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Power-electronic-converter-induced motor bearing currents are a widespread problem in the field of electrical drives. Parasitic capacitances between the electrical machine's parts provide a path for leakage currents, which finally harm metallic ball bearings. Remembering that end-windings have a significant contribution in building up stray capacitances, a countermeasure affecting both the lamination stack and end-winding areas is needed. This article focuses on a countermeasure against the noncirculating bearing currents in the cluster of solutions at the motor side. The electrostatic shielding approach, which is a known principle to reduce capacitive couplings, is applied in electrical machines every now and then. In this article, the principle of slot-embedded grounded electrodes is extended to cover also the end-windings. Thus, the electrodes provide a better shaft-to-ground voltage mitigating effect compared to the case where electrodes are applied only in the lamination stack area. The feasibility and effectiveness of such a countermeasure are investigated. Different options in terms of scaling of both the machine size and diameter of the electrodes were analyzed and corresponding conclusions were pointed out. [ABSTRACT FROM AUTHOR]

Fast and reliable dc line protection is one of the key techniques for flexible dc grid with the development of flexible dc transmission technology. However, the serious overcurrent caused by dc faults has a prominent contradiction with the weak overcurrent capability of power electronics. In this article, the high-fidelity dynamic model of the transmission line is first established based on the frequency-dependent characteristic of line parameters. Then, a new dynamic state estimation based protection (DSEBP) scheme is proposed, which uses the redundancy feature of state estimation to improve the dependability of protection. Finally, the actual measurements and the estimated states are compared with the similarity to identify the fault by the chi-square distribution. The proposed method's effectiveness is verified through simulations power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) and experiments, and the factors affecting the performance of DSEBP are analyzed. Compared with the existing protection methods, the proposed method is more dependable, more sensitive, and available for actual projects. [ABSTRACT FROM AUTHOR]

Integrated gate-commutated thyristors (IGCTs) have successfully demonstrated to be well-suited devices for an application in medium-voltage dc transformers based on LLC resonant converter topology. This appli- cation enables unusually high switching frequencies in kilohertz range thanks to the zero-voltage switching while maintaining the high conversion efficiency. Moreover, the clamp circuit that is an inseparable part of every hard-switched IGCT-based converter can be completely omitted—further lowering the converter complexity and cost. Nevertheless, without the clamp circuit, the effect of shoot through becomes fatal, considering that the IGCTs have a defined mode of failure in short circuit and the desaturation effect is practically nonexistent. To prevent the shoot through, this letter proposes a simple, yet effective, protection method based on anode-voltage measurement that can be implemented locally on the IGCT gate unit. The validity of the solution is demonstrated using a custom IGCT gate unit in a medium-voltage resonant test setup. [ABSTRACT FROM AUTHOR]

Due to the unbalanced load connection in the sensitive load bus (SLB), the ac microgrid may suffer from voltage unbalance in the system. To overcome this issue, this article presents a new distributed control scheme to achieve the unbalanced voltage compensation for islanded ac microgrid with limited noncontinuous communication among the distributed generation (DG) units. In this article, a two-layer control framework, including the cyber layer and the primary control layer, is employed. The proposed control strategy that is applied in the cyber layer implements an event-triggered communication to effectively compensate for the unbalanced voltage in the SLB. In contrast with the centralized control strategy, the proposed control strategy is fully distributed, and the information exchange among the DG units at only the event-triggered times. As a result, the communication burdens can be measurably reduced while the control performance is not affected. The stability is analyzed with the Lyapunov function in this article. Finally, several experimental case studies are provided to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

High voltage direct current (HVdc) detection is essential to ensure the suitability and operation of electrical systems, as well as personal safety. Today there are commercial sensing devices equipped with a safety system that emits audible warnings, but they do not indicate voltage and polarity levels. Likewise, although the scientific literature describes various solutions with satisfactory results, very few of these achievements are found in real-world applications. The purpose of this article is to present a technological alternative based on the study and development of a simple and portable electronic device to enable the detection and quantification of high voltage and polarity in HVdc systems. The principle is based on the detection of corona current by means of an aluminum tip held at a distance of about 5 mm from the energized surface through a radial contact rod. The detected electrical current signal is collected and processed through an electronic system. The performance was analyzed by means of corona discharge models and high voltage experimental tests in real-world conditions. The results demonstrated the satisfactory response of the proposed approach in the detection, quantification, and identification of polarity in a ±600 kV HVdc transmission system, with an error varying from 1.79% to 2.72% compared to theoretical values, as well as its ability to withstand the influence of temperature variations between 18 °C to 29 °C, relative humidity between 56% and 78%, and an atmospheric pressure kept constant at 101.6 kPa. The proposed approach contributes to HVdc monitoring and inspection activities, helping to ensure their operation and suitability. [ABSTRACT FROM AUTHOR]

Gallium nitride high electron mobility transistors outperform Silicon devices due to their excellent physical properties. However, being an immature technology, it exhibits dynamic on-state resistance ($R_{\text{ds}, \text{on}}$). This causes increased conduction loss and leads to reduced operating efficiency. To evaluate the dynamic $R_{\text{ds}, \text{on}}$ of the device, a measurement circuit is required. In literature, a standardized double pulse test is widely used for the measurement of $R_{\text{ds}, \text{on}}$. However, due to the uncontrolled off-state time and inability to independently adjust, the test conditions result in restricted measurement. This article proposes a measurement circuit of the device in power electronics operations. The circuit uses an H-Bridge-derived topology with capacitive storage to enable forward and reverse conduction mode measurement of the device. In all the modes, the circuit allows measurement from the first switching cycle and independent control over the testing conditions by using a hysteresis current control. The proposed measurement circuit is validated using simulation and experimentation. Finally, analytical efficiency compared with the state-of-the-art measurement circuits is provided. [ABSTRACT FROM AUTHOR]

Online aging monitoring is the basis for high reliability operation of Insulated gate bipolar transistors (IGBTs). Most monitoring methods focus on the package-related aging. Leakage current (Ileak) has been proposed as a potential chip-related aging (CRA) indicator for IGBTs. However, this method has not been implemented online due to the difficulty in accurate online leakage current measurement. An effective online CRA monitoring method is still required for IGBTs. A novel online CRA monitoring method based on Ileak for IGBTs is proposed in this article. First, an online Ileak measurement circuit is proposed. Second, based on this circuit, an aging monitoring strategy is presented. Finally, accelerating aging tests validate the effectiveness of the proposed method. The on-state voltage drop is selected as an aging indicator for comparison. The proposed method has three advantages. The online CRA monitoring is achieved. It can be used in slight aging situation with high sensitivity because Ileak is linear to the CRA levels. The measurement circuit required by this method is simple and low-cost. [ABSTRACT FROM AUTHOR]

In this article, we propose a monitoring procedure based on a multilayer neural network with multivalued neurons (MLMVN) capable of preventing catastrophic failures of dc–dc converters. The neural classifier allows both the detection of any malfunction and its localization. Thanks to the low computational complexity, the proposed method operates online, estimating the deviations of the passive components from their nominal values: this allows control strategies to be promptly adopted and operation of the dc–dc converter to be kept in high efficiency and reliability conditions. Since measuring the voltage and current on each component increases the complexity of the system, a testability analysis is proposed with the aim of identifying the minimum number of measurements needed to distinguish the classes of failure. To make the testability phase easier and more intuitive, a graphical representation is proposed. As a case study, prognostic analysis has been applied to prevent catastrophic failures in a synchronous Zeta converter. Several fault conditions have been analyzed through simulations and experimental tests. The obtained results confirm the ability of the proposed method to prevent failures and, also, show that the application of MLMVN results in a better performance than classic solutions available in the literature, such as support vector machine. [ABSTRACT FROM AUTHOR]

The open-circuit fault detection and localization (FDL) technique can improve the reliability of the modular multilevel converter (MMC). However, the conventional software-based FDL methods usually have a heavy computation burden or a limited localization speed. This article proposes a simplified and fast software-based FDL approach for the grid-connected MMC. First, the errors between the measured state variables (the output current and the circulating current) and their estimated values are calculated. By comparing these errors with their threshold values, the switch fault can not only be detected but also be localized to the specific arm. Then, the capacitor voltages in this faulty arm are collected, and the submodule (SM) with the highest capacitor voltage is selected. To confirm the switch fault in this SM, a modified Pauta criterion is presented to check the abnormal voltage data. As a result, the computation burden of the proposed software-based FDL approach is significantly reduced, and the faulty SM can be localized in a short period. Simulation and experimental results verify that the proposed approach can effectively detect and localize different open-circuit faults, and it is immune to the step of power references. [ABSTRACT FROM AUTHOR]

The presence of asynchronous absolute and relative measurements has posed a great challenge to the current multisensor positioning method in robotic systems. Although traditional factor graph methods possess a capability of plug-and-play, only a compromised performance can be obtained when dealing with an increasing number of asynchronous observations. In this article, a novel plug-and-play factor graph method for asynchronous absolute/relative measurements fusion in multisensor positioning is proposed. Different from traditional methods, a fixed-rate graph model is formed. The variable nodes in the graph are built at a fixed update rate to do the optimization, which is not affected by the arrival of measurements. Asynchronous absolute and relative measurements between two successive variable nodes are associated with corresponding variable nodes in the graph via the propagation of closed-form inertial measurement unit (IMU) preintegration. The simulations, datasets, and field tests are carried out to validate the proposed method. The results indicate that the closed-form IMU preintegration method has better dynamic adaptability in fusion system to formulate the association with asynchronous measurements. On this basis, the proposed method can integrate asynchronous measurements in a plug-and-play manner and achieve better performance compared to current methods. Meanwhile, the computational load can also be reduced. [ABSTRACT FROM AUTHOR]

Insulation aging of underground power cables may lead to severe fault and system outages. Condition monitoring of cable insulation is essential to maintain power system reliability. However, most existing insulation monitoring methods can only work in offline mode and cannot describe cable aging severity quantitatively. In this article, a novel online monitoring scheme for underground power cable insulation based on common-mode (CM) leakage current measurement is proposed. An online neutral-point voltage injection approach is proposed, and CM leakage current distribution model for both the cables with and without metal sheath under the injected voltage is derived. The insulation capacitance can therefore be monitored online without disturbance to the system operation. Simulations and experiments are conducted to prove the effectiveness of the proposed method. With the aid of a designed CM leakage current sensor, CM leakage current smaller than 5 mA can be detected and the accurate evaluation of aging severity is achieved. The key feature of the proposed method lies in its nonintrusiveness and online fashion: the normal operation of the system will not be interrupted, and accurate quantitative monitoring of cable insulation can be achieved online. [ABSTRACT FROM AUTHOR]

This article proposes an online diagnosis scheme for transistor faults of asymmetric half-bridge converter (AHBC) in switched reluctance motor (SRM) drives. In order to extract more information from the phase current to identify faults, based on the conventional current measurement method, two novel current measurement methods are presented by reconstructing current sensors. According to the novel current measurement methods, a current prediction method is raised. The phase current at the kth sampling time is available so that the estimated current can be calculated. The fault can be detected and located by analyzing the given and actual switching states, which are deduced by comparing the measured and estimated currents. Compared with existing methods, the proposed scheme can be applied to diagnosis of multiple faults in n-phase AHBC, which can operate at various control strategies and chopping modes. With a single current sensor in each phase, the scheme will not increase the cost and complexity of the SRM drive. Furthermore, the scheme does not require complicated computation, making it easy to implement online. The experimental results confirm the effectiveness and flexibility of the proposed scheme. [ABSTRACT FROM AUTHOR]

Soft starters are a well-known solution for starting induction motors in industrial applications. With a predictive algorithm approach the losses in motor and soft starter can be lowered significantly. This article presents an algorithm which can be implemented in industrial devices with a concomitant speed control option. This speed control is necessary to fit the users requirements for start-up. Besides the speed control, the characteristic behavior of the predictive algorithm is analyzed in detail. The suitability of the novel predictive closed loop approach for different representative industrial applications is proven by measurements and discussed in detail. [ABSTRACT FROM AUTHOR]

In this article, a fault-tolerant model-free predictive controller (FT-MFPC) for cascaded H-bridge multilevel inverters (CHMLIs) is proposed. FT-MFPC is based on an association of model-free predictive controller (MFPC) and a proportional--integral (PI) like structure known as current variation controller (CVC). As in MFPC, the dynamic structure (DS) that is used for the prediction of the system output is obtained from past measurements of current variations, but CVC modifies the dynamics before they are stored for prediction. As a consequence, even if the converter operates with bypassed modules, FT-MFPC adapts its DS to represent the real dynamics of the system and enables a closed-loop response with balanced load currents in unbalanced CHMLIs. Simulation and experimental results validate the adaptability of the proposed strategy to operate a seven-level inverter under various configurations of bypassed H-bridge modules. The experimental results show that, for different postfault operations, the maximal current total harmonic distortion and imbalance factor at steady state in the worst case scenario are below 5% and 2%, respectively. [ABSTRACT FROM AUTHOR]

Aiming at the misdiagnosis problem of the interturn short-circuit (ITSC) fault detection method caused by the inverter nonlinearity and the current measurement errors, a d-axis residual voltage-based fault diagnostic strategy is proposed for sensorless control of the surface permanent magnet synchronous motor (SPMSM). The model of the three-phase wye-connected SPMSM with ITSC fault is established, and the expression of the d-axis residual voltage caused by the ITSC fault, the inverter nonlinearity, the current measurement errors and the motor parameter errors is derived. The proposed fault diagnostic strategy can eliminate the current relative gain coefficient error and locate the ITSC fault by using the eighth and second harmonics of the estimated d-axis residual voltage, respectively. The experimental results verify the effectiveness of the proposed fault diagnostic strategy. [ABSTRACT FROM AUTHOR]

In this article, a sensorless control method based on signal injection and a high-pass filter (HPF) circuit is presented to control the unsymmetrical bistable multimagnetic circuit permanent magnetic actuator. In this method, a high-frequency sinusoidal signal was indirectly injected into the idle phase via a HPF circuit, and the peak of the high-frequency capacitance current was measured, which was used to calculate the idle phase inductance. Thereafter, the mover position was calculated by the one-to-one relationship between the idle phase inductance and the mover position. Combined with the HPF circuit and the proposed average current peak algorithm, the influences of back-EMF and coil resistance were eliminated. The magnetic saturation effects can also be ignored in the proposed strategy. The estimated noise, caused by measurement noise and signal distortion, was filtered using a simple mathematical filter. The flexibility and accuracy of the presented strategy were verified by simulation and experimental investigation. [ABSTRACT FROM AUTHOR]

The wide bandwidth impedance of grid and inverter are the critical parameters for small-signal stability analysis and control optimization of grid-tied inverter systems. The impedance measurement is an effective way to obtain the grid and inverter impedance by injecting a series of perturbations into the measured system. However, previous studies fail to fully consider the adverse grid voltage conditions; including harmonics, unbalance, frequency deviation, voltage sag, and phase jump; which may bring errors to the measured impedance. In this article, a cascaded delayed signal cancellation (CDSC)-based method is proposed to accurately obtain the impedance of the measured system under adverse grid voltage conditions. The proposed CDSC-based method is mainly composed of the perturbation extraction module (PEM) and frequency adaptive module (FAM). Different CDSC blocks are applied to implement the PEM and FAM to extract the injected perturbations adaptively, under various adverse grid voltage conditions. Simulation and hardware-in-the-loop experiment results are presented to validate the effectiveness and feasibility of the proposed impedance measurement method. [ABSTRACT FROM AUTHOR]

Accurate rotor position estimation is important to ensure the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To suppress the estimated rotor position harmonic error (ERPHE) caused by inverter nonlinearities, flux spatial harmonics, and the current measurement error in high-frequency signal injection-based schemes, an adaptive iterative learning control-based online suppression method is proposed in this article. This method constructs a P-type iterative learning rotor position observer with the forgetting factor to obtain the tracking error and generate the compensation value in real time. The stability, the convergence, and the parameter sensitivity of this observer are analyzed in detail. To improve the suppression effect of the ERPHE for different loads and speeds, an iterative learning gain self-tuning strategy is investigated. The proposed method does not require the offline detection and the discrimination of harmonic frequencies, which has strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW interior PMSM drive platform. [ABSTRACT FROM AUTHOR]

This article presents a novel configuration of the eddy current speed sensor to measure the rotating speed of iron rods and shafts up to 3000 r/min. The proposed eddy current speed sensor has an axial airgap structure with one excitation coil and two antiserially connected pick up coils. The speed sensor is mounted in the end shaft part region. Different solid iron materials for rotating shaft are considered in the measurements and calculations to evaluate solid iron material effect on the eddy current speed sensor performance. Two-dimensional (2-D) and 3-D finite element method is utilized for the performance analysis of the speed sensor. Also, a 2-D analytical method is developed for parametric analysis. A copper rod is also used to compare the speed sensor with the rotating iron shaft and copper shaft. Finally, two thin copper discs with different diameters are mounted on the solid iron shaft and their influences on the eddy current speed sensor were evaluated and measured to increase sensitivity and decrease sensor dependency on the permeability of the solid iron shaft. The achieved nonlinearity errors are about ±0.2%. [ABSTRACT FROM AUTHOR]

The eddy current coil is widely adopted to measure the thickness of copper (Cu) film on the silicon (Si) based wafer. However, the lift-off distance (LOD) variation between the coil and Cu film has a strong negative effect on the accuracy and repetitiveness of the thickness measurement. Therefore, it is necessary to eliminate the impact of LOD variation. In this article, a high-precision thickness measurement method is proposed to determine the thickness of Cu film on the Si-based wafer by using the techniques of the erasable printed eddy current coil (EPECC) and the high-sensitivity associated circuit. The theoretical feasibility and sensitivity improvement of the conceptual design are analyzed in detail. As a proof of concept, a prototype of the proposed method is fabricated. The EPECC is prepared on the back surface of the wafer, and the LOD is unvaried during the measurement. Experimental results show that comparing with the traditional eddy current coil, the measurement stability, precision, and accuracy of the Cu film thickness by the proposed method are significantly improved even under severe vibration conditions. The relative error is 2% in repeated measurements. [ABSTRACT FROM AUTHOR]

Accurately estimating the capacity of lithium-ion batteries in electric vehicles (EVs) is critical for making correct management decisions. However, the randomness of the charging voltage range of EVs can lead to missing observations or reduced accuracy of capacity estimation methods. This article proposes an adaptive battery capacity estimation method suitable for arbitrary charging voltage range based on incremental capacity (IC) analysis and data-driven techniques. All charging conditions of EVs are divided into three categories according to the charging voltage range. Three data-driven estimation submethods with sequential application priority are designed for the three charging conditions separately, including back-propagation neural network with IC peak coordinates as input, ensemble learning with local high IC curve as input, and linear regression with ampere-hour coordinate transformation. The method is based on a priori knowledge to select a suitable estimation submethod under different charging conditions, so as to improve the adaptability. Experimental data is collected from eight commercial lithium-ion battery modules for model establishment and verification. Over 250 000 experimental samples at different states of health and random charging ranges show that the method can accurately estimate battery capacity under arbitrary charging conditions, with a maximum error of 2%. [ABSTRACT FROM AUTHOR]

The inevitable battery ageing is a bottleneck that hinders the advancement of battery-based energy storage systems. Developing a feasible health assessment strategy for battery pack is important but challenging due to the joint requirements of the computational burden, modeling cost, estimation accuracy, and battery equalization. This article proposes a balancing current ratio (BCR) based solution to achieve reliable state-of-health (SoH) estimations of all series-connected cells within a pack while significantly reduce the overall reliance on cell-level battery models. Specifically, after employing BCR to describe the properties of the balancing process, the voltage-based active balancing is combined into the SoH estimator design for the first time, leading to a weighted fusion strategy to effectively estimate SoHs of all cells within a pack. Hardware-in-the-loop experiments show that even if a parameter-fixed open-circuit-voltage-resistance model is used for modeling, the typical estimation error of our proposed solution can still be bounded by only 1.5%, which is 70% lower than that of the benchmarking algorithms. Due to the model-free nature of the integrated voltage-based balancing, the robustness and flexibility of the proposed pack SoH estimation solution are also significantly improved. [ABSTRACT FROM AUTHOR]

The insulation impedance monitoring methods such as capacitance/dissipation factor monitoring methods have been proposed for the online stator insulation condition monitoring. By measuring the insulation leakage currents and the phase-to-ground voltages, the groundwall and phase-to-phase insulation impedances can be calculated in frequency domain. In the existing methods, the calculation is based on the assumption that the differential mode phase-to-ground voltage decreases linearly along the stator winding and no phase angle deviation is considered. However, the phase angles of the induced electromagnetic forces in stator winding in different slots depend on the slot positions. The assumption in the existing methods neglects this phase deviation and causes errors in the monitoring results. In order to eliminate this effect, the effect of the phase angle deviation on monitoring results is analyzed in this article. Its dependency on the turn number, the winding configuration and the frequency of the selected monitoring signals is studied. A compensation method is proposed and the compensation coefficients are calculated for different winding cases for the demonstration purpose. The online experimental results prove that the accuracy of the online monitoring results is improved after the compensation. [ABSTRACT FROM AUTHOR]

The measurement for levitation gap is a very important part of levitation control system. The traditional levitation gap sensors have some shortcomings such as small measurement range and specific installation requirements, and usually need nonlinear correction and temperature compensation to meet the control requirements of the magnetic levitation system. In our work, two novel measurement methods for levitation gap based on computer vision are proposed. First, the levitation gap is measured by calculating the image pixel area of the region of interest. The error of the pixel area model can be limited within ±0.250 mm, and the mean absolute error (MAE) is 0.095 mm for full scale (FS). Second, the model named SelfConvNet based on convolutional neural network is designed for measuring the levitation gap. The error of SelfConvNet model can be limited within ±0.048 mm, and the MAE is 0.013 mm for FS. The measurement results show that the SelfConvNet model is better than SqueezeNet and Visual Geometry Group 16 models, which has high measurement accuracy and strong anti-interference ability. The method based on pixel area has lower measurement accuracy but higher processing speed. Finally, the proposed gap measurement methods have been verified in closed-loop experiment of maglev ball control system. [ABSTRACT FROM AUTHOR]

Online monitoring for underground power cable insulation will lead to early alarms of insulation faults in distribution grids, which has become an urgent need in the industry. However, the existing approaches require complicated monitoring devices, and cannot provide an estimation of insulation ageing severity. A novel online monitoring method for underground power cable insulation based on common-mode (CM) signal injection is proposed in this article. A CM monitoring signal injection device is designed by modifying the secondary side of current transformer in the system, with no need of extra injection voltage source. A monitoring scheme based on CM leakage current measurement at selected monitoring frequencies is proposed and an ageing feature extraction method based on principle component analysis (PCA) is developed which provides an estimation of the insulation ageing severity. Simulations and experiments are conducted, which proves the effectiveness of the proposed device and method under different system operating conditions with different parameters. [ABSTRACT FROM AUTHOR]

For power batteries used in the electric vehicle, accurate state-of-charge estimation is important. However, as one of the most commonly used estimation method, the least square support vector regression is hard to balance the accuracy and efficiency. To solve this problem, the fuzzy information granulation based on asymmetric Gaussian membership function is proposed to improve the utilization efficiency of the effective data and enhance the prediction accuracy of battery states. In addition, the performance of the proposed method is compared with that of other commonly used membership functions. In experiments, the dynamic stress test condition and the urban dynamometer driving schedule condition are used to verify the effectiveness. Compared with the most commonly used triangle membership function, the proposed method improves the accuracy of estimation by 6.47% and 2.18% under two current conditions, respectively. [ABSTRACT FROM AUTHOR]

Geomagnetically induced currents (GICs) are referred to as the quasi-dc current flows in power networks, driven by complex space weather-related phenomena. Such currents are a potential threat to the power delivery capability of electrical grids. To mitigate the detrimental impacts of GICs on critical infrastructures, the GICs should be monitored in power systems. Being inherently dc from the power frequency point of view, the components of GICs are, however, challenging and costly to monitor in ac power grids. This article puts forward a novel methodology for the real-time estimation of GICs in power transformers. Such aim is attained by means of an extended Kalman filter (EKF)-based approach, mounted on the nonlinear state-space model of the transformer, whose parameters can be derived from standard tests. The proposed EKF-based algorithm employs the available measurements for the transformer differential protection. The proposed approach, relying on the differential current, can properly deal with the external sources of interference like harmonic excitation and loading. The EKF-based estimator presented is validated by simulation and experimental data. The results verify the ability of the proposed approach to robustly estimate the GIC level during various operating conditions. [ABSTRACT FROM AUTHOR]

Due to the complex structure of flexible dc distribution systems with distributed photovoltaic power, single-ended measurement based protection cannot work well. The dc line-to-line faults are also difficult to locate due to a short time span with fault characteristics that is affected by various converter structures and control algorithms. To resolve these issues, a new fault detection and location method based on active converter injection is presented. The proposed method modifies the converter to become a frequency-controllable injection source by actively utilizing the coordinated control between local protection and the converters, which can build a clear protection boundary. Moreover, this method can locate the faulted area accurately by selecting the appropriate injected harmonic frequency, which is affected by the outlet capacitance of the dc/dc converter and the cable-distributed capacitance. Compared with current dc protection techniques, this method does not require additional injection equipment and high data sampling frequency. Hardware tests and simulation results are carried out, illustrating that the proposed mechanism is effective to achieve both control and protection through the controllability of power electronics. [ABSTRACT FROM AUTHOR]

In this article, we propose a communication-free, continuously regulated, and no additional circuit control scheme to ensure the constant current (CC) output under the inevitable variation of coupling effect between the transmitter and the pickup of wireless power transfer (WPT) systems. By comparing with previous studies on the impact of varying loads, the corresponding key technical challenge is to deal with the untestability of the mutual inductance. Especially for single-side and communication-free control schemes, the impact of coupling effect significantly increases the difficulty for the CC control of WPT systems. Thus, a communication/model-free (C/M-free) CC control is proposed and implemented by using the pretrained neural network, which aims to ensure the expected output current with respect to varying relative position between the transmitting and the pickup coils. Particularly, the pretraining scheme is adopted to reduce the implementation difficulties and the impact of the measurement inaccuracy. In addition, the analysis of robustness and generalization is also carried out to reveal the impact of parameter drifting and load disturbance on the performance of the proposed C/M-free CC control. In this article, the exemplified WPT prototype can realize the constant output current control with the accuracy of 97.6%. [ABSTRACT FROM AUTHOR]

The diode-front-end cascaded H-bridge (CHB) inverters have prevailed in the nonregenerative industry drive domain for high-power medium-voltage applications. The regenerative version of the CHB drives is made possible by adding the extra active-front-end rectifier in each power cell, such as a three-phase PWM rectifier. However, due to the instantaneous power unbalance, the dc-link capacitors of the regenerative power cell need to be overdesigned to maintain a stable low ripple dc-link voltage. To reduce the dc-link capacitance, this article proposes a novel closed-loop voltage ripple controller for the regenerative CHB drive without adding extra sensors. In the proposed method, dc-link voltage ripple amplitude and phase angle are accurately detected with a high-performance adaptive filter. Moreover, a latent instability issue is discussed and is avoided in the proposed controller. The performance of the proposed control strategy is validated experimentally on a seven-level regenerative CHB drive. [ABSTRACT FROM AUTHOR]

Electric drives immune to failures of selected elements of the power system or measuring sensors have been the subject of research in recent years, due to the growing interest in systems with an increased level of safety. This article concerns the analysis of the direct field-oriented control induction motor drive after the failure of all stator current sensors. An adaptive virtual current sensor (AVCS) was used to estimate the stator current, based on the measurement of the motor angular velocity and the voltage in the $\text{DC}\ (u_{\text{DC}})$ of the voltage-source inverter. This article presents the possibility of improving the accuracy of stator current estimation using the original approximation of changes in rotor resistance depending on the drive operating point when the measurement information about the stator current has been lost. This approximation was determined experimentally during the normal operation of the drive using a rotor resistance estimator. The determined approximate lookup functions were used to adapt the rotor resistance in the AVCS during the drive system operation in a postfault mode. This approach has made it possible to significantly improve the accuracy of the stator current reconstruction, especially under low speeds and load torques, which was demonstrated in experimental studies. [ABSTRACT FROM AUTHOR]

In this article, a phase-shifting fault-tolerant control (PS-FTC) method with single-phase current sensor is proposed for primary permanent-magnet linear motor traction system. The phase with healthy sensor is defined as the first phase, while the other two phases without healthy sensors are, respectively, defined as the second and third phases. In PS-FTC, hysteresis current control is adopted. The actual currents of the second and third phases are replaced by the estimated values, while the reference values are obtained by phase shifting of the estimated first-phase current. Although the linear motor parameters have been used in the calculation of the estimated currents, the parameter variations do not affect the performances of PS-FTC. Compared with the conventional fault-tolerant control (C-FTC) method and the existing fault-tolerant control schemes with single-phase current sensor, PS-FTC is robust and shows better steady-state performances. Furthermore, a hybrid strategy combining PS-FTC and C-FTC is adopted to improve the transient-state performances. The effectiveness of PS-FTC and the hybrid strategy are verified by the theoretical analysis and experimental results. [ABSTRACT FROM AUTHOR]

The closed-loop fluxgate current transducer (CFCT) is the only current sensor whose measurement accuracy can reach a level of the parts per million (ppm) at present. However, the false balance, which makes the CFCT unable to work, caused by an excessive offset current is the inherent flaw of the CFCT. The high di/dt (rate of current change) of the primary current is the main factor resulting in the offset current overload. Therefore, the CFCT is currently only applied for steady-state direct-current measurements. In this article, an approach is proposed to eliminate the false balance of the CFCT in the dynamic process by adding a feedforward branch, which provides a follow-up bias point for the CFCT to make the CFCT always work in a small-signal range, where a risk of magnetic saturation does not arise. The zero-flux state of the CFCT still only depends on the feedback branch, so its high measurement accuracy is maintained. The experiments prove that the CFCT can measure a flat-top pulsed current with an accuracy of the ppm level by this method. [ABSTRACT FROM AUTHOR]

A lithium-ion battery has advantages such as high energy density and long calendar life, but it suffers from the risk of thermal runaway. Overcharge-induced thermal runaway accidents hold a considerable percentage. This article discovers that the slope of the dynamic impedance in the frequency band of 30–90 Hz turns positive from negative when the cell just starts to overcharge and proposes the theoretical explanation. Taking 70 Hz impedance as an example, the thermal runaway accident can be successfully avoided by cutting off the charging when the slope turns positive from negative during charging. The warning time is 580 s ahead of the thermal runaway. This feature is easy to identify and requires no complex mathematical models and parameters. Besides, the prediction method based on this feature can be conducted by using an online dynamic impedance measurement device designed by us, which is suitable for large-scale applications. Thus, the overcharge-induced thermal runaway accidents can be avoided. [ABSTRACT FROM AUTHOR]

Developing accurate and efficient measurement systems for blade profiles has always been a vital issue in blade manufacturing. Nowadays, optical-based systems for measuring blade profiles have attracted significant interest due to their high efficiency and flexibility. However, as key steps in optical measurement of blades, system calibration and establishment of measurement datum are normally accomplished based on calibration objects, which may introduce uncertainty and affect the accuracy of the measurement. In this article, we propose a novel method for blade-profile measurement based on blade self-features. A measurement system based on a four-axis platform and laser scanning sensor (LSS) is developed. A calibration method based on the blade datum plane feature is introduced to eliminate the pose error of the system without using additional calibration objects. A feature-matching algorithm based on the covariance matrix of the blade local leading-edge feature is further proposed to establish the measurement datum. The proposed method requires smaller system-motion space and fewer LSS viewpoints, which would improve the efficiency and flexibility of the measurement system. Furthermore, less error accumulation can be achieved using our method, thus, resulting in higher measurement accuracy. The experimental results reveal the feasibility and good practical application prospect of this method. [ABSTRACT FROM AUTHOR]

This article identifies the parameters of an induction machine using limited and nonintrusive observations of available input voltages, stator currents, and the rotor speed. Parameter extraction is formulated as a nonconvex estimation problem, which is then relaxed to a convex conic optimization problem. While the resulting relaxation could exhibit a satisfactory performance, there might be cases where the solution of convex relaxation fails to satisfy the dynamic equations of the machine. This is remedied through a local search approach initiated using the solution obtained from the relaxed problem. The proposed method is experimentally verified on a squirrel-cage induction machine with missing measured data. Using the measured signals as the benchmark, time-domain transients produced by the parameters estimated using the proposed method show almost 20% better match compared to time-domain transients produced by the parameters obtained via conventional testing. [ABSTRACT FROM AUTHOR]

On-line detection of fault characteristic gases released by the insulation oil of transformers is developed as a scientific basis for estimating explosion accidents. However, the performance of most gas sensors, such as H2 and C2H2 sensors, is usually affected by temperature, and there exists large detection error when the temperature of transformer oil changes in operation. And the existing temperature compensation methods suffer from problems such as low integration, large volume, and high costs. Herein, a sensor array based on three triple-electrode sensors with carbon nanotubes was fabricated. Each of the three sensors has three vertically stacked electrodes with various interelectrode distances. The first and second sensors were used to detect H2 and C2H2, respectively, and the third sensor was used to measure temperature. All the detection mechanisms are based on the dependence of discharge current on gas concentration and temperature. The sensor array could detect H2/C2H2 mixture and temperature due to the exponential function between the output currents and electrode separations. The proposed sensor exhibited low relative and repeatability error values less than 5.1% and 4.9%, respectively, and displayed humidity compensation potential like temperature. High integration makes the sensor array superior among the other mechanism sensors. [ABSTRACT FROM AUTHOR]

The current sampling errors in dual-motor group (DMG) cause more adverse effects on system performance than that in a single motor system. To solve this problem, in this article, a synergistic correction strategy for the abovementioned problems in DMG fed by double inverters is proposed. First, an orthogonal pulsewidth modulation carriers strategy is proposed to imitate the “shutdown” status of motor subsystems to obtain ascertainable current relations. Then, the current values with sampling errors in DMG at several “fixed” sampling points are derived, based on which the sampling errors in DMG are corrected. Meanwhile, the rules for the action time of active vectors and output voltage range in each inverter are analyzed for each “fixed” sampling point. Finally, the proposed strategy is verified by experimental results on a DMG system, which show that the sampling errors can be precisely estimated with the proposed strategy. [ABSTRACT FROM AUTHOR]

Earth current generated by the operation of urban rail transit can enter into the neutral point of grounding transformer, which will result in the deterioration of transformer operation performance and cause electrical safety problems. In this article, the neutral current for 220 kV transformers has been measured in the real power system, the characteristics of dc and harmonic current are analyzed, and a novel suppression method for the dc and harmonic current simultaneously combining an active converter with a dc blocking capacitor is proposed, which solves not only the traditional dc bias problem but also the intrusion of the harmonic current from urban rail transit. The active converter is designed to compensate harmonic voltage to suppress harmonic current, and the capacitor provides blocking for the dc current. The protection scheme in case of the high fault current of the neutral point is presented. The improved control method is designed to control the neutral current and adjust the fundamental impedance for the requirements of relay protection. The effectiveness of the proposed method is verified by the digital simulations and the laboratory experiments based on the field working conditions, and the results demonstrate the satisfying performances. [ABSTRACT FROM AUTHOR]

Model-based predictive control that highly depends on system parameters is widely investigated. In contrast, model-free predictive current control (MFPCC) can be performed based on input or output measured data, rather than on any system model information, hence eliminating the influence of parameter uncertainties. In such a strategy, the current gradients due to each of the possible voltage vectors are stored and used to predict future currents. Current gradient knowledge therefore provides a significant foundation for MFPCC. In conventional MFPCC, however, the stagnation existing in the current gradient update always impacts the reliability of current gradients and further worsens the control performance. In this article, an improved MFPCC with an advanced current gradient updating mechanism is proposed. In the proposed strategy, to guarantee the reliability of the current gradients, two contiguous measured current gradients due to the applied voltage vectors are used to estimate the current gradients for all the possible voltage vectors. This simple method takes advantage of the mathematical relationships between the voltage vectors. In this way, all the current gradients can be obtained within one control period, effectively reducing the stagnation effect in conventional MFPCC. The proposed MFPCC scheme is evaluated on a permanent magnet synchronous machine drive setup to demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

The feasibility and the diversity of cantilever-based current sensing mechanism, which mainly comprised a cantilever with a permanent magnet on its free end, are verified for desirable applications of wireless sensor network (WSN) in Internet of Things (IoT). In the noninvasive multiphase current measurement, the applied current induced magnetic force is passively converted into a cantilever vibration via the magnet. The cantilever vibration can be further converted to an output voltage as a function of the applied current via diverse detecting units, enabling the diversity of cantilever-based current sensing mechanisms. In this article, cantilever-based methodology is verified to be applicable to multiphase current measurements, with considering decoupling and reconstructing in case of unbalanced ones. As a typical demonstration, three-phase four-wire ac current is passively measured via the positive piezoelectric effect of the piezoelectric detecting unit. Since the measurement of current is physically the noninvasive passive measurement of the gradient of the superimposed magnetic field, the cantilever-based current sensing methodology is applicable to a wide range of diverse current measurements of WSN in various IoT use cases. [ABSTRACT FROM AUTHOR]

Solid-state transformers (SSTs) have a great ability to improve power quality problems. In this article, an effective strategy is proposed to improve voltage unbalance conditions by these transformers. A searching optimization algorithm is presented to estimate the optimal required negative-sequence current vector. Injection of this current vector into a medium-voltage network provides maximum compensation in the voltage unbalance factor. In this method, the amplitude of the negative-sequence current vector is determined based on the current limitation of the SST and its phase angle is optimized to maximum improve the voltage unbalance conditions. Parametric analysis proves that the proposed injection current vector is unique. This negative-sequence current vector is obtained based on a simple process that is presented in the form of a flowchart. Independence from the extraction of positive and negative sequences of the measured currents is one of the main advantages of the proposed control method. Simulation and experimental results by using a laboratory three-stage SST approve the proposed optimization method. These results show that SSTs can acceptably decrease grid unbalanced voltage by an optimal injection current. [ABSTRACT FROM AUTHOR]

This article describes the design of an energy management system for a stand-alone cellular-connected outdoor trail camera that can operate without a power grid connection for a long duration. The primary focus of the study is to increase the operational lifetime of the system while decreasing human interference and the demand for maintenance, thereby enhancing the user experience. This is achieved by actively hybridizing three different battery types and a charging circuit supplied by a solar photovoltaic (PV) panel to harvest additional energy. This article investigates different user types and energy requirements for a hunting application. Considering the heterogeneous energy demand and cost requirements of the different user types, the battery energy storage, and PV system size are flexibly adjusted to satisfy the demand of the different types of users. While the proposed energy management circuit comes with an incremental cost increase to the trail camera, it provides essential functionality that will sustain stand-alone operation for a total five years with at most eight maintenance visits, decreasing the maintenance demand of the camera considerably. [ABSTRACT FROM AUTHOR]

Current research about battery-less fuel cell-based point-of-care (POC) devices study energy extraction and the measurement separately. In this article, we purpose a self-powered architecture that extracts energy efficiently from a fuel cell and performs a measurement simultaneously. The prototype uses a discrete power management unit based architecture with a power consumption lower than 36  $\mu$ W. We have tested it with ethanol, lactate, and methanol-based fuel cells, being able to perform a fuel concentration measurement while it extracts energy from fuel cells. The solution exhibited a minimum efficiency and maximum start-up time for the ethanol, lactate, and methanol-based fuel cells of 80% and 12 s. The architecture applies to other fuel cells, and the results show how this solution can help us face the current POC's autonomy challenge. [ABSTRACT FROM AUTHOR]

Online identification of a battery model can capture the parameter variations in real time, thus, providing an accurate model under various conditions, such as a wide temperature range, different aging degree in electric vehicle application. However, the measurement noise and sampling asynchronization of voltage and current are usually inevitable in the battery management system (BMS), which can lead to a large identification error. In this article, the mechanism of sampling asynchronization and measurement noise is analyzed first, and then the identification sensitivity analyses on noise and sampling asynchronization are carried out. Simulation results indicate that even a small fluctuation as small as 5 mV or the sampling latency between voltage and current within 10 mS can cause relatively large identification errors, especially for polarization parameters. In order to guarantee the online identification accuracy and robustness in the BMS application, an improved robust recursive least-squares (RLS) algorithm with adaptive outlier boundary is proposed to eliminate the input outlier caused by sampling latency and suppress the effect of measurement noise utilizing the bias compensation method. The experimental results demonstrate that the proposed method can provide sufficient accuracy and robustness under noise interference and sampling latency in BMS application. [ABSTRACT FROM AUTHOR]

With the global trend to develop digital substation automation systems, measurement devices are required to be reliable, of small size and light weight and of acceptable accuracy in a wide frequency band. This article presents a combined high voltage direct current measurement method which comprises the above-mentioned features that makes it suitable for smart grids protection and control applications. The proposed measurement method utilizes Hall sensor array for dc current measurement. DC voltage is measured using a voltage divider circuit while the harmonic currents are measured using a square Rogowski coil made of four straight bars along with a high precision digital integration algorithm. A four-spectral line interpolation fast Fourier transform algorithm based on trapezoidal convolution window is proposed to improve the extraction accuracy of the dc and harmonic components from the measured signal. Experimental results show that the error variation of the proposed method is less than 0.098% for voltage measurement while it is less than 0.104% for current measurement. The harmonic measurement ratio error is less than 0.2% and the angle error is less than 8'. [ABSTRACT FROM AUTHOR]

The basic principle of a noncontact method of measurement of conductivity of liquids, presented earlier, is analysed to evolve design rules to have minimal error in the measurement. In this method, the current is sent through the liquid whose conductivity is to be measured by induction and the voltage across the liquid column is measured using capacitive coupled electrodes and the conductivity computed therefrom. Hence, problems that arise due to contamination or corrosion of contacting electrodes are eliminated. The signal conditioning circuit is developed such that the measurement of the voltage-drop across the column of the liquid and hence the determination of the conductivity of the liquids unaffected by the coupling capacitances of the potential electrodes. Thus, small deviations that can creep in during manufacturing of the probe (manufacturing tolerances) do not affect the performance. An error analysis of the proposed system was carried out and the practicality of the scheme verified by developing and testing a prototype. The test results showed a worst-case error of 0.82% in conductivity measurements. The facts that the proposed method is unaffected by the coupling capacitors and the presence of materials kept outside of the probe were also verified. [ABSTRACT FROM AUTHOR]

Gate electrode inductance is a key factor for the controllable current capacity of unity-gain turn-off devices. However, the precise and credible measurement of this nH-level inductance is very difficult due to the compact structure of housing package. In this article, a precise measurement methodology of nH-level gate electrode inductance based on calculation-error-free algorithm for unity-gain turn-off devices is proposed. First, the turn-off process was modeled and discussed. Based on the feature of different stages, a customized extraction method is proposed for nH-level inductance measurement with ultrahigh accuracy. Then, a gate current measurement method for separate cathode rings with minimum inductance introduction was invented and discussed. After careful measurement and calculation, the gate electrode inductance for each region was derived and the abrupt change in gate contact region was observed and analyzed. The inductances measured in this article can be further utilized for housing structure optimization and lateral arrangement of segments on unity-gain turn-off chips. [ABSTRACT FROM AUTHOR]

Insulated gate bipolar transistor (IGBT) collector current measurement based on the package parasitics between the power emitter (E) and the Kelvin emitter (E′) is a lossless and real-time monitoring method. A step to improve accuracy is to precisely match the time constant (Rf × Cf) of the measurement circuit against the package parasitics (LEE′/REE′). This article proposes an automated time constant matching method to realize the tuning of Rf × Cf to LEE′/REE′, and a detection circuit to continuously measure the IGBT collector current using the package parasitics. In the proposed method, the Miller plateau voltage is first sampled, and a polynomial curve fit is carried out to determine the fitting parameters associated with the IGBT collector current (IC). A programmable resistor Rf is then adjusted automatically based on the step response of the readout voltage until the time constant is matched. A ratio between the readout voltage and a known IC is then calculated based on the Miller plateau voltage. The proposed system is verified using a field-programmable gate array controller and discrete components. Experimental results confirmed the functionality of the proposed method, showing that the readout voltage versus IC relationship has good agreement in the range of 0–165 A, with less than 3% error. The proposed method can also be used for overcurrent protection with a detection time of less than 0.7 μs. [ABSTRACT FROM AUTHOR]