Extended Operating Region Algorithm for PV Array Connected to Microgrids for Wide Frequency and Amplitude Variations

Abstract

The employment of microgrids and distributed power generation have exponentially increased over recent decades, due in part to the increased inclusion of renewable energies as these technologies become cheaper to install. However, microgrids are highly sensitive to power variation, leading to distortion of the grid voltage (amplitude and frequency changes) which could destabilize the entire microgrid under variation of loads and/or other power sources. In this context, a new control strategy is proposed for a photovoltaic grid connected system, operating under voltage variations typical of a low inertial electric power network. The main problem related to voltage fluctuation is that the variables may take the power converter out of the operating region, and therefore, all controllers, including the maximum power point tracking, will not work as designed. The analysis, based on the mathematical operating region, demonstrates that the control strategy can include overmodulation compensation—to overcome problems related to weak microgrids and systems variations—through the addition of smart power factor imposition and DC-link voltage variation in transient time when the variables are far from the nominal values. The proposal is validated through simulation in PSim®/Matlab® and implementation on a laboratory prototype, showing the feasibility of the designed algorithm.