Interaction Dynamics Analysis and Active Stabilization of a Weak Grid-Tied Hybrid PV-Wind Power Generator

This paper addresses the dynamic stability of a hybrid photovoltaic (PV) and wind turbine (WT) system tied to a weak grid by back-to-back voltage-source converters (VSCs). The overall system stability is assessed by developing a detailed time-domain nonlinear model (TDNLM) and a linearized state-space model (LSSM). The dynamic interactions at both the peak-power point (PPP) and off-PPP operation of the PV and WT power characteristics curves have been examined. The results reveal that the complete system is stable under PV-only and WT-only generation scenarios at the PPP and off-PPP operation regions. However, the PV-WT hybrid system experiences low- and high-frequency fluctuation instabilities in the current-limited region (CLR) of the PV characteristic due to the interaction between the high dynamic resistances of the PV-WT source and the weak grid. Conversely, the system remains stable at the PPP and voltage-limited region (VLR) of the PV characteristic and in all operational regions of the WT characteristic. Motivated by these challenges, a novel active damping method is proposed to mitigate the interaction dynamics, maintaining overall system stability by relocating unstable eigenmodes and reshaping the dc-link transfer function. The proposed damping method offers several benefits: 1) it is simple yet efficient and can be implemented and modeled using linear analysis tools; 2) it allows for dynamic and stable operation across various operating regions; 3) it does not interfere with steady-state performance in both stiff and weak grid operations; 4) it facilitates successful low-voltage-ride-through (LVRT) at different operating regions; and 5) it effectively addresses its shortcomings by eliminating the need for additional voltage or current sensors, thereby enhancing simplicity and reducing cost in comparison to other approaches. Detailed offline and real-time simulations validate the analytical findings and the effectiveness of the proposed stabilization method under different operational scenarios.