In this paper, the oscillation phenomena of the scalar magnetic potential of iron pieces of spoke permanent magnet (PM) machines are analyzed and the effects of the oscillation on the air gap flux and back electro-motive force (EMF) are deeply investigated, especially for flux modulation machines such as vernier and flux switching PM (FSPM) machines. To these ends, the formula of the scalar magnetic potential is derived for a generalized spoke PM structure. It reveals that the oscillation phenomena depend on the slot/pole combination, consequently resulting in different behavior according to the machine types such as vernier and FSPM machines. Next, each core’s potential given as a discrete function is developed into a continuous function of an air gap magneto-motive force (MMF) rotating and oscillating through Fourier series expansion. Making use of the developed MMF and the specific permeance of air gap, the equations of air gap flux density and back EMF are derived, which enable acc... [more]

This paper presents a study on long-distance wireless power transfer (WPT), which formulates the voltage gain in terms of the coupling coefficient between the power transmitting unit (PTU) and the power receiving unit (PRU) coils. It is proposed that maximum power transfer efficiency (PTE) can be reached when maximum voltage gain is achieved under a matching condition between the coil quality factor and the coupling coefficient. In order to achieve maximum power delivered to load (PDL), we need to elevate the input voltage as high as the high breakdown-voltage of gallium nitride (GaN) high-electron mobility transistors (HEMT) along with class E amplifier circuit topology. In order to promote voltage gain, knowledge of the coupling coefficient between two coils including the factors of the coil diameter, wire diameter, coil turns, and the coil resistance are derived. It was observed that a lower coil resistance leads to a reduced parallel quality, which facilitates long-distance wireles... [more]

In recent years, renewable energy (RE) has shown promise as a sustainable solution to the rising energy demand worldwide. Photovoltaic (PV) technology has emerged as a highly viable RE alternative. The majority of PV schemes use specific PV models with specified parameters. This study proposes a PV model with generic specifications, a PV array, a DC/DC converter, a DC/AC inverter, maximum power point tracking (MPPT), and grid synchronization using a feedback control system under the MATLAB/Simulink environment. Various MPPT techniques have been adapted to track the PV’s maximum power point (MPP); however, there are various uncertainties. To address these challenges, this paper presented a perturb and observe (P&O) strategy to track the MPP of PV systems reliably. The MPP of a PV system varies according to meteorological order, such as solar radiation and cell temperature. The MPPT primarily gathers the maximum current and voltage of the PV array and provides them to the load using a bo... [more]

Recent research has shown an increasing interest in wireless power transfer (WPT) technology for drone batteries. The inconvenience of wired charging, especially for drones, is a huge obstacle. In this research project, a WPT platform was proposed by applying four transmitting coils and a single receiving coil. To meet the industrial standards required for transmitter Tx and receiver Rx, a calculation of the parameters was implemented. An H-bridge MOSFET was used as a DC−AC inverter, a bridge diode was used as an AC−DC rectifier, and a Pi low pass filter was added to the receiver circuit design to filter the high-frequency noise. Experimental investigations were conducted to study the maximum power and power efficiency of the coil’s alignment. The focus of this article was to design and fabricate workable multiple-transmitter coils and a single-receiver coil for a wireless power transfer system, in order to charge a 3S LiPo drone’s battery. It not only covers an overview of wireless po... [more]

In this paper, an asymmetric rotor interior permanent magnet (ARIPM) motor with high demagnetization prevention capability and robust torque performance is proposed. The key contribution of this paper lies in two aspects. On the one hand, a novel asymmetric rotor with a shifted magnet axis is proposed to improve the demagnetization prevention capability and torque density. In order to obtain a proper asymmetric rotor topology of the ARIPM motor, the multi-physical performances, especially the PM demagnetization characteristics of five types of PM arrangements, are analyzed. Furthermore, an asymmetric rotor with V- and VV-type PM arrangement is preliminarily designed, considering the multi-physical performance balance and the potentially high anti-demagnetization ability. On the other hand, it is found that the asymmetric rotor structure can not only improve the nominal value of motor performance but also can enhance the resistance to the influence of manufacturing uncertainties. Theref... [more]

Grid-connected converters (GCCs) are used extensively for the integration of DC power sources with AC power sources. However, since it is a complex topic, there are many possibilities for regulating grid-injected currents, as well as different modulation techniques for generating full-bridge PWM voltages. The control techniques are directly related to the type of output filter, as well as to the topology of the converter, since a complex plant can require more sophisticated controllers to keep the system stable, and with good regulation performance. Furthermore, a discussion of the applicability of these converters in weak and very weak grids with high inductance content has recently been growing, which adds a greater degree of complexity to the control structure of the converter. In this brief overview are outlined some topics about topologies, output filters, and control, focusing on the current regulation of grid-connected converters. In addition, a discussion of the main challenges... [more]

This is a conference extension of the paper ‘Investigation on the mature storm cloud’s electric field using long airborne antennas’. The use of vertical antennas (including the VEDs—Vertical Electric Dipoles), lifted up by aerostats to high altitudes without being anchored to the ground, presents numerous advantages in comparison with large terrestrial VLF (Very Low Frequency) antenna structures. A slow-moving floating-earth conductor—a vertical wire antenna—is subjected to intense electrification mechanisms in the atmosphere and inside the cloud layers, producing additional risks for the transmitter and the flight train itself. The electrical potential achieved in this process is, therefore, compared with the flashover voltages over the antenna’s upper fixing point, defining the voltage margins at which the VLF transmitter is able to operate. The electrification processes are also compared to the model based on experimental data on the occurrence of corona discharges over a long, vert... [more]

Many new HVAC power cable installations on wind farms, both on- and offshore, have long lengths. In contrast to traditional power cable connections of a few kilometers, the failures of those systems usually result in much higher repair and unsupplied energy costs. To support the quality assurance of newly installed cable systems as well as to create a sound basis for condition-based maintenance, this paper discusses the technical challenges of the field testing of long-length power cable systems using a damped AC testing method and also discusses the best practical applications for the testing and diagnosis of these wind farm HVAC cable systems.

This paper presents a single-phase transformerless bidirectional power factor corrector (PFC). A capacitor is inserted into a conventional full-bridge PFC by connecting the ac line terminal and a terminal of DC voltage. The functions of this inserted capacitor have two roles: to bypass the common-mode leakage current from the stray capacitor; to form an LCL filter to reduce the inductor current ripple. A hybrid modulation method is employed in this PFC. The unipolar switching scheme is applied to modulate the PFC, which can achieve high efficiency. Meanwhile, an additional modulation is inserted into the blank time of low-frequency switches to decrease the changing speed of the voltage on the inserted capacitor, and to decrease the spike on the inductor current and leakage current. The performance of the PFC is experimentally verified using a 5 kW prototype.

In 1927, the most recognized power theory in the frequency domain was proposed by Budeanu. The second power theory in the frequency domain, which is currently catching a lot of supporters, is the approach proposed by Czarnecki. Both theories have common features in the form of the description of active power and are completely different in terms of the description and interpretation of reactive power. This article presents the possibility of using mutual elements of both approaches: thus, it is possible to interpret the physical meaning of the reactive power (reactive current) proposed by Budeanu and the power before the deformation obtained from the mathematical description.

The total current of dielectrics under DC voltage consists of relaxation current and conduction current, which contains the information about the relaxation polarization and conduction. The time-domain spectrum (TDS) is an effective method to study the dielectric properties of insulating dielectrics. In this paper, the TDS method is also used to study the dielectric properties of the compressed inorganic hexagonal boron nitride (BN) and magnesium oxide (MgO) insulating powders. It is interestingly found that these inorganic insulating powders shows an abnormal TDS, where the current decreases monotonically to a certain level at first and then increases with time while in normal TDS the current decreases monotonically with time and finally reaches a steady value which is conduction current. The experiments verify that the abnormal phenomenon is attributed to the moisture absorption of powders during the testing process, which causes an increase in conductivity and leads to the increasin... [more]

With the growth of the world’s population and faster-developing industries, larger amounts of electric energy are needed [...]

In this paper, different mathematical expressions are derived to compute the residual magnitude of voltage caused by faults along the line and on the bus. Symmetrical and unsymmetrical faults are taken into consideration, and the consequences of the various fault distributions are considered. A new way of assessing a sag is proposed that incorporates the method of fault position and mathematical expression based on sequence currents and voltages. The fault impedance is introduced to obtain a better result. A fast and efficient load flow analysis technique produces quick computational results. In addition, the sag analysis is performed using the bivariate joint discrete probability distribution method that gives a clear idea about the probability of occurrence of sag in a meshed network. The suggested approach is applied in the IEEE 39-bus system and with an existing real-time electrical power distribution system in India.

The urban power distribution system is one of the most complex artificial systems in the world [...]

This paper devises an output-feedback multi-loop positioning technique adopting the speed observer and multi-motor synchronizer, targeting the dual (master and slave) motor elevator system applications, providing the three contributions. First, the order-reduction observer continuously extracts the speed information from the motor position measurement, independent of the system model information. Second, the order-reduction stabilizer accomplishes the speed synchronization tasks for both the master and slave motors. Third, the resultant feedback system guarantees to exponentially recover the desired first-order transfer function from the reference to the actual motor position despite the model-plant mismatches. The prototype elevator system adopting the dual motor experimentally validates the practical advantages of the proposed technique.

In this paper, the theoretical properties of transients in three-phase networks, including the fourth wire and unbalanced source, are systematically investigated by resorting to several analytical tools. First, a Cartesian space vector is introduced to provide the geometrical three-dimensional representation of a three-phase voltage/current transient. It is shown that a voltage/current transient can be always represented as a three-dimensional trajectory leaving one plane (corresponding to the previous steady state) towards another plane (corresponding to the new steady state at the end of the transient). The quantity driving the trajectory from one plane to another is the Park/Clarke zero component. Second, the Clarke transformation is used to study the original three-phase circuit as a superposition of two independent transients: the transient of the Clarke space vectors and the transient of the Clarke zero components. Third, the Park transformation is used to evaluate the dq0 compon... [more]

In this study, we propose the use of a short-distance and fixed-type wireless power transmission transformer via a half-bridge LLC resonant converter. A ceramic insulating layer was used instead of an air gap, meaning that the heat generated from the transformer core and the PCB winding was quickly transferred to the external metal case, with the ceramic insulating layer acting as a heat pipe. In order to stabilize the output voltage, we proposed the use of IR photo tunnel technology, and it was applied to two ceramic insulating layers so that the voltage error signal of the secondary output voltage could be transmitted as light to the primary side. As a result, it was possible to physically separate the primary and secondary sides of the power circuit centering on the ceramic insulating layer. The experiment was carried out with the input voltage of 400 V, the output voltage of 54 V, the maximum output power of 1 kW, and the switching frequency of 1.3 MHz or higher. As a result, the m... [more]

In the high-speed rail industry, the overhead contact line erected along the railroad is used to supply the electricity to the high-speed train via a pantograph on the carbody’s roof. This work attempts to explore the effect of contact line pre-sag on the contact quality between the pantograph and the contact line. A nonlinear finite element approach is implemented to build the overhead contact line system with accurate description of the pre-sag of the contact line. Through a nonlinear solution, the effect of contact line pre-sag on the contact force is analysed with different train speeds and tension classes. The analysis result indicates the feasibility of tuning the pre-sag to improve the interaction performance at a given speed and tension class. In the low-speed range, the change of pre-sag does not have a significant effect on the interaction performance. However, when the speed increases up to a certain value, the effect of pre-sag on the contact force is nonnegligible. The inc... [more]

In this paper, qualitative theoretical derivations, finite element analysis (FEA) and experiments are used to investigate the electromagnetic force (EF) and vibration characteristics of end windings. In contrast to previous studies, this study focuses not only on end winding EF/vibration under normal and radial static air gap eccentricity (RSAGE) conditions, but also for the cases of radial dynamic air gap eccentricity (RDAGE) and radial dynamic static hybrid air gap eccentricity (RHAGE). Firstly, the magnetic flux density (MFD) is derived for normal and radial air gap eccentricity (RAGE) faults, and detailed EF expressions are obtained before and after the RAGE fault. The finite element analysis (FEA) and experimental studies were performed on a four-pole DFIG at a speed of 1500 rpm to verify the proposed theoretical analysis. It is shown that RSAGE only enlarges the EF/end winding vibration and does not introduce new frequency components. RDAGE not only increases EF/end winding vibra... [more]

This work presents a comparative analysis among four power MOSFET technologies: conventional Silicon (Si), Superjunction (SJ), Silicon Carbide (SiC) and Gallium Nitride (GaN), indicating the voltage, current and frequency ranges of the best performance for each technology. For this, a database with 91 power MOSFETs from different manufacturers was built. MOSFET losses are related to individual characteristics of the technology: drain-source on-state resistance, input capacitance, Miller capacitance and internal gate resistance. The total losses are evaluated considering a drain-source voltage of 400 V, power levels from 1 kW to 16 kW (1 A−40 A) and frequencies from 1 kHz to 500 kHz. A methodology for selecting power MOSFETs in power electronics applications is also presented.

Charging and discharging current behavior under high DC electric field in polypropylene (PP) film is closely related to the charge transport and accumulation process, which has an important effect on the electrical insulating properties of PP. In this paper, the dependence of the charging and discharging current of polypropylene films on time and electric field has been comprehensively studied. The results showed that the transient and steady current values of the charging and discharging process increase with the increase of electric field. Dependence of the charging current on the electric field conformed well to the space charge limited current (SCLC) theory with a transition electric field of 270 kV/mm, at which the charge transport changed from ohmic conduction to SCLC conduction. The carrier mobility derived from the discharging current became significantly smaller with increase of the charging electric field. The charge accumulation after discharging was derived from the integra... [more]

The dynamic process of demographic aging is an important reason for the systematic increase in the share of people with reduced mobility in Polish society [...]

This article presents the electric field distribution E and dielectric losses ΔPdiel. in the insulation system of high-voltage cables. Such a system consists of inner and outer semiconductor screens and XLPE insulation. The aim of this study was to compare the values of E and ΔPdiel. between semiconductor screens and XLPE insulation. The objects of the research were high-voltage cables of 110 kV, 220 kV, 400 kV, and 500 kV. The geometrical dimensions of the cables, especially the radii of individual layers of insulation, as well as the electrical properties of the screens and XLPE, were taken from the literature. Semiconductor screens and XLPE insulation were treated as a system of three concentric cylinders. When determining the electric field distribution, both the electrical permittivity and electrical conductivity, which, in the case of semiconductor screens, play important roles, were taken into account. The obtained results prove that both the electric field distribution E and di... [more]

In this article, a new non-inverting buck-boost converter with superior characteristics in both bucking and boosting is presented. The proposed converter has some distinct features, such as high step-up/-down ability and low voltage/current stress on its switching devices. The voltage gain of the proposed converter is double the reported value for the traditional buck-boost converter. Although it has three switches, the three switches operate simultaneously, hence no dead-time is required. Two out of the three switches are under voltage stress equal to half of the output voltage. The overall efficiency of the system is promising because of the ability to select devices with low voltage drops. Converter analysis and steady-state performance in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are presented in detail. A 1 kW hardware prototype of the converter was implemented in the laboratory; with a step-up ratio of 3.5 and 1 kW power, the measured efficienc... [more]

This paper introduces an effective and non-iterative technique for the determination of full lightning impulse voltage parameters in high-voltage tests. In the waveform parameter determination, the base curve parameters are determined on the basis of precomputed models that are utilized to correct the base curve parameters. Using the data from the cases collected from the standard, the correction factors are computed from the deviation of the parameters which are determined by the proposed and standard recommended method. With the accurate base curve parameters, the waveform parameters can be calculated precisely. Because there is no iterative process in the technique, the proposed method has a simplified computational algorithm and becomes an attractive method.