Search

An efficient maximum power point tracking technique is developed, which realises the fractional open‐circuit voltage (FOCV) algorithm through a unique on‐line procedure. The proposed method continuously estimates the open‐circuit voltage by measuring instantaneous voltage, current, and temperature of the photovoltaic module without disconnecting the power flow to the load. Simultaneously, the open‐circuit voltage (Voc) value can be measured at any operating point of the I–V curve and does not require any perturbation to the specific point. Three methods i.e. proposed algorithm, analytical FOCV, and conventional offline FOCV are modelled in Matlab/Simulink environment and also the numerical computations are carried out. Finally, the proposed FOCV and the conventional offline FOCV are tested through the experimental setup. The comparative analysis indicates the following advantages: (i) interruption‐free output power; (ii) accurate measurement of Voc under any weather condition, especially variable temperature condition; and (iii) continuous measurement and tracking of maximum power point (MPP). Owing to the aforementioned advantages, the proposed method exhibits better MPP tracking and superior dynamic plus steady‐state efficiencies as compared to the analytical FOCV and conventional offline FOCV methods. [ABSTRACT FROM AUTHOR]

Monitoring of rotor temperature in permanent magnet synchronous machines (PMSM) is of great importance as high temperature could cause partial or even irreversible demagnetisation of the permanent magnets (PMs). Rotor temperature measurement unfortunately is particularly difficult in practice, since it is difficult to access temperature sensors on a rotating shaft. Nevertheless, rotor temperature can be obtained indirectly with the information of rotor magnet flux linkage, as PM remanence decreases with rotor temperature. Here, a simple and relatively accurate method for online estimation of PM flux linkage is presented, based on the measurement of current response to the standard space-vector pulse width modulation (SV-PWM). This method uses the already-existing PWM voltage as the excitation signal in order to avoid any form of signal injection which produces undesirable disturbance to the system. Knowledge of machine parameters, such as inductances which may vary due to saturation, is not required. The proposed methodology has been verified in real-time simulation. [ABSTRACT FROM AUTHOR]

Soil sparkover is one of the key factors that affect the impulse characteristics of grounding devices under lightning current. In this study, the polyester‐based sensitive films are applied to observe the morphology features of the sandy sparkover around a horizontal grounding rod 1 m in length buried in a hemispheric pool 8 m in diameter under impulse current. Moreover, the releasing current distribution of the grounding rod is measured by modular multi‐channel simultaneous signal acquisition system. Along with injected impulse current increasing, the ratio of current released from two ends of the rod increases because the spark discharge leads the redistribution of the dissipating current. The discharge in the sand becomes more intense with current increasing. The discharge on middle segments spreads around the electrode‐like cluster, while sparkover at the terminal develops into tree creeping discharge finally. Analysis based on combining observation images with current measurement result suggests that sparkover morphology is related to not only electric field value but also electric field distribution. The sparkover strength is determined by electric field intensity, while the sparkover concentration depends on electric field uniformity. [ABSTRACT FROM AUTHOR]

This study is concerned with the linear estimation problem for networked systems with one‐step random delay and multiple packet dropouts. At each moment, the estimator may receive one or two data packets or nothing. The predictor of sensor measurement at the current instant is used as a compensator if the current measurement does not arrive at the estimator. Based on the developed compensation model, the optimal linear estimators including filter, predictor and smoother are proposed by the innovation analysis approach. Compared with the estimators based on the compensation of using the latest measurement previously received in the existing literatures, the proposed estimators have higher estimation accuracy and smaller computational burden. Simulation results show the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

Battery electric city bus model has been created and validated with measurement results from a full‐scale city bus prototype. The model utilises multi‐physics modelling approach with multiple‐domains from friction‐tyre and transmission model to electrical drive and a simplified battery model. For the electrical drive model, four approaches to model the losses were studied. The modelled and measured motor torque, speed, current in the battery and inverter, and the bus speed were compared under two bus line driving cycles using three payloads. The simulated results were in good agreement with the experimental results; the error between the simulated and measured energy consumptions was 1.5% with the most accurate model. [ABSTRACT FROM AUTHOR]

In this study, a new algorithm for directional protection, based on cross correlation of Fourier transform components of voltage and current for each phase is proposed. The fault is detected using k‐nearest neighbour algorithm. By comparing the fifth‐nearest neighbour of each sample with an adaptive threshold, the fault is detected. The adaptive threshold is derived by a moving window with length equal to 1 ms. Using Fourier transform, the fifth sinusoidal component of the measured voltage and current for each phase is extracted. Then the cross correlation of the voltage and current components is calculated. The calculated cross correlation signal is passed through a low‐pass filter. By comparison of the filtered signal with a predefined threshold, fault direction is determined. It is confirmed that the fault direction can be identified in less than 8 ms with high accuracy of nearly 99%. More than 6500 scenarios are considered for different fault conditions to evaluate the proposed method. Furthermore, using some experimental results the proposed method performance is confirmed. The simulation and experimental results show that the proposed method has high speed, good accuracy, and sensitivity. [ABSTRACT FROM AUTHOR]

This study proposes a new method for modelling of metal‐oxide surge arresters (MOSAs) thermal balance diagram based on power loss and heat dispersion curve. Adaptive network‐based fuzzy inference system (ANFIS)‐based method was offered to compute surge arrester power loss characteristic. Thermal stability (TS) of surge arrester, which is analysed by thermal balance diagram, has a great influence on their proper functions. MOSA material variation is an important factor that has an influence on its TS. Degradation factor (DF) was introduced as a new index in this study to represent material variations of MOSA. Therefore, applied voltage, temperature and DF were considered as inputs in ANFIS model to obtain accurate power loss which is a very important factor in TS characteristic. Heat dispersion curve was obtained as a main feature in the thermal balance diagram from surge arrester cooling curve. Degrading effect was considered using voltage and current measured from MOSA which are degraded by utilisation in the network. In addition, effect of assembling process has been considered by using new different varistors in experimental measurements. This study shows that the thermal balance diagram of surge arrester is predictable with a good accuracy by using artificial model. [ABSTRACT FROM AUTHOR]

An estimation procedure for transmission line parameters is developed that combines a new method of determining line parameters with others available in the technical literature. Each estimation method has certain advantages and restrictions that depend on the operating conditions of the transmission system (e.g. the load profile), the physical characteristics of the line (e.g. the length and the geometry) and electromagnetic phenomena (e.g. single‐ or multiphase faults). The proposed estimation procedure exploits the major attributes of both the new determination method developed in this study and other well‐established methods previously presented in the technical literature. Based on current and voltage measurements obtained from synchronised fault records from both line terminals, a combination of multiple methods can be used to accurately estimate most line parameters, a task that is typically impossible using a single method. [ABSTRACT FROM AUTHOR]

An incipient and self‐clearing arcing fault can be utilised as a precursor of an imminent permanent failure for monitoring of underground cables. Due to very short duration of the incipient faults, generally they cannot be detected by conventional protection relays. This study presents a new method for detection of incipient cable failures by using measured current and voltage at one end of the cable. The incipient faults are detected using an innovation signal calculated from the measured fault current via a Kalman filter. Upon change detection by the innovation signal, the change is checked for discriminating possible incipient fault from other similar conditions. The proposed method is evaluated using several simulations and field data collected from a real network. The results confirm that the method can achieve high accuracy and speed for detection of cables incipient faults. [ABSTRACT FROM AUTHOR]

There are a few components of the current signal that may lead to inaccurate current measurement in power systems, and therefore, may cause malfunction on numerical protective relays and control devices. Some of these components include harmonics, the decaying DC offset, and noises. In this study, a phasor estimation method based on artificial neural networks is proposed, which will provide fast response time and accuracy. The method uses the multilayer perceptron structure to precisely estimate the amplitude and phase angle of the current waveform by determining its input weights during an online training process. The proposed algorithm is tested and compared with other reliable and well‐known methods for a performance evaluation. [ABSTRACT FROM AUTHOR]

This study proposes long‐term dynamic planning of distributed generation (DG) units in distribution networks considering active management (AM). In the AM operation mode, the distribution network equipment is controlled in real time based on the real‐time measurements of system parameters (voltage and current). The proposed model determines the optimal size, location and time of investment of DG units. The uncertainty of energy price and rate of load growth is handled using a scenario‐based modelling approach. To demonstrate the advantages of dynamic DG planning, its results are compared with those of static model. Also the results of optimal DG planning in active network are compared with those of the passive operation mode. In addition, a technical evaluation and comparison between conventional, passive and active networks have been performed. The proposed model is successfully applied to the 33‐bus radial distribution network. The results indicate that using AM, the cost function and losses are decreased effectively compared to the passive management. Computation of the optimal DG planning in AM environment is formulated as a mixed integer non‐linear problem which can be solved using commercial optimisation packages like as GAMS. [ABSTRACT FROM AUTHOR]

In this study, the authors report on two different electronic interfaces for low‐power integrated circuits electric current monitoring through current‐to‐frequency (I–f) conversion schemes. This proposal displays the intrinsic advantages of the quasi‐digital systems regarding direct interfacing and self‐calibrating capabilities. In addition, as current‐sensing devices, they have made use of the giant magnetoresistance (GMR) technology because of its high sensitivity and compatibility with standard complementary metal oxide semiconductor processes. Single elements and Wheatstone bridges based on spin‐valves and magnetic tunnel junctions have been considered. In this sense, schematic‐level simulations for integration in Austria Microsystems 0.35 μm technology have been corroborated by means of experimental measurements with the help of printed circuit board prototypes and real GMR devices. Tables with relevant parameters (silicon area, power consumption, sensitivity etc.) have been constructed as practical tools for designers. Electric currents down to 2 μA have been resolved in this way. [ABSTRACT FROM AUTHOR]

Analytical models are the key tools in the model‐based control design of electric drives. The inductances together with the stator resistance are the fundamental parameters of these models. In this study three methods to determine the inductances of the decoupled d–q model of double‐star permanent‐magnet (PM) synchronous machines are studied. These methods have commonly been used to determine the inductances of conventional three‐phase PM machines. Two of the evaluated methods are based on the phase‐variable inductance waveforms and flux linkages and are thus analysed with finite‐element analyses only. The third method, based on the analytical stator voltage equations, can be applied straightforwardly with the real drive system supplied with voltage‐source inverters (VSIs). This method requires only the knowledge of the rotor position and the existing current measurements of the VSIs that are used for the current control. Experimental results are provided to verify the applicability of the voltage‐equation‐based method to determine the inductances. On the average, the presented methods provide similar values, but also some discrepancies between the obtained values can be observed. The measured inductance parameters are validated using model‐based closed‐loop controllers. [ABSTRACT FROM AUTHOR]