Sharif Digital Repository

The necessity for flexible electric systems, energy saving, loss reducing and environmental impact are providing Impetus to the development of Distributed Generation (DG). DG Includes the application of small generators, scattered throughout a power system, to provide the electric power needed by electrical customer. Such locally distributed generation, has several merits from the viewpoint of environmental restriction and location limitations, as well as transient and voltage stability In the power system. The exact solution of the DG allocation can be obtained by a complete enumeration of all feasible combinations of sites and sizes of DGs In the network. The number of alternatives could... 

Contrary to the widespread understanding, this paper shows by means of mathematics and numerics that a perfect power factor correction cannot be made at the load terminals only. To achieve a perfect power factor correction, the supply commitment is required as well. In the absence of such commitment, the power factor cannot reach unity unless we refine the very definition of power factor. But the refined power factor is then slightly higher than the conventional one. The refined expression for power factor is a function of the load parameters as well as the line characteristics. For an ideal power system (with no line losses), this coincides with the conventional formula. © 2008 IEEE  

One of the most important aspects in evaluating system reliability is to have a complete understanding of the engineering implications of the system and its associated components. The next step involved in reliability assessment is to appropriately model the system components to represent their characteristics and functions in the overall system. The unified power flow controller (UPFC) is an important flexible AC transmission system controller that can be used to enhance power system reliability. A complete reliability model of a UPFC is developed. A UPFC consists of three subsystems, and a reliability model associated with each subsystem is developed. The individual equivalent models are... 

This paper investigates several current control methods for load balancing and power factor correction based on distribution Static Compensator (STATCOM). Two different configurations are considered for STATCOM; a three leg inverter, and three single phase inverters. It is assumed that the STATCOM is associated with a load that is remote from the supply. After a brief introduction, control structure based on PWM method and simulation results using PSCAD are presented. Next, the same system is simulated using hystersis control method. Both methods employ the instantaneous symmetrical components theory for load balancing and power factor correction. At the end, a comparison between two methods... 

This paper investigates a predictive control strategy for a single-phase PFC rectifier exploiting the Sheppard-Taylor converter. By using this converter, the detuning problem occurring in conventional PFC rectifiers, especially at low input voltages, is avoided. This paper addresses a predictive method for designing the current controller of the Sheppard-Taylor PFC converter. The control law is derived for an ideal circuit as well as a more accurate model of the converter including parasitic elements. Input voltage feed-forward compensation provides sinusoidal input current and a desired output voltage even if the input voltage is distorted. To investigate the dynamic performance of the PFC... 

Power factor correction (PFC) converter circuits are non-linear system due to the contribution of their multiplier. This non-linearity reflects the difficulty of analysis and design. Models that reduce the system to a linear system involve considerable approximation, and produce results that are susceptible to instability problems. Our goal is to design a controller that achieves some performance specifications despite these uncertainties in modeling. This paper addresses a robust H∞ control problem for switched circuits with parameter uncertainties. The necessary and sufficient conditions for existence of strong robust H∞ dynamic compensators and static output feedback controllers are... 

Sensorless control of permanent magnet synchronous motors allows reducing cost and complexity, and increasing mechanical robustness and noise immunity. Sensorless methods based on high frequency carrier injection have attracted considerable attention in recent years as they can estimate rotor position in a wide speed range. These methods employ anisotropic properties of rotor to estimate rotor position in ac machines. With internal permanent magnet motors, the high frequency signal injection method can deliver precise sensorless control, however in surface-mounted permanent magnet machines, where a small saliency arises from main flux saturation, the estimation of rotor magnet position is... 

A gas-turbine cogeneration system with a regenerative air preheater and a single-pressure exhaust gas boiler serves as an example for application of CHP Plant. This CHP plant which can provide 30 MW of electric power and 14kg/s saturated steam at 20 bars. The plant is comprised of a gas turbine, air compressor, combustion chamber, and air pre-heater as well as a heat recovery steam generator (HRSG). The design Parameters of the plant, were chosen as: compressor pressure ratio (rc), compressor isentropic efficiency (ηac), gas turbine isentropic efficiency (ηgt), combustion chamber inlet temperature (T3), and turbine inlet temperature (T4). In order to optimally find the design parameters a... 

Predictive functional control (PFC) as a new active queue management (AQM) method in dynamic TCP networks supporting explicit congestion notification (ECN) is proposed. The ability of the controller in handling system delay along with its simplicity and low computational load makes PFC a privileged AQM method in the high speed networks. Besides, considering the disturbance term (which represents model/process mismatches, external disturbances, and existing noise) in the control formulation adds some level of robustness into the PFC-AQM controller. This is an important and desired property in the control of dynamically-varying computer networks. In this paper, the controller is designed based... 

In this paper CCM/CVM operation and modeling of the Sheppard-Taylor topology is reviewed and a predictive control strategy is applied for a Sheppard-Taylor-based power factor correction (PFC) rectifier. Compared to conventional boost or buck - boost PFC's, this topology allows a better current tracking at the AC side, with a relatively reduced voltage at the DC side. Consequently, the high frequency AC filters required by the buck PECs are avoided, and the voltage stresses on the boost switches are significantly reduced. Furthermore In predictive control strategy the duty cycle required to achieve unity power factor in a half line period can be calculated in advance. The main advantage of... 

PFC converters for higher power are commonly designed for continuous conduction mode (CCM). However, at light load, discontinuous conduction mode (DCM) will appear close to the crossover of the line voltage, causing the converter to switch between the two conduction modes. As a result, the converter dynamics change abruptly, producing input current distortion. In this article a piecewise affine approximation has been employed in modeling a boost power factor correction converter operated in the mixed conduction mode. This approach makes the new model very useful in large signal analysis of PFC rectifiers and design of controller. The results obtained from the proposed model are compared with... 

A problem associated with modeling and control of the power factor correction rectifiers is that the ac variations in duty cycle, as well as in the ac input voltage and current are not small, and hence the traditional small signal analysis is not justified. Nonetheless, the low-frequency components of the converter can be modeled via the circuit averaging technique, but the resulting equivalent circuits are, in general, time varying and highly nonlinear. Nonlinear stability analysis methods are not appropriate for analysis and control design of such complicated circuits. In this paper a piecewise affine approximation is introduced for modeling of switching circuits. This approach makes the... 

In this study, we have used a single link system with a pair of muscles that are excited with alpha and gamma signals to achieve both point to point and oscillatory movements with variable amplitude and frequency. The system is highly nonlinear in all its physical and physiological attributes. The major physiological characteristics of this system are simultaneous activation of a pair of nonlinear musclelike- actuators for control purposes, existence of nonlinear spindle-like sensors and Golgi tendon organlike sensor, actions of gravity and external loading. Transmission delays are included in the afferent and efferent neural paths to account for a more accurate representation of the reflex...