Droop Control-Based Grid Forming Inverters with an Auxiliary Grid Support Control for Frequency Regulation in a Low Voltage Microgrid

Abstract

Aim: Improving the frequency regulation in a Low Voltage (LV) microgrid during grid mode transition using Grid Forming Grid Support (GFGS) converters with inertia emulation. Background: The ever-increasing demand for energy and the depleting fossil fuels has increased the proliferation of converter-fed Renewable Sources (RES) in the conventional grid. The reduced system inertia results in frequency regulation issues which are further aggravated by the unpredictable nature of RES and dynamic switching of loads. This scenario results in blackouts, unwanted load shedding, power quality issues, and discrepancies in protection schemes. Objective: A control scheme is presented on the principle of swing equation-based synchronization to regulate the active power output of a grid-tied voltage-source converter operating in a grid forming grid supporting mode in a low voltage PV-based microgrid. The Virtual Synchronous Machine control (VSM) is implemented for controlling the active power output, which follows the grid frequency deviations, ensuring the safe State of Charge (SoC) limits of the Battery Energy Storage System (BESS). Methods: The stability issues due to the absence of inertia in an inverter-fed LV microgrid are staved off by giving auxiliary grid support by implementing VSM control in a BESS inverter in the grid forming mode. The LV microgrid model with all the converters in the GFGS converter is developed in the MATLAB/Simulink environment. Particle Swarm Optimization (PSO) is used to fine- tune the control parameters. The effectiveness of the control strategy has been investigated for unintentional islanding events. Results: The droop control-based GFGS grid-tied converters with power balance equation-based VSM control gave frequency regulation within the range stipulated by the grid codes during the islanding events. Conclusion: The work demonstrates the effectiveness of VSM control in providing the auxiliary grid support for droop-based grid forming converters in an LV microgrid.