Due to deregulated electricity market and renewable energy targets, integration of distributed generator (DG) at distribution level has been gaining importance in recent years. In comparison to large conventional power plants, this form of generation has different characteristics. Some of the DG technologies, based on renewable resources, also exhibit intermittency problem. Introduction of these DG units results bi-directional power flow in feeders and makes distribution networks more active. The increasing penetration of DG into the existing passive distribution networks is reaching a critical point and hence it can no longer be installed in the typical “fit and forget” manner without analysing their impact on network operation and stability. Grid standards have been developed with set of regulations to allow flawless integration of DG in the main grid.
The focus of this thesis is to develop necessary methodologies, which are compatible with existing grid standards and hence results in improvement of DG share in distribution networks. An extensive literature review reports that proper site, size and interface of DG help to improve system stability condition. However, a reliable index is required for appropriate selection of locations for DG. The significance of load models in distribution systems have been studied in detail, and reactive power margin has been established as a reliable index for distribution system.
Because of the market liberalisation, utilities have to welcome independent power producers (IPP) or nonutility generators (NUG). For these DG units, location and technology are prearranged factors and connection of those units can create new bottlenecks rather than improving the situation. Large scale DG units are facilitated with two supportive features: voltage control mode of operation and fault-ride through capability. However, small scale generators lack fault ride through capability and in most cases they have to operate in power factor control mode. This results in frequent tripping of small DG units under current grid standards. IPPs place various Flexible AC Transmission System (FACTS) controllers at point of common coupling (PCC) to meet grid requirements, which results in a large number of controllers in a DG integrated system.
This thesis has developed a sensitivity index for placement of STAtic COMpensator (STATCOM) utilizing the basic features of the Voltage Source Converter (VSC) construction. The proposed index has been utilized to develop a step by step methodology, which eventually reduces the number of STATCOMs in an effective manner. Methods proposed have been tested for various generation technologies following Low Voltage Ride-through (LVRT) and High Voltage Ride-through (HVRT) operation of small DG units. Though, STATCOM is capable of fast and accurate reactive power compensation, the soaring cost associated with this device stands as its principal drawback. Hence, along with reduction in number of STATCOM installations, tuning method has been applied to reduce the dynamic rating of STATCOM. All proposed methodologies have been tested and validated using two IEEE distribution systems.