Robust controller for grid-connected quasi-admittance source inverter for photovoltaic system

Abstract

This paper presents a robust control technique, such as an H∞ control technique, for a grid-connected quasi-admittance source inverter (QYSI). A QYSI inherits all the advantages of a quasi-impedance source inverter, such as high voltage conversion gain, and draws continuous current from the source and reliable grid operation. The QYSI has high boost capability, reducing the voltage stresses on devices and suppressing the start-up inrush current. A closed-loop controller system design is significant in a QYSI, as it influences the boosting of photovoltaic voltage (PV), maximum power point tracking (MPPT), and grid connection. In grid connection, variations in grid impedance may cause system instability when the grid current controllers are not robust. Hence, in this work, a robust controller is proposed to enhance the stability margin and reliability of the system. Along with this control, it is essential to extract the maximum power from the PV source and hence, a reinforcement learning-based MPPT algorithm is used to track a maximum power point from the PV. The proposed system is compared with a proportional resonant controller. The QYSI system is tested for variations in grid impedances, grid frequency, and voltage amplitude. The simulation results show the effectiveness of the proposed controllers in terms of power quality. The simulation results are validated with real-time experiments.