فصلنامه روشهای هوشمند در صنعت برق
پیاپی 15 (پاییز 1392)

In this paper، a second order universal filter with the ability of electronically tuning central frequency (ω0) and quality factor (Q)، based on the inverter as transconductance block which realizes multi-mode responses (voltage، current، transconductance، transresistance) in sub-threshold region، is presented. Biasing transistors in sub-threshold region، reduces the power consumption of the proposed filter and the grounded capacitors are used to reduce the parasitic effects which is another advantage of the proposed filter circuit. Furthermore، low sensitivity of the performance of the proposed filter to the values of gmi، Ci is considered as another advantage of the proposed circuit. In addition، realizing the proposed filter based on the inverter circuit leads to a reduced value of layout area as well as power consumption. Finally، the proposed filter performance is simulated in HSPICE using 0. 18 µm (LEVEL49) CMOS technology parameters. As it is shown in the paper، the proposed filter consumes only 64. 69 nW power in a ±0. 3V supply voltage.

The purpose of this paper is design of a neuro-adaptive controller for SCARA mechanical arm. First، a brief description of the work that has been done on similar systems will be presented and then using the Euler - Lagrange، based on kinetic and potential energy of the system، the dynamical equations of system will be calculated. The proposed controller is used to provide a suitable Lyapunov function، expression and comparative law will guarantee the stability of the closed loop system. All signals in the closed loop system are limited and the error signal tends asymptotically to origin. The control system is designed to demonstrate the efficacy of proposed controller on three links SCARA robot is implemented، the results of the controller performance guarantees.

Syllable، as a sub-word unit، nowadays plays an active role in the field of speech processing and recognition research according to its robust relation to human speech production and cognition. Automatic syllable boundaries detection is an important step forward in the areas of speech prosody، natural speech synthesis and speech recognition. In this paper، a novel method in automatic syllabification of Farsi continuous speech based on acoustic structure is proposed. Our previous studies، showed the proficiency of energy contour fuzzy smoothing method، compared with other prominent works in this area. This paper suggests that the conventional methodology-used in speech enhancement based on wavelet coefficient thresholding would improve syllable segmentation by decreasing insertion error. This process declines the energy in high energy consonants which are responsible for extra peaks in short term energy contour. Experimental results showed that utilizing proposed method along with fuzzy smoothing would diminish insertion error about 8% with no reasonable effect on other efficiency criteria. More than 94% of syllables are automatically segmented using presented technique with less than 50ms error.

Doubly fed induction generator has numerous advantages in wind power generation over other types of generators. Once a DFIG is subjected to a large voltage dip، a large rotor voltage induces in the rotor windings. This leads to a large transient current in rotor circuit and the dc-link overvoltage، and may block power electronic converter operation. This paper first discusses dynamic modeling of DFIG wind turbines with the stator flux orientation. Then، by small signal analysis، it is found that the dynamic behavior of the DFIG based WT during voltage dip، is strongly affected by the stator dynamics. Next، a nonlinear control strategy based on flatness is proposed to improve the DFIG transient performance. The main interest of this control method is the possibility to define the behavior of the state variable system in the steady state as well as in transients. Since the DFIG electrical dynamics are nonlinear; better control performance is achieved with nonlinear control، compared with the linear control scheme. The proposed approach stabilizes the stator dynamics through rotor and grid side filter voltage control. The results of time domain simulations validate the effectiveness the nonlinear control strategy during voltage dip of generator terminal.

Recently image fusion has prominent and applicable roles in medical image processing. Digital subtraction angiography (DSA) image is applied to display map of blood vessels. In this essay، a new fusion algorithm for DSA serial images based on discrete wavelet transform coefficients is proposed. Fusion of high frequency coefficients is based on proposed fusion map and four evaluation criteria which introduce level of coefficient''s energy. Our algorithm will be compared for different wavelet transforms and activity criteria for high frequency coefficients. The comparisons are based on the objective evaluation criteria which show measure of noise existence، sharpness and correlation between the fusion result and reference image. Finally، Meyer discrete wavelet transform is resulted as the best wavelet transform، and sum of modified Laplacian، local energy are introduced as activity level measurment for high and low frequency coefficients in process of brain vessel map extraction.

In this paper، to estimate the rotor position in sensorless BLDC motor drive، the method of the ratio functions line by line flux is used. This method، compared to other methods which are evaluated to estimate the rotor position، has low software volume and therefore، its implementation is easy and also manufacturing cost is less. Also this method has an appropriate efficiency in a wide range of speed and estimate the rotor position is independent of speed and rotor frequency. Also in this paper، the method Direct Torque Control (DTC) is used to design sensorless BLDC motor drive. DTC method is one of the most innovative and efficient methods in control of the electrical machine. High speed response to changes in torque، simplicity of implementation، independence to machine parameters and needs of less computation are the advantages of this method. At the end of this paper، simulation results by using software MATLAB shows good performance of sensorless BLDC motors with DTC method compared to the switching function method.

A new soft-switching resonant inverting-buck converter with high efficiency is presented. The proposed converter steps down and inverts the input voltage. The zero-current-switching (ZCS) technique is employed to reduce switching losses and Electromagnetic Interferences (EMI). An LLC resonant network is utilized to provide soft-switching conditions for all semiconductor devices. Experimental results verify the integrity of the proposed converter operation and the presented theoretical analysis.

In this paper we consider two networks، a primary network and a secondary cooperative communication network. In the secondary network، a source is assisted by cognitive relay nodes which allow it to coexist with the primary network. The secondary users must work under the noise floor of the primary network to achieve low interference for the primary network. Simultaneously، the secondary users should be able to complete their duty. Therefore، the cooperative system utilizes the incremental and selective decode-and-forward (ISDF) relaying protocols. In ISDF protocol، the relay sends signal in necessary situations. Thus، the ISDF cooperative scheme is considered for the secondary network in order to reduce the interference to the primary users. Under some constraints on the transmitting power from the source and relay nodes in the secondary network، they can operate below the noise level of the primary network. Under these constraints، we minimize the symbol error rate of the secondary network. It is seen that in the ISDF protocol the interference produced with the relay to the primary users is very low.