Cooperative Voltage Regulation Method between on-Load-Tap-Changers and Smart Inverters in Distribution Systems Using Communication

With the expected massive introduction of photovoltaic (PV) in the distribution system, there is a need for more sophisticated voltage regulation methods to address complex power flows. Smart inverters (SINVs) are expected to contribute to the advancement of control because they have additional voltage regulation and communication functions. The voltage in the distribution system is regulated by SINVs and an existing voltage control equipment on-load-tap-changer (OLTC). However, because the response speed of SINVs is faster than that of 0 LTC, the voltage regulation burden may tend to be concentrated on SINVs in terms of an increase in reactive power injection. The increase in reactive power injection will result in a shortage of SINV capacities, and PV output curtailment will be caused. To address these problems, a cooperation scheme between OLTC and SINVs is required. SINVs communication functions are considered useful for realizing cooperation because the function induces distribution system operators to monitor the SINVs output condition. In this study, we propose a cooperative voltage regulation method in which OLTC switches control modes; normal mode and cooperative mode based on the amount of reactive power injection of each SINV obtained through communication functions. The numerical simulation was conducted using a Japanese six-feeder distribution system model that penetrated large amounts of PVs to evaluate the effectiveness of the proposed method in terms of voltage violations, reactive power injection from SINVs, and number of OL TC tap changes.