Harmonic Analysis and Control of Grid-Connected Solar PV Inverter under Normal and LVRT Operating Modes

Abstract

Environmental factors and active involvement in grid-connected solar PV inverter ancillary operations may impact the quality of the current injected into the grid. The future grid-connected solar PV system with ancillary facilities (e.g., low voltage ride-through (LVRT)) will be more active and intelligent, which will degrade grid current reliability. The grid current distortions are specifically caused by the dc-link voltage variations and the modulation of pulse width (PWM) control applied to the PV inverter. This article analyzes the current harmonic distortion under the two-stage grid-connected PV system's regular (MPPT) and fault (LVRT) condition. Furthermore, a dc-link voltage variation control system for the two-stage photovoltaic (PV) inverter is presented during low voltage ride-through (LVRT) operation mode..The dc-link voltage differences are regulated under the fault condition to preserve the high modulation ratio in order to considerably mitigate the distortion rate of the grid current. Besides, the proposed system of control is designed to protect the PV inverter from the overcurrent failure under the faults to meet the modern LVRT grid codes. The conducted simulation tests have confirmed that the proposed control scheme leads to reduce a grid currents harmonics level by controlling the dc-link voltage variations.