Time filter

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Rashtian M.,Civil Aviation Technology College | Hashemipour O.,Shahid Beheshti University | Navi K.,Shahid Beheshti University | Jalali A.,Shahid Beheshti University
Journal of Circuits, Systems and Computers | Year: 2011

In this paper, a new switched opamp is presented in order to improve the operation of auto-zeroed switched capacitor circuit. This approach results in a considerable reduction in power consumption and a moderate speed improvement. Based on the above improvement, a second-order band-pass filter with a center frequency of 833 kHz and quality factor of 8 is realized and compared with previous works. The proposed switched opamp is also utilized in the structure of a novel z to -z2 block for the design of pseudo two-path band-pass filters. A second-order pseudo two-path band-pass filter with the same specification of the previous work is designed, simulated, and compared. © 2011 World Scientific Publishing Company.

Effatnejad R.,Islamic Azad University at Karaj | Zare A.,Islamic Azad University at Karaj | Choopani K.,Islamic Azad University at Karaj | Effatnejad M.,Civil Aviation Technology College
2016 International Conference on Industrial Informatics and Computer Systems, CIICS 2016 | Year: 2016

Damping low frequency oscillations of power systems is one of the most important determinants of system stability. Due to the increasing growth of wind farms with high penetration levels in power systems as well as their participation and control, it seems important to increase the damping system oscillations. In this paper, doubly fed induction generators (DFIGs) were used for damping the power oscillations. For this purpose, a fuzzy controller as a power oscillation damper (FPOD) was applied to DFIG control loop as backup control and also input and output scales of fuzzy controller were optimized by particle swarm optimization (PSO) algorithm. The main reason was use this hybrid approach is to enhance disturbance rejection and reduction, through fuzzy systems. In order to clarify the DFIG capability in mitigating the inter-area oscillations, non-linear simulations were carried out by MATLAB/Simulink. Simulation study in a four-machine two-area power system show that the DFIG with a FPOD controller was superior to the conventional POD in terms of stabilizing effect as well as robustness against various power generating and loading conditions, unpredictable network structure, and random wind patterns. © 2016 IEEE.

Rashtian M.,Civil Aviation Technology College | Hashemipour O.,Shahid Beheshti University | Navi K.,Shahid Beheshti University | Jalali A.,Shahid Beheshti University
International Journal of Engineering, Transactions B: Applications | Year: 2010

In this paper, a modified auto zeroed integrator is used to design and simulate a low-voltage high-Q switched capacitor pseudo 2-path filter. The filter is a sixth-order Chebyshev band-pass filter operating at sampling frequency of 1MHz and center frequency of 250 kHz with a quality factor of 50. The proposed filter has both low-voltage and high speed properties of the auto zeroed integrators and accurate center frequency of N-path band-pass filters. The operating voltage is 1.5v with no use of voltage bootstrapper circuit. Simulation is done using HSPICE and 0.25μm CMOS technology.

Mashreghi A.R.,University of Yazd | Saberifar S.,Iran Alloy Steel Company IASCO | Hejazi S.J.,Civil Aviation Technology College
Journal of Failure Analysis and Prevention | Year: 2013

In this study, the fracture of a locomotive engine oil pump shaft is investigated. According to the reports, all oil pump shafts of this type fail in short periods of time due to the fracture at a location on the shaft which is in contact with a pinion. Stress analysis showed that the shaft bears torsion and cyclic bending stresses in the fracture site. The fracture surface observations revealed that the cracks are generated from the surface, and fatigue fracture occurs due to the cyclic bending stresses. According to the laboratorial analysis, the shaft is a surface-hardened low alloy steel. The lack of suitable pre-heat treatment and surface hardening and the roughness created by the slippage between the shaft and the pinion are concluded to be responsible for the failure of the oil pump shaft. © 2013 ASM International.

Rashtian M.,Civil Aviation Technology College | Hemmatyar A.M.A.,Sharif University of Technology | Hashemipour O.,Shahid Beheshti University
International Journal of Electronics | Year: 2012

Thermal noise is one of the most important challenges in analogue integrated circuits design. This problem is more crucial in switched-capacitor (SC) filters due to the aliasing effect of wide-band thermal noise. In this article, a new simple method is proposed for estimating the power spectrum density of output thermal noise in SC filters, which have acceptable accuracy and short running time. In the proposed method, first using HSPICE simulator, accurate value of accumulated sampled noise on sampler capacitors in each clock state is achieved. Next, using difference equations of the SC filter, frequency response of the SC filter is shaped by time domain analysis. Based on the proposed method, a SC low-pass filter and a second-order SC band-pass filter are analysed. The results are validated by comparing to the previously measured data. © 2012 Copyright Taylor and Francis Group, LLC.

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