Energy Management System for DC Microgrid

DC Distribution Systems and Microgrids, 2018

— As the number of DC loads are growing in our daily uses, the low voltage DC (LVDC) distribution system is becoming important. Power supplied through the low voltage AC (LVAC) distribution system needs both the AC/DC rectifier and the DC/DC converter to supply the DC loads. In comparison, LVDC system would only need the DC/DC converter to supply the DC loads. Integration of renewable energy sources at LV level, like rooftop photovoltaic (PV), fuel cells, etc. would be relatively easier with the LVDC system than the LVAC. So, the LVDC can be the viable solution to reduce multiple conversion losses in the system. This paper presents comparison between the existing LVAC with the prospective LVDC distribution system in terms of converter conversion efficiency. Constant AC and DC loads, generally used in household applications, are simulated using PSCAD/EMTDC for both the LVAC and the LVDC distribution system. The analysis of the effectiveness of LVDC system over LVAC distribution system has been presented.

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.

Environmentally friendly technologies such as photovoltaics and fuel cells are DC sources. In the current power infrastructure, this necessitates converting the power supplied by these devices into AC for transmission and distribution which adds losses and complexity. The amount of DC loads in our buildings is ever-increasing with computers , monitors, and other electronics entering our workplaces and homes. This forces another conversion of the AC power to DC, adding further losses and complexity.In this study, an equivalent AC and DC distribution system are compared in terms of efficiency. 1. Advantages and Disadvantages of DC power transmission and distribution over the conventional AC power system Advantages of DC Transmission; • There are no Inductance and Surges (High Voltage waves for very short time) in DC transmission. • There is no concept of Skin effect in DC transmission. Therefore, small cross sectional area conductor required. • There are two conductors used in DC transmission while three conductors required in AC transmission. • Due to absence of inductance, there are very low voltage drop in DC transmission lines comparing with AC (if both Load and sending end voltage is same) • There is no concept of Skin effect in DC transmission. Therefore, small cross sectional area conductor required.

This chapter titled "Hybrid AC/DC Microgrids: Solution for High Efficient Future Power Systems" presents a new configuration for future power systems which is the hybrid AC/DC gird for high efficient connection of the inherent AC and DC sources and loads. Three-phase AC power systems have been in dominant position for over hundred years due to invention of transformer and the inherent characteristic from fossil energy-driven rotating machines. However, the gradual changes of load types and distributed renewable generation (DRG) in AC local distribution systems provide food for consideration of adding DC networks. Renewable sources such as fuel cells and solar photovoltaics are DC inherent and should be connected to AC grid through DC/AC conversion techniques whereas some AC inherent renewable sources like wind generators also need DC links in their conversion systems to increase efficiency and mitigate power variation caused by intermittency and uncertainty. The disadvantage of AC grids for connection of DC inherent sources and loads as well as AC loads with DC links is that additional DC/AC or AC/DC converters are required, which may result in efficiency loss from the reverse conversion. In the other hand DC grids are resurging due to the development and deployment of renewable DC power sources and their inherent advantage for DC loads in commercial, industrial and residential applications. The number of power conversions in a DC microgrid has been significantly reduced to enhance system energy efficiency. A more likely scenario is the coexistence of both AC and DC microgrids, which is so-called the hybrid AC/DC microgrid in order to reduce processes of multiple reverse conversions in an individual AC or DC microgrid and facilitate the connection of various renewable AC/DC sources and loads to power system. Therefore the concept of hybrid microgrids, which can harmonize both AC and DC sources and loads, has been proposed for future high efficient power systems. Conventional AC and DC grids are interconnected together through the bidirectional AC/DC converter. The component model has been introduced. The control and operation of individual sources and energy storages are presented. The coordination control and power sharing techniques are also introduced.

The paper devoted to the developing of DG system on the base of hybrid AC/DC network. The attention paid to microgrids with hybrid power sources (wind, PV-solar, fuel cell, bio gas and so on) with ability to deliver electrical energy on twin power buses for further supplying of customers with AC and DC power. As an example micro grid with dc and ac power sources supplying parking area was investigated.

This paper discussed the advantages and challenges of DC microgrid for commercial building. The data obtained from the DC microgrid constructed at Xiamen University shows that DC microgrid with rooftop solar system is an efficient way to power varies DC loads inside the building. The capacity of the solar system on the rooftop normally will be enough to power the LED light loads in commercial buildings, even for high rise buildings. In order to power heavy loads such as air conditioning and EV charging stations, extra power are required, which can be obtained from the BIPV on the sidewall, glass window, or adjacent parking lots. To ensure the stable bus voltage and continuous operation of the DC microgrid, a suitable energy storage unit and two way AC/DC invertors are needed. Therefore we believe to use the solar power only for the matched DC loads, and keep existing AC power in the building to power the rest loads (or an AC and DC hybrid microgrid) maybe a more viable solution. The economical analysis shows that installation cost of a DC microgrid system is about $2.2/W, which is becoming a marketable technology.

2021

Various statistics indicate that many parts of India, especially rural and island regions, have either limited or no access to electricity. It is very expensive and difficult of installation of transmission line in these areas because of their geographical location. This problem leads to the uses of renewable energy sources to supply power to these remote areas. Most of these renewable energy source produce electricity in the form of DC. In today scenario most of people use invertor in house to store electricity in a battery which will reused during cut off hour. While electricity generation of renewable source is in the form of DC and transmission of this supply is in the form of AC. And a wide variety of daily utility devices such as cell phone chargers, laptops, laptop chargers, electric vehicle etc. operate on DC electricity. So to supply power from generation unit to the consumer multiple time of conversion from AC to DC and vice versa take place. Because of this conversion los...

Energies

The world has witnessed a rapid transformation in the field of electrical generation, transmission and distribution. We have been constantly developing and upgrading our technology to make the system more economically efficient. Currently, the industry faces an acute shortage of energy resources due to overconsumption by industries worldwide. This has compelled experts to look for alternatives to fossil fuels and other conventional sources of energy to produce energy in a more sustainable manner. The microgrid concept has gained popularity over the years and has become a common sight all over the world because of the ability of a microgrid to provide power to a localized section without being dependent on conventional resources. This paper focuses on development of such an AC hybrid microgrid, which receives power from distributed energy resources (DERs) such as a PV array alongside a battery storage system, and also uses an emergency diesel generator system and an online uninterrup...

IEEE Transactions on Smart Grid, 2014