Development of coordinated voltage control mechanism for MV networks with large scale solar penetration

Abstract

With the rapidly increasing solar PV penetration to the Utility Distribution Network (UDN) over the past decade, numerous operational challenges including Power Quality (PQ) problems have become substantial compared with the conventional UDN globally. Primarily, solar photovoltaic (PV) systems were connected to the UDN via Low Voltage (LV) side, however, global trend has been advanced to extract solar energy through Medium Voltage (MV) networks up to date via large scale solar farm integration. Steady state voltage rise in the distribution feeders is reported as one of the main constraining factors for limiting solar PV deployment in LV and MV networks. In Sri Lankan context, recent studies proved that over voltages stay unavoidable in LV networks with high solar PV penetration. Further, preliminary system studies has shown that over voltages will give rise due to the connection of proposed 1 MW Solar Farms at MV level under the “Battle for Solar Energy” program. This thesis is a comprehensive study to identify the PQ issues correlated to such MV networks, especially asses the over voltage occurrences during the day time where solar penetration at its maximum. A coordinated decentralized control mechanism is adapted to control the over voltages and maintain the voltage levels within its stipulated limits. Coordination between two decentralized voltage controllers; reactive power control of solar PV inverter and distribution static compensator (DSTATCOM), is proposed to harness the maximum amount of clean energy into the UDN avoiding voltage violations, splitting the MV network into multiple controllable zones. The coordinated voltage control mechanism was modeled using DIgSILENT PowerFactory simulation platform for IEEE 33-bus radial network, which was further extended to the Mauara feeder of the Embilipitiya Grid Substation of Sri Lanka in order to verify the mitigation of over voltages due to large scale solar penetrations. Finally, the influence of the DSTATCOM location and the dead band voltage of the PV inverter on the voltage profile of the Mauara feeder were analyzed.