Due to inherent advantages of DC system over AC system such as compatibility with renewable energy sources, storage devices and modern loads, Direct Current Microgrid (DCMG) has been one of the key research areas from last few years. The power and energy management in the DCMG system has been a challenge for the researchers. MG structure and control strategies are the integrated part of the power and energy management system. This paper covers all the aspects of the control of DCMG, whether it is DC bus voltage, power or energy related. Different MG Structures with their comparative analysis has been given in this paper. Various control schemes: Basic control schemes like centralized, decentralized and distributed control and multilevel control scheme such as hierarchal control has been discussed. The Power management in grid-connected, Islanded mode and transition mode has been presented. Different energy management strategies have been presented as energy management plays very important role in optimizing the size and rating of energy storage system and their maximum utilization. The energy management of a battery and super capacitor based HESS in all configurations has also been discussed and finally, future trends in further research are presented.

A review on overall control of DC microgrids

In this paper, a distributed local control scheme for dc microgrid is proposed along with the basic droop control. It eliminates the limitations of droop control when the distributed generators are geographically distributed, for which, the line resistances cannot be neglected. Effects of line inductance and constant power loading (CPL) are investigated by analyzing the voltage tracking transfer function for single source system. Stability of two sources single load microgrid with proposed controller is investigated. Simulated responses are presented for two sources single load microgrid (for the sake of simplicity) to depict the proper load sharing and voltage improvement capability of the proposed control method with the consideration of line resistances. However, this can be extended to multiple-source multiple-load configuration connected to the dc bus. A comparison of the result is presented to show the better performance of the proposed control scheme as compared to the conventional droop control and hierarchical secondary control. The interconnected operation of the microgrid is also investigated to show the applicability of the proposed control in the interconnected mode. A centralized controller in each area is used to make the tie-line power flow zero at steady state.

An Enhanced Droop Control Method for Accurate Load Sharing and Voltage Improvement of Isolated and Interconnected DC Microgrids

This paper presents planning and optimization of standalone DC microgrids for rural and urban applications in India. Load profiles in the form of a rural village, an urban residential building and a business organisation are considered for the study. Using these load profiles, different microgrid configurations with generation from PV, wind turbine and biodiesel generators are constructed. Optimization studies are then carried out using Homer Energy software to determine the optimal system configuration which has the lowest cost of energy. Historical data of hourly solar irradiation and wind speed were also used in the study to obtain a realistic result. A special case study for the rural scenario with a partial connectivity to the grid is also conducted which is reminiscent to the poor reliability of supply in India. The study also gives a detail comparison between the various cost components, electrical productions, energy management and emissions for each of these systems. The results of optimization show reasonable cost of electricity for reliable supply of power for the various load configurations as compared to the actual grid prices.

Planning and optimization of autonomous DC microgrids for rural and urban applications in India

This article provides a detailed analysis of the power electronics solutions enabling bipolar dc grids. The bipolar dc grid concept has proven to be more efficient, flexible, and higher in quality than the conventional unipolar one. However, despite its many features, these systems still have to overcome their issues with asymmetrical loading to avoid voltage imbalances, besides meeting regulatory and safety requirements that are still under development. Advances in power electronics and the large-scale deployment of dc consumer appliances have put this growing architecture in the spotlight, as it has drawn the attention of different research groups recently. The following provides an insightful discussion regarding the topologies that enable these architectures and their regulatory requirements, besides their features and level of development. In addition, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

/pdf/bipolar-dc-power-conversion-state-of-the-art-and-emerging-31x0o40s4p.pdf

Bipolar DC Power Conversion: State-of-the-Art and Emerging Technologies

Classical wind energy conversion systems are usually passive generators. The generated power does not depend on the grid requirement but entirely on the fluctuant wind condition. A dc-coupled wind/hydrogen/super capacitor hybrid power system is studied in this paper. The purpose of the control system is to coordinate these different sources, particularly their power exchange, in order to make controllable the generated power. As a result, an active wind generator can be built to provide some ancillary services to the grid. The control system should be adapted to integrate the power management strategies. Two power management strategies are presented and compared experimentally. We found that the “source-following” strategy has better performances on the grid power regulation than the “grid-following” strategy.

https://www.jetir.org/papers/JETIR1604051.pdf

Energy Management and Power Control of a Hybrid Active Wind Generator for Distributed Power Generation and Grid Integration

This paper proposes a new demand-side management (DSM) scheme for the autonomous DC microgrid for the future building. The DC distribution system is considered as a prospective system due to the increase of DC loads and DC power sources such as photovoltaic (PV), and battery bank (BB). The BB responds to the changes in a power imbalance between PV generation and demand within an autonomous DC microgrid. The power loss during charging/discharging of the battery is the great challenge for the autonomous DC microgrid supplied by PV. It decreases the system efficiency. The control objective of the proposed DSM scheme is to use the PV energy more efficiently. The proposed control algorithm shifts the deferrable load from non-sunny hours to sunny hours and decreases the building demand during non-sunny hours. In this way it decreases the charging/discharging cycles of the batteries. This is reducing the power losses in the battery and improves system efficiency. The proposed scheme reduces the size of the PV plant, storage and capital cost of the system. The results showing a clear shifting of the load so that to get significant reduction in the system cost which is given numerically as percentatge saving.

/pdf/demand-side-management-system-for-autonomous-dc-microgrid-cukzk2zqcy.pdf

Demand-Side Management System for Autonomous DC Microgrid for Building

This paper proposes an algorithm for coordinated control of the distributed generators integrated to a DC microgrid (DCMG), in islanded and grid connected modes of operation. The proposed DCMG connects photovoltaic (PV) panels, energy storage (i.e. battery bank and hybrid vehicle) and public utility access to supply the load of a house. The integration of distributed sources with DCMG depends on their feed in tariff (i.e low feed in tariff high integration priority). Moreover the microgrid electricity price is the function of feed in tariff of a power source, and their power feed in the DCMG. Therefore, DCMG prices are dynamic. The non energy storable appliance (NESA) and energy storable appliance (ESA) control algorithm has been proposed for load controlling. The electricity price is one of the parameter for ESA control algorithm. The ESA control algorithm shifts the operating time of energy storable appliances without affecting the user comfort to optimize the electricity bill with the same amount of energy consumption. The control action of NESA control algorithm depends on the occupant presence and other parameters such as illumination, temperature in the house. So the NESA control algorithm reduces the energy consumption in the house as well as cost of the energy. The SCADA system is used to interface with the smart sensors of the house and to execute the NESA and ESA control algorithms to switch the appliances. The results from a case study of a home in Alinagar (India) is presented in this paper in order to evaluate the energy efficiency of the load control system and to analyses the luminous, and temperature conditions and occupancy obtained through the application of this technology. The environmental and energy performances, together with the degree of users' satisfaction and acceptance of this control system, were analysed for a day to verify the potentiality and operation of this load control system. The obtained results regarding the potential in savings of energy (31%) and electricity bill (35%) were evaluated taking into account both the monitored annual electric energy consumption (for operation) and the parasitic energy consumption due to the installed devices (sensors and controllers), and were compared with the estimated energy consumption with manual load control.

Building automation system for grid-connected home to optimize energy consumption and electricity bill

DC microgrids are desired to provide the electricity for the remote areas which are far from the main grid. The microgrid creates the open horizontal environment to interconnect the distributed generation especially photovoltaic (PV). The stochastic nature of the PV output power introduces the large fluctuations of the power and voltage in the microgrid and forced to introduce the controller for voltage stability. There are many control strategies to control the voltage of a DC microgrid in the literature. In this paper the proportional-integral-derivative (PID) and fuzzy logic PID (FL-PID) controller has been designed and compared in term of performance. Performance measures like maximum overshoot and settling time of FL-PID compared with the PID proved that the former is better controller. The controllers are designed and simulated in the MATLAB programming environment. The controllers has been tested for the real time data obtained from Pecan Street Project, University of Texas at Austin USA.

/pdf/design-and-analysis-of-pid-and-fuzzy-pid-controller-for-1bh7ua8t1r.pdf

Design and analysis of PID and fuzzy-PID controller for voltage control of DC microgrid

 Abstract—The renewable energy sources (RES) such as photovoltaic (PV) are basically DC power sources. In the present scenario, the integration of RES to power distribution infrastructure necessitates the DC-AC converter. Moreover the DC loads in the buildings is ever increasing with the use of CFL, LED, refrigerator, TV, fan, air conditioner, laptop, and other electronics in workplaces and homes. This forced to introduce the internal or external AC-DC converter to tie the DC load to AC distribution infrastructure of existing power system. This is further adding losses and complexity. This AC-DC converter stage can be reduces up to a certain level by DC distribution system (DCDS). Secondly the multi voltage rating of RES and DC load insists to introduce DC-DC converter in DCDS infrastructure. This will further add losses and complexity. In this paper a standard voltage level DCDS is proposed to minimize the system losses, complexity. To verify the simulated results in terms of building load and converter losses, a DCDS equipped with different energy sources like solar panel (PV), public utility (PU) and battery bank (BB) is compared with ACDS.

Voltage Standardization of DC Distribution System for Residential Buildings

This paper presents a novel intelligent energy management system (IEMS) for a DC microgrid connected to the public utility (PU), photovoltaic (PV) and multi-battery bank (BB). The control objectives of the proposed IEMS system are: (i) to ensure the load sharing (according to the source capacity) among sources, (ii) to reduce the power loss (high efficient) in the system, and (iii) to enhance the system reliability and power quality. The proposed IEMS is novel because it follows the ideal characteristics of the battery (with some assumptions) for the power sharing and the selection of the closest source to minimize the power losses. The IEMS allows continuous and accurate monitoring with intelligent control of distribution system operations such as battery bank energy storage (BBES) system, PV system and customer utilization of electric power. The proposed IEMS gives the better operational performance for operating conditions in terms of load sharing, loss minimization, and reliability enhancement of the DC microgrid.

Rajeev Kumar Chauhan

Papers

Demand-Side Management System for Autonomous DC Microgrid for Building

Building automation system for grid-connected home to optimize energy consumption and electricity bill

Design and analysis of PID and fuzzy-PID controller for voltage control of DC microgrid

Voltage Standardization of DC Distribution System for Residential Buildings

Intelligent Energy Management System for PV-Battery-based Microgrids in Future DC Homes