The application of wireless power transfer technology in the underwater environment proposes both opportunities and challenges to undersea power feeding. Due to the attenuation of electromagnetic waves in seawater, the distance between transmitter and receiver is always maintained at a minimum value, which results in tight coupling between the transmitter and receiver. The tight coupling condition provides a low impedance loop for high-order harmonic, so the component of the harmonic wave is thus significantly increased and cannot be ignored in the power transmission system. In order to fully utilize the harmonic energy, a fundamental-harmonic dual-channel system was proposed and studied in this paper. Compared with single-channel systems transmitting fundamental wave only, the dual-channel system has higher power transmission capability, while the loss in dual channel system can be less than that of a single-channel system after proper optimization. A 3 kW experiment platform is estab... [more]

This paper presents the design procedure of an electric circuit that can perform the battery state diagnosis and, simultaneously, provide its charging. A fast and embedded impedance measurement method is also proposed; this is based on a broadband current signal excitation on the battery during the constant current charging phase. The proposed solution performs the electrochemical impedance spectroscopy (EIS), which is known to provide useful information about battery chemical−physical property changes due to aging or failure events. To demonstrate the functionalities of the proposed method, the spectroscopy is implemented in the control in the wireless charging system. An EIS charging test is simulated on an equivalent circuit model, which emulates the battery impedance properties in a specified frequency band. Circuit parameters are evaluated by experimental data. According to the obtained results, the proposed method allows us to reach an accurate estimation of the battery state and... [more]

The joint arrangement in rock masses is the critical factor controlling the stability of rock structures in underground geotechnical engineering. In this study, the influence of the joint inclination angle on the mechanical behavior of jointed rock masses under uniaxial compression was investigated. Physical model laboratory experiments were conducted on jointed specimens with a single pre-existing flaw inclined at 0°, 30°, 45°, 60°, and 90° and on intact specimens. The acoustic emission (AE) signals were monitored during the loading process, which revealed that there is a correlation between the AE characteristics and the failure modes of the jointed specimens with different inclination angles. In addition, particle flow code (PFC) modeling was carried out to reproduce the phenomena observed in the physical experiments. According to the numerical results, the AE phenomenon was basically the same as that observed in the physical experiments. The response of the pre-existing joint mainl... [more]

This paper presents a novel method to control sinusoidal distributed winding or sinusoidal back electromotive force (back-EMF) multi-phase permanent magnet (PM) machines under open-circuit fault conditions. In this study, five different fault conditions are considered: single-phase, adjacent double-phase, non-adjacent double-phase, adjacent three-phase, and non-adjacent three-phase open circuit conditions. New current sets for the remaining healthy phase under open-circuit fault conditions are obtained by compensating the direct-quadrature (d-q) axes currents. For this purpose, an iterative method has been used to get the new set of currents. D-q axes currents, due to faulty phase/phases, are shared to the healthy phases to obtain the same d-q axes currents as in the healthy condition. Therefore, the same torque is produced as in the healthy condition. The developed method is simulated in MATLAB/Simulink by using a d-q modelled sinusoidal back-EMF five-phase machine. A vector control b... [more]

In a motor control system, the parameters tuning of speed and position controller depend on the value of the moment of inertia. A new moment of inertia identification scheme for permanent magnet motor system was proposed in this paper. This is an extension of the existing acceleration deceleration methods, which solves the large moment of inertia identification error caused by variable angular acceleration, large calculation error of inertia torque, and large measurement noise in the acceleration process. Based on the fact that the angular acceleration is not constant and the sampling signal is noisy, the integral chain differentiator was used to calculate the instantaneous angular acceleration at any time and suppress the sampling signal noise at the same time. The error function with instantaneous angular acceleration and inertia torque as parameters was designed to estimate the moment of inertia. In order to calculate the inertia torque accurately, viscous friction torque was consid... [more]

Permanent Magnet Synchronous Motor (PMSM) failures are currently widely discussed in the literature, but the impact of these failures on the operation of control systems and the ability to detect selected failures despite the compensating effect of control algorithms being relatively rarely analyzed. The article presents the impact of damage to the stator winding of a PMSM motor on the operation of two frequency control structures, scalar and vector control. The mathematical model of PMSM that takes into account the influence of a different number of shorted turns in the stator winding phase was presented, and its experimental verification was performed. Then, the influence of various degrees of damage to the stator winding on the waveforms of the motor state variables in an open scalar control structure and in a closed field-oriented control structure was analyzed. Based on the analysis of phase currents and rotational speed of the motor as well as the influence of the PMSM motor oper... [more]

Voltage transformers (VTs) are an important element of the measuring system that allows measuring the energy flow in medium and high voltage networks. Additional problems with the accuracy of the measurement introduced by the appearance of sources and nonlinear receivers cause deformation of the voltage shape in the energy system. Due to the high metrological requirements, the design of voltage transformers requires high accuracy (for class 0.2 ΔU ≤ 0.2, phase displacement ≤10 min), which is not possible with the use of analytical methods using approximate models. Therefore, only the application of numerical modeling by the finite element method, taking into account real three-dimensional phenomena, allows achieving high modeling accuracy. The article concerns the phenomenon of the influence of voltage higher harmonics of supply voltage on the accuracy (up to the 100th harmonic) of the measuring inductive voltage transformer (IVT). The applied modeling method takes into account the phe... [more]

Infrared thermography (IRT) has become a commonly applied non-destructive testing method for assessing building envelopes. Like any diagnosis tool, IRT requires an appropriate experience and principle understanding, mainly when the method is used for quantitative analyses. The challenges of the IRT often deal with the dynamic properties of building partitions. Climatic conditions have a certain variability, and the accumulated energy storage in the building components can affect their temperature as well as the calculated thermal performance. This paper aims to analyze how stationary and dynamic regimes of a quantitative IRT test could impact the measured thermal transmittance of heavy multi-leaf walls. Investigation in two European countries with different climatic conditions are reported. In this way, it is discussed which boundary conditions should be guaranteed to provide reliable information about a building envelope using quantitative IRT. In order to check the quality of the mea... [more]

The Dutch Offshore Wind Atlas (DOWA) is validated against wind speed and direction measurements from the Cabauw meteorological mast for a 10-year period and at heights between 10 m and 200 m. The validation results are compared to the Royal Netherlands Meteorological Institute (KNMI) North Sea Wind (KNW) atlas. It is found that the average difference (bias) between DOWA wind speeds and those measured at Cabauw varies for the different heights between −0.1 m/s to 0.3 m/s. Significant differences between DOWA and KNW are only found at altitudes of 10 m and 20 m, where KNW performs better. For heights above 20 m, there is no significant difference between DOWA and KNW with respect to the 10-year averaged wind speed bias. The diurnal cycle is better captured by DOWA compared to KNW, and the hourly correlation is slightly improved. In addition, a comparison with the global European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim and ERA5 reanalyses (used for KNW and DOWA, resp... [more]

Two widely investigated methane hydrate promoters, tetra-n-butyl ammonium bromide (TBAB) and cyclopentane (CP), for methane hydrate formation and dissociation were comparatively investigated in the quiescent reactor at 2.5 °C and 8 MPa. The results indicated that the increase in the mass fraction TBAB decreased the induction time. However, it did not significantly affect the methane uptake. In the presence of CP, the increase in the CP concentration resulted in an increase in the induction time due to the increasing thicknesses of the CP layer in the unstirred reactor. Moreover, the methane uptake was varied proportionally with the CP concentration. The addition of TBAB resulted in a higher methane uptake than that of CP, since the presence of TBAB provided the cavities in the hydrate structure to accommodate the methane gas during the hydrate formation better than that of CP. On the contrary, the presence of CP significantly increased the induction time. Although the methane recovery... [more]

This study analyzed the wind speed data of the met mast in the first commercial-scale offshore wind farm of Taiwan from May 2017 to April 2018. The mean wind speed and standard deviation, wind rose, histogram, wind speed profile, and diurnal variation of wind speed with associated changes in wind direction revealed some noteworthy findings. First, the standard deviation of the corresponding mean wind speed is somewhat high. Second, the Hellmann exponent is as low as 0.05. Third, afternoons in winter and nights and early mornings in summer have the highest and lowest wind speed in a year, respectively. Regarding the histogram, the distribution probability of wind is bimodal, which can be depicted as a mixture of two gamma distributions. In addition, the corresponding change between the hourly mean wind speed and wind direction revealed that the land−sea breeze plays a significant role in wind speed distribution, wind profile, and wind energy production. The low Hellmann exponent is disc... [more]

Boundary conditions of high kinds (fourth and sixth kind) as defined by Carslaw and Jaeger are used in this work to model the thermal behavior of perfect conductors when involved in multi-layer transient heat conduction problems. In detail, two- and three-layer configurations are analyzed. In the former, a thin layer modeled as a lumped body is subject to a surface heat flux on the front side while it is in perfect (fourth kind) or in imperfect (sixth kind) thermal contact with a semi-infinite or finite body on the back side. When dealing with a semi-infinite body in imperfect contact, the temperature solution is derived by means of the Laplace transform method. Green’s function approach is also used but for solving the companion case of a finite body in perfect contact with the thin film. In the latter, a thin layer with internal heat generation is located between two semi-infinite or finite bodies in perfect/imperfect contact. For the sake of thermal symmetry, such a three-layer stru... [more]

Multiphase systems provides benefits compared to three-phase systems, such as improved torque per ampere, high power density, better fault tolerance, lower current per phase (due to power-splitting among a higher number of phases), and lower torque ripple, among others. Depending on the application, the system must meet determined requirements, such as the presence of harmonic content, power losses, and common-mode voltage (CMV) generation. This paper presents a comparative analysis of space vector modulation (SVM) techniques applied to a five-phase voltage source inverter with SiC switches to provide an overview of their performance. The performance of five-phase 2L SVPWM (space vector pulse width modulation), 2L+2M SVPWM, 4L SVPWM techniques, and their discontinuous versions, are analyzed by focusing on harmonic content, power losses, and CMV generation using SiC semiconductor devices. Matlab/Simulink and PLECS simulations are performed to achieve the above mentioned goal. The use of... [more]

In this paper, the design procedure of an electric vehicle (EV) wireless charger is presented. Unlike most of the systems available in the literature, the proposed charging system is regulated from the vehicle side. The on-board electrical circuit automatically adapts the resonant compensation to guarantee compatibility with the primary inverter characteristics and achieve high transmission efficiency without communication between sides. Moreover, the proposed control strategy, used to regulate the secondary full active rectifier (FAR), allows the supply of the the EV battery, maximizing the efficiency during the whole charging process.

Methanol is hygroscopic in a gaseous state and is a promising alternative fuel for internal combustion engines. It is understood that adding water can improve the antiknock performance for spark ignition engines, but this will also affect the flame speed and stability. In this work, laminar flame characteristics of methanol/water/air mixtures were experimentally investigated at a temperature range of 380−450 K, a pressure range of 1−4 bar, and water fractions (vaporous water molar fraction in the water−methanol fuel gas) of 0−40%. The results show that laminar burning velocity increases with temperature but decreases with pressure. The burning velocity decreases linearly with water fraction at a stoichiometric ratio. For rich mixtures and high pressures, the laminar flames tend to be more sensitive to stretch and, thus, more prone to being unstable. Increasing the water fraction can slightly increase the Markstein length. Increasing the initial pressure enhances the general flame insta... [more]

This paper investigates the feasibility of using the three-dimensional omnidirectional inductive channel for power transfer and as a power line communication (PLC) for ground-based vehicle, electric air vehicle, or space applications. The simulation results were performed by the advanced design system software using lumped equivalent circuit model. The power transfer efficiency was determined based on multiport scattering (S)-parameters numerical simulation results while the theoretical channel capacity was calculated based on Matlab software as a function of the coupling coefficient considering an additive white Gaussian noise. Furthermore, the magnetic field distribution was evaluated as function of the misalignment angle θ between the receiver and the three orthogonal transmitters coils.

This study examined the application of high-gradient magnetic separation (HGMS) for recycling of super-paramagnetic polymer adsorbent (MPA), namely, polyvinyl acetate-iminodiacetic acid. The HGMS can be incorporated with the adsorption and desorption processes (ADPs) with fresh or regenerated desorbed MPAs and exhausted adsorbed MPAs, respectively. This combines the permanent magnet’s advantage of low running costs with the easy operation using the solenoid to flush the filter in place. The effects of the inlet concentration of MPA in solution (CLF) and the fluid velocity (v0) or volumetric flow rate (QLF) on the performance of the recovery of MPA via HGMS were assessed. The results indicated that the separation efficiency (η or P0), breakthrough time (tB) and exhaustion time (tE) of HGMS reduce as CLF, as well as v0, increases. Further, the filter saturated capture capacity (σS) of HGMS also decreases with increasing v0. The effect of v0 on tB proportional to 1/v02 is more significant... [more]

The Special Issue “Recent Developments in Building Physics” was established to provide extended outputs from the 4th Central European Symposium on Building Physics that was held in Prague, Czech Republic, on 2−5 September 2019 [...]

In this paper, an application of the recently developed Grasshopper Optimization Algorithm (GOA) for calculation of switching angles for Selective Harmonic Elimination (SHE) PWM in low-frequency voltage source inverter is proposed. The algorithm is based on insect behavior in the food foraging swarm of grasshoppers. The characteristic feature of GOA is the movement of agents is based on the position of all agents in the swarm. This method represents a higher probability of convergence than Particle Swarm Optimization (PSO) Modifications of GOA have been examined regarding their effect on the algorithm’s convergence. The proposed modifications were based on the following techniques: Grey Wolf Optimizer (GWO), Natural Selection (NS), Adaptive Grasshopper Optimization Algorithm (AGOA), and Opposite Based Learning (OBL). The performance of GOA and its modifications were compared with well-known PSO. Areas, where GOA is superior to PSO in terms of probability of convergence, have been shown... [more]

The design and analysis of a permanent magnet synchronous generator (PMSG) are presented. The interior permanent magnet (IPM) rotor was designed asymmetric and with the consequent pole approach. The basis for the design was a series-produced three-phase induction motor (IM) and neodymium iron boron (Nd-Fe-B) cuboid magnets were used for the design. For the partial demagnetization analysis, some of the magnets were extracted and the results are compared with the finite element analysis (FEA).

Concerns about greenhouse gas emissions are a key topic addressed by modern societies worldwide. As a contribution to mitigate such effects caused by the transportation sector, the full adoption of electric mobility is increasingly being seen as the main alternative to conventional internal combustion engine (ICE) vehicles, which is supported by positive industry indicators, despite some identified hurdles. For such objective, power electronics technologies play an essential role and can be contextualized in different purposes to support the full adoption of electric mobility, including on-board and off-board battery charging systems, inductive wireless charging systems, unified traction and charging systems, new topologies with innovative operation modes for supporting the electrical power grid, and innovative solutions for electrified railways. Embracing all of these aspects, this paper presents a review on power electronics technologies for electric mobility where some of the main t... [more]

The in situ hygro-thermal behavior of a wet masonry wall during its drying process is presented in this paper. The considered wall is a part of a basement of a historic building that was subjected to renovation works. The building is located in the City of Łowicz (Poland). The drying process was implemented by applying the thermo-injection method and a novel prototype of the drying device used for this method. The dedicated acquisition system was developed to in situ monitor parameters of the drying process. The air temperature and relative humidity in various locations in the basement, temperatures and moisture contents at several points of the wet wall as well as the electrical parameters of the drying device were registered. Based on variations of the monitored parameters, the hygro-thermal behavior of the wall during drying was studied. After 6 days of drying, the wall temperature in the drying zone was increased to approximately 40−55 °C, while the moisture content was reduced to... [more]

Small sized electric motors providing high specific torque and power are required for many mobile applications. Air gap windings technology allows to create innovative lightweight and high-power electric motors that show low phase inductances. Low inductance leads to a small motor time constant, which enables fast current and torque control, but requires a high switching frequency and short sampling time to keep current ripples and losses in an acceptable range. This paper proposes an optimal torque feedforward control method, minimizing either torque ripples or motor losses, combined with a very robust and computation-efficient modal current feedback control. Compared to well-known control methods based on the Clarke-Park Transformations, the proposed strategy reduces torque ripples and motor losses significantly and offers a very fast implementation on standard microcontrollers with high robustness, e.g., against measurement errors of rotor angle. To verify the accuracy of the propos... [more]

In modern aircrafts, hydraulic or pneumatic actuators have been already replaced with electric counterparts, but the advancement of the inverter and motor technology has made possible that the propulsion system can be powered by electrical sources. These high power requirements can not be efficiently fulfilled by using a typical two level converter; the multi-level converter represents a suitable solution for this application. This paper presents a cascaded H-bridge, a 9-level permanent magnet synchronous motor drive for full electric aircrafts. Harmonic analysis is presented considering different levels of a multi-level inverter. Simulation results and experimental validation with a test-rig confirms the accuracy of the proposed system.

This paper focuses on the matter of cogging torque reduction by combining various methods of cogging torque minimization. Due to the high costs of prototype construction, cogging torque is minimized during the design phase by using numerical methods, while computer simulations are used to find a magnetic circuit arrangement for which the cogging torque has the smallest possible value. Cogging torque occurs as a result of combined impact of the magnetic field of a permanent magnet located at rotor and stator with variable magnetic conductivity depending on an angle of rotation. It is a pulsating torque and occurs permanently during machine operation, impacting the operation of the entire device cooperating with the electric machine and causing vibrations, tension, and noise. It results in braking torque and subsequent power losses and leads to faster wear and tear of machine structural elements. High cogging torque values cause problems with rotational speed adjustment. In the case of e... [more]