Virtual frequency construction-based vector current control for grid-tied inverter under imbalanced voltage

This paper proposes a fast phase capture (FPC) scheme and applies it to the control strategy of grid-tied inverters under imbalanced voltage. Firstly, a method for quickly extracting sequence components of power signals is derived through the symmetrical component method, and a real-time phase calculation method is proposed based on the rotating reference frame, thus avoiding the phase-locked loop (PLL) closed-loop adjustment process. Secondly, the grid-tied inverter suppresses the negative sequence current or power fluctuations through the direct resonance controller, so there is no need to separate the dynamically changing sequence current components. Finally, the experimental comparison with the PLL control strategy is carried out based on the RT-LAB platform. Compared with the previous phase-locking scheme, the FPC scheme has a faster phase-locking speed. Therefore, the fault ride-through capability of the grid-tied inverter is improved.