Sharif Digital Repository

This paper discusses various aspects of unified power flow controller (UPFC) control modes and settings and evaluates their impacts on the power system reliability. UPFC is the most versatile flexible ac transmission system device ever applied to improve the power system operation and delivery. It can control various power system parameters, such as bus voltages and line flows. The impact of UPFC control modes and settings on the power system reliability has not been addressed sufficiently yet. A power injection model is used to represent UPFC and a comprehensive method is proposed to select the optimal UPFC control mode and settings. The proposed method applies the results of a contingency... 

In this paper, a reliable low power single phase grid-connected inverter for photovoltaic modules is proposed. The inverter has improved lifetime since large electrolytic capacitor is replaced with small film capacitor due to circuit topology, power processing and proper control scheme. Thus the main limiting component in single phase grid connected inverters is obviated. The proposed inverter consists of two power processing stages. First a dual active bridge (DAB) converter boosts the voltage of PV panel to approximately 440 V and eliminates impact of high dc bus voltage ripples. A proper feed forward control is proposed to regulate the dc bus voltage with high ripple. Simulation results... 

Harmonic pollution minimisation in voltage-source programmed pulse-width modulation (PPWM) inverters is defined as a time-limited optimisation problem in real-time applications with variable DC sources. In order to obtain minimum total harmonic distortion (THD) as the objective function, shuffled-frog-leaping algorithm (SFLA) is modified and employed to calculate the switching angles and compared with non-linear programming as a traditional optimisation method. In addition, particle swarm optimisation and three of its modified versions as popular evolutionary optimisation algorithms are employed to ensure the capability of the proposed optimisation method. Moreover, modified sinusoidal PWM... 

This paper discusses various aspects of unified power flow controller (UPFC) control modes and settings and evaluates their impacts on the power system reliability. UPFC is the most versatile flexible ac transmission system device ever applied to improve the power system operation and delivery. It can control various power system parameters, such as bus voltages and line flows. The impact of UPFC control modes and settings on the power system reliability has not been addressed sufficiently yet. A power injection model is used to represent UPFC and a comprehensive method is proposed to select the optimal UPFC control mode and settings. The proposed method applies the results of a contingency... 

The overall system status calculated by pflower flow analysis is the most basic information used for all decisions taken by power system operators and planners. While conventional AC pflower flow solutions are computationally tractable, approximate DC models are employed in many applications, such as optimal power flow studies and unit commitment problems, mainly due to the linear nature of DC models. These models do not provide any information on the reactive power and voltage magnitude quantities and occasionally inaccurate results of the active power values. This paper presents an efficient power flow approach compromising both the con icting aspects of speed and accuracy. The proposed... 

One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between the different levels normally involve voltage clamping or capacitor charge and discharge control. However, traditional Flying Capacitor Converter (FCC) may be quite limited by the voltage unbalance of flying-capacitors that is the most serious problem. This paper describes operating principles of a new softswitching seven-level converter topology based on FCC for self-voltage stabilization and balancing. By adding power electronic devices to the traditional FCC topology, the proposed topology regulates the DC bus voltage and balances the... 

This paper presents a modified particle swarm optimization (MPSO) algorithm for solving the optimal power flow (OPF) problems. The main distinction of this approach is in using particle's worth experience in stead of the best previous experience. The proposed approach is evaluated on the IEEE 30-bus test system which minimizes the total fuel cost considering operational constraints such as power flow equations, transmission flow limits, bus voltages and reactive power of generators. The results obtained using the proposed approach are compared with results of other optimization methods  

With the introduction of restructuring concepts to traditional power systems, a great deal of attention is given to the utilization of distributed generation. Since the integration of DG units has been known as an alternative for main grid as a resource for energy supply, the determination of optimal sizing and sitting is an important issue in the planning procedure of DG. This work presents a comprehensive multi-objective model for integration of distributed generations into a distribution network, regarding various technical, economical and environmental issues such as reduction of carbon dioxide emissions and investment & running costs while the bus voltages shall be kept within... 

In this paper, a unified hybrid vector control of vector modulated VIENNA I rectifier is presented. Feedback linearization technique is used for the DC-link voltage control. For this purpose, at first a mathematical model of the VIENNA I rectifier is derived. Using this model, it is shown that the dynamic of the rectifier falls into two categories; linear inner dynamic which consists of inner current control and neutral-point potential control and nonlinear outer dynamic which consists of the DC-link voltage control. Based on these facts, a hybrid vector control scheme meaning linear vector control of inner dynamics and nonlinear vector control of outer dynamic is devised. Simulations... 

This paper proposes a comprehensive analytic method for applying various optimal remedial actions to improve critical electromechanical modes damping without jeopardizing damping of non-critical modes and violating security constraints of power system. Generators and reactive power sources redisptach, demand side management and the generators voltage reference tuning are remedial actions that are considered here. Dynamic equations of the flux-decay dynamic model of generators, standard dynamic models of excitation system and power system stabilizer and algebraic equations of active and reactive powers balance are formulated in the quadratic eigenvalue problem framework. With simultaneous use...