In this type of microgrid, the bus voltage is AC, hence referred to as an AC microgrid (Kumar et al., 2017). It incorporates renewable power sources such as PV and wind power, illustrated in Figure 1 (Kumar et al., 2017). The AC bus is depicted in blue and is synchronized with the medium voltage distribution network through a bypass switch. PV, generating DC voltage, requires conversion to a suitable level using DC choppers. This is then transformed into AC through an inverter for connection to the AC Bus. Similarly, the fluctuating AC voltage from the wind turbine is converted to DC power through a rectifier and then adjusted to the required voltage level using an inverter. The battery and flywheel produce DC power for backup in the AC microgrid, which is converted to AC using an inverter. The AC microgrid features two load terminals, a purely DC load terminal comprising mobile, fan, and personal computer, supplied by the AC bus through a rectifier. An electric vehicle charger, considered a DC load in the AC microgrid, is connected through a rectifier. An AC load, represented by an AC motor, cannot be directly connected to the AC bus due to voltage disparities. Thus, it undergoes conversion to DC through a rectifier and is then transformed back to AC using an inverter for connection to the AC motor. This complexity in conversion stages is a characteristic of AC microgrids.

In this type of microgrid, the bus voltage is DC, leading to its designation as a DC microgrid (Kumar et al., 2017). In residential and commercial applications, such as computers, battery chargers, and highly efficient lighting systems, DC power is required. Consequently, these appliances necessitate AC-DC conversion to be compatible with the conventional AC supply available. The multiple conversion stages involved can reduce the reliability and overall system efficiency. However, these challenges can be mitigated by utilizing highly efficient DC-DC converters, offering the possibility of directly connecting devices to the DC grid. In a DC microgrid, renewable energy sources and power electronics can be connected effectively and efficiently to loads by selecting a suitable voltage level, ensuring fewer conversion stages, as depicted in Figure 2 (Kumar et al., 2017).

Two different types of buses are available in this form of microgrid; one type provides AC voltages, while the other type provides DC voltages (Kumar et al., 2017). When both AC and DC type generation from renewable energy sources are available, as in Figure 3 (Kumar et al., 2017), this setup works best for the application.

Table 1 higlights some ke strength of DC microgrids amon the weakness of AC microgrids (Rangarajan et al., 2023).

The battle between Westinghouse and Tesla vs Edison and J.P. Morgan regarding “What Comes Next” is referred to as the “War of the Century (Blasi, 2013). Both sides are on the point of realizing how much the future infrastructure of electricity would be worth financially (Blasi, 2013).

In the late 18th century, in 1880, the director of the Edison Illuminating Company, Thomas Edison, developed a small power plant in Pearl Street Station to supply customers with DC power to operate low-voltage DC-powered lamps (Xu and Cheng, 2011). The power of that plant was distributed in three lines (i.e., a bipolar distribution) with +110, 0, and −110 voltage levels (Seyedmahmoudian et al., 2015) The main drawback of that power was that the voltage drop is high in power lines; therefore, power transmission towards remote areas and other residential neighborhoods away from the main generating station was not a suitable choice. There was no voltage transformation; the small plant and loads were only incandescent lamps and DC motors (Seyedmahmoudian et al., 2015).

Nikola Tesla, in 1886, introduced the concept of alternating current by utilizing transformers to change the voltage levels. The debate strengthened in 1887, when Nikola Tesla registered several patents in the United States (Seyedmahmoudian et al., 2015). Patents were based on the AC Distribution Scheme and supported by Westinghouse Electric and Manufacturing Company. The findings of Tesla widely affected the superiority of the AC system in the BATTLE OF CURRENTS. In 1893, Westinghouse won a contract to build a hydroelectric dam to harness the power of Nigeria Falls and transmit it to Buffalo, New York. The project was finished on 16 November 1896, and AC Power began to power industries in Buffalo. This milestone marked the decline of DC in the United States by providing a successful experience for future worldwide power transmission and distribution projects (Sulzberger, 2003; Moser, 2008).

Edison exerted considerable efforts to increase the efficiency of the DC system and reduce line loss in the 1880s by using a series of motor generators to create the HVDC system (Seyedmahmoudian et al., 2015). Such a model was capable of power transmission over longer distances. But HVDC was never adapted because of maintenance and high installation costs, almost for a century (Seyedmahmoudian et al., 2015).

After the invention of the transistor in 1947 by John Bardeen, the electronic revolution started. The invention of high-voltage power electronic devices in particular has made a comeback of DC possible (Van Willigenburg et al., 2022), when there was an advancement in the power electronics field, DC-DC converters (i.e., Buck, Boost, and Buck-Boost) were introduced. These were able to transform DC power to different voltage levels as per the desired appliance requirement (Gelani et al., 2021). This was the time when supremacy was enjoyed by DC over AC. DC power has started in the field of generation by utilizing renewable energy sources, i.e., solar, fuel cells, etc. Generated DC power is transmitted over longer distances through HVDC transmission (Gelani et al., 2021).

Microgrids were initially introduced in 2001 by Bob Lasseter, who led the IEEE PES WM Panel, as evidenced by his conference paper (Glinkowski et al., 2017) and the CERTS Report (Kondoleon et al., 2003) in 2002. Currently, major countries worldwide, including the United States, the European Union, Japan, and China, have conducted research on microgrids.

The Consortium of Electric Reliability Technology Solutions (CERTS) in the United States is a renowned institution for Micro Grid Research (Barnes et al., 2007). It introduced the pioneering concept of Micro Grid in a White Paper known as the “Micro Grid Concept,” prepared for the California Energy Commission and the DOE. CERTS Micro Grid developed the concept of peer-to-peer with plug-and-play strategies, successfully demonstrated in a test bed with American Electric Power (LI et al., 2014). Northern Power Systems (NPS) implemented a Micro Grid installation in MAD RIVER, Waitsfield, Vermont (Barnes et al., 2007), featuring a central Microgrid Controller (Northern Power Systems, 2005). In the Boston Bar system of British Columbia Hydro, a single large generating station is effectively employed (Barnes et al., 2007) to control the net subsystem behavior using Micro Grid Control. The General Electric Corporation is in the process of field trials for its Microgrid Concept (Barnes et al., 2007) and is actively working on developing the Micro Grid Energy Management System.

Major projects have been carried out in the European Union on microgrids, including the MicroGrid Project and More MicroGrid Project, in order to take advantage of renewable energy sources and enhance their use for microgrid improvement (LI et al., 2014). The Micro Grid project is linked to concepts, challenges, and laboratory tests, while the More Micro Grid Project has designed seven pilot installations, with the first distributed-generated application also in Micro Grids on the island of Kythnos (Vasilakis et al., 2020). Kythnos Microgrid was constructed on Kythnos Island (LI et al., 2014), providing electricity to 12 houses in a small valley (Schwaegerl, 2006). A low-voltage microgrid (CESI Test Facility) in Milan was developed, which is synchronized with a medium-voltage grid for the testing of distributed generation technologies (Barnes et al., 2007; LI et al., 2014). This system is used as part of the More Microgrid Project.

The Labein Research Institute in Spain has put together a test system for distributed generation and microgrid research (the Labein Microgrid) (Barnes et al., 2007). The Portuguese Electricity Utility (EDP Feeder) is in the process of upgrading the far end section of a small commercial radial feeder in order to undertake microgrid studies (Barnes et al., 2007). Together with EMforce and Germanos, Continuon upgraded a holiday park it runs in the Neitherlands into a microgrid (Continuon Holiday Park microgrid) (Barnes et al., 2007). The first EC Micro Grid Project used the Demotec facility at ISET in Kassel to develop methodologies for the control of distributed generation in microgrids (Barnes et al., 2007). In Mannheim, Germany, the substation network connected to the MVV headquarters has been identified by MVV as a site to investigate microgrids (Barnes et al., 2007). The Shimizu Corporation has built both a pilot and large-scale microgrid at its research labs in Tokyo (Shimizu Extended Microgrid) (Barnes et al., 2007). The Regional Power Grid with Renewable Energy Resources Project, an initiative of the New Energy and Industrial Technology Development Organizations (NEDO), has commenced three demonstrations (Zhou et al., 2015).

• Hachinohe System; this project is a collaboration between Hachinohe City, the Mitsubishi Research Institute, and Mitsubishi Electric (Barnes et al., 2007; Marnay and Firestone, 2007). This system contains PV, wind turbines, battery energy storage, and three large gas engines fed by sewage and waste gas.

Commonly, most devices used in homes, such as laptops and mobiles, operate on DC power for charging. However, the supply available in homes is typically AC. Consequently, there is a need for a two-step conversion process–first from AC to DC and then again from DC to a compatible form for the appliance (Manandhar et al., 2016), as illustrated in Figure 4. This dual conversion process leads to an overall reduction in efficiency. As noted in (Sulzberger, 2003), rectifiers, a crucial component in this conversion, are observed to have higher losses.

The Low Voltage distribution system is explored and operating at 48V DC. This system proves advantageous for appliances that necessitate DC power for their operation. These appliances can be connected directly or through a DC-DC converter in case the voltage levels are mismatched (Sulzberger, 2003), as depicted in Figure 4 above. However, household appliances typically run on AC power. If power is generated using a photovoltaic system, which produces DC, it must be converted to AC using an inverter. As noted in (Sulzberger, 2003), it has been observed that an inverter incurs fewer losses compared to a rectifier. In order to compute the efficiencies of both the LVAC and LVDC distribution systems, the networks are simulated in PSCAD software (Manandhar et al., 2016). Based on the input and output power of each conversion, the efficiencies at each stage comprises of rectifier and chopper for LVAC system, and for LVDC system it comprises of chopper and inverter. It has been observed from PSCAD simulation results of (Manandhar et al., 2016) that the total conversion efficiency of the LVAC system consists of rectifier and chopper efficiency. So the overall conversion efficiency of the LVAC system according to (Gwon et al., 2014) is 78.24% and for the LVDC system the efficiency is 84.6%.

In (Gwon et al., 2014), an LVDC distribution system is simulated using EMTP software with a DC voltage level of 380 V at the DC bus. Both the AC load and DC load models have been connected through a DC bus as shown in Figure 5, and power across each conversion stage is obtained.

In this LVDC system, the utility is assumed to be DC-like generation from photovoltaic modules. Further it is divided in AC and DC load models.

• AC load model composed of a rectifier, buck converter, and constant power load, which is basically DC load. Here, AC input comes from an inverter (Gwon et al., 2014)

Considering the model of an AC load with two power conversion stages, The efficiency is calculated at each conversion stage (Gwon et al., 2014), including 75% rectifier efficiency and 91% inverter efficiency. This yields an overall efficiency of 68.25%.

Considering the model of DC load, there is one conversion stage. So the total efficiency is basically the efficiency chopper. The total DC load model efficiency is 90.44%. It has been observed from simulation results of (Gwon et al., 2014) that the conversion efficiency of the AC load model is reduced. The AC load model contain three power converters, i.e., inverter, rectifier and a buck converter. Due to these multiple conversions, the LVDC system is not suitable for AC load model. Whereas, in the DC load model, it only needs one power conditioner, i.e., buck converter, therefore it is reliable to utilize to DC load model with LVDC Distribution System.

In (Anam et al., 2018), AC Microgrid and DC Microgrid are compared for efficiency by utilizing solar wind hybrid renewable energy systems. Two systems are simulated, one for AC System and the other for DC system, which is basically the extension of the AC System. Figure 6 (Anam et al., 2018) show the renewable sources are connected to common AC bus, which is supplied by wind turbine with a 5 KW rating and solar panels with a 5.3 KW rating. The wind turbine is directly connected with AC Bus, while solar panel is connected through an inverter towards AC bus. In the AC system, the load is static load with an 8 KW rating; similarly in DC system, two buses have been created AC and DC by utilizing rectifier, and static DC load is used with an 8 KW rating. Power flow analysis is performed, which yields voltage levels and branch losses for both buses as a function of the equal load on both buses. It has been observed that the voltage drop in the AC bus somehow increase compared to the DC bus, and the AC system has increased losses as compared to the DC system.

In (Justo et al., 2013) the AC and DC distribution Line has been compared in terms of efficiency by considering the parameters such as resistance and reactance. It has been observed from the comparative analysis performed in (Justo et al., 2013) that in terms of power transfer capability, the DC line has fewer losses as compared to the AC line, hence the overall efficiency of the DC system is improved as compared to the AC system.

In (Sabry et al., 2020), the compatibility of household appliances that are powered with AC and DC has been analyzed. An energy measurement (Sabry et al., 2020) has been performed to validate the power profile of inverter driven air conditioner under operating conditions, a normal AC power supply and a proposed 310 V DC supply as depicted in Figure 7. The results show that such an air conditioner consumes a daily power up to 11.466 kW h, which contains DC to AC (inverter) for the DC source-inverter load configuration, but when such air conditioners are directly coupled to the DC source-load configuration, the daily power consumption up to 9.850 kW h has been observed.

To show the efficiency of the proposed (DC Source Appliances) configuration with conventional (DC Source Inverter Appliances) based on energy savings, as shown in Figure 7 that the proposed DC bus is efficient due to somehow less energy consumption than conventional AC. Therefore, great reduction in power consumption has been obtained for the DC system, which makes it more robust and efficient.

In (Saputra et al., 2019), the comparative analysis of hybrids on grid A photovoltaic system is performed by utilizing AC and DC grids, which supply households. The analysis was performed by utilizing the efficiency of power converters in order to compute the power loss in each converter. Utilization of DC grid ultimately reduces the AC Conversion losses to DC and vice versa. It can be observed by considering the efficiency of AC and DC grids that which system is robust and efficient with photovoltaic generation and can be synchronized with main utility grid. As observed the efficiency of AC grid yields efficiency of 90.13% while with DC grid the efficiency has been obtained up to 93.20%. So from this analysis, it has been depicted that the performance of the DC grid is better under load change as compared to the AC grid system.

The study carried out in (Jinchi et al., 2019) focuses on comparing the energy efficiency of AC and DC microgrids. the authors explore three different power supply modes. They analyze the distribution scenarios, including components, loads, and photovoltaic power generation. The results reveal that DC power distribution has advantages over AC power distribution, with an overall efficiency improvement of 6.5%–7.9% The authors in (Thakur, 2020) provides valuable insights into the stability analysis of a DC microgrid connected with renewable energy sources. The authors in (Sayed et al., 2019), investigated the six terminal DC microgrid in simulation and applied droop control methods. The proposed method has been well investigated and tested in simulation environment at multiple scenarios, there is need that the system to be analyzed during symmetrical and asymmetrical faults. In (Xiong and Yang, 2020), the paper presents a photovoltaic-based DC microgrid system designed with a control strategy for optimizing power utilization and ensuring stability based on discrete time mapping model for stability analysis, The proposed method has increased computational burden. In (Saha et al., 2019), the stand-alone solar micro-grid system was designed and simulated. The system components, including the single-phase full bridge DC to AC inverter, DC to DC boost converters, battery discharge condition, and backup condition, were analyzed through simulation. Different cases of the stand-alone solar micro-grid system were analyzed through simulation to verify the validity of the models. But there is a lack in hardware prototype and efficiency comparisons. In (El-Shahat and Sumaiya, 2019), the author presents a standalone solar PV system with a DC microgrid, including components like boost DC/DC converter, MPPT techniques, bidirectional DC/DC converter, DC-AC inverter, and batteries. Their main target was comparing MMPT techniques, their system lacks efficiency comparison and reasons to promote DC systems for remote areas. In (Basantes et al., 2023), the authors investigated the islanded DC microgrid based on MPC technique having multiple complex current and voltage loop to maintains stability of the system, but multiple load scenarios and different faults scenarios needs to be analyzed.

The STP250-20/Wd solar panel has been used in this work. Its specifications are mentioned in Table 2. For the analysis, four solar modules have been utilized, arranged in a series-parallel combination.

The first string contains two solar panels connected in series, yielding 30.7 V + 30.7 V = 61.4 V and 8.15 A. The second string has the same configuration as the first string, but it is connected in parallel with the first string this increases the current rating to 8.15A+ 8.15 A = 16.30 A. The total power generation is therefore 61.4 V * 16.30 A = 1000.68 W = 1 kW.

Absorbed Glass Mat (AGM) Type battery has been utilized in hardware prototype. Two batteries are utilized in parallel combination; single battery rating and overall rating of battery bank is described in Table 2.

The purpose of utilizing the MPPT charge controller is to operate the photovoltaic panels at their maximum power point to obtain maximum power generation. The power generation through solar is greater than the voltage level of the battery bank; therefore, the MPPT charge controller converts the excessive solar voltage into amperage for fast charging of batteries.

For analysis and comparison of the proposed DC system with the existing AC system, DC lighting loads with a 12 V rating have been utilized in the proposed system.

The photovoltaic module utilized in this simulation is the same as that of the hardware prototype, with a slight change in the voltage rating of the DC microgrid that has been selected as 500 V DC (Ardriani et al., 2021), and the power rating has been extended to 20 kW (Elmorshedy et al., 2023).

Initially, in one string of PV systems, eight modules are utilized in series, which yields 30.7 V * 8 = 245.6 V DC and 8.15 A. Through this, only a 2 kW system is obtained. By utilizing a series combination of strings, 90 other strings are created, and a total of ten strings are utilized in parallel, which yields 245.6 V DC and 81.5 A. Overall power is now 245.6 V * 81.5 A = 20,016.4 W = 20.01 kW. In order to achieve 500 V DC, a boost converter is utilized with an MPPT algorithm. The preferred MPPT algorithm utilized in simulation is the incremental conductance method (Mishra and Tiwari, 2021).

The wind turbine integrated with DC Microgrid possesses a power rating of 10 kW (Aloo et al., 2023; Khodabakhsh et al., 2020). Initially, wind turbines provide AC power because, in simulation, a permanent magnet synchronous generator is used. So to convert AC power into DC power, the controller is designed for rectifier mode operation that converts three-phase AC voltages into proper DC voltage up to 500 V DC.

The battery bank is added inside the system to maintain the reliability and stability of the system. The main purpose is to maintain the power flow, stabilize the voltage, and generate maximum power (Aemro et al., 2020).

The DC load targeted in the simulation environment is linear and nonlinear. The voltage rating of a DC resistive load is 300 V; therefore, a buck converter is designed to produce 300 V from 500 V DC. And in nonlinear loads, a DC motor is added; the same voltage rating of the buck converter is used.

The three-phase AC grid is also coupled to the proposed DC microgrid. Initially, AC voltages are obtained, but in order to integrate them with the DC microgrid, AC voltages are needed to be converted to DC by using a converter operating in rectifier mode.

This includes specific performance metrics such as efficiency, stability, fault recovery time and reliability

This includes the proper installing of precise measuring instrument in both DC and AC mcrogrid systems. Make sure that both system are settled up the same way and check each system individually

Performed multiple testing sessions under changing load and record data continuously

Calculated efficiency and validated the results by observing the stability

While newer approaches exist, the PI controller (Vijayan et al., 2022) remains relevant for several reasons.

⁃ Robustness: The PI controller is less sensitive to parameter variations, making it suitable for practical implementations.

As most of the DC appliances are operated on a standard DC voltage level of 12 V DC, similarly, the lighting load installed for this purpose is also based on a 12 V DC supply, which is given by the MPPT Charge Regulator to DC Loads. Figures 11, 12 shows solar voltage and current and battery voltage and current, respectively.

Total wattage rating of DC lighting loads analyzed is 7  Watt ∗ 8  Bulbs = 56  Watts

The input voltage from solar is measured as 61.9 V.

In order to measure the efficiency of a conventional AC system, the AC lighting loads have been operated using an inverter that is supplied by a constant DC source.

Initially battery has been connected with inverter the input voltage of battery is observed as 12.19 V as mentioned in Figure 13.

Figure 14 below shows inverter voltage and load current that is noted using clamp meter.

Total Input Power can be wriiten as Solar Input Volt × Solar Input Current 61.9   V × 1.32   A = 81.708  Watts Total Output Power can be written as Battery Volt × Total Current Drawn 12.19   V × 6.2   A = 75.578  Watts Efficiency = Output   Power Input   Power = 75.578 81.708 Efficiency = 92.5   %

Total Input Power can be written as Battery Voltage × Current Drawn 12.19   V × 4.50   A = 54.855  Watts Total Output Power consumed by load through Inverter can be written as Inverter Output Voltage × Load Current 234.7   V × 0.18   A = 42.246  Watts Efficiency = AC   Power DC   Power = 42.246 54.855 Efficiency = 77   %

Figure 15 gives the solar voltage round about 245 V and the current of 81 A. Overall the total power obtained in simulation from solar side is 20 kW. This suggests that designed DC system is capable of providing a substantial amount of electrical energy which could potentially meet the demand of various applications. The generated power may be adequate for powering residential, commercial and industrial loads.

Figure 16 shows the wind turbine that is designed to generate a constant output power of 10 kW, which significantly indicates that it has great potential to contribute significant electrical energy to DC microgrid. Initially there is a peak transient that last up to 0.1 s.

In Figure 17, Stable DC voltage and current indicates that the controller has ability to regulate voltage and current within desired limits ensuring consistent performance of the connected load. Scaling the power rating of the load in per unit allows for easier analysis and compatibility assessment within the DC microgrid.

Figure 18 shows the simulation results that demonstrate stable DC voltages of up to 500 V at each terminal. Fewer transients and a shorter settling time are observed in the voltage behavior. This stability is essential for maintaining reliable power distribution and operation. Furthermore, the reduction in transients and settling time indicates improved system performance and dynamic response, contributing to the overall efficiency and effectiveness of the microgrid.

The addition of the motor load in Figure 19 initially induces a transient voltage perturbation, commonly termed as a “jerk.” However, over time, this disturbance dissipates, leading to a rapid stabilization of the bus voltage. This mitigation of transient effects suggests enhanced system dynamics and control mechanisms, crucial for optimizing the microgrid’s stability and operational efficiency.

Following are the fault scenarios observed in this work.