In this study, a new robust non-integer order controller is presented for the secondary load frequency control (LFC) of the shipboard microgrid (MG). During the design phase of the controller, the time delays between the controller and the sensor as well as the actuator are also taken into account, and a robust controller design against these time delays has been realized accordingly. The system frequency is regulated by a single input interval type-2 fuzzy fractional-order PI (SIT2-FFOPI) controller. The basic FOPI parameters of the SIT2 controller are determined offline with the help of the stability boundary locus (SBL) method depending on the time delay and integral order. For the determination of basic FOPI parameters, the characteristic equation of the shipboard MG LFC model is obtained, and the necessary arrangements are made. The geometric centroid is calculated to obtain the basic parameter values in the SBL curve obtained. The performance of the proposed controller design is assessed using real-world marine wave and solar irradiation data in the shipboard MG. Also, the process of verification of the applicability of the proposed method from a systemic perspective is done by real-time hardware-in-the-loop (HIL) simulation based on OPAL-RT.

This study proposes a new application for delay-dependent stability analysis of a shipboard microgrid system. Gain and phase margin values are taken into consideration in delay dependent stability analysis. Since such systems are prone to unwanted frequency oscillations against load disturbances and randomness of renewable resources, a virtual gain and phase margin tester has been incorporated into the system to achieve the desired stabilization specification. In this way, it is considered that the system provides the desired dynamic characteristics (e.g. less oscillation, early damping, etc.) in determining the time delay margin. Firstly, the time delay margin values are obtained and their accuracy in the terms of desired gain and phase margin values are investigated. Then, the accuracy of the time delay margin values obtained by using the real data of renewable energy sources and loads in the shipboard microgrid system is shown in the study. Finally, a real-time hardware-in-the-loop (HIL) simulation based on OPAL-RT is accomplished to affirm the applicability of the suggested method, from a systemic perspective, for the load frequency control problem in the shipboard microgrid.