Study On Methods For Selecting Locations, Capacities And Types Of Typical Flexible AC Transmission Systems Devices In Power System

Due to unbalanced energy distribution and economic development, high voltage, large capacity and long distance power transmission and interconnection of bulk power systems have become one of the major development trends of modern power systems all over the world. With the rapid development of power grids, how to improve their operational effectiveness without compromising the reliability has caused widespread concerns of domestic and foreign scholars.The birth and development of FACTS provide new control technology and effective tools to achieve the above goal. During the development of FACTS technology and its marketing, researchers gradually recognize that the effects of applying FACTS in a bulk power grid heavily depend on the placement of FACTS devices. Therefore, how to select the locations, capacities and types of FACTS devices according to the practical demands of a power grid is an immediate problem needed to be solved, which has direct effects on reliability of grid operation and profitability of investments in FACTS devices.Currently, placement of FACTS devices in power grids is mainly relied on simulation trials or project experience, which obviously can not meet the demand of popularization of FACTS devices in a modern power system; therefore, it is necessary to make a systematical study on selection of locations, capacities and types of FACTS devices. Organized around the optimal placement of FACTS devices to improve operational effectiveness of a power grid with typical FACTS devices as the research subjects, the dissertation discusses the optimal placement methods thoroughly and applies them to a real power grid. As a result the theoretical architecture on the optimal placement methods of FACTS devices is built. The main research contents and accomplishments of the dissertation are summarized as follows.Based on basic principles, functional properties of typical FACTS devices such as improving static voltage stability, transfer capability and transient stability of power systems are introduced. Then the application range of a device is analyzed by comparing output characteristic curves, the relationship between series (or shunt) compensation and active power increment of transmission line, and the impact on power system transient stability. The cost function of FACTS devices is established based on domestic and international case studies to instruct the choice of device types. The evaluation index of improving operational effectiveness of power grid is given, which provides guidelines for selection of locations and capacities of FACTS devices.For purposes of targeting weak buses of voltage stability, key lines of improving transfer capability and locations with severe impacts on the grid during fault contingencies, voltage stability margin of load buses, line participation factors and system transient stability margin are obtained by continuation power flow, modal analysis method and extended equal area criterion respectively. Based on the above calculations, buses and lines in the power grid are ordered by their priority of installing FACTS devices to guide the selection of locations.Based on local and hierarchical balance of reactive power and taking minimum active power losses caused by transferring reactive power as the constraints, the strict mathematical relationship among active power losses caused by transferring reactive power, bus voltage and reactive compensation capacity is established using economic voltage difference to determine capacities of FACTS devices reasonably. Through the sensitivity index which reflects the impact of compensation capacity variation on transient stability margin, determination of compensation capacity under large disturbance is treated as the quantity problem of minimizing compensation cost with the constraints of system stability.Aimed at improving static voltage stability, transfer capability and transient stability of power grids, a mathematical model of optimal FACTS devices placement is designed based on the study of selection of locations, capacities and types of FACTS devices. Calculation method is given to obtain single objective optimal solutions considering functional characteristics of several typical FACTS devices and the cost function. A method is proposed to obtain a minimal representation of Pareto frontier of multi-objective function using smart Pareto filter, which reflects the tradeoff among different schemes to yield an optimal choice.Placement scheme of FACTS devices to improve operational effectiveness of real power grids is studied to validate the proposed method and model with impacts of the load model on the study considered in simulation. The study provides theoretical basis for engineering decision-making. For extreme faults, a synthetic strategy including various countermeasures to enhance transient stability such as reactive power compensation, HVDC power emergency support and generator tripping is given, and guidelines for reliable grid operation in contingency are presented.