The protection systems of ship generators enable them to eliminate potential failures that pose a significant threat to the safety of the crew and the use of the ship. However, due to the fact that marine classification societies do not require the protection of generators against the loss of excitation, such protection is only used sporadically. This article presents an LOE (loss of excitation) analysis of ship generators that operate in parallel. This analysis is supported by simulations and experimental research. The test results show that the positions of the operating points of each generator are interrelated, and changes in the excitation of one (damaged) generator cause automatic changes in the excitation, as well as changes in electromagnetic and energy processes, in the second (efficient) generator. An LOE in one generator causes a dangerous increase in armature currents in both generators. The results of this study prove that the lack of LOE protection at lower levels of exci... [more]

The formation and evolution of (normal) fault affect the formation and preservation of some reservoirs, such as fault-block reservoirs and faulted reservoirs. Strain energy is one of the parameters describing the strength of tectonic activity. Thus, the formation and evolution of normal fault can be studied by analyzing the variation of strain energy in strata. In this work, we used physical simulation to study the formation and evolution of normal fault from a strain energy perspective. Based on the similarity principle, we designed and conducted three repeated physical simulation experiments according to the normal fault in the Yanchang Formation of Jinhe oilfield, Ordos Basin, China, and obtained dip angle, fault displacement, and strain energy via the velocity profile recorded by high-resolution Particle Image Velocimetry (PIV). As a result, the strain energy is mainly released in the normal fault line zone, and can thus serve as channels for oil/gas migration and escape routes con... [more]

In most high power industrial applications, the low switching frequency modulations (LSFM) are usually implemented to reduce power loss and heat dissipation pressure. However, there are some unexpected influences caused by the low order harmonic sinusoidal pulse width modulation (SPWM), such as the imbalanced submodule power in cascaded half-bridge inverter (CHB) and limited output power capability in H-bridge neutral-point-clamped (HNPC) converter. This paper starts by generalizing the basic characteristic of two-level SPWM, then deeply investigates the influences of low-frequency modulation on the operation of the circuits. They are classified into three mechanisms and generally named as harmonic overlap effect (HOE). The corresponding solutions to copy with the mechanisms are proposed and verified in some topologies through high-power simulations in simulations. In addition, a comprehensive summary of the influences and solutions of these effects on typical high power converters is... [more]

Undoubtedly, Low-Altitude Unmanned Aerial Vehicles (UAVs) are becoming more common in marine applications. Equipped with a Global Navigation Satellite System (GNSS) Real-Time Kinematic (RTK) receiver for highly accurate positioning, they perform camera and Light Detection and Ranging (LiDAR) measurements. Unfortunately, these measurements may still be subject to large errors-mainly due to the inaccuracy of measurement of the optical axis of the camera or LiDAR sensor. Usually, UAVs use a small and light Inertial Navigation System (INS) with an angle measurement error of up to 0.5∘ (RMSE). The methodology for spatial orientation angle correction presented in the article allows the reduction of this error even to the level of 0.01∘ (RMSE). It can be successfully used in coastal and port waters. To determine the corrections, only the Electronic Navigational Chart (ENC) and an image of the coastline are needed.

This paper analyzes how over-coupled coils affect odd harmonic current and electromagnetic interference (EMI) in a wireless power transfer (WPT) system, and proposes design considerations for series inductors to solve the EMI problem. When the air gap of the coils of the WPT system decreases below a certain level and the coils are over-coupled, the odd harmonic component of the input impedance of the system decreases and odd harmonic currents increase. The increase in the odd harmonic components current quickly aggravates the EMI issues. To solve the EMI problem of the over-coupled WPT system, additional series inductors were applied to the system, and considerations for designing the series inductors were analyzed. When designing additional series inductors, power transfer efficiency, maximum power transfer, input impedance and odd harmonic components current must be considered. Using simulations and experiments, it was confirmed that the WPT system designed with analyzed consideratio... [more]

Within large turboalternators, the excessive local temperatures and spatially distributed temperature differences can accelerate the deterioration of electrical insulation as well as lead to deformation of components, which may cause major machine malfunctions. In order to homogenise the stator axial temperature distribution whilst reducing the maximum stator temperature, this paper presents a novel non-uniform radial ventilation ducts design methodology. To reduce the huge computational costs resulting from the large-scale model, the stator is decomposed into several single ventilation duct subsystems (SVDSs) along the axial direction, with each SVDS connected in series with the medium of the air gap flow rate. The calculation of electromagnetic and thermal performances within SVDS are completed by finite element method (FEM) and computational fluid dynamics (CFD), respectively. To improve the optimization efficiency, the radial basis function neural network (RBFNN) model is employed... [more]

Although rare earth materials are the critical component in high torque density permanent magnet machines, their use has historically been a commercial risk. The alternatives that have been in the recent industry focus are synchronous reluctance machines (SyRM). They have lower torque density but also relatively low material cost and higher overload capability. Multi-layer IPM and SyRM machines have significant geometric complexity, resulting in a high number of parameters. Considering that modern machine design requires the use of optimization algorithms with computational load proportional to the number of parameters, the whole design process can take several days. This paper presents novel SyRM parameterization with reduced number of parameters. Furthermore, the paper introduces the novel forced feasibility concept, applied on rotor barrier parameters, resulting in improved optimization convergence with overall optimization time reduced by 12.3%. Proposed approaches were demonstrate... [more]

Deep and even ultra-deep petroleum resources play a gradually increasing and important role with the worldwide continuous advancement of oil and gas exploration and development. In China, the deep carbonate reservoirs in the Tarim Basin are regarded as the key development areas due to their huge reserves. However, due to the unreasonable design of production pressure differential, some production wells suffered from severe borehole collapse and tubing blockage. Therefore, the main purpose of this paper is to optimize a more practical method for predicting the critical production pressure differential. The commonly used analytical methods with different failure criteria for predicting production pressure differential were summarized. Furthermore, their advantages and disadvantages were analyzed. A new numerical model is established based on the finite element theory in order to make the prediction of production pressure differential more accurate. Additionally, both analytical and numer... [more]

In this paper, a coordinated DC voltage control strategy is proposed based on the VSG (virtual synchronous generator) method for the VSC-HVDC transmission system to participate in the frequency regulation of the connected weak grid. The voltage and power control capability of the VSC-HVDC is explored to attenuate the rate of change of frequency and to diminish the deviation of frequency. This is realized by the coordinated control of DC voltages at both the sending and the receiving ends with the VSG method. A small-signal model is established to investigate the dynamics of the control system. A tuning method for the selection of control parameters is also discussed in detail. The validity and superiority of the proposed control strategy are tested in the scenarios of sudden load changes and short circuit faults.

The Territorial Sea Baseline (TSB) allows coastal states to define the maritime boundaries, such as: contiguous zone, continental shelf, exclusive economic zone and territorial sea. Their delimitations determine what rights (jurisdiction and sovereignty) a given coastal state is entitled to. For many years, the problem of delimiting baseline was considered in two aspects: legal (lack of clear-cut regulations and different interpretations) and measurement (lack of research tools for precise and reliable depth measurement in ultra-shallow waters). This paper aimed to define the seasonal variability of the TSB in 2018−2020. The survey was conducted in three representative waterbodies of the Republic of Poland: open sea, river mouth and exit from a large port, differing between each other in seabed shape. Baseline measurements were carried out with Unmanned Surface Vehicles (USV), equipped with Global Navigation Satellite System (GNSS) geodetic receivers and miniature Single Beam Echo Soun... [more]

The purpose of this study is to analyze the evolution of the scientific research regarding the relationship between energy and economic growth, in order to reveal preferred topics and less approached themes. We conducted an occurrence and cluster analysis, followed by a correspondence analysis using articles published between 1979 and 2019 in journals indexed in the Web of Science. The analysis was split into three periods taking into account the major economic and energetic milestones. The analysis focused on distribution of the topics studied both by years and by journals. The research revealed some major trends: there has been an explosive increase in studies based on Asian countries over the three periods as concerns for sustainable development intensified, and environmental issues were associated with research on the relationship between energy and economic growth. Even if the journals cover different scientific areas, during the last 10 years they contain articles with very simil... [more]

This paper presents a method that has been developed to reduce the torque ripples under healthy and open-circuit fault-tolerant (OCFT) conditions for a multiphase permanent magnet (PM) machine. For smooth torque, both the phase current and the back electromotive force (back-EMF) should be purely sinusoidal. To improve the torque in a multiphase machine, higher-order current harmonics are injected, which are related to the harmonics in the back-EMF. For this reason, generally, multiphase machines are designed with higher-order back-EMF harmonics. However, these harmonics produce ripples in the torque. In light of this, a torque ripple cancellation method has been developed that first determines an additional current component from the harmonic content of the back-EMF and then injects these additional components to cancel the torque ripple. It has been found that this new torque ripple cancellation method works for both faultless and faulty conditions in a five-phase PM machine. The meth... [more]

This paper presents a method for the performance analysis of high-speed electric machines supplied with pulse-width modulated voltage source inverters by utilizing a fast analytical model. By applying a strict mathematical procedure, effective expressions for the calculation of rotor eddy current losses and electromagnetic torque are derived. Results obtained by the approach suggested in this study are verified by the finite element model, and it is shown that the proposed method is superior in comparison to the finite element method in terms of computation time. The proposed method enables fast parameter variation analysis, which is demonstrated by changing the inverter switching frequency and electric conductivity of the rotor and analyzing the effects of these changes on rotor eddy current losses. The presented work separately models effects of the permanent magnet and pulse-width modulated stator currents, making it suitable for the analysis of both high-speed permanent magnet mach... [more]

In order to improve the customers’ continuous usage of electrical vehicles (EVs) and reduce the weight of the energy storage devices, wireless charging technology has been widely studied, updated, and commercialized in recent decades, regarding to its distinct superiority of great convenience and low risk. A higher coupling coefficient is the key factor that impacts the transmission efficiency, thus in most medium-power (hundreds of watts) to high-power (several kilowatts) wireless charging systems, ferrites are used to guide the magnetic flux and intensify the magnetic density. However, the weight of the ferrite itself puts an extra burden on the system, and the core loss during operation also reduces the total efficiency and output power. This paper proposes an optimized design algorithm based on a core-less method for the magnetic core, where the core loss and the coupling coefficient are consequently balanced, and the overall weight and efficiency of the system can be optimized. Th... [more]

In the field of air navigation, there is a constant pursuit for new navigation solutions for precise GNSS (Global Navigation Satellite System) positioning of aircraft. This study aims to present the results of research on the development of a new method for improving the performance of PPP (Precise Point Positioning) positioning in the GPS (Global Positioning System) and GLONASS (Globalnaja Nawigacionnaja Sputnikovaya Sistema) systems for air navigation. The research method is based on a linear combination of individual position solutions from the GPS and GLONASS systems. The paper shows a computational scheme based on the linear combination for geocentric XYZ coordinates of an aircraft. The algorithm of the new research method uses the weighted mean method to determine the resultant aircraft position. The research method was tested on GPS and GLONASS kinematic data from an airborne experiment carried out with a Seneca Piper PA34-200T aircraft at the Mielec airport. A dual-frequency du... [more]

The article proposes a proprietary approach to the diagnosis of induction motors allowing increasing the reliability of electric vehicles. This approach makes it possible to detect damage in the form of an inter-turn short-circuit at an early stage of its occurrence. The authors of the article describe an effective diagnostic method using the extraction of diagnostic signal features using an Enhanced Empirical Wavelet Transform and an algorithm based on the method of Ensemble Bagged Trees. The article describes in detail the methodology of the carried out research, presents the method of extracting features from the diagnostic signal and describes the conclusions resulting from the research. Phase current waveforms obtained from a real object as well as simulation results based on the field-circuit model of an induction motor were used as a diagnostic signal in the research. In order to determine the accuracy of the damage classification, simple metrics such as accuracy, sensitivity, s... [more]

Electromagnetic modelling of electrical machines through finite element analysis is an important design tool for detailed studies of high resolution. Through the usage of finite element analysis, one can study the electromagnetic fields for information that is often difficult to acquire in an experimental test bench. The requirement for accurate result is that the magnetic circuit is modelled in a correct way, which may be more difficult to maintain for rare earth free permanent magnets with an operating range that is more likely to be close to non-linear regions for the relation between magnetic flux density and magnetic field strength. In this paper, the inclination angles of the magnetic flux density, magnetic field strength and magnetization are studied and means to reduce the inclination angles are investigated. Both rotating and linear machines are investigated in this paper, with different current densities induced in the stator windings. By proper design of the pole shoes, one... [more]

In this paper, a sliding mode control is presented for direct torque and stator flux control of interior permanent magnet synchronous motor in a rotor speed sensorless drive system. The control scheme is developed in a specific synchronous rotating reference frame (X-Y) in which the stator current space vector coincides with the direct (X) axis. For this control technique no need to have any knowledge of machine parameters such as stator two-axis inductances, rotor permanent magnets flux linkage, and even the rotor initial position. However, the on-line actual stator resistance value is required to estimate the stator flux components in the stator stationary two-axis reference frame. In this control strategy, two simple methods are described for estimating the rotor speed and stator resistance. Some simulation and experimental results are presented to support the validity and effectiveness of the proposed control scheme.

This paper presents a finite element method (FEM)-based model, which describes the magnetic circuit of the BMW i3 traction machine. The model has been reconstructed based on data available in the public domain. The reader is provided with numerical data regarding flux linkage surfaces in d- and q-axes, as well as with all the information needed to develop a space-vector model of the machine in steady-state, taking into consideration the non-linearity of the magnetic circuit. Hence, the data of a highly-saturated machine from a renowned product are provided, which can serve as a reference design for research. After that, torque curve and partial load operation points are calculated. Finally, the machine model is linearized and the calculations are repeated with the simplified linearized model. The results from both models are then compared with each other. This comparison is intended to assess the magnitude of the expected inaccuracies, when simplified analytical tools are applied to hi... [more]

This paper presents a novel topology of dual airgap radial flux permanent magnet vernier machine (PMVM) in order to obtain a higher torque per magnet volume and similar average torque compared to a conventional PMVM machine. The proposed machine contains two stators and a sandwiched yokeless rotor. The yokeless rotor helps to reduce the magnet volume by providing an effective flux linkage in the stator windings. This effective flux linkage improved the average torque of the proposed machine. The competitiveness of the proposed vernier machine was validated using 2D finite element analysis under the same machine volume as that of conventional vernier machine. Moreover, cogging torque, torque ripples, torque density, losses, and efficiency performances also favored the proposed topology.

In this study, we implemented a depletion (D)-mode gallium nitride high electron mobility transistor (GaN HEMT, which has the advantage of having no body diode) in a class-E amplifier. Instead of applying a zero voltage switching control, which requires high frequency sampling at a high voltage (>600 V), we developed an innovative control method called the minimum power input control. The output of this minimum power input control can be presented in simple empirical equations allowing the optimal power transfer efficiency for 6.78 MHz resonant wireless power transfer (WPT). In order to reduce the switching loss, a gate drive design for the D-mode GaN HEMT, which is highly influential for the reliability of the resonant WPT, was also produced and described here for circuit designers.

This paper compares the energy economy and vertical vibration characteristics of in-wheel drive electric vehicles (IEVs), in-wheel drive electric hydraulic hybrid vehicles (IHVs) and centralized drive electric vehicles (CEVs). The dynamic programming (DP) algorithm is used to explore the optimal energy consumption of each vehicle. The energy economy analysis shows that the IEV consumes more energy than the CEV due to its relatively lower electric motor efficiency, even with fewer driveline components. The IHV consumes much more energy than the IEV and CEV because of the energy loss in the hydraulic driveline. The vertical vibration analysis demonstrates that both IEV and IHV degrade the vehicle driving comfort due to increased unsprung mass. Taking the advantage of high power density of the hydraulic motor, IHV have less unsprung mass when compared with the IEV, which helps to mitigate the vibration problems caused by increased unsprung mass.

In order to expand the speed range for an indirect matrix converter−surface mounted permanent magnet synchronous motor drive (IMC-SPMSM), a wide speed range operation control strategy based on a flux-weakening control and an over-modulation method is proposed in this paper. In the stage of the inverter, an IMC over-modulation method is designed, which increases the fundamental voltage transmission ratio (VTR) to 1. In addition, considering the variation of the voltage limit boundary of the IMC with motor speed, flux-weakening control is implemented based on the voltage error feedback method, which maximizes the voltage utilization rate by setting the endpoint of the output voltage vector on the voltage boundary during the flux-weakening operation. In the stage of the rectifier, over-modulation is automatically switched on or off according to operation requirements by a modulation depth controller. Finally, experimental results show that the proposed strategy increases the maximum speed... [more]

This paper presents a new soft-switching solution recommended for three-level neutral-point-clamped inverters. The operation principles of the proposed solution, working stages, selection of elements, and the control algorithm are comprehensively discussed herein. The control method of the inverter main switches is the same as that of the switches of an inverter operating according to the hard-switching technique. The correctness of the proposed solution was confirmed by the results of different tests using a laboratory neutral-point-clamped inverter with rated parameters of 3 kW, 2 × 150 V, 12 A, and 3 kHz. Numerical analyses were performed for the inverter of rated power 1.2 MW. The switching losses of the inverter operating with the proposed solution were compared with those of an inverter with hard-switching method. The proposed soft-switching solution increased the inverter efficiency and its competitiveness in relation to other proposals because there were no connections between... [more]

This paper presents a multi-objective optimal rotor design for an interior permanent magnet synchronous motor (IPMSM) based on finite element analysis. Due to the importance of torque characteristic in electromagnetic design of IPMSMs, the main efforts of this study are focused on finding a proper trade-off for its torque profile challenges. In this regard, in order to attain high average torque and low torque ripple, the influence of several key factors, such as the permanent magnet (PM) arrangements, PM positions and PM sizes, are examined. Subsequently, according to the outcomes of the performed sensitivity analysis, the appropriate variation interval of the parameters as well as their initial values is determined. Employing such a deterministic optimization algorithm, which does not need large sample points, minimizes the finite element computational cost and leads to accelerate the convergence process. The two-dimensional finite element model (FEM) of an IPMSM is used to perform a... [more]