Hierarchical control technique-based harmony search optimization algorithm versus model predictive control for autonomous smart microgrids

Abstract

This paper proposes a robust hierarchical control technique for islanded smart microgrids (SMGs). The proposed technique is composed of three control levels to optimally adjust the microgrid (MG) voltage and frequency and improve its power quality by reducing the total harmonic distortion (THD) in islanded mode. The primary control level is based on adjusting the MG voltage and frequency to an acceptable limit after the system load variations using the droop controller. The secondary control level is depending on retaining the MG voltage and frequency to their nominal values after any load changes by proposing a multi-stage H-infinity (H∞) controller. The tertiary control level is proposed to optimally evaluate the multi-stage H∞ controller weighted parameters based on the harmony search (HS) optimization algorithm. To verify the effectiveness of the proposed hierarchical control technique, a model predictive control (MPC) method is designed and simulated. For the sake of comparison between the two methods, different indices are used including maximum frequency deviation, integral of square error (ISE), THD, and controller response time. Robustness analysis is performed based on the impact of line impedance changes and filter parameters variations. Moreover, the system stability is analyzed based on the system step response, singular value decomposition (SVD), and the bode diagram. The proposed control technique and the MPC method are modeled and simulated using MATLAB/Simulink program. The results are reported and analyzed to prove the effectiveness of the proposed control technique.