Received December 26, 2018, accepted January 7, 2019, date of publication January 14, 2019, date of current version February 8, 2019. Digital Object Identifier 10.1109/ACCESS.2019.2892747 Enhanced Virtual Inertia Control Based on Derivative Technique to Emulate Simultaneous Inertia and Damping Properties for Microgrid Frequency Regulation THONGCHART KERDPHOL 1 , (Member, IEEE), FATHIN SAIFUR RAHMAN 1 , (Student Member, IEEE), MASAYUKI WATANABE 1 , (Member, IEEE), YASUNORI MITANI 1 , (Member, IEEE), DIRK TURSCHNER 2 , AND HANS-PETER BECK 2 1 Department of Electrical and Electronic Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan 2 Institute of Electrical Power Engineering and Energy Systems, Clausthal University of Technology, 38678 Clausthal-Zellerfeld, Germany Corresponding author: Thongchart Kerdphol (kerdphol@ieee.org) This work was supported, in part by the Power System and Renewable Energy Laboratory (Mitani-Watanabe Lab), Kyushu Institute of Technology, Kitakyushu, Fukuoka, Japan, and in part by the Institute of Electrical Power Engineering and Energy Systems, Clausthal University of Technology, Lower Saxony, Germany. ABSTRACT Virtual inertia control is considered as an important part of microgrids with high renewable penetration. Virtual inertia emulation based on the derivative of frequency is one of the effective methods for improving system inertia and maintaining frequency stability. However, in this method, the ability to provide virtual damping is usually neglected in its design, and hence, its performance might be insufficient in the system with low damping. Confronted with this issue, this paper proposes a novel design and analysis of virtual inertia control to imitate damping and inertia properties simultaneously to the microgrid, enhancing frequency performance and stability. The proposed virtual inertia control uses the derivative technique to calculate the derivative of frequency for virtual inertia emulation. Trajectory sensitivities have been performed to analyze the dynamic impacts of the virtual inertia and virtual damping variables over the system performance. Time-domain simulations are also presented to evaluate the efficiency of the virtual damping and virtual inertia in enhancing system frequency stability. Finally, the efficiency and robustness of the proposed control technique are compared with the conventional inertia control under a wide range of system operation, including the decrease in system damping and inertia and high integrations of load variation and renewable energy. INDEX TERMS Frequency stability, isolated microgrid, virtual inertia regulation, virtual synchronous machine. I. INTRODUCTION Recently, the transition in electricity from centralized gener- ation to distributed/decentralized generation (DG) has made microgrids attractive and suitable for integrating renewable energy sources (RESs). The microgrid infrastructure has proven to be an alternative strategy for solving the challenges of the energy crisis and environmental concerns, as it consists of DG/RESs, energy storage systems (ESS), and distributed loads [1]. With the rising share of RESs-based generation, it raises the new stability issues in regulating the microgrid. One of the major problems is the lack of system inertia and damping owing to the replacement of traditional generations (i.e., synchronous generators) by RESs-based generation. The main reason for system inertia reduction is because of the converter/inverter that is usually used to connect the RESs to the microgrids. The inverter/converter does not possess any inertia or damping properties, leading to the degradation of system inertia and damping, larger frequency excursion, and system instability and collapse, see for an example [2]. On the contrary, high system inertia and damping generated by the 14422 2169-3536  2019 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. VOLUME 7, 2019