Analysis Of Vulnerable Areas Of Voltage Sags In Distribution System Containing Distributed Generation

With the widely use of sensitive equipment in modern power systems, voltage sags has become one of the most prominent power quality problems, attracting the high attention of power enterprises and users. More and more distributed generation connected to the distribution network, not only inject new vitality to the electric system, but also bring effects to power quality especially to voltage sags which can not be ignored. Therefore, in order to realize the optimization of current grid, it is an important issue to study the distribution network voltage sags and vulnerable areas containing distributed generation. Besides, the reasonable configuration of distributed generation has theoretical significance and practical value to reduce voltage sags, raise the LVRT capability of distributed generation and prevent distributed generation out off network.Firstly, in this paper, summary of detection method for characteristic value of voltage sags is introduced, and the method RMS can extract voltage sag characteristics accurately. Then the paper present with algorithm about vulnerable areas of voltage sags with distributed generation. Providing an overview of basic concepts and types of distributed generation, the two ways connected to the grid of synchronous machine and electronic equipment are described in detail, as well as voltage control strategy and power factor control strategy of distributed generation.Based on theoretical analysis of grid-connected distributed generation, selecting synchronous wind turbine as example, simulation model is built in PSCAD/EMTDC and incorporated into the18node distribution networks, simulated in voltage control strategy and power factor control strategy respectively, then import data to Matlab. The influence of access point voltage to vulnerable areas under voltage control strategy and the influence of power factor to vulnerable areas under power factor control strategy are studied. Under two control strategies, synchronous wind turbine connected to the system can reduce the areas of vulnerability. More closer the distance access point of synchronous wind turbine to sensitive load is, the better compensation effect for voltage sag is. The access of synchronous wind turbine does not have significantly effect to the duration of voltage sag. In addition, under different control strategy, the different capacity of synchronous wind turbine has different effects for voltage sags.Selecting of permanent-magnet direct-drive wind turbine and photovoltaic power plants with inverter interface as examples, simulation model is built in PSCAD/EMTDC and incorporated into the18node distribution networks, simulated in voltage control strategy and power factor control strategy respectively. The effects of changes of wind speed in permanent magnet wind turbine and changes of temperature and light intensity in the PV for the voltage sag of sensitive load are studied. Besides, distributed generation capacity, location and numbers also change areas of vulnerability and duration. Simulation analysis indicates that the distributed generation with inverter interface can reduce the duration of areas of vulnerability and duration of voltage sag, and it can ease voltage sag problems effectively. Vulnerable areas are smaller at different access points with equal capacity of DGs to distribution network than at one access point with the same total capacity of DG. The voltage sag depth and duration of the access point of distributed generation are also reduced compared without DG.