Iranian Journal of Electrical and Electronic Engineering
Volume:11 Issue: 2, Jun 2015

In this paper, five conditions that have been proposed by Cobb and Shenoy are studied for nine different mappings from the Dempster-Shafer theory to the probability theory. After comparing these mappings, one of the considerable results indicates that none of the mappings satisfies the condition of invariance with respect to the marginalization process. In more details, the main reason for this defect is that the classic projection process in DST loses some probabilistic information. Therefore, as regards this subject, a solution is presented for solving this problem for two mappings: the pignistic probability and the normalized plausibility transformation.

Impressive development of computer networks has been required precise evaluation of efficiency of these networks for users and especially internet service providers. Considering the extent of these networks, there has been numerous factors affecting their performance and thoroughly investigation of these networks needs evaluation of the effective parameters by using suitable tools. There are several tools to measure network's performance which evaluate and analyze the parameters affecting the performance of the network. D-ITG traffic generator and measuring tool is one of the efficient tools in this field with significant advantages over other tools. One of D-ITG drawbacks is the need to determine input parameters by user in which the procedure of determining the input variables would have an important role on the results. So, introducing an automatic method to determine the input parameters considering the characteristics of the network to be tested would be a great improvement in the application of this tool. In this paper, an efficient method has been proposed to determine optimal input variables applying evolutionary algorithms. Then, automatic D-ITG tool operation would be studied. The results indicate that these algorithms effectively determine the optimal input variables which significantly improve the D-ITG application.

In this paper, we extend the sliding mode idea to a class of unmatched uncertain variable structure systems. This method is achieved with introducing a new terminal sliding variable and the finite time stability of proposed method is proved using a new particular finite time condition in both reaching and sliding phases. In reaching phase new sliding mode controller is derived to guarantee the finite time stability of sliding surface with considering matched uncertainty. Also in sliding phase, because of introducing a new terminal sliding variable, the finite time stability of state variables with considering unmatched uncertainty has been guarantee. Therefore in proposed algorithm we are able to adjust reaching and sliding times in the presences of both matched and unmatched uncertainty. This algorithm is applied to designing control law for a moving cart system with bounded matched and unmatched uncertainties. Simulation results show the effectiveness and robustness of the proposed algorithm.

Uncertain switched linear systems are known as an important class of control systems. Performance of these systems is affected by uncertainties and its stabilization is a main concern of recent studies. Existing work on stabilization of these systems only provides asymptotical stabilization via designing switching strategy and state-feedback controller. In this paper, a new switching strategy and a state-feedback control law are designed to exponentially stabilize Uncertain Discrete-Time Switched Linear Systems (UDSLS), considering a given infinite-horizon cost function. Our design procedure consists of three steps. First, we generalize the exponential stabilization theorem of nonlinear systems to UDSLS. Second, based on the Common Lyapunov Function technique, a new stabilizing switching strategy is presented. Third, a sufficient condition on the existence of state-feedback controller is provided in the form of Linear Matrix Inequality. Besides, convergence rate is obtained and the upper bound of the cost is calculated. Finally, effectiveness of the proposed method is verified via numerical example.

Evaluation of the reliability parameters in micro-grids based on renewable energy sources is one of the main problems that are investigated in this paper. Renewable energy sources such as solar and wind energy, battery as an energy storage system and fuel cell as a backup system are used to provide power to the electrical loads of the micro-grid. Loads in the micro-grid consist of interruptible and uninterruptible loads. In addition to the reliability parameters, Forced Outage Rate of each component and also uncertainty of wind power, PV power and demand are considered for micro-grid. In this paper, the problem is formulated as a nonlinear integer minimization problem which minimizes the sum of the total capital, operational, maintenance and replacement cost of DERs. This paper proposes PSO for solving this minimization problem.

This paper develops an effective control framework for DC voltage control and power-sharing of multi-terminal DC (MTDC) grids based on an optimal power flow (OPF) procedure and the voltage-droop control. In the proposed approach, an OPF algorithm is executed at the secondary level to find optimal reference of DC voltages and active powers of all voltage-regulating converters. Then, the voltage droop characteristics of voltage-regulating converters, at the primary level, are tuned based on the OPF results such that the operating point of the MTDC grid lies on the voltage droop characteristics. Consequently, the optimally-tuned voltage droop controller leads to the optimal operation of the MTDC grid. In case of variation in load or generation of the grid, a new stable operating point is achieved based on the voltage droop characteristics. By execution of a new OPF, the voltage droop characteristics are re-tuned for optimal operation of the MTDC grid after the occurrence of the load or generation variations. The results of simulation on a grid inspired by CIGRE B4 DC grid test system demonstrate efficient grid performance under the proposed control strategy.

This paper provides a detailed comparative study concerning the performance of min-projection strategy (MPS) and model predictive control (MPC) systems to control the three-phase grid connected converters. To do so, first, the converter is modeled as a switched linear system. Then, the feasibility of the MPS technique is investigated and its stability criterion is derived as a lower limit on the DC link voltage. Next, the fundamental equations of the MPS to control a VSC are obtained in the stationary reference frame. The mathematical analysis reveals that the MPS is independent of the load, grid, filter and converter parameters. This feature is a great advantage of MPS over the MPC approach. However, the latter is a well-known model-based control technique, has already developed for controlling the VSC in the stationary reference frame. To control the grid connected VSC, both MPS and MPC approaches are simulated in the PSCAD/EMTDC environment. Simulation results illustrate that the MPS is functioning well and is less sensitive to grid and filter inductances as well as the DC link voltage level. However, the MPC approach renders slightly a better performance in the steady state conditions.

The aim of the relay coordination is that protection systems detect and isolate the faulted part as fast and selective as possible. On the other hand, in order to reduce the fault clearing time, distance protection relays are usually equipped with pilot protection schemes. Such schemes can be considered in the distance and directional overcurrent relays (D&DOCRs) coordination to achieve faster protection systems, while the selectivity is maintained. Therefore, in this paper, a new formulation is presented for the relay coordination problem considering pilot protection. In the proposed formulation, the selectivity constraints for the primary distance and backup overcurrent relays are defined based on the fault at the end of the transmission lines, rather than those at the end of the first zone of the primary distance relay. To solve this nonlinear optimization problem, a combination of genetic algorithm (GA) and linear programming (LP) is used as a hybrid genetic algorithm (HGA). The proposed approach is tested on an 8-bus and the IEEE 14-bus test systems. Simulation results indicate that considering the pilot protection in the D&DOCRS coordination, not only obtains feasible and effective solutions for the relay settings, but also reduces the overall operating time of the protection system.

Locational Marginal Pricing (LMP) is a method for energy pricing in deregulated power systems. Loss and congestion cause different prices for energy at load or generation buses. In this pricing method there is a different between payments of customers and revenue of generators which is called Merchandizing Surplus (MS). Independent System Operator (ISO) receives MS and generally renders it to Transmission Company (Transco). It is rational that the MS be allocated among power market participants fairly instead of granting whole MS to Transco. In this paper a novel method is proposed to allocate MS among market participant according to their role in the congestion of system. In the presented method by decomposing LMP and identifying congestion part of LMP, the part of generators’ revenue and customers’ payments which caused by congestion are calculated. Then MS is allocated among market participants as the payment of customers to be equal to revenue of generators. The proposed method has been tested on five bus test system. Results indicate the effectiveness of the proposed method to allocate MS between power market participants.

This paper presents a new method for evaluation and simulation of inrush current in various transformers using operational matrices and Hartley transform. Unlike most of the previous works, time and frequency domain calculations are conducted simultaneously. Mathematical equations are first represented to compute the inrush current based on reiteration and then Hartley transform is used to study harmonic effects in the frequency domain. Being a real valued function and accordingly giving results with the higher speed of calculations are the main features of Hartley transform. The inrush problem is initially solved for single-phase transformers for switching at different angles of the voltage waveform using this method and then the results of harmonic domain are compared with that of Fourier transform. The methodology is also applied to three-phase three-limb transformers since the analysis of their transient behavior is significant owing to the flux coupling interactions in multi-leg core structures. The feasibility and efficacy of the method is illustrated with appropriate circuits and MATLAB code is developed to get the time and frequency domain waveforms with high accuracy. The results are helpful to identify and evaluate inrush current harmonic effects in various transformers and hence the efficiency of the method is verified.