Distributed Secondary Frequency and Voltage Control of Parallel-Connected VSCs in Microgrids: A Predictive VSG-Based Solution
Oluleke Babayomi
Abstract
The need for converter-based synthetic inertia has become more important due to the increasing level of renewable generation penetration in power systems. In this paper, the distributed secondary regulation of frequency and voltage is implemented for model predictive-controlled (MPC) voltage source converters (VSCs) in an AC microgrid (MG). A virtual synchronous generator (VSG) provides inertia-emulation to reduce the rate of change of frequency (ROCOF) that arises from sudden load changes. First, a small-signal stability analysis for parallel-connected VSG-based inverters in a MG is analyzed. Next, the secondary control of voltage and frequency in a distributed AC MG (with parallel-connected inertia-emulating VSCs) is realized. In addition, for the applied load changes in this study it is shown that the proposed control scheme effectively reduces the load change-induced ROCOF by up to 89% and also has very fast and accurate dynamic response that supports robust and rapid recovery from perturbations to MG stability. Index Terms-AC microgrid, inertia emulation, model predictive control, power converter, rate of change of freguecy (ROCOF), smallsignal stability, virtual synchronous generator.