The popularity of renewable energy systems has contributed significantly in the last years to the utility of low voltage direct current microgrids. However, these systems come with new challenges. This survey focuses on introducing a state-of-the-art low voltage direct current distribution system and sheds light on the challenges that must be faced in order to complete energy transition. This literature review was systematically carried out using the two largest scientific databases (SCOPUS and WOS) where the query (low voltage direct current microgrid) resulted in 198 articles. The purpose of this paper is not to reiterate the comparison of direct current with alternating current systems, which has already been discussed extensively. Instead, the objective of this survey is to assess the feasibility of the low voltage direct current distribution system and its impact on social development. To this end, this work provides valuable information for renewable energy planners, giving some insights or solutions to bridge the gap between the current energy network and the future DC energy microgrids. In particular, this article focuses on parameters such as grid topologies, distribution and voltage standardization efforts. The three major findings are: (i) the off-grid solutions enhance the efficiency rate in energy facilities (from 15% to 30%), and the vast majority of them are supported with energy storage systems to increase their reliability. However, in economic terms the most suitable systems still are the grid-connected solutions. Another finding is that (ii) the bus configurations are most used as well as the best in terms of their effectiveness to distribute low voltage and direct current energy within the microgrid. Lastly, (iii) the voltage value standardization around 48 V and 380 V, and even though there seems to be a clear convergence between them, the lack of agreement is delaying the massive implementation of these solutions worldwide. Finally, a novel assessment of social impacts and reflections on low voltage direct current microgrids is also included. 

Is it feasible a massive deployment of low voltage direct current microgrids renewable-based? A technical and social sight

WITHDRAWN: Fuzzy Logic-Based energy Management system design for residential Grid-Connected micro grids

The application of Particle Swarm Optimization (PSO) tuning for Artificial Neural Networks (ANNs) is an effective method for maximizing power output from photovoltaic (PV) panels in a DC microgrid system under changing irradiance conditions. This technique can be used to optimize the performance of a PV system, particularly in locations with variable weather conditions. This study proposes a new approach of implementing ANN that is tuned using practical swarm optimization technique. The ANN is trained using data generated by MATLAB Software on the weather conditions and the power output of the PV system and the PSO algorithm is then used to tune the parameters of the ANN model. The optimized ANN model can then be under severe proposed changes in irradiance and to adjust the power converter to achieve the maximum power output. The DC microgrid system used in this study is composed of multiple PV panels and battery along with a super capacitor for a storage system to feed a resistive load. The results of this study illustrate that the PSO tuning of ANNs is an effective method for maximizing power output from PV panels in a DC microgrid system under changing irradiance conditions reaching a precision of 99.7% from the PV panels and response time of 0.11s.

A PSO Tuning ANN for Extracting the MPP from a DC Microgrid System under Changing Irradiance

In this paper, a power compensator using supercapacitors in parallel to protect grid-connected devices connected to the distributed power supply in the case of a low-voltage ride-through (LVRT) situation in designed, and a grid-connected device control method with improved responsiveness is proposed. In the LVRT situation, the distributed generation power may boost the DC_link voltage, increasing the risk of destroying grid-connected devices. To prevent this, the power compensator designed in this study absorbs active power in a fault situation and stores it in the supercapacitor to suppress the DC_link voltage rise and efficiently use the power. In addition, we propose methods to improve the response of the grid reactive power through the reactive power compensation of the power compensator in LVRT situation. To this end, the power angle (θPW) was extracted through the formula, and the reactive power command, to be compensated by the power compensator, and the reactive power command, compensated by the grid-connected devices, were calculated according to the active power value. In this way, the grid power controlled by the power compensation device and the grid-connected devices was controlled by the active/reactive power of the same power angle and analyzed mathematically. Active power control and static grid support were performed in the normal state where the reduction rate of the normal value of the grid voltage was around 10%. However, when the grid voltage dropped by 10% to 100%, the reactive power control was appropriately performed with dynamic grid support by increasing the voltage from 10% to 20% or more. We conducted a simulation of the new and renewable energy grid-connected devices using the OPAL-RT-based Hardware-in-the Loop Simulation (HILS) system to control the proposed active/reactive power.

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Methods to Improve Dynamic System Response of Power Compensators Using Supercapacitors in Low-Voltage Ride-Through (LVRT) Conditions

This chapter aims to present the currentCurrent practices, challengesChallenges, and opportunities for various energy storageEnergy storage technologies for utilizationUtilization in electrical networksNetwork. Renewable energy sourcesRenewable energy sources (RERs) powerPower outputOutput cannot meet the immediate demandDemand of customers due to their intermittentIntermittent behavior and hence there is a requirement for energy storage systemsEnergy storage systems (ESSs). The ESS plays a deciding role in the effective utilizationUtilization of electric vehiclesElectric vehicle (EVs). In comparison with the existing technologies in ESSs such as ultracapacitors, fuel cells, and batteryBatteries packs, the most economically viable option is considered as the batteryBatteries packs. There are different types of ESSs such as supercapacitors, fuel cells, flywheels, and various electrochemical and non-electrochemical storagesStorage. This chapter discusses and analyzes the characteristics, size, functionsFunction, applications, stabilityStability, cost, etc. of various ESSs. 

Energy Storage Technologies for Next-Generation Electrical Power Systems

In this paper explained off-grid supercapacitor-based Photovoltaic system with energy storage. The proposed system will operate in all possible conditions. In a conventional system supercapacitor govern at only high voltage. DC microgrid supercapacitor starts to self-discharge up to lower values. This nature of supercapacitor is making DC microgrid unstable at low values of supercapacitor voltages. So, in this study change in supercapacitor voltage and stability of DCMG is calculated., with adequate supercapacitor voltage. A new method of design is used to confirm DC Microgrid stability in all operations conditions. The firmness of the DC micro-grid with DC voltage controller for the DC link is analyzed and assessed by MATLAB Simulink platform and test results.

Stability Analysis of Supercapacitor based DC Microgrid System with Energy Storage

This paper addresses DC microgrid stability by deploying a PV system with integrated energy storage. The integrated energy storage contains battery and supercapacitors for which the battery satisfies the normal load requirement and supercapacitor to fulfill the requirement of a transient load by saving battery life from unwanted charging and discharging cycles. In the conventional design method, a supercapacitor is observed only at the rated voltage. Generally, the supercapacitor voltage decreases because of self-discharge and it is observed that the typical controller design strategy will make microgrid unstable at low supercapacitor voltage. Proposed system is working on a low voltage of supercapacitors and observes the stability of DC microgrid under this condition. Also, this system works in all the designed operating modes. So, the complete performance of microgrids is investigated and adequate system operating conditions with stability are verified. Finally, the structure is verified through simulation and test results.

Sangita B. Patil

Papers

Stability Analysis of Supercapacitor based DC Microgrid System with Energy Storage

Innovative Architecture and Stability Assessment of DC microgrid with Integrated Energy Storage