Operation and Control of DC Microgrid

Power harnessing technology from the renewable energy resources has been developed over the past two decades. This technology enabled us to integrate renewable energy-based power generation to the conventional electric power grid. This study aims to improve the dynamic response and the load regulation using improved control strategies of the dc converters used to interface utility and renewable energy-based power generation. The power sharing between multiple dc microgrids/ac-dc microgrids is also investigated

Enhanced earth grid performance by improved conductor properties

Encroaching built environment with increased fault current levels is demanding a robust design approach and prolonged improved performance of the earth grid. With this in mind, the aim of the project was to perform a sensitivity analysis of the earth grid and an earthing performance evaluation with graphene coated conductors. Subsequent to these, a conceptual design to continuously monitor the performance of the earth grid was developed. In this study, earth grid design standards were compared to evaluate their appropriate use in determining the safety condition. A process to grow a thin film of graphene on the surface of cylindrical copper rods was developed to evaluate earthing performance in terms of conductivity and corrosion susceptibility

Earth grid safety criteria determination with the standards IEEE-80 and IEC-60479 and optimization of installation depth

Major generating or switching stations are normally operated with their neutral points directly earthed (usually an earth grid is buried in the earth). Metallic structures in the yard of generating or switching station, are electrically connected to the earth grid. The dimensions of earth grids are usually up to some hundreds of meters on a side. The design of earthing systems requires a worst-case approach. It ensures that a conductor forming the grid will not fail thermally or mechanically in the worst case of maximum fault current persisting for a fault of maximum duration. Over the life time of the electrical substation and its associated earth grid (30-50 years), it is important to maintain safety. Therefore before installing an earth grid its design is assessed according to the earth grid installation standards. In this paper safety criteria assessment of a design is evaluated with both IEEE-80 and IEC-60479. In addition, a new method for determining the earth grid's installation depth has been proposed. It is based upon the soil model of particular substation instead of installing it in 0.5 meters depth for any substation.</p

An investigation of Earth grid performance using graphene-coated copper

Abstract: Large power systems are normally operated with their neutral points directly earthed. At a major generating or switching station, this results in the provision of a large earth grid buried in the ground. The design of earthing systems requires a worst case approach. There is a possibility of heavy currents flowing into the earth grid from the overhead earth wires through the tower during a line conductor fault and from lightning strikes. The flow of earth current during a fault or lightning conditions results in a rise of earth grid potential with respect to a physically remote earth point, which can lead to unsafe conditions under some conditions for personnel and connected electrical plant. This paper aims to investigate the potential of adding novel coatings to the conventional copper earth grid conductors to enhance overall conductivity and diminish corrosion. This contributes to lowering the rise of earth grid potential. Graphene-coated copper performance as an earth grid conductor is evaluated with staged low voltage fault and the corrosion behavior in both a destructive and nondestructive environment. A comparison of the simulation software packages CDEGS and CST is also carried out using lightning strike conditions

Bidirectional power sharing in an ac/dc system with a dual active bridge converter

This study introduces a bidirectional power sharing scheme between an ac electric utility and a dc microgrid. These two are connected together through an interlinking converter (IC) and a dual active bridge (DAB). The proposed control scheme allows predefined amount of power to be supplied from the ac to dc side or the other way around. The DAB is connected at the dc side of the IC and it controls the bidirectional power flow. The dc microgrid contains dc-dc converters, where boost converters are used with the sources and buck converters are used to supply loads. These dc-dc converters and the DAB are controlled by state feedback with integral control in a linearised discrete domain. The DAB linearisation and control law are presented in detail. The dc microgrid is controlled by conventional V-P droop where the power from/to the ac side is considered as negative/positive load. Detailed simulation results are presented to validate the proposal. Also some hardware results are included that support the findings