Sharif Digital Repository

Online voltage stability assessment is essential for preventing the failure in power systems. Voltage instability in power systems usually occurs in consequence of contingency situations or continuous load increasing or both of them. A new method for online voltage stability assessment using the data acquired from phasor measurement units (PMUs) and offline trained decision trees is presented in this thesis. The index of voltage stability margin (VSM) is used for security assessment and considering WSCC criterion, different operation points are divided in two classes: safe and unsafe. In order to obtain the voltage stability margin and generate the database, a new method which has been named... 

Although voltage control and stability issues are not new to the electricity industry, but nowadays, in most modern power systems, special attention has been paid to this issue. Once, only weak systems with long lines were involved in voltage instability, while today due to heavy loading, voltage stability is a serious concern even in developed networks. Over tim, with increasing demand for electricity and emergence of electricity market and economic constraints, power systems are more exposed to voltage instability and even voltage collapse. Therefore, reliable operation of the system in such circumstances requires evaluating voltage stability of the network at both stages of planning and... 

oltage stability is a dynamic phenomenon. The time frame of interest for voltage stability phenomenon may vary from a few seconds to tens of minutes. Therefore, voltage stability may be either a short-term or a long-term phenomenon. The past proposed voltage stability protection schemes have major drawbacks in both static and dynamic aspects. To mitigate the drawbacks of the previously proposed voltage stability protection schemes in both static and dynamic domains two system protection schemes are proposed. In static domain, the proximity to the collapse point(i.e. proximity is measured by a voltage stability indicator) as well as the instability mechanism (i.e. determination of the most... 

Nowadays, According to the improvement of technology, especially in power electronics, electric shipboards are preferred over traditional ones. Better maneuverability, lower emission, higher efficiency and reliability are the most conspicuous merits of this type of ships. Notwithstanding the fact that electric shipboards have many advantages, some serious problems may arise in these ships. Since the thruster motors of these ships are usually induction motors and they are fed by the microgrid of the ship, and taking into ACcount that thruster motors consume a huge amount of the generated power by the synchronous generators, the concept of infinite bus is inexistent in these microgrids. Hence,... 

With the increasing penetration of renewable energies as distributed generation (DG) in power systems, technical problems arise in both distribution and transmission system level. Voltage rise is the main barrier for connection of DGs in rural areas, while excessive reactive power demand from transmission system is the major concern for Transmission System Operators (TSO). Here, a centralized control scheme based on the Smart Grid is proposed to reduce the impact on the transmission system voltages and improve its stability, while mitigating the voltage rise issue in the distribution network. Reactive power output of DGs, substation capacitors and tap setting of transmission transformer are... 

Given the growing advantage of exploiting renewable energy resources over fossil fuels and using distributed generation systems, microgrids seem to be the best solution for reaching the energy-efficient world of the future. Hybrid microgrids are the best options among all other types of microgrids because they make it possible to use AC and DC sources and loads together and at the same time. Since connecting AC and DC sections of a hybrid microgrid leads to the interaction between them, proper control of interlinking converter(s) is crucial for the reliable and stable operation of the entire microgrid. In this study, small signal model of a hybrid AC/DC microgrid consisting of static and... 

One of the main objectives in operating a power system is to maintain the system voltage properly to avoid equipment damage and transfer power efficiently. Automatic control of transmission network voltage provides significant improvements in security, quality and efficiency of power system operation. This thesis investigates coordinated voltage control of power systems in normal, alert and emergency states. The aim is to propose a comprehensive framework for real-time operation of practical power systems, ensuring secure operation of the system in the normal state and after occurrence of sever contingencies.
At the first, a new coordinated voltage control scheme is proposed to ensure...