Most receiving antenna arrays suffer from the mutual coupling problem between antenna elements, which can critically influence the performance of the array. In this work,
a novel and accurate form of compensation matrix is applied to compensate the mutual coupling in a uniform linear array (ULA). This is achieved by applying a new method
based on solving a boundary value problem for the whole ULA. In this method, both self and mutual impedances are exploited in an accurate characterization of mutual impedance
matrix which results in a perfect mutual coupling compensation method, and hence a very accurate direction of arrival (DOA) estimation. In the new scheme, the compensation ma-
trix is obtained by using the relationship between measured voltage and theoretical coupled voltage based on the MOM. Numerical results show that using DOA estimation algorithms
to the decoupled voltage obtained by using this method leads to an excellent performance of DOA estimation with higher accuracy and resolution.
Nowadays, the development of smart grids has been the focus of attention due
to its advantages for power systems. One of the aspects of smart grids defined by using
distributed generation (DG) in a low voltage network is a microgrid (MG). Based on its
operational states, MG can operate in different configurations such as grid-connected mode
or off-grid mode. The switching between these states is one of the challenging issues in
this technical area. The fault currents in different buses have higher value compared to
islanded mode of MG when the MG is connected to the main grid, which influences the
protection equipment. In this situation, some electrical devices may be damaged due to the
fault currents. Application of a fault current limiter (FCL) is considered as an effective way
to overcome this challenge. The optimal size of these FCLs can optimize the performance
of an MG. In this paper, an index for FCL size optimization has been used. In addition,
two optimization algorithms (Bat Algorithm and Cuckoo Search Algorithm) have been
applied to the problem. The application of an FCL has been studied in grid-connected and
islanded-mode. In addition, the application of the capacitor bank in both modes has been
investigated. The results of simulations carried out by MATLAB have been presented and
compared.
This paper presents simulation and experimental results obtained with a Dead-Beat predictive current controller for a Permanent Magnet Synchronous Machine (PMSM)
drive system. With means of combined field and circuit simulations, an efficiency map and required current in a direct- and quadrature-axis are defined. A control algorithm was
implemented within an open-interface inverter from Texas Instruments. Dynamic response for both axis currents was defined and verified as well as current ripples for different set
currents in the quadrature axis.
This paper presents an enhanced internal model control (EIMC) scheme for a time-delayed second order unstable process, which is subjected to exogenous disturbance
and model variations. Even though the conventional internal model control (IMC) can provide an asymptotic tracking response with desired stability margins, the major limitation
of conventional IMC is that it cannot be applied for an unstable system because a small exogenous disturbance can trigger the control signal to grow unbounded. Hence, modify-
ing the conventional IMC structure to guarantee the internal stability, we present an EIMC scheme which can offer better trade-off between setpoint tracking and disturbance rejec-
tion characteristics. To improve the load disturbance rejection characteristics and attenuate the effect of sensor noise, we solve the selection of controller gains as an H¥ optimization
problem. One of the key aspects of the EIMC scheme is that the robustness of the closed loop system can be tuned via a single tuning parameter. The performance of the EIMC
scheme is experimentally assessed on a magnetic levitation plant for reference tracking application. Experimental results substantiate that the EIMC scheme can effectively coun-
teract the inherent time delay in the model and offer precise tracking, even in the presence of exogenous disturbance. Moreover, by comparing the trajectory tracking performance of
EIMC with that of the proportional integral velocity (PIV) controller through cumulative power spectral density (CPSD) of the tracking error, we show that the EIMC can offer
better low frequency servo response with minimal vibrations.
A solar photovoltaic (PV) system has been emerging out as one of the greatest potential renewable energy sources and is contributing significantly in the energy sector. The PV system depends upon the solar irradiation and any changes in the incoming solar irradiation will affect badly on the output of the PV system. The solar irradiation is location specific and also the atmospheric conditions in the surroundings of the PV system contribute significantly to its performance. This paper presents the cumulative assessment of the four MPPT techniques during the partial shading conditions (PSCs) for different configurations of the PV array. The partial shading configurations like series-parallel, bridge link, total cross tied and honeycomb structure for an 8×4 PV array has been simulated to compare the maximum power point tracking (MPPT) techniques. The MPPT techniques like perturb and observe, incremental conductance, extremum seeking control and a fuzzy logic controller were implemented for different shading patterns. The results related to the maximum power tracked, tracking efficiency of each of the MPPT techniques were presented in order to assess the best MPPT technique and the best configuration of the PV array for yielding the maximum power during the PSCs.
Nowadays, non-integer systems are a widely researched problem. One of the questions that is of great importance, is the use of mathematical theory of a non-integer
order system to the description of supercapacitors (capacitors with very high capacitance). In the description of electronic systems built on a microscale, there are models with dis-
tributed parameters of fractional derivatives, which can be successfully approximated by finite-dimensional structures, e.g, in the form of various types of ladder systems (chain). In
this paper, we will analyze a ladder system of an RC type consisting of supercapacitors.
This paper presents an analytical model of a three-phase axial flux coreless generator excited by permanent magnets, with special focus on determining the model pa-
rameters. An important aspect of this model is the derivation of a coefficient that corrects the flux on the inside and outside edges of the magnets. The obtained parameters are ver-
ified by performing field analyses and measurements. A comparison of the results show satisfactory convergence, which confirms the accuracy of the proposed analytical model.
The paper presents a phenomenon of directional change in the case of a LQR controller applied to multivariable plants with amplitude and rate constraints imposed on
the control vector, as well as the impact of the latter on control performance, with the indirect observation of the windup phenomenon effect via frequency of consecutive resat-
urations. The interplay of directional change of the computed control vector with control performance has been thoroughly investigated, and it is a result of the presence of con-
straints imposed on the applied control vector for different ratios of the number of control inputs to plant outputs. The impact of the directional change phenomenon on the control
performance (and also on the windup phenomenon) has been defined, stating that performance deterioration is not tightly coupled with preservation of direction of the computed
control vector. This conjecture has been supported by numerous simulation results for different types of plants with different LQR controller parameters.
A novel in-phase disposition (IPD) SPWM pulse allocation strategy applied to a cascaded H-bridge (CHB) converter is presented in this paper. The reason causing the
power of the CHB converter imbalance is analyzed according to the traditional structure, the conception of power imbalance degree is introduced and the principle of the novel
in-phase disposition SPWM allocation strategy is deduced in detail. The new pulse allocation scheme can ensure the power balance in 3/4 cycles through interchanging the PWM
pulse sequence of the different CHB cell, meanwhile it makes the full advantage of the IPD control strategy, lower the total harmonic distortion (THD) of line voltage compared
to a carrier phase shifted (CPS) control strategy, which is verified by theoretical derivation. A seven-level cascaded inverter composed by three H-bridge cells is taken as the exam-
ple. The simulation and experiment is performed. The results indicate the validity of the analysis and verify the effectiveness of the proposed SPWM allocation strategy.
This paper proposes a new dc-side active filter for wind generators that combines 12-pulse polygon auto-transformer rectifier with dc-side current injection method
and dual-buck full-bridge inverter having not the “shoot-through” problem in conventional bridge-type inverters, and therefore this system with the character low harmonic distortion
and high reliability. The proposed dc-side active filter is realized by using dual-buck full bridge converter, which directly injects compensation current at dc-side of two six-pulse
diode bridges rectifiers. Compared with the conventional three-phase active power filter at ac-side, the system with the dc-side active filter draws nearly sinusoidal current by shaping
the diode bridges output current to be triangular without using the instantaneous reactive power compensation technology, only using simple hysteretic current control, even though
under load variation and unbalanced voltage disturbances, and while an acceptable linear approximation to the accurate waveform of injection current is recommended. The perfor-
mance of the system was simulated using MATLAB/Simulink, and the possibility of the dc-side active filter eliminating current harmonics was confirmed in steady and transient
states. The simulation results indicate, the system has a total harmonic distortion of current reduced closely to 1%, and a high power factor on the wind generator side.
The paper presents an identification procedure of electromagnetic parameters for an induction motor equivalent circuit including rotor deep bar effect. The presented proce-
dure employs information obtained from measurement realised under the load curve test, described in the standard PN-EN 60034-28: 2013. In the article, the selected impedance
frequency characteristics of the tested induction machines derived from measurement have been compared with the corresponding characteristics calculated with the use of the adopted
equivalent circuit with electromagnetic parameters determined according to the presented procedure. Furthermore, the characteristics computed on the basis of the classical machine
T-type equivalent circuit, whose electromagnetic parameters had been identified in line with the chosen methodologies reported in the standards PN-EN 60034-28: 2013 and IEEE
Std 112TM-2004, have been included in the comparative analysis as well. Additional verification of correctness of identified electromagnetic parameters has been realised through
comparison of the steady-state power factor-slip and torque-slip characteristics determined experimentally and through the machine operation simulations carried out with the use of
the considered equivalent circuits. The studies concerning induction motors with two types of rotor construction – a conventional single cage rotor and a solid rotor manufactured from
magnetic material – have been presented in the paper.
Partial discharges (PD) are influencing electrical insulating systems of high voltage electrical devices. Typically, in laboratory and diagnostics AC tests focused on
measuring and analysis of PD, a pure sinusoidal voltage waveform is assumed. However, in practice the spectral content of the working voltage is rarely so ideal and additional
spectral components have a significant impact on the discharge behaviour in electrical insulation systems. In this paper the influence of voltage harmonics on PD behaviour and
phase-resolved PD patterns evolution is analysed. The presented experiments were conducted on a specimen representing a gaseous inclusion embedded in electrical insulation.
The experimental results showed that various harmonic compositions superimposed on the fundamental sinusoidal waveform have a significant impact on PD intensity and maximum
charge. In consequence, the derived patterns of PD phase, and magnitude distributions are distorted, and statistical parameters calculated on their basis are changed. In certain en-
vironments, neglecting harmonic content in the testing voltage may lead to a misleading interpretation and assessment of PD severity.
Finding the most critical contingencies in a power system is a difficult task as multiple evaluations of load and generation scenarios are needed. This paper presents
a mathematical formulation for selecting, ranking, and grouping the most critical N-1 network contingencies, based on the calculation of a Power Constraint Index (PCI) obtained
from the Outage Transfer Distribution Factors (OTDF). The results show that the PCI is only affected by the impedance parameter of the transmission network, the topology, and
the location of all generators. Other methods, such as the Performance Index (PI) and the Overload Index (OL) are affected by the power generation and demand variations. The
proposed mathematical formulation can be useful to accelerate the calculation of other methods that evaluate contingencies in power system planning and operation. Furthermore,
the fast calculation of indices makes it suitable for online evaluation and classification of multiple events considering the current topology. The results showed that the proposed al-
gorithm easily selected and ranked the expected contingencies, with the highest values of the index corresponding to the most critical events. In the filtering process, the computa-
tional calculation time improved without losing the robustness of the results.
Author presents an analytical method of calculation of unit power losses
in magnetic laminations used in electrical machines and transformers. The
idea of this method, based on the solution of Maxwell's equations in the
lamination material, was described by the author in the previous work [3],
taking into account approximation of constitutive static hysteresis loop
by elliptic form of the function B = f(H) depending on magnetic
saturation. In the previous formula for new isotropic and anisotropic
materials it is needed to introduce so called "anomaly coefficient"
deduced from the comparison of measured and calculated value of power
losses in arbitrary excitation frequency for assumed induction. The method
was tested by comparison with the results of experiments presented in
commercial catalogues [1, 2]. Assuming superposition of harmonic power
losses it is possible to enlarge this method for the estimation of
overloss coefficient in dynamo sheet during axial magnetization with
nonsinusoidal flux generated e.g. by PWM voltage supply.
The article describes a shock safety modeling method for low-voltage
electric devices, based on using a Bayesian network. This method allows
for taking into account all possible combinations of the reliability and
unreliability states for the shock protection elements under concern. The
developed method allows for investigating electric shock incidents,
analysing and assessing shock risks, as well as for determining criteria
of dimensioning shock protection means, also with respect to reliability
of the particular shock protection elements. Dependencies for determining
and analysing the probability of appearance of reliability states of
protection as well as an electric shock risk are presented in the article.
This work presents the co-simulation approach to the analysis of control
systems containing detailed models of electromagnetic and
electromechanical converters. In this method of analysis the attention is
paid to the whole system and not only to its electromagnetic part. The
latter is described by equations resulted from the two-dimensional finite
element discretisation of the Maxwell equations, and is coupled weakly
with the remaining part of the system. The simulation is carried out in
Matlab/Simulink environment wherein the coupling is realised through the
S-function. Example results regarding simulation of the operation of the
control system of an electrical machine and the operation of a power
electronic converter are presented and compared with available reference
data.
A role of radial corona current in a lightning discharge is discussed in
the paper. It is shown that the corona current concept previously
introduced by Cooray for lightning return stroke models of
distributed-current-source (DCS) type, and later, by Maslowski and Rakov
for lumped-current-source (LCS) type models enables to show duality
between these two types of models. Further, it is demonstrated that the
corona current is useful during consideration of dynamics of the
lightning-channel corona sheath. As an example of application of presented
approach a relaxation model of charge motion in the corona sheath is
analysed together with plots which show the rate of expansion and
shrinkage of the lightning corona sheath on both microsecond and
millisecond time scales.
Description of program tools simplifying simulation applications building
for physical phenomenons described by differential equations in state
equations form modeling is presented in the paper. A method for using
prepared libraries for squirrel-cage motors including any motor damages
modeling had been described. For that purpose, squirrel-cage motor
mathematical model in natural coordinates system had been presented.
Presented solutions provide also supply sources (inverters) modeling,
including their microprocessor implementation and other phenomenons, that
assume state equation structure step changes, depending on variable
limitations and time value.
This research presents a method for the simulation of the
magneto-mechanical system dynamics taking motion and eddy currents into
account. The major contribution of this work leans on the coupling the
field-motion problem considering windings as the current forced massive
conductors, modelling of the rotor motion composed of two conductive
materials and the torque calculation employing the special optimal
predictor combined with the modified Maxwell stress tensor method. The 3D
model of the device is analysed by the time stepping finite element
method. Mechanical motion of the rotor is determined by solving the second
order motion equation. Both magnetic and mechanical equations are coupled
in the iterative solving process. Presented method is verified by solving
the TEAM Workshop Problem 30.
In this paper, the power factor correction system consisted of: bridge
converter, parallel resonant circuit, high frequency transformer, diode
rectifier and LFCF filter is presented. This system is controlled by a
pulse density modulation method and the principle of its operation is
based on the boost technique. The modeling approach is illustrated by an
example using AC/HF/DC converter. Verification of the derived model is
provided, which demonstrated the validity of the proposed approach.
This paper addresses the state-variable stabilising control of the power
system using such series FACTS devices as TCPAR installed in the tie-line
connecting control areas in an interconnected power system. This
stabilising control is activated in the transient state and is
supplementary with respect to the main steady-state control designed for
power flow regulation. Stabilising control laws, proposed in this paper,
have been derived for a linear multi-machine system model using direct
Lyapunov method with the aim to maximise the rate of energy dissipation
during power swings and therefore maximisation their damping. The proposed
control strategy is executed by a multi-loop controller with frequency
deviations in all control areas used as the input signals. Validity of the
proposed state-variable control has been confirmed by modal analysis and
by computer simulation for a multi-machine test system.
The paper presents a formula useful for prediction of loss density in
soft magnetic materials, which takes into account multi-scale energy
dissipation. A universal phenomenological P(Bm, f) relationship is used
for loss prediction in chosen soft magnetic materials. A bootstrap method
is used to generate additional data points, what makes it possible to
increase the prediction accuracy. A substantial accuracy improvement for
estimated model parameters is obtained in the case, when additional data
points are taken into account. The proposed description could be useful
both for device designers and researchers involved in computational
electromagnetism.
The purpose of that paper is to develop of unified equations of
electromechanical energy converters accounting for the magnetic
non-linearity of the main magnetic circuit of a converter. The concept of
applying higher order forms of winding currents for the description of the
co-energy function is introduced in order to derive the structure of
converter equations via mathematical analysis. Also, another concept of
equivalent magnetizing currents is applied to determine the higher order
forms for selected converters designs. The structure of circuital
equations for converters with multiple windings has been unified by means
of the introduction of matrices of dynamic and nonlinear inductances
following the higher order forms of the co-energy function.
An extension of the modified Jiles-Atherton description to include the
effect of anisotropy is presented. Anisotropy is related to the value of
the angular momentum quantum number J, which affects the form of the
Brillouin function used to describe the anhysteretic magnetization.
Moreover the shape of magnetization dependent R(m) function is influenced
by the choice of the J value.