Abstract
Hybrid AC/DC microgrids (HMG) are emerging as an attracting method for integrating AC/DC distributed energy resources (DERs). In the isolated hybrid AC/DC microgrid (IHMG), the key problem is how to balance power variation and regulate voltage and frequency. Various energy storage systems (ESS) and interlinking converter (IC) technologies are viable for this application. The present study proposes a novel unified power flow (PF) model which can be applied to compare and analyze the practical operation modes of the IHMG and, further, to evaluate and compare the abilities of the ESS with different connection topologies and ICs with different control approaches to maintain the voltage and frequency stability of the IHMG. Five operation modes of the IHMG are defined and explained. Then, a set of generic PF equations are derived. Moreover, three binary matrices are applied as input parameters of the unified power equations. These matrices enable a single operation mode of the IHMG at a time to be constructed in the power equation. Finally, the accuracy and effectiveness of the proposed scheme are verified against the time domain simulation result. The quasi-steady-state behaviors of multi-DC subgrids IHMG in different modes after a range of load fluctuation are investigated. The results show that the use of multiple grid-forming units in the AC and DC subgrids, when IC adopted normalized.
Highlights
In renewable power generation systems, new features, such as the increment of the DC sources and loads, and rapid developments in DC energy storage systems (ESSs) are emerging
ESS and interlinking converter (IC) units play a decisive role in the frequency and voltage stability of the AC/DC isolated hybrid AC/DC microgrid (IHMG)
A new power flow (PF) model was In Conclusions widely applicable hierarchical control architectures, there are various primary control modes proposed for analyzing various operating characteristics of the IHMG system in adopting different adopted by units for maintaining the stable operation of the IHMG
Summary
In renewable power generation systems, new features, such as the increment of the DC sources and loads, and rapid developments in DC energy storage systems (ESSs) are emerging. This is more pronounced at the distribution level. It should be indicated that HMG projects are widely adopted worldwide [1,2,3]. Each subgrid contains distributed generations (DGs), ESSs, and loads. An interlinking converter (IC) links the AC and DC subgrid together
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