Optimal allocation of wind energy based distributed generation in distribution networks to improve voltage stability and relieve transmission lines congestion.

摘要

Recently, the penetration level of conventional and renewable distributed generation (DG) has increased. Voltage stability is the main issue in determining optimal size and location of the distribution generator into the power grid. Distributed generators (DGs) connected to the power grid at point of distribution are capable to improve voltage profile of the system. Integrating DGs at candidate bus (weakest) is a mostly used phenomenon which utilizes an appropriate index (or parameter). The impact of voltage stability when a wind-turbine-based distributed generator is integrated into the power grid has become a challenging issue. Squirrel cage induction generator (SCIG) based distributed generator (DG) is widely used technology to support the voltage in the power grid due to its advantages such as robustness, easy and relatively mass production. SCIG also operates at a constant rotating speed when it is connected to large grid, providing stable frequency control. The main disadvantage of SCIG-based DG is its poor reactive power capability. On the other hand, variable speed wind turbine with a doubly fed induction generator (DFIG) has its advantages over SCIG such as the capability to supply reactive power to the grid and a higher operational wind speed range (usually ranges from -25% to +25% of rated wind speed). However, the high cost of DFIG based DG is the main drawback when compared to SCIG based wind DG. The next considerable issue in the power system to optimally size and locate distributed generator (DG) is transmission line congestion. Congestion index contributes its part in determining the type, size and location of DG.;In this thesis, I have proposed a new combination of SCIG and DFIG-based DG configuration. In the proposed configuration, the poor reactive power capability of SCIG is overcome by the reactive power supplied by DFIG, and it results in a system that operates (nearly) at unity power factor. This makes the system meet the IEEE 1547 standards. Two algorithms are developed to optimally size and locate the proposed DG unit in the power grid based on voltage index and congestion index respectively. This methodology involves the probabilistic nature of load flow with an objective function of improving voltage profile and relieving transmission line contingency. The proposed DG configuration incorporates the attractive advantages of both SCIG and DFIG.