| Summary: | In the control of grid-connected power inverters, the frequency and amplitude information of fundamental positive-sequence component of grid voltage need to be obtained quickly and accurately, especially when the grid voltage is imbalance, harmonic pollution is serious and DC offset is mixed. A novel phase-locked-loop (PLL) with an improved-dual adaptive notch filter (IDANF) and multi-variable filter (MVF) was proposed in this paper. On one hand, the PLL with IDANF can not only remove the negative sequence components but also achieve an excellent suppression to the fundamental frequency oscillations caused by DC offset. On another hand, PLL with MVF can greatly filter out harmonics on the stationary $\alpha \beta $ reference frame. Finally, the results of simulation and experimental examples show that the proposed method is able to accurately obtain the information of grid synchronization signal when the grid voltage is distorted, unbalance and mixed DC Offsets.
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