Predictive Control of TN-DN Boundary Bus Voltages with Long-Term Stability Constraints

This paper presents a controller based on model predictive control that regulates bus voltages in weakened networks without compromising their long-term stability. The controller acts directly on load tap changers of step-down transformers, and requests additional support, when available, from Distributed Energy Resources (DERs). One of its salient features is that it only requires a static model of the transmission network. By casting the voltage regulation as a constrained quadratic program, the controller is able to compute the actions that maintain acceptable voltages over a receding horizon while minimizing the DER efforts. Furthermore, to ensure that the voltages remain long-term stable, an online stability indicator (New LIVES) is included as a constraint of the optimization problem. The controller is tested on a small system and the results show that the transmission voltages can be regulated without overusing the power reserves in the distribution network.