Second Harmonic Injection-Based Recovery Control of PV DC Boosting Integration System

The photovoltaic (PV) DC boosting integration system should have ability of low-voltage ride through (LVRT). Normally, the LVRT controls of whole system require DC/DC converters to switch off the maximum power point tracking (MPPT) control when the AC voltage surges. However, DC/DC converters are difficult to automatically switch back to their original MPPT control for some disturbances which cause small voltage variations. In this article, a recovery control strategy based on inverter second harmonic injection is proposed. By modifying the negative sequence current reference of converter, the second harmonic is actively injected to the system in a short time when the disturbance disappears, then DC/DC converters can switch back to the MPPT control in time by monitoring the amplitude of DC voltage second harmonic component without additional communications between them. In addition, the threshold settings of second harmonic voltage are investigated. The simulation results show that the control strategy of DC/DC converters can reliably and quickly switch back to MPPT after the disturbance disappears under various grid fault types. The proposed method effectively improves the power generation efficiency of PVs during grid disturbances.