| Popis: |
Energy storage system based on grid-forming converter (GFMC) is regarded as the key equipment in photovoltaic (PV) system for energy consumption and inertia improvement. However, the design of GFMC aiming at stability improvement of PV & energy storage system (PVESS) is still open to public. Hence, this study takes the PVESS composed of photovoltaic grid-following converter (GFLC) and energy-storage GFMC as the research object, explores the impact of GFMC on the PVESS stability under different operating conditions, and proposes a stability-oriented parameter design method for GFMC. Firstly, the impact of operating conditions on the output impedance of GFLC and GFMC in PVESS is analyzed. Secondly, by treating the GFMC and the grid as an equivalent grid (i.e., an equivalent subsystem) and taking into account the operating status of PVESS, the system stability under different operating conditions is discussed in detail. Results show that the PVESS stability is the worst when the PV output is maximum, and, because the output impedance of GFMC in low-to-mid frequency range is dominated by its filter inductor, the strength of the equivalent grid is seriously affected by the GFMC filter inductor. Hence, as the key factor affecting the PVESS stability, the GFMC filter inductor deserves a careful selection. Subsequently, a comprehensive design for GFMC filter and control parameters is proposed, which can effectively improve the PVESS stability under the weak grid. Hardware-in-the-loop (HIL) experiments are conducted to verify the effectiveness of the proposed method. |
