School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai200240, China

The characteristics of negative resistance caused by the phase-locked loop of the grid-following converters are prone to resulting in oscillations in a weak power grid. The improved strategies for the phase-locked loop have been widely studied. In particular, the synchronization control strategy based on the voltage matrix has received much attention due to the lack of phase-locked loops. However, there is no rigorous theoretical proof of its stability. The analysis in this paper indicates that the voltage matrix based control strategy without the phase-locked loop is essentially an open-loop orientation approach based on the arctan calculation of the voltages at the point of common coupling (PCC). This strategy removes the phase-locked loop, but cannot improve stability. Since this strategy does not reduce the negative resistance characteristic brought by voltage perturbation on current control, how to reduce the effect of PCC voltage perturbation on current control is the key to improving the stability of grid-following converter in a weak power grid. Therefore, this paper proposes an adaptive band-pass filter to reduce the bandwidth of the synchronization loop, so as to improve the stability of the grid-following converter in a weak power grid. Finally, the correctness of the theoretical analysis and the effectiveness of the proposed strategy are verified by the impedance model and experimental results.