Quantitative Impacts Analysis of the Inner Current Loop on Grid-Tied Converters’ Transient Synchronous Stability

In most of the previous studies about the transient synchronous stability of grid-tied converters, the dynamics of the inner loops are often neglected. However, under non-ideal inner loops conditions, the adverse effects must be considered to avoid an over-optimistic estimation of stable boundary. Otherwise, unacceptable stability misjudgment will occur. There are seldom quantitative and analytic large signal analyses take the current loop dynamics into account. To fill this gap, an altering equal area criterion is proposed based on the iterative equal area criterion in our earlier paper. Firstly, the model of the inner current loop and line dynamics are deduced, which can be found decoupled with the phase-locked loop (PLL). Time-domain analytic solutions of these dynamics are thus obtained. Then a conservative estimation of the inner current loop's impacts on PLL is given based on the proposed altering equal area criterion. Simulation and hardware in the loop experiment verify the effectiveness and superiority of the proposed method.