Stability Analysis of Primary Plug-and-Play and Secondary Leader-Based Controllers for DC Microgrid Clusters

Abstract

In this paper, we propose a new hierarchical control scheme for Microgrid (MG) clusters, given by the interconnection of atomic dc MGs with ZIP loads, each composed by both gridforming and grid-feeding converters. In the primary level, we develop a new Plug-and-Play (PnP) voltage/current controller in order to achieve simultaneous voltage support and current feeding function with local references. The coefficients of each stabilizing controller are characterized by explicit inequalities, which are related only to local electrical parameters of the MG. Moreover, we provide a sufficient condition on the ZIP loads to guarantee passivity and asymptotic stability of electric system. The robustness of performance to system uncertainties is also demonstrated. In the secondary level, a leader-based voltage/current controller is proposed to achieve both voltage and current regulation for the MG cluster without specifying the individual setpoints for each MG. The proposed distributed controller requires a communication network where each regulator exchanges information with its communication neighbors only. With the proposed scheme, each MG can plug-in/out seamlessly, irrespectively of the power line parameters and models of other MGs. Closed-loop stability proof of MG clusters is formally proved independently of the cluster topology. Moreover, theoretical results are validated by extensive hardware-in-loop (HiL) tests showing robustness of the closed-loop cluster against perturbations in the loads, PnP operations and noises/delays in the communication network.

Non-linear controller for storage systems with regulated outputvoltage and safecurrent slew-rate for the battery

“…Therefore, the current requested by the load is provided protecting the battery from high-frequency transients. Moreover, it must be pointed out that this solution adopts the same number and type of converters reported in other solutions such as [8,10,12,18,26,27,28,29,30,31,32]; hence no additional costs are introduced due to the power stages. Similarly, the controllers have the same nature that the solutions reported in [8,15,18]; hence no additional costs are introduced due to the control stages.…”

“…Such a technique introduces a hysteresis band H around the sliding-surface to limit the switching frequency, which transforms the sliding surface (3) to the practical expression given in (30). Basedon that practical sliding-surface, and on the reachability, conditions given in (8), the control laws for the SMC of both the first and second stages are reported in (31) and (32), respectively.…”

Review of hierarchical control strategies for DC microgrid

“…To overcome this, a novel coordinated control method has been proposed to achieve a flexible and autonomous power handling capability of the cluster. The slack terminal, power terminal and bidirectional buck-boost DC-DC converter containing coordinated power control ensure high stability and offers a unified control approach in case DC bus fault and slack terminal failure [70,74,75].…”

Review of Power Sharing, Voltage Restoration and Stabilization Techniques in Hierarchical Controlled DC Microgrids

“…In order to isolate the dc fault and ensure the stable operation of the local dc bus, an islanded bidirectional dc-dc converter (IBDC) is proposed in [29], the grid-connected mode and islanded mode can be transformed automatically and seamlessly. In addition, to realize the plug-and-play function in islanded and grid-connected mode, two-layer hierarchical control of the MGC is presented in [87]. However, the communication data drop between the two-layer may not be considered.…”