AUT Journal of Electrical Engineering
Year:2017 | Volume:49 | Issue:1|Papers Count:10

Thyristor rectifiers are widely used in electric railways in order to control the speed. As a consequence of their usage in addition to substantial input lead current, an enormous amount of harmonics is injected into the grid. To avoid such harmonics as well as reactive power compensation, reactive power hybrid filters consisting of active and passive filters are utilized. Regarding different passive and active filters connection in a hybrid filter, various configurations of hybrid filters are possible. Each of these configurations has different functionality in harmonic elimination and reactive power compensation. Since electric railway has a non-linear and variable nature, a novel hybrid filter structure is designed that compensates reactive power and eliminates harmonics to attain desired harmonic level regarding the conventional allowable harmonics level standards. The designed filter model is simulated in MATLAB/SIMULINK and then applied to a harmonic model of an electric railway. Since electric railways are single phase loads, specific three-phase to two-phase transformers are required to feed the load. To attain such purpose, an adaptive transformer is utilized in this paper. The proposed model has properly overcome the deficiencies of active and passive filters as well as demonstrating an appropriate performance in the reduction of total harmonic distortion (THD).

Human stress is a physiological tension that appears when a person responds to mental, emotional, or physical chal-lenges. Detecting human stress and developing methods to manage it, has become an important issue nowadays. Auto-matic stress detection through physiological signals may be a useful method to solve this problem. In most of the earlier studies, long-term time window was considered for stress detection. Continuous and a real-time representation of the stress level are usually done through one physiological signal. In this paper, a real-time stress monitoring system is pro-posed which shows the user a new signal for feedback stress level. This signal is the combination of weighted features of galvanic skin response and photoplethysmography signals. The features are defined in 20-sec time windows. Correlation feature selection and linear regression methods are used for feature selection and feature combination, respectively. Furthermore, a set of experiments was conducted to train and test of the proposed model. The proposed model can represent the relative stress level perfectly and has 79% accuracy for classifying the stress and relaxation phases into two categories by a determined threshold.

In this paper, we propose an accurate and fast numerical method to obtain scattering fields from lossy dispersive inhomogeneous planar layers for both TE and TM polarizations. A new method is introduced to analyze lossy inhomogeneous Planar Layers. In this method by applying spline based Galerkin’s method of the moment to scalar wave equation and imposing boundary conditions, we obtain reflection and transmission from the inhomogeneous layer. Moreover, we obtain both electric and magnetic fields in the inhomogeneous layers. The method employs a set of spline-harmonic basis functions and leads to one-dimensional integrals for system matrix elements. This fact along with the higher order nature of the basis functions provides an accurate method for the analysis of the aforementioned dispersive lossy inhomogeneous layers. The accuracy and the convergence behavior of the method are studied through several numerical examples and the results are compared with the exact solutions to establish the validity of the proposed method.

In this paper, an iterative incremental relay selection (IIRS) scheme is considered for wireless cooperative networks in order to increase the reliability of transmission. Different from the conventional incremental relay selection which incrementally selects the best relay for only one iteration; the IIRS scheme iteratively applies the incremental relaying and relay selection processes. To evaluate the performance of the proposed scheme, outage probability and average capacity of the system are investigated through analysis and simulation. This scheme provides (I+1) diversity order in a system of I relays as the highest diversity order which can be provided by all participate (AP) cooperative scheme. Also, it is shown that the IIRS scheme combats with the spectral efficiency loss resulted from applying all of the relays. As the cost of the improvement, it is seen that the average required feedback bits to implement the IIRS scheme leads to I´log2 (I+1) bits of low signal to noise ratio (SNR), while it leads to log2 (I+1) bits at higher SNRs which is acceptable for implementation. Considering the provided improvement along with the limited feedback reveals that the IIRS scheme can be applied as an efficient scheme compared to the other common cooperative schemes. Finally, numerical results indicate the validity of the analysis, especially at high SNRs.

Harmonic analysis has become an important issue in modern power systems. The widespread penetration of non-linear loads into the emergence of power systems has turned power quality analysis into an important operation issue under both steady state and transient conditions. This paper employs a Dynamic Harmonic Domain (DHD) based framework for the dynamic harmonic analysis of VSC-HVDC systems. These systems are widely used in modern power systems in both distribution and transmission levels in order to provide voltage profile improvement, power flow control, and power loss reduction. In this paper, appropriate modeling of VSC-HVDC systems for harmonic propagation is performed by means of switching function which provides a connection between DC and AC sides. Also in this paper, dynamics related to DC side capacitor are taken into account which can greatly affect the transient response. In order to validate the results, the proposed method has been successfully tested on a test system and the obtained results are compared to those of a time-domain software, followed by a discussion on results.

There has been a great resolution calling for smart grids in recent years. The introduction of new technologies that make the network flexible and controllable is the main part of smart grid concept and a key factor to its success. A transmission network as a part of system network has drawn less attention. Transmission switching as a transmission service can release us from load shedding and remove the constraints’ violations. In addition to removing the congestion and decreasing the system cost, transmission switching may damage generating units due to transient states in the instance of reconfiguration. Therefore, in optimal transmission switching, the system security, practical limitations, and possible damages should be considered. Considering dynamic constraints in the proposed model avoids the occurrence of transient instability when opening the line in transmission switching action.A network reduction method based on modified Jacobean AC Newton-Raphson technique power flow considering a switchable line in technique is used for speeding up the calculation, efficiency, and simplicity. An approach for selecting the best lines in switching operation in the network is proposed. Based upon this approach, the lines with the highest effect on cost reduction are considered as the candidate switchable line. To investigate the efficiency of the proposed strategy, IEEE 57 bus test system is studied.

In this paper, a new steganography scheme with high embedding payload and good visual quality is presented. Before embedding process, secret information is encoded as a block using Reed-Muller error correction code. After data encoding and embedding into the low-order bits of the host image, modulus function is used to increase the visual quality of stego image. Since the proposed method is able to embed secret information into more significant bits of the image, it has improved embedding payload. The steps of extracting data from the host image are independent of the original image. Therefore, the proposed algorithm has a blind detection process which is more suitable for practical and online applications. The simulation results show that the proposed algorithm is also able to retrieve destroyed data by intentional or unintentional attacks such as the addition of noise and filtering due to the use of the error correction code. In addition, the payload is improved in comparison with the same techniques.

In this paper, a new integrated model of the dynamic environmental/economic dispatch (DEED) problem and emergency demand response program (EDRP) has been presented by which their interactions are investigated. DEED schedules the online generators power output over the whole dispatch period subject to some practical constraints so that the fuel costs and emission are reduced simultaneously. EDRP is one of the incentive-based demand response programs in which incentives are paid to the customers to reduce their consumption during peak hours or shift it to the off-peak or valley hours. The proposed integrated model is a multi-objective optimization problem which aims to minimize both the fuel costs and emission and determines the optimal incentive of EDRP under some practical constraints of units such as valve-point loading effect, multiple fuels, prohibited operating zones, and spinning reserve requirements. The proposed model has been applied on a ten generation units test system. The results indicate the effectiveness of the integrated model in reducing fuel costs and emission, improving load curve characteristics, spinning reserve, and consequently the network reliability.

In this paper, a miniaturized coplanar waveguide fed (CPW-fed) tapered slot antenna (TSA) is introduced for breast cancer detection. Here, a modified CPW to slot-line transition structure with an air-bridge is employed to broaden the transition bandwidth and increase the radiation efficiency. Through these applied modifications, negative features of the original TSA (limitation of transition) and antipodal Vivaldi antenna (bad cross-polarization) are both removed, while all the positive features remained. We have developed a FDTD-UPML method in lossy environment by using Debye model. To validate the results, a prototype of the proposed antenna is fabricated and tested. By immersing the antenna in alcohol ethanol as a lossy coupling medium and inserting it close to a two-layer breast phantom, near-field parameters are calculated in different probe locations. Results show that the proposed structure offers a broad bandwidth of 0.5–19 GHz and also exhibits an appropriate current distribution with high radiation efficiency. Images of energy flux density (EFD) and fidelity factor (FF) confirm the good performance of the antenna in near-field region.

To reduce the sampling rate in global navigation satellite system (GNSS) -radio occultation receivers, it is essential to establish a suitable estimation of Doppler frequency from the received signal in the satellite onboard receiver. This receiver is usually located on low earth orbit satellite and receives GNSS satellites signal in the occultation situation. The occurred Doppler on the signal contains the Geometric and Atmospheric segments. The Geometric Doppler’s value depends on the orbital situation of transmitter and receiver. However, Atmospheric Doppler depends on the signal propagation environment conditions. To investigate the nature of these two types of doppler, we establish different missions on STK software environment for receivers located on different orbits from 450km altitude to 800km and 1500km with different orbital parameters and by considering the Global Positioning System satellites as the transmitters. We also study the value and nature of the atmospheric doppler by utilizing and analyzing the data produced by the COSMIC Data Analysis and Archive Databases Center. In signal tracking part of the receiver, the variation of Doppler is also important, in addition to the Doppler that is called phase acceleration. Therefore, the derivatives of Geometric Doppler related to the LEO satellites in different altitudes need to be considered.