In India, more than 200 million people live in rural areas without access to grid-connected power. A convenient & cost-effective solution would be hybrid power systems which can reduce dependency on grid supply, improve reliability. For a typical domestic load a solar –wind hybrid system is designed with charge controller to charge a conventional battery. To optimize system efficiency, a simple algorithm is developed for system sizing. Total cost of unit is calculated using life cycle cost analysis and payback period

1. DC GRID INITIATIVE IN INDIA
SIET, VIJAYPUR Dept. of EEE Page 1
CHAPTER 1: INTRODUCTION
Increasing energy demand with the growing population putting a challenge to existing
power network since centralized power system existed for decades with lack of
expandability due to its increased cost and expenditures for new generation and
transmission. Increasing the conventional power generation to meet the growing demand
is not an effective solution with respect to its environmental impacts. Supplying the
demand locally by using non conventional energy sources such as photovoltaic, wind,
biomass, etc given new paradigm to grid called Micro grid. This has numerous
advantages over the conventional grid in terms of low losses, less cost and more reliable
in case of grid failures.
Mainly two micro grids AC and DC are available and are discussed. But major supply
available is AC because of its advantages in transforming voltage level as per requirement
and its inherent characteristic from the fossil energy driven rotating machine. Most of
micro grids existed so far are AC grids. With advancement of power electronics, use of
DC equipment has increased significantly from last two decades. This requires power
conversion from available AC supply. DC micro gird is gaining the importance due to its
own merits over AC microgrid such as:
1) Control of DC voltage is easy in comparison with AC grid voltage and frequency
2) Low system cost and reduced losses since it requires fewer conversion stages as
DC loads are directly connected.
3) Readily available renewable energy sources in form of DC which include
photovoltaic and fuel cell.
Use of DC distribution makes easier connection of storage elements which are
in form of DC (Lead acid and Li batteries), that substantially increase continuity of
supply even when fault occurred on AC grid and distributed generation (DG). Only one
control element makes DC grid to have fast switching between grid connected and
islanded mode of operations without complexity in control scheme unlike the two
parameters (grid voltage and frequency) in AC. Apart from these, DC provides increased
line carrying capacity for same capacity of AC, minimizing the weight and size of
equipment required for transfer of power from source to load.

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Though it has above advantages, still DC power system is restricted to
shipboard systems, electric vehicles, telecommunication systems, traction, and power
transmission (HVDC) due to some of the drawbacks which are as follows:
1) Need a separate line for construction of DC grid.
2) DC protection is difficult than AC because there is no natural zero crossing
occurrence.
3) Adapted loads required for high system efficiency.
Present evolution of technology in protection makes the DC grid more suitable at low
voltage end of distribution.

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CHAPTER 2: CURRENT POWER SCENARIO IN INDIA
Though India stood at fifth place in producing electricity around the globe, still it
is having power deficiency. Over coming years demand rises with economy because of
strong correlation between them. Continuous efforts are put by Government of India in
generating the power at increasing rate. However, the gap is still present between
generation and demand. This leaves the distribution of electricity in stress and degrades
electric supply in the country.
2.1 Generation
Power generation from various sources is shown in Fig. 2.1. Presently coal
and gas alone contributes around 70% of generation in India. If coal consumption is
continued at current rate then it lasts around 200 years. Then generation becomes more
problematic in the future, hence India should more concentrate on local generation near
the demand so that transmission and distribution losses are reduced and demand is
effectively met. The states having gap between demand and supply (Central Electricity
Authority 2014) are Jammu & Kashmir, Uttar Pradesh, Karnataka and Andhra in
descending order respectively. India started using alternative sources of energy in order to
compensate the coal consumption for producing power to meet the gap and to cover the
future demands in India. As per report given in (Ministry of New and Renewable Energy
2013) major available alternative energy sources are solar and wind.
Fig. 2.1: Power Generation chart in India.

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2.2 Potential of DC Grid
Especially solar is having more potential compared to other renewable
energy, in generating the power at distribution level to meet domestic and commercial
loads in highly demanded states. Effective solution of meeting the demand locally yields
the formation of local grid called Microgrid. Here the available local generation at low
voltage end or in low power scale is solar PV. Wind is not suitable at this level. As local
power generation is in DC and also major loads available at home, commercial consumers
(office buildings, shopping malls, etc) cover DC loads in the form of lighting load and
computers, TVs (LEDs and LCDs), drives, etc. These loads need DC input internally but
as supply is AC now, rectifiers are used to convert the AC into DC. Though there are two
types of microgrids (AC and DC) exist, above point necessitates the formation of local
DC grid which requires few conversion stages and is less costly.
Further development of DC technology and increased concern about the
environmental impacts, advantages of DC loads over AC loads for the same usage, makes
the DC loads more common in supplying the basic needs like lighting, cooling system
and entertainment. Therefore DC grid can replace AC in near future at low voltage side.
By considering this point of view a modern DC grid is structured with DC loads mainly
explained in next section. Coming to Indian context there are villages or rural areas where
distribution of AC supply is difficult to achieve, there it is easy to implement DC grid
with less cost and more reliability. Even in areas where demand is high as explained
above in order to have local demand compensation, DC grid is best solution since
availability of solar PV near load and major type of loads used are DC.

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CHAPTER 3: TYPICAL DC GRID
DC power system existed so far is limited to HVDC only. But increase in
use of DC in end user equipment given more importance to low voltage DC (LVDC)
distribution system. The typical structure of this in Indian consumer point of view is
shown in fig. 3.1. In this model constant DC link voltage is maintained between the
source and load. The value of DC link voltage varies depending upon configurations.
Solar Photo voltaic (PV) is considered as basic source of energy since huge potential of
solar PV and installation is very easy at the low voltage consumer end. Output voltage of
PV connected to DC grid through the DC-DC converter with Maximum power point
technique (MPPT). Battery is connected to grid through bidirectional DC–DC converter
in order to charge and discharge with availability of solar power so that continuous supply
is maintained throughout without any disturbance in voltage. DC loads considered in this
model basically are fan, TV and LED lighting load. In addition to these loads, AC loads
such as refrigerator, washing machine, Owen, etc. which is used in typical house
connected to AC side of bidirectional voltage source converter (VSC). VSC can able to
transfer power from DC to AC side when excess power available at DC side and also it
can transfer power from AC grid or Utility to DC side when DC link voltage dropped
below nominal value.
Fig. 3.1: Typical structure of DC smart grid in India.
Nowadays laptops/computers and mobile phones become common load at every
home with increased people’s life quality. These can be connected to same DC link
through the DC–DC converters, as input to these appliances varies slightly from
manufacture to manufacture. Apart from this, load shedding is also possible by
connecting the load controller near the loads, but this is still under development in India.

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CHAPTER 4: MODIFIED DC GRID CONFIGURATION
Considering the replacement of existing lighting system (incandescent
lamps, CFL), cooling system (fans, air conditioners, air coolers), personal appliances
(Mobile chargers, Laptop chargers, computers, televisions) in terms of DC loads with
appropriate DC technology. Few modifications are proposed to existing DC grid in order
to suit the conditions of loads depending upon the type of loads used, availability of AC
supply and minimization of VSC or AC-DC converters. The following configurations are
more suitable for remote locations where there is no supply available and also applicable
to newly constructed homes or buildings or homes in Suburban or Urban or Metro cities.
In this each home consists of basic loads in DC only for serving basic
needs like lighting, cooling and entertainment. Ratings of the components used in each
DC home model are given in the Table 4.1. For simplicity configurations are divided into
two categories based on connection as Autonomous DC grid and Utility connected DC
grid.
Table 4.1 Ratings of components of DC grid
4.1 Autonomous DC grid
In this two configurations are explained. Fig. 4.1a) shows typical structure
for three DC homes. As home uses only DC loads and generation, hence named as DC
homes. AC loads are not considered here. Common voltage suitable for appliances used is
24 V. Internal connection diagram of each home as shown in Fig. 4.1b). This type of
configuration is more suitable where there is no AC supply available and no

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electrification is done yet. In India around 20 thousand villages are still unelectrified as
per report in (Central Electricity Authority 2015) till 31 Jan 2015.
Power sharing is done by the power vs. voltage droop characteristics and
voltage is common control element for all the three homes and actual DC link voltage is
always compared with reference for closed loop operation. This type of configuration
provides more flexibility in power sharing among the homes and less fluctuations in DC
voltage since they are all interconnected. In this main drawback is every home is having
individual storage and its associated converters, this increases individual expenditure and
maintenance cost. But it is having more reliability of supply even if one of home is not
getting proper supply from connected source and battery to meet the load then it is
compensated from other two homes. Second type of configuration in this category is
shown in Fig. 4.2. Control part is same as previous configuration except that storage is
common to three homes which decrease the overall cost but reliability of supply
decreases when battery fails there is no alternative to supply the load. Total load depends
on PV generation only and as generation from PV is intermittent in nature hence
decreases the reliability. Battery capacity installed is around two times the single battery
installed in previous case in order to harness the optimum usage.
Fig. 4.1: a) Type 1 structure for connecting 3 DC homes in autonomous mode.
b) Internal connection diagram of each DC home.

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Fig. 4.2 a) Type 2 structure for connecting 3 DC homes in autonomous mode.
b) Internal connection diagram of each DC home.
4.2 Utility connected DC grid
This kind of configuration is mainly introduced to suit the urban areas where most of
newly constructed houses and commercial buildings (example malls, offices, etc). Control
methods for converters are same as typical grid except the structure which explained in
previous section.
In Fig. 4.3a) each area consists of three DC homes which are not interconnected. Every
DC home has its internal structure shown adjacent to main diagram. Single AC-DC
converter is used to balance individual DC link voltage. In this each home having
generation from PV to meet the demand .When generation is greater than load then it
charges battery otherwise battery discharges to meet the demand. If battery is at minimum
state of charge (SoC) then utility starts feeding the load in home.

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Fig. 4.3 a) Typical configuration for an isolated three DC homes in area with internal structure.
b) Type 3 configuration for connection of DC homes in utility connected mode.
Table 4.2: Comparison of modified DC grid structures
If the DC homes in particular area are combined to give reduced conversion
stages with same reliability and decreased cost which is as shown in Fig. 4.3 b). In this
type the AC-DC converter becomes common to balance the DC link voltage. The
comparison of discussed structures is given in Table 4.2 with their merits and demerits in
application point of view.

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CHAPTER 5: AC HOME V/S DC HOME
In this basic loads are considered for analysis of AC vs DC home. Keeping
in view of all types of domestic consumers, a typical Indian home is considered which
consists of four lamps, two fans and one TV. These loads are described in terms of AC
and DC with their ratings in the following Table 5. Both these AC and DC loads serve the
same purpose without any difference. For example 60W incandescent bulb gives an
illumination of 800 lumens and same illumination is given by the LED lamp of 6 W.
Table 5.Comparison AC load vs DC loads in typical Indian home
*-Very short; **-Medium; ***-High; ****-Very high; ^-TV considered here is 21
inches;
If all loads are replaced by DC then total savings Rs 2016 per year. This savings
compensates the cost difference between the AC and DC appliances.

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CHAPTER 6: Benefits of DC Grid
6.1 Advantages
1) Control of DC voltage is easy in comparison with AC grid voltage and frequency
2) Low system cost and reduced losses since it requires fewer conversion stages as
DC loads are directly connected.
3) Readily available renewable energy sources in form of DC which include
photovoltaic and fuel cell.
4) Use of DC distribution makes easier connection of storage elements which are in
form of DC (Lead acid and Li batteries), that substantially increase continuity of
supply even when fault occurred on AC grid and distributed generation (DG).
5) Only one control element makes DC grid to have fast switching between grid
connected and islanded mode of operations without complexity in control scheme
unlike the two parameters (grid voltage and frequency) in AC.
6) Apart from these, DC provides increased line carrying capacity for same capacity
of AC, minimizing the weight and size of equipment required for transfer of
power from source to load.
6.2 Disadvantages
DC power system is restricted to shipboard systems, electric vehicles, telecommunication
systems, traction, and power transmission (HVDC) due to some of the drawbacks which
are as follows:
1) Need a separate line for construction of DC grid.
2) DC protection is difficult than AC because there is no natural zero crossing
occurrence.
3) Adapted loads required for high system efficiency.

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CHAPTER 7: CONCLUSION
DC Grid is more effective compare to the AC Grid because losses are less
and cost required is less in DC Grid. DC Grid related DC loads consume low voltage
compared to the AC grid.
A comparative analysis between them is also given in the table.
Comparison between AC and DC home shows that even though cost of DC equipment is
high but significant reduction in losses and power consumption gives more importance to
DC grid.

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REFERENCES
[1] Central Electricity Authority, 2014b. Load Generation Balance Report,
[2] Central Electricity Authority, 2015. Progress report of village electrification,
[3] Chan, C.C., 1993. An Overview of Electric Vehicle Technology. In Proceedings of
the IEEE (Institute of Electrical and Electronics Engineers);(United States). pp. 1202–
1213.
[4] Ciezki, J.G. & Ashton, R.W., 2000. Selection and Stability Issues Associated with a
Navy Shipboard DC Zonal Electric Distribution System. IEEE Transactions on Power
Delivery, 15(2), pp.665–669.
[5] Cuzner, R.M., 2008. The Status of DC Micro-Grid Protection. In Industry
Applications Society Annual Meeting. pp. 1–8.
j