Optimal planning and control of grid-connected distributed generation in power systems.
With the rise of concerns about environment and depleting energy resources, a significant penetration of distributed generation (DG) into distribution systems has been increasing around the world in recent years. The DG sources can bring several technical benefits to distribution systems such as loss reduction, voltage profile improvement, voltage stability and reliability. There may have several aspects of the challenges on the DG applications, we focus on the two challenges of loss reduction and controllability. The challenges in DG applications for loss reduction are the selections of proper locations, appropriate sizes and operating strategies.A Even if the location is fixed due to some other reasons, the improper size would increase the losses in the system beyond the losses for the case without DG sources. Another challenge is controllability of DG sources under the intermittent condition. As one of important DG sources, solar PV and wind power both have intermittent and unpredictable generation; hence, they may cause stability issues for voltage and frequency. This thesis work starts from the optimal size and operating strategies of DG sources in both transmission and distribution systems with the semidefinite programming technique. The optimal sizing problem is formulated with the multiobjective performance index which includes the size of DGs and loss reductions subject to the load flow and restrictions of voltage magnitude for each bus. The second goal of this work is to design a disturbance rejection control of the grid-connected DGs in power systems. The integration of DG can enhance the performance and stability of systems when solving the issues caused by the intermittency of renewable energy. Interface of a DG to power grid is challenging because of the high nonlinearities of DGs and the power conditioning system (PCS). A final goal of this work is to show that the coordinate control in a micro-grid which connects to the distribution system. Micro-grid worked on this thesis consists of solar photovoltaic (PV) unit, SOFC and ultra-capacitor. Through the coordinate control, SOFC and ultra-capacitor keep maintaining power balances between the power demand and the output power of the solar PV.