In this study, the influence of slot opening on the leakage reactance, power factors, winding current, and air gap flux density, as well as other parameters of the surface-mounted permanent magnet synchronous motor driven by an inverter is analyzed using the two-dimensional time-step finite element method. Thus, the law of permanent magnet power loss caused by slot opening under PWM qa obtained. The results show that the leakage reactance of the motor increased when the slot opening decreased from 7 mm to 2 mm. Then, the armature ripple current caused by the inverter was found to be suppressed well, and the high harmonic current was filtered well. This reduced the amplitude of the high-order harmonic of the air gap flux density, and the permanent magnet power loss was reduced by nearly 75%. Finally, two prototypes with different slot openings were tested for permanent magnet temperature rise, which verified the analysis method and calculation results proven in this paper.

High-voltage fuses are found in most electrical installations, where they are used for overcurrent protection and are the pieces of equipment providing the highest degree of protection for the lowest initial cost. This article focuses on the behavior of high-voltage fuses containing a fuse element entirely made of aluminum. We made high-power linear electrical circuits for experiments on these fuses under the most severe operating conditions. The article presents the construction details of the fuse element and its features, as well as various arc extinguishing media. The heating behavior and time−current characteristics were studied in comparison with fuses made of copper. We obtained the maximum instantaneous value of the current reached during interruption for a 24 kV, 50 kA, 50 A fuse, as well as the value of the minimum breaking current.

With the phase angle and shape modifications for carriers, two improved carrier-based pulse width modulation (CPWM) methods with common-mode voltage (CMV) suppression effects for the five-phase open-winding drive topologies are introduced. Theoretical analysis reveals that, by employing reversed triangular carriers for two inverters under the carrier-reversed PWM (CRPWM), CMV contributions of two bridge legs belonging to the same phase can be cancelled, realizing the zero CMV effect. By dynamically employing positive and negative sawtooth carriers for all bridge legs under the carrier-switching PWM (CSPWM), the CMV contribution of each inverter can be reduced, decreasing both the amplitude and step frequency of the CMV. Current qualities and dead-time effects on CMV under the above PWM methods are analyzed. Moreover, performances of two PWM methods are verified by experiments implemented on a five-phase open-winding topology with the induction motor load.

A common-mode voltage (CMV) suppression strategy, namely double zero-sequence injection common-mode voltage (DZICMV), is proposed in this paper for an asymmetrical six-phase induction motor fed by two-level dual three-phase voltage source inverters (VSIs). In this strategy, the sinusoidal waveforms injected by double zero-sequence signals are employed as modulation signals, and two opposite triangular waveforms are used as carriers. The fundamental period is divided into 24 sectors. In each sector, the carrier used by the medium amplitude phase is distinct from the carriers used by the other two phases in each set of three-phase windings. Using this method, the zero vectors (000) and (111) in each set of three-phase windings can be eliminated, and the peak values of sub-CMV and total CMV can be reduced from ±Udc/2 to ±Udc/6. The experiment results show that the root mean square (RMS) value of common-mode leakage current in DZICMV can be reduced by 51.83% compared with the double zero-s... [more]

In this article, the stator winding circulating current inside parallel branches (CCPB) of a doubly fed induction generator (DFIG) is comprehensively investigated. Different from other studies, this study not only focuses on the CCPB in radial static air-gap eccentricity (RSAGE) and radial dynamic air-gap eccentricity (RDAGE) but also takes the radial hybrid air-gap eccentricity (RHAGE) cases into account. Firstly, the detailed expressions of CCPB in normal and radial air-gap eccentricity (RAGE) are obtained. Then, the finite element analysis (FEA) and experimental studies are performed on a four-pole DFIG with a rated speed of 1470 rpm in order to verify the theoretical analysis. It is shown that the RAGE increases the amplitude of the CCPB and brings new frequency components to the CCPB. For RSAGE, the CCPB brings new frequency components, which are f1 (50) and fμ (540/640). For RDAGE, the newly generated frequency components are f1± f (25/75), f (515/565/615/665, and k = ±1). F... [more]

This paper presents a new technique to mitigate the high voltage stress on the secondary gallium nitride (GaN) transistor in a high step-up flyback application. GaN devices provide a means of achieving high efficiency at hundreds (and thousands) of kHz of switching frequency. Presently however, commercially available GaN is limited to only a 650 V absolute voltage rating. Such a limitation is challenging in high step-up flyback applications due to the secondary leakage. The leakage imposes high voltage stress on the secondary GaN rectifier during its turn-off transient. Such stress may cause irreversible damage to the GaN device. A new method of leakage bypass is presented to mitigate the high voltage stress issue. The experimental results suggest that when compared to conventional secondary active clamp, a 2.3-fold reduction in overshoot voltage stress percentage is achievable with the technique. As a result, it is possible to utilize GaN as the rectifier while keeping the peak voltag... [more]

This article describes a simple cogging torque minimization procedure for interior permanent magnet synchronous machines (IPMSMs), consisting of a progressive modification of the rotor lamination geometry. This procedure can be generalized for the main topologies of PMSM, independently of the number of stator slots or the location of the permanent magnets. For this purpose, a basic IPMSM structure is analyzed by means of the FEM (finite element method) approach, and then, several other IPMSM geometries, obtained by adequately modifying the rotor lamination geometry of the basic IPMSM model without changing its stator configuration, are proposed and discussed. The trends of the cogging torque generated by each model are computed and compared. From this comparison, it is demonstrated that, by simply acting on the shape of the rotor lamination and by choosing the optimized pattern, the cogging torque components can be theoretically canceled.

This article presents a new method for the estimation of active power losses based on a “field” approach, i.e., on the theory of the electromagnetic field and the theory of propagation of electromagnetic waves in a dielectric medium. Electromagnetic waves are assumed to transmit energy from the traction substation to electric rolling stock through the airspace of the inter-substation zone (i.e., not through the wires of the traction network) and meet electrically conductive surfaces on their way. The waves are partially reflected from the surfaces and partially penetrate them, thus creating thermal losses, the determination of which is the main task of this article. The analytical expressions for specific losses of active power are obtained by solving the system of Maxwell’s equations. Calculations of specific power losses in the catenary, rails, roofs, and bottoms of carriages and electric locomotives are performed. Power losses in carriages and electric locomotives are found to be at... [more]

A variety of modulation strategies for suppressing output common-mode voltage (CMV) of indirect matrix converters (IMC) have been proposed, but most of them mainly reduce the peak of CMV by 42.3%. The frequency-domain characteristics of CMV have not been deeply analyzed. In order to improve the theory of frequency-domain characteristics of output common-mode voltage of IMC, this paper proposed a common-mode frequency domain analysis of five common-mode voltage peak suppression modulation methods for IMC. The common-mode voltage spectrum corresponding to the five modulation methods is obtained by the triple Fourier series, and the variation laws of the output common-mode components of the five modulation methods under different modulation indexes are compared and analyzed. By comparing and analyzing the low-frequency amplitude characteristics and high-frequency amplitude characteristics of five modulation methods, the suppression performance of the five modulation methods is evaluated.... [more]

The circuit topology of a submodule (SM) in an modular multilevel converter (MMC) defines many of the functionalities of the complete power electronics conversion system and the specific applications that a specific MMC configuration can support. Most prominent among all applications for the MMC is its use in high-voltage direct current (HVDC) transmission systems and multiterminal dc grids. The aim of the paper is to provide a comprehensive review and classification of the many different SM circuit topologies that have been proposed for the MMC up to date. Using an 800-MVA, point-to-point MMC-based HVDC transmission system as a benchmark, the presented analysis identifies the limitations and drawbacks of certain SM configurations that limit their broader adoption as MMC SMs. A hybrid model of an MMC arm and appropriate implementations of voltage-balancing algorithms are used for detailed loss comparison of all SMs and to quantify differences among multiple SMs. The review also provide... [more]

This paper investigates the electromagnetic torque by considering back electromagnetic force (back-EMF) trapezoidal degrees of ironless brushless DC (BLDC) motors through the two-dimensional finite element method (2-D FEM). First, the change percentages of the electromagnetic torque with back-EMF trapezoidal degrees, relative to those of PMs without segments, are investigated on the premise of the same back-EMF amplitude. It is found that both PM symmetrically and asymmetrically segmented types influence back-EMF trapezoidal degrees. Second, the corresponding electromagnetic torque, relative to that of PMs without segments, is studied in detail. The results show that the electromagnetic torque can be improved or deteriorated depending on whether the back-EMF trapezoidal degree is lower or higher than that of PMs without segments. Additionally, the electromagnetic torque can easily be improved by increasing the number of PMs’ symmetrical segments. In addition, the electromagnetic torque... [more]

The FDS (Frequency-domain Dielectric Spectroscopy) of oil-immersed insulation paper, and semi-conductive paper with different moisture content, has been measured. The data measured are fitted as a function of frequency and moisture content using the amendatory Cole−Cole model utilizing the least square technique. Then, the broadband MTL model of the insulation system of IOCT (Inverted-type Oil-immersed Current Transformer) is established considering the capacitive electrodes thin layer, and the distribution parameters consider the moisture and frequency dependence. A new method for VFTO (Very Fast Transient Overvoltage) distribution calculation of insulation systems is proposed.

In this work, the vibrations on the surfaces of the tank wall, stiffeners, and the cover of a 5 MVA transformer experimental model were measured during open-circuit and short-circuit transformer tests. Vibration measurements of a transformer tank side were conducted at discrete points using two different voltage sources in no-load test. Using interpolation functions, the RMS values of acceleration and vibration velocity are visualized and compared for each considered measurement configuration (no-load and load tests and two different excitation sources). Significant differences in mode shapes and amplitudes of vibrations at different frequencies are observed. The maximum RMS values of acceleration, velocity and displacement in the open-circuit test are 0.36 m/s2, 0.31 mm/s, and 0.42 µm, respectively. The maximum values in short-circuit test are 0.74 m/s2, 1.14 mm/s, and 1.8 µm, respectively. In the short-circuit test, the frequency component of 100 Hz is dominant. In the open-circuit t... [more]

This paper analyses the condition of a partial short-circuit in a brushless permanent magnet motor. Additionally, the problem was analysed for three stator winding configurations: star, delta and star-delta connection. The paper presents an original mathematical model allowing a winding configurations to be analysed. What is more, the said mathematical model allows taking account of the partial short-circuit condition. Frequency analysis (Fast Fourier Transform—FFT) of the artificial neutral point voltage was proposed for the purpose of detecting the partial short-circuit condition. It was demonstrated that a partial short-circuit causes a marked increase in the diagnostic frequencies of the voltage signal. The proposed brushless permanent magnet motor diagnostic method is able to detect the fault regardless of the stator winding configuration type.

This paper deals with the possibility to replace rare-earth permanent magnet (PM) motors in direct drive applications. According to previous researches, there are alternatives such as surface-mounted PM motors and spoke-type motors adopting Ferrite PMs, synchronous reluctance motors, with or without the assistance of low-energy PMs. Few studies have been carried out to compare all models at once, thus it is hard to choose which type motor is to be preferred as a valid alternative of rare-earth PM motors in direct drive applications. In this paper, the representative candidates listed above are analyzed and the results are compared with that of a rare-earth PM motor, which is considered as a reference motor. Additionally, the demagnetization phenomenon of the motors with Ferrite PMs is deeply analyzed because this kind of PM may be easily demagnetized by the stator flux. Finally, both strengths and weaknesses of each alternative motors are highlighted.

Stability metrics are used to quantify a system’s ability to maintain equilibrium under disturbances. We did not identify the proposition of a stability metric using sensitivity analysis within the literature. This work proposes a system stability metric and its application to an electrical repowering system. The methodology for applying the proposed metric comprises: (i) system parameters sensitivity analysis and spider diagram construction, (ii) determining the array containing the line segments inclination angles of each spider diagram curve, and (iii) stability calculation using the array mean and maximum inclination value of a line segment. After simulating the model built for the electrical repowering system and applying the methodology, we obtain results regarding the sensitivity indices and stability values of system inputs relative to their outputs, considering the original system and with reduced parameters. Using the stability study, it was possible to determine different st... [more]

The paper presents a description of the method and the results of calculating the leakage reactance of high-power synchronous generator end windings using the finite element method. This reactance is one of the components of the stator leakage reactance of synchronous generators. The calculations were carried out under the assumption of a three-dimensional field distribution in a synchronous generator. The thus calculated value of the leakage reactance of the end windings was compared with the calculation results obtained using traditional, analytical formulas known from the literature. The analysis of the influence of the reactance value of the end windings on the transient waveforms at a three-phase short-circuit of the stator windings was performed based on a two-dimensional field-circuit model.

The improved discrete ordinates method (IDOM) developed in our previous paper is extended to solve radiative transfer in three-dimensional radiative systems with anisotropic scattering medium. In IDOM, radiative intensities in a large number of new discrete directions are calculated by direct integration of the conventional discrete ordinates method (DOM) results, and radiative heat flux is obtained by integrating radiative intensities in these new discrete directions. Ray effects and false scattering, which tend to compensate each other, are investigated together in IDOM. Results show that IDOM can mitigate both of them effectively with high computation efficiency. Finally, the effect of scattering phase function on radiative transfer is studied. Results of radiative heat flux at boundaries containing media with different scattering phase functions are compared and analyzed. This paper indicates that the IDOM can overcome the shortages of the conventional DOM well while inheriting its... [more]

This paper investigates the impact of parameter variation between parallel connected SiC MOSFETs on short circuit (SC) performance. SC tests are performed on parallel connected devices with different switching rates, junction temperatures and threshold voltages (VTH). The results show that VTH variation is the most critical factor affecting reduced robustness of parallel devices under SC. The SC current conducted per device is shown to increase under parallel connection compared to single device measurements. VTH shift from bias−temperature−instability (BTI) is known to occur in SiC MOSFETs, hence this paper combines BTI and SC tests. The results show that a positive VGS stress on the gate before the SC measurement reduces the peak SC current by a magnitude that is proportional to VGS stress time. Repeating the measurements at elevated temperatures reduces the time dependency of the VTH shift, thereby indicating thermal acceleration of negative charge trapping. VTH recovery is also obs... [more]

Due to the internal dynamics of the modular multilevel converter (MMC), the coupling between the positive and negative sequences in impedance, which is defined as frequency coupling, inherently exists in MMC. Ignoring the frequency coupling of the MMC impedance model may lead to inaccurate stability assessment, and thus the multi-input multi-output (MIMO) impedance model has been developed to consider the frequency coupling effect. However, the generalized Nyquist criterion (GNC), which is used for the stability analysis of an MIMO model, is more complicated than the stability analysis method applied on single-input-single-output (SISO) models. Meanwhile, it is not always the case that the SISO model fails in the stability assessment. Therefore, the conditions when the MIMO impedance model needs to be considered in the stability analysis of an MMC system should be analyzed. This paper quantitatively analyzes the effect of frequency coupling on the stability analysis of grid-connected M... [more]

This paper proposes a second-order thermal model for electrical machines. The goal of this model is the prediction of the average winding temperature during short and long thermal transients up to the steady-state conditions. First, the thermal parameters of the electrical machine are determined by a DC test. Then, the proposed model is characterized and validated using AC tests. The accuracy of the proposed thermal model has been verified comparing the computed temperatures with the measured ones. The maximum error found during the thermal transient is lower than 3%, an excellent result comparing the complexity of a total enclosed fan cooled induction motor and the simplicity of the proposed model.

The switching loss of the secondary side rectifiers in LLC resonant converters can have a noticeable impact on the overall efficiency of the complete power supply and constrain the upper limit of the optimum switching frequencies of the converter. Two are the main contributions to the switching loss in the secondary side rectifiers: on the one hand, the reverse recovery loss (Qrr), most noticeably while operating above the series resonant frequency; and on the other hand, the output capacitance (Coss) hysteresis loss, not previously reported elsewhere, but present in all the operating modes of the converter (under and above the series resonant frequency). In this paper, a new technique is proposed for the measurement of the switching losses in the rectifiers of the LLC and other isolated converters. Moreover, two new circuits are introduced for the isolation and measurement of the Coss hysteresis loss, which can be applied to both high-voltage and low-voltage semiconductor devices. Fin... [more]

This paper deals with a well-known problem of the transient DC-bias current occurring during a phase shift transition in dual active bridge (DAB) DC/DC converters. This phenomenon, if not compensated, can cause damage to the converter or deteriorate its performance. One aim of this paper is to present a solution which allows for the elimination of the undesired transient DC-bias component in current waveforms. This solution is the dual rising edge shift (DRES) compensation algorithm. It provides a very simple implementation and fast settling time within the first half of a switching period. Moreover, the solution is independent on any measurements or system parameter values. It is based on the double-sided single phase shift (DSSPS) modulation, which is described in detail along with a converter model in steady-state. Then, the mechanisms leading to the transient DC-bias are explained, and the compensation algorithm is derived. The performance of the algorithm has been tested using a l... [more]

A method for computation of the lightning channel base current from the corresponding vertical component of lightning electric field was presented. The algorithm was developed by applying Laplace transform. The lightning current was estimated from its deconvolution with a special transfer function. The transfer function includes information about geometry and physical properties of entire lightning impulse generation system. The method was verified for a Heidler-type base current and a MTLL model of its propagation within the lightning channel. Research was done for close, middle, and far distance to the lightning strike point. Optimum performance was obtained for the middle distance of several kilometers where the electrostatic, induction, and radiation components of the transfer function were of the same range. An analysis was done for input electric field with and without noise superimposed on its time domain waveform. Relative uncertainties for the electric field and calculated lig... [more]

In this study, the lightning protection system and grounding system of one plant of the petrochemical industry were investigated, evaluated, and improved. The methods used in this study were rolling sphere and angle protection methods. The grounding system of the building under study was modeled and simulated using ATP/EMTP (Alternative Transient Program/Electromagnetic Transient Program) software. The results show that the external lightning protection system of the prilling tower studied does not adhere to IEC 62305 and IEC 1024-1-1 standards. Moreover, the grounding configuration of the DCS building was not appropriate for protecting sensitive equipment inside. Lightning causes an enormous potential difference between lightning ground rods in the grounding system. Additionally, disabling the existing surge protective device (SPD) causes an increase in the magnitude of Ground Potential Rise at the DCS building. Improvement of the lightning protection system of the prilling tower and... [more]