Effective Reactive Power Reserve Procurement for Economic Operation of MTDC-AC Systems

The reactive power reserve (RPR) procurement is essential in multi-terminal high-voltage direct current-alternating current (MTDC-AC) systems, considering the voltage source converter (VSC) stations, phase reactors and AC lines. Therefore, this paper proposes an optimal power flow (OPF) model for economical, effective reactive power reserve (EQR) procurement in the MTDC-AC systems. The model consists of two stages. The first stage generates economic active-power base-case dispatch points. The second stage is a multi-objective function that maximizes the EQR while minimizing the deviation of active power from its economic base case obtained in stage 1. Compared to the existing models, the constraints for this OPF model are simplified with a modified Y-Bus matrix. This modification includes the converter AC buses in the conventional Y-Bus matrix. Two variations of the proposed method are presented, one for constant reactive power reserve (CQR) and another for EQR. These two models are compared with three existing methods. The model is implemented on the IEEE 14-Bus system for validation.