Abstract
Flywheel energy storage system is a popular energy storage technology, in which inverters are the center of electrical energy conversion, directly affecting the power capacity. Parallel operation of three-level inverters is an effective approach to achieve larger motor drive power and the interleaved operation can improve the harmonic characteristics. However, harmonic analysis models of the interleaved parallel three-level inverters are rare in the literature and how the neutral-point potential imbalance affects the harmonics characteristics has not been discussed. This article establishes the harmonic calculation for balanced and unbalanced neutral-point potential through the five-level voltage capability of the interleaved parallel three-level inverters. Moreover, a neutral-point potential control method based on zero-sequence voltage injection is proposed. The implement process of the method is proposed, and how the operating frequency affect the ability of the neutral-point potential balance is studied. Finally, the simulation and experiment results verify the feasibility and practicability of the established harmonic analysis models and the neutral-point potential control method.
Highlights
Flywheel energy storage system (FESS) is a sustainable and environmentally friendly energy storage system for the efficient and safe utilization of intermittent renewable energy (Mir and Senroy, 2018; Rafi and Bauman, 2021)
For harmonic analysis of the interleaved parallel three-level inverters (TLIs) system when DC offset inevitably emerges in neutral-point potential, the distribution regions of the switching function are unchanged, but the values in the regions, called the leg output levels are different in the unit cell
The harmonic characteristics of interleaved operation is significantly better than the synchronous operation
Summary
Flywheel energy storage system (FESS) is a sustainable and environmentally friendly energy storage system for the efficient and safe utilization of intermittent renewable energy (Mir and Senroy, 2018; Rafi and Bauman, 2021). The interleaved parallel three-level inverters have both inherent problems of neutral-point potential control and circulating current suppression.
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