فصلنامه روشهای هوشمند در صنعت برق
پیاپی 24 (زمستان 1394)

This paper Analytically investigates the effects of system and controller parameters and operating conditions on the dynamic and transient behavior of wind turbines (WTs) with doubly-fed induction generators (DFIGs) under voltage dips and wind speed fluctuations. Also, it deals with the design considerations regarding rotor and speed controllers. The poorly damped electrical and mechanical modes of the system are identified, and the effects of system parameters, and speed/rotor controllers on these modes are investigated by modal and sensitivity analyses. The results of theoretical studies are verified by time domain simulations. It is found that the dynamic behavior of the DFIG-based WT under voltage dips is strongly affected by the stator dynamics. Further, it is shown that the closed loop bandwidth of the rotor current control, rotor current damping, DFIG power factor and the rotor back-emf voltages have high impact on the stator modes and consequently on the DFIG dynamic behavior. Moreover, it is shown that the dynamic behavior of DFIG-based WT under wind speed fluctuation is significantly dependent on the bandwidth and damping of speed control loop.

Edge detection is one of the most important issues in image processing and machine vision. Edge detection in image processing is a low order process, so that the performance of the higher order processes such as object identification, segmentation and coding of images is directly related to the efficiency of this process. The estimation of edge parameters with using gradient vector calculation is usually not accurate. Keeping the structure of edge is one of the most important problems in edge detection, especially in detecting noisy images. For practical applications that accurate edges are needed, subpixel edge detection is done. In this paper a new edge detection method based on edge figure and obtained model from neighboring pixels effect and spatial relation of image pixels is introduced. Then an iterative restoration process based on presented edge detector is suggested. The purpose of this method is to increase the accuracy in recognition of subpixel position, curvature, orientation and change in intensity in noisy images.

In this paper a compound boost- sepic converter with soft switching for high voltage application is proposed. One of the advantages of this converter is that, the main switch is turned on under the ZCS condition without need to any auxiliary switch so we have lower switching loss. In order to increase the voltage gain in this topology, a boost converter used in series with the output stage of sepic converter, therefore the output voltage of boost converter added to the output voltage of sepic converter and the voltage gain has been increased. Also a coupled inductor has been used in the boost converter topology which leads to a further increase in the voltage gain of the converter. In order to evaluate the operation of the proposed converter, simulation results and analysis of converter operational modes are presented. In addition, experimental results are presented for a typical boost-sepic converter. These results verify the proper operation of proposed converter.

In this paper, lift and drag forces of permanent-magnet electrodynamic suspension (PMEDS) System have been studied by considering the skin effect. Electrodynamic suspension is based on repulsive force between two magnetic fields with the same polarity. In this research the electrodynamic suspension system consists of a moving permanent magnet block levitated over a flat conducting plate with 2 mm thickness. At first, the analytical model of the PMEDS is proposed. For this propose, permanent magnet poles are modeled by the current sheets. Then the eddy current is calculated on aluminum sheet by considering the skin effect. Finally, the lift and drag forces are calculated in difference speed. The 2D finite element method is utilized to investigate the effect of speed variations on the performance of PMEDS at two different airgap. Two-dimensional finite element model, the accuracy of proposed analytical model is validated. The results of the finite element method are compared with results obtained by analytical model. It shows the accuracy of the analytical model in the estimation of the lift and drag forces of an electrodynamic suspension system.

Quality of Service (QoS) provisioning is very important in next computer/communication networks because of increasing multimedia services. Hence, very investigations are performed in this area. Scheduling algorithms effect QoS provisioning. Lately, a scheduling algorithm called Regulated Burst Service Scheduling (RBSS) suggested by author in [1] to provide a better service to bursty and delay sensitive services such as video. One of the most significant feature in RBSS is considering burstiness of arrival traffic in scheduling algorithm. In this paper, an upper bound of queue length or buffer size and service curve are calculated by Network Calculus analysis for RBSS. Because in RBSS queue length is a parameter that is considered in scheduling arbitrator, analysis results a differential inequality to obtain service curve. To simplify, arrival traffic is assumed to be linear that is defined in the paper clearly. This paper help to analysis delay in RBSS for different traffic with different specifications. Therefore, QoS provisioning will be evaluated.

In this paper, a new single-chip MEMS capacitor microphone on a silicon wafer by minimizing the size and the reduction of mechanical strength using a circular diaphragm with a fixed center is proposed. In the proposed microphone, the diaphragm includes a number of holes to pass the air through the gap between the back plate and diaphragm, and thus reduces the damping of the sound from the microphone. Novelty of this method, creating a circular microphone with fixed center, which the diameter of diaphragm is less than the conventional condenser microphone. At first, the mechanical analysis was conducted on microphone diaphragm in order to achieve the pull-in voltage. The pull-in voltage of the proposed circular microphone is 14 volts. According to the obtained pull-in voltage, the bias voltage were applied to the microphone, and various parameters such as capacitance and sensitivity were measured. Based on the simulation results of COMSOL, the proposed microphone with diaphragm diameter of 400 μm and a thickness of 1.5 μm, the sensitivity of -23 dB is shown. In comparison with previous works, the proposed microphone with lower supply voltage is provided the better frequency performance, and higher sensitivity, in order to sense the sound.