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Microgrid coordinated controllers are designed so as to optimize the utilization of energy available in existing energy storage system (ESS) as well as the energy being generated from prevailing renewable energy sources (RES). If there is a surplus in the generated renewable energy, it will be used to charge the ESS if their capacity permits, otherwise, the surplus energy is curtailed. However, during a grid loss, i.e. during unintentional islanding, the surplus energy can lead to an increase in the DC link voltages feeding the DC-AC inverters, which may subsequently trip them off. Clearly, this has an adverse effect on the reliability of the microgrid. In this paper, a new strategy of microgrid control is proposed for enhancing the microgrid reliability by protecting it against unintentional islanding instability. In this strategy, the DC link voltage is used as a feedback parameter in the droop control loop. This bounds the DC link voltages and consequently leads to reliable operation. The validity of the proposed control scheme was verified by software simulations using MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

Highlights • Analyse the issues of implementing DMPPT on various DC-DC converter topologies. • Present Hybrid Techniques with direct control offering a combination of the MINC and different MCNM techniques. • Comparatively analyse the proposed HT against the conventional MINC direct control technique. • A guide for future work on DMPPT utilizing different MCNM techniques. Abstract Application of Classical Numerical Methods (CNM) for Digital maximum power point tracking (DMPPT) confronts many issues. The issues highlighted in this paper include limited range of operation, PV array dependence and accuracy of the initial guess. In order to address such shortcomings of CNM for DMPPT, Hybrid Techniques (HT) have been proposed. The HT are a combination of the modified incremental conductance method (MINC) and various modified CNM. An overview of the considered MCNM, which are applied to the photovoltaic (PV) application, has also been provided. The HT not only address the issues confronted by the CNM, but also improve the transient response time and remove the steady state oscillations for the conventional MPPT technique. In addition, for DMPPT the DC-DC converter topology under consideration cannot be treated as a black box, by ignoring the effects of the converter topology and control dynamics. Here, a theoretical analysis has been provided to ascertain the optimum performance of DMPPT applications on various DC-DC converter designs. To measure the effectiveness of the proposed HT, Boost, 2-Stage Switch Capacitor Based (2-SSC) Boost, and Optimum Buck Converters (OBC) have been employed. Simulation and experimental results are provided to validate the effectiveness of the proposed HT. [ABSTRACT FROM AUTHOR]

Highlights • Explain the operation of the proposed high gain Boost and buck-boost converters based on extendable Switch Capacitor cells. • Highlight the modes of operation for the proposed converters to justify converter utility for stand-alone PV systems. • Comparatively analyse the voltage gain and efficiency of the proposed converters against the conventional converters. • Guide for future work on B-BBC with extendable SC cells. Abstract This paper presents transformerless high gain boost and buck-boost DC-DC converters (B-BBCs) with extendable switched capacitor cells (SCs), suitable for applications operating at high voltage, above 300 V. Boosting low voltage to a high-enough level, with low duty ratio, is beyond the practical capability of the conventional boost converter. In addition, high duty ratio needed for operation of the boost converter, results in higher component stress that suppresses the overall efficiency of the converter. Therefore, by a convenient integration of SCs with conventional B-BBCs, increased voltage gain is attained with fewer losses. Such converters can be employed for Photovoltaic (PV) systems. The operational principles and modes of operation are analyzed to justify the utility of converters for stand-alone PV systems. Moreover, the proposed modular structure allows to increase SC cells in order to obtain reduced voltage stress on switching components with a higher voltage gain. Simulation and experimental results based on 100 W laboratory prototype extol the theoretical analysis. [ABSTRACT FROM AUTHOR]