| Summary: | In this paper, a novel low voltage ride-through (LVRT) technique for three-phase grid-connected inverters is proposed. The proposed technique consists of two parts: a nonlinear phase locked loop based on complex-coefficient filters (NLCCF-PLL) and an LVRT control scheme. Generally, the synchronization process of three-phase grid-connected inverters is performed via PLL with a relatively low bandwidth, which delays the detection of voltage sag and recovery during the LVRT process. To accelerate the synchronization process, the NLCCF-PLL with adaptive controller gains is proposed to improve both the filtering capability and dynamic performance of PLL at the same time. The stability of the NLCCF-PLL is validated by the second method of Lyapunov in the nonlinear model, and the superiority of its operating performance is verified. The proposed LVRT control scheme consists of a reference current calculation block to effectively suppress the power ripples and an inner loop controller with strong robustness as well as fast dynamic response. By comparing the proposed LVRT technique with the existing LVRT technique on the basis of experimental results, the superiority of the proposed LVRT technique is confirmed.
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