Robust Passivity-Based Control of Boost Converters in DC Microgrids

This work deals with the design of a robust and decentralized passivity-based control scheme for regulating the voltage of a DC microgrid through boost converters. A Krasovskii-type storage function is proposed and a (local) passivity property for DC microgrids comprising unknown 'ZIP' (constant impedance 'Z', constant current 'I' and constant power 'P') loads is established. More precisely, the input port-variable of the corresponding passive map is equal to the first-time derivative of the control input. Then, the integrated input port-variable is used to shape the closed loop storage function such that it has a minimum at the desired equilibrium point. Convergence to the desired equilibrium is theoretically analyzed and the proposed control scheme is validated through experiments on a real DC microgrid

Suppression of Second-Order Harmonic Current for Droop-Controlled Distributed Energy Resource Converters in DC Microgrids

Droop-controlled distributed energy resource converters in dc microgrids usually show low output impedances. When coupled with ac systems, second-order harmonics typically appear on the dc-bus voltage, causing significant harmonic currents at the converters resource side. This paper shows how to reduce such undesired currents by means of notch filters and resonant regulators included in the converters control loops. The main characteristics of these techniques in terms of harmonic attenuation and stability are systematically investigated. In particular, it is shown that the voltage control-loop bandwidth is limited to be below twice the line frequency to avoid instability. Then, a modified notch filter and a modified resonant regulator are proposed, allowing to remove the constraint on the voltage loop bandwidth. The resulting methods (i.e., the notch filter, the resonant regulator, and their corresponding modified versions) are evaluated in terms of output impedance and stability. Experimental results from a dc microgrid prototype composed of three dc-dc converters and one dc-ac converter, all with a rated power of 5kW, are reported

A Robust Consensus Algorithm for Current Sharing and Voltage Regulation in DC Microgrids

In this paper a novel distributed control algorithm for current sharing and voltage regulation in Direct Current (DC) microgrids is proposed. The DC microgrid is composed of several Distributed Generation units (DGUs), including Buck converters and current loads. The considered model permits an arbitrary network topology and is affected by unknown load demand and modelling uncertainties. The proposed control strategy exploits a communication network to achieve proportional current sharing using a consensus-like algorithm. Voltage regulation is achieved by constraining the system to a suitable manifold. Two robust control strategies of Sliding Mode (SM) type are developed to reach the desired manifold in a finite time. The proposed control scheme is formally analyzed, proving the achievement of proportional current sharing, while guaranteeing that the weighted average voltage of the microgrid is identical to the weighted average of the voltage references.Comment: 12 page

Power sharing of parallel operated DC-DC converters using current-limiting droop control

In this paper, a nonlinear current-limiting droop controller is proposed to achieve accurate power sharing among parallel operated DC-DC boost converters in a DC micro-grid application. In particular, the recently developed robust droop controller is adopted and implemented as a dynamic virtual resistance in series with the inductance of each DC-DC boost converter. Opposed to the traditional approaches that use small-signal modeling, the proposed control design takes into account the accurate nonlinear dynamic model of each converter and it is analytically proven that accurate power sharing can be accomplished with an inherent current limitation for each converter independently using input-to-state stability theory. When the load requests more power that exceeds the capacity of the converters, the current-limiting capability of the proposed control method protects the devices by limiting the inductor current of each converter below a given maximum value. Extensive simulation results of two paralleled DC-DC boost converters are presented to verify the power sharing and current-limiting properties of the proposed controller under several changes of the load

Convertidores de potencia para microrredes y sistemas de generación distribuidos

This paper presents an overview and critical discussion about the utilization of power converters in several microgrid configurations that incorporate non-conventional renewable energy sources and energy storage. The methodology is developed over 69 works published in this research topic. The papers are selected from databases in electrical engineering, e.g., IEEExplore, ScienceDirect, Springer, MDPI, etc. Then, the papers are classified depending on its focus, i.e., power converters in microgrids or power converters in distribution systems. At least, three classifications are proposed and one of them is made over more than 40 papers about power converters used in microgrids and electric distribution systems. Given the wide variety of microgrids and their configurations, the selection of appropriate power converters for every scenario is not trivial; therefore, this work also classifies the converters in their most common application, their advantages and disadvantages, and also point out the study domain, i.e., simulation or physical implementation. One of the main conclusions made from the overview is a gap identified in the study of direct current/ direct current microgrids despite being the simplest configuration among the three analyzed configurations. This is because hybrid and alternate current microgrids are more widely used since they allow taking advantage of the infrastructure of the current electrical systems.Este artículo presenta una visión general y una discusión crítica sobre la utilización de convertidores de potencia en varias configuraciones de microrredes que incorporan fuentes de energía renovable no convencionales y almacenamiento de energía. La metodología se desarrolla sobre 69 trabajos publicados en este tema de investigación. Los documentos se seleccionan de bases de datos en ingeniería eléctrica, p. ej. IEEExplore, ScienceDirect, Springer, MDPI, etc. Luego, los artículos se clasifican según su enfoque, es decir, convertidores de potencia en microrredes o convertidores de potencia en sistemas de distribución. Se proponen al menos tres clasificaciones y una de ellas se realiza sobre más de 40 artículos sobre convertidores de potencia utilizados en microrredes y sistemas de distribución eléctrica. Dada la gran variedad de microrredes y sus configuraciones, la selección de convertidores de potencia apropiados para cada escenario no es trivial; por lo tanto, este trabajo también clasifica a los convertidores en su aplicación más común, sus ventajas y desventajas, y también señala el dominio de estudio, es decir, simulación o implementación física. Una de las principales conclusiones extraídas de la visión general es una brecha identificada en el estudio de las microrredes de corriente continua / corriente continua a pesar de ser la configuración más simple entre las tres configuraciones analizadas. Esto se debe a que las microrredes híbridas y de corriente alterna son las más utilizadas ya que permiten aprovechar la infraestructura de los sistemas eléctricos actuales