A General Design Procedure for Multi-Parallel Modular Grid-Tied Inverters System to Prevent Common and Interactive Instability

Based on the equivalent circuit model, the interactions of multi-parallel modular grid-tied inverters and their coupling effect with grid impedance are analyzed in this letter. The analysis shows that interactive instability could happen in the inverter system even when identical inverters have been used. However, if the control and circuit parameters are designed in a systematic manner, the system can be exempted from both common and interactive instability. The outcome of this research provides a practical general design paradigm for modular grid-tied inverters with LCL filters which can be used in the parallel operation with unknown numbers of modules. Experimental results are provided for verification.