Control of Multistage SVRs using Voltage Sensor in Distribution System with Large Amount of Photovoltaic Generations

In Japan, in order to reduce greenhouse gas emissions, Photovoltaic generation (PV) is being focused on recently. According to Japanese governmental policy, a large amount of PVs will be introduced into the distribution system in the near future. However, the output of PV depends on weather conditions and climate may change rapidly or randomly. As a result, voltage in distribution system with many PVs will fluctuate; nevertheless, distribution network operator must keep voltage in network within adequate range determined by law. By contrast, Step Voltage Regulator (SVR), which is located on distribution line to control voltage, has time delay to operate against voltage change. Hence, SVR could cause voltage deviation from adequate range when a large amount of PVs are connected to network. From this point of view, several novel equipment that control voltage flexibility such as Static Var compensator (SVC) and Battery are being noted lately. Although, this kind of device using power electronics technology is usually expensive, and huge cost is necessary to introduce these devices into many distribution systems in which there are lots of PVs. For this reason, it is necessary to control voltage with established device such as LRT (Load Ratio control Transformer) and SVR over the next 10 or 20 years, but these devices have several issues such as voltage deviation in case that there are a lot of PVs. The authors focused on SVR and analyzed the cause of voltage deviation by SVR. By analyzing several cases, the authors found the causes of voltage deviation and effective control method of SVR. In proposed method, it can realize to both reduce the cost and keep voltage within adequate range even if there are a lot of PVs in the distribution system.