فصلنامه روشهای هوشمند در صنعت برق
پیاپی 19 (پاییز 1393)

In this paper, a low voltage and low power (LV/LP) Operational Transconductance Amplifier (OTA) using FGMOS (Floating-Gate MOS) transistor is proposed. The relative tuning range of 50 is achieved in this OTA while only consumes 40 µW with 1.0 V supply voltage in TSMC 0.18 µm CMOS technology. The simulation results of the proposed OTA show an open loop gain of 30.2 dB and a unity gain frequency of 942 MHz. In comparison with previous works, the proposed OTA, with lower supply voltage, is provided the better frequency performance, higher output voltage swing, better linearity and lower power consumption. The proposed OTA is used in the second-order  filter to show a good tuning range from 100 kHz to 5.6 MHz which is suitable for the wireless specifications of Bluetooth (650 kHz),CDMA2000 (700 kHz) and Wideband CDMA (2.2 MHz). The active area occupied by the designed filter on silicon is .

Reliable and efficient spectrum sensing plays an important role in cognitive radio networks. On the other hand, accurate and fast sensing of spectrum is the main function of a cognitive radio for cognitive users to avoid harmful interference in licensed users. However, detection performance issues are often shadowing, fading and receiver uncertainty. To mitigate the impact of these issues, cooperative spectrum sensing as an effective method is presented to improve the detection performance with help of spatial diversity. Cooperative spectrum sensing leads to CR detection performance improvement. In order to execute the cooperative spectrum sensing among cognitive radio users, data fusion schemes are superior to that of decision fusion ones in terms of the detection performance but suffer from the disadvantage of huge traffic overhead when bandwidth constraint of communication channels is taken into account. The overhead contains additional sensing time, delay, energy and sensing actions dedicated to cooperative sequential sensing any also contains any performance degradation that is caused by cooperative sensing. The purpose of this paper is reviewing of the cooperative sensing techniques with sequential methods. The simulation results show that with reducing the number of examined samples, the sensing time and the energy will be reduced and as the result, the overhead will be reduced.

This paper is concerned with network based leader following consensus for a distributed multi agent system with interval time varying delays in the presence of uncertainty and disturbances. A network based consensus control protocol under a directed graph is proposed. The nonlinear time varying coefficients derived from Jenson's integral inequality is approximated with an estimation method. Finally with convex combination, less conservative stability criteria are provided. In this method, the output feedback H∞ control is proposed to leader following consensus and robust stability of the closed loop system. In the presence of uncertainty and disturbances in the system, using H∞ control along with dynamic output feedback controller has led to better results in tracking the reference signal. This study provides H∞inf stability criteria in the forms of linear matrix inequalities (LMIs) and convex programming standard form. Numerical examples are given to show the effectiveness of the obtained theorems and results.

In this paper, robust text-independent speaker recognition is taken into consideration. The proposed method performs on manual silence-removed utterances that are segmented into smaller speech units containing few phones and at least one vowel. The segments are basic units for long-term feature extraction. Sub-band entropy is directly extracted in each segment. A robust vowel detection method is then applied on each segment to separate a high energy vowel that is used as unit for pitch frequency and formant extraction. By applying a clustering technique, extracted short-term features namely MFCC coefficients are combined with long term features. Experiments using MLP classifier show that the average speaker accuracy recognition rate is 97.33% for clean speech and 61.33% in noisy environment for -2db SNR, that shows improvement compared to other conventional methods.

Nowadays, the control of mechanical systems with fewer inputs than outputs (Under-actuated systems) has become a challenging problem for control engineers. Two-wheeled balancing robots is one of the appealing examples of this category. This type of robot contains two parallel wheels and an inverted pendulum. In this research, designing of controller have been investigated for flat surfaces. For controller design, the extract dynamics of the system has been achieved based on Kane's method. Then for the two-wheeled balancing robot, one sliding mode controller has been designed for yaw angle, and another sliding mode controller has been designed to control both position and pitch angle based on a proposed sliding surface. The main feature of the proposed controllers is that all of controllers have been designed based on the nonlinear dynamics of system. Also, considering the limits of uncertainties while designing systems, the robustness of controllers have been increased. The common problem of sliding mode control is chattering phenomenon that has been greatly reduced using saturation function instead of sign function. Simulation results comparision of the designed controller with a LQR controller, validates the effectiveness of the proposed controller.

Recently to eliminate the harmonics and improve the power factor of the power networks, much attention has been attracted to active filters. The advantages of these filters are lower volume and their better compensating characteristics than the passive filters. In conventional sliding mode controllers, the source current waveform is fluctuated in near to zero values. In this paper, using a new sliding technique, lower Total Harmonic Distortion (THD) in source current is obtained and the current waveform is improved. As well as, two novel control strategies for two types of active filters, VSI and CSI is proposed and then these two types of filters are compared to reduce THD value of source current.The proposed controlled strategies are simulated by MATLAB/Simulink. The Simulation results confirm that the proposed strategies reduce the THD of source current more than other strategies, and active filter based on CSI has a better performance than active filter based on VSI with a dead time area (for avoiding short circuit of the source) in high powers.

In this paper we presents a soft switch sepic, flyback converter. At first the converter have hard switching in main switch and completely analysis then added auxiliary circuit for soft switching Auxiliary circuit in the converter is not only soft switching condition for the main switch but also prevents the spike voltage across the main switch when turned off that because leakage inductance. Therefore, the proposed converter efficiency in comparison with the previous converters increased and voltage stress on the main switch is reduced. Also the auxiliary switch in the converter have soft switching and thereby decrese losses. this converter Control with pwm.These converter have higher efficiency than the similar converters and the cost is low. Auxiliary circuit in the converter is not only soft switching condition for the main switch but also prevents the spike voltage across the main switch when turned off that because leakage inductance. Therefore, the proposed converter efficiency in comparison with the previous converters increased and voltage stress on the main switch is reduced.

In modern and big greenhouses, it is necessary to measure several climate parameters to automate and control the greenhouse properly. Monitoring and transmitting by cable may lead to an expensive and stiff measurement system. Since, Wireless Sensor Network (WSN) is a distributed system that consists of small-size wireless sensor nodes equipped with radio and one or several sensors; it is a low cost option to build the required monitoring system. In this paper, we introduce and implement an intelligent monitoring system based on WSN by using Xbee modules. The Xbee Series 2 hardware uses a microchip from Ember Networks that enables several different flavors of standards-based ZigBee mesh networking. All gathered information by sensors, are sent to a remote center in form of GPRS packets through a GSM network and viewed by monitoring software. The proposed system has low power consumption, low cost and simple driver circuits. Furthermore, it can support various types of digital and analog sensors