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This paper presents a transient analysis of various configurations of DC distribution systems. A combination of theoretical and practical methods were used to investigate the behavior of the system's variables after the occurrence of faults and the protection operation. A number of networks of varying complexity were built with detailed cable models using the EMTP/ATP software package in order to...
Connecting large dc distribution grids on the same voltage level can allow superior utilization of infrastructure. Selective ground fault protection is necessary and can be done using low impedance grounding. Distributed energy resources would allow for higher resilience of the grid if islanding operation of dc microgrids is allowed. For safety, grounding is essential in these islanded microgrids...
Inside the meshed LVDC distribution grids the power flow is predominantly limited by the line impedances. In order to achieve economical and flexible operation of the meshed LVDC distribution grids, it is required to control the power flow. For that end, the line impedances need to be adjustable. The line impedance can be controlled by a DC-DC transformer, however, it needs to be rated for the full...
Nodal pricing or LMP is one option to deal with congestion in the distribution grids that are expected due to the emergence of electric vehicles. When optimal power flow (OPF) with losses is used to determine optimal dispatch and locational marginal prices (LMP) of a power systems, the prices include marginal losses. Marginal losses are double the amount of the real physical losses. This leads to...
This article describes the circulating current phenomenon that takes place in bipolar, meshed DC distribution grids. A difference in resistance between the conductor changes the distribution of the current on the conductors. This provokes a net current to flow, which is in turn measured by the residual current protection scheme, used to detect and isolate ground faults in the system, even though there...
This study evaluates the dynamics of DC microgrids (DCMG) with the integration of voltage dependent demand response (VDDR). Previous work evaluates price prediction models for grid operators to estimate local price as a demand side management (DSM) technique. VDDR has been proposed to implement DSM without the need of a dedicated communication link. The dynamic response of a DCMG with VDDR has been...
Distributed Generation has created the need for new types of smart dc grids developments. The multiple generation sources, bi-directional power flow, power flow time co-ordination and management bring significant benefits as well as challenges for current ac electrical grids and emerging dc microgrids. In particular, the effect of voltage weak distribution systems on protection concepts and approaches...
This paper reviews the currently available dc micro-grids and dc grids. Currently, commonly existing and proposed dc microgrids are designed to provide sufficeint energy during system disturbance as in ac grid and, are mainly voltage stiff systems. It also compares the voltage stiff systems to a low energy system, which represents voltage weak dc system, from systems point of view. First, the definition...
This paper proposes a method to mitigate the problems related to series arcing in low voltage dc (LVdc) micro-grids by performing voltage drop detection using the power electronic device at the load-side. Specifically, the selectivity of the designed series arc detection algorithm is shown for two constant power loads connected in parallel at the point of common coupling with a stable voltage dc micro-grid...
Unplugging of energized loads in dc microgrids can cause safety concerns to users in residential areas. Sustained series arcs are more relevant in dc systems than in ac due to absence of current zero crossing. In this paper, the series arcs are detected from the load side, wherein, the proposed algorithm monitors the drop in load capacitor voltage associated with the intial electrode dependent series...
The emergence of distributed energy resources can lead to congestions in distribution grids. DC distribution grids are becoming more relevant as more sources and loads connected to the low voltage grid use dc. Bipolar dc distribution grids with asymmetric loading can experience partial congestion resulting in a nodal price difference between the two polarities. In order to take into account this price...
Micro-grid for villages using renewable energy is becoming a trend for developing countries like in Africa. Commonly, ac microgrids are used for the simple reason of ac household equipments and protection abilities. DC microgrid is a better choice in terms of efficiency, control simplicity and converter prices. However, whether it is an AC or DC, the demand-supply management is the most basic problem...
The traditional ac power system is challenged by the increased amount of distributed energy resources. Enormous changes and investments are necessary in order to achieve an ac smart grid capable of coping with the challenges introduced. In dc, solutions seem to be more straightforward since most of the distributed energy sources and most of the loads connected to the low voltage grid operate with...
Due to the absence of current zero crossing, dc arcs do not extinguish as easily as ac ones. It is essential to detect and eliminate series arc faults in dc microgrids in order to ensure safety, particularly while unplugging loads. Several detection and extinction methods using various means are known in literature. In this paper a novel arc detection method is proposed. It detects the load side input...
The increasing amount of distributed energy resources requires significant changes to today's power systems. Most of the distributed resources are dc inherently or have a dc link. Therefore, connecting them with a dc distribution system seems beneficial. This paper presents the opportunities and challenges of dc distribution systems, starting with the requirements of future power systems. It will...
Meshed dc distribution grids have advantages over radial connected ones. Challenges arise when this is done on the same voltage level and the full potential power might not be usable in certain configurations. This paper shows how the power flow in meshed dc grids can be increased by limiting the currents at congested lines. This can be done in a decentralized way with only local current measurements...
This paper describes the behavior of voltage weak dc microgrids. These are dc microgrids with a relatively small system capacitance. The large amounts of stored energy in the passive component of a network has a considerable effect on the size of the fault currents, control and reliability. The use of a complex control approach to stabilize voltage weak microgrids is a possibility that requires further...
DC microgrids can connect directly dc renewable energy sources with increasing amount of dc loads. In this paper it is looked for possible architectures for integrating PV panels into dc microgrids, by means of microconverter strings. Three topologies are considered, featuring only buck microconverters and only boost microconverters, since they promise higher efficiency due to fewer semiconductors...
DC renewable energy sources and dc loads are gaining attraction and they are preferably connected in dc microgrids. To increase the availability of dc microgrids, voltage dependent demand response should be used to switch off low priority loads in case of insufficient supply. This is possible even without communication with the loads. In this paper it is shown that using a voltage hysteresis with...
DC has several advantages over ac. In relation with the changes needed in todays ac power system to deal with dominating amounts of fluctuating renewable energy, it seems wise to consider dc as an alternative. One of the problems with introducing dc grids is the lack of availability of dc devices. DC ready devices that work on both - ac and dc - would simplify a smooth introduction of dc there, where...
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