Analysis of the effect of clock drifts on frequency regulation and power sharing in inverter-based islanded microgrids

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Local hardware clocks in physically distributed computation devices hardly ever agree because clocks drift apart and the drift can be different for each device. This paper analyses the effect that local clock drifts have in the parallel operation of voltage source inverters (VSIs) in islanded microgrids (MG). The state-of-the-art control policies for frequency regulation and active power sharing in VSIs-based MGs are reviewed and selected prototype policies are then re-formulated in terms of clock drifts. Next, steady-state properties for these policies are analyzed. For each of the policies, analytical expressions are developed to provide an exact quantification of the impact that drifts have on frequency and active power equilibrium points. In addition, a closed-loop model that accommodates all the policies is derived, and the stability of the equilibrium points is characterized in terms of the clock drifts. Finally, the implementation of the analyzed policies in a laboratory MG provides experimental results that confirm the theoretical analysis.Peer ReviewedPostprint (author's final draft

Electric spring and smart load: technology, system-level impact and opportunities

Increasing use of renewable energy sources to combat climate change comes with the challenge of power imbalance and instability issues in emerging power grids. To mitigate power fluctuation arising from the intermittent nature of renewables, electric spring has been proposed as a fast demand-side management technology. Since its original conceptualization in 2011, many versions and variants of electric springs have emerged and industrial evaluations have begun. This paper provides an update of existing electric spring topologies, their associated control methodologies, and studies from the device level to the power system level. Future trends of electric springs in large-scale infrastructures are also addressed