Abstract
In this study, a DC micro-grid consisting of multiple paralleled energy resources interfaced by both bidirectional AC/DC and DC/DC boost converters and loaded by a constant power load (CPL) is investigated. By considering the generic dq transformation of the AC/DC converters' dynamics and the accurate nonlinear model of the DC/DC converters, two novel control schemes are presented for each converter-interfaced unit to guarantee load voltage regulation, power sharing and closed-loop system stability. This novel framework incorporates the widely adopted droop control and using input-to-state stability theory, it is proven that each converter guarantees a desired current limitation without the need for cascaded control and saturation blocks. Sufficient conditions to ensure closed-loop system stability are analytically obtained and tested for different operation scenarios. The system stability is further analysed from a graphical perspective, providing valuable insights of the CPL's influence onto the system performance and stability. The proposed control performance and the theoretical analysis are first validated by simulating a three-phase AC/DC converter in parallel with a bidirectional DC/DC boost converter feeding a CPL in comparison with the cascaded PI control technique. Finally, experimental results are also provided to demonstrate the effectiveness of the proposed control approach on a real testbed.
Highlights
Driven by the energy crisis, environmental pollution and greenhouse gas emissions [1,2,3], the seamless integration of renewable energy sources (RESs) has been actively pursued worldwide, over the past decades
In DC micro-grids, distributed generations (DGs) units are connected to a common DC bus through AC/DC and/or DC/DC converters, often operating in parallel leading to a series of non-trivial issues such as voltage regulation and accurate distribution of the load power
Inherently nonlinear systems, opposed to only unidirectional boost converter [31], or only buck converters, as studied in [20] which have linear dynamics; (ii) compared to [20], a new droop control structure that achieves improved power sharing and output voltage regulation closer to the rated value is proposed and analysed; (iii) an inherent current limitation is introduced via the proposed control design for all power converters; (iv) in contrast to [40] where a linear resistive load was considered, in this paper closed-loop stability is analytically guaranteed for the constant power load (CPL) case
Summary
Driven by the energy crisis, environmental pollution and greenhouse gas emissions [1,2,3], the seamless integration of renewable energy sources (RESs) has been actively pursued worldwide, over the past decades. (iv) in contrast to [40] where a linear resistive load was considered, in this paper closed-loop stability is analytically guaranteed for the CPL case For this reason, in this paper, two novel nonlinear droop control strategies are proposed for parallel operated bidirectional threephase AC/DC and DC/DC boost converters feeding a CPL in a DC micro-grid architecture to ensure accurate distribution of the load power among the paralleled units in proportion to their power ratings and inherent overcurrent protection. (i) the parallel operation of both bidirectional three-phase AC/DC and DC/DC boost converters is investigated here, which are proving closed-loop system stability of a DC micro-grid with a CPL using the nonlinear model of the bidirectional threephase AC/DC and the DC/DC boost converters together, while guaranteeing improved power sharing accuracy, load voltage regulation and an inherent current-limiting property is to the best of our knowledge novel. Let On ∈ Rn and On × n ∈ Rn × n be the n-dimensional vector and n × n square matrix, respectively, with all elements zero, In be the identity matrix and let 1n ∈ Rn and 1n × n ∈ Rn × n be the ndimensional vector and n × n square matrix, respectively, with all elements equal to one
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