Dynamic modeling, sensitivity assessment, and design of VSC-based microgrids with composite loads

Abstract

Microgrids are seen as useful for increasing the flexibility of distribution networks and integrating large amounts of distributed generations. Ensuring the dynamic stability of power converter-dominated microgrids that is robust to a range of load conditions is a significant challenge and essential for ensuring reliability. Induction motor (IM) loads are widespread and have substantial impacts on the dynamic behavior and stability characteristics of low-inertia microgrids. The stability assessment and design of microgrids considering composite loads have not been sufficiently addressed in the current literature, where static loads are commonly used to simplify the modeling and analysis. In this paper, the dynamic stability of voltage source converter-based microgrids is investigated, considering composite loads as dynamic element. A complete state-space model of the microgrid with both IM load and static load is developed. Participation factor analysis is conducted to identify the contribution of the composite loads to the dominant oscillatory modes of the microgrid. Furthermore, sensitivity assessment of the dominant eigenvalues is presented to further identify the appropriate ranges of variations in the control parameters, operating conditions and operating points of the microgrid. It is shown that composite loads in a realistic microgrid significantly affect the dominant oscillatory modes and, consequently, the system stability margin. Ignoring the composite load dynamics in microgrid stability studies may lead to misleading analytical results. Simulations based on MATLAB/Simulink and experimental tests based on a laboratory prototype microgrid are implemented to demonstrate the theoretical analysis.