Iranian Journal of Electrical and Electronic Engineering
Volume:8 Issue: 4, Dec 2012

This paper proposes a novel scheme for multi-static passive radar processing, based on soft-input soft-output processing and Bayesian sparse estimation. In this scheme, each receiver estimates the probability of target presence based on its received signal and the prior information received from a central processor. The resulting posterior target probabilities are transmitted to the central processor, where they are combined, to be sent back to the receiver nodes or used for decision making. The performance of this iterative Bayesian algorithm comes close to the optimal multi-input multi-output (MIMO) radar joint processing, although its complexity and throughput are much less than MIMO radar. Also, this architecture provides a tradeoff between bandwidth and performance of the system. The Bayesian target detection algorithm utilized in the receivers is an iterative sparse estimation algorithm named Approximate Message Passing (AMP), adapted to SISO processing for passive radar. This algorithm is similar to the state of the art greedy sparse estimation algorithms, but its performance is asymptotically equivalent to the more complex l1-optimization. AMP is rewritten in this paper in a new form, which could be used with MMSE initial filtering with reduced computational complexity. Simulations show that if the proposed architecture and algorithm are used in conjunction with LMMSE initial estimation, results comparable to jointly processed basis pursuit denoising are achieved. Moreover, unlike CoSaMP, this algorithm does not rely on an initial estimate of the number of targets.

This paper presents the design and a new low-cost process for fabrication of a second-order micromechanical filter using UV-LIGA technology. The micromechanical filter consists of two identical bulk-mode ring resonators, mechanically coupled by a flexural-mode beam. A new lumped modeling approach is presented for the bulk-mode ring resonators and filter. The validity of the analytical derivation is investigated using the finite element method by ANSYS software. The new low-cost fabrication process is used to achieve a high aspect ratio of 16 with 3 μm gap spacing. The rigid graphite serves as a low-cost primary substrate and plating base of nickel as structural material. The fabrication process needs only three UV-lithography steps with Mylar masks to fabricate the main structure and pattern the printed circuit board as a secondary substrate. The frequency response of the fabricated filter is characterized as a function of the DC-bias voltage using a fully differential drive and sense interface circuit. The experimental results demonstrates micromechanical filter with center frequency in the vicinity of 10.31 MHz and percent bandwidth less than 0.3% using a DC-bias voltage of 60 V. The detailed fabrication process can be applied as an appropriate low-cost alternative to X-ray LIGA and silicon-based micromechanical filters.

A new and highly efficient architecture for elliptic curve scalar point multiplication is presented. To achieve the maximum architectural and timing improvements we have reorganized and reordered the critical path of the Lopez-Dahab scalar point multiplication architecture such that logic structures are implemented in parallel and operations in the critical path are diverted to noncritical paths. The results we obtained show that with G = 55 our proposed design is able to compute GF(2163) elliptic curve scalar multiplication in 9.6 μs with the maximum achievable frequency of 250 MHz on Xilinx Virtex-4 (XC4VLX200), where G is the digit size of the underlying digit-serial finite field multiplier. Another implementation variant for less resource consumption is also proposed. With G=33, the design performs the same operation in 11.6 μs at 263 MHz on the same platform. The results of synthesis show that in the first implementation 17929 slices or 20% of the chip area is occupied which makes it suitable for speed critical cryptographic applications while in the second implementation 14203 slices or 16% of the chip area is utilized which makes it suitable for applications that may require speed-area trade-off. The new design shows superior performance compared to the previously reported designs.

Recently several robust control designs have been proposed to the load-frequency control (LFC) problem. However, the importance and difficulties in the selection of weighting functions of these approaches and the pole-zero cancellation phenomenon associated with it produces closed loop poles. Also the order of robust controllers is as high as the plant. This gives rise to complex structure of such controllers and reduces their applicability in industry. In addition conventional LFC systems that use classical or trial-and-error approaches to tune the PI controller parameters are more difficult and time-consuming to design. In this paper, a bisection search method is proposed to design well-tuned PI controller in a restructured power system based on the bilateral policy scheme. The bisection search is a very simple and rapidly converging method in mathematics. It is a root-finding approach which repeatedly bisects an interval and then selects a subinterval in which a root must lie for further processing. The new optimized solution performance has been applied to a 3-area restructured power system with possible contracted scenarios under large load demand and area disturbances. The results evaluation shows the proposed method achieves good performance compared with a powerful robust ILMI-based controller. Moreover, this newly developed solution has a simple structure, and is fairly easy to implement in comparison to other controllers, which can be useful for the real world complex power systems.

Islanded operation of distributed generators is a problem that can take place when they are connected to a distribution system. In this paper an islanding detection method is presented for inverter based distributed generation (DG) using under/over voltage relay. The method is an adaptive one and is based on the change of DG active power reference (Pref) in inverter control interface. The active power reference has a fixed value in normal condition, whereas, if the point of common coupling (PCC) voltage changes, Pref has determined as a linear function of voltage. The slope of Pref is dependent to the load active power (Pload) and should be changed if Pload changes. The non-detection zone (NDZ) of the proposed method is dependent on the accuracy of the voltage measurement equipment; if changing of the PCC voltage is sensed, then, islanding will be detected if it is occurred. Also it does not have any negative effects on the distribution system in normal conditions. Moreover, the proposed technique can be applied when two-DG is in the island. The proposed method is evaluated according to the requirements of the IEEE 1547 and UL 1741 standards, using PSCAD/EMTDC software.

In a typical competitive electricity market, a large number of short-term and long-term contracts are set on basis of energy price by an Independent System Operator (ISO). Under such circumstances, accurate electricity price forecasting can play a significant role in improving the more reasonable bidding strategies adopted by the electricity market participants. So, they cannot only raise their profit but also manage the relevant market more efficiently. This conspicuous reason has motivated the researchers to develop the most accurate, though sophisticated, forecasting models to predict the short-term electricity price as precisely as possible. In this article, a new method is suggested to forecast the next day''s electricity price of Iranian Electricity Market. The authors have used this hybrid model successfully in their previous publications to predict the electric load data of Ontario Electricity Market [1] and of the Spinning Reserve data of Khorasan Electricity Network [2] respectively.

Congestion in the transmission lines is one of the technical problems that appear particularly in the deregulated environment. The voltage stability issue gets more important because of heavy loading in this environment. The main factor causing instability is the inability of the power system to meet the demand for reactive power. This paper presents a new approach for alleviation congestion relieving cost by feeding required reactive power of system in addition to re-dispatching active power of generators and load shedding. Furthermore with considering different static load models in congestion management problem with both thermal and voltage instability criteria, tries to the evaluated congestion management cost become more real, accurate and acceptable. The voltage stability is a dynamic phenomenon but often static tools are used for investigating the stability conditions, so this work offers new method that considers two snapshots after contingency to consider voltage stability phenomena more accurate. This algorithm uses different preventive and corrective actions to improve unsuitable voltage stability margin after contingency. The proposed method is tested on IEEE 24-bus Reliability test system, the simulation results shows the effectiveness of the method.