Abstract
An investigation on qualitative dynamics in a voltage-current dual-loop controlled flywheel energy storage system (FESS) operating in discharge mode is presented in this paper, providing novel insights into the effect of two-timescale characteristics on the safety and stability of energy transmission of FESS. Based on singular perturbation theory, a two-timescale approach is proposed to separate the FESS into the fast and slow subsystems. Stability analysis of the transient fixed points confirms the effects of systemic parameters on FESS’s dynamics and indicates that the FESS shifts from the spiking state to the quiescent state when the slow variable crosses the bifurcation point of the fast subsystem. Mechanism analysis reveals that the root cause of the qualitative dynamics is the voltage instability of the FESS. Moreover, the feasibility boundaries of key parameters are derived, and application requirements of the proposed approach are also discussed, guiding the extension of the approach to engineering applications and solving the dynamics analysis problem to some extent at a theoretical analysis level. Constant voltage discharge experiment is performed based on the FESS test bench built in Key Laboratory of Smart Grid of Ministry of Education, Tianjin University, which validates the theoretical results.
Highlights
Permanent magnet (PM) brushless dc motor (BLDCM) controlled flywheel energy storage system (FESS), with the advantages of high density, low maintenance, long lifetime, and good compactness, has become a new trend for energy storage, applied more and more in the uninterruptible power supply, rail transportation, and smart grids [1, 2]
Due to the existence of the intrinsic nonlinearity, various nonlinear dynamics occur during the operation of FESS when the system state changes, which has an influence on the safety and stability of energy transmission
We aim to present evidences that as FESS operating in discharge mode, a small change in parameter values around the bifurcation points of FESS’s fast system will lead to qualitative dynamics of the full-system, and investigate the effect of two-timescale characteristics on such dynamics, which is similar to nonrecurrent bursting
Summary
Permanent magnet (PM) brushless dc motor (BLDCM) controlled FESS, with the advantages of high density, low maintenance, long lifetime, and good compactness, has become a new trend for energy storage, applied more and more in the uninterruptible power supply, rail transportation, and smart grids [1, 2]. Few researchers have revealed that, as a strongly coupled system, FESS has more complex nonlinear dynamics due to the interaction and difference between the mechanical part and the electrical part. This complex nonlinear dynamics has much more direct influence on the safety and stability of energy transmission and affects the safety and stability of FESS. We aim to present evidences that as FESS operating in discharge mode, a small change in parameter values around the bifurcation points of FESS’s fast system will lead to qualitative dynamics of the full-system, and investigate the effect of two-timescale characteristics on such dynamics, which is similar to nonrecurrent bursting.
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