Implementation and comparison of droop control, virtual synchronous machine, and virtual oscillator control for parallel inverters in standalone microgrid

Abstract

In recent times, renewable energy sources (RESs) have been potential alternatives over the conventional generation systems connected to the grid. The power electronic inverters are the principal media of interface for connecting the RESs to the utility grid system. This work is primarily focused on the comparative analysis of Droop, virtual synchronous machine (VSM), and virtual oscillator control (VOC) techniques for the parallel operated inverters in a standalone Microgrid (MG). Droop control emulates only the droop characteristics of synchronous machines such that the transient response of this controller is not significant. VSM imitates not only the droop characteristics of synchronous machines but also the swing equation. Therefore, VSM has a remarkable difference in the dynamic performance of the system. In droop and VSM, the feedback signals such as voltage and current are measured to calculate the averaged real and reactive powers. However, the VOC works on instantaneous feedback signals such that it achieves much faster synchronization and good power-sharing. The philosophy of the proposed VOC is to control an inverter such that it emulates the behavior of a nonlinear dead-zone oscillator. The performance analysis of the system with the aforementioned controllers has been studied based on MATLAB/Simulink and Opal-RT digital simulation. From the comparative analysis, it is observed that the VOC gives a better performance compared to droop and VSM control. The experimental results show the efficacy of the proposed VOC control method.