Novel Supervisory Control Method for Islanded Droop-Based AC/DC Microgrids

This paper presents a novel supervisory control method for an islanded hybrid ac/dc microgrid (HMG) with a high renewable energy source (RES) penetration. Droop control can respond to inevitable uncertainties in the load and RES. However, this leads to frequency and voltage deviations, and the generator output power may deviate from the optimal point. To restore the frequency and voltage of both ac and dc grids while reducing generation cost at short time intervals, a model predictive control based optimization problem is formulated to update the set-points of the available resources including the interlinking converter and distributed generators. With the sensitivities, which help to linearly express the frequency and voltage for resource output power, the problem can be approximated to a quadratic programming model. In addition, to consider the effect of the reactive power on the frequency and improve the accuracy, the second-order frequency sensitivity is calculated and applied selectively. The proposed method was tested on a modified IEEE 33-bus system connected to a sample dc grid. The simulation results validate its performance for reliable and economic operation in an islanded HMG.