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Abstract-This paper presents a robust distributed secondary control (DSC) scheme for inverter-based microgrids (MGs) in a distribution sparse network with uncertain communication links. By using the iterative learning mechanics, two discrete-time DSC controllers are designed, which enable all distributed energy resources (DERs) in a MG to achieve the voltage/frequency restoration and active power sharing accuracy, respectively. In special, the secondary control inputs are merely updated at the end of each round of iteration, and thus each DER only needs to share information with its neighbors intermittently in a lowbandwidth communication manner. This way, the communication costs are greatly reduced, and some sufficient conditions on the system stability and robustness to the uncertainties are also derived by using the tools of Lyapunov stability theory, algebraic graph theory, and matrix inequality theory. The proposed controllers are implemented on local DERs, and thus no central controller is required. Moreover, the desired control objective can also be guaranteed even if all DERs are subject to internal uncertainties and external noises including initial voltage and/or frequency resetting errors and measurement disturbances, which then improves the system reliability and robustness. The effectiveness of the proposed DSC scheme is verified by the simulation of an islanded MG in MATLAB/SimPowerSystems.

This paper develops a new distributed secondary cooperative control scheme to coordinate distributed generators (DGs) in islanded microgrids (MGs). A finite time frequency regulation strategy containing a consensus-based distributed active power regulator is presented, which can not only guarantee the active power sharing but also enable all DGs' frequencies to converge to the reference value within a finite time. This enables the frequency and voltage control designs to be separated. Then an observer-based distributed voltage regulator involving certain reactive power sharing constraints is proposed, which allows different set points for different DGs and, thus, accounts for the line impedance effects. The steady-state performance analysis shows that the voltage regulator can accurately address the issue of global voltage regulation and accurate reactive power sharing. Moreover, all the distributed controllers are equipped with bounded control inputs to suppress the transient overshoot, and they are implemented through sparse communication networks. The effectiveness of the control in case of load variation, plugand-play capability, communication topology change, link failure, time delays and data drop-out are verified by the simulation of an islanded MG in MATLAB/SimPowerSystems.

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Mast cell-derived chymase is implicated in myocardial fibrosis (MF), but the underlying mechanism of intracellular signaling remains unclear. Transforming growth factor-beta 1 (TGF-beta1) is identified as the most important profibrotic cytokine, and Smad proteins are essential, but not exclusive downstream components of TGF-beta 1 signaling. Moreover, novel evidence indicates that there is a cross talk between Smad and mitogen-activated protein kinase (MAPK) signaling cascade. We investigated whether chymase activated TGF-beta 1/Smad pathway and its potential role in MF by evaluating cardiac fibroblasts (CFs) proliferation and collagen synthesis in neonatal rats. MTT assay and 3H-Proline incorporation revealed that chymase induced CFs proliferation and collagen synthesis in a dose-dependent manner. RT-PCR and Western blot assay demonstrated that chymase not only increased TGF-beta1 expression but also upregulated phosphorylated-Smad2/3 protein. Furthermore, pretreatment with TGF-beta 1 neutralizing antibody suppressed chymase-induced cell growth, collagen production, and Smad activation. In contrast, the blockade of angiotensin II receptor had no effects on chymase-induced production of TGF-beta 1 and profibrotic action. Additionally, the inhibition of MAPK signaling had no effect on Smad activation elicited by chymase. These results suggest that chymase can promote CFs proliferation and collagen synthesis via TGF-beta 1/Smad pathway rather than angiotensin II, which is implicated in the process of MF.

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This paper proposes a distributed hierarchical cooperative (DHC) control strategy for a cluster of islanded microgrids (MGs) with intermittent communciation, which can regulate the frequency/voltage of all distributed generators (DGs) within each MG as well as ensure the active/reactive power sharing among MGs. A droop-based distributed secondary control (DSC) scheme and a distributed tertiary control (DTC) scheme are presented based on the iterative learning mechanics, by which the control inputs are merely updated at the end of each round of iteration, and thus each DG only needs to share information with its neighbors intermittently in a low-bandwidth communication manner. A two-layer sparse communication network is modeled by pinning one or some DGs (pinned DGs) from the lower network of each MG to constitute an upper network. Under this control framework, the tertiary level generates the frequency/voltage references based on the active/reactive power mismatch among MGs while the pinned DGs propagate these references to their neighbors in the secondary level, and the frequency/voltage nominal set-points for each DG in the primary level can be finally adjusted based on the frequency/voltage errors. Stability analysis of the two-layer control system is given, and sufficient conditions on the upper bound of the sampling period ratio of the tertiary layer to the secondary layer are also derived. The proposed controllers are distributed, and thus allow different numbers of heterogeneous DGs in each MG. The effectiveness of the proposed control methodology is verified by the simulation of an AC MG cluster in Simulink/SimPowerSystems.