Volume 67 (2016): Issue 5 (September 2016)

This paper introduces a novel polyphase filter working at high centre frequency using multi-output current differencing transconductance amplifiers (MOCDTAs). The MOCDTA possesses characteristics of low input impedance, high output impedance, wide work frequency and linearly adjustable transconductance. The proposed filter consists of two MOCDTAs, two grounded capacitors, and no resistors. The features of low input impedance and high output impedance make it suitable for cascade. The bandwidth and centre frequency could be adjusted independently by external bias voltage V_C and V_Ca. The image rejection ratio (IRR) could reach 31.6 dB at the centre frequency of 114 MHz, and its bandwidth could be 11.1 MHz. Besides, the centre frequency could be tuned from 38 MHz to 150 MHz with bandwidth of 20.1 MHz. Simulation results which verify the theory are included.

The intent of this paper is to investigate the effect of the interturn short circuit fault (ISCF) in rotor on the magnetic flux density (MFD) of turbo-generator. Different from other studies, this work not only pays attention to the influence of the faulty degrees on the general magnetic field, but also investigates the effect of the short circuit positions on the harmonic components of MFD. The theoretical analysis and the digital simulation through the FEM software Ansoft are performed for a QSFN-600-2YHG turbo-generator. Several significant formulas and conclusions drawn from the analysis and the simulation results are obtained to indicate the relation between the harmonic amplitude of the MFD and the faulty degree (via n_m, the number of the short circuit turns), and the relation between the MFD harmonic amplitude and the faulty position (via α_r, the angle of the two slots in which the interturn short circuit occurs). Also, the developing tendency of the general magnetic field intensity, the distribution of the magnetic flux lines, and the peak-to-peak value of MFD are presented.

This paper presents a new high speed induction motor drive based on the core advantage of field orientation control (FOC) and hysteresis current comparison (HCC). A complete closed loop speed-controlled induction motor drive system is developed consisting of an outer speed and an inner HCC algorithm which are optimised to obtain fast and stable speed response with effective current and torque tracking, both during transient and steady states. The developed model, being speed-controlled, was examined with step and ramp speed references and excellent performances obtained under full load stress. A speed response comparison of the model with the standard AC3 (Field-Oriented Control Induction Motor Drive) of MATLAB Simpower systems shows that the model achieved a rise time of 0.0762 seconds compared to 0.2930 seconds achieved by the AC3. Also, a settle time of 0.0775 seconds was obtained with the developed model while that of the AC3 model is 0.2986 seconds confirming, therefore, the superiority of the developed model over the AC3 model which, hitherto, served as a reference standard.

This paper proposes an adaptive current control method for Hybrid Active Power Filter (HAPF). It consists of a fuzzy-neural controller, identification and prediction model and cost function. The fuzzy-neural controller parameters are adjusted according to the cost function minimum criteria. For this reason, the proposed control method has a capability on-line control clings to variation of the load harmonic currents. Compared to the single fuzzy logic control method, the proposed control method shows the advantages of better dynamic response, compensation error in steady-state is smaller, able to online control is better and harmonics cancelling is more effective. Simulation and experimental results have demonstrated the effectiveness of the proposed control method.

This paper uses a new algorithm namely biogeography based optimization (BBO) intended for the simultaneous placement of the distributed generation (DG) units and the capacitor banks in the distribution network. The procedure of optimization has been conducted in the presence of nonlinear loads (a cause of harmonic injection). The purpose of simultaneous optimal placement of the DG and the capacitor is the reduction of active and reactive losses. The difference in the values of loss reduction at different levels of the load have been included in the objective function and the considered objective function includes the constraints of voltage, size and the number of DG units and capacitor banks and the allowable range of the total harmonic distortion (THD) of the total voltage in accordance with the IEEE 519 standards. In this paper the placement has been performed on two load types ie constant and mixed power, moreover the effects of load models on the results and the effects of optimal placement on reduction of the THD levels have also been analyzed. The mentioned cases have been studied on a 33 bus radial distribution system.

The high power dissipation is one of the most important problems of the z-source inverter (ZSI). By using an appropriate optimization scheme, the losses can be significantly reduced without any negative impact on the other characteristics of the inverter. In this paper, a multi-objective optimization is implemented in order to reduce the ZSI total losses as well as to improve the z-source active power filter (APF) performance. The optimization is focused on the four important objectives including power losses of the Z-source APF, the initial cost of the system components, the voltage and current ripples, and the boost factor of the z-source network. For these purposes, the multi-objective genetic algorithm (MOGA) is employed. The numerical and simulation results are presented to evaluate the optimization performance. The results show that a good balance can be achieved between the switching power losses, the voltage-current ripple levels, the component costs and the boost factor using the optimized parameters.

In this work, an amorphous alloy with the nominal composition of Fe₇₈Si₉B₁₃ was produced by a melt spinning method. Using different velocities of a quenching cooper wheel enabled us to study the influence of quenching rate upon the structural characteristics of the resulting ribbons. Structural features of the samples were checked by Mössbauer spectroscopy and X-ray diffraction. The latter performed in a grazing angle geometry enabled us to explore both sides of the as-quenched ribbons. The onset of crystallization was estimated by differential scanning calorimetry (DSC) measurements. Surface features of the ribbons were examined by Scanning Electron Microscopy (SEM). In order to observe structural relaxation phenomena the samples were annealed below the onset of crystallization at 450 °C for 1 hour in Ar protective atmosphere. Even though the annealed ribbons are still amorphous relevant changes were observed in their hyperfin parameters as derived from Mssbauer spectrometry.

Multi carrier modulation techniques such as MC-CDMA are used in high-speed communication applications. Due to MC-CDMA being a multiuser in technology, the subcarrier quantity allocated per user decreases in case the quantity of active users increases. Consequently, data rates per user are reduced with the increase in the bit error rate (BER). Efficient allocation of subcarriers to users within the system can aid the overcoming of this problem. This study develops a new algorithm for subcarrier allocation and system performance improvement in terms of BER, and data rates in comparison to other algorithms were ensured.

This paper is dedicated to electro-physical characterisation of a GaAs p-i-n structure grown for solar cell applications, which was carried out by light and dark current-voltage (I–V) and Deep Level Transient Fourier Spectroscopy (DLTFS) methods. The conversion efficiency and open-circuit voltage were determined from I–V measurement at 1 and 20× sun light concentrations. Three electron like defects TA_n1, TA_n2, TD_n and one hole like defect TBp obtained by DLTFS measurements were confirmed. The origin of these defect states was stated as native GaAs impurities.

A new type of microwave position sensor is introduced. It is a microstrip stub resonator with slotted ground plane under the stub. It produces frequency-modulated signal with frequency corresponding to covering of the slot in the ground plane. The sensing is performed by sliding the metal plate over the slot. The structure is simple, low fabrication cost and compact. It is without multilayers, coupling, via holes, air bridges, active or discrete components.

A numerical analysis of microstrip meander delay lines is considered. Results of quasi-static and electromagnetic simulations are given. It is shown that when increasing a number of turns and proportionally reducing their length, distortions of a pulse signal in the line are reduced. At the same time, despite structure’s electrical width increase, the agreement between the results of quasi-static and electromagnetic analyses is improved. Thus, it is demonstrated that when designing the microstrip meander delay lines with minimal distortions, the quasi-static analysis is relevant.