Utility intertie multi-photovoltaic-inverters-based microgrid control for solar rooftop

Abstract

The solar photovoltaic (PV)-based microgrid is one of the most ideal renewable energy resources. This paper presents a utility grid intertie multi-PV-inverter-based microgrid (MG) control for the solar rooftop application. The main and ancillary voltage source converters (VSCs) DC links are assimilated with PV arrays of independent maximum power point tracking (MPPT) algorithms for the economical and efficacious single-stage configuration. At the point of common coupling (PCC), parallel VSCs arrangement increases the MG's power rating with distinctive local loads. In normal circumstances, the current control methodology is employed by the main VSC under the grid-interactive mode. Conversely, in some grid contingency conditions under the isolated mode, its control transfers to the voltage control, which regulates the frequency and the voltage at PCC and acts like a grid-forming inverter. The ancillary VSC operation is implemented with the current control algorithm. The main VSC supplies the active power towards the grid and accomplishes the load requirement, whereas the ancillary VSC retains its load demand in a grid-interactive mode and also regulates the load requirement in an islanded mode of operation. The utilization of feed-forward components for PV arrays powers in the VSCs current control techniques improves the MG dynamic performance. The seamless mode transfer performance of the main VSC is implemented via a power electronics switch. The MATLAB software is used to model a microgrid and its performance is analysed via RT-LAB in real time through the OPAL-RT (OP4510) controller for various scenarios, that is, varying solar insolation, load alterations and unbalanced non-linear loads. The utilization of the modified Kwong's algorithm-based current control enhances the power quality such as harmonics current elimination and improvement in the power factor. The voltage profile of PCC voltages is enhanced via using a modified Kwong's algorithm-based filter in the voltage controller. The modified Kwong's algorithm has fast convergence, reduces misadjustments and gives very good performance compared to the least-mean-square (LMS) and Kwong's approaches. The total harmonic distortion (THD) of grid currents and PCC voltages THD in an isolated mode is found according to the limits of the IEEE-519 standard.