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The integration of renewable energy resources to DC microgrid has captured the attention of the researchers in recent years. One of the active field of application of DC distribution is the islanded DC microgrid (DC ImG). The DC ImG present numerous challenges to researchers. Among many challenges, the regulation of voltage and stability of the system is indispensable to efficient operation. The voltage stability problem becomes more prominent when the system is exposed to disturbances and possess uncertainties in parameters. However, challenges can be overcome by skilful design of a robust controller for the system. Therefore, in this paper, an output-feedback based centralized robust control scheme is proposed. The proposed controller is designed to maintain good control performance in the presence of parametric uncertainties and exogenous disturbances. The uncertainties of the DC microgrid is modelled as a linear time-varying state-space system. The upper and the lower bounds of the time-varying parameters are determined by a Lebesque-measurable matrix. To attenuate the exogenous disturbances of the system [Formula: see text] based output-feedback controller is designed. The system stability is assured by the Lyapunov function candidate. The output-feedback controller needs only the voltage measurement; therefore, it requires less communication bandwidth as compared to the state-feedback. To obtain the controller parameters linear matrix inequality constraints are formulated and solved. The performance of the proposed controller is verified via simulations and compared with the existing schemes.

Abstract:With the recent developments in power electronics technologies, increased deployment of distributed energy resources (DER) with DC output type at distribution voltage levels and significant increase in the number of sensitive AC and DC loads integrated in distribution network have enforced the traditional power network in the continuous renovation process. In this paper, the load flow solution of hybrid AC/DC distribution networks with the multi-terminal configuration is studied. The impact of voltage source converter (VSC) losses and AC and DC line losses in the presence of DER in the distribution system are assessed. The motivation of this analysis is to consider an increase in the number of converter stations which might result in non-negligible converter losses and the presence of various DER within the network imposing different network scenarios. The proposed schemes are simulated on two modified IEEE 33 bus hybrid AC/DC distribution network test system equipped with VSC-MTDC and the results are presented. Obtained results show that by considering the network losses and the converter losses with large number of converters within the network could lead to very different load flow solution and power transfer between networks, especially considering the AC or DC bus dominated network.

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A low voltage direct current (LVDC) distribution network is a promising technology to meet the standards of future energy demands for smart loads. An LVDC distribution network can not only supply efficient, smooth and clean energy, but also makes the integration of renewable energy resources in the distribution system easy. A major obstacle in the implementation of the LVDC distribution network is the protection of the network during abnormal grid conditions, such as transients and faults. This paper analyzes DC fault characteristics considering an LVDC distribution network, highlights the worst case scenario during a fault and protection related issues and proposes the protection schemes for the LVDC network. In the proposed protection scheme, a fault is detected and located through superimposed components. To minimize the effect of the DC fault on the distribution network, distributed fault current limiters are introduced and the final decision to disconnect or reconnect the affected line is made on the basis of the type of fault. In addition, a reclosing scheme for a temporary fault is proposed to avoid high inrush currents and false tripping, which eventually increases the reliability. A fast communication-based backup protection is also suggested, and to reduce dependency, a secondary backup is used in the case of communication delay or failure. The proposed scheme is verified using the modified IEEE 13 node test system, which is implemented in ATPDraw. The results show that the proposed scheme can successfully detect, locate and limit a DC fault in an LVDC distribution network with different fault resistances or locations. Moreover, the network is restored successfully in the case of temporary faults.