• Energy Research

DC microgrids are gaining attention of researchers and engineers due to the increasing deployment of renewable energy sources with energy storage systems, enhanced utilization of DC power electronics devices, and added advantages of no harmonics and synchronization issues. They are viable solutions for providing electricity to off-grid remote communities, like islands and remote areas. However, they need energy management systems for optimally scheduling the distributed energy generation and storage systems. Hence, this paper proposes a supervisory energy management system for optimal operation of islanded DC microgrid. Energy management system is responsible for determining optimal scheduling of each energy source and ensuring maximum utilization of renewable energy sources and supply demand balance. The proposed energy management model has been validated experimentally and practical results prove the effectiveness of the proposed method.

The conventional electric power system is undergoing a transition from high fossil fuel dependence to significant renewable energy share primarily due to decreasing costs of renewable technologies, increasing environmental pollution, and favorable energy policies. The introduction of distributed energy resources with minimal power losses has also recently promoted the DC power systems deployment at small scale such as community-based DC microgrids. These systems allow the possibility of trading surplus energy from distributed energy resources with peer-to-peer (P2P) energy sharing. As power losses in a sharing scheme are non-linear concerning the distance between trading prosumers and power trade level, therefore, P2P energy sharing cannot be optimally managed with conventional factory-warehouse transportation techniques. In this work, we modeled a DC microgrid system with P2P sharing using a non-linear programming technique which allows the users to share their surplus energy from distributed energy resources with minimal system losses including distribution losses as well as conversion losses in comparison to conventionally employed factory-warehouse transportation technique. The proposed model is applied to a community microgrid having independent photovoltaic (PV) and battery systems installed at each house. Results show that the total system losses are reduced by up to 25% with the proposed optimization framework as compared to conventional factory-warehouse transportation sharing mechanism.

Partial shading on photovoltaic (PV) arrays reduces the overall output power and causes multiple maximas on the output power characteristics. Due to the introduction of multiple maximas, mismatch power losses become apparent among multiple PV modules. These mismatch power losses are not only a function of shading characteristics, but also depend on the placement and interconnection patterns of the shaded modules within the array. This research work is aimed to assess the performance of 4 × 4 PV array under different shading conditions. The desired objective is to attain the maximum output power from PV modules at different possible shading patterns by using power electronic-based differential power processing (DPP) techniques. Various PV array interconnection configurations, including the series-parallel (SP), total-cross-tied (TCT), bridge-linked (BL), and center-cross-tied (CCT) are considered under the designed shading patterns. A comparative performance analysis is carried out by analyzing the output power from the DPP-based architecture and the traditional Schottky diode-based architecture. Simulation results show the gain in the output power by using the DPP-based architecture in comparison to the traditional bypassing diode method.

Renewable energy incorporation in many countries takes different forms. In many developed countries, grid-tied solar photovoltaic (PV) installations are widely coupled with lucrative Feed-in-Tariffs (FiT). However, conventional grid-tied solutions are not readily viable in many developing countries mainly due to intermittent grids with load shedding and, in some cases, lack of net-metering or FiT. Load shedding refers to an intentional electrical power shutdown by the utility company where electricity delivery is stopped for non-overlapping periods of time over different parts of the distribution region. This results in a non-continuous availability of the utility grid for many consumers over the course of a day. In this work, the key challenges in the integration of solar energy explicitly in residential power back-up units are reviewed and system hardware level requirements to allow optimized solar PV utilization in such intermittent grid environments are analyzed. Further, based upon the low-cost sensing and real-time monitoring scheme, an online optimization framework enabling efficient solar incorporation in existing systems to achieve minimum grid dependence in intermittent grid environments is also provided. This work is particularly targeted for over 1.5 billion residents of semi-electrified regions in South Asia and Africa with the weak and intermittent grid.

Photovoltaic solar home systems (SHSs) provide a cost-effective solution for the limited electrification of remote off-grid communities. However, due to their standalone nature, the benefit of usage diversity cannot be extracted. In this paper, we present the power electronic interface along with the decentralized control scheme for the integration of standalone SHSs for driving community load applications. Power electronic interface consists of an isolated boost converter capable support dc bus integration, thereby it formulates a dc microgrid through the interconnection of multiple standalone SHSs. Power aggregation is achieved through decentralized controlled resource sharing based upon the resource availability and installed capacity in the individual solar home system. To ensure cost affordability and to avoid the deployment of any communication infrastructure, modified I-V droop control is designed for the intended application. Thereby, power aggregation through the proposed power electronic interface and its decentralized control allows us to extract the benefit of usage diversity and drive high power community power loads at a village scale. The overall schematic is simulated using MATLAB and scaled down model is implemented on hardware. Results of power aggregation from various resource sharing scenarios are illustrated.

The concept of DC power distribution has gained interest within the research community in the past years; especially due to rapid prevalence of solar PVs as a tool for distributed generation in DC microgrids. Various efficiency analyses have been presented for the DC distribution paradigm, in comparison to the AC counterpart, considering a variety of scenarios. However, even after a number of such comparative efficiency studies, there seems to be a disparity in the results of research efforts - wherein a definite verdict is still unavailable: 'Is DC distribution a more efficient choice as compared to the conventional AC system?' A final verdict is absent primarily due to conflicting results. In this regard, system modeling and the assumptions made in different studies play a significant role in affecting the results of the study. The current paper is an attempt to critically observe the modeling and assumptions used in the efficiency studies related to the DC distribution system. Several research efforts will be analyzed for their approach towards the system upon which they have performed efficiency studies. Subsequently, the paper aims to propose a model that may alleviate the shortcomings in earlier research efforts and be able to give a definite verdict regarding the comparative efficiency of DC and AC networks for residential power distribution.

This paper presents the power flow modelling for AC/DC hybrid islanded microgrids including droop-controlled distributed generation units, secondary frequency and voltage restoration control for the AC side of the microgrid, and secondary voltage restoration control for the DC side of the microgrid. The interlink converter between the AC and DC microgrids includes a frequency-voltage droop control, and considers the effect of the secondary control for the AC microgrid side. Two case studies are presented for the power flow model evaluation, in the first case a microgrid with linear loads and equal droop characteristic for the distributed generation units are used; in the second case, voltage dependent loads for both AC and DC microgrids are included, and different droop characteristic are chosen for each distributed generation unit. Comparisons between the power flow solutions through the proposed modelling and the professional simulator MATLAB/Simulink are presented. Additionally, the computational speed and convergence rate of the power flow method are shown. The obtained results corroborate the reliability and effectiveness of the proposed power flow modeling to represent the controlled AC/DC hybrid microgrid including hierarchical controllers.

Renewable energy sources (RESs) are the replacement of fast depleting, environment polluting, costly, and unsustainable fossil fuels. RESs themselves have various issues such as variable supply towards the load during different periods, and mostly they are available at distant locations from load centers. This paper inspects forecasting techniques, employed to predict the RESs availability during different periods and considers the dispatch mechanisms for the supply, extracted from these resources. Firstly, we analyze the application of stochastic distributions especially the Weibull distribution (WD), for forecasting both wind and PV power potential, with and without incorporating neural networks (NN). Secondly, a review of the optimal economic dispatch (OED) of RES using particle swarm optimization (PSO) is presented. The reviewed techniques will be of great significance for system operators that require to gauge and pre-plan flexibility competence for their power systems to ensure practical and economical operation under high penetration of RESs.