Control of inertia in hybrid microgrids from a regulated DC microgrid system

Abstract

A methodology for controlling the inertia of the interlinking converter of a hybrid AC-DC microgrid working in both grid connected and isolated modes, is presented in this paper. The DC microgrid system is a Photovoltaic Generator (PVG) and a battery based energy storage (BES) based system, with constant impedance loads. The purpose of the DC microgrid is to manage the power within the DC system and to provide the necessary inertial support to the AC system. For the control of the interlinking voltage source inverter, a DC link voltage based virtual inertia strategy is formulated, which is formed as a lead-lag compensator with the change in the DC link voltage as the input, and the frequency as the output. The proposed method serves a two-fold advantage as a unified controller, i.e., the requisite inertial response is provided, as the compensator is the outcome of the swing equation, and the same controller can act as a bus signalling control, therefore managing the power flow to the utility in the grid connected mode of operation. Time domain analysis of the microgrid system verifies the efficacy of the proposed approach for both power flow based on utility command, as well as inertial support in the isolated mode. The compensator tuning is achieved with the help of a small signal analysis of the cascaded inertial controller deployed.