A Two-Stage Solution to the Bi-Objective Optimal Voltage Regulation Problem

In this paper, a two-stage approach is introduced to efficiently solve the optimal voltage regulation problem in radial medium-voltage (MV) distribution networks. The proposed method uses the available reactive power of distributed generation units and the on-load tap changer (OLTC) of the high-voltage/MV transformer to regulate network voltages, while also minimizing two conflicting objectives, namely the network energy losses and the frequency of tap changes. This bi-objective optimal voltage regulation problem is addressed in two distinct stages. In the first stage, the network is linearized and a simplified optimal voltage regulation problem is solved to determine the candidate OLTC operating plans (COOPs). For each COOP, a new reactive power allocation method is employed in the second stage to regulate the network voltages and minimize network losses. This method follows a rule-based approach, also allowing its implementation under real-field conditions. The final outcome of this two-stage process is the Pareto-front which can be used by the distribution system operators to select the most preferable solution for the real-time network operation. The proposed methodology is characterized by reduced computational complexity compared to the application of conventional optimization techniques. Time-domain and time-series simulations on a radial MV distribution network are employed to thoroughly evaluate the performance of the proposed method.