Coordinated control of load tap changers and distributed energy resources for voltage regulation in active distribution systems

This paper introduces a voltage control method for active distribution systems based on the coordinated operation of on-load-tap-changers (OLTCs) and distributed energy resources (DERs). Primarily, DERs are assigned to control local voltage when overvoltage/undervoltage conditions appear in the system. DER control actions are initiated based on predetermined local voltage criteria and they result in properly changing the active and/or reactive power output of DERs. In case DER control is not adequate to keep voltages within the acceptable operation limits, the LTCs of the MV/LV power transformers are properly controlled to restore local voltages. As a tertiary measure, the LTC of the main substation power transformer regulates the voltage to keep network voltages within permissible limits. Coordination between local voltage control actions is guaranteed with appropriate selection of thresholds. Several scenarios considering hourly time-varying load demand and variable electricity production from DERs are simulated. The proposed voltage control method is tested against several scenarios. Simulation results show that the proposed method efficiently controls voltage in active distribution systems.