Abstract
This article proposes a fully decentralized control approach, based on AC bus signaling, to integrate the operation of voltage- and current-controlled converters that exist in an isolated low-voltage microgrid, so they may be fully steered under grid-feeding, grid-supporting, and grid-forming control principles. The proposed strategy, devised by classic and modified droop-based controllers, allows control of the microgrid active power relating to the system frequency, while regulating the reactive power related to the voltage, dispensing any need for communication infrastructures. Beyond ensuring proper microgrid power balance at all times, the control strategy prioritizes energy extraction from non-dispatchable sources (i.e., photovoltaic-based systems), whereas it uses dispatchable sources (i.e., battery-based systems) to share active and reactive power proportionally to their capabilities. As a consequence of the proper and novel management of battery-based converters, battery overvoltage and overcurrent are avoided, supporting a prolonged lifespan. Simulation results considering an autonomous microgrid operating under several scenarios are presented, to demonstrate the capabilities of the proposed control scheme on steering the different topologies of converters.
Highlights
P OWER electronic converters are becoming key players on supporting the decentralization of electrical systems [1]
Regarding the MG infrastructure and its operational aspects, the following additional considerations are important to be highlighted: i) the MG operation dynamics is determined by the GFC unit, since this converter imposes the voltage amplitude (V ) and angular frequency (ω) for the entire system; ii) the GSC and GFdC units operate responding to the variations of (V ) and (ω), adjusting their active and reactive powers ; and iii) the AC bus signaling principle and droop-controllers regulate the active and reactive power processed by the converters, being described as follows
Five simulation scenarios are presented to assess the main features of the proposed control methods, in which it is demonstrated that: A) active power injection generated from renewable energy sources (RESs) is prioritized over generation from dispatchable sources (i.e., battery energy storage systems (BESSs)); B) battery-based converters support the injection of active power if RESs are not able to properly supply the loads; C) batteries are recharged proportionally among converters comprising such systems, according to their rated power, regardless of their control topology; D) power curtailment is adequately performed to avoid overvoltage/overcurrents in BESSs; and E) the modified droop control proposed for reactive power sharing is presented and compared with classic droop control
Summary
P OWER electronic converters are becoming key players on supporting the decentralization of electrical systems [1]. BESSs, both current- and voltage-controlled modes are supported, steering their converters without causing overvoltage or overcurrent of batteries, which improves the lifespan of such systems; As conventional droop control is inherently affected by mismatches in line impedances existing over the MG, a modified droop-based strategy, which is based on the voltage drop compensation of the line resistance in the voltage reference, is proposed to improve reactive power sharing accuracy and regulation of load bus voltage; its operational features are compared to a classic droop method. It is worth reinforcing that, with regard to the abovementioned contributions and the work found in [32], this paper: i) presents a different coordination approach for the converters, which uses different droop curves and limiting operational parameters; ii) incorporates the controllable overvoltage/overcurrent capabilities not previously discussed in [32]; and iii) brings more extensive literature review, as well as further discussions and simulation results to demonstrate the wide range of capabilities of the proposed methods.
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