This paper presents the latest comprehensive literature review of AC and DC microgrid (MG) systems in connection with distributed generation (DG) units using renewable energy sources (RESs), energy storage systems (ESS) and loads. A survey on the alternative DG units' configurations in the low voltage AC (LVAC) and DC (LVDC) distribution networks with several applications of microgrid systems in the viewpoint of the current and the future consumer equipments energy market is extensively discussed. Based on the economical, technical and environmental benefits of the renewable energy related DG units, a thorough comparison between the two types of microgrid systems is provided. The paper also investigates the feasibility, control and energy management strategies of the two microgrid systems relying on the most current research works. Finally, the generalized relay tripping currents are derived and the protection strategies in microgrid systems are addressed in detail. From this literature survey, it can be revealed that the AC and DC microgrid systems with multiconverter devices are intrinsically potential for the future energy systems to achieve reliability, efficiency and quality power supply.

AC-microgrids versus DC-microgrids with distributed energy resources: A review

The significant benefits associated with microgrids have led to vast efforts to expand their penetration in electric power systems. Although their deployment is rapidly growing, there are still many challenges to efficiently design, control, and operate microgrids when connected to the grid, and also when in islanded mode, where extensive research activities are underway to tackle these issues. It is necessary to have an across-the-board view of the microgrid integration in power systems. This paper presents a review of issues concerning microgrids and provides an account of research in areas related to microgrids, including distributed generation, microgrid value propositions, applications of power electronics, economic issues, microgrid operation and control, microgrid clusters, and protection and communications issues.

State of the Art in Research on Microgrids: A Review

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Power Electronics Converters Applications And Design

Microgrids energy management systems: A critical review on methods, solutions, and prospects

Impedance networks cover the entire of electric power conversion from dc (converter, rectifier), ac (inverter), to phase and frequency conversion (ac-ac) in a wide range of applications. Various converter topologies have been reported in the literature to overcome the limitations and problems of the traditional voltage source, current source as well as various classical buck-boost, unidirectional, and bidirectional converter topologies. Proper implementation of the impedance-source network with appropriate switching configurations and topologies reduces the number of power conversion stages in the system power chain, which may improve the reliability and performance of the power system. The first part of this paper provides a comprehensive review of the various impedance-source-networks-based power converters and discusses the main topologies from an application point of view. This review paper is the first of its kind with the aim of providing a “one-stop” information source and a selection guide on impedance-source networks for power conversion for researchers, designers, and application engineers. A comprehensive review of various modeling, control, and modulation techniques for the impedance-source converters/inverters will be presented in Part II.

Impedance-Source Networks for Electric Power Conversion Part I: A Topological Review

Sliding mode control (SMC) is recognized as robust controller with a high stability in a wide range of operating conditions, although it suffers from chattering problem. In addition, it cannot be directly applied to multiswitches power converters. In this paper, a high performance and fixed switching frequency sliding mode controller is proposed for a single-phase unipolar inverter. The chattering problem of SMC is eliminated by smoothing the control law in a narrow boundary layer, and a pulsewidth modulator produces the fixed frequency switching law for the inverter. The smoothing procedure is based on limitation of pulsewidth modulator. Although the smoothed control law limits the performance of SMC, regulation and dynamic response of the inverter output voltage are in an acceptable superior range. The performance of the proposed controller is verified by both simulation and experiments on a prototype 6-kVA inverter. The experimental results show that the total harmonic distortion of the output voltage is less than 1.1% and 1.7% at maximum linear and nonlinear load, respectively. Furthermore, the output dynamic performance of the inverter strictly conforms the standard IEC62040-3. Moreover, the measured efficiency of the inverter in the worst condition is better than 95.5%.

Fixed Switching Frequency Sliding Mode Control for Single-Phase Unipolar Inverters

This paper describes a control approach applied on a doubly fed induction generator (DFIG) to provide both voltage and frequency regulation capabilities, and hence, an improvement in the dynamic behavior of a microgrid system. The microgrid system is assumed to be a portion of a medium voltage distribution feeder and is supplied by two distributed generation (DG) units, i.e., a gas-turbine synchronous generator and a variable-speed wind turbine with DFIG. A control approach algorithm is proposed for the DFIG unit to improve both voltage and primary frequency controls. Two distinct operation modes, i.e., grid-connected and islanding mode, are used in the proposed approach for proper transfer from normal to islanding operation. Case studies are simulated based on both planned and unplanned islanding scenarios to evaluate the performance of the control approach. The study results show that the proposed control approach for DGs in the microgrid increase the microgrid system's dynamic performance, reduce frequency changes, and improve bus voltages regulation during islanding and autonomous operations.

Microgrid Dynamic Performance Improvement Using a Doubly Fed Induction Wind Generator

Vienna rectifier as generator-side converter of wind energy conversion system (WECS) using a permanent-magnet synchronous generator (PMSG) has several advantages compared to conventional back-to-back inverter, such as higher efficiency and improved total harmonic distortion. On the other hand, direct torque control (DTC) of the generator in WECS is of interest, particularly for low-power applications due to several merits, including fast torque response, insensitivity to PMSG model and associated parameters, elimination of rotor position sensor, and reduced computations. In this paper, the effects of Vienna rectifier voltage vectors on instantaneous PMSG torque and stator flux are derived, and DTC of PMSG by the Vienna rectifier is implemented, considering the constraints imposed by the Vienna rectifier. Experimental tests for a 1-kW prototype are presented, which confirm the simulations and theoretical results.

Vienna-Rectifier-Based Direct Torque Control of PMSG for Wind Energy Application

Recently, nine-switch inverter and nine-switch-z-source inverter have been proposed as dual output inverters. In this paper, the space vector modulation (SVM) of nine-switch inverter and nine-switch-z-source inverter is proposed. The proposed method increases the sum of modulation indices up to 15% in contrast with the conventional, scheme in which the sum of modulation indices is equal or less than one. The extra voltage available for a given input dc-voltage, translates to a higher torque-a critical factor for defining the capacity of products in marketplace. Also, in order to further reduce the cost of power devices and also thermal heat effect, and to reduce the number of semiconductor switching, specific SVM switching pattern is presented. This feature will be advantageous for high-power inverter applications where cost and efficiency are key decision factors. Furthermore, a novel SVM is proposed for minimizing total harmonic distortion. The performance of the proposed SVM for both nine-switch inverter and nine-switch-z-source inverter is verified by simulation. Experimental results validate the simulation results as well as the superiority of the proposed SVM.

Space Vectors Modulation for Nine-Switch Converters

Multiterminal converters are used in hybrid energy systems as a replacement for several conventional two-terminal converters to reduce volume and cost. This paper proposes a hybrid electric vehicle (HEV) based on a bidirectional z-source nine-switch inverter. A unidirectional z-source nine-switch inverter, which was proposed by the authors, has been improved to allow bidirectional power flow. The proposed converter has two ac and one dc bidirectional terminals that can be used in HEV. Performance of the proposed HEV has been verified by simulation and experimental results.

Mustafa Mohamadian

Papers

Fixed Switching Frequency Sliding Mode Control for Single-Phase Unipolar Inverters

Microgrid Dynamic Performance Improvement Using a Doubly Fed Induction Wind Generator

Vienna-Rectifier-Based Direct Torque Control of PMSG for Wind Energy Application

Space Vectors Modulation for Nine-Switch Converters

Hybrid Electric Vehicle Based on Bidirectional Z-Source Nine-Switch Inverter