**4. Establishment of the DC microgrid layout**

The previously detailed aspects demonstrate the efficiency of DC power distribution.

Although DC grids show many advantages and most home appliances are able to operate by using DC power, the development of these power distribution grids has yet to face several challenges, including:


Moreover, potential users do not yet have access to home appliances provided with DC power options. In terms of developing standards, several international organizations such as Emerge Alliance, ETSI-IEC, and IEEE are taking steps in order to establish regulations which are needed for the implementation of DC systems designed for residential applications.

According to IEC 60038 standard, distribution systems using low-voltage direct current should not exceed 1500 V. In this respect, the voltage levels' diagram which is currently used for DC power supply is shown in the following (**Figure 10**).

The transition from current distribution systems to DC grids must be gradually achieved, by ensuring parallel operation of both systems in order to ensure continuity of the power supply. DC power distribution is considered a solution

**53**

*Assessment of the Main Requirements and Characteristics Related to the Implementation of…*

only if it can easily be adapted to household consumers or when it can be efficiently implemented by direct connection to renewable energy sources such as photovoltaic panels. **Figure 11** shows a DC grid structure using several voltage levels depending

As in the case of alternating current distribution systems, the energy flow can be transmitted through two conductors (single phase) or four conductors (threephase). The DC grid power can also be transmitted in a similar configuration: two-wire (unipolar) and three-wire (bipolar) systems. The difference between the

The need for fast integration of renewable energy sources (such as photovoltaic panels) and storage units into distribution systems has highlighted the benefits of

On the other hand, the power supply related to any distributed energy source is not time constant due to weather condition dependence. Therefore, the AC grid interface is very important in order to improve the reliability and availability of the microgrid [22]. There are several ways to connect the DC grid to an AC grid, of which there are

• Radial configuration—for which the DC path starts from the AC grid through an AC/DC converter, supplying the line consumers through a single DC bus. This configuration has certain advantages such as the simple mounting and operation as well the multiple voltage level option. However, this configuration is not flexible under defective conditions. For example, a single failure in the input power end may affect all the connected consumers afterward. A radial

Various radial DC microgrids are currently implemented and operating throughout the world. Several microgrid test beds from the United States are to be mentioned: University of Miami test bed, Florida; Sandia National Lab Test bed,

two grid configurations is given by the number of available voltage levels.

*DOI: http://dx.doi.org/10.5772/intechopen.84413*

on the consumers' requirements.

*DC grid provided with multiple voltage levels [22].*

DC grid model is shown in **Figure 12**.

Washington, DC; and UT Arlington test bed, Texas.

using DC microgrids.

**Figure 11.**

to be mentioned:

#### **Figure 10.**

*Voltage levels currently adopted for DC power distribution [22].*

*Assessment of the Main Requirements and Characteristics Related to the Implementation of… DOI: http://dx.doi.org/10.5772/intechopen.84413*

**Figure 11.** *DC grid provided with multiple voltage levels [22].*

*Micro-Grids - Applications, Operation, Control and Protection*

**4. Establishment of the DC microgrid layout**

yet to face several challenges, including:

and AC/DC converters, respectively.

• In-service safety and fuse protection.

systems designed for residential applications.

*Voltage levels currently adopted for DC power distribution [22].*

port, and aerospace industry.

distribution.

The previously detailed aspects demonstrate the efficiency of DC power

Although DC grids show many advantages and most home appliances are able to operate by using DC power, the development of these power distribution grids has

• The necessity of using bidirectional energy conversion equipment, DC/DC

• Universally accepted standard voltage regarding the operation of household appliances, as well as telecommunication equipment, electric vehicle trans-

Moreover, potential users do not yet have access to home appliances provided with DC power options. In terms of developing standards, several international organizations such as Emerge Alliance, ETSI-IEC, and IEEE are taking steps in order to establish regulations which are needed for the implementation of DC

According to IEC 60038 standard, distribution systems using low-voltage direct current should not exceed 1500 V. In this respect, the voltage levels' diagram which is currently used for DC power supply is shown in the following (**Figure 10**). The transition from current distribution systems to DC grids must be gradually achieved, by ensuring parallel operation of both systems in order to ensure continuity of the power supply. DC power distribution is considered a solution

**52**

**Figure 10.**

only if it can easily be adapted to household consumers or when it can be efficiently implemented by direct connection to renewable energy sources such as photovoltaic panels. **Figure 11** shows a DC grid structure using several voltage levels depending on the consumers' requirements.

As in the case of alternating current distribution systems, the energy flow can be transmitted through two conductors (single phase) or four conductors (threephase). The DC grid power can also be transmitted in a similar configuration: two-wire (unipolar) and three-wire (bipolar) systems. The difference between the two grid configurations is given by the number of available voltage levels.

The need for fast integration of renewable energy sources (such as photovoltaic panels) and storage units into distribution systems has highlighted the benefits of using DC microgrids.

On the other hand, the power supply related to any distributed energy source is not time constant due to weather condition dependence. Therefore, the AC grid interface is very important in order to improve the reliability and availability of the microgrid [22].

There are several ways to connect the DC grid to an AC grid, of which there are to be mentioned:

• Radial configuration—for which the DC path starts from the AC grid through an AC/DC converter, supplying the line consumers through a single DC bus. This configuration has certain advantages such as the simple mounting and operation as well the multiple voltage level option. However, this configuration is not flexible under defective conditions. For example, a single failure in the input power end may affect all the connected consumers afterward. A radial DC grid model is shown in **Figure 12**.

Various radial DC microgrids are currently implemented and operating throughout the world. Several microgrid test beds from the United States are to be mentioned: University of Miami test bed, Florida; Sandia National Lab Test bed, Washington, DC; and UT Arlington test bed, Texas.


A complete grid structure regarding typical households which include usual appliances, consumers, battery storage units, and renewable energy sources as generation units is shown in **Figure 14**.

Some of the DC microgrids worth mentioning with ring or interconnected configurations are deployed as follows: Bosch DC Microgrid at California

**Figure 12.** *Radial DC grid topology [22].*

**55**

Denmark.

**Figure 14.**

*energy sources.*

**5. Conclusions**

*Assessment of the Main Requirements and Characteristics Related to the Implementation of…*

Honda Facility; Burlington DC Microgrid Canada, North America, Ontario; Xiamen University DC Microgrid China; Intelligent DC Microgrid Living Lab

*Topology of a household DC power distribution system which integrates typical consumers as well as renewable* 

Depending on the costs and consumer requirements, the DC layout which is outlined above may vary. When taking into account the perspective of renewable energy production, the variation along with the site's weather conditions must be considered. Moreover, the predicted power varies over time, throughout the day, or depending on the season. Thus, the connection to the public distribution grid is necessary if available. Storage systems also allow the accumulation of surplus

The current chapter envisages and analyzes both advantages and several topolo-

Various analyses regarding energy savings and voltage levels while addressing LVDC distribution systems have been presented. Studies have shown that DC grids will increase energy efficiency and power quality. There are still solutions to find to the challenges that DC grid systems have to overcome compared to existing AC

LVDC distribution systems provide particular advantages when integrating renewable energy sources along with storage systems. The development of DC power solutions designed for on the market household appliances may be the next step for the promotion of LVDC systems, especially when minor changes are required. Isolated areas without access to public electricity grid can opt for energy generation from renewable sources. In this case, LVDC grids are the first energy

For the time being, the home appliance industry is mainly focused on AC power supplied products. There is an increasing number of DC-powered equipment that uses switching mode power supplies for AC conversion as well as for voltage level

energy when consumption is low in relation to production capacity.

gies of LVDC distribution systems for residential applications.

systems, such as equipment safety and protection.

distribution options given the low deployment costs.

*DOI: http://dx.doi.org/10.5772/intechopen.84413*

**Figure 13.** *Annular interconnected DC grid [22].*

*Assessment of the Main Requirements and Characteristics Related to the Implementation of… DOI: http://dx.doi.org/10.5772/intechopen.84413*

#### **Figure 14.**

*Micro-Grids - Applications, Operation, Control and Protection*

generation units is shown in **Figure 14**.

ers can still be supplied without any inconvenience.

• Ring or loop configuration—consisting of two or more DC paths powered by converters in a single node or across multiple grid nodes. This configuration uses fast switches in order to isolate the defective circuit so that other consum-

• Interconnected configuration—the reliability of the DC microgrid can be further improved by providing alternative AC busses in the event of one of the AC/DC converters' failure. An example of an annular grid which is intercon-

A complete grid structure regarding typical households which include usual appliances, consumers, battery storage units, and renewable energy sources as

Some of the DC microgrids worth mentioning with ring or interconnected

configurations are deployed as follows: Bosch DC Microgrid at California

nected at multiple nodes with the AC grid is shown in **Figure 13**.

**54**

**Figure 13.**

**Figure 12.**

*Radial DC grid topology [22].*

*Annular interconnected DC grid [22].*

*Topology of a household DC power distribution system which integrates typical consumers as well as renewable energy sources.*

Honda Facility; Burlington DC Microgrid Canada, North America, Ontario; Xiamen University DC Microgrid China; Intelligent DC Microgrid Living Lab Denmark.

Depending on the costs and consumer requirements, the DC layout which is outlined above may vary. When taking into account the perspective of renewable energy production, the variation along with the site's weather conditions must be considered. Moreover, the predicted power varies over time, throughout the day, or depending on the season. Thus, the connection to the public distribution grid is necessary if available. Storage systems also allow the accumulation of surplus energy when consumption is low in relation to production capacity.

### **5. Conclusions**

The current chapter envisages and analyzes both advantages and several topologies of LVDC distribution systems for residential applications.

Various analyses regarding energy savings and voltage levels while addressing LVDC distribution systems have been presented. Studies have shown that DC grids will increase energy efficiency and power quality. There are still solutions to find to the challenges that DC grid systems have to overcome compared to existing AC systems, such as equipment safety and protection.

LVDC distribution systems provide particular advantages when integrating renewable energy sources along with storage systems. The development of DC power solutions designed for on the market household appliances may be the next step for the promotion of LVDC systems, especially when minor changes are required. Isolated areas without access to public electricity grid can opt for energy generation from renewable sources. In this case, LVDC grids are the first energy distribution options given the low deployment costs.

For the time being, the home appliance industry is mainly focused on AC power supplied products. There is an increasing number of DC-powered equipment that uses switching mode power supplies for AC conversion as well as for voltage level

regulation. These devices can be easily modified by eliminating the rectifying and power factor correction stages.

Most switching mode power sources are already very efficient even with DC/ AC conversion module included. Therefore, imposing a different power grid supply for households must be justified especially by the advantages related to the energy production and distribution stages and less by the aspects which regard the final consumer.

It can be concluded that modifying switching home appliances to DC power configurations can be achieved without any significant problems or at significant costs. The transition is easier when using new equipment that mainly embeds switching power supplies or *Inverter* technology to drive washing machine motors or compressors for refrigerators and air conditioning systems.

Older generation equipment that still uses transformers or AC motors require more significant changes of the power sources or the use of DC/AC converters.

The lack of both commercially available electronic devices and systems, and their required standards and regulations, is a major challenge that hinders the rapid development of this field. Currently, it is difficult to identify converters, fuses, or chargers which are necessary for the implementation of DC systems as well as to design and implement a DC microgrid, especially when operating at different voltage levels.

Moreover, potential users do not yet have access to home appliances provided with DC power options. In terms of developing standards, several international organizations such as Emerge Alliance, ETSI-IEC, and IEEE are taking steps in order to establish regulations which are needed for the implementation of DC systems designed for residential applications.

Even though the DC grid system protection is more difficult to be achieved than in the case of AC systems, a corresponding selection of a grounding configuration can be established by using adequate protection devices.

### **Acknowledgements**

This work was supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI-UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0391/ CIA\_CLIM—Smart buildings adaptable to the climate change effects, within PNCDI III.

Also, the authors acknowledge the financial support of MCI through the contracts no. 35N/2018 and 30PFE/2018 between the National R&D Institute for Electrical Engineering ICPE-CA and Romanian Ministry of Research and Innovation (MCI).

### **Conflict of interest**

The author declares that there is no conflict of interest. Thus, there are no conflicts of interest to disclose.

**57**

**Author details**

Lucia-Andreea El-Leathey

ICPE-CA, Bucharest, Romania

provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

National Institute for Research and Development in Electrical Engineering

\*Address all correspondence to: andreea.elleathey@icpe-ca.ro

*Assessment of the Main Requirements and Characteristics Related to the Implementation of…*

*DOI: http://dx.doi.org/10.5772/intechopen.84413*

*Assessment of the Main Requirements and Characteristics Related to the Implementation of… DOI: http://dx.doi.org/10.5772/intechopen.84413*
