Stability Investigation of Three-Phase Grid-Tied PV Inverter Systems Using Impedance Models

With the increasing penetration of power-electronic-based renewable generations, stability issues become challenging due to interactions between converters and the grid. This article develops a framework to investigate the stability of grid-tied photovoltaic inverter systems using impedance models (IMs). IMs are developed considering the complete system dynamics for both proportional-integral (PI) control and proportional-resonance (PR) control structures. Different stability investigation methods are elaborated with a focus on the Bode plot and the generalized Nyquist criterion. Sensitivity analyses are conducted utilizing Bode plots to observe the impact of different factors in the frequency domain. Followed by that, an impedance-resonance analysis method is proposed to identify the cause of resonances according to the critical interactions of diagonal impedances and the frequency range of resonances. The performance of PI and PR controls is compared with a focus on the influence of the outer control loops. The analyses are validated through experiments in a down-scale test bench.