The fixed-frequency synchronous reference frame-based direct power control (FSRF-DPC) strategy is investigated in this study, which can avoid the phase-locked loop. However, the existing research are focused on its application in a strong grid, where grid impedance is assumed as zero. The effect of grid impedance on FSRF-DPC strategy is ignored, and the stability of FSRF-DPC controlled converter in a weak grid is not clear. To fill this gap, the impedance-based stability analysis is adopted. The sequence domain impedance of FSRF-DPC controlled grid-connected converter is developed in this study. The equivalent decoupled sequence domain impedance of FSRF-DPC controlled converter is further extracted by loop decomposition technique. The impacts of controller parameters and grid impedance on the equivalent sequence domain impedance are studied. A damping method by modifying the voltage feedforward term is investigated based on the stability requirement on the impedance characteristic. Finally, simulations and experiments are carried out to verify the correctness of the proposed impedance model of FSRF-DPC controlled converter as well as the effectiveness of the proposed damping method.

中文翻译：

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并网变流器FSRF中DPC的稳定性分析

本文研究了基于固定频率同步参考帧的直接功率控制（FSRF-DPC）策略，该策略可以避免锁相环。然而，现有的研究集中在其在强电网中的应用，在强电网中电网阻抗被假定为零。电网阻抗对FSRF-DPC策略的影响被忽略，并且在弱电网中FSRF-DPC控制的转换器的稳定性尚不清楚。为了填补这一空白，采用了基于阻抗的稳定性分析。这项研究开发了FSRF-DPC控制的并网转换器的序列域阻抗。通过环路分解技术进一步提取了FSRF-DPC控制转换器的等效解耦序列域阻抗。研究了控制器参数和电网阻抗对等效序列域阻抗的影响。基于对阻抗特性的稳定性要求，研究了通过修改电压前馈项的阻尼方法。最后，通过仿真和实验验证了所提出的FSRF-DPC控制变换器阻抗模型的正确性以及所提出的阻尼方法的有效性。