetic interference compensation method for geomagnetic field vector measurement

Ferromagnetic interferential field from platforms is one of the most dominating error sources for magnetometer. For magnetic vector and gradient tensor measurement, what is cared about most is the effect of compensating magnetic field vector. In this paper, a magnetic compensation method is proposed, which uses host platform’s attitude from inertial sensor as auxiliary information and sets up a vectorial compensation model. By introducing three intermediate parameters, the issue of parameter estimation is linearized and solved with least squares method. Simulations show that errors of magnetic field vector and magnitude can both be reduced to several nT after compensation. Experiment has been conducted with a geomagnetic vector measurement system and results suggest that the method is an effective way for compensating both magnetic field magnitude and vectors.     

大跨距孔同轴度误差快速视觉测量方法

为快速、准确测量大型零件大跨度孔的同轴度误差,设计了对侧布置的线激光扫描四目视觉测量系统,通过两套视觉测 量单元分别采集两孔端面点云数据,进一步拟合端面圆心和端面法线,得到两个独立的单侧孔轴线。 提出了大跨距无公共视场 视觉系统标定方法,设计了多标定板相固连的靶标,通过 4 块标定板的位姿关系传递,得到两套视觉测量单元的坐标系转换关 系,实现了两侧孔测量数据的坐标系统一。 精度验证实验表明,该系统对于 1. 15 m 跨距的标准球组球心距测量均方根误差为 0. 161 mm。 使用该系统对一压路机振动轮两侧轴承孔的同轴度进行了测量,并与三坐标测量机的测量结果进行了对比,结果 表明两者测量结果偏差小于 5% ,测量精度能够满足工业生产需求。     

基于多波长协作的切削液残留表面激光位移测量误差补偿方法

在加工测量一体化过程中,工件表面切削液残留形成的油膜会严重影响光学在机测量的精度。 现有的误差补偿方法通 常需要获取油膜介质的先验信息,如成分、厚度等。 而这些信息受加工形质、切削液随机分布等因素的影响难以实时获取。 为 此,本文提出一种基于多波长协作的切削液残留表面激光位移测量误差补偿方法。 首先设计并搭建了基于激光三角位移测量 的多波长激光测量系统,可利用多波长激光测量同一被测点位移。 通过引入柯西色散规律,建立光学系统与激光波长的解析关 系,并基于此推导出多波长激光测量内在的差分特性,最终实现误差补偿。 本文依此方法进行了实验。 结果表明补偿后测量误 差绝对值小于 0. 01 mm,与未补偿的测量数据对比,误差降低了至少 92% 。