Passivity-based stability analysis of parallel single-phase inverters with hybrid reference frame control considering PLL effect

•The passivity analysis of single-phase grid-connected inverter controlled in synchronous reference frame (SRF) is presented.•The influence of multisampling, capacitor current feedback active damping (CCF-AD) and various PLLs on the passivity properties of single-phase grid-connected inverter are presented.•The passivity of inverter admittance in the high-frequency band is affected by the multisampling and the CCF-AD, and the passivity in the low-frequency band is influenced by the PLLs, using delay-based PLL and SOGI-PLL as case studies for validation.•The stability of the inverter-grid system under inductive and capacitive grid conditions is also evaluated. The passivity-based stability criterion (PBSC) is an effective tool to analyze the interactive stability issues between the multi-parallel inverters and the grid. However, when using the passivity theory to evaluate the interactive stability, the influences of grid synchronization and multisampling on the passivity of inverter output admittance are overlooked in previous studies. To fill this gap, the impact factors in the grid-connected control, such as multisampling, capacitor current feedback active damping (CCF-AD) and various phase-locked loops (PLLs), on the passivity of inverter output admittance is investigated in this paper. Moreover, the stability of the interconnected system in the inductive and capacitive grid scenarios are also assessed. Since the effective control delay are determined by the multisampling coefficient, the passivity of inverter output admittance in the high-frequency range is mainly affected by multisampling and CCF-AD, whereas the passivity in the low-frequency range is related to the bandwidth of PLLs. In case of an identical PLL bandwidth, the non-passive region of admittance when using SOGI-PLL appears in a lower frequency band, and thus the non-passive region is the smallest in comparison, which provides stronger robustness. Finally, simulation studies and experimental results are presented to verify the effectiveness of the theoretical analysis.