نشریه مهندسی برق و مهندسی کامپیوتر ایران
سال هفدهم شماره 1 (پیاپی 50، بهار 1398)

This paper presents a new model for a DC-DC buck-boost converter considering its all controlled and uncontrolled switching phenomena in both continuous and discontinuous conduction modes. The proposed model is developed based on hybrid systems theory using mixed-logical dynamical (MLD) systems, and an improved version of these systems called as extended mixed-logical dynamical (EMLD) Systems. Compared to the existing MLD and EMLD models of the DC-DC converters, the proposed model contains fewer numbers of integer variables and inequalities, and, as a result, leads to the less complexity and solution time of the mixed integer optimization problems arising from the corresponding hybrid model predictive controllers. The advantage of the proposed modeling and control method is evaluated via the comparison of the existing MLD models and hybrid predictive controllers as well as classic proportional-integral (PI) controllers. Moreover, the theoretical challenges for the closed-loop stability proof are discussed and in this regard some future research outlines and ideas are introduced. The steady state and transient performance of the closed-loop control system over a wide range of the operation points show the satisfactory operation of the proposed modeling and control scheme for the DC-DC buck-boost converter.

In this paper, a new method is proposed for maintenance scheduling of generation units in a competitive electricity market environment. The problem of productive maintenance scheduling is one of the most important problems in the restructured power system due to its impact on the safety and emission of pollutants and producers' profits. In order to consider producers' risk, productive maintenance scheduling has been modeled from the producer's point of view using non-cooperative game theory, which is used to achieve an optimal Nash equilibrium strategy. On the other hand, the independent system operator seeks to achieve a level of appropriate reliability and pollution reduction. In this paper, load response programs are one of the options for influencing energy policy decision-making. Also, the coordination procedure has been used to coordinate producers' maintenance programs with reliability-pollution maintenance program. The proposed model has been implemented on the IEEE-RTS Modified 24 Bus. The results indicate the effectiveness of the proposed method.

One of the main components of distribution systems is transformer, and their failure will cause irreparable damage in power systems and distribution companies. These failures are to increase the losses of the transformers due to the increase of harmonics, especially the current harmonics. These losses increase the temperature of transformers and reduced the lifetime of distribution transformers. In this paper evaluated losses and lifetime in the presence of harmonic loads in Ilam distribution transformers. Technical and practical assessments of the presence of harmonic loads and their effect on the lifetime of transformers have been investigated. According to the obtained results the useful lifetime of some transformers from 30 years to 17 years are decreased.

Public sensitivity to environmental issues in the economic dispatch is also impressive. In this case it is necessary to consider the costs of pollution in the economic dispatch. Before the introduction of the concept of power system security, the subject of economic load dispatch normally focused on economic aspects rather than security of the system. Today, with the expansion of the power grid and system load, combination of stability and economic load dispatch indices has become a critical necessity. This article will consider the issue of solving the economic dispatch of power plants considering the emissions and security indices of the network. Using penalty functions, system security indices are added to the objective function of economic load dispatch problem. Since fuel costs and emission reduction targets are relatively contrasting, problem solving of economic load dispatch and emission reduction leads to a multi-objective optimization problem. Given the complexity of objective functions and necessity of the considering the practical constrains of power plants operation and security indices reveal more than ever the need to use efficient methods to optimize. In this article Multi Objective Harmony Search algorithm (MOHS) has been used to solve the problem. The results show that MOHS algorithm is excellent for convergence and accuracy compared to other employed methods. The proposed testing system used to solve the problem is IEEE test system with 10 power generation units, 39 bus and 46 transmission line.

Considering economic and environmental factors, it is expected that the number of plug-in electric vehicles (PEVs) will be increased, rapidly. The high penetration of EVs, can affect the power system. Therefore, in recent years, various studies have paid their attention to the impacts of PEVs charging on the network. In this paper, a probabilistic model based on the queueing theory is extracted using Monte Carlo simulation for modeling EV charging station load. It is assumed that the vehicles are the taxis of Amol city in Mazandaran province. Required data such as the time of arrival and the state of charge of the battery before charging, were collected and extracted using three methods from intra-city taxis in the city of Amol. To obtain the demand load of EV charging, the traffic-based behavior of drivers is needed. This behavior is stochastic. Therefore, its related variables will not be deterministic and must be evaluated using probabilistic methods.

Today, the brushless DC motors (BLDCs) have been widely used in industry due to their unique advantages. These motors are generally fed from voltage source inverters (VSIs). These inverters have a very simple structure, but have problems such as unwanted short circuit across dc-bus and using bulky capacitor in the dc-bus. Using the current source inverters (CSI) is one of the ways to reduce the mentioned problems in VSI-BLDC motor drives. In this paper, the space vector modulation (SVM) strategy is employed for switching in CSI-BLDC motor drive in order to reduce the switching losses, minimize current and torque ripple and increase the reliability of the drive. The BLDC motor drive model is implemented in the Proteus simulator software and the motor behavior is simulated at different speeds. In order to confirm the simulation results, an experimental setup system is designed, implemented and tested.

This paper presents a voltage controlled oscillator (VCO) based on a cross-coupled pair and Colpitts structures for K-band applications. By employing cross-coupled pair and Colpitts structures, the dc power consumption and phase noise was reduced. By using inductors between cross-coupled pair and Colpitts structures, the effective transconductance was enhanced and robust the start-up condition. In order to cover a wide frequency tuning range, a capacitor bank was used. The VCO has been designed and simulated in TSMC 0.18 µm CMOS technology. Simulation results showed that the simulated phase noise of center frequency (24.25 GHz), at 1-MHz offset frequency is-120 dBc/Hz and the figure of merit is -195.67 dBc/Hz. The covering frequency range and tuning range of this VCO are 1.4 GHz and 5.7%, respectively. The occupied area of the layout is 335 µ2m and the power consumption of this VCO was 15.92 mW from 1.5 V supply voltage.

In this paper, a new decentralized observer scheme based on combination of two large scale interconnected subsystems is proposed. It discusses design problem of flow measurement by partial differential equation (PDE) observer for state estimation of a quasi linear system without external disturbance and without measurement noise. The measurement system is decomposed into two subsystems according to their locations, condensate and gas pipes, such that each subsystem has interconnection with other. By using matrix form Navier Stocks equations and Lyapunov technique, inequality at each subsystem, a Lyapunov-based design of PDE observer is developed such that the resulting estimation error system is exponentially stable and presented in terms of standard linear matrix inequalities (LMIs). The first mean value theory for integrals is used in the observer design development. The proposed method may be used as a backup for existing systems in the operation field or as a main system for new established plants.