Distributed control of active distribution networks for frequency support

It is a new trend to utilize highly distributed energy resources (DERs) scattered in distribution networks to support power system frequency control. However, in a power system, there may be thousands or millions of DERs, and it is impractical to control these DERs directly by the control center. To solve this challenge, we regard each distribution network with DERs as a distributed energy resource cluster (DERC) which serves as the intermediary between DERs and the control center. For each DERC, the primary objective is to quickly follow the active power change command given by the control center. However, due to the high R/X ratio of lines in distribution networks, the active power changes of DERs can also lead to voltage issues such as voltage variation and violation in a distribution network. To overcome these issues, this paper develops a novel distributed control framework for DERCs to support frequency control, which consists of two modules: an active power sharing module and a voltage regulation module. The former one aims to rapidly track the active power change command from the control center by coordinating the active power of DERs in an optimal distributed manner. The latter one aims to regulate bus voltages within the acceptable limits by changing the reactive power of each DER based on local voltage information. The effectiveness of the proposed control framework has been tested through an 8-bus distribution system.