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This paper proposes an analytical model for the prediction of air gap magnetic field distribution for axial flux permanent magnet (AFPM) machine with various types of misalignments. The AFPM machine geometry is first transformed to a polar representation. Consequently, the subdomain model based on current sheet technique is developed. Then the stator coordinate system is chosen as reference coordinate to consider both static/dynamic angular and axis misalignments. The back electromagnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the proposed approach agrees with the finite-element method. The model is further validated by experiments under healthy, dynamic angular and axis misalignment conditions, which can validate the proposed approach. It turns out that the proposed approach can predict the performance of AFPM machines with types of misalignment quickly and effectively, which is greatly significant for further fault detection. [ABSTRACT FROM AUTHOR]

Battery safety is one of the most crucial issues in the utilization of lithium-ion batteries (LiBs) for all-climate electric vehicles. Short circuit, overcharge, and overheat are three common field failures of LiBs. In this paper, online fault diagnosis for external short circuit (ESC) of LiB packs is investigated. The experiments are carried out to obtain and compare ESC characteristics of 18650-type NMC battery pack and single cell. Based on the analysis of experimental results, a two-step equivalent circuit model is established to describe the ESC process and an online model-based scheme is proposed to diagnose ESC faults of battery packs. The proposed scheme is evaluated by experimental data. The results show that it can effectively diagnose ESC faults in 3.5 s after their occurrences with the terminal voltage error less than 25 mV. The proposed scheme has shown great generalization ability. ESC faults of battery packs under different number of cells connected in series and unavailable current information can also be diagnosed at the terminal voltage error less than 48 and 60 mV, respectively. [ABSTRACT FROM AUTHOR]

In order to improve the pulp quality and to reduce the energy consumption, the fiber length distribution (FLD) is generally employed as one of the important technological indexes in the refining process. Considering that the traditional mean and variance of fiber length are unable to adequately characterize the non-Gaussian distribution properties, this paper proposes a novel geometric analysis based double closed-loop iterative learning control (ILC) method for probability density function (PDF) shaping of output FLD in the refining process. Primarily, a radial basis function (RBF) neural network with Gaussian-type is utilized to approximate the square root PDF in the inner loop, where the RBF basis function parameters (center and width) are tuned between any two adjacent batches by using an ILC law, and the subspace identification method can be applied to establish the state-space model of weight vector. Then, for the sake of accelerating the convergence rate of the closed-loop system, a geometric analysis based ILC method is adopted in the outer loop. Finally, both simulation and experiments demonstrate the effectiveness and practicability of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, the procedure for designing a sliding-mode controller for maximum power point tracking photovoltaic (PV) applications is proposed. It is applied to a single-ended primary inductor converter, thus to a fourth-order topology, but it can be extended to a wide class of converters suitable for PV applications. The reachability and existence conditions give rise to a number of design inequalities that add to the classical steady-state conditions in order to have the desired closed-loop converter's performances. The superiority of the control technique over the classical tracking methods is analytically demonstrated through the procedure proposed in this paper. The analytical results have been validated by means of both simulations and experiments. [ABSTRACT FROM PUBLISHER]

In most multiobjective optimization problems of electrical machines, the weighted function method is used to convert them into single-objective optimization problems. This paper applies a kind of new multiobjective evolutionary algorithms (MOEAs), called adaptive multiobjective black hole (AMOBH) algorithms, to achieve effective multiobjective optimization of a tubular coreless linear permanent magnet synchronous motor (LPMSM). To reduce the computation cost of the MOEAs, a one-layer analytical model (AM) is presented for the tubular coreless LPMSM in this paper. The accuracy of the simplified one-layer AM is verified by comparisons with multilayer AM and finite element analysis (FEA) under different structure parameters. It is found that the simplified AM has good accuracy and can decrease the computation cost significantly. AMOBH algorithm is subsequently introduced. The optimal Pareto front with regard to thrust, copper loss, and permanent magnet volume are analyzed, and more diversified optimization results are provided. The final Pareto solution can be selected directly by practical physical values according to the application requirements. Finally, a prototype is fabricated for the selected design; its experimental results are provided and compared with those of the FEA results. [ABSTRACT FROM AUTHOR]

The key function of rotating machine condition monitoring (CM) is to detect structural changes during machine operations. This paper presents a novel statistical time-frequency analysis method for this purpose. In particular, frequency spectrum is extracted from the machine condition signals based on periodogram estimation. Undirected weighted graph is then constructed from the resulting periodograms, where the so-called median graph is introduced and adopted to describe the normal machine status. Statistical analysis is performed to investigate newly observed data with respect to the median graph for change decision making. The proposed method has been applied to three different engineering applications to evaluate its effectiveness: load CM; early bearing failure detection; and speed CM. The results were compared with some benchmark methods reported in the literature, where significant improvements of the proposed method were demonstrated, indicating its good potentials in engineering applications. [ABSTRACT FROM AUTHOR]

A novel analysis for a new type of variable reluctance resolvers (VR-Resolvers) with toroidal windings based on the magnetic equivalent circuit (MEC) method is presented in this work. Different cases including various windings configurations as well as different rotor structures are considered in order to investigate the performance of the resolver precisely. The position error of both healthy and eccentric resolvers are studied by a flexible MEC model. The effect of the eccentricity fault on the resolvers with different specifications is also evaluated to analyze the manufacturing tolerance due to the eccentric rotor for several cases. It is notable that the presented MEC provides the opportunity to adjust accuracy and model several structures in both healthy and faulty conditions by just a single model. Finally, the MEC results are confirmed by finite element method and experimental results to show the effectiveness of the proposed model. In general, development of a new VR-Resolver and analyzing its performance under different windings configurations and rotor structures by proposing a modified MEC approach are the paper novelties. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for the prediction of airgap magnetic field distribution for axial flux permanent magnet (AFPM) machine with partial magnet demagnetization. The AFPM machine geometry is first converted to a polar representation. Consequently, the subdomain model based on current sheet technique is developed. Then current sheet representation of PM is derived to consider the partial demagnetization using superposition principle. The back electromagnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the results of proposed approach agrees with that of finite-element method. The model is further validated by experiments under both healthy and demagnetized conditions, which can validate the proposed approach. Main contribution of the work is to consider the partial irreversible demagnetization. Moreover, the proposed method is applicable for both AFPM and radial flux permanent magnet machine. [ABSTRACT FROM AUTHOR]

In this paper, the thermal analysis of a hybrid excitation linear eddy current brake is presented. The air gap flux of the hybrid excitation linear eddy current brake is provided by the excitation windings and the permanent magnets. Therefore, the braking force produced by the eddy current brake is large and controllable. But, on the other hand, there is a high heating value in the excitation windings and conductor plate; hence, it is necessary to analyze thermal characteristics of the eddy current brake to avoid the declination of braking performance or even damage of the device. First, the structure and working principle of the eddy current brake are described. Second, the analytical model of the eddy current brake is built, and then the thermal network model of the eddy current brake is built taking the actual airflow around the eddy current brake into consideration. Finally, the validity of the thermal network model is verified by steady and dynamic thermal experimental measurements. [ABSTRACT FROM AUTHOR]

Microgrids (MGs) are often unbalanced due to the integration of single-phase generators, unbalanced loads, and asymmetrical faults. To better analyze such MGs, this paper presents an approach to analyze the transient response for an inverter-based MG under the unbalanced condition. The dynamic phasor (DP) concept is used for the MG modeling under the stationaryabcreference frame. First, the DP model of the inverter-based distributed generation (DG) is developed. The influence of unbalanced conditions on the inverter including oscillations on the dc side is considered in this paper. Then, the model of the network and loads is developed. Finally, all the submodules are combined on a time-variable system frequency to obtain the complete DP model of the unbalanced MG. To validate the proposed approach, the DP method is applied to an MG test system with three-phase and single-phase DGs. Small-signal analysis is carried out to derive the dominant modes and their influence on the system response. Simulation results from the DP model are compared against the detailed model built in MATLAB/SimPowerSystem. The results from load disturbances and asymmetrical faults are used to verify the DP model. [ABSTRACT FROM AUTHOR]

The paper deals with some new results on the averaging theory approach for the analysis of feedback controlled pulsewidth modulation power electronic converters. It develops some considerations regarding the averaging approximation of time-variant differential systems proving an analytical relationship between the accuracy with which the solution of the averaged model converges to the solution of the original time-variant model (i.e., the switched model) and the switching frequency of the converters. This relation is valid both for stable and unstable systems. Moreover, this paper confirms, as corollary, that under suitable conditions (verified during the standard operations of the power electronic converters) the averaged model uniformly converges to the switched model. [ABSTRACT FROM AUTHOR]

Slotted axial-flux machines have excellent power and torque densities. However, it is difficult to reduce their cogging torque due to the complexity associated with implementing classical techniques. In this paper, slot-opening widths and tooth profiles will be shown to be significant in mitigating cogging torque in these machines. In particular, varying the slot opening reduced it by 52%, whereas a parallel-tooth (rectangular) profile lowered it by 24%, when compared with a conventional trapezoidal-tooth profile. An analytical quasi-3-D analysis was formulated and used to analyze and determine cogging torque. It was validated numerically and experimentally. Its versatility is in its ability to analyze different shapes of poles and slot openings, which can be extended to model air-gap nonuniformity. This paper also presents cogging torque minimization techniques that maintain the ease of manufacture of the parallel-tooth stator. Experimental results showed 73% and 48% reduction in cogging torque, which are achieved by the use of alternating pole arcs and skewed poles. [ABSTRACT FROM PUBLISHER]

The article discusses papers published within the issue including one on data-driven control for batch processes, and another on a derivative-free Kalman filtering method.

The quasi- $Z$ source (qZS) cascaded multilevel inverter (CMI) (qZS-CMI) presents attractive advantages in application to photovoltaic (PV) power system. Each PV panel connects to an H-bridge qZS inverter (qZSI) to form a power generation module. The distributed maximum power point tracking and all modules' dc-link peak voltage balance can be achieved. However, it is the same with the conventional CMI that the second-harmonic ( $2\omega$) voltage and current ripples exist in each qZSI module. It is crucial for a qZS-CMI to design the reasonable qZS network parameters to limit the ripples within a desired range. This paper proposes an analytic model to accurately calculate the $2\omega$ voltage and current ripples of each qZSI module. A qZS impedance design method based on the built model is proposed to limit the $2\omega$ ripples of dc-link voltage and inductor current. Simulated and experimental results through using the designed 1.5-kW prototype validate the proposed analytic model and the design method. Furthermore, this paper analyzes all of the operating states for a qZSI module and calculates the power loss. The measured efficiency from the prototype verifies the theoretical calculation, and the qZS-CMI-based grid-tie PV power system is tested in practical. [ABSTRACT FROM PUBLISHER]

In this paper, an ambient power harvester with a single-diode device is proposed for simultaneously scavenging both radiofrequency (RF) and thermal energy in a mixed and cooperative manner. This cooperative harvesting process is theoretically examined through a proposed model of the diode and then validated by simulation and measurement. In the proposed cooperative power harvester, the harvested dc voltage from a thermal source is used to bias the diode for improving the diode's RF-to-dc power conversion efficiency (PCE). An accurate analytical model of the Schottky diode is developed for specifying the constraining parameters of RF-to-dc PCE and accurately predicting diode's performances in a low RF power range $({ \leq - \text{25}\;{\text{dBm}}})$ , respectively. The calculated results are found to be in a good agreement with the simulated ones obtained by the harmonic balance simulator in the advanced design system. For demonstration and validation, the proposed mixed cooperative power harvester is designed and prototyped on the basis of diode SMS7630. A total measured output dc power around 0.8 μW is obtained with an RF-to-dc PCE around 33.4%, when the two injecting power sources at the diode are both −30 dBm. In addition, rectennas with and without a matching network are both fabricated and tested. By eliminating the L matching network, the rectenna is found to offer a higher dc output power. The proposed mixed cooperative power harvester is hoped to find potential real-world applications in an ambient atmosphere with RF coverage and temperature gradient. It not only helps to produce a higher power but also provides a reliable way of improving the resilience of dc power production. [ABSTRACT FROM AUTHOR]

This paper presents an analytical prediction and a multiconstrained nonlinear optimization of slotted permanent magnet linear synchronous motors (PMLSMs). Preferentially, an analytical model is developed for the fast and accurate design of slotted PMLSMs. In the process, two key techniques are used for the performance prediction: first, the Schwarz–Christoffel conformal mapping is used to take into account the slotting effects, and as a result, the normal and transverse components of the flux density produced by permanent magnets (PMs) and three-phase current can be calculated; and second, the two-dimensional end effects due to the finite length of moving parts are roughly reflected by the half-side leakage analysis, thereby predicting the second-order harmonic of the force/thrust pulsation. Subsequently, a systematic approach to the design optimization based on an iterative scheme is presented to search for solution set that belongs to the Pareto front. With no need for finite-element analysis or multivariable equation set, the proposed model can save much computational time to reach an optimal solution. The validity of analytical results is confirmed by finite element and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, from a new perspective of flux and charge, we present in-depth analyses of two ideal memristor emulators and the fifth-order memristive Chua's circuit constructed based on them. The constitutive flux–charge relations of the two adopted memristor emulators are first formulated, and their initial-dependent characteristics are numerically revealed and experimentally verified. Thereafter, with these two constitutive relations, a third-order dimensionality decreasing flux–charge model for the fifth-order memristive Chua's circuit is constructed, in which five extra constant system parameters are introduced to indicate the initial states of the five dynamic elements. Numerical simulations confirm that this newly constructed model possesses several determined equilibria and maintains the initial-dependent dynamics of the original voltage–current model. Thus, the complex and sensitive initial state-related extreme multistability phenomenon can be deeply explored through theoretical analyses and hardware measurements. It is demonstrated that the sensitive extreme multistability phenomenon becomes detectable in the flux–charge domain, which is efficient for exploring the inner mechanisms and further seeking possible applications of this special phenomenon. [ABSTRACT FROM AUTHOR]

The uniform magnetic field coil can be placed in the magnetic shielding room (MSR) to provide a more accurate magnetic source. The coil could generate a uniform magnetic field by the conventional design method, but when placed in the MSR, the uniformity of the field would be affected. The magnetic field analysis model of coil based on cuboid ferromagnetic boundary condition is constructed by the image method. This paper proposes a new design method of coil parameters based on the deviation of magnetic field distribution in volumes boundary. The coil system in the shield designed by the new method is compared with the conventional coil system, which not only solves the problem of uniformity reducing, but also further improves the uniformity of the magnetic field. The influence of the ratio kt of coil side length to MSR side length on coil parameters is found. The correspondence between the coil parameters and the kt can be used to guide the design of the coil system under the future ferromagnetic boundary conditions. The validity and significance of the analytical model as well as the new design method are proved by the results of finite-element software and experiments. [ABSTRACT FROM AUTHOR]

The long and enduring history of utilization of the wound-field synchronous generator in a large number of applications makes it one of the most known and consolidated electrical machine technologies. Thus, its design, modeling, and analysis processes have been widely exploited and implemented through various and different methods, including the equivalent circuit approach. When a damper cage is embedded within the rotor of the synchronous generator, its theoretical analysis becomes quite complicated. Thus, today numerical tools are being used. In this paper, an alternative way of modeling symmetric damper cages of salient-pole synchronous generators is presented. The proposed approach is embedded in the circuital model of the generator. A hybrid analytical–numerical model is implemented, permitting to accurately predict the voltage waveforms of the generator with excellent accuracy, however, at a lower cost of computational resources than the pure numerical method. A case study of an off-the-shelf 400 kVA machine is considered to develop and validate the proposed technique. The results are compared with the corresponding finite-element and experimental evaluations for validation purposes. [ABSTRACT FROM AUTHOR]

An introduction to various articles published within the issue is presented including the design of a sports car's direct-driven interior permanent-magnet synchronous motors (IPMSMs), a claw-pole double-rotor synchronous machine and the electromagnetic sizing procedure for an electrical machine.

Reliability is extremely important for control systems of energy distribution and generation. The IEC 61850 standard specifies an open architecture and communication protocols for such applications. The standard defines an open control architecture for networked control systems composed by intelligent electronic devices, stating some requirements that must be accomplished when developing reliable controllers for such systems. In this paper, we present a systematic and formal methodology to be adopted to achieve the correct implementation of the communication requirements of this standard. The methodology consists in five steps: modeling of real-time communication requirements defined by the standard; simulation of the obtained model; formal verification of the model, improved in the previous step; translation of the global model (simulated and verified) into the input language of the real controller; and finally, application of conformance testing technique to the computational routine implemented in the real controller. Presented research deals with the proposition of a strategy to synthesize and validate models of systems developed under IEC61850 real-time requirements (GOOSE and SMV) through simple operational conditions cases that, once validated, can be used in performance and conformance testing of more complex systems. The proposed methodology allows designers to synthesize reliable systems under IEC61850 real-time communication requirements. [ABSTRACT FROM AUTHOR]

This paper analyzes and simulates wind shear and tower shadow effects in doubly-fed induction generators, which are known to induce a low-frequency oscillation. Such oscillation is called a 3p oscillation, which can cause shaft torsion load aggravation and shaft torque oscillation, it inevitably lead to electromagnetic torque and power fluctuation in the generator and further affect the whole wind power system. By analyzing a two-mass model, it can be known that a flexible drive train has a low-damping characteristic and an amplification of the input of low-frequency wind torque disturbances. Based on this point, this paper presents a new control scheme to restrain 3p oscillation is presented, which is a damping torque observation. A novel torque observer is designed to ascertain the required damping torque. A small-signal model is established for the system and used to analyze the system's static and dynamic characteristics. The effectiveness of the proposed strategy is finally verified by simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents an improved analytical method for predicting the magnetic field and forces in linear permanent-magnet synchronous machines (LPMSMs) accounting for both the primary end effect and secondary end effect. So far, the magnetic field calculation of LPMSM in most studies is conducted in Cartesian coordinate, whereas the end effect is neglected by applying periodic boundary. In this paper, to implement the analytical model, a polar presentation of the machine geometry is proposed and the subdomain method is applied to calculate the magnetic field. Then, according to the developed model, the tangential thrust and normal forces are calculated based on the Maxwell stress theory. Numerical results are subsequently obtained by finite-element method and employed to validate the analytical model. Finally, an LPMSM prototype is manufactured and experiments are conducted. The results show that the developed analytical model has high accuracy for predicting the magnetic field and forces. [ABSTRACT FROM AUTHOR]

A quasi-three-dimensional (3-D) analytic method is presented for calculating the performance of single-sided linear induction motor with the ladder secondary. To simplify the analytic model, the ladder aluminum plate is equivalent to the flat-solid one, and the equivalent conductivity is derived and given. In the direction of the motion, the finite primary length and end effect are considered by the method of the Fourier transform and Residue theorem. In the transverse direction, considering finite width of the primary core and the region between the overhang of the primary windings and the secondary, the equivalent integral length is given. Finally, the thrust, vertical force and secondary efficiency are calculated and compared with the results of the 3-D finite-element method and experiment, it is shown that the method presented in the paper is much simpler and the accuracy of the analytic method is verified. [ABSTRACT FROM AUTHOR]

The magnetic resonant wireless power transfer (WPT) system with a class E inverter has wide application in mid-range power transmission, especially for several megahertz scenario. However, it is cumbersome for the existing modeling and analysis methods to obtain the analytical solution to the system variables, which limits the evaluation of system characteristic. This paper proposes a nonlinear mathematical model for the WPT system with a class E inverter. The equivalent small parameter method (ESPM) is first adopted to solve the proposed six-order nonlinear model, and symbolic-form steady-state periodic solutions are yielded. During the whole solving process, only three iteration steps are needed for the proposed method. Compared with other existing modeling and analysis methods, the symbolic periodic results acquired by the ESPM exhibit sufficient accuracy by virtue of the combination of more higher harmonics. Meanwhile, the calculation complexity is simplified remarkably. Simulation and available experiments validate the effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

The high penetration of renewable energy generation (REG) systems influences the dynamics of power systems. Accurate transient simulations and dynamic models are indispensable for the research on the dynamic behavior of REG systems. A large-scale REG system consisting of numerous grid-connected inverters consumes a large amount of computation time, so a dynamic aggregated model is needed for efficient simulation. The aggregated model established by coherent equivalence fits the detailed model well, and thus it is widely used in the aggregation of large-scale dynamic systems. Presently, the key challenge of the application of the coherent-equivalence method is to identify inverters that have similar dynamic characteristics. The Hamilton principle expressed by Hamilton's action has a simple form and indicates the comprehensive dynamic characteristics of inverters. Thus, this paper proposes a coherent-equivalence method of inverters based on Hamilton's action. The proposed method is applied to a wind farm of 16 permanent magnet synchronous generator-based wind turbines for demonstration. Compared with the existing equivalence method without considering coherency, the proposed method shows advantages in effectiveness and accuracy. [ABSTRACT FROM AUTHOR]

Estimation of critical control parameters is a desirable tool feature for stability analysis and impedance shaping of high voltage dc (HVdc) connected wind farms. Accurate estimation of such parameters would be enabled by access to detailed models, which is not always the case in real wind farms. Industrial secrecy is one of the main factors hindering the access to such models. This paper proposes a gray-box method that, with basic assumptions about the control structure of the wind energy conversion system (WECS), can estimate the parameters of its controllers. The method is based on the measurements of frequency domain equivalent impedance combined with nonparametric impedance identification used in the solution of an inverse problem. The method makes possible to specify which part of the equivalent WECS impedance has a major impact on the stability of the system and according to this, reshape the impedance to enforce stability. Once the critical controller bandwidth is identified with this method, an instability mitigation technique is proposed based on reshaping the impedance by retuning the critical controllers of the interconnected converters. In order to avoid interaction between the HVdc rectifier and the WECS inverter, the controllers of both converters need to be retuned in such a way that the q-axis impedance magnitude of the HVdc system is kept lower than the q-axis impedance magnitude of the wind farm at the frequency of the phase-locked loop bandwidth. The results show that the method ensures the stability of the system by retuning only the critical controller parameters. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is very attractive in a high-voltage dc (HVdc) transmission system due to its high modularity and scalability. It is also a promising candidate for medium-voltage applications. An MMC has many power devices that lead to a relatively low reliability based only on a direct failure rate calculation. The reliability of an MMC can be improved by redundant designs. Lots of redundant designs and strategies have been proposed in recent years, while their reliability improvements are hardly quantified in existing literature. In practice, reliability improvement with constraint costs is a challenge. In view of these, this paper proposes a reliability and cost assessment scheme for MMC redundant designs and strategies. Reliability and cost are quantified for comparison purposes. A medium-voltage application is used to demonstrate the reliability and cost assessment scheme. The reliability analysis is based on a combinatorial model and the Poisson process model. The cost analysis focuses on capital cost and power loss cost. The proposed reliability and cost analysis scheme provides a guideline for MMC redundant design and redundant strategy selection. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for the small-signal modeling of the dc–dc LLC resonant converter aimed to supply high-power light-emitting diodes (LEDs). This small-signal modeling procedure is based on the extended describing function method, where for a reliable small-signal model of the LLC LED driver, the equivalent piece-wise linear circuit of the LED has to be considered under some conditions throughout the model development. Otherwise, the obtained model does not reflect the real dynamic behavior of the converter. Furthermore, a numerical analysis is presented showing the conditions where the proposed model better describes the real dynamic behavior of the converter in relation to the traditional approach where the LED is modeled by an equivalent resistance. From the obtained model, the feedback compensator is designed and implemented in order to track the average current reference and avoid output current ripple, consequently sidestepping output light modulation (flicker). Experimental results show the feasibility of the proposed small-signal model and the active ripple compensation through a dimmable digitally controlled LLC LED driver under closed-loop operation. [ABSTRACT FROM AUTHOR]

This paper presents a practical approach to model and analyze transient thermal effects in air-cooled electric traction motors. The developed thermal modeling method enables accurate estimation of temperature in motor critical parts including winding and bearing. Advantages of both numerical and analytical modeling methods are exploited with the aim of realizing accurate estimation of hot spot temperatures in traction motors while keeping the computation time within a reasonable range. Computational fluid dynamics simulations are carried out to model air flow in the motor in order to provide heat transfer boundary inputs to the developed combined finite-element (FE) and lumped parameter (LP) thermal models. The combination of the FE and LP models keeps the size of the model relatively small and enables running transient calculations reasonably fast. Also, the developed model provides the possibility to study the influence of stator and rotor duct blockages on the motor thermal performance, which is a common root of failure in traction applications during operation in dirty environments. The proposed thermal model is verified using experimental results on a traction motor equipped with temperature sensors at different running conditions and a good agreement between the estimated and measured temperatures is achieved. [ABSTRACT FROM AUTHOR]

The closed-loop distribution system has become a trend, owing to increasing demands of electric power reliability in high-tech parks or in metropolitan areas. Harmonic propagation caused by power-factor correction capacitors and system inductors may lead to significant harmonic amplification throughout a closed-loop distribution feeder. This paper proposes a novel equivalent model of a closed-loop distribution feeder that a closed-loop distribution feeder can be equivalent to a radial feeder. This paper analyzes the harmonic propagation in a closed-loop distribution feeder and proposes a long-feeder simulator-based active power filter (LFS-APF) to damp out the harmonic propagation, based on the novel equivalent model. The proposed LFS-APF is installed at the middle point of a closed-loop feeder. The LFS-APF has better capability of harmonic damping than the resistive APF (RAPF), especially in response to variation of both nonlinear loads and power-factor correction capacitors or even if the installation location has to deviate from the middle point. Both simulation and experiment results are provided to validate the correctness and effectiveness of the novel equivalent model and the proposed LFS-APF. [ABSTRACT FROM PUBLISHER]

Permanent-magnet synchronous machines (PMSMs) are well suited for high-speed (HS) applications due to their high efficiency, power density, and dynamic response capability. The heat extraction area decreases as the speed increases, making thermal effects more dominant at high speed. The temperature-dependent properties of permanent magnets necessitate high-detail thermal models. This paper presents a 2-D analytical model for a HS PMSM magnet. The diffusion equation is solved where three of the PM boundaries experience convection heat flow; as the case is in radial flux machines. The heat generated on the rotor surface due to eddy currents is also taken into account. The model is verified using numerical techniques and shows good correlation (within 1.5%). The model is also validated through experiments performed on a 4 kW, 30 000 r/min PMSM. [ABSTRACT FROM PUBLISHER]

A wireless power converter topology with a small size and a high conversion efficiency has an increasing demand on small-power applications. Some design techniques to transmit power by customized cores have been already developed. However, when transferring energy by wide-gap transformers employing small-sized commercialized cores, the power losses on the winding greatly increase as the frequency increases. Then, the efficiency of the contactless power system decreases significantly due to the conduction loss and reactive components in the resonant circuit. Even though series–parallel resonant converters are largely employed, which can provide an infinite shunt impedance regardless of the coupling coefficient, when a commercialized core is employed for loosely coupled contactless power transfer applications, the large leakage inductance of the transformer significantly influences the additional power dissipation on the transformer windings. In this paper, an operating principle on how the contactless transformer with commercialized core contributes to the low efficiency is discussed. Also, a new frequency-dependent $R$– $L$ ladder circuit model is introduced for the design-oriented analysis of wide-air-gap contactless power converters including the frequency-dependent losses of the transformer. A new design procedure with the proposed model is suitable for the contactless transformers employing commercialized cores. The proposed design approach is validated by 98.8-W hardware experiments. Finally, the simulation waveforms and the hardware results are compared to verify the accuracy of the frequency-dependent transformer model. [ABSTRACT FROM PUBLISHER]

In this paper, we report on the new design of an electric field sensor based on piezoelectric bending effect in a capacitive-sensing method. The bipolar electric field sensor with a range from −22 to 22 kV/cm concentrates on a bending structure to enlarge the piezoelectric effect and to control its bending orientation. It performs with a much higher sensitivity of 0.448 pF/(kV/cm) or 5.78%/(kV/cm) and has a better resolution of 7.0 V/cm at $E=0$. Factors influencing the capacitance response are also discussed, which might further optimize the sensitivity. Moreover, the analytical model and experimental results make an agreement on the reasonability of this electric field sensor, gaining an insightful guide to the potential capacitive-sensing electric field chip sensor widely distributed in sensor networks. [ABSTRACT FROM PUBLISHER]

This paper presents a digitally master–slave controlled parallel system of multiple LLC resonant converters with an inner resonant current control loop in each module. Theoretical analysis of the stability of individual modules and the system with an inner resonant current loop is proposed based on the envelop model, which reveals the principle of the performance improvement brought by the resonant current control loop. Moreover, the inner resonant current loop eliminates the differences in small-signal characteristics among different static operating points, thus facilitating the voltage loop design. The analysis of parallel operation and a complete control loop design guide for paralleled LLC resonant converters is presented based on a small-signal model rather than on software simulation. Finally, the stability analysis and design are elaborated and verified through a 16-kW experimental system of four modularized LLC resonant converters. [ABSTRACT FROM PUBLISHER]

This paper presents a simplified analytical model based on one slot per pole for predicting the open-circuit AC winding loss of surface-mounted permanent-magnet machines accounting for the influence of tooth-tips but neglecting the redistribution effect of eddy currents. The comparison between the analytical models and finite-element results shows that the simplified analytical model has similar accuracy as the analytical model accounting for all slots together. The influence of various design parameters, such as conductor layout, slot width, slot opening width, tooth-tip height, magnet pole-arc to pole-pitch ratio, and gap between tooth-tips and conductors, on the open-circuit AC winding loss is investigated. It shows that the open-circuit AC winding loss gradually decreases with the number of radial conductor layers if the number of circumferential layers is larger than 1, although the radial segmentation is ineffective when there is no circumferential segmentation. The loss decreases greatly when the number of circumferential layers changes from 1 to 2, but reduces slowly when the conductors are further circumferentially segmented. [ABSTRACT FROM PUBLISHER]

In this paper, a novel analytical-based kinematic and dynamic modeling and control approach is developed for reference speed tracking of a multijoint robotic fish. The kinematic model is improved by the introduction of input signal for controlling body undulation amplitude without distorting the model structure. Next, the dynamic model is developed in the discrete-time domain primarily because fish swimming pattern generates oscillating continuous thrust where the effect of thrust over one cycle of undulation can be calculated through averaging. Hence, the dynamics can be discretized according to the undulation rate. The novelty in developing the discrete-time dynamical model is three fold. First, the thrust gradient is derived with assistance of Lighthill's large amplitude elongated body theory. More importantly, affine-in-control dynamical model form, essential for designing a real-time model-based control algorithm, is derived by inclusion of the updated kinematic model. Second, the thrust delay is studied via pulse input response of the motion system, and incorporated in the dynamical model. Third, drag force coefficient calculation is also proposed by comparing the thrust model and empirically recorded steady-state speeds of the robotic fish. Finally, discrete-time model-based sliding-mode control (SMC) is designed for speed tracking. Experimental results verify that SMC based on the proposed dynamical model, can significantly improve speed tracking performance of a multilink robotic fish. [ABSTRACT FROM PUBLISHER]

Vibration-based fault diagnosis of a planetary gearbox is challenging due to the revolving planet gears inducing modulation of vibration signals. For accurate fault diagnosis, researchers have suggested that vibration signals should be extracted by window function when the planet gears are positioned under the sensor. However, vibration modulation characteristics can be affected by operational and geometrical uncertainties. Thus, fault-related features can be inadvertently discarded when the window function is employed. Alternatively, periodicity analysis of anomalies can be employed with the entire vibration signal without the use of window function. However, it is challenging in a planetary gearbox because the fault-related features are also modulated. This paper proposes a health data map for toothwise fault identification in a planetary gearbox. In the proposed approach, samplewise health data are aligned in the domains of a pair of gear teeth of the planetary gearbox. The proposed approach represents the health state of every pair of gear teeth, while making it possible to isolate the location of any faulty teeth in the gears. For demonstration of the proposed method, two case studies are presented: an analytical model and a 2-kW testbed. The results suggest that the proposed method performs well even under unexpected vibration modulation characteristics. [ABSTRACT FROM PUBLISHER]

In this paper, the design and development of a novel interleaved tri-state boost converter (ITBC), which produces lower ripple and exhibits better dynamic response, is discussed. Boost converters are frequently connected in parallel and operate in an interleaving mode for the reduction of ripple content in source current and in output voltage. In this way, interleaved boost converter (IBC) is conceived, which improves the power handling capabilities and increases the overall system rating. It also has the advantage of reduction of the ripple content in source current and output voltage, but when control-to-output transfer function of IBC is derived under continuous conduction mode of operation, then a right-half-plane (RHP) zero appears in the transfer function. Due to the presence of RHP zero, IBC has nonminimum phase problem, which deteriorates the dynamic performance. The tri-state boost converter (TBC) is the best choice for RHP zero elimination, but due to the extra freewheeling mode, ripple content will also be increased. The proposed converter is a parallel combination of two TBC and operates in an interleaving mode. Therefore, the proposed converter has both of the advantages of TBC and IBC. The performance analyses of ITBC, TBC, and IBC have been studied based on simulation and experimental results. From the comparative analysis, it is observed that ITBC is performed better than other two converters. The ripple comparisons between three converters have also been done. It is found that the ripple content in ITBC is slightly greater than IBC but is less than TBC. [ABSTRACT FROM PUBLISHER]

A developing trend of traditional industrial systems is the integration of the cyber and physical domain to improve flexibility and the efficiency of supervision, management, and control. But, the deep integration of these industrial cyber-physical systems (ICPSs), increases the potential for security threats. Attack detection, which forms initial protective barrier, plays an important role in overall security protection. However, most traditional methods focused on cyber information and ignored any limitations that might arise from the characteristics of the physical domain. In this paper, an anomaly detection approach based on zone partition is designed for ICPSs. In detail, initially an automated zone partition method, ensuring crucial system states can be observed in more than one zone, is designed. Then, methods of building zone function model, which do not require any prior knowledge of the physical system are presented before analyzing the anomaly based on zone information. Finally, an experimental rig is constructed to verify the effectiveness of the proposed approach. The results demonstrate that the approach presents a high-accuracy solution, which also performs effectively in real time. [ABSTRACT FROM PUBLISHER]

This paper presents the implementation of a machine learning approach for replicating highly adaptive avian perching behavior. With full consideration of both the configuration of flying vehicles and perching principles, a bioinspired aerial robot comprising one flight subsystem and one perching subsystem is designed. Based on the real-time landing speed and attitude, a novel type of soft grasping mechanism for dexterous perching is proposed to provide adhesive force and absorb impact force. During the critical perching phase, the dynamics of the perching actuator change with the touchdown conditions and the type of perching target. A hybrid automation of a time-to-contact theory-based attitude controller and a robust self-localization system are utilized to regulate the desired perching maneuvers. The experimental results are provided to attest to the effectiveness of the proposed perching method. [ABSTRACT FROM PUBLISHER]

Adding the auxiliary switches to the conventional H-bridge inverter is an effective way to eliminate the leakage current for transformerless PV systems, such as H5, H6, etc. Inspired by the newly developed embedded-switch H6 topology, a novel embedded-switch inverter (ESI) is proposed in this paper for three-phase transformerless PV systems. First, the operation principle and characteristics of the proposed ESI are analyzed. Second, the common-mode model of the three-phase ESI is established, based on which the main factors that affect the leakage current are discussed. The finding reveals that the switching states with conventional modulation strategy result in high-frequency common-mode voltage, which is the source of leakage current. In order to solve the problem, a new modulation strategy is presented for ESI to eliminate the high-frequency leakage current. Finally, the time-domain simulation and the experimental tests are carried out. The results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper presents a method for small-signal dynamic studies of power systems including utility-scale PV energy systems considering the effects of dc-side components. Existing methods commonly model a PV energy system as a dc source connected to a grid-tied inverter. This paper shows that the dc components of a PV energy system can also contribute in the dynamics of the power system in the range of small-signal studies. The paper first develops the model of a PV energy system by merging the submodels of dc- and ac-side components. Then, a method to obtain the augmented model of the power system including a PV energy system will be explained using a study system. The study system consists of a PV energy system in parallel with a synchronous generator connected to a grid. Then, based on eigenvalue analysis, verified by time-domain simulations, it is shown that the dc-link capacitor, front-end converter, and its controller can introduce oscillatory modes in subsynchronous range of frequencies. Furthermore, it is shown that the damping of the sensitive modes can significantly vary with respect to the parameters of the dc-side components. [ABSTRACT FROM PUBLISHER]

This paper shows the feasibility of a novel decentralized control scheme for the grid-tied ac-stacked photovoltaic (PV) inverter architecture. The proposed decentralized control scheme with low-bandwidth communications requirements enables a fully distributed PV inverter architecture. Detailed modeling and theoretical analyses will be provided to support the existence of such decentralized control scheme. Simulation and experimental results on a representative laboratory-scale prototype will be presented under symmetrical and asymmetrical conditions as well as 10% grid voltage sag to show the effectiveness of the proposed control scheme in different operating conditions. [ABSTRACT FROM PUBLISHER]

In this paper, the design optimization of a nonsalient high-speed permanent magnet synchronous machine (PMSM) for electric vehicle applications is presented. It will be shown how, with a new approach, it is possible to find a deterministic solution to solve the sizing of the machine from a given driving cycle. The optimal geometry and the optimal control strategy over the cycle minimizing both the energy losses and the volume of the machine will be calculated. At first, the one-dimensional analytical model used is presented and validated for the most significant point of the driving cycle using a finite element method. Then, the design methodology and the results through a specific application are detailed. Particularly, it will be shown how the flux weakening, directly given by the design process via the optimization of the control strategy, allows reducing both the energy losses and the constraints on the power converter. At last, in order to validate the solution considering the whole cycle while keeping a reduced computation time, a reluctance network model of the PMSM is used. This model validate the energy losses and the flux densities in the steel parts over the cycle. The study will be done considering the urban dynamometer driving schedule. [ABSTRACT FROM AUTHOR]

This paper deals with an analysis of a middle-frequency resistance spot-welding (RSW) system with a dc welding current controlled by a pulsewidth modulated inverter, which supplies a welding transformer with a full-wave rectifier mounted at the secondary. Welding transformers in the automotive industry are usually mounted on the arm of a moving robot, so the weight is important. To achieve the same welding power with a large welding current, the transformer's weight can be reduced with a higher PWM switching frequency. This higher frequency allows a reduction in the transformer's iron-core cross section with shorter primary and secondary windings. Unfortunately, the leakage inductances prevent the RSW system from achieving the same nominal welding current at higher frequencies. The frequency-dependent maximum welding current is a characteristic behavior of the RSW system, which can be determined by sophisticated and time-consuming simulations or with the expensive measurements. The third option presented in this paper is determination of an analytical solution, which allows calculation of the maximum welding current as function of frequency or any parameter of the RSW system circuit model. The analytically calculated frequency-dependent function of the maximum welding current was completely confirmed by measurements on an industrial RSW system and by numerical simulations. [ABSTRACT FROM AUTHOR]

This paper presents hybrid automaton modeling, comparative model validation, and formal verification of stability through reachability analysis of pulse width modulation (PWM) dc–dc converters. Conformance degree provides a measure of closeness between the proposed hybrid automata models and experimental data. Nondeterminism due to variations in circuit parameters is modeled using interval matrices. In direct contrast to the unsound and computationally-intensive Monte Carlo simulation, reachability analysis is introduced to overapproximate the set of reachable states and ensure stable operation of PWM dc–dc converters. Using a 200 W experimental prototype of a buck converter, hybrid automata models of open-loop, and hysteresis-controlled converters are first validated against experimental data using their conformance degrees. Next, converter stability is formally verified through reachability analysis and informally validated using Monte Carlo simulations and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a novel parallel actuation dual-stage system that delivers nanometric positioning over a large displacement. Unlike those traditional dual-stage designs, the translator of fine actuator in the proposed design is mechanically connected to the coarse translator via the flexure mechanism, while the actuation coils of both the coarse and fine actuators lay underneath the translators in parallel. The merits of the proposed parallel actuation dual-stage design are mainly twofold. First, both the coarse and fine actuators utilize the moving-magnet configuration, hence the translators do not need to carry any cables for power supply. Second, the coarse motion can exhibit better dynamics and energy efficiency due to the minimized moving size and weight. In this work, an analytical current–force model is established for the coarse actuator considering higher order harmonic magnetic field, and based on the proposed model, the force ripple of coarse actuator is quantitatively analyzed both in theory and in practical. Furthermore, a disturbance observer is employed in the dual-feedback configuration to deal with the uncertainties with the proved asymptotic stability. The experimental results show that the proposed dual-stage positioning system is capable to achieve 20 nm step resolution with a root mean square error of 13.15 nm, and the 5 mm point-to-point positioning error can achieve less than 40 nm. [ABSTRACT FROM PUBLISHER]

Clock drift in digital controllers is of great relevance in many applications. Since almost all real clocks exhibit drifts, this applies in particular to networks composed of several individual units, each of which being operated with its individual clock. In the present paper, we demonstrate via extensive experiments on a microgrid in the megawatt range that clock drifts may impair frequency synchronization in low-inertia power systems. The experiments also show that—in the absence of a common clock—the standard model of an inverter as an ideal voltage source does not capture this phenomenon. As a consequence, we derive a suitably modified model of an inverter-interfaced unit that incorporates the phenomenon of clock drifts. By using the derived model, we investigate the effects of clock drifts on the performance of droop-controlled grid-forming inverters with regard to frequency synchronization and active power sharing. The modeling and analysis is validated via extensive experiments on a microgrid in the megawatt range. [ABSTRACT FROM PUBLISHER]

The penetration of wind power has been increasing in the past few decades all over the world. Under certain nonideal situations where the wind power generation system is connected to the weak grid, the doubly fed induction generator (DFIG)-based wind power generation system may suffer high-frequency resonance (HFR) due to the impedance interaction between the DFIG system and the weak grid network whose impedance is comparatively large. Thus, it is important to implement an active damping for the HFR in order to ensure a safe and reliable operation of both the DFIG system and the grid-connected converters/loads. This paper analyzes and explains first the HFR phenomenon between the DFIG system and a parallel compensated weak network (series RL + shunt C). Then, on the basis of the DFIG system impedance modeling, an active damping control strategy is introduced by inserting a virtual impedance (positive capacitor or negative inductor) into the stator branch through stator current feedforward control. The effectiveness of the DFIG system active damping control is verified by a 7.5 kW experimental downscaled DFIG system, and simulation results of a commercial 2 MW DFIG system is provided as well. [ABSTRACT FROM PUBLISHER]