Analysis and damping of high-frequency oscillations at the presence of distributed constant power loads

Distributed power system can be subjected to a high penetration level of constant power loads (CPLs). In this circumstance, the system stability is a matter of concern. In this paper, the distribution effect of grid-connected CPLs is analyzed in an AC distributed power system. In fact, the interaction dynamics between different arrangements of distributed CPLs and the grid are completely compared. To this aim, the total power of all arrangements of distributed CPLs is considered constant that is called fixed-power arrangements in this work. Accordingly, first, the linearized model of tightly regulated voltage source rectifier (VSR), treating as a CPL, is developed. Then, the obtained model is generalized for multiple VSRs to provide distributed CPLs model. Further, by applying the bode diagram method and eigenvalues-based analysis, the distribution effect of CPLs on their stability is evaluated. The conducted analysis reveals that the distribution of CPLs is accompanied by different responses in their interactions with the grid, which is mainly highlighted at their high-frequency (HF) behavior. Moreover, it is obtained that more distribution of CPLs can deteriorate their HF interaction and lead to a reduction in system stability. According to these achievements, it can be deduced that ideal models of CPLs by negative impedances are not valid anymore, especially at higher frequencies. Afterward, a proper active damper is implemented to reduce the mentioned HF oscillations. The simulation studies of several distributed CPLs cases, as well as a centralized CPL, confirm the validity of the performed analysis.