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Corrections to “The Dielectric Strength of Nomex 410 Paper in Liquid Nitrogen under Boiling Situations” [ABSTRACT FROM AUTHOR]

In this paper, two methods Adomian Decomposition Method (ADM) and Laplace Adomian Decomposition Method (LADM) were adopted to solve the telegraph equation. The essence of this research is to establish a relationship between the two analytical methods. It was observed that the two methods were consistent as the results obtained from the numerical examples on the two methods were the same. We also generated the telegraph equation to help provide a solid basis for the application of the telegraph equation. The telegraph equation is one of the nonlinear partial differential equation and it’s application to solving practical problems were suggested for further studies. [ABSTRACT FROM AUTHOR]

Inductive wireless power transfer is a promising technology for powering smart wearable devices. The spiral coil shape is widely used in wireless power transfer applications. Nevertheless, during the coil design process, there are many challenges to overcome considering all the design constraints. The most important is to determine the optimal coil parameters (internal radius, external radius, spacing, wire width, and conductive wire) with the aim of obtaining the highest coil quality factor. Coil modeling is very important for the wireless power transfer system's efficiency. Indeed, it is challenging because it requires a high computational effort and has convergence problems. In this paper, we propose a new approach for the approximation of spiral coils through concentric circular turns to reduce the computational effort. The mathematical model determines the optimal coil parameters to obtain the highest coil quality factor. We have chosen the smart textile as an application. The system operates at a frequency of 100 Khz considering the Q i guidelines. To validate this approach, we compared the approximated circular coil model with the spiral coil model through a finite element method simulation using the COMSOL software. The obtained results show that the proposed approximation reduces the complexity of the coil design process and performs well compared to the model corresponding to the spiral shape, without significantly modifying the coil inductance. For a wire width smaller than 1 mm, the total deviation is around 4% in terms of the coil quality factor in a predetermined domain of its parameters. [ABSTRACT FROM AUTHOR]

Voltage source inverters (VSIs) with vector control based on phase-locked loop (PLL) suffer instability when connecting to a very weak AC grid (short circuit ratio (SCR) $ < $ 1.3). The conventional inductive grid impedance compensation for the PLL by virtually reducing the grid impedance can stabilize this connection. However, the analysis in this paper indicates that its stabilization effectiveness is sensitive to grid impedance variance and, indeed, overcompensation causes the PLL instability. Therefore, in this paper, an improved grid impedance compensation for the PLL is proposed to achieve the same stabilization for very-weak-grid connection and possess a good tolerance of grid impedance variance and overcompensation. A comprehensive small-signal model of the VSI using the proposed PLL’s grid impedance compensation is derived for stability analysis and parameter design. The time-domain simulation for this VSI is built to validate the stability analysis. Comparison studies for both proposed and conventional PLL’s grid impedance compensation are conducted including the stability effectiveness, VSI performance and grid impedance variance. [ABSTRACT FROM AUTHOR]

This paper proposes a systematic method for the identification of the load circuit parameters (say the $\boldsymbol{R}$ , $\boldsymbol{L}$ , and $\boldsymbol{C}$ elements) based only on the information of the instantaneous voltage and current measured at the point of common coupling (pcc). Geometric Algebra (GA) and concepts of differential geometry are used to produce a rigorous mathematical framework. The identification is formulated as a multidimensional geometrical problem that is solved conveniently by means of GA. Once the passive elements of the load have been identified, the active and reactive powers can be computed from first electromagnetic principles (Maxwell Equations). The theory is general and is verified with linear and nonlinear circuits. The paper shows single-phase circuits but the theory can be extended to three-phase circuits. The method is easy to program and has shown to be very robust for all tested cases. Because of its generality, the method presented will find applications beyond electric circuits. [ABSTRACT FROM AUTHOR]

The Potential Transformer (PT) plays an important role in the measurement and monitoring of the power system. The accurate modeling of the PT is very important but not yet perfect. The stray capacitance will have a non-negligible effect on the performance of a PT. However, the influence of stray capacitance is rarely considered in existing models, which makes the broadband simulation performance weak and provides limited references in engineering. In this paper, a calculation method of PT stray capacitance is proposed to analyze the performance of the PT at different frequencies and extract the capacitive current of the PT port. This paper used a non-destructive method to obtain the test data of a PT, calculated the value of the stray capacitance, and drew the hysteresis loops of the iron core. A corresponding simulation model was established to predict the PT performance at different frequencies. The simulation results are in good agreement with the experimental data, which proves the accuracy of the modeling parameters. The data processing logic is clear and is easy to be simplified by programming, which makes it promising in engineering. [ABSTRACT FROM AUTHOR]

This paper analyzes the unsymmetrical operation of the dc/dc MMC caused by parametric uncertainty. The unsymmetrical operation is referred to as the condition in which parameters involved in ac power generation are not equal in the phase-legs of the converter. Because existing models in the literature cannot exhibit the unsymmetrical operation of the dc/dc MMC, new detailed and simplified steady-state models are developed in this paper. In the developed models, the connection between the operation of different phase-legs shows itself when the dc-link impedance is considered. Using the developed models, the parameters that can force the converter to operate in unsymmetrical conditions are identified, and the maximum variation that the converter can tolerate is found. It is shown that even a small parameter variation leads to the leakage of the ac circulating current into the dc-link, which is not acceptable. By conducting various case studies, the impacts of the dc-link length, the transmitted power, and the conversion ratio on the unsymmetrical operation of the dc/dc MMC are characterized. The results showed that the converter would be more sensitive to the parameter variation as these parameters increase. Comparative analysis and simulation results confirm the validity and effectiveness of the presented models and analysis method. [ABSTRACT FROM AUTHOR]

In actual line-commutated converter based high- voltage direct-current (LCC-HVDC) projects, multiple HVDC transmission lines are usually installed on the same tower to save transmission corridors and reduce construction costs. However, electromagnetic coupling effect between adjacent lines can cause commutation failure (CF) in the non-fault poles when a line or pole fails. Hence, this paper deeply investigates the mechanism and the prevention strategy of CFs caused by line coupling effect in single- and double-circuit HVDC systems. The influencing factors of line coupling effect and the coupling characteristics under fault conditions are analyzed first based on the modeling of parallel transmission lines and the traveling wave theory. Then the mechanism of CF caused by line coupling effect is investigated with the consideration of different fault conditions, different line structures, and different system operation modes. Based on the above analyses, prevention strategies for CFs of non-fault poles in single- and double-circuit systems are proposed. Finally, the simulation results verify the correctness of the theoretical analyses and the effectiveness of the proposed control strategies. [ABSTRACT FROM AUTHOR]

This paper describes experimental verification of single-phase variable inductor prototypes rated at 2.4 kVAr (75 mH, 10 A, 230 V, 24 kg) and 12 kVAr (43 mH, 30 A, 400 V, 78 kg). Results for much smaller devices rated at 1-10 Var are also shown. The variability of inductance of the main AC winding was achieved by adding a DC winding, wound through the apertures placed symmetrically in the core such that both windings were magnetically orthogonal. Local saturation caused by the magnetic field due to DC winding creates virtual air gaps. This method is capable of lowering the main inductance by over 90% if no real air gap is present, but for industrial applications the range of variability is likely to be closer to 20-30% range, depending on the size of the real air gap in the magnetic circuit. The amount of variation/control can be improved by using more than one control winding. Very good repeatability of performance was observed, with relatively small total harmonic distortion introduced due to control. The experimental findings agree with a generalised analytical model. [ABSTRACT FROM AUTHOR]

Accurate knowledge of the natural frequencies and shapes of corresponding standing waves are essential for gaining deeper insight into the nature of response of coils to impulse excitations. Most of the previous analytical studies on coils assumed shape of standing waves as sinusoidal but numerical circuit analysis and measurements suggest otherwise. Hence, this paper revisits the classical standing wave phenomenon in coils to ascertain reasons for this discrepancy and thereafter extends it by analytically deriving the exact mode shape of standing waves for both neutral open/short conditions. For this, the coil is modeled as a distributed network of elemental inductances and capacitances while spatial variation of mutual inductance between turns is described by an exponential function. Initially, an elegant derivation of the governing partial differential equation for surge distribution is presented which is then analytically solved, perhaps for the first time, by the variable-separable method to find the complete solution (sum of time and spatial terms). Hyperbolic terms in spatial part of solution have always been neglected but are included here, thus, yielding the exact mode shapes. Voltage standing waves gotten from analytical solution are plotted and compared with simulation results on a 100-section ladder network. The same is measured on a large-sized single layer coil. So, it emerges that, even in single layer coils, shape of standing waves deviates considerably from being sinusoidal and this deviation depends on spatial variation of mutual inductance, capacitive coupling, and order of standing waves. [ABSTRACT FROM AUTHOR]

The dual-active bridge (DAB) topology is commonly preferred in bidirectional applications due to several attractive features, including auto-adjust of power flow, galvanic insulation, wide voltage gain, and zero voltage switching (ZVS) capability over some power ranges. However, the efficiency of the converter drops at light loads because the ZVS range is directly dependent on the circulating current. Assuming that the processed power is variable, the DAB converter's design must find a compromise between extending ZVS ranges and reducing the reactive power processing to ensure higher efficiency. Aiming this compromise, many papers propose hybrid approaches in which the modulation strategy is selected according to the processed power. However, this is not a simple solution because it demands multivariable control and offline optimizations. This paper proposes a modulation strategy to ensure ZVS and reduce the circulating current for the DAB converters. While the usual phase-shift modulation provides ZVS operation in a range of 40% to 100% of rated power, the proposed asymmetrical pulse-width modulation can obtain ZVS operation in a range of 2% to 100% of rated power. Experimental results demonstrated that the proposed strategy improves the converter efficiency for all power ranges, especially at light loads. [ABSTRACT FROM AUTHOR]

Flexible DC distribution networks have been widely developed because of their advantages of high efficiency, low cost, and easy access to renewable energy. However, as distribution networks have more ends than the two-terminal transmission line, it is more challenging to protect them and locate their faults. Therefore, this paper proposes a modified T-source circuit breaker to protect against DC faults. Based on the proposed circuit breaker, an integral fault location method using double-terminal asynchronous data is proposed. The accuracy of the algorithm is not affected by the fault resistance. There are no differential terms in the algorithm, which greatly reduces the sensitivity to noise. The integral algorithm can remain steady when the voltage and current are zero in oscillation and attenuation periods. This constitutes the main contribution of this paper. Finally, it is verified by simulation and experiment that the proposed circuit breaker can isolate the power source within a short time in the typical DC distribution network. Under a noise of 30 dB for simulation, the location error of the proposed algorithm is <0.4% when the fault resistance is 0.5 Ω–500 Ω. [ABSTRACT FROM AUTHOR]

Deadbeat predictive current control (DPCC) can predict motor behavior based on SPMSM model. However, during the operation of motor system, motor parameters (such as stator inductance and flux linkage) vary frequently according to different working conditions, which may lead to controller parameter mismatch, causing current harmonic content to increase and efficiency to decrease. In order to solve these problems caused by parameter variation, first, this paper proposes a current prediction error model by considering uncertainties of model parameters. Second, stator inductance and flux linkage are decoupled based on current prediction error model, which can reduce the interaction between parameters. Finally, the Kalman Filter (KF) algorithm is presented to filter the decoupled parameters. It is shown that the stator inductance and flux linkage can be identified accurately and the complexity of computation can be simplified. The traditional DPCC method, Extended Kalman Filter (EKF) based DPCC method and the proposed DPCC method are comparatively analyzed in this paper. Simulation and experiment indicate that the proposed parameter decoupling identification method can effectively reduce current harmonic content, current fluctuation and current tracking errors caused by parameter mismatch. [ABSTRACT FROM AUTHOR]

A variable reluctance electric machine with a two-degree of freedom rotor motion characterized by rotation around the center of the rotor and orbiting around the center of the stator is studied. One motivation for adopting such rotor motion would be to allow torque generation through both the radial and tangential components of the electromagnetic forces created in the airgap, as opposed to common rotary machines in which torque is a byproduct of only the tangential component of the airgap electromagnetic forces. Furthermore, the rotor motion provides a built-in gearing action similar to that of a cycloidal drive, which allows natural torque multiplication and the tight integration of the electromagnetic and mechanical systems. The two-degree of freedom rotor motion also results in a counter-intuitive inertia characteristic of this machine concept which is elaborated in this paper for the first time. Due to the reluctance nature of the torque, and because of the distinctive rotor motion profile which resembles the motion of a cycloid, the studied machine is called a cycloidal reluctance (CR) electric machine (CRM). In this paper, the principle of operation of the CRM is explained, and its performance is compared to a counterpart switched reluctance machine (SRM). A prototype is built, and the theoretical torque calculations are validated by experimental measurements. [ABSTRACT FROM AUTHOR]

The paper addresses an optimization-based reference calculation method for Modular Multilevel Converters (MMC) operating in normal and constrained situations (when the converter needs to prioritize its quantities as it has reached voltage or current limitations, e.g. during system faults). The optimization problem prioritizes to satisfy the external AC active and reactive current set-points demanded by the grid operator through the corresponding grid code. If the operator demands are fulfilled, it uses the available MMC degrees of freedom to minimize the arm inductance losses. Otherwise, if the operator demanded AC set-points cannot be accomplished, the optimization attempts to minimize the error prioritizing between either AC active or reactive currents. The optimization problem constraints are imposed through a steady-state model considering simultaneously the external and internal AC and DC magnitudes of the converter. The steady-state model also includes the voltage variation in the equivalent arm capacitors (considering the ripple). Then, the imposed limitations are the maximum allowed grid and arm currents, the maximum allowed arm voltages and the sub-module capacitor maximum voltages. The paper presents a detailed formulation of the optimization problem and applies it to several case studies where it is shown that the presented approach can be potentially used to obtain the MMC references both in normal and fault conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a model predictive current control (MPCC) method of six-phase permanent magnet synchronous hub motor (PMSHM) using auxiliary voltage vectors. First of all, 26 voltage vectors can be obtained from the switching states of six inverters, and 24 auxiliary voltage vectors can be generated by combining them. Second, four virtual voltage vectors can be found through the required locations, and the two vectors with the lowest cost will be selected by cost function. Then, additional current error correction module can better track the current. Finally, the proposed method is compared with the conventional MPCC method and another method with virtual voltage vectors. The innovation of this paper is that the recombination of vectors can better track and predict the current. A current error compensation module is added to reduce the error between the actual current and the predicted current. And the experimental results show that the proposed method has better performance such as smaller torque ripple and current THD both in steady and dynamic states. Finally, the strategy proposed in this paper was applied to the vehicle model through HIL test platform. The possibility of applying the strategy proposed in this paper to pure electric vehicles was verified under New European Driving Cycle (NEDC). [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel class of networks named as quaternion-valued inertial memristor-based neural networks (QVIMNNs) by introducing inertial term and memristor into traditional quaternion-valued neural networks (QVNNs). The problem of fixed-time synchronization of the QVIMNNs is investigated based on the variable transformation and Lyapunov functional method. It is shown that two types of activation functions are considered and a novel criteria guaranteeing fixed-time synchronization for each cases are then achieved by designing different types of controllers. This paper attempts to pave a new way to investigate neural networks classes with numerical simulations support to demonstrate the correctness of the obtained results. [ABSTRACT FROM AUTHOR]

A new hybrid analytical model (HAM) based on conformal mapping (CM) method and magnetic equivalent circuit (MEC) model is presented in this paper for electromagnetic modelling of cage rotor induction motors (CRIMs) used in electric submersible pumps (ESPs). For every operating point, the iron parts are modelled with a non‐linear MEC model to calculate the equivalent virtual currents, which represent the influence of magneto motive force (MMF) drops and MMF sources in stator and rotor cores. The effects of the equivalent virtual currents on the air‐gap magnetic field are then considered using the CM method and Hague's solution. This approach for calculating the air‐gap field is also used to prepare a 3‐D lookup table (3‐D LUT) for each element of inductance matrix and derivative of inductance matrix in terms of rotor position. These LUTs are then used for transient modelling and analysis of CRIM under no‐load and loading conditions. The accuracy of proposed HAM is validated by comparing the results obtained through HAM with corresponding results obtained from finite element method and experiment set‐up. [ABSTRACT FROM AUTHOR]

Leakage and magnetizing inductances of transformer windings are routinely measured by power utilities during scheduled maintenance. They are often used to confirm the diagnosis of mechanical damages in windings after Swept Frequency Response Analysis shows a mismatch. Inductance measurements performed at power frequency can possibly reveal the presence of damages that have substantially progressed but cannot detect them at their nascent stages since inductances at power frequency remain almost unaltered. This paper investigates the possibility of using high-frequency inductance to this end considering a frequently encountered mechanical damage, viz., disk-space variation in a disk winding. Effect of disk-space variation is investigated in this article using FEM at first and inductances at different frequencies are considered: magnetizing and leakage inductances at 50 Hz, and inductance at a higher frequency region corresponding to winding resonances, say, 500 kHz. The inductance at high frequencies not only exhibited increased sensitivity compared to that at power frequency, but also captured the extent of damage. Simulations performed using Ansys Maxwell and experimental results on an actual 1- $\phi$ transformer are reported. Results show that the high-frequency inductance not only offers a considerably increased sensitivity to disk-space variation in windings compared to the power frequency inductances, but also provides insight regarding the extent of movement which is not apparent from the frequency response. [ABSTRACT FROM AUTHOR]

To calibrate non-contact sensors with fast response and high scale factor, it is critical to develop step pulse generators capable of generating standard high voltage step pulses and accurately measuring the generated waveform. In this paper, two types of step pulse generators are designed with output voltages of 2 kV and 100 kV. The 2 kV step pulse generator can generate a step pulse with a rise time of ∼300 ps and an adjustable pulse width. A step pulse with a rise time less than 5 ns and a pulse width over 1 μs can be generated with the 100 kV step pulse generator. The uncertainty of 2 kV step pulse generator is then analyzed by simulations and experiments. Finally, a performance comparison with step pulse generators in previous studies is carried out. Bandwidth, linearity and repeatability of the sensors can be verified with the designed two step pulse generators. [ABSTRACT FROM AUTHOR]

The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T/s without quench. Quench detection by voltage measurements is likely to be the fastest available technical solution to avoid coil's damage caused by quench, but the voltage detection is a real challenge due to large noise induced by the power supply in alternating current operation. The pick-up sensors, comprising the co-wound wire (CWW) and the co-wound tape (CWT), are used in the CSMC quench detection system for noise compensation and suppression. To accurately compensate all related induced voltage in the multi-pulse coil system, the foremost task is to estimate the static inductance matrix between the CSMC and its pick-up sensors. In this paper, a numerical model is developed for inductance calculation and analysis. Moreover, several numerical simulations with this design model to evaluate the maximum inductive noises and quench detection signals by CWW and CWT have been conducted for the case of the worst test scenarios. [ABSTRACT FROM AUTHOR]

Skin and proximity effects can cause a non-uniform current distribution in the electrical conductors used in alternating current (ac) busbar systems, which increases resistance, decreases internal inductance, and causes asymmetries in the electromagnetic fields and forces. As no explicit solution for the ac resistance or the ac internal inductance of a rectangular conductor has been found, numerical methods are needed to obtain the distribution of the currents inside the busbars. In this paper, a novel numerical approach, based on the fast Fourier transform (FFT) and the convolution theorem, is proposed to model the rectangular conductors of the busbar system, based on the subdivision of the conductor in filamentary subconductors. This technique is know to lead to a dense, huge inductance matrix, that must be multiplied by the current vector, which limits its practical application. The proposed method replaces this matrix-vector multiplication with a simple element-wise vector product in the spatial frequency domain. The FFT speed makes the proposed method very fast and easy to apply. This approach is theoretically explained and applied to an industrial busbar system. [ABSTRACT FROM AUTHOR]

Traditional single-ended fault location method is influenced by the fault resistance, and the remote in feed, which reflects as the two equations built by fault phase have four unknowns. And in the grid-connected converter system, the weak feedback characteristic further reduces the performance of the method. To solve it, a single-ended fault location method based on control and protection coordination is proposed in this paper. First, using the high controlled-ability of the converter, the control strategy for fault ride-through (FRT) operation is divided into two stages by switching control modes. Then, according to the electrical quantities under two stages, four uncorrelated equations can be established, and the equations still have four unknown parameters. The fault distance can be calculated by solving them. The simulation results show that the proposed method has high accuracy and is immune to fault resistance and fault location, it solves the problem of insufficient equations in principle. [ABSTRACT FROM AUTHOR]

Solid-state transformers (SST) are emerging technologies to replace the conventional low-frequency main transformer (MTR) in railway vehicles. In order to isolate the load side from the AC 25 kV high-voltage (HV) side and to reduce the whole size of the SST, HV insulation and high-frequency transformers should be used in DC/DC converters. Furthermore, due to the severe constraint of installation space and difficulty of heat dissipation management in the bottom of railway vehicles, high-power density and minimum transformer loss should be considered. To satisfy such design requirements of the proposed SST for railway vehicles, high efficiency integrated transformers, which inherently have leakage inductance, are proposed for dual-active-bridge (DAB) converters in this paper. In order to obtain appropriate equivalent leakage inductance for the DAB converters, a calculation methodology for the leakage inductance has been introduced and verified by simulation. Two separated winding structures in the center-core are adopted to improve the core loss, and appropriate winding turns with 60 kV HV insulation capability are selected, according to the proposed design procedure of the integrated transformers. In order to compare the proposed transformers with the conventional transformer having additional inductors and to verify the major characteristics of the transformers, two 125 kW proposed transformers and conventional transformers have been built and evaluated by an 250 kW SST module, operating at 10 kHz switching frequency. Under a 125 kW full-load condition, 99.7% transformer efficiency was obtained by the proposed integrated transformers, which are 4.7% smaller and 7.0% lighter than the conventional transformer. As a result, 26°C maximum temperature improvement has been obtained and 60k V HV insulation capability has been satisfied by the proposed integrated transformers. [ABSTRACT FROM AUTHOR]

With the increase in number of VSC based HVDC systems, it is inevitable that there would be interconnections with weak ac grids. The paper presents the analytical basis for identifying coupling in the power loops which is dependent on grid inductance and operating point by utilizing the impedance based modeling technique. The formulation is used to define an inverse-based decoupling outer-loop controller for VSC-HVDC system. The concept is extended to HVDC grids and it is shown that the gains obtained using simple inverse may lead to instability. Robust controller tuning with pole-placement and minimization of $H_\infty$ norm is presented for HVDC grids, which form a restricted feedback system. The results show that the proposed method of decoupling results in effective decoupling of the power loops over a large range of grid inductance values as compared to that with traditional vector control. The system stability is also maintained over a large range of grid inductance values and PLL gains when a sudden variation of parameters is considered. The stability margins can be enhanced by pole-placement. The observations from the small-signal models are confirmed using detailed time-domain simulations. The proposal is expected to be useful in controller design for single VSC as well as HVDC grids, especially, during planing stage. [ABSTRACT FROM AUTHOR]

Due to the scalability and flexibility of various modular power electronic converters, integrating split energy storage components (such as batteries and supercapacitors) is feasible and attractive. This paper investigates the operational and economic characteristics of different ac/dc fault-resilient schemes using energy storage integrated modular converters in ac-dc conversion applications. Based on the topological features between the energy storage system (ESS) and the ac and/or dc system, four energy storage based modular converter deployment schemes are presented. Through a case study, operational performance including fault isolation and power compensation under extreme ac/dc fault conditions are verified using time-domain simulation. System losses are evaluated, whereas detailed design considerations, major component usage and estimated capital costs are articulated. The four schemes are compared and selection guidelines are presented. In general, the schemes with independent ESSs would be preferable for such ac-dc conversion applications due to their high operational flexibility. [ABSTRACT FROM AUTHOR]

In this paper, a new pilot protection scheme for AC line connected to LCC-HVDC inverter based on composite-mode model is proposed. First, taking commutation failure into consideration, 1-mode and 2-mode equivalent instantaneous models of inverter in different operating conditions are built. Second, according to the equivalent instantaneous inductances of inverter in different combinations of operating conditions, the equivalent models of inverter are summarized into 4 operation states. Then, the 1-mode and 2-mode equivalent models are combined to establish the composite-mode model of AC/DC hybrid system. And then, using multi-time section information, the instantaneous inductances of backside composite-mode model are calculated. Thus, protection criterion is constructed on the difference between composite-mode models of in-zone faults and that of out-of-zone faults for fault locating. Finally, RT-LAB simulation tests show that, the proposed method offers high sensitivity and reliability, unaffected by commutation failure. [ABSTRACT FROM AUTHOR]

Asymmetric interior permanent magnet (AIPM) rotor topologies can achieve torque enhancement in IPM synchronous machines without the increase of PM usage due to utilizing magnetic-field-shifting (MFS) effect by reducing the current angle difference between maximum PM and reluctance torque components. This paper investigates the influence of armature reaction on MFS effect in AIPM machines. A general model of IPM machines considering MFS effect is analytically developed and the AIPM and IPM machines using the same stator, rotor diameter and total PM amount are comparatively studied. It shows that the armature reaction affects the MFS effect in both AIPM and IPM machines and the influence is more significant in AIPM machine. The relationships between MFS effects in PM flux-linkage and inductance characteristics and current angles for maximum PM and reluctance torque components are revealed. It confirms that the change of current angles of torque components is due to the MFS effect in PM flux-linkage and inductance characteristics in both AIPM and IPM machines. Besides, the developed machine model considering MFS effect is verified by finite element analysis. Finally, a small-scale AIPM machine prototype is fabricated and measured to validate the finite element analysis. [ABSTRACT FROM AUTHOR]

Dual three-phase permanent magnet synchronous motors (DTP-PMSMs) feature a satisfactory capability of the fault-tolerant operation due to the inherent multiphase configuration. To improve the control performance of the DTP-PMSMs under the open-phase fault, accurate inductances are critical. This paper presents an extended Kalman Filter (EKF) based inductance estimation strategy for DTP-PMSMs with one phase opened. Firstly, the multi-synchronous-rotating frame (MSRF) based DTP-PMSMs modeling under the single open-phase fault is presented. Secondly, the system space-state model and proposed EKF based estimation algorithm considering inverter nonlinearity are presented. Finally, the inductance estimation is performed by experiments under both steady and transient states. The estimation results have been verified by torque measurements which confirm the validity of the proposed method. [ABSTRACT FROM AUTHOR]

The Roebel bar conventional design of large AC machines uses the classical strand-slot inductance model (CSSIM). Suitable alternatives are missing as the CSSIM is favored for its inherent simplicity based on the ideally permeable iron core hypothesis. However, saturated armature slots can lead to high variations of the slot inductance, where the CSSIM cannot represent this precisely. An accurate prediction of the strand inductances is crucial when optimizing the transpositions of large Roebel bars to be competitive on efficiency and low measurement tolerances. This fact is crucial in under-roebeling, having less than a 360-degree transposition over the active part. In the end, the goal is to compensate the winding overhang parasitic field with the slot-parasitic field. This paper proposes a differential strand-slot inductance model (DSSIM) based on the concept of differential inductance (DI). It is compatible with a circuital lumped-element model (LEM) that considers the strand topology, geometrical dimensions, saturation level, and small-scale effects. Numerical simulations showcase the performance improvement of the DSSIM against known models. Finally, a 20-strand prototype of a slot model with actual Robel bar strands corresponding to a simplified bar cross-section in a large AC machine’s slot demonstrates the presented DSSIM’s precision. [ABSTRACT FROM AUTHOR]

This paper presents a new sensorless control strategy with the fault-tolerant ability for switched reluctance motors (SRMs). Nowadays, many rotor position detection methods are utilized, but most of them increase the system cost due to the additional hardware or complex calculations. To address this problem, various methods of using phase inductance to estimate the rotor position and speed have been proposed. However, the traditional inductance detection method will cause signal distortion due to the presence of interference signals and the unbalanced phase inductance. In particular, the turn-ON angle is advanced. To further improve the stability of the control system, the interference signals are eliminated via establishing the reference time of the inductance characteristic point and the error band in this work. When the position signal disappears, the inductance characteristic points of adjacent phases will be adopted for signal compensation to realize fault-tolerant control. Finally, an SRM drive system is used to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Position estimation error caused by the cross-saturation effect seriously affects the performance of signal injection based sensorless control, especially for the surface permanent-magnet synchronous motor (SPMSM) with load. In this paper, a position estimation error compensation method is proposed to improve the accuracy and stability of sensorless control for a dual three-phaseSPMSM. Based on the space vector signal injection, the initial position is obtained by the demodulation of high-frequency current response. By analyzing the relationship between the stator flux and stator current, the optimal compensation angle can be achieved. The position estimation error can be dynamically compensated under load conditions with the combination of initial position and compensation angle. Due to the convergence of compensation angle, the compensation process has weak dependence on prior knowledge of the motor. Simulation and experimental results are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

The inductance of a winding segmented permanent magnet linear synchronous motor (WS-PMLSM) is affected by winding disconnection and coupling length variation, which makes the variation of inductance more complicated, and this paper proposes incremental inductance, apparent inductance, and positional inductance to reveal this phenomenon, which gives a theoretical basis for mathematical modeling and thrust fluctuation suppression. First, an analytical approach is used to derive a fully coupled state model using the magnetomotive force and specific permeability function. Second, the domain of the specific permeability function is extended and the inductance expressions are calculated for the whole moving range. Finally, the inductance of the prototype WS-PMLSM with a two-phase winding is experimentally verified, and it is proposed that the effects of the three inductive components on the system should be considered comprehensively when implementing control of the WS-PMLSM. [ABSTRACT FROM AUTHOR]

Eddy-current sensors are widely used for precise displacement sensing and non-destructive testing. Application of printed-circuit board (PCB) technology for manufacturing sensor coils may reduce the cost of the sensor and enhance the performance by ensuring consistency. However, these prospects depend on the uniformness of the sensor coil. Inductance measurements of sample coils reveal rather considerable variations. In this paper, we investigate the sources of these variations. Through image analysis of cut-away cross-sections of sensor coils, four factors that contribute to the inductance variations are identified: the distance between layers, the distance between tracings, cross-sectional areas, and misalignment among layers. By using and extending existing method of calculating inductance of spiral coils, the inductance distributions are obtained when these factors are randomly varied. A sensitivity analysis shows that the inductance uncertainty is most affected by the uniformness of the spacings between coil traces and the distances between layers. Improvements in PCB manufacturing process can help to reduce the uncertainty in inductance. [ABSTRACT FROM AUTHOR]

Lateral misalignment along the driving direction may achieve half the length of a transmission coil in a dynamic wireless charging system for electric vehicles, which is called limit misalignment. This limit misalignment may cause the dynamic wireless charging system to malfunction because of the large fluctuation in mutual inductance. In this paper, an asymmetric and reverse series coil (ARSC) structure is proposed. In the ARSC structure, the transmission coil is smaller than the receiving coil in size to smoothen the fluctuation in mutual inductance. The receiving coil consists of a large coil ($\boldsymbol{R}_{\mathrm {x1}}$) and a small coil ($\boldsymbol{R}_{\mathrm {x2}}$) and $\boldsymbol{R}_{\mathrm {x1}}$ is reversely connected to $\boldsymbol{R}_{\mathrm {x2}}$ in series. The purpose of this design is to further reduce the fluctuation in mutual inductance. A calculation method of mutual inductance is then proposed based on the vector potential to calculate the mutual inductance of the ARSC structure. The law of mutual inductance is analyzed by the proposed calculation method for the ARSC structure. Moreover, an optimization method of coil parameters is proposed to obtain quasi-constant mutual inductance. The ARSC structure and optimization method are not only simple but can also make the mutual inductance nearly constant. Calculation, simulation, and experimental results validating the proposed method and structure are shown. [ABSTRACT FROM AUTHOR]

In past years, LLC resonant converters have become a mainstream topology for dc–dc power conversion due to their advantages, such as the superior efficiency obtained with the soft switching of MOSFETs. In order to further improve the efficiency of the converter, synchronous rectification (SR) can be implemented as an alternative for diode rectification. As a result, the vast majority of the literature related to this field of study presents different LLC SR control algorithms, which aim to improve the operation of the rectification. Unlike prior work on SR controllers, this paper contributes to the area of power loss estimation using rectifier current equations (RCE). The developed method based on time-domain analysis of SR currents provides a new analytical framework to characterize the behavior of SR. Implications in SR power losses of different time delays are investigated using the developed loss estimation method. In addition, different converter design parameters, such as choice of inductance ratio, can be analyzed. The RCE captures the true discontinuous and complex behavior of SR, which is often oversimplified by the conventional first-harmonic approximation (FHA). As a result, the proposed method facilitates the design of LLC resonant converters and provides increased precision in SR power loss estimation when compared to FHA, and in a considerably faster fashion when compared with precise yet computationally intensive simulation software. This paper is validated with simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study on current loop auto-tuning for self-commissioning of sensorless interior permanent magnet synchronous machine (IPMSM) drives. Well-tuned current controllers are essential for both high-performance operation and self-commissioning procedure. However, current controller design parameters, i.e., $L_{d}$ and $L_{q}$ , are not known at the beginning of the self-commissioning procedure where their estimation also has unique challenges. For example, an initial rotor position to determine the actual d- and q-axes is not known. Also, feedback controllers cannot be used in the estimation because they are not tuned yet. As a solution, this paper proposes a method to estimate the spatial inductance map by spatially scanning the motor via sinusoidal voltage injection in a controlled manner. Then it uses the estimated inductance values to tune the current controllers. The proposed method identifies $L_{d}$ and $L_{q}$ values using open-loop voltage injection without needing actual d- and q-axis positions. The whole procedure takes around a second. Practical considerations such as an automatic selection of the injection voltage, and digital control and dead-time effects are carefully addressed. The findings are experimentally verified on a 3-phase IPMSM drive. Furthermore, its applicability to different motor types is also demonstrated. [ABSTRACT FROM AUTHOR]

This paper deals with the high accurate current set-points solution for interior permanent-magnet synchronous motors (IPMSM) in wide-speed range applications. Considering voltage and current constraints, the operating regions can be divided into maximum torque per ampere, maximum current, field weakening, and maximum torque per voltage regions, which requires solving different nonlinear functions in real time to obtain optimal current set-points. Traditional methods including curve-fitting methods and polynomial approximation (PA) methods are not easy to obtain these solutions, especially involving magnetic saturation problems. In this paper, Newton–Raphson algorithm for improving the control accuracy of the current set-points is proposed. Meanwhile, parameters influence including magnetic saturation and resistive voltage drop is fully investigated. Compared with PA method, the proposed method is able to converge to accurate solutions in few numbers of iterations with reduced execution time, which can be easily implemented on an off-the-shelf digital signal processor. Both simulation results and experimental results on an 8-kW IPMSM rig are conducted showing good agreement with the expected results. [ABSTRACT FROM AUTHOR]

This paper proposes short circuit and overload gate-driver dual-protection scheme based on the parasitic inductance between the Kelvin- and power-source terminals of high-current SiC mosfet modules. The paper presents a comprehensive analysis of the two schemes in question, including worst-case analysis used to assess their parametric dependence due to manufacturing tolerances and temperature variations, as well as the in-depth design procedure that can be generally applied to any power module containing a Kelvin-source. For verification, a compact 1.2-kV, 400-A half-bridge module integrating the two protection circuits was developed. The results obtained demonstrate a response time within tens of nanoseconds, and effectively validate their functionality under short circuit and overload scenarios. Finally, a 100-kW, 400-V dc three-phase voltage-source inverter was used to demonstrate the gate-driver with integrated protection functions under 105°C ambient temperature conditions. [ABSTRACT FROM AUTHOR]

The nonresonant single-phase dual-active-bridge (NSDAB) dc–dc converter has been increasingly adopted for isolated dc–dc power conversion systems. Over the past few years, significant research has been carried out to address the technical challenges associated with modulations and controls of the NSDAB dc–dc converter. The aim of this paper is to review and compare these recent state-of-the-art modulation and control strategies. First, the modulation strategies for the NSDAB dc–dc converter are analyzed. All possible phase-shift patterns are demonstrated, and the correlation analysis of the typical phases-shift modulation methods for the NSDAB dc–dc converter is presented. Then, an overview of steady-state efficiency-optimization strategies is discussed for the NSDAB dc–dc converter. Moreover, a review of optimized techniques for dynamic responses is also provided. For both the efficiency and dynamic optimizations, thorough comparisons and recommendations are provided in this paper. Finally, to improve both steady-state and transient performances, a combination approach to optimize both the efficiency and dynamics for an NSDAB dc–dc converter based on the reviewed methods is presented in this paper. [ABSTRACT FROM AUTHOR]

Flux reversal permanent magnet generators are well suited for use as wind turbine generators owing to their high torque generation ability and magnetic gear. However, they suffer from poor voltage regulation due to their high winding inductance. In this paper, a design optimization method is proposed for flux reversal generators in wind turbine applications. The proposed method includes a new multiobjective function. Cost, volume of the generator, and mass of the permanent magnet are considered in it independently and simultaneously. Besides the new objective function, the main superiority of this paper compared with published papers is considering winding inductance in optimization procedures as a constraint and analyzing the optimization results for different values of it. Also, for the first time, the equations for permanent magnet sizing are considered based on a demagnetization curve for designing a flux reversal generator. For this purpose, a step-by-step design procedure is proposed and sensitivity analysis is performed to determine the sensitivity of output parameters to specific electrical loading, the height of the permanent magnets, and the machine length-to-diameter ratio. Then a multiobjective optimization based on a genetic algorithm is carried out and the best combination of pole number and number of slots/pole/phase is obtained. Then, for this combination, the optimum value of the constraint is obtained, too. Then specifications and dimensions of the optimum flux reversal machine as a wind turbine generator is presented. Finally, a time-stepping finite element method is used to validate the design and optimization results. [ABSTRACT FROM AUTHOR]

This two-part paper presents a method to mitigate half-cycle saturation of transformers caused by monopolar operation of neighboring HVDC transmission lines while keeping the ability to detect the zero-sequence fault currents (ZSFC) when ground faults occur. Part I of this paper has presented the mitigation principles and device design of the proposed neutral current blocking switch. In Part II, the performance of the proposed method to permit the circulation of zero-sequence current is investigated. An operation strategy is proposed that simultaneously allows the mitigation of half-cycle saturation and the detection of ZSFC. Simulations on a widely-used 500 kV system show that the proposed mitigation technique, using a sub-synchronous switching frequency (no higher than 30 Hz), can effectively mitigate the half-cycle saturation while allowing the circulation of ZSFC. The novel mitigation method exploits the characteristic differences between half-cycle saturation (dc) and asymmetric faults (ac). The method provides an implementable solution to the dc-bias phenomenon because it delivers concurrently dc-bias mitigation, minimal impact on ground fault detection, and no switching stresses on the power electronic switches. The proposed technique can also be applied to the mitigation of geomagnetically induced currents. [ABSTRACT FROM AUTHOR]

With the increasing of switching frequency in pulsewidth modulated motor system, common mode current (CMC) seriously affects the reliable operation of motor system and it has become a problem that cannot be ignored. This paper proposes a mathematical model of CMC and conducts detailed time–frequency characteristics analysis of CMC. The influence of several key parameters of motor system, such as distributed capacitance, dc bus voltage, and inverter switching frequency, on CMC characteristics has been analyzed in detail, and the corresponding variation rule of CMC oscillation amplitude and attenuation period/time has been summarized. The experimental results are presented to verify the correctness of theoretical analysis. The conclusions of this paper can lay theoretical foundation for the effective suppression of CMC in various practical applications. [ABSTRACT FROM AUTHOR]

It is quite often to utilize the transformer leakage inductance in the resonant tank of the LLC resonant converter to allow for a drastic reduction in the converter cost, weight, size, and volume. The effects of the secondary leakage inductance on the operation of the LLC resonant converter are not well discussed in the relevant literature, and it is the purpose of this paper to give an insight into these effects. The contribution of this paper lies in the following: first, highlighting that it is not always an accurate assumption to consider that the values of the primary and secondary leakage inductance are identical, specifically in asymmetric magnetic core structures. Second, it has been disclosed that the well-known coupling factor (k12) cannot properly express the unequalized leakage inductance distribution in the proposed asymmetric transformer. Therefore, the authors bring the primary coupling factor (k1) and secondary coupling factor (k2) into practice to appropriately express the unequalized leakage distribution on the primary and secondary windings, which can be controlled by the allocation of the relevant winding with respect to the air gap, utilizing the noise absorber, and changing the distance between the winding. Several transformer prototypes had been built and experimentally tested to validate these hypotheses. Third, it has been observed that the transformer voltage gain and efficiency can be improved when the transformer leakage inductance is concentrated on the secondary side to avoid the voltage drop inflicted by the relatively large value of the magnetizing current $(i_{m})$ , especially at the light load condition. Fourth, it has been reported that in a transformer structure with a concentrated value of leakage on the secondary side would decrease the resonant tank input impedance, vertically widen the voltage–gain curve of the converter, and eventually increase the frequency control bandwidth with respect to the load variation. Transformer prototypes had been constructed and tested in a 390 V/12 V–220 W LLC resonant converter to evaluate the proposed analysis. [ABSTRACT FROM AUTHOR]

In order to increase the efficiency of modern microprocessor power supplies used in data centers, 380-V dc power distribution systems have been attracting attention due to their high efficiency and high reliability. This paper presents an innovative single-stage approach for 380-V voltage regulator modules (VRMs) based on a quasi-resonant multilevel topology constant on-time operation. The proposed topology inherently integrates the multiphase approach, providing fast phase shedding and flat high-efficiency curves even at light-load conditions. This is a unique advantage, which is not possible to establish in the two-stage approach, which is very important in server architectures, and where high efficiency is required even at light-load conditions. This paper analyzes the circuit topology and proposes a control architecture for fast transient response, including current-sharing capabilities. The digital controller has been implemented in 0.16- $\mu$ m lithography together with a digital pulsewidth modulation with a 195-ps resolution and a 40-MS/s 7-bit analog-to-digital converter. Experimental results show an efficiency of 93% for a 120-A 380–1.8-V VRM power supply. [ABSTRACT FROM AUTHOR]

In this paper, many impedance-source inverters with coupled inductors have been investigated to obtain a high step-up boost ratio. However, the leakage inductors in these topologies induce great voltage spikes at the dc link, which will increase the voltage stress of switches. Thus, the power level of inverters is limited. Furthermore, the efficiency of the inverters can be degraded by the losses associated with leakage inductors. To address abovementioned issues, this paper proposes a family of low-spike high-efficiency Y-source inverters. The proposed inverters have the ability of eliminating voltage spikes at the dc link and recycling the leakage energy via the additional diode and capacitor. In order to show the excellent characteristics of the proposed topologies, this paper compares the performances of the proposed inverters and the improved-Y-source inverter in many aspects. Simulation and experimental results have verified the abilities of the proposed inverters. [ABSTRACT FROM AUTHOR]

Fault diagnosis and fault tolerant (FT) control of electric drive systems have been extensively studied by many researchers. Naturally, one would like to use fault diagnosis information to improve FT control to achieve good post-fault performance while it is safe to do so. In this paper, a novel FT control method is proposed for permanent magnet synchronous motor with inter-turn short circuit fault. Given fault severity, the proposed FT control can reduce torque ripple while keeping reasonable torque output. The theoretical derivation, simulation, and experimental validation are presented in this paper. [ABSTRACT FROM AUTHOR]

This paper presents an enhanced current controller for improving the performance of a class of single-phase grid-connected inverters operating in weak and distorted grid conditions. An inverter designed to operate at normal (strong or stiff and clean) grid conditions may not perform satisfactorily during weak and distorted grid conditions. One major reason is the interfering dynamics of the synchronization or phase-locked loop (PLL). This paper proposes an enhanced control structure for a popular class of single-phase inverters to address this problem. The proposed idea is to include the PLL state variables into the main inverter controller thereby minimizing the undesirable interactions of the PLL with the other components. A method for optimally designing the controller gains is also proposed. Compared to the conventional one, the proposed controller is shown to have a more robust performance over a substantially wider range of weak and distorted grid conditions. Extensive simulation and experimental results are presented to validate the proposed controls. [ABSTRACT FROM AUTHOR]

This paper presents a scheme for rotor position estimation from standstill to nominal speed. The proposed scheme is particularly suited for surface mounted permanent magnet synchronous motors and for slotless permanent magnet synchronous motors with completely smooth cylindrical rotor, which cannot be operated with state-of-the-art sensorless methods seamlessly from standstill. At standstill and very low speed, the position is estimated by using signal injection. A systematic distortion in the position estimation that is due to asymmetries in the motor parameters is identified and compensated. The rotor polarity is identified by a special process based on the estimation of the back electromotive force (back EMF) induced by a minimal rotor motion. At high speed, the position is estimated by using a linear back EMF observer. Different observer gains are used at different speed ranges, so that the position estimate is reliable even at low speed. The combination of these two approaches enables sensorless motor control in the full speed range including standstill. Experiments demonstrate the accuracy of the proposed estimation scheme and its robustness under different thermal conditions. This paper is accompanied by two videos demonstrating sensorless operation. [ABSTRACT FROM AUTHOR]

This paper proposes a resonant switching cell model to analyze and design the single-ended resonant dc–dc converters. The single-ended zero-voltage switching (ZVS) converters such as the Class E converter are efficient for megahertz switching because they feature low turn-on and turn-off switching losses. Also, they use only a ground-referenced switch, allowing a simple gate drive circuit. In this paper, we investigate the single-ended resonant converter with the small input inductance, whereas the conventional Class E converter has a large input inductance. The main contribution of this paper is to propose the resonant switching cell as an analytic model that simplifies the analysis and the design of the resonant dc–dc converters. Furthermore, this paper presents the design method of the resonant switching cell model for minimizing the resonant current magnitude and conduction loss while the converter maintains ZVS property. The experimental results from a 10-MHz GaN-based prototype demonstrate the feasibility and effectiveness of the analysis and design based on the proposed resonant switching cell model. [ABSTRACT FROM AUTHOR]