ALBERT

Description: The emergence of various power electronic devices, including voltage source converters (VSCs), has greatly changed the dynamics of power systems. It is a great challenging to put forward new theories for modeling, analysis, and understanding of power-electronic-based power systems. In this paper, we first establish a detailed nonlinear model of multiple VSC systems, and then, by using the singular perturbation technique, obtain a reduced-order nonlinear model within the DC-link timescale. The latter model consists of differential algebraic equations (DAEs) and keeps slow dynamics in transient processes, showing a balance between computational accuracy and system complexity. Furthermore, the model is compared with the traditional electromechanical dynamical model of power systems, which are dominated by synchronous generators (SGs). Our model of multi-converter systems can be put into a similar diagram to the traditional power system dynamics, with which most of power electrical engineers are familiar. Finally, wide simulation results verify the efficiency of the proposed model.

Description: Traditional power systems have been gradually shifting to power-electronic-based ones, with more power electronic devices (including converters) incorporated recently. Faced with much more complicated dynamics, it is a great challenge to uncover its physical mechanisms for system stability and/or instability (oscillation). In this paper, we first establish a nonlinear model of a multi-converter power system within the DC-link voltage timescale, from the first principle. Then, we obtain a linearized model with the associated characteristic matrix, whose eigenvalues determine the system stability, and finally get independent subsystems by using symmetry approximation conditions under the assumptions that all converters’ parameters and their susceptance to the infinite bus (Bg) are identical. Based on these mathematical analyses, we find that the whole system can be decomposed into several equivalent single-converter systems and its small-signal stability is solely determined by a simple converter system connected to an infinite bus under the same susceptance Bg. These results of large-scale multi-converter analysis help to understand the power-electronic-based power system dynamics, such as renewable energy integration. As well, they are expected to stimulate broad interests among researchers in the fields of network dynamics theory and applications.